| The physico-chemical properties change of jujube fruits from various cultivars, different growth stages or dehydrated by diverse drying methods were evaluated. At the same time, the effects of ripening process and dehydration methods on the pectic polysaccharide properties and its related enzyme activities of jujube fruits were assessed. The main results were shown as follows:(1) Jujube fruits were rich in nutrients and sucrose was the dominant sugar in the six different cultivars jujube fruits, followed by fructose and glucose, while malic acid and succinic aid were the principal organic acids in jujube fruits. Jujube fruits contained plenty of free amino acids and the primary free amino acids of the six various cultivars jujube fruits were proline and aspartic acid, in the mean while, proline accounted for more the68%of total free amino acids. The main phenolic compounds in the six cultivars jujube fruits were (+)-catechin, vanillic acid, coumaric acid,(-)-epicatechin, and rutin, while small amounts of caffeic acid and syringic aicd were also detected. Among the six various cultivars jujube fruits, the antioxidant capacities of ’jinsixiaozao’ and ’muzao’ were higher than those of the rest. All of six different jujube fruits had a high level of cAMP and cGMP, and ’hamidazao’ contained the highest level of cAMP among these jujube fruits, while ’jinsixiaozao’occupied the maximum level of cGMP among the above jujube fruits. The main volatiles of fresh maturated jujube fruits were consisted of micro-molecule aldehydes and organic acid with straight chains.(2) The contents of CWM, WSP, CSP, and SSP and the neutral monosaccharides of pectic polysaccharides (WSP, CSP, and SSP) were affected by the source of jujube fruits. The main neutral monosaccharides of WSP and SSP were the same, including arabinose, rhamnose, galactose, and glucose, which differed from those of CSP, which was consisted of arabinose, glucose, and fucose. The molecular weight distribution of pectins was not only influenced by the source of jujube fruit but also by the type of pectins. The activities of PG, PME or POD were dependant on the cultivars of jujube fruits and the higher PG activities the cultivars jujube fruits occupied, the wider molecular weight distribution of WSP in the low molecular weight segment showed.(3) During the ripening process of jujube fruits cv ’jinsixiaozao’, a series of physico-chemical changes had happened, including its appearance, pH value, moisture, colorness, chlorophyll, nutrients, bioactive compounds, antioxidant capacities and its related compounds, volatiles, enzyme activities. Sucrose, TSS, totol free amino acids, proline, aspartic acid, cAMP and cGMP were accumulated during the growth stages of jujube fruits. SPS and SS were the critical enzymes when accumulating sucrose during the ripening of jujube fruits. However, the green of jujube fruits disappeared due to the degradation of chlorophylls, at the same time, the antioxidant capacities, total phenolics, total flavonoids, L-ascorbic acid, a-tocopherol,β-carotene contents of jujube fruits decreased during the various growth stages. The volatiles of jujube fruits were synthesized at the later periods of ripening.(4) Softening phenomenon in jujube fruits cv ’jinsixiaozao’was observed during the process of ripening due to the degradation of cell wall pectic polysaccharide and its related degradation enzymes. The contents of CWM, WSP, SSP in jujube fruits showed a decrease tendency during the softening process, while the CSP content exhibited an increase trend in the earlier softening periods of jujube and showed a decrease tendency in the following softening periods. The backbone of RG-I in WSP was depolymerized gradually during the softening process while the backbones of RG-1in CSP or SSP were not depolymerized. In the mean while, all of the branches of RG-I in WSP, CSP or SSP were depolymerized at the later softening stages duo to the loss of arabinose and galactose. What’s more, higher ratio of arabinose was released during the growth stages of jujube fruits. The activity of PME jujube fruits decreased as the fruits became softened, while the PG activity increased, especially in the later softening periods, which played an important role in the depolymerization of pectin polysaccharides.(5) With the exception of FD, dehydration of jujube fruits led to a significant decrease of sorbitol and sucrose content (p<0.05). The retention rate of sucrose treated by MD or SD was higher than treated by AD, while the contents of glucose or fructose treated by MD or SD was lower than treated by AD. Drying of jujube fruits also generated browning of jujube pulp, introducing a different level of HMF content and MD caused the most significant increase of HMF content among the various drying treatments of jujube fruits. The higher of drying temperature was applied, the more serious browning index of jujube fruits generated. A fine retention rate of cAMP and cGMP was achieved by FD of jujube fruits, while a significant decrease of cAMP and cGMP occurred when employed AD, MD or SD. A higher retention rate of cAMP and cGMP was obtained at the same time by AD50treatment when compared to AD60, AD70, SD, and MD treatments. Too high or too low drying temperatures could result in a bad retention of cAMP and cGMP. Dehydration of jujube fruits by different drying methods posed different effects on the various antioxidant compounds but all dehydration of jujube fruits result in a significant decrease of antioxidant capacities in jujube fruits (p<0.05). The antioxidant capacities of jujube fruits, including the ability of scavenging DPPH free radical, ABTS free radical and FRAP showed a significant correlation with L-ascorbic acid (p<0.05) and the capacity of scavenging ABTS free radical or FRAP also exhibited a significant correlation with total phenolics (p<0.05). FD or MD treatment of jujube fruits could lead to a significant increase of (+)-catechin or (-)-epicatechin.(6) Dehydration of jujube fruits by various drying methods could led to a significant of CWM, WSP, SSP contents (p<0.05), while introduced a significant increase of CSP content. Too high or too low drying temperature could cause a more decrease of CWM, WSP, and SSP contents. Dehydration of jujube fruits also influenced the structure of pectic polysaccharides. Too high drying temperature or too low temperature could led to a more serious depolymerization of high molecular weight segment in WSP and AD50treatment of jujube fruit introduced a more centralized molecular weight distribution of WSP. However, Dehydration of jujube fruits could led to a increase of high molecular weight segment in SSP while introduced a decrease of low molecular weight segment in SSP. In the mean while, too high or low drying temperature could introduce a more serious depolymerizaion of low molecular weight segment in SSP. |
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