Abstract:
Abstract: In order to extend the freshness period of post-harvest Cucurbita pepo and lessen the consumption of nutrient substance, this study aims to determine the cold preservation effects of forced-air pre-cooling at different temperatures on post-harvest Cucurbita pepo. In the experiments, the pre-cooling temperatures were set at ?3, 0, 3 and 6 ℃, while the target cold preservation temperature was 10 ℃. The sample was examined every 4 days to determine a variety of indices. The results indicate that the pre-cooling rate at 6 ℃ is the slowest and that at ?3 ℃ the fastest. At the end of cold preservation period (on the 16th day), the ascent percentages of malondialdehyde (MDA) at 0 and 3 °C pre-cooling treatment are 66.76% and 71.63% respectively, when compared to the content before the cold preservation period, which are significantly lower than that of the other 2 treatments; the descent levels of firmness in the 4 groups (-3, 0, 3 and 6 ℃) are 9.89%, 7.46%, 7.89% and 11.19% individually; catalase (CAT) activity of 4 groups on the 16th day is 16.25, 19.79, 17.58 and 16.63 U/(min?g), respectively; at the same time, the falling ranges of vitamin C content are 32.61%, 20.65%, 26.09% and 30.87% and the relative contents of aldehydes at the end of period are 69.94%, 76.33%, 71.47% and 70.97% respectively. When compared to ?3 and 6 ℃ pre-cooling groups, temperatures between 0 and 3 ℃ were seen to provide the optimal cold preservation effects on Cucurbita pepo, as the respiration and ethylene production rates are lower at these temperatures, which is helpful in decreasing the senescence rate and prolonging the shelf life of these vegetables, and this temperature range effectively delays the decline rate of firmness. Moreover, the accumulation of MDA and the extent of tissue damage are both inhibited at a pre-cooling temperature from 0 to 3 ℃. Additionally, the pre-cooling treatment at 0 and 3 ℃ is also shown to inhibit peroxidase (POD) enzyme activity and maintain a higher level of CAT activity, which assists in reducing reactive metabolism damage by removing reactive oxygen and free radicals. In contrast, pre-cooling temperatures of ?3 and 6 ℃ demonstrate higher respiration rates and ascorbate peroxidase (APX) enzyme activity rises rapidly in the second half of the cold preservation period, during which APX activity at 0 and 3 ℃ pre-cooling remains markedly more stable. And the chilling injury appears when the pre-cooling temperature is ?3 ℃, and there are lots of stains on the surface of Cucurbita pepo in ?3 ℃ treatment. In conclusion, this study finds that the most suitable pre-cooling temperature range for Cucurbita pepo is from 0 to 3 ℃ and therefore this research can provide technological and theoretical support for the development of cold-chain technology of Cucurbita pepo.