Study On The Quality Of Cantonese-style Egg Custard Bun During Freeze-thaw Cycles And Its Steamed-freezing Control

Cantonese-style egg custard bun with high moisture content stuffing was used as raw materials, whch was a kind of traditional Chinese quick-frozen buns may occurring freeze-thaw cycles during cold chain transport and saleing process. The sensory quality evaluation system of egg custard bun was established. The change of quality of egg custard bun during freeze- thaw cycles was studied. In order to reduce the quality degradation of egg custard bun which was caused by the freeze-thaw cycles, the controlling method based on the steamed and freezing process condition was put forward.The sensory quality evaluation system including nine indexes of egg custard bun was established based on the fuzzy mathematical theory. The result showed the priority of the nine indicators and the weight distribution.Meanwhile, five kinds of commercially available egg custard bun were assesed by instrument analysis and sensory evaluation.The qualities including moisture migration, colour, specific volume, textural properties, sensory evaluation and the pore structure of the skin of three kinds of different moisture content of stuffings of egg custard bun during freeze-thaw cycles were studied. The results demonstrated that the rate of temperature decreasing during the freezing and rising during thawing, crust in buns was the fastest, while the stuffing was the slowest. With the increase of water content of stuffing, the undercooling poin, the initial freezing temperature and freezing rate rose but the thawing rate declined. After the same times freeze-thaw cycles, the hardness, viscosity and chewiness of 60 egg custard bun was the greatest, the spring and resilience were the smallest. After the first cycle, the spring and resilience of three kinds of buns declined significantly. The moisture content of skin, whiteness index and specific volume showed a downward trend after twice cycles. The hardness and viscosity had no significant change after four times cycles. The CD value of the egg custard buns after four times consecutive freeze-thaw cycles showed a downward trend but AF value increased. The frost crack rate increased with the increasing of freeze-thaw cycles. After 4 cycles, frost crack rate of 40 and 50 egg custard bun increased to 20% and 37% respectively,whle that of 60 egg custard bun was more than 50%. The sensory score declined during freeze-thaw cycles, the sensory score of 50 egg custard bun was the highest after 4 cycles,and 60 egg custard bun was unacceptable.Using the egg custard bun in normal condition(intermittent steam for 6 minutes and freeze under-35℃) as reference, combined effect of steamed(0 minutes, 2 minutes and 4 minutes) and freezing(-18℃,-35℃) process on the quality of egg custard bun during the freeze-thaw cycles was studied. The results showed that when comparing to the control group, the reducing moisture content of each layer of experimental group had significant changes and were less than those.The each layer moisture content of egg custard buns manufactured in the different steaming time had significant changes. In terms of the egg custard buns manufactured in the same steaming time, the reducing moisture content of each layer of egg custard buns manufactured in-18℃ were less than those of-35℃. The drop rate of whiteness values of experimental group was higher than that of control group. The deterioration of textural characteristics of egg custard buns steamed for 4 mintues and frozen in-35℃ was least serious. The CD and AF value of egg custard buns steamed for 0 mintue and 2 minutes had no significant when comparing to the control group, but those steamed for 4 mintues had significant difference. The sensory evaluation scores of egg custard buns steamed for 4 mintues was higher than that of the control group,while those of egg custard buns steamed for 0 mintue and 2 minutes were both less than the control group. The frost crack rates of experimental group were lower than that of the control group. After 4 times freeze-thaw cycles, the frost crack rate of the control group reached to 36%, while that of egg custard buns steamed for 0minutes,2 minutes and 4 mintues were less than 5%, 25% and 35% respectively. Therefore, appropriatly controlling the degree of steaming of egg custard buns can enhance the ability to fight the bad physical change in certain extent, which will be helpful to mantian the quality of egg custard buns.