Application Of Electronic Tongue Technology In Taste Evaluation Of Soy Sauce

Soy sauce is an important traditional condiment in China,but the competition in soy sauce market becomes more and more fierce with the acceleration of economic globalization.This article takes soy sauce as the main research object,aims to explore the application and associated responses of emerging assessment methods and further to better quantitively and qualitatively assess soy sauce.Most specifically,an electronic tongue technique combined with various pattern recognition and data analysis methods were employed.The main reserch contents are listed as followed:(1)The test conditions of electronic tongue in soy sauce were optimized.Six taste indexes,including sourness,bitterness,umami,umami-aftertaste(richness),saltiness and sweetiness were considered in this thesis.All of the soy sauce samples were diluted 30 times with distilled water.And washing time,the processing time prior to detecting,was 6 seconds.The third,fourth,and fifth detected values were selected for furthering analyzing to improve efficiency.Finally,Partial Least Square(PLS)method was employed to model the relationship between the sensory evaluation results and the outcomes of the electronic tongue.Research showed that the R~2 value of the six selected tastes were all over 0.76,which indicated that the measuring processes above had correct and precise accuracy.(2)The electronic tongue combined with various assessment methods was applied to recognized soy sauce types from different brands,grades,and countries.The study found that the electronic tongue was sensitive to different types of soy sauce.To be specific,PCA can reflect the basic difference of soy sauce samples.DFA can help better categorize,and ANN can help achieve nearly 100%accuracy rate on categorizing samples.The results showed that the electronic tongue combined with PCA,DFA,ANN and other analytical methods could classify soy sauce samples on their taste effectively.(3)The soy sauce from different brands,grades,and countries was selected as research objects to model the relationship between the measured values of electronic tongue and the contents of seven physiochemical indexes,such as amino nitrogen,total sugar,total acid,sodium chloride,umami amino acid,bitter amino acids.Research showed that PLS could predict effectively compared to Stepwise Linear Regression.Specifically,the results of PLS showed that the range of R~2 value of seven physicochemical indexes among soy sauce samples from different brands,grades,and countries were 0.781~0.913,0.859~0.933 and0.820~0.935,respectively.It can be seen that the model showed excellent ability to predict contents of physicochemical indexes accurately.(4)The electronic tongue was used to detect the taste changes of soy sauce in six months.Results showed that the sourness and saltiness enhanced,and the bitterness,umami,richness and sweetness of soy sauce samples all decreased while increasing the storage time.This result was consistent with the change rules of 6 physicochemical indexes.In addition,starting from the second month,the taste of soy sauce was observed obvious differences under high,room,and low storing temperature.The higher the ambient temperature was,the faster the spoilage rate of soy sauce would be.Additionally,ANN was used to distinguish soy sauce under different storage condition and the correct discrimination rate equals to 99.08%.The DFA results indicated that the electronic tongue was able to distinguish soy sauce under different storage time with 100%correct discrimination rate.PLS was used to model and predict the contents of 6 physicochemical indexes of samples under different storage conditions based on the detected signal of electronic tongue.The results found that the R~2value of ammonia nitrogen,total acid,total sugar,sodium chloride,umami amino acid and bitter amino acid were 0.988,0.993,0.994,0.951,0.979 and 0.980,respectively.(5)Adding MSG,NaCl,and sucrose into soy sauce samples separately.The study found that:1)the increase of umami was able to reduce the sourness,saltiness and sweetness but enhance bitterness and richness;2)the enhance of saltiness can help enhance the sourness,bitterness,umami,richness but suppressed sweetness;3)the sourness,bitterness,saltiness reduced but umami and richness enhanced while sweetness increased.Furthermore,this study combined the electronic tongue technology with PCA,which provide a way of simplifying the blending processes of soy sauce and improving product quality.