Abstract
Starches were extracted from chickpea (C.P.), corn (C.S.), Turkish bean (T.B.), sweet potato (S.P.S.), and wheat starches (W.S.). These starches exhibited different amylose contents. The extracted starches were annealed in excess water and in germinated sorghum extract (GSE) (1.0 g starch/9 mL water). The α-amylase concentration in the GSE was 5.0 mg/10 mL. Annealing was done at 40, 50, and 60 °C for 30 or 60 min. The pasting properties of annealed starches were studied using Rapid Visco-Analyzer (RVA), in addition to the swelling power. These starches exhibited diverse pasting properties as evidenced by increased peak viscosity with annealing, where native starches exhibited peak viscosity as: 2828, 2438, 1943, 2250, and 4601 cP for the C.P., C.S., T.B., W.S., and S.P.S., respectively, which increased to 3580, 2482, 2504, 2514, and 4787 cP, respectively. High amylose content did not play a major role on the pasting properties of the tested starches because sweet potato starch (S.P.S.) (22.4% amylose) exhibited the highest viscosity, whereas wheat starch (W.S.) (25% amylose) had the least. Therefore, the dual effects of granule structure and packing density, especially in the amorphous region, are determinant factors of the enzymatic digestion rate and product. Swelling power was found to be a valuable predictive tool of amylose content and pasting characteristics of the tested starches. The studied starches varied in their digestibility and displayed structural differences in the course of α-amylase digestion. Based on these findings, W.S. was designated the most susceptible among the starches and S.P.S. was the least. The most starch gel setback was observed for the legume starches, chickpeas, and Turkish beans (C.P. 2553 cP and T.B. 1172 cP). These results were discussed with regard to the underlying principles of swelling tests and pasting behavior of the tested starches. Therefore, GSE is an effortless economic technique that can be used for starch digestion (modification) at industrial scale.
Highlights
Starch molecular structure contrasts by botanical source
The limited increase in peak viscosity indicates that the amorphous region of the C.S. granule did not undergo significant molecular arrangement, which is the main effect of annealing on the granules, since annealing as a process is described as heating starch in appreciable amount of water above glass transition and below gelatinization temperature
The limited increase in peak viscosity indicates that the amorphous region of the C.S. granule did not undergo significant molecular arrangement, which is the main effect of annealing on the granules, since annealing process is described as heating starch in appreciable amount of water above 7glass
Summary
Starch molecular structure contrasts by botanical source. The X-ray patterns of starches such as corn and wheat have an A-type crystal within the granule, while tubers exhibit B-type. B-type, the A-type crystal is a closely packed arrangement of double helices which is more stable thermodynamically. The temperature during the growth of the plant could influence starch composition (ratio of amylose to amylopectin) and structure [1]. Endothermic transition is observed by DSC when starch is heated in an appreciable amount of water, which is termed gelatinization. The gelatinization temperature is correlated with amylopectin located in the crystalline region of the granule [2]
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