| Castanea henryi(Skan)Rehd.et Wils.is the fruit of the castanea genus in the fagaceae family.It is one of the characteristic edible agricultural products in Fujian Province.At present,the processing of cone chestnut mainly consists of quick-freezing and storage of processed cone chestnut seeds(-18 ℃)as monomone,and then taking them out and thawing,packaging them separately,filling them with nitrogen,and sterilizing them at high temperature to make instant cone chestnut products when necessary for production.However,the browning degree of processed instant cone chestnut varies greatly.The browning of cone chestnut is often mistaken by consumers as quality deterioration and affects sales,which has become a major problem in the cone chestnut industry.Therefore,based on the study on the differences of main chemical components and flavor components of brown instant cone chestnut,this paper explored the main ways and mechanisms of browning in the process of instant cone chestnut,and then developed the control technology of instant cone chestnut browning to improve the quality and efficiency,in order to promote the development of the industry of cone chestnut.Specific research contents are as follows:1.Study on the difference of main chemical constituents of brown instant cone chestnutIn order to analyze the main browning mechanism of instant cone chestnut,the raw materials of cone chestnut with short freezing time(1month)and long freezing time(8 months)were processed into two kinds of instant cone chestnut,and then the unbrowning group,partial browning group and browning group were separated according to the degree of browning,and the browning index was calculated.The browning related chemical constituents and enzyme activities of the four groups in the shortfrozen unbrowning group(DW),the short-frozen unbrowning group(DH),the long-frozen unbrowning group(CW)and the long-frozen unbrowning group(CH)were determined,and the polyphenol components were identified by liquid chromatography-tandem mass spectrometry(LC/MS).The results showed that the browning index increased from 44.75%to 77.50% in the instant cone chestnut raw materials stored for 8 months,indicating that the frozen storage process had an effect on browning.The activities of polyphenol oxidase(PPO)and peroxidase(POD)residues in each group were determined,indicating the possibility of enzymatic browning.The contents of tannin,polyphenol and iron in the browning group were significantly higher than those in the unbrowning group,indicating that non-enzymatic browning may also be involved.Fourteen kinds of polyphenols were detected by liquid chromatography-tandem mass spectrometry(LC-MS).The contents of tannins in the browning group were as high as 90%,indicating that tannins may be the key components of instant cone chestnut browning.2.Study on the difference of flavor components of brown instant cone chestnutEnzymatic browning and non-enzymatic browning both affect the flavor components of food.In order to study the differences of the flavor components of brown instant cone chestnut,electronic nose and electronic tongue technology were used to analyze the composition and differences of flavor substances in groups DW,DH,CW and CH,with a view to exploring the mechanism of browning by difference analysis.The results showed that the main aroma components of the four groups of samples included aromatic components,organic sulfide,inorganic sulfide,methane and other short chain alkane,nitrogen and oxygen compounds.The contents of main volatile substances in the short frozen unbrowning group were significantly higher than those in the other three groups.The differences of taste components are mainly reflected in saltiness,richness,bitterness and umami.The saltiness and richness of samples increased and the bitterness and umami of samples in browning group were higher than those in unbrowning group.This indicated that frozen storage could affect the formation of flavor substances of cone chestnut,which might be related to the effect of frozen storage on enzymatic reaction.3.Study on enzymatic browning control technology of instant cone chestnut during processingIn order to control enzymatic browning of instant cone chestnut,the effects of different scalding and microwave techniques on PPO and POD activities of raw materials of cone chestnut were studied.At the same time,based on the optimal scalding process,the effects of different enzyme inhibitors(EDTA-2Na,citric acid,sodium isoascorbate,sodium metabisulfite)on the browning of cone chestnut raw materials were determined,and the optimal enzymatic browning control process was optimized.The PPO and POD activities of cone chestnut materials were completely inhibited after hot scalding at 90 ℃ for 3min or microwave treatment at 700 W for 4min.However,microwave treatment resulted in water loss and shrinkage of cone chestnut materials.Therefore,scalding at90 ℃ for 3min was selected as the enzyme killing process.Based on this process,different enzyme activity inhibitors were added to the hot scalding solution for treatment.Compared with the blank group,the browning control effect was achieved to a certain extent.From high to low,EDTA-2Na,citric acid,sodium isoascorbate and sodium metabisulfite were successively obtained.The browning index of EDTA-2Na treatment group decreased from 67.00% to 54.25%,but it was still not ideal.4.Study on non-enzymatic browning control technology of instant cone chestnut during processingIn order to further reveal the non-enzymatic browning mechanism of instant cone chestnut and develop control technology,the effects of different heat treatment processes,tannin content control and antioxidant addition on browning index of instant cone chestnut were studied.The results show that:(1)Different heat treatment processes had significant effects on the browning index of instant cone chestnut.Constant temperature treatment at 121 ℃ for 40min(high temperature and atmospheric pressure)had little effect on the browning index(0),while high temperature and high pressure had a greater effect on the browning index.Sterilization at 121 ℃ for 10 min had a higher browning index(65.22%),indicating that high pressure treatment could promote the browning of cone chestnut.However,high temperature and high pressure heat treatment process should be retained for sterilization requirements.(2)Soaking in iron ion solution made the embryo and peel of cone chestnut turn blue and purple.It was speculated that tannin content of embryo and peel of cone chestnut was high,and complexation reaction with iron ion occurred.The results showed that tannin content of embryo and peel of cone chestnut was about 1.5 times more than that of cotyledon.Further experiments showed that the browning index was significantly reduced by desorbing(from 71.62% to 65.25%),and browning was completely inhibited by desorbing.(3)Adding fat-soluble antioxidants butylhydroxyanisole(BHA),dibutyl-hydroxyl-toluene(BHT)and watersoluble antioxidant sodium isoascorbate to instant cone chestnut packaging bags did not significantly inhibit browning,but adding 0.005% sodium metabisulfite could completely inhibit browning.In conclusion,the browning of instant cone chestnut is the result of both enzymatic and non-enzymatic browning,and the main mechanism is oxidative browning of tannins in cone chestnut.In this study,browning of instant cone chestnut was completely inhibited by removing the peel tissue with high tannin content or adding sodium metabisulfite,which indicated that controlling tannin oxidation was the key to inhibiting browning of cone chestnut.This study revealed the browning mechanism of instant cone chestnut and developed the browning control technology,which is of great significance to the development of cone chestnut industry. |
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