Abstract
The fine molecular structure of starch governs its functionality and digestibility, and enzymatic approaches can be utilized to tailor its properties. The aim of this study was to investigate the in situ modification of starch by amylomaltase (AMM) from Thermus thermophilus in model starch systems subjected to hydrothermal treatments under standardized conditions and the relationship between molecular structure, rheological properties and in vitro digestibility. When low dosages of AMM were added to a wheat starch suspension prior to submitting it to a temperature-time profile in a Rapid Visco Analyzer, the increased peak viscosity observed was attributed to partial depolymerization of amylose, which facilitated starch swelling and viscosity development. At higher dosages, the effect was smaller. The low cold paste viscosity as a result of the activity of AMM reflected substantial amylose depolymerization. At the same time, amylopectin chains were substantially elongated. The longer amylopectin chains were positively correlated (R2 = 0.96) with the melting enthalpies of retrograded starches, which, in turn, were negatively correlated with the extent (R2 = 0.92) and rate (R2 = 0.79) of in vitro digestion. It was concluded that AMM has the potential to be used to deliver novel starch functionalities and enhance its nutritional properties.
Highlights
Starch is the most abundant glycemic carbohydrate in the human diet
Different dosages of AMM influenced the viscosity of starch slurries differently
It was remarkable that even though the control sample (2825 mPa·s) and that treated with 45 U/g starch dm exhibited the same peak viscosity (2815 mPa·s), their rapid visco analysis (RVA) profiles and the rate of viscosity development were explicitly different (Figure 1C)
Summary
Starch is the most abundant glycemic carbohydrate in the human diet. It is mainly digested by salivary and pancreatic α-amylase and intestinal mucosal α-glucosidases. Pancreatic α-amylase internally hydrolyzes α-1,4-glycosidic bonds, thereby releasing short-chain hydrolysis products, namely maltose, maltotriose and α-limit dextrins. The latter contain undigested α-1,6-glycosidic bonds [1]. The α-glucosidases on the small intestine epithelium continue the hydrolysis into glucose that is absorbed by the enterocytes [2]. The molecular structure of starch polymers governs starch digestion, especially in the absence of external barriers that impede access/binding of pancreatic α-amylase to starch [3]
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