Analysis And High-value Utilization Of Heat-induced Precipitate In Soy Sauce

Soy sauce is a popular fermented condiment,it can give food bright color and delicious taste,and is rich in nutrients such as amino acids,sugars,organic acids and minerals.In the process of heat sterilization,raw soy sauce will produce precipitate.Due to the huge yield of soy sauce,the amount of precipitate is also very considerable.This part of precipitate is difficult to be separated from the soy sauce by traditional methods such as centrifugation and filtration,and is mainly used as fertilizer and feed at present,which is not fully utilized in the industry.Therefore,it is of great significance to fully explore the avaliable value of soy sauce precipitate and realize its high value utilization.In the first place,the composition and physicochemical properties of the heat-induced turbid soy sauce and soy sauce precipitate were studied.The precipitate in the turbid soy sauce was mainly round,rectangular,fibrous and irregular shape,and the particle size of most precipitate was less than 100 ?m,which led precipitate was difficult to be separated from soy sauce.Appropriate heat-treatment could induce the aggregation of precipitate particles in turbid soy sauce and accelerate the separation of precipitate and soy sauce.Heat-treatment at 50-70? made the mean particle size of precipitate reach 1000 ?m and the separation by centrifugation would be easy.Hydrophobic interaction was the main force for the aggregation of precipitate which was demonstrated in our experiment.Analysis of the separated soy sauce precipitate showed that protein was its main component and the content was 32.59%.Analysis of amino acid showed that the hydrophobic amino acid accounted for 39.78% in total,essential amino acids account for 33.17% and the umami amino acids account for 30.33%.Analysis of metal elements showed that the contents of heavy metals such as plumbum and arsenic were far below the limit standards,but the contents of beneficial metals such as calcium,magnesium and iron were very high,especially magnesium,its content was 911 mg/kg.The results of SDS-PAGE and NSI indicated that precipitate protein could be further degraded and was of high solubility at alkaline condition p H(8-12).Enzymatic hydrolysis was used to realize high value utilization of soy sauce precipitate.The conditions for extensive enzymatic hydrolysis of precipitate optimized by single factor test and orthogonal test were: 37071 alkaline protease,0.2% enzyme addition,p H 10,45? and 12 h,under which the protein recovery and DH reached 83.31% and 28.31% respectively.The results of particle size distribution before and after enzymatic hydrolysis showed that after adjusting the p H(8-12),the particle size of precipitate decreased from micro to submicron or nano scale,the sensitivity of enzymatic hydrolysis was improved,and further decreased to nano scale after enzyme hydrolysis,which also demonstrated this extensive enzymatic hydrolysis method was efficient and industrially achievable.The free amino acids,molecular weight distribution,sensory,color,and volatile aroma substances of enzymatic hydrolysate obtained under optimized conditions were studied,and the factors affecting color and volatile aroma substances were also discussed.After enzymatic hydrolysis,the content of free amino acids and small molecule peptides increased.20.28% of hydrolysate were molecular weight of 500-1000 Da and 79.72% were of <500 Da.The sensory evaluation results showed that the enzymatic hydrolysate had richer taste and aroma,moderate salty and umami taste,and less bitter taste.The enzymatic factors(p H,temperature and time)significantly affected the color of the enzymatic hydrolysate.The red and yellow indexes of hydrolysate decreased to 4.98 and 7.78,and the color depth and color ratio increased to 20.85 and 615.79,respectively.Adjusting p H and enzymatic hydrolysis increased the contents of pyrazines and ketones,and decreased the content of esters,aldehydes and acids.A total of 106 volatile aroma substances in hydrolysate were detected,among which,ketones,pyrazines,aldehydes,alcohols,and esters were of numerous speices,alcohols(49.58%),pyrazines(20.28%),aldehydes(9.45%)and phenols(7.54%)were of high content.Restrictive enzymatic hydrolysis of soy sauce precipitate was used to prepare high foaming protein.The effects of DH,p H,protein concentration and xanthan gum on the foaming properties of precipitate were studied.The results indicated that restrictive enzymatic hydrolysis and adding xanthan gum could improve the foaming properties.Precipitate protein hydrolyzed for 3 h(DH 25.23%)achieved the highest foaming ability and stability.Adding 0.5% xanthan gum could improve the foaming stability significantly.At p H 5 and 4% protein concentration,the foamimg ability and stability of 3 h hydrolysates with 0.05% xanthan gum reached 54.00% and 81.81%,respectively.The mechanism affecting foam properties was complex and needed to be analyzed comprehensively.