Preparation Of Quinoa With High GABA Content And Analysis Of Its Quality Characteristics

Gamma-aminobutyric acid(GABA),an inhibitory neurotransmitter,has a variety of physiological functions such as relieving anxiety,promoting sleep and calming the nerves.As the body ages and mental stress increases,the amount of GABA in the body is not sufficient to meet daily needs and exogenous intake of GABA is required.However,the amount of GABA in plant tissues is very low.Therefore,in this paper,the pre-treatment and fermentation conditions were optimised to enhance the GABA content of quinoa.In this study,quinoa was used as a raw material,further the mechanisms of cold shock and fermentation treatments on the nutritional,physicochemical and quality characteristics of quinoa was elucidated.These have laid the theoretical foundation for the deep processing of quinoa and are of great guidance for the industrialisation of quinoa products.Firstly,this study investigated the effects of three pretreatment methods(sonication,enzymatic digestion and cold shock)on the GABA content and nutrient composition of quinoa.The results showed that ultrasonication,enzymatic digestion and cold shock treatment could all enhance the GABA content of quinoa,with cold shock being the most effective in enhancing the GABA content.Under the conditions of soaking at 34°C for 24 h,cold treatment at 4°C for24 h and soaking at 34°C for 24 h,the GABA content in quinoa was 127.07 mg/100 g,which was 23 times higher than that of untreated quinoa.Three pre-treatments had different effects on the nutritional composition of quinoa.Enzymatic digestion treatment reduced the starch and protein content and elevated the soluble sugar content.Cold shock and sonication both increased the starch,protein and soluble sugar content,but cold shock was more effective than sonication.In addition,the cold shock treatment increased the content of the remaining amino acids,except arginine and tyrosine,with a 3.27-fold increase in glutamic acid.Secondly,the effect of fermentation on the GABA content of quinoa was investigated.The effects of fermentation time,fermentation temperature,water addition and inoculum amount on the GABA content of quinoa were investigated.Moreover,the optimal fermentation conditions for GABA production were optimised by response surface.The results showed that Lactiplantibacillus plantarun No.2 had the highest GABA production capacity.And the optimal conditions for quinoa fermentation by Lactiplantibacillus plantarun No.2 were fermentation time 48 h,fermentation temperature 34°C,water addition 150% and inoculum 4%.Under the optimal conditions,the content of GABA in quinoa was as high as 382.41 mg/100 g,which is a69-fold increase compared to untreated quinoa(5.51 mg/100g).The effect of different concentrations of components(Glucose,Calcium ions,Monosodium glutamate)on the GABA content was also investigated.The results showed that the GABA content reached 393.31mg/100 g at a glucose concentration of 2%,431.15 mg/100 g at a calcium ion concentration of8% and 583.56 mg/100 g at a Monosodium glutamate(MSG)concentration of 90 mg/m L.Thirdly,based on the above findings,the mechanisms of the effects of cold shock and fermentation treatments on the nutritional composition,physicochemical and quality characteristics of quinoa were further investigated.The results showed that both cold shock treatment and fermentation increased the content of the key enzyme activity(GAD)and the key substrate(Glu)in the GABA synthesis pathway of quinoa.The GAD activity reached its maximum at 48 h of fermentation.At the same time,compared to untreated quinoa,the content of GABA in quinoa increased by 1191% under 4°C cold shock treatment.The relative crystallinity of quinoa flour was reduced from 38.89% to 10.60% by 4°C cold shock and to6.15% after 48 h of fermentation.The untreated quinoa protein secondary structure changed at12 h of fermentation,but the cold shock treatment caused a change in protein secondary structure at 24 h of fermentation.Finally,the effects of different concentrations of GABA(0-1%)on the structural and functional properties of quinoa proteins were investigated to reveal the mechanism of GABAinduced changes in protein structure.The results showed that the average particle size of quinoa protein decreased by 36.70% and the ζ-potential increased by 74.12% when the GABA concentration was increased from 0% to 0.8%.Moreover,the endogenous fluorescence values showed a trend of increasing and then decreasing,with the maximum fluorescence intensity at a GABA concentration of 0.8%.Although the surface hydrophobicity showed the same trend,it was highest at a GABA concentration of 0.6%.FTIR spectra showed that α-helix decreased from 19.73% to 0,β-folding decreased from 44.29% to 25.54%,β-turning increased from 22.03%to 28.84% and irregular coiling increased from 13.95% to 45.62%,indicating that different concentrations of GABA had significant effects on the secondary structure of quinoa proteins.In addition,when the GABA concentration was increased from 0% to 0.8%.the emulsification and foaming properties of quinoa proteins were significantly increased and showed a significant GABA concentration dependence.