Luận án tiến sĩ Công nghệ thực phẩm: Corn snack with high fiber content: Effects of materials, extrusion and frying parameters on the product quality

VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

YANG JIN HAN

CORN SNACK WITH HIGH FIBER CONTENT:

EFFECTS OF MATERIALS, EXTRUSION AND FRYING PARAMETERS ON THE PRODUCT QUALITY

DISSERTATION FOR THE DEGREE OF DOCTOR OF PHYLOSOPHY IN FOOD TECHNOLOGY

HO CHI MINH CITY, 2021

VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

CORN SNACK WITH HIGH FIBER CONTENT:

EFFECTS OF MATERIALS, EXTRUSION AND FRYING PARAMETERS ON THE PRODUCT QUALITY

Major: Food Technology Major code: 62 54 01 01

Independent reviewer 1: Assoc Prof., Dr Phan Tҥi Huân

Independent reviewer 2: Assoc Prof., Medical doctor NguyӉn VăQ1Lên

Reviewer 1: Assoc Prof., Dr Trӏnh Khánh SѫQ Reviewer 2: Assoc Prof., Dr Lý NguyӉn Bình Reviewer 3: Assoc Prof., Dr Ngô Ĉҥi NghiӋp

Scientific supervisor: Prof Le Van Viet Man

HO CHI MINH CITY, 2021

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STATEMENT OF ORIGINALITY

The author pledges that this is the work of the author himself The research results and conclusions in this thesis are honest and not copied from any one source and in any form The reference to the sources of documents has been cited and the reference sources are recorded as prescribed

The author of the thesis

Signature

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ABSTRACT

The objective of this study was to clarify the effects of commercial fiber preparations as well as the extrusion conditions on the quality of the fried corn snack In addition, the study also focused on the effects of commercial natural antioxidants as well as the antioxidant content on the quality of palm olein oil during the frying of snack food Finally, the obtained high fiber snack was in-vivo tested with the hyperlipidemia mice model to clarify its healthy benefits The study consists of three sections

Section 1 ± The use of commercial fiber preparation in the snack extrusion for improvement in the fiber content: Addition of fiber preparations such as polydextrose, xanthan gum, gum acacia, inulin, resistant starch and resistant maltodextrin to the extrusion blend changed physical and sensory properties of the obtained snack but the color of the product remained almost constant Among the tested dietary fiber preparations, the polydextrose added snack had comparable physical and sensory quality to the control When the polydextrose content in the blend varied from 0 to 10%, the bulk density of the fried extrudate increased while the radial expansion ratio and the crispiness decreased The product with high polydextrose content had small air cells and thick cell walls For the extrusion conditions, the specific mechanical energy had a significant correlation with the water absorption index, water solubility index and bulk density in the screw speed section while in the die temperature section, there was correlation between instrument texture and sensory properties The appropriate ratio of polydextrose in the mixing blend, extrusion die temperature and screw speed were 7,5%, 100 oC and 180 rpm, respectively

Section 2 ± The use of commercial natural antioxidants in the frying of the extruded corn snack: Commercial natural antioxidant preparations including citronella, nutmeg, clove and rosemary oil effectively prevented lipid oxidation of palm olein oil during the heating and extrudate frying process Among the tested antioxidants, nutmeg and rosemary oils were more effective than tocopherol and BHT and the sample with nutmeg oil showed the highest oxidation stability For the extrudate frying, the nutmeg oil concentration of 4,0 g/kg was able to prevent oil degradation

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Section 3 - Hypolipidemic and hepatoprotective effects of high polydextrose extruded corn snack on Swiss albino mice: The use of high polydextrose snack in the high fat diet reduced the triglyceride, total cholesterol and low density lipoprotein cholesterol content but increased the high density lipoprotein cholesterol content in the mice serum; in addition, the accumulation of lipid droplets in liver and the liver damage of hyperlipidemic mice were significantly attenuated The diet with high polydextrose snack generated hepatoprotective and hypolipidemic effect on the hyperlipidemic mice The obtained results would contribute to development in healthy food product as well as green processing for industrial application

PhD Tran Thi Thu Tra, Ho Chi Minh City University of Technology

PhD Tran Gia Buu, Institute of Biotechnology and Food Technology, Industrial

University of Ho Chi Minh City

PhD Tran Thi Thanh Truc, Ho Chi Minh City University of Social Sciences and Humanities

Do Thi Tuong Vy, Vice Production manager of snack team, Orion Food Vina.Co., LTD Tran Bao Quynh, Food safety center, Orion Food Vina Co., LTD

CHAPTER 2 LITERATURE REVIEW 3

2.1 Production line of snack food with high fiber content 3

2.2 Materials for production of snack with high fiber content 6

2.2.1 Corn meal 6

2.2.2 Fiber materials 7

2.2.3 Commercial dietary fibers 10

2.2.4 Palm olein oil 15

b Chemical and physico-chemical changes 20

c Biological and biochemical changes 22

2.3.2 Effects of fiber types on extrudate quality 22

2.3.2.1 Physical and physico-chemical properties 22

2.3.2.2 Nutritional quality 23

2.4 Frying 24

2.4.1 Transformation of food materials during frying 24

2.4.2 Effects of antioxidants on the frying product and oil quality 26

2.5 Extruded snack with high fiber content 27

2.6 Novelty of this study 28

CHAPTER 3 MATERIALs & METHODs 30

3.5.1.1 Chemical analysis for materials and extrudates 50

3.5.1.2 Chemical analysis for palm olein 51

3.5.2 Physical analysis for extrudates 51

3.5.3 Physico-chemical analysis for extrudates 53

3.5.4 Sensory analysis 53

3.5.5 In vivo test on mice model 54

3.5.5.1 Serum biochemical parameters 54

3.5.5.2 Histopathologic studies of liver 54

3.5.6 Analytical equipments 55

3.6 Statistical analysis 55

CHAPTER 4 RESULTs & DISCUSSION 57

4.1 Use of commercial fiber preparation in the snack extrusion for improvement in the fiber content 57

4.1.1 Effects of various commercial fiber preparations on the snack quality 57

4.1.1.1 Effects of fiber types on chemical composition of the extrudate 57

4.1.1.2 Effects of fiber types on physical properties of the product 59

4.1.1.3 Effects of fiber types on sensory score of the product 63

4.1.2 Effects of polydextrose ratio in the mixing blend on the snack quality 65

4.1.2.1 Effects of polydextrose ratio on chemical composition of the extrudate 65 4.1.2.2 Effects of polydextrose ratio on physical properties of the extrudate 67

4.1.2.3 Effects of polydextrose ratio on sensory score of the product 69

4.1.3 Effects of extrusion screw speed on the snack quality 70

4.1.4 Effects of extrusion temperature on the snack quality 77

4.1.4.1 Effects of extrusion temperature on the chemical composition of the extrudate 77

4.1.4.2 Effects of extrusion temperature on the physical properties of the extrudate 78

4.1.4.3 Effects of extrusion temperature on sensory score of the fried extrudate80 4.1.4.4 Effects of extrusion temperature on instrumental color, water absorption index, water solubility index of the fried extrudate and specific mechanical energy of the extrusion process 81

