| In this paper, firstly, the qualities of six kinds of Cantonese sweet-paste-filling bunsduring pre-cooling quick-frozen and after reheatedwere compared to get the rules of quality change and elect the typical lotus-seed-paste bun. Then, study on the effects of different wet gluten content and specificationson the quality(including cooling curves, water content of each layer, texture properties, color, specific volume and sensory qualities) of Cantonese lotus seed paste buns to determine the suitable wet gluten content and specifications. And systematic studyand optimization on the pre-cooling and frozen conditions, storage, temperature fluctuations and reheatingtechnologies of bun to provide technical guidance and theoretical reference for large-scale industrial production of Cantonese lotus-seed-paste buns.The research results were as follows:(1) The study investigated the influence of different sweet-paste-filling, wet gluten content of flour(16%~38%) and size specifications(30~80g) on the qualities of Cantonese sweet-paste-filling buns, the results showed that the R2 of regression equations in cooling curves of crumbs and stuffing in buns were greater than 0.909 during pre-cooling and quick-freezing, indicating that the temperatures of different buns were significantly correlated with time. The difference of temperature drop rates in different sweet-paste-filling buns were little; the slower wet gluten content and the bigger size, the slower temperature drop rate of stuffing in bun. In addition, the water content of the crust, crumb and stuffing in buns decreased significantly(p<0.05) before and after pre-cooling and quick-freezing, which the crusts and stuffing showed the maximum and minimum reductions of water contents respectively. And the greater water contents of different layers in different stuffing buns, the greater reduction amount; the reductions of water contents in buns’ stuffing of wet gluten content in 30% and 38% were significantly lower than others; the reductions of water contents in buns’ stuffing of 80 g was lower. At the same time the hardness, elasticity, viscosity, resilience and chewiness of different buns had significant difference(p<0.05). With the increasing of stuffing water content in different sweet-paste-filling buns, the hardness, chewiness and viscosity declined, while resilience and elasticity increased; the greater wet gluten content and size specifications, the greater value of each TPA of buns. With the increase of wet gluten content, the specific volume of buns dropped after the first increased, the specific volume of buns in wet gluten content of 30% and 38% decreased significantly(p <0.05); L* values of buns decreased, but a* and b* values increased; the sensory total scores of buns showed a downward after the first rise trend, and the sensory qualities of buns in 22%, 23% and 25% were better than 30%, 38%, 16% and 18%. So wet gluten content of flour between 22% and 25% was more suitable to make the Cantonese lotus-seed-paste bun, and the size specification was about 50 g to have a better quality.(2) The research was on the effect of different pre-cooling time(0~60min), pre-cooling temperature(-5~25℃) and freezing temperature(-30~-18℃) on the qualities of Cantonese lotus-seed-paste buns, the results showed that with the increasing of pre-cooling time and the decreasing of pre-cooling and freezing temperature, the core temperatures of buns were reduced gradually, the cooling rates of each layer were accelerated gradually. And the center temperatures of buns did not reach-5℃ below after frozen in pre-cooling 0min and freezing-18℃ process. In addition, the water content of the crust, crumb and stuffing in buns decreased significantly(p<0.05) before and after pre-cooling and quick-freezing, the water content reductions of the crust, crumb and stuffing in buns were increasing with the increasing of pre-cooling time and the decreasing of pre-cooling temperature, but the water content reductions decreased after quick-frozen; the lower of freezing temperature, the more water content reduction amount of the crust in bun, the less water content reduction amount of the crumb and stuffing. Meanwhile the hardness, elasticity, viscosity, resilience, chewiness and sensory quality were rising with the increasing of pre-cooling time and the decreasing of pre-cooling and freezing temperature. Thus, in order to achieve better quality, the Cantonese lotus-seed-paste bun should be selected the pre-cooling time between 40 min and 60 min, pre-cooling temperature between 0℃and-5℃, freezing temperatures below-30℃.(3) The study investigated the quality variation of Cantonese lotus-seed-paste buns during different storage temperature, including-18℃, 0℃and10℃, and temperature fluctuations, the results showed that the total bacterial count showed an increasing trend with the storage time and temperature fluctuation number. And 10℃, 0℃and-18℃ stored 8d, 14 d and 60 d respectively, the total bacterial count respectively reached to 4.60, 4.08 and 2.26 magnitude; The total bacterial count was rising exponentially with the temperature fluctuations, and the sensory of buns had been unacceptable after temperature fluctuations five times. In addition, after frozen and refrigerated respectively stored 7d and 2d, the water content of the crust, crumb and stuffing and specific volume of buns decreased significantly(p<0.05), and then gradually slow. And the higher the storage temperature, the greater reduction in water content of the crust, crumb and stuffing and specific volume of buns. At the same time the each layer water content of buns decreased significantly(p<0.05) with the number of temperature fluctuations, and after temperature fluctuations five times, the water content reductions of the crust, crumb and stuffing in buns were 5.83%, 3.46% and 0.82%. In addition, elasticity, viscosity and resilience of buns were decreasing with the storage time and temperature fluctuation number, while the hardness and chewiness of buns were an increasing trend during frozen storage, and the first increased and then decreased with the refrigerated storage time and temperature fluctuation number increasing. And the higher of storage temperature, the more obvious changed in the value of each TPA. At the same time, with the increasing of storage time, the values of L* and a* of buns were decreasing, the b* values were rising; while the L*value of buns was decreasing and a* and b* values were rising with temperature fluctuation number. The sensory qualities of buns were decreasing with storage time, storage temperature and temperature fluctuations number, and the lower of storage temperature, the slower the decrease of sensory scores.(4) The research was on the effects of three ways to re-heat, including steam, microwave and dry hot air reheating, on the qualities of Cantonese lotus-seed-paste buns, Results showed that the thermal curves of buns’ each layer were in line with logistic model. And the difference of heat transfer performance k value in bun’s each layer by microwave reheating was not large, but the steam and dry hot air reheating had larger difference; the heating rates of buns’ each layer were the fastest by microwave reheating, steam reheating followed, the dry hot air reheating was the slowest. Compared with the water content of the crust, crumb and stuffing of flesh buns, they decreased after reheating, but the water content of each layer was substantially close to fresh by steam reheating; the water content reductions of the crust and crumb in buns were largest by dry hot air reheating, but the water content of stuffing was higher than the microwave reheating. Meanwhile the sizes of hardness and chewiness of buns were: dry hot airreheating> microwave reheating>steam reheating; the sizes of elasticity, viscosity and resilience were: steam reheating > microwave reheating>dry hot air reheating. In addition, the L* and a* values of buns were the minimum after dry hot air reheating, but the b* value was the maximum;The values by steam reheating were exactly the opposite. And the sensory quality of bun after steam reheating was the best, while the quality by microwave reheating was the worst. |
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