investigate extraction conditions and characterization of pectin from durian rind based on response surface methodology

TECHNOLOGY AND EDUCATIONMINISTRY OF EDUCATION AND TRAININGHO CHI MINH CITY UNIVERSITY OF GRADUATION THESIS FOOD TECHNOLOGYINVESTIGATE EXTRACTION CONDITIONS AND CHARACTERIZATION OF PECTIN

TECHNOLOGY AND EDUCATION

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF

GRADUATION THESIS FOOD TECHNOLOGY

INVESTIGATE EXTRACTION CONDITIONS AND CHARACTERIZATION OF PECTIN FROM DURIAN

RIND BASED ON RESPONSE SURFACE METHODOLOGY

LECTURER: NGUYEN VINH TIEN

STUDENT: HA THI TIEU YEN PHAM THI HONG

SKL012532

SHO CHI MINH UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF INTERNATIONAL EDUCATION

GRADUATION PROJECT

Thesis code: 2023-19116057

INVESTIGATE EXTRACTION CONDITIONS AND CHARACTERIZATION OF PECTIN FROM DURIAN RIND BASED ON RESPONSE SURFACE

METHODOLOGY

Supervisor: NGUYEN VINH TIEN, ASSOC PROF Student: HA THI TIEU YEN 19116057

PHAM THI HONG 19116042

Major: FOOD TECHNOLOGY

HO CHI MINH UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY OF INTERNATIONAL EDUCATION

FOOD TECHNOLOGY

GRADUATION THESIS ASSIGNMENT

Student name: Ha Thi Tieu Yen Student ID: 19116057 Student name: Pham Thi Hong Student ID: 19116042 Major: Food Technology Class: 19116CLA

Supervisor: Nguyen Vinh Tien, Assoc Prof Email: tiennv@hcmute.edu.vn Date of assignment: 10/08/2023 Date of submission: 22/01/2024

1 Thesis title: Investigate Extraction Conditions And Characterization Of Pectin From Durian Rind Based On Response Surface Methodology

2 Thesis assignment:

+ The process of extracting pectin from durian rind + The properties of pectin

+ Optimization parameters of extraction conditions

The content and requirements of the graduation thesis have been approved by the Chair of the Food Technology program

Ho Chi Minh City, 22nd January 2024

CHAIR OF THE PROGRAM SUPERVISOR (Sign with full name) (Sign with full name)

ACKNOWLEDGEMENTS

Our sincere gratitude goes out to all of the instructors in the University of Technology and Education of Ho Chi Minh City's Food Technology Department for their invaluable instruction and knowledge-sharing throughout our studies They also built all the facilities and tools necessary to help us finish the thesis as effectively as possible Also, we had to face and conquer every obstacle we came across during the project in order to finish and obtain the outcomes we have now Additionally, we receive a lot of inspiration, support, and motivation from our cherished classmates and families

We especially acknowledge the teacher who oversaw this graduation project, PhD Nguyen Vinh Tien During the project, he provided us with valuable guidance and instruction on how to utilize equipment and operate machinery in the laboratory, along with quick feedback At the same time, the teacher always creates a friendly and supportive environment, even when we run into problems with the research process

Sincerely, we would like to express our gratitude to Ms Ho Thi Thu Trang of the Department of Food Technology for facilitating and assisting us in using the measuring tools and equipment available at the Faculty of Chemical and Food Technology's laboratory

Owing to our inexperience, ignorance, and time constraints, errors may have occurred in the thesis's execution We sincerely hope you will pardon us and provide us with helpful criticism so we can get better We would like to send the Faculty of Chemical and Food Technology our warmest regards We hope your life is filled with prosperity and good health

Sincerely thank,

Ha Thi Tieu Yen & Pham Thi Hong

DECLARATION

We declare that the outcome of the graduation thesis is our own work, all project results are the product of our surveys and research, and all project references are correctly cited in compliance with regulations