4.2 Use of commercial natural antioxidants in the frying of the extruded corn snack84 4.2.1 Effects of natural antioxidants on the palm olein oil quality during the heat treatment 84

4.2.2 Effects of nutmeg concentration on the palm olein oil quality during the heat treatment 90

4.2.3 Effects of nutmeg oil on the palm olein oil quality during the extrudate frying 94

4.3 Hypolipidemic and hepato protective effects of high polydextrose extruded corn snack on swiss albino mice 97

4.3.1 Feed and energy intake 97

4.3.2 Effects of high polydextrose snack on body weight 97

4.3.3 Effects of high polydextrose snack on the lipid profile serum parameters of the mice 99

4.3.4 Effects of high polydextrose snack on liver function 100

4.3.5 Effects of high polydextrose snack on fat accumulation and liver structure 101

CHAPTER 5 CONCLUSION & DISCUSSIONS 104

5.1 Conclusions 104

5.2 Suggestion 106

Reference 107

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LIST OF TABLES

Table 2.1 Corn products defined by particle size and fat content (Gwirtz & Casal, 2014) 6

Garcia-Table 2.2 Composition of dry-milled corn grits (Nor et al., 2013) 7

Table 2.3 Components of dietary fiber according to the AACC (2001) 8 Table 2.4 Preparations containing dietary fiber (% w/w on dry basis) used in extruded snack food 8 Table 2.5 The origin, chemical structure, technological properties and applications of commercial dietary fibers to food industry are listed 11 Table 2.6 Nutritional benefits of high fiber content extrudates 24 Table 2.7 Physical and chemical changes in food during the frying process (Pokorny, 1998) 25 Table 2.8 Main groups of compounds formed in oil during the frying process (Bordin

et al., 2013) 26

Table 3.1 Chemical and physical property of palm olien oil * 30 Table 3.2 Dietary fibers used in the study and their approximate composition (g/kg).31 Table 3.3 Natural and synthetic antioxidants * 31 Table 3.4 Chemicals used in the study, their purity and producers 33 Table 3.5 The mixing formula for the mice feeding 48 Table 3.6 Approximate composition (calculated on % dry weight basis) of each diet group 48 Table 3.7 Tools & equipments used in the experimental analysis 55 Table 4.1 Effects of fiber types on chemical composition (g/kg) of the fried extrudatea 57 Table 4.2 Effects of fiber types on physical properties of the fried extrudatea 60 Table 4.3 Effects of various fiber types on color of the fried extrudatea 63 Table 4.4 Effects of polydextrose content on chemical composition (g/kg) of the fried extrudatea 66 Table 4.5 Effects of polydextrose content on physical properties of the fried extrudatea

68 Table 4.6 Effects of polydextrose content on color of the fried extrudatea 69

Table 4.7 Effects of extrusion screw speed on approximate composition (g/kg) of the f

ried extrudatea 71

Table 4.8 Effects of extrusion screw speed on physical properties of the fried

extrudatea 73

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Table 4.9 Effects of extrusion screw speed on instrumental color of the fried extrudate

and specific mechanical energy (SME) of the extrusion processa 75 Table 4.10 Effects of extrusion temperature on chemical composition (g/kg) of the fried extrudatea 78 Table 4.11 Effects of barrel temperature on physical properties of the fried extrudatea 80 Table 4.12 Effects of barrel temperature on Color & SME of the fried extrudatea 83 Table 4.13 Quality changes in palm olein oil during the heat treatmen with various antioxidants 88 Table 4.14 Effects of nutmeg content in palm olein oil during frying process 92

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LIST OF FIGURES

Figure 2.1 Production line schema of snack food processing (Moscicki & Van Zuilichem, 2011) 3Figure 2.2 Screws in a twin-screw extruder (Moscicki & Van Zuilichem, 2011) 4Figure 2.3 Continuous frying system (Heat & Control.Co) 5Figure 3.1 Flow chart of snack production 36Figure 4.1 Scanning electronic micrographs of the fried extrudate with various fiber sources: a) Control, b) Polydextrose, c) Xanthan gum, d) Gum acacia, e) Inulin, f) Resistant starch, g) Resistant maltodextrin 62Figure 4.2 Effects of fiber types on sensory score of the fried extrudate 64Figure 4.3 Scanning electronic micrographs of the fried extrudate with various poly-dextrose contents The polydextrose content (% of dry weigh basis) in the blend was: A) 0; B) 2,5; C) 5; D) 7,5 and E) 10,0 % 67Figure 4.4 Effects of polydextrose content on sensory score of the fried extrudate 70Figure 4.5 Scanning electronic micrographs of the fried extrudate on screw rpm variables: a) 150rpm, b) 160rpm, c) 170rpm, d) 180rpm e) 190rpm 71

Figure 4.6 Effects of extrusion screw speed on sensory score of the fried extrudate

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Figure 4.7 Effects of extrusion screw speed on water absorption index (WAI) and

water solubility index (WSI) of the fried extrudate 76Figure 4.8 Scanning electronic micrographs of the fried extrudate with 7,5 % poly-dextrose content and various die temperatures: A) 60, B) 70, C) 80, D) 90, E) 100 and F) 110oC 79Figure 4.9 Effects of barrel temperature on sensory properties of the fried extrudate 81Figure 4.10 Effects of barrel temperature on WAI and WSI of the fried extrudate 82Figure 4.11 Effects of the heat treatment on instrumental color of the palm olein oil with various antioxidants 89Figure 4.12 Effects of the heat treatment on instrumental color of the palm olein oil with nutmeg content 93Figure 4.13 Effects of nutmeg oil on the stability of palm olein oil during the extrudate frying (for 15 batches per day and for 5 consecutive days): a) Free fatty acid, b)Conjugated dienes, c)Conjugated trienes, d)Peroxide value, e)Malonaldehyde content 96Figure 4.14 Daily feed and energy intake of Swiss albino mice during the twelve-week experiment (CD: Control diet group, HFD: High-fat diet group, HFFD: High-f

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at and fiber diet group) 97Figure 4.15 Change in body weight of mice during the twelve weeks 98Figure 4.16 Serum lipid profile and glucose concentration of mice in the three diet groups; CD: Control diet group, HFD: High fat diet group, HFFD: High-fat and fiber diet group, HDL- and LDL-cholesterol is high density lipoprotein and low density lipoprotein cholesterol, respectively 100

Figure 4.17 Liver weight, fat mass, AST and ALT of the mice ; CD: Control diet

group, HFD: High fat diet group, HFFD: High-fat and fiber diet group, AST: aspartate aminotransferase, ALT: alanine aminotransferase) 101Figure 4.18 Histological analysis of epididymal fat tissue of three groups Epididymal adipose segment; the tissues were magnified by 200 times; A) control diet group; B) high fat diet group; C): high-fat and fiber diet group 102

