Resistant starch (RS) in battered fried products: Functionality and high-fibre benefit

Abstract

The functionality and suitability as a source of fibre of type 3 resistant starch (RS3) in low oil content fried battered squid rings prepared without pre-frying were analysed.

The addition of RS3, even at levels of 20%, did not affect the ability of the methylcellulose batter to increase its consistency upon heating at a temperature of approximately 35 °C. Replacement of wheat flour by 20% RS3 increased the total dietary fibre content from 5.0% to 13.2%. After frying, a significant increase in the hardness and fragility of the batter crust and a more intense golden-brown colour were found. An acceptability test performed by a panel of 50 consumers rated all the fried battered food equally (no RS3, 10% RS3 and 20% RS3). This result shows that RS3 can be incorporated into the battered food as a source of dietary fibre, up to a concentration of 20%, without comprising consumer acceptability.

Introduction

The greater awareness by consumers of the relationship between a good nutritious diet and health and well-being has been one of the reasons for the increase in popularity of novel food with better nutritional properties.

The advent of fried food that absorbs less oil during frying is an example. A new industrial process to produce battered food without pre-frying has recently been developed (Fiszman et al., 2003). The advantage of the new process is that the battered food product does not contain industrial oil and the amount of oil absorbed during frying prior to consumption is lower than in a conventional process. For this reason, it can be considered a healthier alternative to the conventional process.

Crispness is one of the most important quality aspects of battered food. Extensive research has been conducted to investigate the influence of batter ingredients on crispness development. High-protein wheat flour or vigorously mixed batters are associated with a soggy and unpleasant texture. Cereal starches tended to produce fried batters with better properties than root and tuber starches (Matsunaga, Kawasaki, & Takeda, 2003). Crispness has been found to be positively correlated with amylose content (Altunakar, Sahin, & Sumnu, 2004; Mohamed, Hamid, & Hamid, 1998). Starch resistance to gelatinization and granule disintegration are linked to a crispier fried batter (Matsunaga et al., 2003). These authors explained that amylose contributes to crispness because it restrains the disintegration of the starch granule structure. In comparison to native wheat starch, modified corn starch, or dried egg and gluten, the use of corn dextrin (at a level of 7.5%) has shown the highest contribution to crispness in battered squid rings prepared without pre-frying (Salvador, Sanz, & Fiszman, 2005). In conventional battered food, the use of corn dextrin produced a prolonged period of crispness retention after frying (Baixauli, Sanz, Salvador, & Fiszman, 2003).

Incorporating a source of resistant starch (RS) into waffles increased the sensory score for crispness (Yue & Waring, 1998). However, it would appear that the effect of RS on the crispness of fried battered food has not yet been studied. Adding RS to food has the additional advantage of increasing the food's nutritional properties.

RS is defined as the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals (Asp & Björck, 1992). According to the latest definition of dietary fibre (De Vries, 2003), RS is considered fibre and it is determined as such by the latest official method of fibre analysis (AOAC 991.43) (Haralampu, 2000). The fact that RS escapes digestion in the small intestine confers many positive health effects. Some of the benefits are like those of traditional fibre and others are unique to RS. One of the interesting characteristics of RS is its fermentation pattern, mainly the profile of short-chain fatty acids (SCFA) which is produced and its relatively slow rate of fermentation. Indeed, its production of butyrate, one of the three main SCFA produced during colonic fermentation, is higher than for most dietary fibres. Food rich in RS is also suitable for controlling blood glucose levels, due to the slow digestion of RS.

Different types of RS have been identified (Champ, 2004). RS type 1 (RS1) is a physically inaccessible starch found in starchy foods, which are not fractionated and refined, mostly pulses and some cereals. RS type 2 (RS2) refers to native RS granules. RS type 3 (RS3) comprises retrograded starches. Since the first commercial RS was introduced in Australia in 1993 (Sajilata, Singhal, & Kulkarni, 2006), sources of RS2 and RS3 have been commercially available for including in foods. Of particular interest is the high thermal stability of RS3, which allows it to remain stable during most normal cooking operations. Finally, RS type 4 (RS4) is made up of chemically modified starches with a far higher number of modifications (starch esters, ethers and cross-bonded) than the usual chemically modified starches authorised in Europe. RS4 is not authorised in Europe, though it is in Japan.

Up to now, the types of food that have been enriched with RS are mainly low and moderate moisture foods, such as baked products (bread, muffins, cakes, biscuits, cereal bars), extruded cereals and pasta. In these foods, enrichment with RS has been found to increase the total fibre content while influencing the sensory properties less than enrichment with traditional fibre. This result has been associated with the lower water retention capacity, white colour, fine particle size and bland flavour of RS (Baghurst, Baghurst, & Record, 1996; Salvador, Baixauli, & Fiszman, 2006; Yue & Waring, 1998; Zallie, Altieri, Chiu, & Henley, 1996).

The objective of the present investigation was to study the suitability of including RS in battered food prepared by a process without pre-frying. Due to the high temperatures necessary for frying (180–190 °C), a source of RS3 (Novelose 330) was selected because of its higher thermal stability. The specific aspects investigated were the influence of RS on the thermo rheological behaviour of the batter, its influence on the fibre content, crispness, colour and oil and moisture content of the batter-coated food and, finally, the consumer acceptability of the new battered food.