1.5 Scientific and practical significance 3

CHAPTER 2: LITERATURE REVIEW 4

2.1 Introduction about pectin 4

2.1.1 Structure and chemical compositions of pectin 4

2.1.2 Gelation mechanism of pectin 6

2.1.3 Classification of pectin 7

2.1.4 Properties of pectin 9

2.1.1 Pectin extraction technique 10

2.1.2 Applications of pectin 12

2.2 Overview about durian 13

2.3 Response surface designs 15

2.4 Summary of previous studies on durian rind 18

CHAPTER 3: MATERIALS AND METHODS 20

3.1 Materials, chemicals, and equipment 20

3.3.1 Durian rind drying 23

3.3.2 Alcohol insoluble preparation 25

3.3.3 Pectin extraction process 27

3.4 Analytical method 29

3.4.1 Moisture content of durian rind and pectin powder 29

3.4.2 Ash content of durian rind and pectin powder 29

3.4.3 Pectin yield 30

3.4.4 Total Anhydrouronic Acid Content 30

3.4.5 Degree of esterification 31

3.4.6 Intrinsic viscosity and viscosity- average molecular weight 32

3.4.7 Morphological analysis 33

3.5 Experiment design 34

3.5.1 Experimental design of pectin extraction optimization 34

3.5.2 Solve multi-objective optimization problem 36

CHAPTER 4: RESULTS AND DISCUSSIONS 37

4.1 Moisture and ash content of durian rind 37

4.2 Results of experimental design 37

4.3 Effect of extraction parameters on DE 38

4.4 Effect of extraction parameters on pectin yield 41

4.5 Effect of extraction parameters on AUA 49

4.6 Optimization of the experiment and validation of the model 56

4.7 Optimal durian rind pectin process 58

4.8 Moisture and ash content of optimum pectin 58

4.9 Degree of esterification and structural propertie 61

4.10 Result of of intrinsic viscosity and viscosity-average molecular weight 63

4.11 Morphology properties 65

CHAPTER 5: CONCLUSION 66

REFERENCES 68

APPENDIX 75

LIST OF FIGURES

Figure 2.1 Pectin chemical structure 4

Figure 2.2 Pectin structure 5

Figure 2.3 The gelation mechanism of LMP 7

Figure 2.4 Durian 13

Figure 2.5 A Box-Behnken design for three Factors 15

Figure 2.6 Generation of a Central Composite Design for two Factors 15

Figure 2.7 Comparison of the Three Types of Central Composite Designs 16

Figure 2.8 Central composite rotatable design (CCRD) 17

Figure 3.1 Durian rinds 20

Figure 3.2 Diagram of experimental research 22

Figure 3.3 Flowchart diagram for durian rind drying 23

Figure 3.4 Flowchart diagram for alcohol insoluble preparation 25

Figure 3.5 Flowchart diagram for pectin extraction process 27

Figure 3.6 FT-IR spectrum of pectin 32

Figure 4.1 The perturbation plot 43

Figure 4.2 One-factor plot illustrating the effect of temperture on pectin yield 44

Figure 4.3 One-factor plot illustrating the effect of S:L ratio on pectin yield 45

Figure 4.4 One-factor plot illustrating the effect of time on pectin yield 46

Figure 4.5 The 3D response surface graphs and countor demonstrate the relationship of extraction parameter 47

Figure 4.6 Predicted and Actual values of Yield 49

Figure 4.7 The perturbation plot 52

Figure 4.8 One-factor plot illustrating the effect of temperture on AUA 53

Figure 4.9 One-factor plot illustrating the effect of S:L ratio on AUA 53

Figure 4.10 The relationships of the extraction parameters were displayed by 3D surface response graphs and countor 54

Figure 4.11 Predicted and actual value of AUA 55

Figure 4.12 Optimal durian rind pectin process 58

Figure 4.13 Pectin extract after precipitating with alcohol 59

Figure 4.14 Pectin powder 60

Figure 4.15 Comparing FT-IR spectrum of pectin (A) durian, (B) commercial 61

Figure 4.16 Huggins, Kraemer, and Martin plot for durian rind pectin 64

Figure 4.17 Morphological configurations of DP captured using SEM at x30 and x200 magnification 65

LIST OF TABLES

Table 3.1 Factor settings for CCRD model for three factors 35

Table 4.1 Moisture and ash content in durian rind 37

Table 4.2 Experimental results of objective responses 38

Table 4.3 ANOVA for linear model Y2 (DE) 39

Table 4.4 ANOVA for quadratic model Y2 (DE) 40

Table 4.5 Summary model response of yield 41

Table 4.6 ANOVA for linear model Y1 (Yield) 42

Table 4.7 Summary model response of AUA 50

Table 4.8 ANOVA for quadratic model Y3 (AUA) 51

Table 4.9 The response of verified samples at the optimal extraction conditions (90 °C, 1:50, 210 minutes) 57