Figure 4.19 Micrographs of liver tissue of mice for 3 groups (×100); a) control

diet group, b) high fat diet group, c) high-fat diet and fiber diet group 102

EI: Expansion index HDF: High-fat diet

HFFD: High-fat and fiber diet

IUPAC: International Union of Pure and Applied Chemistry IV: Iodine value

PO: Palmitoyl Oleoyl glycerol PG: Propyl gallate

TAG: Triacyl Glycerol

TBHQ: Tert-Butylhydroquinone

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CHAPTER 1 INTRODUCTION

Dietary fiber has been receiving increasing attention as consumers have become more

concerned about eating food with health benefits (Dhingra et al., 2012) Lack of

adequate dietary fiber in diet is associated with various diseases including constipation,

diverticulosis, cardiovascular diseases and colon cancer (Lairon et al., 2005) Although

many consumers say that they are making efforts to consume foods with high dietary fiber content, dietary fiber consumption around the world fails to meet daily

recommendation (Stephen et al., 2017) Snack foods are highly convenient in modern

society since they provide calories to satisfy short-term hunger and often eaten promptly Fried snacks are sources of carbohydrate, lipid, protein and mineral with specific aroma components to provide tasty appeal to the consumers (James & Nwabueze, 2013) As a result, there has been a remarkable growth in the variety and popularity of snack products because they are affordable, tasty, simple to make and nutritive (Coutinho & Batista, 2013) According to Vivoxa market analytics (2019), the global snack food market was valued at 450 billion USD in 2017 and is expected to reach the value of 638 billion USD by 2023 Unfortunately, extruded snack foods do not contain enough dietary fiber and they have not been considered as high-fiber foods According to USDA National Nutrient Database, popcorn is the snack food with the highest dietary fiber content of 5,2% followed by corn-based extruded snack with 4,0% fiber content (USDA, 2016) Therefore, many studies have focused on the use of

fiber materials in snack food processing such as pumpkin flour (Nor et al., 2013), cassava bran (Hashimoto & Grossmann, 2003), corn bran (Mendonca et al., 2000) and soy fibers (Jin et al., 1995) to increase the fiber content However, the use of fiber

materials changed the product quality such as reduced expansion volume and increased

hardness which are less preferred by consumers (Robin et al., 2012) In addition, fried

snack foods always contain antioxidants to prevent lipid oxidation during the processing and preservation of foods Synthetic antioxidants including butylated

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hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tertiary butylhydroquinone (TBHQ) have been widely used due to their low cost and high stability in snack food processing However, through the enhancing public awareness of health issues and clean label foods, the use of natural antioxidants in food processing has attracted great attention since the consumers prefer to use foods without synthetic additives (Lim & Han, 2016) Accordingly, natural antioxidants, such as rosemary oil, are applied for industrial purpose (Jaswir & Man, 1999) Moreover, there has been an increasing interest in developing natural antioxidants, especially those from herbs, spices and other plant materials, but their efficacy in snack food processing is still limited (Park & Kim, 2002) At present, commercial dietary fibers and natural antioxidants are available in the world market but their application in the processing of extruded corn snack has not been considered The aim of this research is to clarify the effects of various commercial fiber preparations as well as the extrusion conditions on the quality of the fried corn snack In addition, the research also focused on the effects of different commercial natural antioxidants as well as the antioxidant content on the quality of palm olein oil during the frying process of snack foods Finally, the produced snack with high fiber content was in-vivo tested with the hyperlipidemia mice model to clarify its healthy benefits Hopefully, the results of this research would contribute to the development in healthier snack food in the near future

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CHAPTER 2 LITERATURE REVIEW

2.1 Production line of snack food with high fiber content

The technology of snack food and snack food with high fiber content is absolutely similar Figure 2.1 shows the technological schema for the manufacture of snack food which appears most frequently in snack food manufacturing plants (Nikolaou, 2006) Although the production line is simple, various fried extruded products are produced due to differences in materials, ingredients and formulations

PreparationMixingExtrusion Drying

Frying Seasoning Packaging

Snack foods

Figure 2.1 Production line schema of snack food processing (Moscicki & Van Zuilichem, 2011)

Preparation of raw material

The main cereal-based material must be properly ground, screened and weighed according to the recipe Other ingredients are also weighed or measured by volume for the following formulation When conditioning is required, before mixing, water in some quantity is necessarily added for the preparation of the material (Moscicki & Wojtowicz, 2011)

Mixing

The purpose of mixing is to homogenize various ingredients for the blended raw materials Mixing is usually performed in a ribbon blender The mixing tool inside the vessel is in the shape of a spiral ribbon which rotates through a reduction gear and electric motor All the dry ingredients, along with liquid ingredients such as lipids, emulsifier and water, are loaded in measured amounts to the blender and mixed in a required time (Ajita & Jha, 2017)

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Extrusion

Extrusion is one of the latest processing technologies to design expanded food matrices since it combines different operations including mixing, kneading, shearing, cooking, and shaping (Fellows, 2017) In this changed rheological status, the food is conveyed under high pressure through a die or a series of dies and the product expands to its final shape This result in very different physical and chemical properties of the extrudates when various types of raw materials and ingredients are used (Moscicki & Wojtowicz, 2011) In addition, extrusion cooking is a continuous process It is flexible as on-line process adjustments can be made to achieve desired product characteristics Furthermore, the same extruder can be used to manufacture different types of products (Karwe, 2009) The use of thermoplastic extrusion in food processing is facilitated by the dynamism of extruders, which can be divided into two types: single-screw and twin-screw extruders (Riaz, 2000) Variety of extruders with different configurations and performances has been developed and they are categorised based on their applications and design They can vary with respect to screw, barrel and die configuration (Riaz, 2000)

Figure 2.2 Screws in a twin-screw extruder (Moscicki & Van Zuilichem, 2011) The screw configuration comprises screw of only one piece or screw of multiple pieces Twin-screw extruders are composed of two axis that rotate inside a single barrel, usually the internal surface of the barrel of twin-screw extruders is smooth

Frying is a process in which a snack is cooked by floating or being immersed in hot oil Continuous fryers (Figure 2.3) are used for large scale operations (up to 2,270 kg/hr throughput), while batch (kettle-style) fryers are experiencing a comeback among small scale producers (<90 kg/hr) which concentrate on specialty products In spite of simple concept, the design and operation of manufacturing processes for fried snacks pose interesting challenges The key concern is low-cost production of nutritious snacks at consistent quality and minimum waste (Nikolaou, 2006)

Figure 2.3 Continuous frying system (Heat & Control.Co)

Seasoning

The practical objective of flavoring snacks is to apply the seasoning in a uniform and

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consistent manner Usually, the seasonings are in dry form and they also can be flavored oils or two-phase slurries Slurries are produced by blending dry flavors with a liquid carrier Oil-based slurries are common in the savory snack industry, but water-based solutions or slurries are used for sweet snacks (Hanify, 2001)

Packaging

The primary concern for packaging is to ensure long shelf life of the finished product (Nikolaou, 2006) Snack food should be packed in flexible thermoplastic films of multi layer or monolayer construction or their laminates with paper or aluminium foil in order to provide a high resistance to the passage of oxygen, light and water vapour and

to produce an effective heat seal (Navale et al., 2015)

2.2 Materials for production of snack with high fiber content

2.2.1 Corn meal

Among the cereal based materials, corn meal is the most common material that is used

in extruded snack foods (Nor et al., 2013) Industrial dry milling includes particle size

reduction of clean whole maize with or without screening separation, retaining all or some of the original corn germ and fiber (Brubacher, 2002) Table 2.1 identifies the commonly accepted terms according to ranges of particle size for corn products

