Effect Of Low Intensity Ultrasound On Soy Sauce Quality And Its Preliminary Mechanism

Moromi fermentation lasts for 6 months to obtain “perfect” aroma of soy sauce,however,its key taste compounds can reach the highest levels within the first 30 days of fermentation,suggesting that soy sauce's aroma maturation far lags behind its taste.In addition,there are a large number of free amino acids and decarboxylase-producing microorganisms in moromis,leading to increased content of harmful substances-biogenic amines in soy sauce.Low-intensity ultrasound has a wide application potential in fermented foods.This study explored the effects of low-intensity ultrasound on the aroma formation,biogenic amines content and antioxidant activity of soy sauce.It provided references for increasing the utilization rates of space and capital of enterprises and enhancing the edible safety and added value of soy sauce.(1)The effect of ultrasound on the formation of soy sauce aroma substances was studied.On the basis of preliminary experiments,the best ultrasonic process conditions were selected: 68 k Hz,60W/L,ultrasonic 8 times(10 min/time,on 10s/stop 5 s).Quantitative description analysis(QDA),solid phase microextraction-gas chromatography-mass spectrometry technology/gas chromatography-sniffing technology(SPME-GC-MS/GC-O)and hierarchical cluster analysis(HCA)were used to identify the aroma components and key aroma-active components in soy sauce.The results showed that 34 and 33 key active compounds were detected from 85 volatile compounds in the ultrasound and control soy sauce.The contents of dimethyl trisulfide,3-(methylthio)propionaldehyde,ethyl 3-methylbutanoate,2-ethyl-3-methylpyrazine,benzeneacetaldehyde,5-methylfurfural,2-methylpropanol,3-methyl-1-butanol,2-methyl-1-butanol,3-methylbutanoic acid,benzoic acid,2-phenylethanol,2-furanmethanol,acetic acid,butanoic acid,and ethanol increased significantly.QDA and HCA confirmed that ultrasound could reduce 90 days of fermentation timeand improve aroma quality of soy sauce.Appropriate low-intensity ultrasound could accelerate the formation of soy sauce aroma substances.(2)The effect of ultrasound on the content of biogenic amines in soy sauce was studied.Firstly,the biogenic amine-degrading strain was screened and inoculated into moromis and treated by ultrasound.The content of biogenic amines was determined by high performance liquid chromatography,and the effect of ultrasound on the content of biogenic amine in moromis was studied.The results showed that Z.rouxii could degrade 8 kinds of biogenic amines.The degradation rate of biogenic amines in soy sauce by Z.rouxii was significantly improved by ultrasound.In the medium concentration group,the degradation rates of histamine and tyramine were increased by 18.47% and 12.74%,respectively.In the high concentration group,the degradation rates of histamine and tyramine were increased by 16.43% and 17.34%,respectively.(3)The effect of ultrasound on the antioxidant activity of soy sauce was studied.DPPH,ABTS free radical scavenging rate,reducing power and metal chelating power,total phenols,total flavonoids,?-glucosidase activity,Maillard reaction products,peptide molecular weight,amino acid content were detected to analyze the effects of ultrasound on soy sauce antioxidant activity and antioxidant substances.The results showed that ultrasound significantly enhanced the antioxidant activities of soy sauce.It significantly increased the contents of total phenols(26.71%),amino acids(12.45%)and 1-3 k Da peptides(12.28%)in moromi.Among them,amino acids contributed 53.45% and 65.88% to the DPPH free radical scavenging ability and metal ion chelating ability of soy sauce,respectively.(4)The preliminary mechanism of accelerated aroma formation,reduced biogenic amine content and enhanced antioxidant activity by ultrasound was studied.The effects of ultrasound on the number,structure of microorganisms and substrate structure were analyzed by scanning electron microscopy and microbial counting methods.The results showed that ultrasound destroyed the surface structure of soybeans and increased the specific surface area of the substrate.It favored to the degradation of proteins,starches,etc.into amino acids and monosaccharides,and accelerated the reproduction of aroma-producing and biogenic amine-degrading microorganisms,and improved the cell permeability of microorganisms in moromis.This should be the preliminary mechanism of ultrasound accelerating aroma formation and increasing biogenic amine degradation rate of soy sauce.In addition,ultrasound promoted the formation and release of antioxidants.It should be the preliminary mechanism of ultrasound improving the antioxidant activity of soy sauce.