Table 4.10 Moisture and ash content of durian rind pectin 58

Table 4.11 Comparing FT-IR spectrum of pectin commercial, durian rind 63

Table 4.12 Intrinsic viscosity and viscosity-average molecular weight of durian rind pectin 64

LIST OF ABBREVIATIONS

ABSTRACT

Pectin is a complex, high molecular weight, structurally acidic heteropolysaccharide that is present in the cell walls and leaf blades of terrestrial plants It helps plants set up and firm their tissue Because it can provide food products more stiffness and texture, pectin is a widely used component in culinary applications Pectin is also a naturally occurring biopolymer that has several uses in the food industry and can be used to make pectin powder at a reduced cost In order to examine the effects of extraction temperature (75–95 °C), duration (30–270 min), and solid-to-liquid ratio (S:L) (1:20–1:60 g/mL) with 0.001M H2SO4

on the yield of pectin from durian rind, as well as the esterification degree (DE), purity (AUA), and other pectin properties, a central composite rotatable design was employed in this study The findings show that extraction temperature, duration, and S:L all have a substantial impact on pectin production and AUA, with extraction temperature having the greatest positive impact on both pectin output and purity Conversely, DE is not much impacted by these extraction parameters The experimental yield (11.25%) and AUA (72.258%) values obtained under ideal extraction conditions (90 °C, S:L 1:50 g/mL, 210 min) nearly matched the expected values The extracted pectin's richness in polygalacturonic acid was demonstrated by the FT-IR spectra With its uniform, smooth-surfaced granules resembling slabs, the pectin derived from durian rind shows promise as a low-methoxyl pectin source that can thicken low-calorie foods and drinks considerably

CHAPTER 1: INTRODUCTION

1.1 Problem

Vietnam's agricultural sector accounts for a high proportion of the economy In addition to rice output, which is always among the world's largest exporters, Vietnam also develops fruit tree cultivation in large quantities and with a variety of types As one of the fruit trees with high economic value, durian is increasingly popular and is widely consumed not only in the domestic market but also for export Durian is a genus of plants in the mallow family, currently there are more than 30 identified species, of which about 9 species have edible

fruits, Durio Zibethinus is the most common species on the market The distribution area of

durian is in Southeast Asian countries, including Vietnam In addition to directly using the fruit flesh, durian is also processed into many dishes such as ice cream, candy, and jam

The durian rind typically accounts for over half of the total fruit weight, presenting a green to yellowish-brown, thick, semiwoody composition adorned with sharply pointed pyramidal thorns The excessive disposal of durian rinds during the durian season raises environmental concerns The rind of durian are highly cellulose-containing, according to research done in Thailand on using durian peels to make particleboard with lower heat conductivity [1] Particleboard, also known as chipboard in the UK, Australia, and some other countries, is an engineered wood product made by pressing and extruding wood particles- such as wood chips, sawdust, or shavings from sawmills- with a synthetic resin or other appropriate binder A variety of polysaccharides, including cellulose, hemicelluloses, lignin, and pectin, make up the majority of the plant cells in durian [2] This agricultural waste might also be used to make a low-cost sorbent that would remove acid dye from aqueous solutions by acting as a gelling agent, tablet disintegrator, and binder[3] The water-soluble polysaccharide fraction from the rind of durian trees that has a high pectin content is particularly interesting [4]

1.2 Research objective

- The process of extracting pectin from durian rind - The properties of pectin

- Optimization parameters of extraction conditions

1.3 Object and scope of the research

- Research Object: Pectin extracted from durian rind

- Scope of the study: This study was carried out on a laboratory scale

1.5 Scientific and practical significance

- Provide complete pectin extraction process This serves as a premise for further studies

