Study On The Physical And Chemical Properties Of Preserved Kumquat Fruit After Different Sugar Osmosis Processing

Kumquat,as a unique citrus fruit in south China,is rich in various nutrients.It is characterized by being eaten with the skin and flesh together.The throat is full of fragrance after chewing.Kumquat has high medicinal and edible values.But fresh kumquat is seasonal strongly,and contains high moisture content which makes it is not easy to store.At present,the main product on the market is candied fruit with sugar osmosis,which has a long shelf life.However,the sugar content of preserved fruit is too high in the traditional sense.Nowadays,people's main demand for food changes to the healthy quality.Therefore,the research and development of"low-sugar"preserved kumquat fruit is a general trend.How to effectively improve the processing efficiency and maintain the original quality and nutritional components of kumquat are two main problems up to now.How to use the new technology to monitor the processing process in real time and get the better quality are two main research contents of this paper.The traditional normal pressure processing method is for the control group,meanwhile the method of vacuum infiltration as the processing group.This experiment is designed to get the best processing conditions and better products'quality characteristics by using the latest technology to demonstrate the quality characteristics changes.The research results obtained in this paper are as follows:(1)Low field nuclear magnetic resonance(LF-NMR)results showed that there was less immobilized water content in kumquats under vacuum condition osmosis with sugar(VSKs)compared to that of the kumquats under atmospheric pressure osmosis with sugar(ASKs)after immersion via the lower relaxation times(T₂₂)and corresponding peak area(A₂).There also existed lower freedom of water in kumquats under vacuum impregnation with sugar and then hot air-drying(VS-ADKs)rather than that of kumquats under atmospheric pressure osmosis with sugar and then hot air-drying(AS-ADKs).Magnetic resonance imaging(MRI)results revealed that the water release of VSKs was higher than that of ASKs via the proton signals with different color.Especially the final water distribution of VSKs was more uniform than that of ASKs.The intake of sucrose produced a more pronounced depressing influence on the T_gof VSKs than that effect on the T_gof ASKs.The T_gof VS-ADKs also showed a more remarkable decreasing trend than that of AS-ADKs,which precisely due to the plasticising effect of low molecular weight sugar.(2)SEM observed that VSKs tissues were relatively dense,but the cell cavity of ASKs was ruptured,while VS-ADKs tissues were dense and AS-ADKs tissues were loose,but all the cells had folde.Compared to ASKs and AS-ADKs,VSKs and VS-ADKs had higher hardness,chewiness and gumminess.Compared with VS-ADKs,AS-ADKs showed a greater decline in L*,a*and b*values.Compared with the FKs group,the treatment of osmotic dehydration led to the decrease of total polyphenol content in the ASKs group and the VSKs group,while the stable trend of total polyphenol content in the VS-ADKs group which may be attributed to the protective effect of sucrose uptake.With the increase of infiltration time,the content of total flavonoids in ASKs group and VSKs group increased.In the ASKs group and the VSKs group,"?-carotene"increased gradually under the effect of infiltration.The difference between the two methods of penetration and the effect of drying on the properties of preserved kumquat were elucidated.(3)The effects of two different processing methods on the volatile components of candied kumquats were investigated via Headspace-Gas Chromatography-Ion Mobility Spectrometry(HS-GC-IMS).The characteristic volatile fingerprints of fresh kumquats(FKs),VS-ADKs group,and AS-ADKs group were established using3D topographic plots.From the fingerprints,40 signal peaks for 22 compounds were confirmed and quantified in all types of kumquats,namely,two terpenes,four esters,seven aldehydes,three ketones,and six alcohols.3-Pentanone was identified as the major component of FKs,followed by 1-hexanol and the Z-3-hexen-1-ol dimer.The hexanal dimer,2-hexen-1-ol,and the ethyl acetate dimer were the major markers of VS-ADKs.Benzaldehyde and furfurol were the prominent constituent parts of AS-ADKs.Compared with that in FKs,the pentanal and dimethyl ketone contents of VS-ADKs and AS-ADKs exhibited a dramatic increase.By contrast,the change in ethanol dimer tended to decrease.Principal component analysis(PCA)clearly showed that the samples could be well-distinguished,which were distributed in a separate space.Furthermore,the similarity of different processed kumquats and their corresponding volatile components were demonstrated via heat map clustering analysis.The results confirmed the potential of HS-GC-IMS-based approaches to evaluate processed kumquats with various volatile profiles.