| Lemon(Citrus limon L.Burm.f.)is one of the important cultivated Citrus species in tropical and subtropical areas.External color of citrus fruits is a key factor that affects consumer acceptability.Lemon fruits with typically "lemon-yellow" color are more appealing to consumers and have higher commercial value.The development of fruit peel and pulp are two independent processes.Under natural conditions,the chlorophylls in the lemon peel begin to degrade and carotenoids accumulate only when the temperature reach a sufficiently low level,and then fruit peel turned gradually from green to yellow.However,commercially harvesting of lemon begins when the percentage of juice is higher than 30%when the external rind color is still green.Thus,preharvest or postharvest treatment is needed to improve fruit color in fresh market to meet commercial acceptance.Preharvest fruit bagging is a traditional and effective method to improve fruit color and has been widely used in fruit crops.But bagging treatment may inhibit the accumulation of vitamin C and synthesis of some sugars and organic acids.In recent years,some studies have explored the use of phytochemicals,such as ethylene or abscisic acid,to improve fruit external color.Postharvest ethylene or ethephon degreening is widely used to promote peel degreening,and studies have shown that postharvest ethylene or ethephon degreening would have no harmful effects on early-maturing citrus fruits quality.But the effects of ethylene or ethephon degreening on lemon fruits color and internal quality have not been systematically reported.In this study,'Eureka' lemon fruits were selected as the materials,and the green-peeled fruits were treated with ethephon solution(1000 mg/L),then stored under the condition of 20?,RH85%.The variations of fruits color,flavor and antioxidant capacity were investigated during the degreening process,and the qualities of ethephon-degreened fruits were compared to those of yellowish bagged fruits.Besides,the correlations between fruit color,flavor and antioxidant capacity were studied,and the effects of ethephon degreening on fruit quality was evaluated by PC A model.This study aimed to provide possibly new mothed for the degreening of lemon fruits and useful information for improving industrial efficiency.The main results are as follows:1.Effects on fruit color:CCI and C*value increased continuously,while the h°and chlorophyll content decreased after treatment with ethephon.At day 9,the values of color index and content of chlorophyll were closed to those of bagged fruits,which suggested that ethephon treatment could promote lemon fruit degreening in 9 days(about 1 week).2.Effects on fruit flavor:As compared to the untreated fresh fruits,titratable acidity(TA)was increased,while soluble solids content(SSC),SSC/TA ratio and vitamin C(VC)was decreased slightly at day 9.And TA value of degreened fruit was lower than that of bagged fruits,while SSC,SSC/TA ratio and VC content were higher than those of bagged fruits.During the degreening process,in fruit peel,citric acid showed an obviously decrease trend,and the total content of organic acid decreased after ethephon treatment.Sucrose was decreased during the degreening process both in fruit peel and pulp,while the contents of fructose and glucose were increased.The total sugar content was also increased after treatment with ethephon.The bitterness,sweetness and umami taste amino acids were increased during the degreening process,and the total amino acid contents were increased by 77.59%and 46.50%in fruit peel and pulp after 9 days,respectively.After treatment of ethephon,the total content of volatile compounds was increased by about 1 time in fruit peel.Although variations of selected components were observed in fruit pulp,the total content of volatile compounds showed a tiny change after ethephon treatment.Overall,as compared to the flavor quality of bagged fruits,ethephon degreening would not have deleterious effects on lemon flavor quality.3.Effects on fruit antioxidant capacity:After ethephon degreenning treatment,the total phenolics and total flavonoids content were both increased in fruit peel,but kept relatively steady in fruit pulp.In degreened fruits,ABTS,DPPH and FRAP values of peel and/or pulp reached the highest value at day 9 during storage,all of which were significantly higher than those of bagged fruit(p<0.05).The results showed that ethephon degreening treatment was more beneficial to enhance the antioxidant activity of lemon fruit than fruit bagging.4.The results of correlation analysis showed that there was no significant correlation between the color index and most flavor components and antioxidant capacity.There was a negative correlation between glucose and malic acid,citric acid,Ile and Arg,while a positive correlation was found between glucose and other flavor components and antioxidant capacity.Malic acid and citric acid were positively correlated with Ile and Arg,but negatively correlated with other flavor components and antioxidant capacity.Taste-active amino acids(except Ile and Arg)were positively correlated with volatile compounds and antioxidant capacity.Total phenolics and total flavonoids were significantly positively correlated with ABTS,DPPH and FRAP(p<0.01).The results of PCA analysis based on the fruit internal quality of the three different treated fruits showed that as compared to the beginning,the quality of fruit pulp was closed to each other,while the fruit peel showed obviously differences.Besides,the quality of degreened fruit peel was closer to bagged fruit peel as compared to the control.These data suggested that lemon fruit peel was more affected by the ethephon degreening treatment than fruit pulp. |
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