Studies on the Technology of Longan (Dimocarpus longan Lour.) Fruit Storage and Vacuum Deastringency of ''Bull Heart'' Persimmon(Diospyros kaki L.)

• Main Authors: Fong-Jhen Chu, 朱峯震
• Other Authors: Ching-Chang Shiesh
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/76675603241725110009

碩士 === 國立中興大學 === 園藝學系所 === 97 === Longan summary: The objective of this experiment was to investigate longan postharvest handling technique and to find a suitable temperature to extend postharvest fruit life. Longan is a tropical fruit and thus prone to low temperature injury, decay and browning being the principal visual symptoms. It has a very short postharvest shelf life of 4 days at ambient temperature which limits consumption; therefore, requires immediate treatment after harvest. Fruits were stored 1、3、6、9、12、15 and 25℃. Result showed that the lower storage temperature allowed for longer fruit storage period. At temperatures of 1℃ and 3℃, the storage period was up to 25 days, but as storage at low temperatures continued, fruit showed progressive browning and fruit shelf life was shortened. For example, on the 20th day, when fruit was returned to ambient temperature, shelf life was only one day. Therefore, for storing longan up to two weeks, 6℃ should be used; storing longan beyond two weeks, 1℃, 3℃ temperature should be used. Before fruit were harvested, they grew larger and heavier, the fruit skin turned from green to yellowish brown, flesh mass increased, as did total soluble solid (TSS). On the other hand, TSS of over-ripened fruits decreased, flesh withered and lost flavor. Fruits harvested on 8/13 were not the most mature or of the highest quality, but sold well because of consumer demand during the middle year holiday. But fruits harvested on 9/5 had the best flavor for consumption. Fruits harvested between 8/23-9/5 had the highest TSS and had better tolerance of long distance transportation and longer term storage. Fruits were subjected to one of five treatments (sodium hypochlorite, hot water bath, SO2, chitosan, and wax) then stored at different temperatures. Only at 1℃ was the respiration rate found to be significantly lower than at 6℃. Both sodium hypochlorite treatment and hot water bath treatment were harmful to fruits. Fruits treated with sodium dioxide were excellent in quality, outer appearance and respiration rate. However, the flesh turned opaque white, gave a numbing sensation when eaten (possibly caused by a residual amount of SO2 in the fruit), and thereby 1ost market value. Fruits treated with chitosan or wax maintained the best quality over the other treatments. Further study may be done to improve postharvest handling techniques of longan fruits. persimmon summary: The objective of these experiments was to investigate whether vacuum packaging facilitates the deastringency of ‘Bull Heart’ persimmons. Among the different treatments, vacuum method showed the fastest deastringency rate, followed by carbon dioxide and alcohol. Deastringency by calcium carbonate suspension was the slowest caused by the longer time CaCO3 took to remove astringency. However, this group showed the highest fruit firmness and best peel color. In contrast, vacuum deastringency not only had the highest deastringency rate but also preserved the quality of persimmons (including fruit firmness and peel color) better than the groups treated with carbon dioxide or alcohol. As a result, the vacuum method is the ideal way to remove astringency. In the experiment investigating the effects of temperature on vacuum packaging, it was found that deastringency rate increased as temperature rose. As long as the temperature was above 25°C, the fruits could meet all market standards, with an astringency index under 2, after one day of cold temperature treatment. However, if the temperature was higher than 40°C, fruit firmness declined on the second day after treatment. Therefore, the most proper temperature for carrying out ‘Bull Heart‘ persimmon vacuum packaging is between 30 and 35°C. Following vacuum deastringency, the persimmons still wrapped in vacuum bags were stored under different temperatures. All the groups showed no difference in firmness and TSS during the first two weeks of storage, except the fruits stored under 12°C. However, when the storage time exceeded two weeks, the fruits possessed an acidic taste due to the accumulation of acid resulting from anaerobic respiration. Nevertheless, three days after the vacuum bags were removed and the fruits returned to room temperature, acidity gradually abated. It was also found that using PE bags instead of vacuum bags resulted in lowering fruit acidity.