- Research the factors affecting the extraction process in order to improve the efficiency

and quality

- Enhance the value and widen the range of applications of durian rind

CHAPTER 2: LITERATURE REVIEW

2.1 Introduction about pectin

Pectin is a powder that ranges in color from white to light brown and is commonly made from apple pomace and citrus peel Although pectin was once only accessible as a liquid extract, its use as a dried powder has increased since it is easier to handle, store, and transport As a water-soluble fiber that is used in a variety of food products, including ice cream, jam, yogurt drinks, and fruity milk drinks Pectins are also included as nutritional supplements because of their possible health benefits Multiple research studies have documented the advantageous impacts of a diet rich in fiber on various areas By modifying the gut microbiota, recent research has also investigated the effects of pectin on allergic sensitization, which has been shown to have positive benefits of pectin supplementation on allergies [5]

2.1.1 Structure and chemical compositions of pectin

Figure 2.1 Pectin chemical structure

The molecular structure of pectin is derived from pectic acid, which itself is a polymer of galacturonic acid linked together by α 1-4-glycoside bonds The length of the polygalacturonic acid chain can vary from a few units to hundreds of galacturonic acid units The molecular weight of pectin isolated from different fruit sources varies widely, depending on the number of galacturonic acid molecules, and typically falls within the range of 10,000 to 100,000[6] In terms of glucid substances, when comparing molecular length, pectin has a higher molecular weight than starch but lower than cellulose For instance, in apple sources, pectin is obtained with a molecular weight of 25,000-35,000, while pectin from oranges can have a molecular weight of up to 50,000 [7] The pectin content of 1% in the

D-solution has high viscosity When 60% sugar is added and the pH is adjusted to a range of 3.1-3.4, coagulation of the product occurs

Commercial pectin does not have a definite molecular weight but depends on the raw material, extraction method, and type of product The pectin unit molecule is D-galacturonic acid Additionally, there are some neutral sugars such as rhamnose, galactose, arabinose, and some other sugars in smaller amounts Carboxyl groups (-COOH) can exist freely or in the form of ester bonds with methanol, phenolic acid or in the form of salts of Na+, K+, NH4 , etc In amidized pectins, a portion of the carboxyl radicals in the pectin molecule is amidized to form an amide group (-CO=NH2).[8]

Three major types make up the structure of pectin: rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and homogalacturonan (HGA)[9] Furthermore, due to their similar main chains to HGA, xylogalacturonan (XGA) and apiogalacturonan (AGA) are frequently regarded as pectins [10] Within the primary and mid cell walls, all three forms of polysaccharides are believed to form a pectin network through covalent bonds Enzymes on the cell wall control the structure of this network [11]

Figure 2.2 Pectin structure

HGA is the most common form of pectin About 100 GalA units make up HGA, a linear homopolymer composed of a-(1-4)-D-GalA linkages Additionally, some of the carboxyl groups are esterified with methanol or acetyl groups[9, 12] HGA is also known as the smooth region due to its linear structure [13]

RG-I accounts for about 20-35% of the structural form of pectin A primary chain with a molecular weight of roughly 100 kDa, comprising repeated disaccharides [-α -D-GalA-1,2-a-L-Rha-1-4-]n, makes up the structure of RG-I The expression of the RG-I construct depends on the growth of the species and the number of sugar residues and branched oligosaccharides attached to the main chain of RG-1[14] The side chains contain galactose and arabinose residues attached at C-4 of the rhamnose residues These side chains consist of monosaccharides or combined chains of arabinan, galactan, or arabinogalactan RG-I is known as a hairy region because of its branching structure[13]

RG-II is the pectin with the most complex structure, accounting for 10% of pectin It has a low molecular weight of 5-10 kDa GalA (HGA-like) residues with a minimum of eight α -(1-4)-D-GalA links form the main chain of RG-II's structure RG-II has more branches than HGA Additionally, the branch chains contain 12 different sugars linked to C-2 and C-3[9]

2.1.2 Gelation mechanism of pectin

Pectin is a charged hydrocolloid, which means that variations in pH and the kind and concentration of cations present in the solution can affect it These features allow it to be separated into two categories: acid gel and calcium gel, which are derived from HMP and LMP, respectively

Figure 2.3 The gelation mechanism of LMP

The gelation process is facilitated by the free electron pairs of the oxygen atoms bound between the monomer units, in the ring, and in the hydroxyl groups, as illustrated in figure 2.3[16]

cross-2.1.3 Classification of pectin

Classification based on the solution: [18]

