Study On Composition Changes Of Gannan Navel Oranges During Storage Based On Metabolomics Technology And Deep Processing Of The Products

Gannan navel orange(Citrus sinensis Osbeck)is the most distinctive geographical indication agricultural by-product in Jiangxi Province,and its yield is increasing year by year.Navel orange has a bright appearance,rich fruity aroma,sweet and sour,juicy taste,and has a long reputation in Chinese and overseas markets.Navel orange is rich in essential oils,flavonoids,carotenoids,phenolic acids,limonin,vitamins and other nutrients.It has physiological effects such as anti-cancer,anti-oxidation,anti-inflammatory,lowering cholesterol levels and regulating immunity.Therefore,eating more navel orange is very beneficial to human health.As a seasonal fruit,navel orange has been extending its shelf life because of its increasing yield year by year.The quality of navel orange is constantly changing during storage,including volatile components,non-volatile components and active components.The storage of navel oranges is also disturbed by storage environment,storage conditions and preservatives.At present,a large number of studies have been conducted on the effects of changing storage conditions and using preservatives on the storage of navel oranges at home and abroad.However,there are still few studies on the composition dynamics of navel oranges stored under natural conditions,which is not deep and comprehensive enough.Therefore,this study used chromatography-mass spectrometry combined with chemometrics methods to study the changes in the types and contents of volatile and non-volatile components and the changes in antioxidant enzyme activities of Gannan navel oranges during storage,and to clarify the changes in the chemical composition and antioxidant enzyme system of navel oranges during storage.The main research content is as follows:(1)The volatile components of Gannan navel orange during storage were studied using headspace solid-phase microextraction(HS-SPME)combined with gas chromatography-mass spectrometry.A total of 62 compounds were identified through the NIST database and relevant literature,and principal component analysis showed significant differences in volatile components among them.In addition,it was explored that the types and relative content of compounds were constantly changing throughout the storage process,and the compounds with aroma characteristics were described.A total of 32 VOCs with FC values>2 or<0.5 and p<0.05 showed significant differences before and after storage,of which 11 were down regulated and21 were up regulated.In addition,19 metabolic foreign bodies were selected and correlation clustering analysis was conducted on them.The results showed that alcohols and aldehydes were clustered into two categories,while esters and terpenes were clustered into one category,with different trends in their content changes.But in the later stage,its content and aroma overall decreased.(2)Ultra high performance liquid chromatography tandem time of flight mass spectrometry(UPLC-QTOF-MS)was used to monitor the non volatile compounds in Gannan navel orange pulp at different storage periods.After identification,a total of68 non volatile components were identified.The PCA results showed that navel oranges were clearly distinguished under different storage periods;Using partial least squares discriminant analysis and one-way ANOVA to identify the differential components of navel oranges with different storage periods,a total of 27 differential metabolites were selected,among which flavonoids were the main metabolic foreign bodies.The correlation heat map showed that they had a high correlation,with the content first increasing and then decreasing during the storage period.KEGG was enriched into six main metabolic pathways,indicating that the main metabolic pathway affecting the production of differential metabolites is flavonoid biosynthesis(map00941).(3)During storage,navel oranges undergo oxidation,and under oxidative stress,they produce oxygen free radicals,which directly promote cell aging and compound oxidation,greatly reducing the quality of navel oranges.This study measured the MDA content and enzyme activity in the flesh and peel of navel oranges during different storage periods,including SOD,POD,CAT,APX,PPO.The MDA content showed a decrease throughout the entire storage period,and both the peel and flesh showed the greatest decrease from 6 weeks to 9 weeks.SOD,POD,APX,CAT and other antioxidant enzymes exhibit different activity trends during storage.These enzymes,which are in the first line of defense against oxidation,all show reduced activity in the flesh at the third week.However,the flesh is wrapped in the skin,so its oxidation level is not high.Therefore,the enzyme activity in the skin,except for APX and PPO,is generally higher than that in the flesh.The activity of PPO fluctuates in the peel,but it rapidly increases in the flesh in the later stages.The correlation results indicate that APX,POD,and PPO have a high correlation,but CAT,MDA,and SOD both maintain a high correlation.These conclusions provide a basis for the study of antioxidant enzyme systems in navel orange storage.(4)As an agricultural by-product,navel orange has a huge space for development and utilization.This study conducted a series of studies on the deep processing of navel orange products,and optimized and improved the production process of navel orange jam as the development direction.Select appropriate conditional levels and design orthogonal experiments through a three factor five level univariate study.Through sensory evaluation and other methods,a comprehensive evaluation of navel orange jam was conducted,and it was ultimately determined that the optimal quality of navel orange jam can be achieved when the CMC addition amount is 2.5%,the sucrose addition amount is 25%,and the material liquid ratio is 1:1.