| Longan(Dimocarpus longan Lour.) is one of tropical fruit in south part of China with high nutritional, special flavor. Becauce of its easy browning after postharvest, the coinciding of production and the difficult of fresh, the dried longan dominated the market in addition to fresh, the longan pulp was good at processing as rich flavor and nutrient,But kowning the changes of the physical and chemical properties,flavor and nutrition is the key technical problem to develop the processing. Now, the previous researches focus on the optimization in longan drying practice, little research has been available on the changes of its quality and biological activity during the longan drying. In this paper, the moisture ratio, hardness, adhesion and browning during drying process in two ways were analysed to determine the rule of physical and chemical properties during drying process; Then, to evaluate the phenolic content,composition and antioxidant activity of the phenolics present in longan pulp during drying process in two ways, and the changes of composition and antioxidant activities of phenolics during drying of longan fruit were investigated. Meanwhile. transformation of the volatile substance and change of the mian volatile substance in longan pulp during drying process in two ways were analysed to determine the formation of the volatile of dried longan. The major results are as follows:1. Changes of the physical and chemical properties during longan drying process:The moisture ratio, hardness, adhesion and browning during first drying, softening, second drying in two ways, which were the whole fruit drying and the longan pulp drying,were analysed. The results show:during the first drying about whole fruit, the moisture ratio significantly decreased as linearvariation(P<0.05), and the decreasing ratio was 79.28%, the hardness, adhesion and browning significantly increased (P<0.05),and the increasing ratio were 85.27%,3622.22%,197.73%. During the first drying about longan pulp, the moisture ratio significantly decreased as indexmovement (P<0.05), and the decreasing ratio was 96.22%, the hardness, adhesion and browning significantly increased (P<0.05),and the increasing ratioes were 169.44%,11077.77%,116.13%. During the softening about whole fruit, the moisture ratio, hardness, adhesion and browning significantly decreased (P<0.05) and the decreasing ratioes were 63.46%,12.52%,18.81%,24.42%. During the softening about longan pulp, the moisture ratio significantly increased (P<0.05), and the increasing ratio was 15.79%, the hardness, adhesion significantly decreased (P<0.05), and the decreasing ratioes were 33.89%,62.13%,the browning was no significant difference (P>0.05). During the second drying about whole fruit, the moisture ratio significantly decreased (P<0.05), and the decreasing ratio was 47.37%,the hardness was no significant difference (P>0.05),the adhesion and browning significantly increased (P<0.05), and the increasing ratioes were 84.93%, 51.52%. During the second drying about longan pulp, the moisture ratio significantly decreased (P<0.05), and the decreasing ratio was27.27%, the hardness was no significant difference (P>0.05),the adhesion and browning significantly increased (P<0.05), and the increasing ratioes were64.04%,60.00%.2. Effect of drying on phenolic profiles and antionxidant activity during longan drying:the phenolic content, composition, existence form and antioxidant activity of the phenolics present in longan pulp during drying process in two ways were analysed. The results show:during the drying about the whole fruit, the content of the free phenolics and its FRAP and DPPH antioxidant activities significantly decreased after drying process (P<0.05), while the content of the bound phenolics and its FRAP antioxidant activity significantly increased (P<0.05). Nevertheless, no significant difference were observed for the DPPH antioxidant activity of the bound phenolics (P>0.05). Meanwhile, the contents of monomer phenolics of epicatechin and tetramethyl catechol as the major composition of free phenolics decreased. However, the contents of gallic acid, vanillic acid, coumarate and quercetin increased).Compared with the bound phenolics, the contents of syringic acid, tetramethyl catechol, vanillic acid and epicatechin increased.During the drying about the longan pulp, the content of the free phenolics and DPPH antioxidant activities were no significant difference (P>0.05), its FRAP antioxidant activities significantly decreased (P<0.05), while the content of the bound phenolics was no significant difference (P>0.05), its FRAP and DPPH antioxidant activities significantly decreased (P<0.05). Meanwhile, the contents of monomer phenolics of gallic acid, caffeic acid, epicatechin,tetramethyl catechol as the major composition of free phenolics decreased. However, the contents of vanillic acid and ferulic acid increased. Compared with the bound phenolics, the contents of catechin and epicatechin decreased, the contents of vanillic acid, tetramethyl catechol increased.3. Changes of the volatile during longan drying process:the content and composition of the volatile in longan pulp during drying process in two ways were analysed, and the transformation of the volatile substance and change of the mian volatile substance in longan pulp in longan pulp during drying process were determined. The results show:a total of 24 compounds of the volatile in longan pulp before drying were detected, including alcohols, aldehydes and ketones, easters, olefins,and the olefins were the main volatile material. During the longan drying, there is the biggest changes in first drying. During the first drying in two ways, the content of alcohols increased, the content of aldehydes and ketones was no significant difference,the contents of easters and olefins decreased. During the softening about the whole fruit, the contents of alcohols, aldehydes and ketones, olefins were no significant difference, the content of easters increased, During the softening about longan pulp, the contents of alcohols, aldehydes and ketones were no significant difference, the content of easters increased, the content of olefins decreased,.During the second drying about the whole fruit, the contents of alcohols, aldehydes and ketones, olefins decreased, the content of easters increased. During the second drying about longan pulp, the contents of alcohols, easters decreased, the content of aldehydes and ketones was no significant difference, the content of olefins increased. In addition,the content of ethanol increased (P<0.05), the content of Z-ocimene significantly increased (P<0.05),as the main volatile substance in longan pulp during drying process in two ways. |
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