Effects of harvest dates on physiological and biochemical properties of Fuping Jianshi (Diospyros kaki Thunb.) in storage process

Abstract:【Objective】Fuping Jianshi persimmon as the main local variety is one of the most popular fruits because of the particular flavor and rich nutrients, with abundant amount of glucose, fructose, vita-min, amino acid, polyphenols, iodine and minerals. The persimmon fruit can always be used as an excel-lent raw material for making dried persimmon favored by consumers as a national geographical indica-tion product. With the dramatical development and growth of the persimmon industry, it is urgent to solve the problems concerning harvesting and storing persimmons, so as to extend the processing period of persimmon fruits. So far, few researches have focused on the physiological and biochemical characteristics of Fuping Jianshi persimmon fruits and its appropriate storage conditions. Therefore, it is indispensable to figure out the optimum harvest date and determine the most suitable storage conditions of persimmon fruits to improve its preservative effects and provide a theoretical reference for the pro-duction and application.【Methods】Hoar-frost fall (October 24, 2019) was chosen as the sampling mid-point, and the first sampling time was October 14. Afterwards, samples were taken every 5 d for a total of 5 times. The sampling time was best controlled between 10:00 and 12:00 in the morning, and 600 per-simmon fruits with similar size, shape and color were selected at random, free from pests and diseases,and mechanical damage. Furthermore, every 100 persimmons were packed in a plastic fruit box, trans-ported back to the laboratory within 1 h and stored in a cold storage at (-2±0.5) ℃ with（85±5）% relative humidity. Each batch of persimmon fruits was divided into two groups (n=3 boxes per group), of which one group was used for weighing and checking the decay rate of persimmon fruits, and another group was used for index measurement. From the day of storage, 10 persimmon fruits would be random-ly selected from each sampling box from 14:00 to 15:00 every 10 d. The physiological and biochemical characteristics of these fruits were investigated, including the weight loss rate, hardness, moisture con-tent, soluble solids content, respiration intensity, tannin content, pectin content, ethanol content, acetal-dehyde content, enzymatic activities of pectinase, alcohol dehydrogenase and polyphenol oxidase.【Results】None of the rotten fruit was found during storage time under the test conditions, so the rotten rate was considered as zero. Besides, it was worth noting that the harvest date had a greater impact on the physiological and biochemical indexes of the persimmon fruits in storage process. Moreover, the respi-ration intensity of the persimmon fruits harvested in different periods was distinct, which decreased sig- nificantly and finally tended to be consistent with the extension of storage time. It was proved that both the harvest date and storage time of persimmon fruits had an impact on the respiratory intensity, and the former was the main factor. The weight loss rate and the contents of soluble pectin, polymerized tannin, ethanol and acetaldehyde of the persimmon fruits increased, while the hardness, soluble solids content,protopectin, soluble tannin content declined, and the enzyme activities of pectinase, alcohol dehydroge-nase and polyphenol oxidase decreased with the delay of harvest dates and the extension of storage time. The change of weight loss rate during storage process was related to the maturity. The later the persimmons were picked, the more the moisture was lost. The soluble tannin content of the persimmon fruits in the early storage period was significantly higher than that in the later period. The main reason was the production of acetaldehyde, resulting from the metabolism of the persimmon fruits during the storage, converting soluble tannins into insoluble tannins, and reducing the astringency of the persim-mon fruits. The earlier the persimmon fruits were harvested, with a longer after-ripening period, the higher hardness the persimmon fruits had, the lower contents of the soluble solids, polymerized tannins and acetaldehyde were. However, the hardness and the soluble solid content gradually decreased, and the contents of the polymerized tannin and acetaldehyde gradually increased with the extension of stor-age time. In addition, the persimmon fruits harvested before Hoar-frost fall, which owned smaller size,heavier astringency, lower soluble solid content and stronger respiratory intensity, might result in poor fruits quality during the after-ripening storage process. If the persimmon fruits were harvested much lat-er with shorter after-ripening period, the hardness of the persimmons decreased significantly and the weight loss rate was quite higher with the extension of storage time, and thus it was not conducive to long-term storage. The suitable harvest date is of great significance to prolong the storage period for per-simmon fruits and the accumulation of fruit flavor substances. To improve the storage quality of Fuping Jianshi persimmon fruits, the harvest date should be controlled at 5 to10 d after Hoar-frost fall.【Conclu-sion】The storage period of Fuping Jianshi persimmon fruits can reach 30 days for dried persimmon pro-cessing if they were harvested between 5 and 10 days after Hoar-frost fall and stored at (-2±0.5) ℃ with（85±5）% relative humidity, showing little fluctuations in various physiological and biochemical in-dexes.