Study On The Composition Change Of Black Garlic Production And Its Quality Evaluation

Black garlic is a processed product obtained by fresh garlic under high temperature and high humidity for a long time.It tastes sour,sweet and glutinous,and has no pungent odor,making it favored by the public.Many producers,merchants,and consumers believe that black garlic is the fermentation product of garlic,claiming that its health benefits are better than garlic.Up to date,the black garlic industry has many problems such as the composition and content of main functional components are unclear,lack of product quality evaluation system,long production cycle(60~90 d)and unable to measure the amount of black garlic in secondary products such as black garlic juice.They all restrict the development of the black garlic industry.In response to the above problems,combined with our team's previous discovery of the initial Maillard reaction products,Amadori Compounds(ACs)in black garlic and they had strong in vitro antioxidant activity,this study monitored the formation of 12 ACs and the changes of alliin and S-allylcysteine(SAC)which originally existed in garlic during the processing of black garlic,and analyzed the formation of 5-hydroxymethylfurfural(5-HMF)and acrylamide.Based on these,the preparation of black garlic was optimized;the contribution of each functional component to the in vitro antioxidant activity of black garlic products was compared and the quality of black garlic products was evaluated.The results have guiding significance for improving production efficiency and quality control of black garlic.The research contents and conclusions are as follows:(1)Simultaneous quantitative method of alliin and SAC was established and applied to the analysis of garlic products to achieve good separation of the target.In order to overcome the shortcomings of high cost and long detection time in the existing simultaneous determination of alliin and SAC,a high-performance liquid chromatography-ultraviolet detector(HPLC-UV)system and the more common mobile phase including 0.1% phosphoric acid water(A)and methanol(B)were applied for the analysis.The established and optimized detection conditions were as follows: X select HSS T3 column(5 ?m,4.6 mm×250 mm);column temperature: 30?;the flow rate: 1 mL/min;the injection volume: 20 ?L,gradient elution procedures: 0~1 min,98% A~95% A;1~3 min,95% A~90% A;3~8 min,90% A~85% A;8~10 min,85% A;10~15 min,85% A~98% A;15~20 min,98% A.The resolution of alliin and SAC increased to 11.95(the minimum required by the Chinese Pharmacopoeia is 1.5),and the detection time was 50% shorter than the existing method;meanwhile,the optimal detection wavelength of the two targets was determined as 208 nm based on the full wavelength scan,which improved the response of the target.Methodological verification results showed that the correlation coefficient of the standard curves were greater than 0.999,indicating the linear relationship was good.The detection limits of alliin and SAC were 0.1683 ?g/m L and 0.1192 ?g/m L;the quantification limits were 0.5609 ?g/mL and 0.3974 ?g/mL;the intra-day precision were 1.80% and 1.75%,and the inter-day precision were 1.98% and 1.61%,respectively;the recoveries of spiked standards were 98.19% and 96.27%,the relative standard deviations were 2.03% and 1.81%.It provided reliable support for the accurate determination of alliin and SAC in garlic products.(2)Optimization of black garlic preparation process: The application of two freeze-thaw treatments combined with fixed temperature and time for the aging process significantly shortened the production time.The study optimized the preparation of black garlic through freeze-thaw treatment to promote direct contact between the two substrates and accelerate the reaction process: Taking the garlic conductivity,release amount of reducing sugar and browning as indicators,the effects of freezing time and freeze-thaw cycle on the processing time were investigated.The results showed that twice freeze-thaw(60 min each time)could significantly improve the conductivity,release amount of reducing sugar and browning rate,indicating that freeze-thaw could promote cell disruption and the release and contact of Maillard reaction substrate,which was conducive to the reaction.Using the formation amount of 12 ACs and SAC,and the retention of alliin as indicators,the parameters of garlic initial water activity,reaction temperature and time were optimized.The results showed that 12 ACs increased significantly,and alliin and SAC accumulated the most when the water activity was maintained at 0.87.It indicated that controlling the water activity at an appropriate point could accelerate the reaction process.At 80?,the ACs(increased by 3 times)and SAC basically reached the peak.At 14 d,12 ACs accumulated the most.Based on single factor and orthogonal experiment,the best preparation process of black garlic was determined: pre-freezing time was 55 min,freeze-thaw twice,initial water activity was 0.82,processing temperature was 82?,processing time was 15 d.The content of ACs,SAC and alliin were 8.68 mg/g,2.95 mg/g and 1.88 mg/g,respectively.As the functional components increased,the processing time was shortened by 75%,and it was confirmed that the formation of black garlic was closely related to the Maillard reaction.(3)Comparison of self-made black garlic and different garlic products.Through analysis,it was proposed that ACs and SAC were the key active components in black garlic.In terms of the components,the amount of 12 ACs in self-made black garlic was far exceeded(up to 50 times)other products.SAC content was higher in self-made black garlic and freeze-dried garlic powder.Alliin content was reduced in all processed products,especially in black garlic(decreased by 52.12% ~ 95.91%).Four in vitro antioxidant tests showed that the antioxidant activity of homemade black garlic was better than commercially black garlic.Among the three antioxidants,black garlic products were significantly better than(up to 5 times)traditional garlic products.The results indicated that the higher the content of ACs and SAC,the stronger the antioxidant activity of the product.Combined with correlation analysis,ACs were significantly correlated with the antioxidant activity of ABTS and FRAP,and SAC was closely related to the antioxidant activity of DPPH and ORAC(p<0.01).It indicated that ACs and SAC were the main antioxidant sources of black garlic.In addition,self-made black garlic had less harmful substances(5-HMF,acrylamide),and its sensory quality was equal to that of commercial black garlic.Therefore,regulating the Maillard reaction of black garlic stay in the early stage and timely terminating the deepening of its late reaction is a novel idea to improve the quality of black garlic.