Study On Fresh-Keeping And Chilling Resistance Technology Of Sweet Potato

As a traditional food crop, Sweet potato is widely favored by consumers because of its abundant nutritional value. The improvement of edible quality is the fundamental guarantee of sweet potato industrial development. Good storage of sweet potato is the most important prerequisite to improve the quality of sweet potato. However, sweet potatoes are cold-sensitive foods. Chilling injury inhibits the development of sweet potato storage technology at low temperature. This paper explored the cryopreservation technique of sweet potato, cold shock treatment to inhibit the effect of chilling injury and physiological biochemical mechanisms, providing theoretical basis for development of sweet potato storage techonlogy. Contents and results are as follows:1.The selection of the optimal storage temperature of sweet potatoSweet potatoes were stored at (7±0.5)℃, (10±0.5)℃, (13±0.5)℃ and (16±0.5)℃ to research the influence of different storage temperatures on respiration rate, weight loss, soluble sugar, soluble protein, starch, cellulose and other indicators. The results showed that breathing can be effectively inhibited at 7℃ and 10℃. Material quality was better maintained, the consumption and degradation of soluble sugar, starch, ascorbic acid and other nutrients were reduced. However, long-term storage at 7℃ caused chilling injury, abnormal breathing and poor quality of sweet potato. There is no occurrence of chilling injury when it was stored above 10℃, but its respiratory intensity was strong, nutrients consumed fast, weightlessness rate was high and easy to cause the soft rot, losing the edible value.Therefore, within the experimental temperature range it can be considered 10℃ is the optimum storage temperature of sweet potato.2. Effect of cold shock treatment on chilling injury of sweet potatosweet potatoes were placed in 0℃ and 5℃ refrigerator for 3h,6h,9h,12h respectively, then stored at 7℃. Results showed that it can effectively reduce the chilling injury incidence and index of sweet potato, stimulate the accumulation of free proline, significantly inhibit the respiration intensity fluctuations and the increase of cell membrane permeability, effectively reduce the loss of soluble solids at 0℃ for 3h or 5℃for 9h. At the same time, it improved the sweet potato’s ability to adapt to low temperature through the osmotic regulation substances such as the soluble sugar, soluble protein and free proline.3. Effect of cold shock treatment on antioxidant ability of sweet potatoThe sweet potatoes which were treated with 0℃ for 3h,5℃ for 9h and the control group were used as materials to study the changes of the composition of vivo antioxidant activity and total antioxidant capacity. The results showed that the antioxidants of sweet potato were effectively maintained, the degradation of ascorbic acid and lost of total phenols and flavonoids was delayed of the cold shock group Meanwhile, the cold shock treatment effectively improved the total antioxidant activity in sweet potato. It played a positive role for maintain antioxidant capacity of sweet potato during the period of stored at low temperature.4. The physiological mechanism of inhibiting chilling injury by cold shock treatmentThe sweet potatoes which were treated with 0℃ for 3h,5℃ for 9h and the control group were used as materials to study the effect of cold shock treatment on active oxygen metabolism and endogenous hormone levels. The results showed that cold shock treatment effectively restrained the accumulation of O2- and H2O2 content of sweet potato during storage, improved the activity of SOD, CAT, POD, APX, boosting the ability of scavenging free radicals. Moreover, the increase of GA3 was inhibited and the content of ABA and IAA was improved, so the chilling injury of sweet potato was delayed. By using principal component analysis and path analysis, we found that the main indicator which cause chilling injury was the content of O2-The key factors affecting the cell membrane permeability were H2O2 and O2-.Active oxygen scavenging enzyme SOD, CAT and non-enzymatic antioxidants total phenols, ascorbic acid worked together reduing the chilling injury of sweet potato.