• Water-soluble pectin: It also known as free pectin, is composed of galacturonic acid radicals Some of these radicals contain (-COOH) groups and are predominantly present in the cell fluid

• Insoluble pectin: It is found in the cell wall, existing in the form of pectin combined with arabinan and is not soluble in water

Classification based on the degree of methylation:

• High Methoxyl Pectin (HMP): DE > 50% (typically 55–75%) It is usually used to produce high-calorie, high-sugar foods Traditional jams and jellies ( high sugar content) are a typical application for it, not recommended for diabetics This type of pectin may increase the viscosity of the product To form coagulation, it is necessary to have pH 3,1 - 3,4 and sugar concentration above 60%.[19]

• Low Methoxyl Pectin (LMP): DE<50%, usually between 20% and 40% The carboxyl groups in pectin can react with calcium ions to form a bond between two negatively charged carboxyl groups Unlike HMP, which requires an excessive amount of sugar, calcium ions can mix with pectin molecules to form a gel It's utilized to make low-sugar, low-calorie foods

Classification based on the state:

• Concentrated liquid Pectin

• Dried pectin extract

• Pectin powder

Classification based on the speed of gel formation:

• Pectin with very fast gelling speed (Ultra Rapid Set)

• Pectin with fast gelation speed (Rapid Set)

• Pectin with medium gelation speed (Medium Set)

• Pectin with a slow gelation speed (Slow Set)

• Pectin with an extremely slow gelation speed (Ultra Slow Set)

Classification based on the application field:

• Food Pectin

• Pharmaceutical pectin: apple pectin, modified citrus pectin

Classification based on the source material:

• Pectin from apple pulp

• Pectin of citrus fruit

Pectin's gelling ability can be understood as a partial dehydration of the molecules at a level in between that of the precipitate and the solution Pectins with high methoxyl content lack sufficient acid groups to precipitate with calcium ions or form gels, in contrast to alginate Although, in some situations, precipitation can be caused by other non-food ions like copper or aluminum Initial pectin can form a gel with a sugar content of approximately 80% (on the refractive scale) as the pH is decreased Additionally, at a lower pH, the gel can be achieved with less sugar At pH values below 3, pectin has an esterification level above 72%, which will produce gels of 55% or less [20]

Solubility of Pectin: Pectin is soluble in water and insoluble in alcohol and most organic solvents However, pectin in powder form is added to water, the formation of lumps can occur easily, making it challenging for the pectin to hydrate Soluble pectin is rapidly degraded by chemical reduction The pH and temperature of the solution affect the rate of breakdown Pectin is most stable at a pH of 4 Glycosidic bond hydrolysis can hasten the breakdown process through low pH and high heat Fee pectin loses its ability to coagulate in the presence of sugar To preserve the gelling capacity of soluble pectin, it is essential to avoid alkaline environments or the action of pectinase enzymes, which can lead to hydrolysis

[7] When soluble pectin is exposed to dilute alkali or pectinase enzymes, it releases the methyl group in the form of methyl alcohol The resulting remaining polysaccharide is then referred to as free pectin acid, indicating the presence of polygalacturonic acid Pectin acid can form calcium pectate salts, which convert into precipitates easily, so they are used to quantify pectin The solubility of pectin depends on various parameters including dissolved solids, reaction type, ionic strength, pH, and temperature.[21]

The rheological properties of pectin solution: Pectin solution exhibits viscosity, but its role as a thickening agent is not more effective compared to other water-soluble polymers.The rheological properties of pectin depend significantly on the presence of salts, especially calcium salts or metals with a valency greater than 1, and pH [22] Pectin with a higher average molecular weight has higher viscosity compared to pectin with a lower molecular weight [23] Pectin with a high ester content does not interact with metals, and its viscosity is higher due to the hydrophobic interactions of methyl groups [24]

2.1.1 Pectin extraction technique

2.1.1.1 Extract by water

There are number of free pectin in the plant cell wall, it can be easily extracted with water

When combining pectin extraction in hot water for an extended period of time, the process efficiency increases However, if pectin extraction at high temperatures for a long period of time, the problem must consider is the pectin degradation as well as the energy factor.[25]

