Preliminary Mechanism Of Enhancing Organic Selenium Content And Quality Of Soy Sauce Using Nano-selenium

Insufficient selenium intake can cause a variety of serious diseases.More than70% of China’s land belongs to selenium poor areas,and more than 1/3 of the population’s selenium intake is lower than the minimum standard recommended by the Chinese Nutrition Society.Therefore,it is of great significance to improve the selenium intake of Chinese residents through diet.At present,selenium supplement products are mainly in the form of inorganic selenium and organic selenium.Inorganic selenium is highly toxic and gradually abandoned by consumers.Organic selenium mainly exists in the form of selenoprotein and seleno amino acid,which has the characteristics of low toxicity and high bioavailability.However,its long production cycle and high price are not conducive to its large-scale popularization and application.High-salt and diluted-state soy sauce is a liquid condiment rich in small components of peptides and amino acids produced by soybean soaking,Aspergillus oryzae koji-making and moromi fermentation,which is a good carrier of selenium.Taking sodium selenite as the selenium control,this study prepared selenium-enriched soy sauce with safe and low toxic nano-selenium,and the mechanism of nano-selenium improving the organic selenium content and quality of soy sauce was studied systematically.(1)Nano-selenium was prepared by chemical method and characterized by TEM and EDS.The results showed that the average diameter of nano-selenium was about53.8 nm,and its morphology was complete and regular spherical,mainly composed of four elements: C,Se,O and Na.(2)The contents of total selenium and inorganic selenium in soy sauce were determined by atomic fluorescence spectrometry(AFS)and atomic absorption spectrometry(AAS).The results showed that total selenium and organic selenium contents in soy sauces prepared by nano-selenium and sodium selenite were increased by 32～191-fold and 29～173-fold compared to the control(without selenium),and organic selenium accounted for over 90% of total selenium.During the soaking process,nano-selenium and sodium selenite were absorbed by soybean,and part of them was converted into organic selenium.In the process of koji-making and moromi fermentation,part of the residual nano-selenium and sodium selenite were absorbed and converted into organic selenium by salt-tolerant microorganism in moromi.Finally,organic selenium was released into soy sauce through the degradation of selenium-enriched soyabean protein and microbial autolysis,which might be the reason for the high conversion rate of organic selenium in all selenium-enriched soy sauce.(3)The effects of nano-selenium on antioxidant activities of soy sauce were analyzed by analyzing antioxidant activities and active ingredients of soy sauce.The results showed that soy sauce prepared using 6 mg/L nano-selenium had the strongest antioxidant activities,which were 9.25～28.02% higher than the control.Nano-selenium(6 mg/L)markedly improved koji’s enzyme activities(9.76～33.59%),promoting release of total phenolics(27.54%),total flavonoids(27.27%)and formation of free amino acids(16.19%),Maillard reaction products(24.50%),so as to enhance antioxidant activities of the selenium-enriched soy sauce.(4)The effects of nano-selenium on key taste compounds and aroma-active compounds of soy sauce were analyzed using QDA,GC-MS and GC-O techniques.The results showed that nano-selenium significantly increased the contents of low molecular weight peptides(≤1 k Da,30.00%),peptide nitrogen(12.20%),sweet and bitter amino acids(15.51～20.43%)and 28 aroma-active compounds(12.29～60.04%),but the contents of 4-Vinylguaiacol(23.47%)and 1-Octen-3-ol(15.88%)decreased significantly(p < 0.05).Cluster analysis showed that the addition of nano-selenium and sodium selenite could enhance the taste and aroma-active compounds in soy sauce,and principal component analysis further showed that the addition of nano-selenium was more conducive to enhancing the taste and aroma-active compounds in soy sauce.(5)During moromi fermentation,nano-selenium enhanced the activities of acid protease and neutral protease in koji,making more soluble proteins and starch degraded to small molecular weight peptide,free amino acids,oligosaccharides and monosaccharides with flavor,these substances also promoted the growth of aroma-producing microbes,which promoted the formation of aroma compounds,such as alcoholic,caramel-like,sour and floral compounds.This might be the preliminary mechanism of using nano-selenium to improve the taste and aroma of soy sauce.In conclusion,nano-selenium markedly improved the organic selenium content and quality of soy sauce.The selenium-enriched soy sauce prepared with nano-selenium as selenium source is expected to become a new generation of daily selenium supplement food to improve the national selenium deficiency,provide new growth points for domestic soy sauce and enhance its international competitiveness.