Table 2.1 Corn products defined by particle size and fat content (Gwirtz & Casal, 2014)

Grits from harder corn are preferred to use by processors since the improved texture of

the product is obtained compared to softer corn grits (Robutti et al., 2002) Corn grain

contains different ratio of hard and soft endosperm Cultivars of corn with almost all

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hard endosperm are called "flint" corn, and those with soft endosperm are called "Dent" corn "Dent" corn cultivars differ in ratio of hard and soft endosperm Under the processing condition, corn grits of harder texture show more expansion, use a less amount of energy during extrusion, and cook faster than the corn grits of softer texture These behaviors are affected by different protein compositions and endosperm textures of cultivars In addition, extrusion alters protein hydrophobicity and degree of

aggregation, though differently between cultivars (Nadeem et al., 2012)

Physical properties of maize grains are associated with total content of proteins in corn grain and zein protein subclasses Protein properties including total protein content,

zein subclass composition (mainly hydrophobic Į-zeins), and protein molecular

fragmentation partially explained the differences between physical kernel hardness and

extrusion-processing performance (Lee et al., 2006) Nutrients of typical dry-milled

corn are shown in Table 2.2

Table 2.2 Composition of dry-milled corn grits (Nor et al., 2013)

Moisture Protein

Fat Crude fiber

Ash Starch

Other polysaccharides

11,5 7,5 0,7 0,2 0,3 78 1,8

2.2.2 Fiber materials

According to the American Association of Cereal Chemists (AACC), dietary fibre is the edible part of plant or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine Dietary fibre includes polysaccharides, oligosaccharides, lignin and associated plant substances The classification of dietary fiber components is presented in Table 2.3 For the functional and technological purposes, dietary fiber is most often

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classified according to its solubility A wide range of commercial preparations containing dietary fiber is available

Table 2.3 Components of dietary fiber according to the AACC (2001)

Non Starch Polysaccharides and Oligosaccharides

Cellulose, Hemicellulose, Arabinoxylans, Arabinogalactans Polyfructoses, Inulin, Oligofractans, Galacto-oligosaccharides Gums, Mucilages, Pectins

Waxes, Phytate, Cutin, Saponins, Suberin, Tannin

These preparations differ in their content of dietary fiber and solubility of the fiber

(Robin et al., 2012) The total dietary fiber content and solubility level of some fiber

materials used in the processing of extruded snack food is given in Table 2.4

Table 2.4 Preparations containing dietary fiber (% w/w on dry basis) used in extruded snack food

Preparations Total dietary fiber

Insoluble dietary fiber

Soluble

dietary fiber Reference

Oat bran 33,3-50,4 10,9-23,9 7,95-53,5 Sibakov et al., 2014

Defatted flaxseed 14,38 9,78 4,6 Trevisan & Areas, 2012 Soybean fiber

Carrot residue Pea hull

16,06 14,26 17,09

determined

Non-determined El-Din et al., 2009

Non-determined

Non-determined Jin et al., 1995 Pumpkin flour Non-determined Non-

determined 14-22 Nor et al., 2013

Non-determined

determined

Non-Hashimoto & Grossmann, 2003 Cereal is an important fiber source for human diet and most fibers are located in the

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bran layer Among cereal grains, oat is rich in ȕ-glucan which has several promoting effects such as reducing obesity and metabolic syndrome (El Khoury et al., 2012) In oat grain, ȕ-glucan is the main soluble fiber while the insoluble fibers mainly include cellulose, lignin and some associated hemicelluloses (Cui et al., 2013) It is

health-reported that defatted wholegrain oat flour or defatted endosperm oat flour are extruded for snack production However, extrudates from defatted wholegrain oat flour have a poor expansion and hard texture, whereas those from defatted endosperm oat flour have a better expandsion and less hard texture In order to increase the fiber content of oat snack, five differently treated oat bran fractions (untreated, ultra-fine ground, enzymatically hydrolysed, hot water-extracted solubles and residue) are consecutively added to defatted wholegrain oat flour or defatted endosperm oat flour for snack extrusion When the ratio of oat bran fractions in the blend varies from 0 to 20%, the total fiber content of the products changes from 6,0 to 53,5 % The extrudates with acceptable expansion and hardness can be produced with defatted oat endosperm from and oat bran fraction Nevertheless, the water-insoluble bran components have a

negative impact on the textural properties of extrudates (Sibakov et al., 2014)

%DUOH\JUDLQDOVRFRQWDLQVȕ-glucan with water-soluble and insoluble fractions Other

fibers in barley grain include arabinoxylan and cellulose (Vasanthan et al., 2002)

When the whole grain barley flour is extruded for snack processing, the total fiber content of the product varies from 6,5 to 6,7 % Increase in extrusion temperature enhances the expansion ratio of barley extrudates but reduces their bulk density (Awan

et al., 2010)

Corn bran, a by-product of the high-fructose corn syrup industry, is a rich source of functional fibers The major fraction of corn bran is insoluble arabinoxylan having less desirable sensory properties than the minor soluble fraction (Manesh & Azizi, 2018) The corn bran content in the blend significantly affects the radial expansion ratio, appearance and general acceptability level in the extrudates All values are decreased with the increase in corn bran content in the blend The optimum ratio of corn bran

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used in snack processing is 2,5% with cornmeal The obtained product contains 15,9%

insoluble and 0,05% soluble fiber (Mendonca et al., 2000)

Defatted flaxseed is a good source of gums, mucilage and insoluble fiber that promote laxation This fiber is mixed with corn-meal to make snack food with high fiber content According to Trevisan & Areas (2012), when the defatted flaxseed ratio was varied from 11 to 28%, total dietary fiber of the product changed from 2,09% to 14,38 %

Soybean fiber can be divided into inner and outer fibers Inner fibers are cotyledon fibers consisting of cell wall polysaccharides with varying degrees of solubility Outer fibers are from seed hull containing mainly water insoluble polysaccharides and some

pectin (Cui et al., 2013) Soybean fiber and corn meal are mixed to produce snack with

high fiber content Increased levels of soybean fiber form extrudates with thick cell

walls and smaller air cells as well as high breaking strength values (Jin et al., 1995)

Vegetables and fruits are sources of soluble fiber, which can affect blood glucose response and lipid metabolism (Lattimer & Haub, 2010) Carrot residue (a by-product from carrot juice processing) or pea hulls were mixed with corn meal at the ratio from 4,63 to 14,26% and from 1,0 to 17,09%, respectively When the carrot residue or pea hull content in the blend is increased, the bulk density of the extrudate is also increased while its expansion ratio and breaking strength are decreased In addition, increasing the fiber content enhances the water solubility index and water absorption index of the

extrudates (El-Din et al., 2009)

2.2.3 Commercial dietary fibers

Most manufacturers of extruded snack foods may simply prefer to make their products from cereal flours since they are cheap and abundant worldwide Innovative sources of dietary fiber such as cereal and vegetable fibers could be beneficial for both manufacturers and consumers due to their low cost In addition, significant progress has been made in utilizing new fiber sources, including by-products of cereal

