ANSWER
Moisture uptake and Oil Absorption – Affecting the Shelf Life of Chip Products
The two main deterioration mechanisms in snack foods are moisture uptake and oxidation; causing loss of crispiness and creates rancid flavor (Cakmak et al., 2016). Thus, the key parameter in prolonging the shelf life of snacks, in this case, salted egg fish skin, is to have a good control of moisture uptake and oil absorption during production. The shelf life of this snack is then guaranteed with a higher degree of crispness with minimal rancid flavour. In storage, optimal crispness at ambient temperatures is often associated with low moisture products (Bhandari & Roos, 2016). Crispy foods will experience deterioration after coming into contact with a high moisture layer. The dry surface of these foods tends to draw moisture from the surrounding environment or in contact with a humid layer. The migration of water will then be prompted from a higher content location to a lower, and the loss of crispiness can be directly related to the kinetics of water uptake (Chen & Engelen, 2012).
Many sensory researches have concluded that the perceived crispness of the chips drops with increased moisture content or water activity of the product. Sharma, et al., (2016) has mentioned that the crispness index of sweet potato chips is negatively influenced with high moisture content. Similarly to tortilla chips, salted egg fish skin with porosity and low moisture content has great crispness (Bhandari & Roos, 2016; Kawas and Moreira, 2001). In most meat and fish snack foods, the water content is greatly reduced so that microbial growth is not supported (Lucas & Rooney, 2001). The introduction of moisture onto the chips will result in deteriorated sensory quality as well as decreased shelf life due to higher susceptibility of microbial attack under high moisture condition. However, removing moisture from these products is cost-ineffective and also affects the flavour and texture changes (Lucas & Rooney, 2001). Hence, the induced reduction of water activity and moisture content enhance sensory characteristics, eating quality as well as create shelf-stable snack chips as are free microbial spoilage (Charalampopoulos & Rastall, 2009; Lucas & Rooney, 2001).
Addition of Hydrocolloids – Improving Crispness and Reducing Rancidity
Hydrocolloids have been used to coat a variety of foods due to their desirable barrier properties against gas such as oxygen and carbon dioxide, moisture and lipids (Rimac-Brnčić et al., 2004; Albert& Mittal, 2002). The additional barrier on the food surface helps to retain aroma and flavour molecules inside the food product (Williams & Philips, 2014), attributed to their ability to modify the rheology of food systems (Saha & Bhattacharya, 2010). Some of the useful hydrocolloids are based from cellulose derivatives such as methyl cellulose (MC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC) and carboxyl methyl cellulose (CMC), which are water soluble with good film-forming properties.
Adding hydrocolloids to coating for crusted products plays a role in the crispness creation of the final product (Roudaut, et al., 2002). Hydrocolloid such as Arabic gum is known for its texturizing capabilities (Williams and Phillips, 2000). Fish skin, in this case, is a food ingredient with rich unsaturated fat. A related interest, to produce products with increased proportions of unsaturated fats, may be met by use of appropriate frying oils high in unsaturated, but note the deleterious effect of these oils on keeping quality due to their greater susceptibility to oxidative rancidity (Ranken, 2012). Thus, the tendency of this product to get rancid during storage is low, if it takes up less oil absorption during its production which could prevent lipid oxidation. Not to mention, the lipolytic enzymes from foreign matters which may be introduced from improper storage, can also lead to production of disagreeable flavours and poor shelf life (Paine & Paine, 2012).
Many studies have been established regarding the positive influence of hydrocolloids on pre-treatment of fried chips. It has been proposed that the moisture retention increased in the chips when coated with increasing concentration of hydrocolloids. The higher initial moisture content of chip is preserved before further processing, for example, frying, which results in a reduced oil absorption. From the work of John & Hathan (2014) involving Taro chips, they proved that hydrocolloids such as pectin, guar gum and methyl cellulose could result in reduced oil absorption and better quality chips in terms of sensory characteristics.
References
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Rimac-Brnčić, S., Lelas, V., Rade, D., & Šimundić, B. (2004). Decreasing of oil absorption in potato strips during deep fat frying. Journal Of Food Engineering, 64(2), 237-241. https://doi.org/10.1016/j.jfoodeng.2003.10.006
Saha, D. & Bhattacharya, S. (2010). Hydrocolloids as Thickening and Gelling Agents in Food: A Critical Review. Journal of Food Science and Technology, 47(6), 587-597.
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Williams, P. A., & Phillips, G. O. (2000). Introduction to food hydrocolloids. In G. O. Phillips, & P. A. Williams (Eds.), Handbook of food hydrocolloids. New York: CRC Press Inc.
Williams, P.A. & Philips, G.O. (2014). Gums and Stabilisers for the Food Indsutry 17: The Changing Face of Food Manufacture: The Role of Hydrocolloids (p. 278). London: The Royal Society of Chemistry.
