Study On The Variation Of Nutrition And Typical Aroma Of Litchi Juice During Processing

Focusing on the variation of nutrition and typical aroma of litchi juice during processing. The following research have been conducted: (1) The comparative study of the nutrition and aroma compounds in different breeds of litchi. (2) Qualitative and quantitative analysis for the free and glycosidically-bound volatile compounds in litchi. (3) The change of typical nutrition and aroma in litchi juice processing as well as aroma-enhancing regulation. (4) The change of aroma compounds of litchi juice during storage. The main conclusions of this paper are as follows.1 .The nutrition and aroma compoundts of different breeds of litchiThe nutrition content differ from various breeds of litchi. The contents of reducing sugar, total sugar, Vc were highest in 'feizixiao'.The total acid content was highest in 'baila' , and the amino acid content was highest in 'yuhebao'. Additionally,The protein and fat contents were low overall and there were little difference between the five cultivals. Five breeds of litchi contained mineral elements K, Ca, Mg, Fe, Na, Zn. The contents of K and P were higher, especially in 'feizixiao'.The aroma compounds of five breeds of litchi were analyzed by SPME/GC-MS methods. The results indicated that the differences of aroma compounds in composition and relative content in five breeds of litchii were significant. 1-Methoxy-2-propanol, 3-Methyl-2-heptanol, 1-Hepten-3-ol, Linalool, 2-Ethyl-2-butenal,β-Pinene, Limonene etc were identified in all five breeds. In addition, every breed of litchi has its particular aromatic components. Geraniol, Phenylethyl alcohol, Linalool, Limonene etc were typical aroma compounds of 'feizixiao'. Citronellyl tiglate, Farnesol had an important contribution to the flavor of 'heiye'. Farnesol, 3,7-Dimethyl-2-octen-1-ol, Isopropyl acetate were typical aroma compounds of 'baila'. Ethyl acetate, Acetoin were typical aroma compounds of 'lizhiwang', and Nerol, 1-Methoxy-2-propanol were typical aroma compounds of 'yuhebao'.Taking both nutrition and aroma compostion into account,, among the five cultivals of litchi tested, 'feizixiao' was the best cultival for processing.2. Free and glycosidically bound volatile flavor compounds in litchiFree and glycosidically-bound volatile compounds were isolated and identified from litchi using an AmberliteXAD-2 column and GC-MS method. The volatile compounds from the bound fraction were released by hydrolysis with almondβ-glucosidase and hemicellulase. In the free fraction , the major volatile compounds found were Geraniol, Citronellol, Octadecadienoic acid, Phenylethyl alcohol,trans,trans-2,6-Dimethyl-2,6-octadiene-1,8-diol, Hexanedioic acid bis (2-methylpropyl) ester ,Hexadecanoic acid methyl ester, Citral etc. In the bound fraction, the latent major volatile compounds found were Geraniol, Citronellol, Phenylethyl alcohol, Benzyl alcohol, Geranic acid, 4- (3-Hydroxy-1-butenyl) -3,5,5-trimethyl-2-cyclohexen-1-one etc. There were considerable part of aroma compounds in the form of glycosidically-bound in litchi. Enzyme hydrolysis can break out the glycosidic bound and release the potential aroma compounds to enhance aroma.3. The variation and aroma-enhancing regulation of typical nutrition and aroma of litchi juice during processingThrough the comparative analysis for the effect of different ultrafiltration membrane on nutrition and aroma, 200nm ultrafiltration membrane has a higher retention rate for both nutrition and aroma in litchi than 50nm ultrafiltration membrane.There was a great impact of sterilization on both nutrition and aroma of litchi. Among the four ways of sterilization tested, Pulsed Electric Field (PEF) has a highest retention rate for both nutrition and aroma in litchi, 100℃sterilization was second, and pasteurization was the worst.The typical nutrition of litchi, such as saccharides, organic acids, amino acid, Vc, soluble solid were lost in some extent during processing. After enzyme hydrolization, the total content of aroma compounds increased 10.4%, but gradually decreased 41.49%,47.47%,37.58% after enzyme inactivation, ultra-filtration and sterilization respectively. The contents of typical aroma compounds of litchi, such as Geraniol, Citronellol, Phenylethyl alcohol, Limonene ,Linalool, Citral etc increased after enzyme hydrolization, but gradually decreased in the late processing of enzyme inactivation, ultra-filtration and sterilization. In general, the typical aroma compounds were lost severely after enzyme inactivation and ultra-filtration.Enzyme hydrolysis could release the bound aromatic components to enhance aroma of litchi juice, and the effect of usingβ-glucosidase combined hemicellulase was better than using each enzyme alone. The optimum enzymatic parameters were that the usage enzyme were 324.45 U/Lβ-glucosidase and 1500 U/L hemicellulase, time was 12h.4.The change of aroma compounds of litchi juice during storageThere were some changes of aroma compounds of litchi juice during storage. In general, most typical aroma compounds had their peak content after four weeks storage. Through the comparative analysis for the effect of 4℃and normal temperature storage on typical aroma compounds, 4℃storage has a higher retention rate for aroma in litchi juice than normal temperature storage.