Effects Of Dissolved Oxygen On Storage Characteristics Of Litchi Mixed Juice Processed By Ultra-high Pressure

The browning of litchi juice,the deterioration of flavor and the change of nutrient composition are all indispensable to oxygen.In this paper,the raw materials were mixed with the juice of huaizhi litchi juice and coconut water.In order to ensure the quality of different pretreatment methods,the concentration of dissolved oxygen in the fruit juice was reduced efficiently,and the optimal treatment method was selected to set different gradient dissolved oxygen content.The changes of nutrition index,amino acid composition and aroma composition in the storage process were discussed,and the main results were as follows:(1)The content of dissolved oxygen,L-ascorbic acid,total phenols,reducing sugars,?-aminobutyric acid(GABA),browning degree and enzyme activity were compared and analyzed.The results showed that the nitrogen displacement treatment can effectively reduce the dissolved oxygen content of the juice,and the dissolved oxygen concentration of the juice was lower than that of the vacuum treatment and ultrasonic treatment.Nitrogen replacement treatment had no significant influence on total phenol,reducing sugar and GABA content.There was no obvious effect on the activity of PPO and POD in the browning index and the mixed juice of litchi,and the retention rate of L-ascorbic acid content was the highest in the other two groups,which was 88.57%.There was no significant difference in the content of L-ascorbic acid between the nitrogen-displaced mixed juice and the untreated mixed juice.(2)During the juice canning process,nitrogen substitution treatment was used to reduce the initial dissolved oxygen concentration of the juice.The initial dissolved oxygen content was DO group: 0.16 mg/L,and CK group: 5.2 mg/L.The contents of dissolved oxygen,VC,total phenols,reducing sugars,GABA,etc.,browning degree,and color of the two groups of juice during storage were measured.The results showed that: DO group litchi mixed juice in the storage process of the nutritional indicators are better than the CK group litchi mixed juice,nitrogen replacement treatment has a certain positive effect.And the nutritional index of the juice stored at 4 °C was better than that stored at 25 °C,and the low temperature was helpful for juice storage.(3)By analyzing the aroma composition and amino acid composition of mixed juice before and after nitrogen replacement + ultrahigh pressure treatment,The results showed that the nitrogen treatment did not contribute much to the loss of aroma components in the juice,and had an effect on the total amount of amino acids.The total amount of amino acids in litchi mixed juice after ultra-high pressure treatment increased significantly,and the total amount of amino acids in litchi mixed juice after nitrogen replacement treatment was higher than that of untreated juice.At the same time,the aroma components and amino acid components in the juice before and after storage were compared.The results showed that with the extension of storage time,the aroma components and content,amino acid composition and its content were all reduced.