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processing (wheat bran, oat bran, corn bran) and vegetable processing (carrot residue, tomato pomace, pea hull) for extruded snacks However, the production of high-fiber snacks has generally resulted in products that are tough in texture and unstable quality due to the difficulty of standardization of these materials Nowadays, different commercial dietary fibers are available in the world market and their properties are well controlled and standardized Table 2.5 presents the origin, chemical structure, technological properties and application of some commercial dietary fibers to food industry

Table 2.5 The origin, chemical structure, technological properties and applications of commercial dietary fibers to food industry are listed

Materials Origin Chemical Structure Technological properties

Odourless, neutral taste, white to cream amorphous

powder Sugar replacer

Breakfast cereals, bread, cookies, cakes, yogurt, beverages and meat products

Veena et al., 2016

Xanthan gum

Napa cabbage

/LQHDUĺ 4) linked ȕ-D-glucose backbone with a trisaccharide side chain on every other glucose

Water soluble, stable in acid and alkaline, suspending and thickening agent

Salad dressing, bakery products beverages, soups, dairy products

Palaniraj & Jayaraman,

enhancer,

encapsulating agent

Confectionary, dairy product Fruit juice and beverage

Patela & Goyal,

2015

Inulin Chicory

Oligo- and polysaccharides : fructose units

linked together by ß(2-) linkages

Soluble in water white, odourless powder

Bakery products, cereals, dairy products, frozen desserts, meat products

Shoaib et al., 2016

Resistant

starch Tapioca

Monosaccharide units linNHGWRJHWKHUZLWKĮ-D-(1- DQGRUĮ-D-(1-6) linkages

Water-insoluble, fine particle size, white color, bland flavor, higher water binding capacity

Cheese, bread, pasta, battered fried products

Homayouni

et al., 2013

Resistant malto-dextrin

Corn starch Į-1,4- glycosidic linkages

DQGĮ-1,6-Odourless, No flavor, water soluble, rapid dispersion, very low viscosity, low sweetness

Beverages, nutritional bar, backed goods, cereals, dairy products

.DSXĞQLDk & Jane,

2007

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Polydextrose

Polydextrose is a low molecular weight polymer of glucose Polydextrose is water soluble and may be used as a replacer of both fat and sugar This random polymerization gives a highly branched structure, with small amounts of free glucose and sorbitol, in which the 1,6 bond predominates Polydextrose is often classified as a resistant oligosaccharide (RO; 1) because its highly branched structure prevents precipitation in 80% ethanol Since it is not broken down by human alimentary enzymes, polydextrose has a reduced caloric value (1 kcal/g) As a result, it passes

through the stomach and reaches the lower intestine (Craig et al., 2000) It has been

successfully incorporated into a wide range of foods, i.e baked goods, confectionery, beverages as well as frozen desserts, while providing the appropriate textural and

mouthfeel properties (Zambelli et al., 2017)

Xanthan gum

Chemically, xanthan gum is a consist of a cellulose backbone of (1,4)-D-glucose units with substituents protruding from the main chain In addition, xanthan gum is a microbial heteropolysaccharide, the chain is substituted on alternate glucose residues with a trisaccharide side chain Xanthan gum is used to improve the texture and moisture retention in cake batters and doughs, increase the volume and shelf life of cereal foods by limiting starch retrogradation, improve their eating quality and

appearance, and enhance the effectiveness of other hydrocolloids (Gimeno et al.,

2004) Xanthan gum is soluble in cold water, and it exhibits very high viscosity at low shear rate range and relatively low viscosity at high shear rate range Strong synergism is observed between xanthan gum and some mannan-containing polysaccharides, such

as galactomannans and glucomannans (Izydorczyk et al., 2005)

Gum acacia

Gum arabic is exuded from the bark of Acacia trees that grow primarily in Africa The main chain is built from (1,3)-linked ȕ-D-galactopyranosyl units with Į-L-

13

rhamnopyranose, ȕ-D-glucuronic acid, ȕ-D-galactopyranose and Į-Larabinofuranosyl

units as side chains (Williams & Phillips, 2009) The highly branched molecular structure is responsible for high solubility Gum arabic is also associated with protein moiety, which is responsible for the emulsifying and foaming properties of the gum In addition, it is usually used as a food emulsifier and stabilizer in the food industry Gum arabic can be easily incorporated into beverages and processed foods without changing the original taste or texture due to its high solubility and relatively low viscosity, thus

becoming an ideal functional dietary fibre ingredient in food (Cui et al., 2013)

Inulin

Inulin occurs in many plants and can also be synthesized in microbes It can be found in banana, chicory, barley, onion and wheat, among others (Meyer & Tungland, 2008) Inulin is built up of 2-60 fructose units with one glucosyl terminal unit The main

structure of inulin is ȕ-(2,1) fructan, and the solubility mostly depends on the chain

length It is very stable at temperatures up to 140°C Inulin is susceptible to acid hydrolysis The hydrolysis may occur at pH lower than 4 Inulin solution has a very low viscosity However, when combined with other ingredients, inulin can compete with other polysaccharides for binding with water molecules, thus changing their rheological behaviour Therefore, inulin can be used for modifying the rheology and texture of food products In the food industry, inulin has been widely used in dairy,

bakery and meat products as a fat replacer, bulking agent and foam stabilizer (Cui et

al., 2013)

Resistant starch

Resistant starches are variety of starch that can resist digestion and pass through the gastrointestinal tract (Taggart, 2009) According to its physical and chemical characteristics, resistant starch is divided into four types: types I, II, III and IV resistant starch In this study type IV resistant starch was used Type IV resistant starch describes a group of starch that has been chemically modified and includes starches

14

which have been etherised, esterified or cross-bonded with chemicals in such a manner as to decrease their digestibility In addition, type IV resistant starch can be produced by chemical modifications, such as conversion, substitution, or cross-linking, which can prevent its digestion by blocking enzyme access and forming atypical linkages

such as a (1o4) and a (1o6) linkages (Fuentes-Zaragoza et al., 2010) Resistant

starches have a low water-binding capacity They can be added to food products at high concentration by controlling the processing conditions, such as moisture content, pH and temperature Recently, resistant starches have been considered as new ingredients for creating fibre-rich food Resistant starches have small particle size, white appearance and bland taste They can be used to replace flour on a one- for-one basis without significantly affecting dough handling or rheology Resistant starches

can also increase swelling, viscosity and gel- forming capacity (Cui et al., 2013)

Resistant maltodextrin

Resistant maltodextrins are produced by purposeful rearrangement of starches or hydrolyzed starches to convert a portion of the normal alpha-1,4-glucose linkages to

random 1,2- , 1,3- and 1,4-alpha or beta linkages (Fuentes-Zaragoza et al., 2010) The

viscosity of resistant maltodextrin is low and similar to other functional fibre sources The stability of resistant maltodextrin is resistant in high temperature processes such as sterilisation, retort and pasteurization In addition, resistant maltodextrins are stable to acidic conditions and do not show signs of hydrolysis or haze over long storage times In addition, resistant maltodextrins have very low sweetness level and can be considered being used for non-sweet product For the industrial application, resistant maltodextrins are readily soluble in water and are suitable for many types of beverages, nutritional bar, backed goods, cereals, and dairy products There are two commercial resistant maltodextrins in the market; Nutriose and Fibresol 2 (Viscione, 2013)

