Effects Of Dehydration On Phenol Metabolism And Cell Membrane Degradation During Seedless Grapes Dried Processing

Grape is a worldwide fruit,it is also the fruit with the highest proportion of processing.Dehydrated drying after harvest is an important method of processing.Xinjiang is the main origin of green raisins in China."Seedless grapes" is the main species of green raisins.Green raisins produced from traditional dry room are likely to browning,it is well acknowledged as a key issues to the development of Xinjiang raisins.In this paper,seedless grapes was taken as the experimental material,through the study on physiological and biochemical changes,phenolic metabolism changes,and membrane degradation during the seedless grapes harvest processing,it was hoped to clarify the relationship between browning and phenol metabolism and membrane degradation of seedless grapes.This study examines the relationship between browning inhibition and enzymes from these two perspectives,the mechanism of browning inhibition was further revealed,which laid a foundation for further research on browning of seedless grapes.The main results were as follows:(1)The content of moisture and titratable acid of seedless grapes decreased in the two dehydration processes,and the content of soluble solids showed an upward trend.Through analysis,there was no significant difference in water content,titratable acid and soluble solids content among the three indexes in the two dehydration treatments.In the process of dehydration and drying of grapes,the browning degree of seedless grapes was significantly negatively correlated with the content of total phenols and total flavonoids in two ways of naturally dried and 40 centigrade hot air drying(P<0.05).(2)During the dehydration process,the activity of Phenylalanine ammonia-lyase(PAL)increased first and then decreased.The activity of 4-coumaryl-Co A ligase,4CL and Cinnamic acid-4-hydroxylase,C4 H showed a continuous upward trend.In the early stage of dehydration,the activity of PAL in naturally dried grapes was significantly higher than that in the hot air dried grapes.In the early stage of dehydration,the C4 H activity of hot air dried grapes was lower than that of naturally dried grapes.However,after the mass loss exceeds 30%,the C4 H activity of the hot-air dried grapes was significantly higher than that of the naturally dried grapes(P<0.05).The 4CL enzyme activity was no significant difference between the two treatments during the whole dehydration process.The key enzymes activities of C4 H and 4CLin phenylpropanoid metabolism were negatively correlated with the total phenols and total flavonoids in the dehydration process of seedless grapes.(3)In this experiment,after seedless grapes were dehydrated in two ways,compared with the naturally dry dehydration,the dehydration treatment by hot air drying at 40�C significantly inhibited the increase of phospholipase D activity(P<0.05),and the contents of its substrates PC and PI remained high.At the same time,the content of hydrolysate PA was lower and it was also lower than that of the naturally dried grapes.After dehydration treatment in two ways,compared with natural dehydration treatment,dehumidification by hot air drying at 40�C could inhibit the increase of LOX enzyme activity of seedless grapes to a certain extent,inhibit the increase in the relative electrical conductivity and malondialdehyde content of the membrane lipid peroxidation product,and reduce the degree of degradation of grape seedless membrane.