Characteristics of Yam Flours and It''''s Application in New Food Products

• Main Authors: Chin-Lin Hsu, 徐慶琳
• Other Authors: Chin-Yin Tseng
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/04996953672352667454

碩士 === 國立嘉義大學 === 食品科學系碩士班 === 91 === Abstract Five major researches were included in this study: (1) chemical compositions, physical properties, and antioxidant activities of yam flours as affected by different drying methods (Chapter 1) (2) studies on the physiochmeical properties and antioxidant activities of raw yam flours (Chapter 2) (3) effect of substitiution ratio on the manufacture of yam bread from cooked yam flour and wheat flour (Chapter 3) (4) effect of substitution ratio on the manufacture of yam bread from raw yam flour and wheat flour (Chapter 4) (5) characteristics of yam flours by differential scanning calorimetry (Chapter 5). From this study, the folowing conclusions can be made: (1)Yams (the tubers of the Dioscorea spp.) consumed and regarded as medicinal food in traditional Chinese herbal medicine are seasonal foods and easily deteriorate during storage. It is of great importance to prolong the storage of yams for supplying in the off-season and without losing the nutritional functionality. Three varieties of yams, Dioscorea alata (cultivars of Tai-Nung no.2 and Ta-Shan) and Dioscorea purpurea (cultivar of Ming-Chien), were made into flours by freeze drying, hot air drying, and drum drying in this resrarch. The chemical compositions and physical properties as well as antioxidant activities of yam flours were analyzed. While drying methods showed significant effects on the moisture content of yam flours, they had no marked effects on other components of yam flours. Color attributes and physical properties all were affected by drying methods with different extent. While freeze drying usually preserved more antioxidant activity of yam flours, yam flours made of different yam variety showed different antioxidant mechanism. (2)Three varieties of yams, Dioscorea alata (Tai-Nung no. 2 and Ta-Shan) and Dioscorea purpurea (Ming-Chien), were made into raw flours with the manufacture procedures including cleaning, blanching, peeling, cutting, freeze drying, and grinding. The chemical compositions, physical properties, and antioxidant activities of the yam flours were analyzed. The raw yam flours obtained from three varieties showed about the same approximate compositions. Contents of diosgenin and total phenolics of raw yam flours were between 136.2~140.7 ng/g and 0.97~1.23 mg/g, respectively. Physical properties (color, flour density, water solubility index, and water absorption index) were significantly different among different yam varieties. Antioxidant activities (radical scavenging activity, ferrous ion chelating activity, total antioxidant capacity, and reducing power) of the raw yam flours increased as the methanol extraction concentration increased. Among all the varieties of yams, Ming-Chien yam had the strongest antioxidant activities. (3)The tubers of Ming-Chien yam (Dioscorea purpurea) were made into cooked flours with the manufacture procedures including cleaning, blanching, peeling, cutting, steaming, freeze drying, and grinding. The cooked yam flour was used to substitute wheat flour in bread formulation. The qualities of breads made of bread formulations with yam flour substitution ratio 0, 5, 10, 15, 20, and 25% were analyzed. When the substitute ratio of cooked yam flours was at 20%, the loaf volume and loaf height of yam bread were 71.14 and 74.63% of the control (bread without yam flour), respectively. The loaf volume and loaf height decreased as the substitute ratio increased. As for the texture properties of crust and crumb, the hardness and springiness increased as the yam flours substitute ratio increased. The gumminess, cohesiveness, and chewiness decreased as the yam flours substitute ratio increased. Free radical scavenging and total antioxidant activities of yam bread increased as the yam substitute ratio and extraction concentration increased. At the 20% substitution ratio, the antioxidant activities of yam bread were significantly higher than the control (bread without yam flour). In sensory evaluation, the sensory scores of the yam bread decreased as the substitution ratio increased with the exception of the color attribute. Although loaf volume, loaf height, and texture properties of yam bread were unfavorably affected by the increasing ratio increase, the antioxidant activities increased as the substitute ratio increased. In conclusion, the upper limit of yam flour substitute ratio in bread formulation would be set at 20%. (4)The tubers of Ming-Chien yam (Dioscorea purpurea) were made into raw yam flours with the manufacture procedures including cleaning, blanching, peeling, cutting, freeze drying, and grinding. The raw yam flour was used to substitute wheat flour in bread formulation. The qualities of breads made of bread formulations with yam flour substitution ratio 0, 10, 20, 30, 35, and 40% were analyzed. Loaf volume and loaf height of yam bread decreased as the substitute ratio increases. When the substitute ratio was 40%, loaf volume and loaf height of yam bread were 70.96 and 74.62% of the control (bread without yam flour), respectively. Texture properties of bread were significantly influenced by the substitute ratio. Free radical scavenging activity and total antioxidant activity of yam bread increased as the substitute ratio and methanol extraction concentration increased. The scores of sensory evaluation decreased as the substitute ratio increased with the exception of color attribute. In conclusion, the upper limit of yam flour substitution ratio in bread formulation was set at 35%. (5)This part of the thesis reports the studies on the fresh yam and dried yam flours with differential scanning calorimetry (DSC). Since the cooked yam flours were completely gelatinized during the flour preparation process and no gelatinization temperature and gelatinization enthalpy could be detected, fresh yam tuber and raw yam flour were tested in the study. The tuber of Ming-Chien yam (Dioscorea purpurea) was made into raw yam flour as described in previous section. The effects of water, sugar, and sodium chloride on gelatinization temperature and gelatinizaiton enthalpy of raw yam flour were studied. the Studies on the water content (water ratio: 1:4 (80% water content), 1:2 (37%), 1:1 (50%), 2:1 (33%)(raw yam flour : water)), sugars (glucose, sucrose, and maltose (5, 10, 20, and 40%)), and NaCl (1, 3, 5%) of gelatinization temperature and gelatinizaiton enthalpy of raw yam flour. Among the tested water ratios of 80, 50, 37 and 33%, gelatinization onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc) of raw yam flour increased as the water content decreased. On the other hand, gelatinization enthalpy (△H) of raw yam flour decreased as the water content decreased. Gelatinization onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of raw yam flour increased as the sugar (glucose, sucrose and maltose) concentration increased from 5 to 40%. But, gelatinization enthalpy (△H) of raw yam flour did not change as the sugars concentration increased. Effect of NaCl on gelatinization temperature and enthalpy were insignificant. Gelatinization enthalpy of raw yam flour decreased as the NaCl concentration increased. The effects of water, sugar and NaCl contents on the thermo-properties yam flour could be served in the future application of yam flour in food processing.