Identification And Control Measures Of Key Cooked Off-Flavor Compounds In Hot Processed Tomato Juice

As an important vegetable crop,tomatoes are grown all over China,while processing tomatoes are only found in northwest areas such as Xinjiang,Inner Mongolia,Qinghai,Ningxia and Gansu.Tomatoes and tomato products are rich in nutrients such as vitamins,minerals and active substances such as lycopene.Lycopene,in particular,has physiological activities such as reducing the risk of cancer and relieving benign prostatic hyperplasia.Tomatoes and tomato products are widely concerned by the whole society.As one of the main processed tomato products,tomato juice has obvious cooked off-flavor,which reduces the market acceptance and leads to poor product sales.The income of tomato processing enterprises and tomato farmers is greatly affected.Therefore,it is necessary to analyze and determine the compounds causing cooked off-flavor,analyze their formation mechanism,and determine their correlation with production process and parameters.On this basis,it is proposed that the control strategy of reducing off-flavor components is the key to realize the technological upgrading of tomato juice processing industry and enhance the market competitiveness of products.This paper carried out a systematic and in-depth study on the above problems,and put forward a reasonable regulation strategy for tomato juice processing.The main results are as follows:(1)The tomato varieties used in the experiment were screened,and the sterilization conditions of tomato juice and the extraction conditions of volatiles were scientifically determined.The off-flavor intensity of five tomato varieties under the same sterilization conditions was compared,and the Qianxi tomato with stronger off-flavor sensitivity was selected.According to the sensory analysis,the off-flavor intensity of Qianxi tomato juice under different sterilization conditions was compared,and the sterilization condition with the strongest off-flavor intensity was selected,that is,heating at 90℃ for 15 min.The volatiles of tomato juice were extracted by headspace solid phase microextraction(HS-SPME)technology,and the extraction conditions were optimized.Finally,a CAR/PDMS extraction fiber was selected,the extraction temperature was 50°C,and the extraction time was 40 min.(2)Gas chromatography-mass spectrometry-olfactory(GC-MS-O)and aroma extract dilution analysis(AEDA)combined with quantitative analysis preliminarily identified the offflavor compounds in tomato juice.The differences of aroma-active compounds in tomato juice before and after sterilization were analyzed and compared using GC-MS-O and AEDA.A total of 17 aroma-active compounds were identified.The FD factor of 7 compounds increased after sterilization.Among them,dimethyl sulfide,dimethyl trisulfide and methional presented unpleasant odor such as cooked cabbage,corn,potato and onion.and the other 4 compounds presented fruity,floral and sweet aroma.The odor activity value(OAV)analysis showed that there were 12 compounds in thermally processed tomato juice with OAV≥ 1,and the compounds with unpleasant odor were mainly dimethyl sulfide,1-octen-3-one,dimethyl trisulfide and methional.(3)Sensory analysis combined with instrumental analysis to verify the cooked off-flavor components,and general verification of cooked off-flavor components was carried out.Odor differences between samples were analyzed using recombination experiment,omission experiments and electronic nose analysis.The recombination experiment showed that the aroma profile of real tomato juice and its reconstituted model were very similar,and there was no significant difference among each aroma characteristic(p > 0.05),which proved the accuracy of the qualitative and quantitative results in this study.The results of omission experiments and electronic nose showed that dimethyl sulfide was the most important off-flavor component,followed by dimethyl trisulfide,1-octen-3-one and methional,respectively.This identification results were verified in 4 other tomato cultivars,and the results showed that 1-octen-3-one existed in only one tomato variety,and three newly formed sulfur-containing compounds were the key compounds causing cooked off-flavor in tomato juice.(4)Sensory analysis combined with quantitative analysis to study the control measures of off-flavor of tomato juice.The effects of adjusting p H,adding glucose oxidase(GOD),cyclodextrin and phenols on the off-flavor of tomato juice were analyzed.The results showed that adjusting p H to 2.0 and adding 0.2 g/L rutin were more effective off-flavor control measures.The former showed the highest inhibition rate against methional,which was 67.26%,and the latter had better inhibitory effects on dimethyl sulfide and dimethyl trisulfide,and the inhibition rates were 38.05% and 53.64% respectively.In order to achieve better off-flavor control effect,the two were used together.The differences in odor intensity,off-flavor components concentration,precursors content,key aroma compounds content and tomato juice color among the combined treatment,single treatment and control were analyzed and compared.The results showed that the combined treatment had the lowest off-flavor intensity and the highest inhibition rate of the three off-flavor compounds,which were 58.77%,69.16% and 64.37%,respectively.The combined treatment had the highest content of off-flavor precursors,which proved that it can better prevent the degradation of precursors.In addition,the combined treatment can increase the concentration of 12 important volatiles in tomato juice,which has a beneficial effect on the aroma of tomato juice,and can also improve the color of tomato juice.