Effects Of Different Freezing And Thawing Methods Of Seabuckthorn Fruit Quality

Seabuckthorn is one of the "Medicinal and Edible" plants, which is belong to Hippophae rhamnoides L. Seabuckthorn fruit is rich in nutrients and active substances, such as Vc, organic acids, soluble sugar, sea buckthorn fruit oil and flavonoids. These nutrients are widely used in many fields like food, medicine, light industry, aerospace, agriculture and animal husbandry and so on. Seabuckthorn fruit is a kind of berry whose fruit is soft and juicy, however, the berry have short picking period, and the quality of the berry has declined rapidly. This not only seriously affect the processing and utilization of seabuckthorn fruit, but also influence the development of industrial production of seabuckthorn. Freezing in a low-temperature is a good way to maintain fruit quality in long-term which has been widely used in the fruit and vegetable industry. However, the quality of frozen fruit closely connected with freezing temperatures, storage time and thawing methods. Therefore, if we want to keep the original quality of seabuckthorn fruit as much as possible, the systematic studies of different freezing temperatures, storage time and thawing methods are needed.By taking Seabuckthorn‘Finland’as the research object, we compared 4 kinds of thawing ways: ultrasonic thawing, microwave thawing, air thawing, hydrostatic thawing on the impact of freezing seabuckthorn fruit quality, and the contents of drip loss, Vc, organic acids, soluble sugar, seabuckthorn fruit oil and flavonoids were measured. Our results showed that mcrowave thawing was the optimal thawing method. On the basis of the optimized conditions, 4 kinds of freezing temperatures: the-20℃,-40℃,-80℃and-196℃(liquid nitrogen freezing) have been compared with the effects of seabuckthorn fruit quality, and frozen in different periods seabuckthorn fruit quality indicators. Finally, we drawn up on optimal thawing way and the best temperature to freeze. The main results of this study were as follows:(1) In the optimization process of four thawing conditions, the final temperature of Seabuckthorn fruit at 0℃could maintain original quality in the maximal degree. During ultrasonic thawing and microwave thawing, the contents of Vc, organic acids, soluble sugar are rising with the thawing power, when it reaches a certain value, the contents of Vc, organic acids, soluble sugar would be reduce with the power and thawing temperature. Thus, higher thawing temperature and thawing power will cause more damages on seabuckthorn fruit nutrients.(2) The kind of microwave thawing was a good way to maintain the original quality of seabuckthorn fruit. The wastage rate of sea buckthorn fruit juice was the lowest during microwave thawing method, whose value was only 0.45%, while the drip loss rate was 1.28% during hydrostatic thawing. The saving rate of Vc was up to 95%, and the contents of soluble sugar and flavonoids of Seabuckthorn fruit were at a high level during microwave thawing. Compared with the microwave thawing, the damage to the nutritional of sea buckthorn fruit was slightly higher in ultrasonic thawing. In a word, the study showed that microwave thawing(microwave power was 420 W, defrost end temperature at 0℃) can better maintain the original quality of sea buckthorn fruit;(3) The seabuckthorn fruit were frozen in-20℃,-40℃,-80℃ and-196℃(liquid nitrogen freezing) respectively and stored at-20℃ environment. With the extension of frozen time, the wastage rate of seabuckthorn fruit juice increasing gradually, and has linear positive correlation with frozen storage time. And the contents of Vc, organic content, soluble sugar, fruit oil and flavonoids of seabuckthorn fruit continues to decrease, the frozen storage as long as 4 months, the fruit nutrients were generally well preserved.The contents of Vc and organic acid were well preserved in 6 months frozen strorage, but after 8 months, the contents of Vc and organic began to decline, and freezing at-20℃has the most serious decline. During the frozen storage, the contents of soluble sugar and seabuckthorn oil were relatively stable, however, after 10 months frozen strorage, it began to significantly decreased. Freezing at-196 ℃(liquid nitrogen freezing) has minimum damages to the nutritional of seabuckthorn fruit and it can maintain the quality of sea buckthorn fruit in a quite long time. Compared to the frozen in liquid nitrogen, freezing at-80 ℃ has the lower damage to the seabuckthorn fruit on the quality. Freezing at-40℃to the extent of the damage to the seabuckthorn fruit quality was slightly higher than frozen in-80℃, and freezing at-20℃have the largest damage to seabuckthorn fruit. Our results showed that-196℃freezing(frozen in liquid nitrogen for 15 min after pre-cooling at 4℃for 4 hours) was the best way to matain the quality of seabuckthorn fruit.Low-temperature frozen on seabuckthorn fruit can significantly inhibit oxidative respiration rate, and slow the rate of consumption of fruit material, which was conducive to keep the original quality seabuckthorn fruit, reaching the fruit storage in long period purposes.