Thus, the use of these dietary fiber materials in snack production would generate the product with stable quality Nevertheless, the application of these commercial fiber preparations to the processing of extruded snack food has not been considered

15

2.2.4 Palm olein oil

Palm olein is the liquid fraction of palm oil and is clear at a room temperature Diacylglycerols derived from palm oil affects the cold stability of palm olein While dipalmitoyl glycerol causes rapid crystallisation of the olein, other diacylglycerols such as palmitoyl oleoyl glycerol (PO) and dioleoyl glycerol do not significantly affect the cold stability The physical characteristics of palm olein are closely related to its chemical composition Solid fat contents are low, 37% at 10°C for normal olein and only 17% for super oleins (Lin, 2011)

2.2.5 Antioxidants

Antioxidants can be classified into two major types based on their source: natural and synthetic antioxidants To prevent or retard the oxidative deterioration of foods, oil-soluble antioxidants have been widely used in snack food processing (Pokorny & Trojakova, 2001)

Oils and lipid-based foods deteriorate through several degradation reactions both on heating and on long-term storage The main deterioration processes are oxidation reactions and the decomposition of oxidation products which result in decreasing nutritional value and sensory quality In addition, these reactions can generate toxic compounds in food products One of the potential methods for lipid oxidation prevention is to use specific additives which inhibit oxidation These are originally called oxidation inhibitors but nowadays, they are mostly called antioxidants (Urquiaga & Leighton, 2000)

Synthetic antioxidant

Synthetic antioxidants are phenolic compounds such as butylated hydroxyanisol (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ) and propyl gallate (PG) The most suitable antioxidant for vegetable oils is TBHQ BHA and BHT are fairly stable to heat and are often used for stabilisation of fats in baked and fried products Some antioxidants, such as BHA and BHT, are used in combination

16

with resulting synergistic effects (Maslarova, 2001) They are mostly used in the food industry because of their effectiveness and being cheaper However, they are toxic and have carcinogenic potential which led to the need for natural alternatives Since 1980, natural antioxidants have appeared as a healthier and safer alternative to synthetic

antioxidants (Bandoniene et al., 2002)

Natural antioxidant

The majority of natural antioxidants are also known as phenolic compounds, and the most important groups of natural antioxidants are the tocopherols, flavonoids and phenolic acids Spices, herbs, tea, oils, seeds, cereals, cocoa shell, grains, fruits and vegetables are considered as sources of natural antioxidants The herbs and spices have the highest antioxidant capacity Experiments are generally focused on plant extracts including different plant organs such as seeds, fruits, leaves and others In addition to plant extracts, essential oils, some plant oils having high stability and active components of the plants have been used as natural antioxidants for stabilizing the polyunsaturated oils The major antioxidative plant phenolics can be divided into 4 general groups: phenolic acids (gallic, protochatechuic, caffeic, and rosmarinic acids), phenolic diterpenes (carnosol and carnosic acid), flavonoids (quercetin and catechin), and volatile oils (eugenol, carvacrol, thymol, and menthol) Phenolic acids generally act as antioxidants by trapping free radicals; flavonoids can scavenge free radicals and chelate metals as well (Brewer, 2011) Accordingly, plant extracts or essential oils can be considered as effective natural antioxidants on the edible oils during heat treatment

2.2.6 Sugar and salt

Sugar provides sweetness and is involved in numerous chemical reactions during

extrusion (Navale et al., 2015) The addition of sugar to the mixture in an amount less

than 10% of the mass does not significantly affect to the extrusion process Under certain conditions, hydrolysis of sucrose can take place together with its degradation to glucose and fructose, which take part in developing the color and taste during the non-enzymatic browning reaction when combined with protein fractions (peptides) Salt

17

added in an amount of 1-1,5% easily dissolves in the dough mass, and, to a lesser extent, affects the extrusion-cooking process If salt is added in larger quantities, it may influence the material pH, which sometimes can be beneficial from the technical point of view but will not always be accepted by consumers because of the salty taste (Moscicki & Wojtowicz, 2011)

2.3 Extrusion

2.3.1 Transformation of food materials during extrusion

Formation of puffed, low-density cellular materials from a hot gelatinized mass is the result of physical and chemical transformation of starch and protein raw materials (biopolymers) into a melted mass, which becomes a final void structure due to rapid

evaporative cooling (Moscicki & Wojtowicz, 2011) In general, the chemical or

physicochemical changes in biopolymers that can occur during extrusion cooking include: binding, cleavage, loss of native conformation, fragment recombination and thermal degradation The composition of raw materials can be altered by physical losses including leakage of oil and evaporation of water as well as volatile compounds at the die Since most chemical reactions occur in the high-pressure zone of the barrel, thermally labile compounds such as flavors and vitamins may be injected immediately before the die to minimize exposure to heat and shear The structure of an extruded product is created by forming a fluid melt from a polymer and blowing bubbles of water vapor into the fluid to form bubble Bbubbles rapidly expand as the superheated water is released very quickly at atmospheric pressure In the extruded structure, the fluid of melted polymers forms the cell wall of air bubbles After air expansion, the rapid drop of temperature is caused by water evaporation and the rapid rise in viscosity due to moisture loss, solidifies the cell structure The rapid increase in viscosity is

followed by the formation of a glassy state (Steel et al., 2012) 2.3.1.1 Changes in lipids

Lipids have a powerful impact in extrusion cooking processes by acting as lubricants,

18

because they reduce the friction between particles in the mix, the screw, barrel surfaces and the fluid melt (Guy, 2001) In the extruder, fats and oils become liquid at temperatures over 40 °C, being mixed with the other materials, and are rapidly dispersed as fine oil droplets The presence of lipids in quantities lower than 3% does not affect to expansion properties, however, in amounts above 5%, reduction in expansion rate is considerable (Harper, 1994) The type of lipid and starch present in the raw material influences the formation of the amylose-lipid complex, with free fatty acids and monoglycerides being more favourable to the formation of this complex than triglycerides (Camire, 2000)

2.3.1.2 Changes in protein

Proteins are biopolymers with a great number of chemical groups when compared to polysaccharides and are therefore more reactive and undergo many changes during the extrusion process, with the most important being denaturation (Camire, 2000) During extrusion, disulfide bonds are broken and may re-form Electrostatic and hydrophobic interactions favor the formation of insoluble aggregates The creation of new peptide bonds during extrusion is controversial High molecular weight proteins can dissociate into smaller subunits (Guy, 2001) Enzymes, also proteins, lose their activity after being submitted to the extrusion process due to high temperature and shear Also, proteins lose their solubility in water and saline solution due to the temperature and specific mechanical energy to which the product is submitted (Camire, 2000) The extrusion process, physically, converts protein bodies into a homogeneous matrix, while chemically, the process recombines storage proteins in some ways into structured fibers (Stanley, 1998) Texturization occurs between the molecules as they flow in the streamlines to form laminar cross-linked products Evaporation of water in the mass creates air bubbles that form alveolar structures held in place by cross-linking in the protein layers (Guy, 2001) Protein reactions, including both non-covalent and disulfide bonds form upon cooling Protein-protein interactions may be enhanced by decreasing temperature and by macromolecular alignment Crystalline aggregation leads to parallel fiber formation of varying length and thickness A wide range of

