Effect Of Heat Treatment On Physicochemical Properties And Flavor Of Noni Juice

Noni is a dicotyledonous Rubiaceae,also known as Euphorbia.There are many active ingredients and nutrients in the fruit.Its internal polyphenols and flavonoids can greatly reduce the activity of peroxidase in human body and alleviate the damage of free radicals to human body.There are many processing methods of Noni fruit,and Noni juice is the main commercial product.Heat treatment is an important part of fruit juice processing industry.The safety period of food through heat treatment is relatively long,but it will damage the nutritional structure of fruit juice and antioxidant activity of active substances,and its flavor will also be affected.In this study,different heat treatments were used to improve the properties of raw materials,and the physical and chemical properties and active components of Noni juice were determined.The volatile components of Noni juice were analyzed by GC-MS to explore the effect of heat treatment on its flavor and its change rule.In view of its unacceptable odor,the juice was prepared by mixing with fresh lemon and flavoring to improve the quality of Noni juice The specific conclusions are as follows:Compared with the ripe and unripe,the firmness and firmness of the fruit were higher than those of the unripe.After heat treatment,the physicochemical properties of Noni fruit juice changed differently.The color of the juice was the darkest when it was treated at 115 ?for 5min,and precipitates appeared,and other colors were deepened to varying degrees.The soluble solid content and p H of the juice had no significant effect.With the increase of heat treatment temperature,the contents of total acid,volatile acid and Vc in the juice decreased,and Vc was seriously damaged.Heat treatment increased the content of flavonoids in fruit juice,especially at 115 ? for 5 min,from 11.11 mg / 100 m L to 14.76 mg / 100 m L.The loss rate of total phenols was 0.14% at 115 ? for 5min,and the total phenol content was 61.45 mg/ 100 m L ? 53.09 mg / 100 m L.Heat treatment had little effect on saponins in fruit juice,and the content ranged from 5.06 mg / 100 m L to 4.03 mg / 100 m L.The effects of untreated and different heat treatments on the flavor of juice were detected by GC-MS,and 28 volatile compounds were detected.There were 7 aldehydes and ketones(3%),3 acids(78.4%),2 alcohols(6.62%),7 esters(7.9%)and 8 terpenes(4.06%).Among them,octanoic acid is the main reason for the formation of "rotten cheese" smell of Noni juice.A variety of esters with rich aroma were also produced after heat treatment,and the intensity of fruit flavor decreased with the increase of heat treatment temperature.Among the effects of heat treatment on the flavor of fruit juice,85 ? for 5min can keep the aroma of Noni fruit and reduce the content of octanoic acid.The results showed that 115 ? for 5 min had the greatestdifference in taste,and 85 ? for 5 min had the smallest difference.The order of acidity of Noni juice treated at different temperatures was as follows: untreated > 85 ? 5min > 100 ?5min > 115 ? 5min;the order of influence on the taste was opposite to that of sour taste.The cluster phenomenon of bitterness,astringency,saltiness and sweetness was obvious.The sensory evaluation score of 85 ? for 5 min was higher and the overall taste was better.The compound juice of Noni and lemon with lower acidity and more volatile substances was prepared.Through response surface analysis,the raw material formula of Noni lemon compound juice with the highest sensory evaluation score was obtained by response surface analysis method: when nori juice 70%,lemon juice 10%,sucrose 8%,citric acid 0.2%,the sensory evaluation score of the compound juice was(95.6667 ± 2.0817),which reached the prediction 32% of the value.The results showed that there were 43 kinds of main aroma components in the compound juice,including 24 terpenes(60.94%),10 alcohols(29.33%),3esters(1.74%),2 alkanes(0.19%),3 aldehydes(2.6%),3 acids(0.64%)and ethers(0.03%).D-terpene,Terpinene and Terpinene,which play the most important role,are the characteristic aromatic compounds of lemon.However,the main source of bad flavor in Noni juice was octanoic acid,which accounted for only 0.64% of the compound juice,indicating that the compound juice of Noni lemon can effectively cover up the unpleasant smell brought by octanoic acid.According to the taste value of compound juice determined by electronic tongue,the sour and sweet taste of compound juice is obvious,and other taste sense is better on the whole,which can provide theoretical basis for the development and utilization of compound juice of Noni.Considering the above factors,85 ? for 5 min can retain the characteristics of Noni juice,reduce the cost and save time.Moreover,it can maintain the aroma of Noni fruit and reduce the content of volatile compounds in bad smell.Response surface methodology was used to optimize the raw material ratio of compound fruit juice,which could effectively cover up the smell of Noni and add flavor.It provides a reliable theoretical basis and new ideas for the further research of compound juice technology of Noni fruit and its application in industrialization in the future.