Ougan juice debittering using ultrasound-aided enzymatic hydrolysis: Impacts on aroma and taste.

The optimal sonication conditions (40 kHz, 80 W/L and 60 min) during Ougan juice debittering by Aspergillus niger koji extract were established. Enzymatic hydrolysis degrees of naringin and limonin were enhanced to 89.90% and 36.16%, and enzymatic hydrolysis time was shortened by 33%. Sonication significantly enhanced activities of α-l-rhamnosidases, ß-glucosidases and limoninases from A. niger koji extract and facilitated break of CO bonds in naringin (p < 0.05). These accounted for the enhanced enzymatic hydrolysis degrees and velocities of bitter compounds. Meanwhile, sonication lowered 40%, 7% and 21%, 13%, 11%, 25% of bitter, sour tastes and green, citrus-like, floral, woody notes, but enhanced 18% and 15% of fruity and sweet notes, resulting in 38% and 33% increases in over-all taste and aroma scores. Lowered levels of bitter compounds, organic acids, green, citrus-like, floral, woody aroma compounds and enhanced levels of fruity, sweet aroma compounds caused by sonication accounted for the flavor improvements.

Accelerating aroma formation of raw soy sauce using low intensity sonication.

Sonication was applied to accelerate aroma formation and shorten fermentation time of soy sauce. Effects of sonication at 68 kHz on the aroma and aroma-producing Zygosaccharomyces rouxii and Tetragenococcus halophilus in moromis were investigated using sensory evaluation, SPME-GC-olfactometry/MS, viable cell counting and scanning electron microscopy. The sensory scores of caramel-like, fruity, alcoholic, floral, malty, smoky, sour and overall aroma in sonicated moromis were enhanced by 23.4%, 23.2%, 13.6%, 12.8%, 7.6%, 6.3%, 5.6% and 14.4%, respectively. Sensory scores of samples fermented for 90-180 days were higher than those of controls fermented for 180 days, suggesting that sonication could reduce fermentation time by 90 days. Thirty-four aroma-active compounds were detected from 85 volatile compounds in soy sauces. Sonication accelerated and elevated the formation of aroma compounds by chemical reactions. It also markedly increased the reproduction and cell permeability of both microorganisms in moromis, which favored the formation of aroma compounds by both strains.

Enhancing Activities of Salt-Tolerant Proteases Secreted by Aspergillus oryzae Using Atmospheric and Room-Temperature Plasma Mutagenesis.

Aspergillus oryzae 3.042 was mutagenized using atmospheric and room-temperature plasma (ARTP) technology to enhance its salt-tolerant proteases activity. Compared to the starting strain, mutant H8 subjected to 180 s of ARTP treatment exhibited excellent genetic stability (15 generations), growth rate, and significantly increased activities of neutral proteases, alkaline proteases, and aspartyl aminopeptidase during fermentation. Mutant H8 significantly enhanced the contents of 1-5 kDa peptides, aspartic acid, serine, threonine, and cysteine in soy sauce by 16.61, 7.69, 17.30, 8.61, and 45.00%, respectively, but it had no effects on the contents of the other 14 free amino acids (FAAs) due to its slightly enhanced acidic proteases activity. Analyses of transcriptional expressions of salt-tolerant alkaline protease gene (AP, gi: 217809) and aspartyl aminopeptidase gene (AAP, gi: 6165646) indicated that their expression levels were increased by approximately 30 and 27%, respectively. But no mutation was found in the sequences of AP and AAP expression cassettes, suggesting that the increased activities of proteases in mutant H8 should be partially attributed to the increased expression of proteases. ARTP technology showed great potential in enhancing the activities of salt-tolerant proteases from A. oryzae.

Enhancing the taste of raw soy sauce using low intensity ultrasound treatment during moromi fermentation.

Sonication can significantly enhance amino acids (AAs) release to accelerate maturation during short-term and low-salt soy sauce fermentation. Here, sonication was applied at 68 kHz (60 W/L/10 min/8 circles) to determine its effects on the taste during long-term and high-salt soy sauce fermentation. The possible mechanisms were explored by analyzing differences in enzymes profile, proximate indices, molecular weight distribution of peptides, AAs composition and microstructures of sonicated moromis and their controls. Sonication greatly elevated levels of organic taste compounds ranging from 8.4% to 22.2%, but lowered levels of NaCl (6.0%), peptides ≤ 1 kDa (5.2%), histidine (20.5%) and glutamic acid (3.4%). Compared to its controls, sonicated raw soy sauces also had a more harmonious and palatable taste. Increased enzymes' activities and formation of more surface area and reaction sites in sonicated moromis might be the possible mechanisms for sonication to elevate levels of taste compounds and sensory quality of soy sauce.