| Ultra-high pressure(UHP)technology is a cold sterilization technology for processing fruit and vegetable products.UHP treatment can reduce the loss of heat-sensitive nutrients in food and better maintain the original texture,flavor and other qualities,which can effectively replace the traditional heat sterilization technology in the future.Hami melon and Korla fragrant pear are the advantageous agricultural products in Xinjiang region.Due to geography,population,consumption and other factors,we must face the storage,transportation and other problems of fresh fruits,so deep processing is particularly important.Hami melon juice owns a single taste but rich and sweet smell,while Korla fragrant pear juice owns a light smell,combined with the complementary flavors of the two fruits to develop a natural,stable,delicious,low-cost mixed beverage,not only improve the additional utilization value of Hami melon and Korla fragrant pear,but also enrich the types of beverages market.This project took Hami melon and Korla fragrant pear as raw materials,and developd Hami melon-Korla fragrant pear mixed beverage for the first time and supplemented with UHP technology,studied the preparation formula of Hami melon-Korla fragrant pear mixed beverage,optimized the UHP treatment process conditions,studied the quality changes under different storage temperatures during storage and predicted the shelf life,finally compared the effect of UHP technology and pasteurization on the flavor of the beverage,the specific study results were as follows:(1)Based on the single-factor experiment,the preparation formula of Hami melon-Korla fragrant pear mixed beverage was determined by using response surface experiment:the volume ratio of Korla fragrant pear juice and Hami melon juice was 1:4,the sugar contents were 0.4%,and the citric acid contents were 0.04%.According to the formula,the beverage was uniformly orange-yellow,with a harmonious odor and mixed aroma of Hami melon and Korla fragrant pear;and had a moderate sweet and sour taste,uniform and stable tissue state,no precipitation,and good fluidity.(2)The optimal process conditions for the UHP treatment were determined using single-factor combined with orthogonal experiments.The optimal process combination was:pressure600 MPa,holding temperature 30°C,holding time 30 min.The total number of bacterial colonies was not detected in the Hami melon-Korla fragrant pear mixed beverage under this process combination,while there was 2.71±0.012 lg CFU/m L in the pasteurized group,indicating that the sterilization effect of the UHP group was better,which could effectively destroy the microbial cell structure,reduce the activity,and significantly reduce the pathogenic and spoilage microorganisms in the beverage;the beverage color was light orange-yellow,the odor was harmonious,the acidity and sweetness were more moderate,and the state was stable and uniform.The p H and turbidity of the UHP-treated beverage were significantly lower than those of the pasteurized and CK groups,and the soluble solids content and total color differenceΔE were not significantly different from those of the pasteurized group.The results showed that the UHP treatment could better stabilize the quality of Hami melon-Korla fragrant pear mixed beverage and reduce the effect of destruction of the active ingredients of the beverage.(3)The quality changes of Hami melon-Korla fragrant pear mixed beverage during storage was studied and the shelf life was predicted using ASLT accelerated shelf life test method combined with Q10 model.The results showed that the total number of bacterial colonies of the beverage was always in the safe range during the whole period,and the soluble solids content,total acid,total sugar and sedimentation rate of the beverage remained stable under the storage temperature of 4℃.The degree of browning at 4°C was lower than that at 27°C and 37°C,and the color remained relatively stable.Compared to the storage temperatures of 27°C and 37°C,the loss of VC content was the lowest at 4°C and the retention of V_C was the best.Under 4℃,27℃and 37℃,the antioxidant activity of Hami melon-Korla fragrant pear mixed beverage were all highest around the 18th day,and the antioxidant effect was the strongest at 4℃.The relative residual activities of PPO enzymes and POD enzymes were significantly reduced at 4°C,which reduced the degree of color darkening of the Hami melon-Korla fragrant pear mixed beverage.The zeta potential of Hami melon-Korla fragrant pear mixed beverage at 4℃,while the zeta potential were all negative at 27℃and 37℃and the absolute value was less than 30 m V,the charges repelled each other and the aggregation binding force was reduced,so the beverage was stable.The mean particle size of Hami melon-Korla fragrant pear mixed beverage at 4℃varied less than that of 27℃and 37℃,and the stabilization effect was better than 27℃and 37℃.Finally,the shelf life under 4℃was predicted to be 50 days.(4)A combination of electronic nose and HS-SPME-GC-MS method was used to comparatively study the effects of UHP treatment and pasteurization on the flavor composition and changes of Hami melon-Korla fragrant pear mixed beverage.The results of electronic nose test showed that aromatics,sulfides and methane contributed to the main flavor in the Hami melon-Korla fragrant pear mixed beverage during storage at 4°C.At the later stage of storage,the effect of UHP treatment on the flavor change of the beverage was more significant and flavor was more prominent than that of the pasteurization.The results of GC-MS showed that the main characteristic flavor categories of the Hami melon-Korla fragrant pear mixed beverage contained alkanes,ketones,alcohols,aldehydes,esters,olefins,and the UHP group contained sulfides.Esters and sulfides were the main source of flavor presentation of the UHP treated Hami melon-Korla fragrant pear mixed beverage,contributing to the characteristic flavor;alcohols,aldehydes and ketones were the main flavor of the pasteurized beverage,with inferior odor.The overall contribution of alkyl olefins to the characteristic flavor of the beverage was not significant.Therefore,pasteurization would destroy the flavor substances of Hami melon-Korla fragrant pear mixed beverage,while the UHP treatment better preserved and improves the flavor.So,pasteurization would destroy the flavor substances of Hami melon-Korla fragrant pear mixed beverage,while the UHP treatment could better preserve and improve the flavor. |
PDF Full Text Request