Flavour differences between fresh and dried fruit of Myrica rubra‘Dongkui'

Abstract: 【Objective】Nutrition and flavor components play an important role in the quality and market-ing of the fresh fruit and processed products. In order to investigate the flavour differences between freshand dried fruit of bayberry(Myrica rubra‘Dongkui') and to develop its deep-processing products,the re-lated components of sugar,acidity and fragrance in the fresh and dried fruit were determined. The possi-ble reasons for the composition changes between the fresh and dried fruit were analyzed,and the nutri-tional value of bayberry's dried fruit was evaluated comprehensively.【Methods】The total sugar,reduc-ing sugar and sucrose of the fresh and dried fruit of bayberry were measured by phenol-sulfuric acid meth-od,film Reagent and the first method of GB /T5009.8-2008 respectively. The organic acid standards(Sig-ma),including oxalic acid,tartaric acid,malic acid,lactic acid,succinic acid and citric acid,were pre-pared in ultrapure water at concentrations from 0.01 to 1.0 g·L^-1. The conditions of HPLC were as follows:Varian C18 column(150 mm×4.6 mm),mobile phase contained 0.5% KH2PO4,the wavelength of the ultraviolet detector 210 nm,and injection volume 20 μL. The fresh and dried bayberry samples wereground with 10 mL ultrapure water,then centrifuged(8 000 r·min-1,10 min) and supernatant fluid wasfixed to 25 mL,respectively. The solutions were analyzed directly by using HPLC. The fresh and driedbayberry samples were ground and homogenized with 5 mL HCl,and then fixed to 25 m L,respectively.After 24 h hydrolysis in vacuo at 110 ℃,sample was cooled,filtered,vacuum dried,and diluted by p H2.2 citrate buffer,amino acid composition was determined on amino acid analyzer(SYKAM S- 433D).The volatile components of bayberry's fresh and dried fruit were extracted by steam distillation at 150 ℃,and 400 m L fraction solution was received after 2 hours steam distillation. The fraction solution was ex-tracted by 5 mL petroleum ether(HPLC grade) twice,the volatile flavor components of extraction were de-termined by gas chromatography-mass spectrometry(GC-MS). The gas chromatography conditions wereas follows: Chromatographic separations on a TG-5MS column(30 m×0.25 mm×0.25 μm),carrier gasHelium at 1.0 m L·min- 1in the constant flow mode. The injector temperature was 250 ℃,transfer linetemperature was 280 ℃;injection volume was 0.5 μL. The oven temperature program was as follow: ini-tial 50 ℃ for 5 min,raised to 250 ℃ at 8 ℃·min-1and held for 30 min. The ion-trap manifold tempera-ture was 280 ℃,the ion energy for electron impact(EI) was set at 70 e V,scan range 50-500 amu. Identi-fication of the volatile compounds was achieved by comparing the GC retention time and mass spectraNIST08 standard library.【Results】The contents of total sugar,reducing sugar and sucrose in the driedfruit were concentrated Compared to that in fresh fruit,and the ratio of reducing sugar to total sugar indried fruit increased with the decrease of sucrose proportion. Based on the peak area and the concentra-tion of each organic acid,the organic acid standard curves were plotted. Regression equations and correla-tive indices were shown as Oxalic acid(y=5×106x+196 096,R2=0.998 5),Tartaric acid(y=106x+46 424,R2=0.994 7),Malic acid(y=481 015x+14 637,R2=0.998 2),Lactate(y=287 663x-19 368,R2=0.991 9),Citric acid(y=579 378x+6 853.5,R2=0.998 5) and Succinate(y=6×105x+1 669.0,R2=0.997 0). Concen-trations of organic acids were positively correlated with peak areas in their chromatograms of HPLC. Fiveorganic acids(including citric acid,malic acid,lactic acid,oxalic acid and tartaric acid) were detectedin dried fruit,while less of an organic acid in fresh fruit,due to very low levels of tartaric acid. The con-tents of citric acid was the highest,accounting for 56 percent of organic acids in both fruits. Non-volatileorganic acids were the main components providing the sour taste. Seven essential amino acids,includingthreonine,valerian leucine,methionine,isoleucine,leucine and phenylalanine,were discovered infresh fruit(1.2 mg·g-1) and dried fruit(6.8 mg·g-1),which accounted 29.4% and 27.2% of the total aminoacid content,respectively. And there were 8 kinds(2.89 mg·g- 1) of non-essential amino acids in freshfruit and 9 kinds(18.3 mg·g- 1) in dried fruit,respectively. Tyrosine wasn't detected in the fresh fruit.The other eight kinds include aspartic acid,histidine,serine,glutamic acid,glycine,alanine,cystineand praline in fresh and dried fruit. GC-MS results showed that 44 and 48 volatile components,includingterpenes,alcohols,ketones,esters and acids,were identified in fresh and dried fruit,respectively. Theterpenes accounted for 90% of the volatile components in flesh fruit,but only 48% in dried fruit. Alde-hydes were unique and critical in dried fruit.【Conclusion】The results indicated that the nutritional andaroma contents of total sugar,reducing sugar,amino acid and organic acid were higher in dried fruit thanin fresh fruit due to the concentrated effect. Fresh and dried fruit have significant differences in the vola-tile aroma components.