Preparation Of Tempeh Milk Rich In Gamma Aminobutyric Acid

Gamma-aminobutyric acid is an important inhibitory neurotransmitter in the human central nervous system.GABA has diverse physiological functions,such as stabilizing emotions,lowering blood pressure,participating in hormone metabolism,promoting the development of the nervous system,and assisting the treatment of mental diseases.The biosynthesis of GABA is divided into the plant enrichment method and the microbial fermentation method.The microbial fermentation method has the advantages of short fermentation period,high GABA content,low cost,etc.It has gradually become a research hotspot in recent years.Tembe is a soybean fermented food staple food in Indonesia.During the fermentation process of tempeh,Rhizopus oligosporus decomposed macromolecules such as polysaccharides and proteins and converted glycosyl soybean isoflavones into free soybean isoflavones.In addition,tempeh also has many physiological functions such as antioxidation,antibacterial activity,and reduction of human cholesterol.Rhizopus oligosporus has its own enzyme system which syntheses GABA,but GABA enrichment by Tempe fermentation process has rarely been reported.In this project,GABA was enriched by the hypoxia fermentation process of tempeh,and on this basis,GABA-enriched tempeh milk was developed to improve the functionality and nutritional value of tempeh products.The main research contents and results are as follows:1.Through the single factor test and orthogonal experiment optimization,the optimal conditions for producing GABA from tempeh hypoxia fermentation were:0.5%inoculation,aerobic fermentation for 28h,40h low-oxygen fermentation for 12h,GABA production can reach 563.89mg/100g.In the process of GABA production by tempeh,the soluble protein increased from 24.64mg/g to 32.03mg/g,and Rhizopus oligosporus decomposed insoluble protein into soluble.The results of SDS-PEGE protein electrophoresis showed that after fermented soybean protein most bands disappeared and some new bands were produced.The RP-HPLC peptide map showed that most of the soluble peptides were decomposed in the fermentation process,and some small peptides were produced.The free amino acid nitrogen during the fermentation increased from 84 mg/100 g to 1045.4 mg/100g.2.After being processed frozen,the hardness of tempeh decreased from 8.72N to 5.73N,and the elasticity decreased from 2.46mm to 1.88mm.tempeh became looser and nutrients dissolved more easily.There are two distinct peaks in the particle size of tempeh milk.Before and after the freezing treatment,there was no significant difference in the particle size of tempeh milk.After freezing,the soluble protein and soluble solid content of tempeh milk increased:Soluble protein increased from 0.64 mg/mL to 1.16 mg/mL,and soluble solids increased from 0.8%to 1.43%.After freezing,the centrifugal sedimentation rate of tempeh milk dropped from 10.71%to about 7.27%,and the stability increased.Tempeh protein has similar subunit composition before and after freezing.Freezing does not lead to protein denaturation.The "L1" value of the frozen tempeh milk was lower than that of the unfrozen tempeh milk.The freezing time increased,the "a" value decreased,and the "b" value increased,indicating that the tempeh milk will gradually become greenish and yellowish.In particular,frozen tempeh milk for 4 days is dark in color and yellowish.Compared with normal temperature processing,the sensory scores of tempeh milk under low temperature processing conditions were higher overall,and the texture,fat,taste,bitterness and astringent taste scores were all higher than those at room temperature.The frozen 4d tempeh milk has a yellowish and dark color,and the score is lower than that of tempeh milk with frozen 1d and 2d.3.Using the coefficient of stability as an indicator,three emulsifiers and three thickeners were selected as single-factor tests and compounding experiments,and single-factor tests of homogenizing pressure were performed.The emulsifier used was lecithin and the thickener was xanthan gum.Then the optimum amount of the stability factor is obtained by orthogonal test:0.5%lecithin,0.2%xanthan gum,and 40 MPa homogeneous pressure.In this condition,the stability coefficient reaches 0.8657.After processing,the GABA content of tempeh milk was 422.6mg/L,and the sensory score was 43.2(The full score is 50 points).