2.1.1.2 Extract by acid

Using acidified water and heat is the most common method for extracting pectin from plant tissue A long period of direct heating should be avoided because it may cause thermal

degradation of the polymer Extraction conditions such as time, temperature and solvent ratio

in different studies depend on the desired ratio of pectin and pectin to be obtained However,

normally the temperature fluctuates from 50 to 100 OC during 0.5 to 5 hours To remove the

pulp, the hot acid extract was filtered through a cheese cloth or using centrifugation The filtrate was then cooled to 4 °C and precipitated with twice as much ethanol After mixing the solvent precipitate combination until the pectin floats, it is eliminated with cloth and

dried [26]

2.1.1.3 Extract by enzyme

In terms of pectin yield, enzymatic pectin extraction is more successful and safer for the environment Pectin extraction uses enzymes that can break down pectin and alter its physical and chemical properties, including hemicellulose, protease, polygalacturonase, cellulose, celluclast, alcalase, α-amylase, and neutrase, xylase, cellulose, β-glucosidase, endopolygalacturonase, and pectinesterase [27]

2.1.1.4 Extract by using microwave

Extraction with the aided of microwave relates to dielectric heating of plant compounds via microwave irradiation Dipolar rotation of water occurs as a result of microwave energy

absorption, resulting in heat creation within plant tissues Many researchers have lately

examined microwave-assisted extraction and discovered that it can significantly boost the quality and yield of pectin [28]

Increased microwave power resulting from higher microwave irradiation energy may enhance solvent penetration into the plant matrix and facilitate the effective delivery of solvent to plant cells for pectin extraction Extractable components can dissolve quickly thanks to the fast energy transfer to the solvent and matrix made possible by molecules interacting with the electromagnetic field Water heats effectively because it is a polar solvent that easily absorbs microwave radiation Moreover, microwave irradiation speeds up cell rupture by producing an abrupt rise in temperature and a spike in internal pressure inside plant sample cells This encourages sample surface destruction and, consequently, the exudation of pectin from plant cells into the surrounding solvents as well as the growth [29]

Through molecular interactions with the electromagnetic field, the increasing energy of microwave irradiation can facilitate solvent penetration into the plant matrix, efficiently deliver materials, and provide a rapid energy transfer to the solvent and matrix, enabling the extraction of components to dissolve The greatest yield from apple pomace and the shortest extraction time were obtained by optimizing the pectin extraction process using microwave assisted extraction as opposed to traditional heating

2.1.2 Applications of pectin

2.1.2.1 In food technology

Pectin is the most crucial gelling agent used to create the structural framework for various foods, particularly those derived from vegetables and fruits Its gel-forming ability is also used as a stabilizer for numerous additives, either in the final product or at an early stage in the manufacturing process.[8]

2.1.2.2 In fruit and vegetable processing technology

Pectin, a gelling agent, is commonly used in large quantities in fruit jams It is naturally present in fruits or can be added separately Soluble pectin is produced by breaking down protopectin during processing Depending on the type of fruit jam, achieving a high dry matter content (60-70%) and maintaining a low pH generally results in optimal gel conditions for HMP Gels will be produced using LMP for jams containing Ca2+ ions and low sugar content[18]

2.1.2.3 In confectionery technology

Pectin is extensively utilized in confectionery technology such as: marshmallows, cream cake tops, and fruit cakes to enhance appeal, create an elastic structure, intensify natural fruit flavors, and achieve a glossy surface for the product

2.1.2.4 In dairy product technology

In fruit yaourt, pectin creates a smooth structure, which evenly distributes small fruit samples in milk, keeps the fruit from being separated from the yaourt, and gives the product a smooth surface In drinking yogurt, pectin protects proteins from being denatured during the sterilization process, prevents protein precipitation, helps stabilize the product, and achieves the best sensory properties

2.1.2.5 In beverage processing technology

Pecin makes the product turbid and has low energy natural carbohydrates

2.1.2.6 Other applications

In addition, application of pectin can be used to make edible packaging and film by dipping the product in low methoxyl pectin solution or natripectate then dipping it in calcium chloride solution

