Distribution of Starch-degrading Enzymes in Rice Grains of Different Cultivars and Elution Behavior during Cooking

Abstract

Rice grains contain starch-degrading enzymes, including α-glucosidases, α-amylases, β-amylase, pullulanase and isoamylases. We investigated the distribution of these enzymes in raw rice grains, and their elution behavior during cooking in Nipponbare and Habutaemochi cultivars. Different distributions and elution behaviors were observed among the different cultivars. These results suggest that differences among cultivars with regard to activation and starch degradation by these enzymes during rice cooking should be taken into consideration.Keywords: starch-degrading enzymes, immunoblot, rice cooking, elution Abbreviations: PBSD medium, sodium phosphate buffer (pH 7.0) containing DTT and NaCl; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis *To whom correspondence should be addressed. E-mail: ookura@affrc.go.jp IntroductionRice (Oryza sativa) is a major food in Asian countries, including Japan. Extensive studies have been carried out to determine how preferable taste can be achieved in rice cooking. It was found that physical properties, such as stickiness and hardness (Okabe, 1979;Maruyama, 1991;Kainuma, 1992;Okadome et al., 1996;Okadome et al., 1999), and chemical components, such as sugars and amino acids, contribute to the taste of cooked rice (Matsuzaki et al., 1992;Tajima et al., 1992;Ikeda, 2001). The amounts of sugars (reducing sugars and oligosaccharides) and amino acids are correlated with the activities of starch-degrading enzymes and proteases, which are activated during cooking (Maruyama et al., 1981;Kasai et al., 2000;Maruyama, 2002). Kasai et al. measured the amounts of reducing sugars and free sugars, which remained in the rice grains or eluted into the cooking water at the point of soaking, heating and murashi duration. They revealed that reducing sugars and glucose showed the largest increase in a temperature range of 40 − 60℃ during cooking in both rice grains and cooking water. They reported this was due to the activation of enzymes to convert starch to reducing sugars in this temperature range. Mabashi et al. (2010) analyzed the hydrolytic activities of the endogenous starch-degrading enzymes for the soluble starch in the various cultivars, and revealed that 60℃ was the common key temperature in various cultivars for the production of glucose by endogenous enzymes.The enzyme isoforms that exist in dormant rice and degrade starch granules during germination are α-amylases (EC 3.2.1.1) (Mitsui et al., 1996;Yu et al., 1996), β-amylases (EC 3.2.1.2) (Matsui et al., 1975;Yamaguchi et al., 1999), isoamylase (EC 3.2.1.68) , pullulanase (EC 3.2.1.41) (Takeuchi et al., 1999) and α-glucosidases (EC 3.2.1.20) (Takahashi et al., 1971;Matsui et al., 1988). Two studies have demonstrated that rice grains contain more than 10 α-amylase isoforms (Daussant et al., 1983;Mitsui et al., 1996). These isoforms are classified into two groups based on their optimal temperatures: α-amylase I (70℃) and α-amylase II (37℃) (Mitsui et al., 1996). These α-amylase isoforms are strongly induced during germ...

Translocation of Barley β-amylase into Rice Grains during Cooking Rice Mixed with Barley (Mugimeshi)

“…proteins To check the possibility that the anti-barley β-amylase antibody (88-1) cross-reacted with rice β-amylase or other rice proteins, immunoblot analysis of the rice grains extract and extract. This observation was consistent with our previous report, which showed that β-amylase in Nipponbare was hardly detected, throughout the rice grains, with anti-rice β-amylase monoclonal antibody (Tsuyukubo et al, 2013).…”

“…To understand how crop starch is hydrolyzed during cooking, we focused on β-amylase as the starch-degrading enzyme. Using immunoblot analysis with an antibody against rice β-amylase, we showed that β-amylase was hardly detected in whole rice grains of the rice cultivar Nipponbare (Tsuyukubo et al, 2013). However, the distribution and functions of barley β-amylase during cooking have not been reported especially when barley is cooked with rice (Mugimeshi).…”

Effect of Rice Variant on the Ease of Swallowing Blender-made Rice Gruel

“…Measured with water (A: no enzyme inhibitors), the peak viscosity for GJ was 1.28 ± 0.05 (×10 3 cP), but when measured with the copper sulfate solution (B: enzyme inhibitors added), the peak viscosity increased to 2.47 ± 0.06 (×10 3 cP), similar to the reports of Shibuya et al (1983) and Shoji and Kurasawa (1988). As α-amylase is an extracellular enzyme in plants from the family Poaceae, it leaches into the water during soaking and cooking, and also acts upon starch in NGJ (Tsuyukubo et al 2013). This appeared to be why the peak viscosity of NGJ+GJ without enzyme inhibitors (A) was lower than that measured with enzyme inhibitors (B).…”