Alkali treatment affects in vitro digestibility and bile acid binding activity of rice protein due to varying its ratio of arginine to lysine

Characterization of rice starch and protein obtained by a fast alkaline extraction method

“…Table 1 also shows the amino acid composition RF and IPPC. The values found are very similar to those found by Kumagai et al (2006) and Yang et al (2012) in rice protein concentrates obtained by alkaline extraction. According to Friedman (1996), high pH induces racemization of L-amino acid residues to D-isomers and the formation of cross-linked amino acids such as lysinoalanine.…”

“…In that study, the authors performed the extraction using 0.2% NaOH under stirring at room temperature for 1h. Yang et al (2012) observed a decrease in cysteine and arginine content in rice protein extracted with 0.3% NaOH compared to rice protein extracted with 0.1% and 0.2% NaOH at room temperature. Faist, Drusch, Kiesner, Elmadfa and Erbersdobler (2000) state that the formation of lysinoalanine is followed by decreased lysine content, which was not observed in the present study.…”

Characterization and In Vitro digestibility of rice protein prepared by enzyme-assisted microfluidization: Comparison to alkaline extraction

“…On the other hand, the difference in hydrolysis behavior may be related to protein denaturation of rice protein under alkaline conditions. In fact, previous studies have confirmed that alkaline treatment improves in vitro and in vivo digestibility of protein due to the structural changes of the prolamin/PB-I particle (Kumaga et al, 2006;Kubota et al, 2010;Yang et al, 2012). Loosened and swollen PB-I structure in alkali-prepared protein had been directly observed using electron microscopy (Kumaga et al, 2006;Kubota et al, 2010).…”

“…It was noteworthy that EM-RP exhibited higher arginine content (Table 1). Dietary arginine, as one of the important factors to affect cholesterol metabolism, is believed to be involved in the regulation of digestibility even if the mechanism of action was not clear (Yang et al, 2012). The richness of arginine in this protein may be favorable to improve the digestibility of rice protein.…”

“…Alkali treatment is considered to break some of the hydrogen, amide, and disulfide bonds in rice glutelin, leading to the reduction in molecular size of protein and the improvement in protein extraction (Hamada, 1997). Recently, it has been reported that this method improves in vitro and in vivo digestibility of rice protein, which is associated with the modification of protein body structure and amino acid composition (Kumaga et al, 2006;Kubota et al, 2010;Yang et al, 2012). Unfortunately, exposing protein to severe alkaline conditions may cause some undesirable side reactions, degradation of protein, and potential toxicity, such as lysinoalanine, resulting in the loss of nutritional value (Shewry and Miflin, 1985).…”