Analysis Of Volatile Components From Fermented Soy Sauces And Application In Soy Sauce Judgement

Soy sauce is one of the oldest condiments, which has become a necessity in people's everyday life. In our country there is an annual soy sauce output of estimated 5 million tons, ranking first in the world. According to related standards in our country, soy sauce can be classified into two kinds: one is fermented soy sauce and the other concocted soy sauce containing acid hydrolyzed vegetable protein(AHVP) seasoning. Driven by the profits, at present, many soy sauce manufacturers have been selling concocted soy sauce or acid hydrolyzed vegetable protein seasoning instead of fermented soy sauce. However, the volatile flavor components in soy sauce, to some degree, can reflect its quality and help to judge whether it is fermented soy sauce. Therefore, the comparison study of volatile flavor components in fermented soy sauce, acid hydrolyzed vegetable protein seasoning, soy sauce essence and caramel, is helpful to further evaluate flavors in soy sauce and is of great significance to construct the detecting methods of fermented soy sauce and non-fermented soy sauce, based on volatile flavor components.In this work, completely-fermented soy sauce and acid hydrolyzed vegetable protein seasoning from soy sauce manufacturers, were investigated. After the optimization of analytical conditions, their volatile flavor components were studied and some of their characteristic volatile flavor components were screened. Meanwhile some experimental achievements were realized and the main work included the following aspects:(1) Different sample pretreatment methods, such as static headspace sample injection, direct solvent extraction and static headspace solid phase microextraction. etc., were employed and combined with GC-MS to analyze the volatile components in fermented soy sauce. From the chromatograms it could be seen that results obtained when using static headspace solid phase microextraction were better than those obtained under other three pretreatment methods. The conditions of this pretreatment method were optimized, with Polyacrylic acid esters (PA) as extraction fiber tip, extraction temperature of 40℃, extraction time of 30min, injection time of 2min and addition of 1.0g of sodium chloride.(2) Under the optimized analytical conditions, volatile components from fermented soy sauce, acid hydrolyzed vegetable protein seasoning, soy sauce essence which was added into the soy sauce products, and caramel were analyzed. At the same time, their characteristic volatile components were screened out, with the results as follows: characteristic volatile components in fermented soy sauce included some alcohols such as ethyl alcohol, isopentanol, 1-octene-3-ol, methylmercaptopropanol and phenethyl alcohol.etc., which means that more reducing volatile components existed in fermented soy sauce; It was also found that 1-octene-3-ol was characteristic component which could distinguish acid hydrolyzed vegetable protein seasoning, soy sauce essence from caramel. While characteristic volatile components existing in acid hydrolyzed vegetable protein seasoning were mainly heterocyclic compounds containing pyrazine functional group. However, because of diversity of its pyrazine compounds and great content difference among them, none of these compounds ontaining pyrazine functional group can be regarded as the characteristic difference component in acid hydrolyzed vegetable protein seasoning. Despite the fact that there was a small amount of levulinic acid in acid hydrolyzed vegetable protein seasoning and that levulinic acid could even not be detected sometimes, the existence of levulinic acid in soy sauce samples still could give some implication that they had been added acid hydrolyzed vegetable protein seasoning. Therfore levulinic acid was finally chosen as the characteristic component to indicate the existence of acid hydrolyzed vegetable protein seasoning. Soy sauce essence indicators included phenylethyl acetate and methyl cyclopentenolone which had a higher and stable relative content and was the ideal characteristic difference component. As for caramel, characteristic difference components included 5-methyl-2-furaldehyde and 5-methyl-2-acetylfuran.(3) According to analytical results in the previous section, several sample judging indexes and detecting methods were proposed.①Relative oxidation value, which can reflect the content of reducing volatile components in soy sauce samples and indirectly reflect the content of fermented soy sauce in these samples, is a simple and feasible detecting method without instrumental analysis.②1-octene-3-ol, the indicator of fermented components, can be detected with a combination of headspace solid phase microextraction and GC-MS, and quantitatively analyzed when adding the internal standards.③Methyl cyclopentenolone, which can indicate the existence of soy sauce essence, can also be detected and quantitatively analyzed with the methods used in 1-octene-3-ol.④5-methyl-2-furaldehyde and 5-methyl-2-acetylfuran, as the caramel indicator, are also detected quantitatively analyzed the same way.⑤Levulinic acid, acting as the characteristic indicator of acid hydrolyzed vegetable protein seasoning, can be detected using GC-MS after direct solvent extraction, with detection limit as 100 mg/L.(4) Then the indexes mentioned above were employed to judge 30 soy sauce samples. It was found that serious adulteration existed in domestic soy sauce. Sample labelled as fermented soy sauce didn't include fermented components, while samples labelled as concocted soy sauce not only didn't have fermented components, but didn't include acid hydrolyzed vegetable protein seasoning. And soy sauce essence and caramels have been added in the production process of all domestic soy sauce.