Cooking, morphological, mechanical and digestion properties of cooked rice with suppression of starch branching enzymes

Abstract

Kernel components and some physicochemical properties of cooked rice were investigated and compared between a popular japonica rice Wu-xiang 9915 (WX) and its transgenic line (WX-SBEI/IIb−) with suppression of starch branching enzyme I/IIb. The starch content, especially amylopectin content, was significantly lower in WX-SBEI/IIb− than in WX. Brown rice flour had markedly higher gelatinization temperature in WX-SBEI/IIb− than in WX. The cooked kernels of WX-SBEI/IIb− had significantly lower volume swelling, leached material amount and wet weight than those of WX during cooking. Starch granules in WX kernel could be gelatinized completely and gradually from the exterior to the interior of endosperm, leading to breakage of cooked kernels. However, aggregate, elongated and small starch granules in the exterior of WX-SBEI/IIb− endosperm could not be gelatinized completely and remained their morphologies during cooking, leading to a high resistance of kernels to cooking. Brown rice flour of WX-SBEI/IIb− had significantly lower pasting viscosities, storage modulus and loss modulus but higher loss angle tangent than that of WX. The cooked kernels of WX-SBEI/IIb− had considerably higher hardness, springiness and cohesiveness but lower adhesiveness than those of WX. The starch in cooked kernels was more resistant to digestion in WX-SBEI/IIb− than in WX.