Study On Quality Protection Of Blueberry Juice Blend By Non-thermal Processing Technology

Although blueberries are extensively cultivated and have high nutritional value,they are mainly consumed fresh.Therefore,the processing of these fruits is not typical.Since ensuring the quality of blueberry products using traditional thermal processing technology is challenging,non-thermal processing methods are currently preferred.Consequently,new non-thermal processing technologies have attracted increasing research attention.Aiming at the bottleneck problem of blueberry industrialization,this article examined the effect of added antioxidants and ultrafiltration（UF）technology on juice quality.It combined ultra-high-pressure and ultrasonic technology to maintain the sensory and nutritional quality of juice,ensure its microbial safety,and extend its shelf life.This is highly significant for the deep processing and utilization of blueberries.The research content is as follows:（1）Changes in the quality of a blueberry juice blend were examined regarding the different antioxidants,such as gallic acid（GA）,ferulic acid（FA）,ascorbic acid（VC）,citric acid（CA）,tea polyphenols（TP）,andα-tocopherol（VE）combined with ultra-high-pressure technology.The results showed that VC,GA,and TP could better maintain the color of the juice,protect the anthocyanin content,and inhibit browning.After storage at 4°C for 4 d,the results showed that adding 2g/L of VC,GA,and TP reduced the degree of juice browning by 27.74%,29.53%,and 23.94%,respectively,compared with the control group.The anthocyanin preservation rates were 114.80%,112.58%,and 112.97%,respectively.In addition,2～4g/L of VC,GA,and TP significantly inhibited the PPO enzyme activity of the blueberry compound juice,protecting its color.Comparing the protective effect of the three antioxidants at the optimal concentration on the juice color during storage revealed that the anthocyanin preservation rate was higher with2g/L added GA while displaying stronger enzyme activity inhibition.This could be attributed to the fact that the stability of the anthocyanins was enhanced by combining them with GA.（2）The effect of different sterilization methods on the quality of the cloudy blueberry juice blend after adding 2g/L GA and the changes during storage at 4℃were studied.The results showed that the total aerobic bacteria（TAB）decreased by at least 2.99 log₁₀CFU/m L,the yeasts and molds（Y&M）were below 1 log₁₀CFU/m L,and the coliform most probable number（MPN）was lower than 3 MPN/m L after high-pressure processing（HPP）,as well as ultrasound（US）and heat（HT）treatments.The TAB changes in the cloudy blueberry juice blend during storage indicated that it could be stored for 72 d,48 d,and over 72 d,respectively,after HPP,US,and HT treatment.No significant changes were evident in the p H,TSS,and turbidity of the cloudy juice before and after these treatments or during the storage period（P>0.05）,while the anthocyanin and VC content decreased significantly.After 72 d of storage,the juice subjected to HPP and HT treatment exhibited a reduction of 56.44%and 31.47%in the anthocyanin content,while the VC content declined by 23.10%and 10.89%,respectively.However,US treatment facilitated the fastest anthocyanin degradation rate at 53.21%after 48 d of storage.The total phenol decline rate was mostly the same among the three treatments,while the DPPH antioxidant activity showed a significant high-strength correlation with total phenols（r=0.832-0.846）and anthocyanins（r=0.787-0.896）（P<0.01）.Analysis of the flavor components revealed that HT treatment before and after processing and during storage reduced the esters and aldehydes,resulting in a reduction in the fruity flavor and green aroma of the cloudy juice.（3）The effect of different sterilization methods on the quality of the clear blueberry juice blend and the changes during storage at 4°C were examined.The results showed that UF reduced the TAB and Y&M in the clear juice by 1.40 log₁₀CFU/m L and 3.09 log₁₀CFU/m L,respectively,while the coliform MPN was below 9.4 MPN/m L.Furthermore,the anthocyanin,total phenol,and VC content were reduced by 26.59%,31.22%,and 26.77%,respectively.After applying different sterilization methods,the clear juice microorganisms met the Food Safety National Standard Beverage requirements.The TAB changes in the clear juice after HPP,US,and HT treatment allowed it to be stored for 104 d,72 d,and over 104 d,respectively.During storage,there was no significant change in p H,TSS.The turbidity increased,while the L*value,and a*value decreased.During storage for 104 d,the light transmittance of the HPP-and HT-treated juice decreased by 15.51%and 17.68%,while the turbidity increased by 40.21%and98.88%,respectively（P<0.05）.The anthocyanin and total phenol content in the clear juice decreased at the same rate during the storage period after applying the three sterilization techniques.However,compared with US and HT treatment,the degradation of VC in the juice was slower when exposed to the ultra-high-pressure treatment.Pearson correlation analysis revealed a strong association between the DPPH antioxidant activity and the active ingredients（total phenols,anthocyanins,and VC）（P<0.01）.The sensory evaluation results showed that the sensory quality of the clear juice decreased significantly with an increase in storage time after the different treatments（P<0.05）.（4）Comparing the microorganism changes in the clear and cloudy juices during storage indicated that HT treatment ensured the microbiological safety of compound blueberry juice to a more significant extent.Comparing the quality index changes in the clear and cloudy juices during storage revealed that US and HT treatment affected the turbidity and clarity of the clear juice,while HT treatment severely impacted the flavor index of the cloudy juice.The VC degradation rate in the juice was faster after US treatment,while HPP treatment had little effect on the sensory and nutritional quality of the juice.The research results revealed HPP and US treatment as potential non-thermal processing methods.