19

interaction energy is possible for protein cross-linking with protein and other molecules due to the diversity of amino acids Also, during the extrusion process, high temperature is normally used, and this favors the Maillard reaction Reducing sugars can be produced during the process and they can react with the free amino groups of

lysine or other amino acids (Steel et al., 2012) 2.3.1.3 Changes in starch

The major difference between extrusion processing and conventional food processing is that in the former starch gelatinization occurs at much lower moisture contents (12-22%) The starch granule consists of two different glucose polymers: amylose and amylopectin, responsible for its physicochemical and functional properties Thermoplastic extrusion, depending on process conditions and raw material composition, causes swelling and rupture of the starch granule, completely or partially destroys the organized granule structure, reduces viscosity and releases amylose and

amylopectin (Camire et al., 1990) During thermoplastic extrusion, amylose and

amylopectin are partially hydrolysed to maltodextrins, due to the high temperatures and shear inside the extruder An important consequence of starch degradation is the reduction in expansion Highly expanded products may crumble easily due to thin cell walls, while dense products are often hard (Riaz, 2000) Inside the extruder, starch goes through several stages The initial moisture content is very important to define the desired product type Once inside the extruder, and at relatively high temperatures, the starch granules melt and become soft, besides changing their structure which is compressed to a flattened form (Guy, 2001) The application of heat, the action of shear on the starch granule and water content destroy the organized molecular

structure, also result in molecular hydrolysis of the material (Mercier et al., 1998) The

starch polymers are then dispersed and degraded to form a continuous fluid melt The fluid polymer continuum retains water vapor bubbles and stretches during extrudate expansion until the rupture of cell structure (Guy, 2001) The starch polymer cell walls recoil and stiffen as they cool to stabilize the extrudate structure Finally, the starch

20

polymer becomes glassy as moisture is removed, which forms a hard-brittle texture The final expanded product presents air cells that are formed due to superheated water vapor pressure (Guy, 2001)

2.3.1.4 Changes in dietary fiber a Physical changes

The combinations of dietary fibers into extruded snacks play a significant role on their structural characteristics The degree of expansion determines the extrudate structure and directly affected its texture High levels of dietary fiber in snacks have often resulted into a tough, compact, non-crispiness and undesirable texture Enriched fibers produced more dense products The influence of processing conditions and material composition on mechanical stress made opposite effects compared to those of porosity, in contrast with the expansion ratio which revealed the similar result Various researches showed the reduction of expansion index (EI) when dietary fiber is added to

the mixture formulation (Vernaza et al., 2009) The reduction of the expansion index

in extrudates due to the fiber addition can be explained through different mechanisms: (i) fibrous materials found in the formulation of extruded products include cellulose, lignin and hemicellulose Under common extrusion conditions, these materials tend to remain firm and stable during extrusion processing, without size reduction The physical properties of fibers in air cell walls reduce the expansion potential of the starch; larger size particles, such as bran, tend to rupture air cell walls of the extruded snack, causing a reduction in expansion index (Riaz, 2000) (ii) non-starch polysaccharides, such as fibers, may bind water more tightly than proteins and starch during extrusion This water binding capacity prevents water loss at the die, as a result, at the exit of the extruder, expansion is reduced (Camire & King, 1991); (iii) the starch cannot be totally gelatinized in the presence of fiber and that is not capable to support expansion (Camire & King, 1991)

b Chemical and physico-chemical changes

The shear forces are generated by the rotating movement of the screws, together with

21

frictional, pressure and compressive forces which provide the necessary environment for physico-chemical changes and rapidly cooking of dietary fiber in extruded snacks

(Nikmaram et al., 2015) The dietary fiber content commonly does not significantly

decrease in extrusion, whereas the ratio of insoluble to soluble dietary fiber often decreases due to solubilization and depolymerization of insoluble fiber components Under severe extrusion conditions, the dietary fiber content could also increase because of the formation of resistant starch or some undigestible Maillard reaction products The polysaccharide-lipid complexes formed during extrusion cannot be separated either enzymatically or chemically, and they were found to contribute to the

insoluble dietary fiber fraction with resistant starches (Gualberto et al., 1997)

During cooking-extrusion process, the gelatinisation and the retro-degradation of the starch could partially change it into undegradable polysaccharides (resistant starch) In addition, the Maillard reaction could generate the formation of protein - polysaccharides complexes, which are very resistant to enzymatic degradation The consequence of these transformations is a reduction in the amount of soluble material which are released by amylase, protease and other used enzymes in the fiber

determination procedure (Esposito et al., 2005) This phenomenon is reported for barley (Ostergård et al   WHII ÀRXU 6WRMFHVND et al., 2010), wheat bran by-product (Esposito et al., 2005) Conversely, extrusion process is also reported for

increasing soluble dietary fiber content The plenty of research has shown that dietary fibers could have transposition of insoluble fiber to soluble fiber This effect would be the result of the breakage of covalent and non-covalent linkages between carbohydrates and proteins associated with the fiber, resulting in small molecular

fragments, which would be more soluble In addition, Gajula et al (2008) reports that

the decrease of insoluble dietary fiber fraction is higher than the increase in the soluble fraction, and recommend that the fragmentation of lignin or cellulose by the extrusion shearing action results in formation of lower molecular weight soluble dietary fiber

residues This phenomenon is reported for orange pulp (Larrea et al., 2005), oat bran (Zhang et al., 2011), wheat bran (Gajula et al., 2008)

22

c Biological and biochemical changes

Destruction of antinutritional factors is observed in extrusion process Mukhopadhyay & Bandyopadhyay (2003) reports that extrusion technology is very effective in reducing the anti-nutritional factor such as tannin from sesame meal In addition, the trypsin inhibitors are usually considered to be the main anti-nutritional factors in soybeans Heat treatment of extrusion cooking is widely used to improve the

nutritional value of soybean (Vandenhout et al., 1998) In another study of Singh et al

(2000), extrusion causes complete destruction of trypsin inhibitor activity in the extruded blends of broken rice and wheat bran Destruction of microorganisms during extrusion process is also reported Likimani & Sofos (1990) indicated that extrusion

processing at low barrel temperatures (80/100°C) resulted in injury to spores of B globigii Extrusion at the higher barrel temperatures (120 and 140°C) resulted in

extensive spore destruction Their results indicated major reduction in spore numbers during extrusion at high temperatures (150-180 °C)

2.3.2 Effects of fiber types on extrudate quality

2.3.2.1 Physical and physico-chemical properties

It is essential to understand that addition of dietary fiber to the blend has great effects on material transformations in extrusion These changes are dependent on the type of dietary fiber source and the presence of associated compounds Cereal dietary fiber preparations typically contain cellulose, lignin and hemicelluloses as well as polyphenolics as dietary fiber components, and most often contain starch and protein as impurities, whereas fruits and vegetables are sources of gums, pectin and mucilage The purity, solubility and other polymer properties of dietary fibers preparations

largely influence the quality of extruded snacks (Elleuch et al., 2011) Molecular

weight controls polymer function with degree and pattern of branching High molecular weight fiber polymers with large hydrodynamic radius result in high viscosity dispersion The molecular weight of soluble dietary fiber preparations (corn fiber gum, arabinogalactan and carboxymethyl cellulose) was found to play a

