The Interaction Between Persimmon Pectin And Persimmon Tannin And Its Effect On The Astringency Of Persimmon

The production of persimmon in China ranks the first in the world.Commonly,it was classified into non-astringent cultivars and astringent persimmon cultivars.Persimmon fruit has abundant nutrition and healthy benefits due to the high contents of tannin and pectin substance.However,condensed tannin could also lead to the strong astringency of persimmon fruit.In addition,pectin plays an important role in the quality and the sensory characteristics of fruits.Previous studies suggested that the interaction between pectin and soluble tannins might involve in the deastringency of persimmon.However,direct evidence is lacking and the underlying mechanism is not clear.Therefore,two non-astringent cultivars?‘Unishiwase'and‘Eshi 1'?,and one astringent cultivar?‘Gongchengshuishi'?were selected as the materials and the possible contribution of interaction of tannin and pectin on the deastringency of persimmon fruits was studied by determining the contents and distribution of both tannin and pectin during the maturity of persimmon fruits.Meanwhile,the electronic tongue,SDS-PAGE and fluorescence spectroscopy were used to explore the influence of persimmom tannin-persimmon pectin interactions on astringency of persimmon tannins.And the interaction mechanism between persimmon tannins and persimmon pectins were also included.The main results were as follows:1.The effect of pectin-tannin interaction on astringency of different varieties of persimmons during the maturationThe tannin content,pectin content and astringency of three kinds of persimmon fruits during maturing were determined.The results showed that the soluble tannin content of the two kinds of non-astringency persimmon decreased to less than 0.1%during the maturation,suggesting the deastringency was completed.But‘Eshi 1'finished its deastringency later than‘Unishiwase'.The soluble tannin content of‘Gongchengshuishi'was above 0.5%during the whole maturity processing,though the soluble tannin content decrease during persimmon maturing.The water-soluble pectin?WSP?content of two non-astringency persimmons decreased first and then increased,but the WSP content of astringency persimmon changed hardly,indicating that the interaction between tannin and pectin might occur during the maturation of persimmon.The results of sections staining further showed that tannin cells development patterns of the three persimmon varieties were different,and the contaction and combination of tannin and pectin was found in‘Unishiwase'and‘Eshi 1'during maturing,but not in‘Gongchengshuishi'.The accumulation of acetaldehyde and interaction between tannin and pectin might be involved in the deastingency of‘Gongchengshuishi'after ethanol treatment.The confocal Raman microspectroscopy was used to locate the tannin cells in‘Unishiwase',‘Eshi1'and‘Gongchengshuishi'after ethanol treatment.The characteristic groups of pectin were found in the Raman spectrum of tannin cells,which further proved the combination of pectin and tannin may be one of the factors reducing the astringency of persimmon.2.The effect of interaction between persimmon tannins and persimmon pectins on astringency of persimmon tanninsThe effects of pectins on tannins astringency were evaluated by an electronic tongue.The astringency of persimmon tannin solutions was significantly reduced by the addition of persimmon pectins,and the decreased intensity of astringency was directly proportional to pectin concentration.Based on the electronic tongue results,pectins decreased the astringency of tannins in the order of water-soluble pectin?WSP?>Na₂CO₃soluble-pectin?NSP?>chelator-soluble pectin?CSP?.SDS-PAGE results indicated that WSP and NSP could reduce the astringency of tannins by disturbing the precipitation of persimmon tannin-salivary protein,while CSP showed little effect.Additionally,fluorescence spectrum and DLS analyzes suggested that WSP reduced astringency of tannins by formation ternary complexes,while CSP and NSP reduced astringency of tannins not only by formation ternary complexes with tannin-mucin but also by competing with mucin for tannin binding.3.Analysis of interaction forces between different types of persimmon pectins and persimmon tanninsThe interaction modes of different soluble persimmon tannins with different types of persimmon pectins were investigated by FT-IR,ITC,DLS and fluorescent probe methods.The results of FT-IR showed that binding of persimmon tannins and persimmon pectins resulted in no new peaks,suggesting that the interaction of pectin and tannin was non-covalent interaction.The results of ITC showed that reactions between persimmon tannins and persimmon pectins were spontaneous and exothermic and the main interaction forces between them were hydrophobic interaction and hydrogen.Meanwhile,the results of Pyrene fluorescence probe method further proved that hydrophobic interaction played an important role in the interaction between persimmon tannins and persimmon pectins.The affinity between tannins and pectins decreased as follows:ST-WSP>ST-CSP>ST-NSP,NST-CSP>NST-WSP>NST.?-potential analyze showed that electrostatic interaction might exist in the interaction of persimmon tannins and persimmon pectins,but it was not dominating force.