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
2 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
LITERATURE REVIEW
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
Frying Seasoning Packaging Snack foods
Figure 2.1 Production line schema of snack food processing (Moscicki & Van
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)
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)
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
After the extrusion process, pellets contain from 20 to 30% of water; therefore, before packing and storage, they must be dried until the moisture content level decreases below 10% A drying phase plays a very important role since the product need to receive the definitive quality characteristics, which are adequate moisture stability during storage, susceptibility to expansion and durability (Moscicki & Van Zuilichem, 2011)
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 (