2.1.2.7 In pharmaceuticals

Pectin has a major impact on blood cholesterol levels It helps lower blood pressure and cholesterol in many individuals, as observed in various test situations following thorough testing It is necessary to consume at least 6 grams of pectin per day to have a temporary cholesterol-lowering effect.[21]

Pectin has attractive potential for pharmaceutical applications, including the preparation of oral medications and injectable drugs aimed at controlling bleeding after maxillofacial surgery, gynecological procedures, and more These simple approaches, combined with its low virulence properties, render pectin an attractive and promising substance for the pharmaceutical industry, both presently and in the future.[30]

2.2 Overview about durian

Figure 2.4 Durian

Durian is a tropical fruit, one of the important fruit trees and high nutritional value in Southeast Asia which belongs to the genus Durio, family Bombacaceae and includes 28 species [31] Therefore, it is known as the "king of fruits" [32] Durian is a fruit tree with very high economic efficiency It is being developed very strongly in Southeast Asian countries such as Thailand, Malaysia, Vietnam However, this fruit tree requires the application of many techniques to improve flowering, yield, and quality In Vietnam, the fruit is harvested in May and July of the year Polysaccharides including cellulose, hemicelluloses, lignin, and pectin make up most of the plant cells in durian fruit.[33]

Durian is suitable for sandy loam or loam soils, alluvial soils, basalt red soils, not suitable for sandy soils, especially sandy soils The tree can be from 27-40m tall in natural conditions

However, in cultivated conditions, it is only 10-12m high and the diameter of the tree is 1.2m This is a woody, erect, coarse-barked plant, with a large and wide crown below, the higher up the top, the smaller it looks like a cone The leaves of the plant are single alternate, thick leaf blades have an oblong ovoid shape, which is usually 5-7cm in length There are small scales surrounding the deciduous leaves, the petioles have a slightly pointed shape Instead of blooming separately, durian flowers grow in clusters of one to fifteen in the main branches, which then bear huge fruits When in bloom, flowers smell quite intense The fruit is shaped like a little sphere The fruit bears small, extremely sharp spines on the outside The shattered shell has a distinct scent when ripe Two to three seed packs with a very thick covering of rice and a fatty, sweet, fragrant, fibrous taste linked to the seeds are found inside each fruit compartment.[34]

In Vietnam, in addition to Monthong durian, Ri-6 is one of the popular cultivars today [34] Most frequently grown in the provinces of Tay Ninh, Binh Duong, Tien Giang, and Dak Lak, Binh Thuan, Dong Nai, and Vinh Long… Durian Ri-6 has quite strong growth, beautiful branches, bears fruit after 4 years of planting and the fruit is quite large It has characteristics: dry, smooth, low-fiber, less swollen, dark yellow, beautiful When ripe, each citrus of the fruit has characteristics: dry, smooth, less fibrous, less swollen, dark yellow, beautiful Distinctive features of Ri6, when young fruits will have a rounded oblong shape, green skin, small and tight spines As ripe, the fruit will have an oblong egg shape to nearly round, weighing about 3-5kg, the wedges expand largely The fruit peel has sharp pyramidal spines, usually weighing more than half the total weight of the fruit is green to yellowish-brown These ripe fruits will often be difficult to crack but easy to separate The fruits are oblong-ovoid or nearly rounded with an average size, weighing from 2 to 4.5 kg, depending on the variety.[34]

In durian, the edible citrus part accounts for only one-third of the fruit's weight, while the seeds (20-25%) and peel are often removed The edible part of the fruit is only 15-30% of the whole fruit mass 65–70% of the durian weight that is inedible are called rinds, and they have the potential to produce a lot of garbage for the environment.[35]

2.3 Response surface designs

It is vital to use modeling approaches to precisely establish the optimal conditions for obtaining high yield, DE, AUA from the material One of the most effective methods for examining the effects of individual parameters and their interactions on the dependent responses is response surface methodology (RSM)[36] RSM exhibits a number of benefits over the traditional single-variable optimizing approach, and a clear expression of the interactive influences of the parameters on the responses using 2D contour and 3D surface profilers [36, 37] [38]

