Effects Of Drying Methods On Properties Of Chinese Jujube

Jujube?Ziziphus jujuba Mill.?is a predominant Chinese herb belonging to the Rhamnaceae family.Jujube fruit is highly appreciated by consumers which is mainly due to its delicious taste and nutritional properties.Owing to its nutrition and taste,the demand for various types of jujube products has increased.Fresh jujube has a brief harvest season and easily deteriorates during storage,therefore,further processing is urgently needed.Drying is the most commonly and widely preservation method,which can ensure microbial safety of biological products and preserve their desirable qualities.Therefore,dehydrated jujubes were obtained by using vacuum-freeze drying?VFD?,mid-infrared drying?MIRD?,microwave-vacuum freeze drying?MVFD?and microwave-vacuum puffing?MVP?separately,and dietary and nutritional properties,antioxidant capacity and the aroma properties were determined.The main results of this study were as follows:?1?Different drying methods show a significantly effects on dietary compounds of jujubes.The contents of total sugar and reducing sugar increased after drying.The contents of total acid were declined except MIRD.There was no significant effect on the color and brown degree after MVFD and MVP.MVFD got the highest retention rate of vitamin C?98.62%?,MIRD got the lowest vitamin C.?2?MVP enhanced the levels of sugars,organic acids while VFD presented higher the content of total phenolic and proanthocyanidins.MIRD was a good choice for the preservation of sugars and cyclic nucleotides.MVP resulted in jujubes with richer phenolic compounds including catechin,chlorogenic acid,vanilic acid,epicatechin and rutin,followed by MVFD,and both lead to a higher antioxidant capacity.The content of total phenolic in jujube after MVP and MVFD significantly increased to 4721.30 mg/100 g DW and4516.25mg/100 g DW.The content of total flavonoid after VFD was significantly higher than other drying methods?p<0.05?.MIRD showed good effects on retaining sugars,cyclic nucleotides and phenolic compounds.Different drying methods had their respective advantages.MVP and MVFD both had significant gains in TPC compared with the fresh samples,which led to a corresponding increase in antioxidant properties.Considering the maximum preservation of nutritional values and shorter processing time,MVP and MVFD can be used as an efficient alternative to dried jujubes.?3?By estabilishing dried jujube quality assessment model,we got the evaluated dried jujube quality assessment total score expression:F=0.9111F₁+0.7608F₂+0.4742F_3.Compared the results of the calculating scores using this model,it showed that MVP was the highest scorer,then MVFD?VFD,and the lowest scorer was ID.The higher the scorer was,the better the quality of dried products were.So,it can be proved that the dried jujube quality evaluation model showed objective evalution function and can offer a new approach for quanltiy evaluation of jujube production.?4?The number of flavor compounds identified by GC-MS coupled with solid phase micro-extraction in four dried jujube chips was 75.The acids?29 kinds?were higher in VFD,MVFD and MVP dried jujube chips,while aldehydes?31 kinds?were the major volatile compounds in ID treated samples.The method of principle component analysis?PCA?was used to establish the aroma quality assessment model.The MVP products showed the higher scores and better aroma quality than VFD,MVFD and ID.Evaluation of aroma quality of jujube chips could be achieved by PCA method,and it could also be used for a reference of jujube chips processing optimization.