Study On Preparation Of Low-alcohol Pineapple Wine Termination Fermentation By Pulsed Electric Fields

Low alcohol fruit wine is a fermented wine with ethanol content of 1～7%Vol.In recent years,it is becoming more and more popular among consumers due to low ethanol content and high nutritional value.Traditional methods for semi-fermentation termination such as heat sterilization or sulfur dioxide bacteriostasis are generally applied for wine production,however,there are some defects of the wine produced by above methods such as poor color and bad aroma of wine,thus reducing the wine quality.In addition,the semi-fermentation with retained sugar has high requirements for the efficiency of fermentation termination and storage stability,which greatly restricts the development of low alcohol wine.The aim of this study is to explore the feasibility of pulse electric field（PEF）as a promising method to terminate fermentation by comparing with heat sterilization and sulfur dioxide bacteriostasis.Subsequently,determining the optimal fermentation conditions of the termination fermentation for low alcohol pineapple wine production by monitoring the changes of nutritional components and aroma of wine.Finally,the effect of different storage temperature on the sensory quality and color of low alcohol pineapple wine was observed.And the shelf life model of low alcohol pineapple wine was established by Weibull hazard value analysis and dynamic series model.The specific research contents and conclusions are as follows:1. The optimal fermentation parameters of low alcohol pineapple wine were determined.The results of response surface analysis showed that fermentation factors affecting wine sensory was yeast inoculation amount,initial acidity and fermentation temperature,respectively.The optimal fermentation conditions were obtained as follows:fermentation temperature 20℃,yeast inoculation amount 85 ppm,initial acidity 6.2 g/L,fermentation 46 h reached the target alcohol level of 4.8%vol.At these conditions,the wine exhibited a typical pineapple aroma with balanced sweetness and acidity,bright and clear color.The sensory score could reach 91.3 points.2. The optimal treatment conditions of PEF for termination fermentation were determined.The results showed that the lethal rate of yeast and the sterilization time caused by pulse electric field for termination fermentation were in accordance with the first-order kinetic equation.Additionally,the fermentation process could be effectively terminated after exposure to 15 k V/cm electric field strength with 80μs treatment duration（w=246.24 k J/L）,while the traditional methods required constant 75℃water bath for 20 min or 150 mg/L sulfur dioxide addition to achieve the same results.It was demonstrated that pulse electric field was a promising method for fermentation termination due to short processing time and high sterilization efficiency.3. The effects of three different methods of fermentation termination on the physical and chemical properties of low alcohol pineapple wine were compared.The results showed that there was no significant difference in the content of residual sugar,total acid,dry extract and volatile acid,while the color changed significantly（p<0.05）.For S_PEF,the value of L^*,a^*increased,and the value of b^*decreased,illustrating that the color of low alcohol pineapple wine(S_PEF)was better than that of other groups.The L^*value of pineapple wine produced by heat sterilization was the lowest,reflecting a severe browning phenomenon.4. The effect of three different methods of fermentation termination on amino acid content in low alcohol pineapple wine was studied.A total of 16 amino acids were measured,the total amount of hydrolyzed amino acids of S_T、S_PEF and S_SO2were 17.371mg/L,15.266 mg/L and 14.197 mg/L,respectively.Compared with amino acid pattern spectrum,the first limiting amino acid in S_T was leucine,while for S_PEF and S_SO2was lysine.5. The effect of different three different methods of fermentation termination on the content of fusel oil in low alcohol pineapple wine was compared.Four kinds of higher alcohols isobutanol,n-butanol,isoamyl alcohol and active amyl alcohol were all detected in low alcohol pineapple wine obtained by three methods(S_T、S_PEF and S_SO2).The total amount of four higher alcohols in three fruit wines were 238.13 mg/L,228.28mg/L and 334.41 mg/L respectively.Compared with pineapple dry wine with a total amount of fusel oil of 402.55 mg/L,the content of fusel oil in low alcohol pineapple wine decreased significantly.Especially,isobutanol in S_PEF decreased about 68.10%with a lowest content of total fusel oil.6. The effects of three different methods of fermentation termination on aroma components and contents of low alcohol pineapple wine were studied.40,33 and 30kinds of aroma compounds were identified in S_PEF,S_T and S_SO2.The contents of 2-methyl-butyrate,2-methyl-butyrate,ethyl butyrate,3-hydroxyhexanoate,4-hydroxy-2,5-dimethyl-3（2H）-furanone of S_PEF possessed highest value in comparison to S_T and S_SO2.The results showed that the pulse electric field as a fermentation termination method could not only help produce more kinds of aroma compounds in wine,but also effectively protect the characteristic aroma components of pineapple.7、The shelf life model of low alcohol pineapple wine was established.The shelf life model of low alcohol pineapple wine established by Weibull hazard value analysis method is as follows:（?）,the relative error of measurement is-1.69%～6.39%.The shelf life model established by chemical kinetics is as follows:（?）the relative error of measurement is-3.11%⁹.28%.The results showed that although the sensory shelf-life model obtained by Weibull hazard analysis had higher accuracy,the evaluation process was tedious and the usage was limited in actual application.Despite of a slightly poor accuracy,the chemical kinetics shelf-life model was more convenient for shelf-life evaluation.