Author : Arporn Jarunrattanasri

Summary : 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 95°C for 12 and 36 hrs (mild hydrolysis) and freeze-dried. Second, RBPc was hydrolyzed by 4.0 N aqueous HCl at 95°C for 72 hrs (strong hydrolysis) and spray-dried. Aroma components of RBPc hydrolysates were identified by using Gas Chroma tography-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 (maltry), hexanal (grass), 2-aminoacetophenone (tortilla), E-2-nonenal (waxy), phenylacetaldehyde (rosy) and beta-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 hrs, showed the similar patterns. Most of the predominant odorants tended to have the higher log3FD factors in the hydrolysis time of 36 hrs than those in 12 hrs. Aroma impact compounds of RBPc hydrolysates, treated with 0.5 N HCl for 12 and 36 hrs, were 2-methoxyphenol (smoky), Furaneol (burnt sugar), sotolon (seasoning) and vanillin (vanilla), 3-methylbutanal (malty), E-2-nonenal (waxy), p-vinylguaiacol (clove) and beta-damascenone (apple sauce). The overall "smoky" and "soy sauce like" aroma character of RBPc hydrolysate, treated with 4.0 HCl for 72 hrs, 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 hrs) and strong hydrolysis, respectively. The aromas with the highest log3FD factors in RBPc hydrolysate (strong hydrolysis) were methional (cooked-potato), sotolon (seasoning).