Several studies have demonstrated that there is a starch fraction resistant to enzymatic digestion in the small intestine. The research group of EURESTA (European Resistant Starch research group) defined resistant starch (RS) as the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals.
Resistant starch production
Liljeberg Elmståhl (2002) determined the resistant starch (RS) content of starchy foods on the Swedish market and estimated an average daily RS intake of 3.2g in a Swedish diet. Due to its health benefits, it was aimed to develop a RS production process and thus to enhance the RS content in food. Beforehand a standardised determination method had to be invented and validated. Several in vitro methods were utilised (Englyst et al., 1982; Berry, 1986; Björck et al., 1987; Englyst et al., 1992; Saura-Calixto et al., 1993; Englyst et al., 1996; Goñi et al., 1996) before Mc Cleary and co-workers developed an official AOAC method for the determination of RS in plant and starch materials (McCleary & Monaghan, 2002; McCleary et al., 2002). This method was applied for our experiments.
The increase of resistant starch (RS) content in starches is based on the recrystallisation, i.e. retrogradation of amylose subsequent to thermal gelatinisation. A favoured approach for the enhancement of RS content was an autoclaving step prior to cooling and/ or drying (Berry, 1986; Berry et al., 1988; Siljeström et al., 1989; Eerlingen et al., 1993a; Escarpa et al., 1996; Shamai et al., 2003). Sievert and Pomeranz (1989) further increased the RS yield by up to 20 autoclaving-cooling cycles. Another proceeding for the RS production was an enzymatic debranching of gelatinised starch or starch degradation product followed by a drying step (Chiu et al., 1994; Kettlitz et al., 2000). Factors influencing the yield of RS were the gelatinisation temperature, treatment steps altering the chemical composition of the starches like defatting and debranching by acid hydrolysis or enzyme hydrolysis, the storage temperature, the storage time, and combinations of treatments e.g. freeze-thawing, freeze-drying, annealing subsequent to acid hydrolysis and autoclaving-storing-cycles (Sievert & Pomeranz, 1989; Eerlingen et al., 1993a; Vasanthan & Bhatty, 1998; Chung et al., 2003).