Effect of domestic cooking on rice protein digestibility.

Kunlun Liu,Fusheng Chen,Jiabao Zheng

doi:10.1002/fsn3.884

Abstract

The effects of washing, soaking, and common domestic cooking methods (normal cooking, high‐pressure cooking, and microwave cooking) on protein content, in vitro protein digestibility, and amino acid composition of japonica and indica rice were investigated. All processes in rice domestic cooking did not affect protein content. However, the gastric and gastrointestinal protein digestibilities decreased significantly after cooking. Protein solubility methods were used to observe the formation of disulfide bonds and hydrophobicity interactions after cooking. Disulfide bonds and hydrophobicity interactions were formed during cooking, and the cooking‐induced disulfide bond cross‐linking decreased the protein digestibility observably. Moreover, the solubility of 13 kDa prolamin subunit sharply decreased after cooking due to intramolecular disulfide bond cross‐linking. Therefore, cooking‐induced formation of intramolecular disulfide linkages might stabilize and strengthen the structure of protein body‐I, which exhibited strong resistance to proteases, particularly pepsin. Cooking had limited effect on amino acids.

Highlights

Rice (Oryza sativa L.) is the predominant staple food and provides over 20% of calorie needs of nearly two-thirds of the world’s population
Zhang et al (2010) reported no significant change was observed in protein content of cooked milled rice
The GI- PD of β-mercaptoethanol cooked rice was significantly higher than that of the rice cooked by deionized water. These findings indicated that the formation of disulfide bond cross-linking during cooking negatively affected the rice protein digestibility, whereas disulfide bonds in the native structure might have a limited effect on protein digestibility

Summary

Introduction

Rice (Oryza sativa L.) is the predominant staple food and provides over 20% of calorie needs of nearly two-thirds of the world’s population. The protein contents in brown and milled rice are 7.1%–8.3% and 6.3%–7.1%, respectively. With regard to the superior quality of rice protein, the yield of utilizable protein in rice is higher than in other cereals (Birla et al, 2017). Factors affecting cereals protein digestibility can be categorized into exogenous and endogenous factors. Exogenous factors mainly include grain organizational structure, starch, and polyphenols. Endogenous factors mainly include secondary structure, hydrophobicity of hydrophobic protein (i.e., kafirins and zeins), and protein cross-linkings (e.g., disulfide cross-linking, hydrophobic cross-linking, and isopeptide cross-linking). After cooking, the protein digestibilities of brown rice and milled rice decreased by 6.8% and 11.4%, respectively (Bradbury, Collins, & Pyliotis, 1984). The decrease might be due to cooking-induced formation of a cysteine-rich core, which can be resistant to proteases rather than isopeptide cross-linkings. Collier, Barber, and Jna (1998) fed cooked and uncooked rice

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