The ideal parameters of FIG vacuum freeze drying process
Vacuum freeze-drying method was used to study the thickness of slices, the temperature of heating plate and the pressure of drying chamber during the freeze-drying process of FIG.
The results showed that the eutectic temperature of FIG was -28℃, the temperature of the eutectic point is -24 ℃. Accordingly, the prefreezing temperature of FIG was determined as -35℃, prefreezing time 2h.
The ideal parameters of FIG vacuum freeze drying process were as follows: material thickness 9.43 mm, heating plate temperature 55.34 ℃, drying chamber pressure 38.40 Pa. The predicted drying rate was 0.51, and the energy consumption was 19.13 kW ·h. According to the actual situation, the thickness of the material is lOmm, the temperature of the heating plate is 55℃, and the pressure of the drying chamber is 40Pa. The actual drying rate is (0.52 _ t: 0.01)h. 1, and the energy consumption of freeze drying is (19.25 ~ 0.14)kw·h.
Freeze-dried figs showed good advantages in physicochemical indexes, nutrient composition and sensory indexes. The Vc retention rate was 95.09%, the total sugar retention rate was 96.89%, the water content was 4.05%, and the water activity value was 0.612, which effectively inhibited the activities of microorganisms and related enzymes, and could achieve safe storage. The rehydration ratio was 6.16, and the rehydration performance was good. The retention rate of all kinds of amino acids was more than 98%, and the essential amino acids accounted for 32.09% of the total amino acids. The retention rate of all kinds of fatty acids was above 90%, and the content of unsaturated fatty acids accounted for 82.22% of the total fatty acids. The highest retention rate of Se was 96.76%, the lowest retention rate of Cu was 90.54%, and the retention rates of Fe and Zn were 92.37% and 91.28%, respectively.
After freeze-drying, the surface brightness of figs increased and the red degree deepened after freeze-drying. The difference of AE* before and after freeze-drying was 5.51, that is, the color change could be recognized by the naked eye. The elasticity, adhesiveness and chewability of the texture parameters are small, and the brittleness is moderate, which indicates that the freeze-dried material is easy to chew, has good taste and is not hard enough. Therefore, vacuum packaging should be used to prevent the extrusion and crushing during transportation.