| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 91 === Starches were isolated from five cultivars of local cassava in Taiwan (genotypes Gu, W, LY, Y and G), commercialized native starches (cassava and sweet potato starch) and modified cassava starches (National 7, National 780148 and Purity 1) were used as test sample in this study. The commercialized cassava starch was used as main material to mix with sweet potato starch or modified cassava starch for preparing starch balls. The physicochemical properties of native and modified starch from different varieties as well as their effects on quality of starch balls were examined.
The results indicated there were not significant difference for all kinds of cassava starches in particle size and shapes of starch granules. The particle diameter of cassava starches were in between at 10.3~12.5μm, and showed having the oval shape which combining with the round and truncated shapes together. The data of constituent analysis showed that the amylose contents of six cassava starches were range at 20.1 to 23.0%, whereas the cross-linked cassava starches, National 780148 and Purity 1 had the lowest amylose contents.
In the physicochemical properties, the starch isolated from genotype W had higher gelatinization onset temperature, enthalpy, lowest swelling power and solubility than other local cassava starches. It appears that the genotype W had higher stability and crystallinity of starch granule. The pasting profile of commercial cassava starch was showing the weaker ability to resistant the high temperature and mechanical shear than starches isolated from five cultivars of local cassava. The commercial sweet potato starch had better cooking quality than native cassava starches. The results of X-ray diffraction patterns showed five cultivars oflocal cassava starches are A-type. The genotype Gu and LY, the local cassava starches, both showed the poor stability in freeze-thaw cycles. Whereas the Purity 1 had the best freeze-thaw stability.
The results of quality analysis for formula of starch balls, the cooking loss of starch balls was observed higher in the formula where the modified cassava starch was added. It seems that the higher cooking loss was relative with solubilized amylose which decreasing where leaching-out from starch granules during cooking. Both National 7 and National 780148 showed the tendency of decreasing the rate of retrogradation of starch ball gels over 14 days of storage period at 4℃.
In the texture profile analysis, the gel consistency, the peak viscosity, the breakdown and the final viscosity of starch showed a significantly negative correlation with hardness, chewiness and gumminess for making starch balls gel.
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