Study On The Relation Between Free Water Content And Quality Of Carrot Under Different Hot Air Drying Temperature

Carrots are rich in β- carotene and Vc, loved by the people. But its a seasonal, not long-term storage. Dehydrated vegetables, dehydrated vegetables is processed into a wet basis moisture content of 8%, and its long-term safe storage and to keep the flavor and nutrients of fresh vegetables and dried products. For dehydrated products, the degree of dehydration determine its shelf life. Free water and bound water content reflects how much water state. The sensory quality and nutritional quality are affected by changes in free water content, so the determination of carrot drying process is particularly important free water content, high-cost nuclear magnetic resonance spectroscopy, can be widely applied. Therefore, this study of new methods(DSC) free water content determination method and research carrots at 65 ℃, 75 ℃, the relationship between freedom and quality of water 85 ℃ and 95 ℃ drying process, is intended to provide some help for the production. The main conclusions are as follows:(1)Four drying temperature analysis shows that the end product, 1) β- carotene content in comparison: 95 ℃> 85 ℃> 75 ℃> 65 ℃. 2) Compare rehydration ratio: 65 ℃> 75 ℃> 95 ℃> 85 ℃. 3) microscopic structure comparison: comparing the amino acid content of 75 ℃> 65 ℃> 85 ℃> 95. 4): 65 ℃> 75 ℃> 85 ℃> 95 ℃. Electronic Nose Analysis : The flavor of fresh and dried products are signif icantly different, the drying temperature between 65 ℃ and 75 ℃ difference is extremely small, difficult to distinguish. Distinguish between the other two both have a high degree temperatures, through electronic nose analysis can achieve better distinction.(2)Carrots appearance quality hot air drying process(L, a, b and browning) and nutritional quality(β- carotene) are affected by changes in free water content, can be seen during drying vegetables measured changes have free water content significance.(3)DSC method and Tg method can measure changes in the free water content of the material, by analyzing the two measurement methods operability principles and methods known, DSC method is better than Tg method.(4)DSC measurement results with the NMR method has a high correlation, the correlation coefficient was 0.941, regression analys is shows that, DSC method and NMR method for the conversion of the equation y =-0.001x3 + 0.126x2-2.51 x + 0.923(x for DSC French test results, the equation for the wet basis moisture content greater than 58%), R2 equation 0.917, fit better.(5)65 ℃, 75 ℃, 85 ℃ and 95 ℃ four drying temperature change was free water containing high concentrations are negatively correlated with browning value, β- carotene and high residual rate showing a positive correlation, the conclusion provide a theoretical basis for optimizing drying of carrots.