| Summary: | 碩士 === 國立嘉義大學 === 食品科學系研究所 === 104 === Several methods was employed on taro for surface-hardening in this study, in case to improve the texture to prolong collapsing time during cooking, elevate the quality and potential of future development. Taro sample were separated into three pre-treatment groups including fresh (F), half-riped (HeR) and fully-riped (FuR). Pre-treated samples were applied with different processing methods for surface hardening to obtain untreated group (U), alginate-applied group (AT), hot-air drying group (HAD), baked group (B) and fried group (Fr). The samples were stored at either -18ºC or -35ºC after treatment for further use. From the result, 6 treatment groups among the samples could extend collapsing time of taro in boiling water, with shortest time in group U within 13 min and longest time in group HAD up to 72 min, meanwhile Fr group could only extend collapsing time to 24 min the longest. 6-month storage experiment was conducted on 8 treatment groups with best result. Stability of group U was the worst during storage period and the alginate in AT group had loss of function to prevent collapsing due to boiling in longer time. Storage stability of group B was better but the cracks formation on the taro surface during baking led to poor appearance. However, large production was not applicable for group B due to individual processing required. HAD group had the best storage stability among the samples with collapsing time longer than 60 min. In order to increase the applicability and multiple product development of frozen taro, the group with best surface hardening effect was manufactured into sweet taro and taro crackers, and the products were stored and analyzed for storage quality. The breaking force of sweet taro increased gradually with increasing storage time in TPA analysis while the color parameter of HAD gave a better result than others during storage. The surface structure of U was significantly softened and gelatinized after further cooking while HAD could remain the partial structure completeness after surface hardening, and the texture could be maintained as well. Water activity and water content of sweet taro were relatively higher and couldn’t be decreased after hot-air drying. Group HAD and U were used as manufacturing material of taro cracker. Different taro content (15-45%) was mixed with waxy rice flour and indica rice flour in different ratio (1:0, 3:1, 1:1, 1:3, 0:1), molding and air-dried (50ºC, 5 h). The manufacturing process was terminated with water activity of 0.75, and the quality comparison of crackers from different formulation was conducted after microwave puffing. The water activity of rice crackers could be decreased to 0.60-0.70 while water content was corresponding to taro amount used in positive correlation that 45%>30%>15%. There was no significant differences between the breaking forces of rice crackers in TPA analysis. L* value decrease with increment of taro usage and the lowest in rice crackers made from HAD. The a* and b* value were increased with higher taro usage but in negative correlation with waxy rice flour usage. In microwave puffing condition determination, incomplete puffing occurred with heating time lower than 1 min while charred appearance was observed with longer heating time. Waxy rice flour had positive impact on puffing rate that shaping could be affected but taro cracker couldn’t be puffed with waxy rice flour percentage lower than 25% and water content had negative impact on puffing rate. The best condition for taro cracker puffing was fresh taro 30% with waxy rice flour: indica rice flour in the ratio of 3: 1, microwave power at 800 W for 1 min. The taro crackers were stored under ambient condition before each quality analysis within 5 months. The breaking force of taro cracker had decreasing trend during storage, the highest in HAD group, indicating higher friability but lower in puffing rate. Increasing trend was found in both groups, better result in HAD group with gradual changes and higher stability in color parameter. The surface structure of group U had obvious increased in surface area after puffing due to higher puffing rate. However, the puffing rate decreased during storage. The water activity of puffed taro cracker was between 0.60-0.70 that microorganism growth could be inhibited. Lastly, the bulk density of taro cracker from group HAD was higher than group U.
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