Study On The Changes Of Quality Characteristics And Bitters In Gannan Navel Orange During Storage And Processing

Gannan navel orange(Citrus sinensis Osb.Var.brasliliensis Tanaka)is a citrus orange belonging to the Citrus subfamily of Rutaceae,and the main planting area is distributed in Ganzhou City,Jiangxi Province.Gannan navel orange is favored by consumers with its unique taste,flavor and aroma,and the fruit contains hesperidin,polyphenols,limonin and other biologically active substances,which have high nutritional and health benefits.Orange juice is the main product of Gannan navel orange processed,but the bitter substances in orange juice(limonin and nomilin,etc.)seriously affect the taste of orange juice.At the same time,the bitter is also the main factor that restricts the processing of navel orange fruit into other products.This thesis aims to explore the changes in the quality characteristics and bitter substances of orange juice during the harvest,storage,processing and storage of navel orange fruit,in order to explore the changes in raw materials,processing and storage of bitter substances and quality characteristics during orange juice storage.The rule is to reduce the content of bitter substances in orange juice as much as possible under the premise of ensuring the quality of orange juice,and to provide a certain reference for the selection of the appropriate navel orange harvest and storage period and processing technology for orange juice processing.First,the physicochemical quality,limonin and nomilin content of orange juice prepared from fruits of different harvest and storage periods were determined,and the navel orange fruit with the lowest bitter substance content was maintained while maintaining the acceptable range of basic quality of orange juice Harvest period and storage period.Secondly,the influence of some key unit operations on orange juice quality during orange juice processing was studied,and the correlation analysis of the changes of various orange juice quality indicators during processing was carried out.Further study the effects of different temperatures and p H values on the quality of orange juice during heat treatment,and study the heat treatment kinetics of limonin and nomilin.Finally,the quality characteristics of orange juice with different sterilization temperature and storage temperature during storage and the changing law of limonin and nomilin were studied.The main findings are as follows:(1)Delayed harvesting of navel orange fruit.After November 13th,with the extension of the harvest period,the juice and whole fruit juice yield changes are not significant,the L*value of the orange juice decreases,a*,b*value as it rises,the soluble solids content,soluble sugar content,p H,and solid acid ratio gradually increase.Titratable acids,vitamin C,biologically active substances,antioxidant capacity,and bitterness contents all show a slow decreasing trend.During the storage of navel orange,the pulp and whole fruit juice yields were not significantly different.With the extension of fruit storage time,the L*value of the prepared orange juice first decreased and then increased,and the a*and b*values showed an upward trend.The content of sugar and acid in orange juice showed a trend of increasing first and then decreasing.The trend of p H value was opposite to that of titratable acid.The solid acid ratio of orange juice showed a trend of decreasing first and then increasing.The content of vitamin C increased first during storage After the downward trend,the biologically active substances,antioxidant capacity,bitter substances and other indicators showed a trend of increasing first and then decreasing.According to comprehensive analysis,the harvest period of navel oranges that are more suitable for processing juice is from December 13 to December 23,and the storage period of navel oranges that are more suitable for processing juice is:30 to 40 days after storage.(2)Homogeneous treatment has little effect on the nutrients and active ingredients in orange juice.Key processing operations such as juice extraction,enzymatic hydrolysis and colloid mill have a greater impact on the content of each ingredient in orange juice,and make the limonin accumulates rapidly.The filtering operation only has a great influence on the composition of the orange juice prepared by crushing.The concentration treatment mainly reduces the vitamin C content and the antioxidant capacity of the orange juice significantly.On the whole,enzymolysis,colloid milling and concentration treatment are the key control points for the quality change in orange juice processing.It is necessary to optimize the enzymolysis process parameters to reduce the heating temperature of orange juice during processing and reduce the heat treatment and oxygen contact time of orange juice.(3)Heat treatment temperature(50℃,70℃,100℃),p H value(3.0,5.0,7.0)and heat treatment temperature(10min,30min)affect the quality characteristics of orange juice to a certain extent,heat treatment leads to the sugar of orange juice Acid degradation occurs,the higher the temperature and the longer the time,the more severe the degradation.High temperature and long-term heat treatment will cause the degradation of vitamin C content,but the degradation is smaller under the condition of air isolation.The content of total phenol,flavonoids,hesperidin and antioxidant capacity in orange juice with different heat treatment temperature and time were not significantly different.Adjusting the p H value of orange juice directly changes the total acid content of orange juice.Both excessive acidity and partial alkalinity will reduce the sugar content of orange juice.The p H value had no significant effect on the changes of vitamin C and hesperidin content.With the increase of p H,the DPPH and·OH radical scavenging rate of orange juice decreased significantly,and the ABTS~+radical scavenging rate increased significantly,while the total reducing ability was the strongest when the p H value was 5.0.The limonin and nomilin in orange juice heat-treated at different temperatures both gradually increased with time,and the higher the temperature,the greater the increase.With the increase of p H,the amount of limonin and nomilin in orange juice gradually decreased.When the p H value was greater than 5.0 and 4.0,respectively,neither limonin and nomilin were detected.The heat treatment at different temperatures and p H values had the best fitting effect on the changes of limonin and nomilin and the combined reaction kinetic model.(4)During the storage of orange juice,the soluble solids content gradually increased,the total sugar content did not change significantly,and the total acid content decreased slightly.With the extension of storage time,the vitamin C,total phenols,total flavonoids,hesperidin and antioxidant capacity in orange juice showed a gradual decrease trend.The stability of total phenol,total flavonoids and hesperidin during storage is significantly stronger than that of vitamin C,which is the main source of the antioxidant capacity of orange juice during storage.Both Limonin and Nomilin reached their peak after 10 days of storage.During storage,the content of Limonin decreased slowly,and the content of Nomilin was maintained between 2.7 and 3.5 mg/L.Nomilin had little effect on the content change during storage.In summary,factors such as the harvest period,storage temperature and time,processing unit operation,orange juice storage temperature and time of navel orange will affect the quality characteristics of orange juice and the changes in the content of bitter substances,the heat treatment process has a greater impact on the quality of orange juice,Especially bitter substances such as limonin and nomilin,it is of great significance to improve the quality of orange juice and reduce the content of bitter substances by determining the appropriate harvest time,storage method,optimizing the processing and storage parameters of orange juice.