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- Aroma Formation from Rice Bran Protein Concentrate by Acid Hydrolysis...
Aroma Formation from Rice Bran Protein Concentrate by Acid Hydrolysis and the Maillard Reaction
Abstract:
The hydrolysates of rice bran protein concentrate (RBPc) were prepared by two different methods of acid hydrolysis. First, RBPc was hydrolyzed by 0.5 N aqueous HCl at 95ºC for 12 and 36 h (mild hydrolysis) and freeze dried. Second, RBPc was hydrolyzed by 4.0 N aqueous HCl at 95ºC for 72 h (strong hydrolysis) and spray dried. Aroma components of RBPc hydrolysates were identified by using gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS). Aroma impact compounds were identified by aroma extract dilution analysis (AEDA) and odor activity value (OAV). The predominant odorants in RBPc were 3-methylbutanal (malty), hexanal (grass), 2-aminoacetophenone (tortilla), E-2- nonenal (waxy), phenylacetaldehyde (rosy), and ß-damascenone (apple sauce). The 2-aminoacetophenone (tortilla), which had 59 ng/g in RBPc, gave the same overall odor as that of RBPc. The FD chromatogram of RBPc hydrolysates treated with 0.5 N HCl for 12 and 36 h showed the similar patterns. Most of the predominant odorants tended to have higher log3FD factors in the hydrolysis time of 36 h than those in 12 h. Aroma impact compounds of RBPc hydrolysates treated with 0.5 N HCl for 12 and 36 h were 2-methoxyphenol (smoky), Furaneol® (burnt sugar), sotolon (seasoning), vanillin (vanilla), 3-methylbutanal (malty), E-2-nonenal (waxy), p-vinylguaiacol (clove), and ß-damascenone (apple sauce). The overall “smoky” and “soy saucelike” aroma character of RBPc hydrolysate treated with 4.0 N HCl for 72 h was dominated by 2-methoxyphenol and 2,6-dimethoxyphenol. The 2-methoxyphenol and 2,6-dimethoxyphenol provided intense smoky notes. Particularly, 2-methoxyphenol gave the highest OAV values of 2,773, 17,650, and 6,265 in the RBPc hydrolysates with mild (12 and 36 h) and strong hydrolysis, respectively. The aromas with the highest log3FD factors in RBPc hydrolysate (strong hydrolysis) were methional (cooked potato), sotolon (seasoning), 2,6-dimethoxyphenol (smoky), and phenylacetic acid (sweet) with values of 7, 5, 5, and 5, respectively. The results of Maillard model system (between the mixture of standard amino acids or single amino acid and fructose treated with 0.5 N HCl for 36 h) indicated that leucine, isoleucine, methionine, and phenylalanine were the precursors that generated 3-methyl butanal, 2-methyl butanal, methional, and phenylacetaldehyde, respectively.