Changes Of Color And Related Substances In Dried Sweet Potato During Processing And Storage

Sweet potato is widely planted in China.It is rich in nutrition and has certain health care function.However,sweet potato is prone to decay,budding and frostbite during storage and transportation,resulting in the decline of processing quality.Processing fresh sweet potato into dry sweet potato can prolong the storage time and improve the color of sweet potato,but improper processing and storage conditions often lead to browning and seriously affect the quality of products.At present,there is little research on the mechanism of color change during sweet potato processing and storage.In this paper,the color,Vc content,total phenol content,carotenoid content,5-hydroxymethylfurfural content,sugar component and its content change,carbonyl compound component and its content change of sweet potato in the process of steaming,drying and the storage of dried sweet potato finished products are determined.The correlation analysis is used to study the relationship between the change of each material content and the color change of sweet potato,and explore the material basis leading to the color change,It is helpful to speculate the reaction pathway of its color change and explore the mechanism of color change during drying and storage.At the same time,the effects of different drying temperatures(60 ℃ 7h,75 ℃ 3h+35 ℃ 4h),storage temperatures(-20,4,20,40 ℃)and color protection pre-treatment methods(sugar pre-treatment and sulfur pre-treatment)on the color change of sweet potato were compared,which has guiding significance for the production of sweet potato with good color and anti-browning.The main results of the study are as follows:(1)Changes of Vc,total phenols and carotenoids in dried sweet potato during processing and storage.During steaming,the contents of Vc,total phenol and carotenoid decreased significantly.After steaming for 30 minutes,the contents decreased by 45.80%,64.59% and 53.67% respectively;In the process of drying,the content of total phenol first increased and then decreased,and the content of carotenoids first decreased and then increased.Compared with steaming(30min),the loss rates of Vc,total phenols and carotenoids decreased in dry(7h).Under the two drying conditions,the content of total phenol and carotenoids changed slightly under the condition of drying at 60 ℃for 7h,but the loss of Vc was large at the end of the drying period.With the extension of storage time,the contents of Vc and carotenoid decreased,and the content of total phenol increased first and then decreased.The retention rate of three components in dried potato prepared under two drying conditions is higher when dried at 75 ℃ 3h +35 ℃ 4h.The higher the storage environment temperature is,the more unfavorable it is for the retention of the three components.The effect of freezing at-20 ℃ and cold storage at 4 ℃ is better,but the humidity should be controlled to prevent the dried sweet potato from mildew.(2)Changes of Maillard reaction related substances during dry processing and storage of sweet potato.In the process of steaming and drying,starch decomposes to produce sucrose,glucose and fructose,sugar accumulates,and the content of 5-hydroxymethylfurfural increases.During storage,the content of reducing sugar,especially fructose,decreased significantly,and the content of carbonyl compounds fluctuated significantly.The content of 5-HMF continued,and the higher the temperature,the greater the rise range.The rise rates of directly dried sweet potato under four storage temperatures were 5.35%,22.91%,58.03% and 71.52% respectively.The content of5-HMF in the dried sweet potato produced under the two drying conditions,which was dried at 75 ℃ for 3h + 35 ℃ for 4h,increased slightly during drying and storage,the content was low,and the color during storage was better.(3)The change of color value and its relationship with the content of related substances during dry processing and storage of sweet potato.During the steaming process,the brightness of sweet potato decreases,the color saturation increases,and the whole is orange.After steaming for 15 minutes,the color will not change significantly.During the drying process,a*,b* and C* increase and the color is more bright.The color quality decreased during storage,and the higher the storage temperature,the more prone the dry sweet potato to browning.Among them,under the storage temperature of 40 ℃,the sweet potato dried at 60 ℃ 7h,75 ℃ 3h + 35 ℃ 4h has browning visible to the naked eye at 1st month and 2nd month respectively.The results of correlation analysis showed that the degradation of total phenol,VC and carotenoid during steaming and drying resulted in the decline of color quality,brightness and red value;Fructose,glucose and sucrose were significantly positively correlated with color during drying;During storage,Vc,carotenoids,fructose,glucose and glyoxal were positively correlated with color changes,while 5-HMF was negatively correlated.(4)Effects of color protection treatment on the changes of color and related substances of sweet potato during dry storage.Sugar pre-treatment and sulfur pre-treatment can significantly improve the color quality of sweet potato during storage.Low temperature environment is conducive to the storage of dried sweet potato.The sugar pre-treatment dried sweet potato showed obvious browning after being stored at 20 ℃ and 40 ℃ for 6th month and 4th month respectively,and the sulfur pre-treatment dried sweet potato did not show visible browning during storage.Both sugar pre-treatment and sulfur pre-treatment can reduce the loss rate of total phenol,Vc and carotenoid,and reduce the accumulation of 5-HMF.Compared with sugar pre-treatment,sulfur pre-treatment has better effect.