23

significant role in determining the degree of expansion (Kale et al., 2010) Various

dietary fiber sources have been studied in extrusion, the main ones being corn brans, oat, wheat, soya and beet fibers Wheat fiber and pectin had opposite effects on

porosity and hardness of the extruded samples (Yanniotis et al., 2007) Wheat fiber

increased hardness and reduced porosity, whereas pectin decreased hardness and increased porosity For instance, reduction in average particle size of wheat bran from

620 nm to 345 nm caused a decrease in hydration properties (Zhu et al., 2010),

whereas the hydration properties of coconut dietary fiber increased when the particle

size decreased from 1, WR  ȝP 5DJKDYHQGUD et al., 2006) Guy (1985) also

reports that particle size distribution of wheat bran influenced the expansion rate Uneven particle-sized fiber preparations can interrupt the matrix, disrupt the bubble wall film and result in failure of air cells before expansion However, reduction in particle size of insoluble fibers, such as cellulose and corn bran, increased extrusion expansion, but only in a limited extent Reduction in particle size of cellulose to less

WKDQȝPGLGQRWLQFUHDVHVHFWLRQDOH[SDQVLRQLQGH[%ODNH  Jin et al (1995)

shows that increasing soy dietary fiber content (10-40%) results in close textured, less

expanded products with thick cell walls in soy fiber corn meal extrudates Lue et al

(1990) conclude a similar trend with oat bran and corn meal extrudates Increasing bran content can cause structure defects of air cell rupture, which will affect the

expansion rate (Mendonca et al., 2000) Typically, about 10-30% of cereal brans have

been used in extrusion experiments Increase of the amount of dietary fiber results in

reduced expansion, tough and non-crisp texture Chassagne-Berces et al (2011)

investigate the effects of the adding oat and wheat bran (0%, 10% and 20%) to whole wheat flours and wholegrain on extrusion Regardless, the addition of bran causes a decrease in expansion index of the pellets

2.3.2.2 Nutritional quality

Addition of dietary fiber improves the nutritional quality of the product Table 2.6 summarizes the nutritional benefits of extrudates with high dietary fiber content

24

Table 2.6 Nutritional benefits of high fiber content extrudates

Materials for extrusion

Dietary fiber change

Nutrition

Red adzuki bean

Non-determined

106 patients, 4 weeks

Blood glycemic control; Inflammation reduction

Liu et al.,

2018

Whole grain wheat

Increased soluble fiber

content; Decreased

insoluble fiber content

Rats feed for 5 days

Increase fermentability Bjorck et al., 1984

Orange pomace

Increase soluble fiber

been discussed in the report by Singh et al (2007) who claimed that there were

conflicting results with respect to cholesterol-lowering properties in animal studies

According to Parada et al (2011), various levels of guar gum as a soluble dietary fiber

source were used in extruded foods made from wheat, potato, maize, rice flour Starch digestibility did not decrease with addition of guar gum; instead of a small increase in rapidly available glucose was observed Viscous gums and other soluble dietary fibers could reduce cholesterol levels by trapping bile acids; increased excretion of bile eventually depletes body stores of cholesterol, which are tapped to synthesise new bile acids

2.4 Frying

2.4.1 Transformation of food materials during frying

Deep fat frying is a simultaneous heat and mass transfer process Heat transfer occured by convection between the oil and the food surface, and by conduction within the food Table 2.7 summarizes the physical and chemical changes in extrudates during the

frying process

25

Table 2.7 Physical and chemical changes in food during the frying process (Pokorny, 1998)

Component Changes during frying

Fat Increased concentration and change in composition Water Significant loss

Reducing sugars Maillard reaction Starch Gelatinization

Proteins Alteration of the structure and composition

Amino acids Maillard reaction and formation of heterocyclic flavoring substances Flavoring substances Formed by oxidative and Maillard reactions

Vitamins Moderate loss Minerals Small loss Antioxidants Moderate loss

When the food is immersed in hot oil, water vapor is formed due to high temperature, and it is transferred through the surface of the product due to pressure and concentration gradients As a result, crust is formed, and pores are developed Surface hydrophilicity of the raw sample is lost as the crust is developed, which results in a higher rate of oil absorption (Sahin & Simnu, 2009) Pores affect oil absorption Oil enters the pore provided by moisture loss In addition, shrinkage may be observed during frying It is important to examine these changes at the micro level Physical properties such as size, shape, surface area, density and volume of pellet change during frying Changes in porous structure affect moisture diffusivity and oil uptake Moisture diffusivity is also affected by temperature, frying time and product moisture content (Sahin & Simnu, 2009) Convective heat transfer coefficient changes with oil temperature and oil degradation The chemical reactions occurred during deep-fat frying involve hydrolysis, oxidation, isomerization and polymerization (Table 2.8) Chemical changes in extrudates being fried and also in frying oil are important in IU\LQJ7KHFKDUDFWHULVWLFFRORUDQGÀDYRURIWKHIULHGSURGXFWDUHSURYLGHGE\0DLOODUGreactions in the crust The formation of acrylamide, which is a potential carcinogen, is also linked to Maillard reactions Some biochemical and biological changes are reported during food frying Inactivatation of lipase (Onyeike & Oguike, 2003), and denaturation of proteins (Sahin & Simnu, 2009) are also observed in the fried product

Oxidized monomers

Oxidized dimers and polymers

Volatile compounds (aldehydes, ketones, hydrocarbons) Sterol oxides

Thermal Temperature

Dimers and non-polar polymers Cyclic monomers

Trans isomers and position isomers

In addition, Abd-El-Aziz1 & Moharram (2016) indicates total viable count (1,9 x 105± 8,0), Coliform count (0,9 x 101 ± 1,6 cfu/g), Enterobacteriaceae count (6,5 x 102 ± 6,2

cfu/g) and Staphylococcus aureus count (6,9 x 101 ± 8,7 cfu/g) before frozen shrimp are fried, respectively However, all of them are not detected in the fried product

2.4.2 Effects of antioxidants on the frying product and oil quality

Edible oils are not stable products; therefore, they deteriorate through a variety chemical reaction in a short time The most important of these reactions is lipid R[LGDWLRQUHDFWLRQ ÕUDODQ 2[LGDWLYHVWDbility is not only a quality parameter,

but also a great indicator of shelf life of oil (Krichene et al., 2010) Autoxidation of

lipids start with a free radical chain reaction that is generally initiated by exposure of

lipids to heat, light, metal ions or ionizing radiation (Bandoniene et al., 2002) This

oxidation process which takes place at the double bond sites in lipid molecules consists of three steps: (ϸ) initiation: formation of free radicals; (Ϲ) propagation: free radical chain reaction; (Ϻ) termination: formation of non-radical products When oil oxidizes, it produces a series of breakdown products in three stages Primary oxidation products are peroxides or hydroperoxides that are formed due to acceleration of oxidation by the high temperature and the availability of oxygen Peroxides are further broken down into secondary oxidation products: alcohols, carbonyls, free fatty acids, aldehydes and ketones The tertiary oxidation products; dimers and polymers are