Figure 2.5 A Box-Behnken design for three Factors

Figure 2.6 Generation of a Central Composite Design for two Factors

There are two response surface designs: Box-Behnken designs (Figure 2.5) and Central Composite Designs (CCD) (Figure 2.6) The Box-Behnken design is an independent quadratic design in the absence of an embedded factorial or fractional factorial design In this design, the treatment combinations are positioned in the center and at the midpoints of

the edges of the process space These designs require three layers of each factor and are rotatable, or nearly so The designs' potential for orthogonal blocking is less than that of central composite designs [39] A Box-Wilson type Central Composite Design, consists of an embedded factorial or fractional factorial design with center points that are supplemented with a number of ‘star points' that allow curvature estimate[39] If the distance from the design space's center to a factorial point is ± 1 unit for each factor, the distance from the design space's center to a star point is |α| > 1 The precise value is determined by the design's desired features as well as the number of components involved

Figure 2.7 Comparison of the Three Types of Central Composite Designs

The features of the three types of central composite designs are central composite circumscribed (CCC), central composite inscribed (CCI), and central composite face centered (CCF) Figure 2.7 depicts three different forms of central composite designs for two elements It is worth noting that the CCC investigates the greatest process space, whereas the CCI investigates the smallest process space The CCC and CCI are both rotatable, while

the CCF is not The design points of the CCC design describe a circle enclosed by the factorial square The CCC design points depict a sphere around the factorial cube for three factors

In this research, the choice of Central Composite Rotatable Design (CCRD) stems from its ability to anticipate responses using a limited set of experimental data This design is particularly advantageous as it allows for the variation of all parameters within a specified range [40, 41]

Furthermore, the flexibility provided by CCRD enhances the construction of more robust models, particularly in scenarios where experimental errors may influence certain experiments [42] Constructing statistical models can prove valuable for predicting and comprehending the outcomes of various experimental factors The key strength of RSM with Central Composite Rotatable Design (RSM-CCRD) lies in its ability to optimize multiple operational variables concurrently through a limited number of experiments, resulting in time and labor efficiency

Figure 2.8 Central composite rotatable design (CCRD)

2.4 Summary of previous studies on durian rind

Durian is a tropical fruit, one of the important fruit trees, and has high nutritional value in Southeast Asia and around the world Because durian peels are frequently discarded as rubbish Thus, it would be highly advantageous to develop it into a value-added product like pectin Therefore, in 2019, Hasem et al researched the extraction and partial characterization of durian rind pectin using the conventional acid extraction method and described the properties of pectin in terms of yield, water activity, moisture, and ash content Pectin was extracted with HCl, pH 2.5 at 85°C, for 60 minutes The results showed that the pectin yield in durian peel was 73.67%, moisture was 11.53%, ash content was 4.67%, and water activity was 0.452 Furthermore, this study demonstrates that pectin extraction was successful and offers possible environmental and economic advantages for industrial pectin extraction[43]

In 2009, Wong Weng Wai et al used the response surface approach to improve the pectin extraction process from durian rind and study the impact of temperature, pH, and heating duration on the degree and performance of esterification (DE) Based on the dry weight of the durian rind, the yield and DE of the extracted pectin were found to range from 2.27% to 9.35% and 47.66% to 68.6%, respectively 85 degrees Celsius, 4 or 1 hour, and a pH of 2 or 2.5 were the ideal parameters for obtaining maximum yield and DE [44] Prakash Maran conducted research using the Box-Behnken response surface methodology to investigate and optimize water extraction conditions for maximizing pectin extraction from durian peel The studied parameters Using the Box-Behnken response surface methodology, Prakash Maran studied and optimized water extraction conditions to maximize pectin extraction from durian rind These conditions included solid-liquid ratios ranging from 1:5 to 1:15 g/ml, pH 2 to 3, extraction times spanning from 20 to 60 min, and extraction temperatures varying from 75 to 95°C The optimal results were determined to be obtained with the following parameters: a pH of 2.8, an extraction time of 43 minutes, an extraction temperature of 86°C, and a ratio of 1:10 g/ml.[45]

In 2023, Sze Hui Jong et al conducted research on the impact of acid type and concentration on durian rind pectin yield, AUA, and DE They utilized five different concentrations (0.0001, 0.001, 0.01, 0.1, and 1.0 M) of different acids, including H2SO4, HCl, HNO3, C6H8O7, tartaric, and acetic As a result, the concentration of acid increased (0.1, 1.0 M), and