Pyrazine yield and functional properties of rice bran protein hydrolysate formed by the Maillard reaction at varying pH.

Interest in plant-based protein sources has grown rapidly. Rice bran contains excellent quality protein, but it is still rare in the market, due to its poor functional properties and undesirable odors. Therefore, we studied the Maillard reaction at different pHs on the formation of pyrazines and improved functional properties of rice bran protein hydrolysate. Protein from rice bran was extracted and hydrolyzed, using alcalase, at 55 °C for 4 h. Fructose was added, and the pH of the hydrolysate was adjusted to pHs between 7.0 and 10.0, before spray drying. Five pyrazines were detected in the hydrolysate powder, with the highest yield at pH 9 ( p < 0.05). The highest odor active value came from 2-ethyl-3,5-dimethylpyrazine (26.26), which contributed coffee, nutty and caramel aromas, followed by 2,5-dimethylpyrazine (9.2) and 2-ethyl-5-methylpyrazine (5.0). Increased pH led to a darker color (L* = 58.5) and redder (a* = 11.7) and yellower (b* = 13.8) powder. Key functional properties-solubility, water and oil binding capacity and emulsion stability index and foaming capacity-were increased with pH ( p < 0.05). The optimum pH for pyrazine formation and improved properties of enzymatic rice bran protein hydrolysate was pH 9.0.

Quantitation of Three Strecker Aldehydes from Enzymatic Hydrolyzed Rice Bran Protein Concentrates as Prepared by Various Conditions.

The quantitation of three Strecker aldehydes-2-methypropanal (2-MP), 2-methylbutanal (2-MB), and 3-methylbutanal (3-MB)-from rice bran protein hydrolysate (RBPH) prepared under various conditions were investigated. The preparation conditions included hydrolysis time (0, 0.25, 2, 4, or 8 h), pH adjustment (pH 4.0, 7.0, or 10.0), and sugar addition (sucrose, glucose, or fructose). These conditions provide a significant potential for aroma generation from the Strecker degradation and Maillard reaction. The Strecker aldehyde quantitation was performed using gas chromatography (GC) with cryo-focusing technique. These combined techniques encourage the precise 2-MB and 3-MB quantitation. The highest concentrations of three Strecker aldehydes were found in RBPH that was prepared by alcalase hydrolysis at 4 h with fructose addition (RBPH-F) and adjusted to pH 7.0 before spray drying. Thirty-nine aroma-active compounds of RBPH-F were discovered using solid-phase microextraction coupled with GC-olfactometry.

Preparation, aroma characteristics and volatile compounds of flavorings from enzymatic hydrolyzed rice bran protein concentrate.

BACKGROUND: Rice bran is a by-product obtained from the rice milling industry. The aims of this research were to add value to rice bran by preparation of enzymatic hydrolyzed rice bran protein concentrate (HRPC) as a flavoring agent and the flavoring which was produced by HRPC has not been investigated. Different drying methods (freeze-drying and spray-drying) and fructose additions were studied for improvement of rice bran protein sensorial aroma characteristics. RESULTS: The most abundant amino acids in liquid HRPC (LH) were glutamic acid, arginine, aspartic acid and leucine. The intensity of desirable aromas, such as cereal-like, nut-like, milk-powder-like, sweet, and cocoa-like aroma, were higher in spray-dried HRPC powder (SHP) than in LH and freeze-dried HRPC. Volatile compounds, such as aldehydes, pyrazines and ketones, were significantly increased in HRPC powders in which fructose was added before spray-drying (SHP-F). Higher amounts of 2-methylbutanal, 3-methylbutanal, phenylacetaldehyde, 2,5-dimethylpyrazine, vanillin, 2-acetylpyrrole and maltol were detected in SHP-F. Moreover, these compounds had high odor active values, which accounted for the cocoa-like, sweet, nut-like, and milk-powder-like characteristics of SHP-F. CONCLUSIONS: These findings could lead to the creation of desirable aroma characteristics of rice bran protein concentrate by different preparation methods. © 2018 Society of Chemical Industry.

Sensory aroma characteristics of alcalase hydrolyzed rice bran protein concentrate as affected by spray drying and sugar addition.

The sensory aroma characteristics of alcalase hydrolyzed rice bran protein concentrate as affected by spray drying and sugar addition were investigated. Rice bran protein concentrate (RBPC) was hydrolyzed by alcalase. Sucrose, glucose or fructose was added to the liquid rice bran protein hydrolysate (LRBPH) and subsequently spray dried. The sensory aroma intensities of the hydrolysates were evaluated. Results showed that after spray drying, the rice bran protein concentrate powder (RBPC-P) had higher sweet and cocoa-like aroma intensities than RBPC (p ≤ 0.05) and hydrolyzed rice bran protein powder (HRBPP) had higher milk powder-like aroma intensities than LRBPH (p ≤ 0.05). The sweet, cocoa-like and milk powder-like aroma intensities in hydrolyzed rice bran protein powder with fructose addition (HRBPP-F) were significantly higher (p ≤ 0.05) than those of hydrolyzed rice bran protein powder with sucrose or glucose addition (HRBPP-S or HRBPP-G). HRBPP-F had the highest overall aroma liking score. These results also indicate that spray drying and sugar addition could improve the sensory aroma characteristics of alcalase hydrolyzed RBPC.