Judul: Karakterisasi sifat fisikokimia dan fungsional fraksi pati dan tepung umbi lima kultivar uwi (Dioscorea alata)
Abstrak: Yam (Dioscorea alata), as a bulbous plant, was rich in starch content. Yam starch pastes naturally had a character that was resistant to high temperatures, and this character was needed in food processing. A fairly high diversity, quitely high plant productivity and easily in cultivation of yam plant indicated the potential utilisation of yam tuber as raw material in food industry. Starch in food processing applications would result in the final product that was affected by refined starch physicochemical properties. As for food processing, information about the starch physicochemical characteristics was necessary, which was typical characteristic to the type (source) of starch. Physicochemical character was influenced by several factors such as the type (source) of starch, granule size, amylose content and starch crystallization. Starch with different on its granules sizes had different chemical composition that was contribute to the different pasting character and paste viscoelastisity. Pasting characters and paste viscoelastisity themselve were important functional characters of the starch in food processing applications as thickeners. In relation to that and for the development usage of yam tuber, this study was aimed to observe and to study the physicochemical characteristics and functional properties of starch granules and flour particle size fractionation from several yam cultivars, especially in the paste formation and paste viscoelastisity profile. The chemical composition of starch was specific for each yam cultivar which influenced the nature of the starch physical and functional properties. It was found that yam starch had unimoda asymmetrical distribution of its granule size with a higher portion on the large size, and the size ranged 7-100 μm. The morphology of yam starch granules was round disc-shaped, elliptical, oval and round with smooth wavy surfaces. The chemical composition of yam starch had lipid content ranged 16-30 % db, amylose ranged 23.44-26.99 % db and phosphorus ranged 268.15- 365.36 ppm db. Yam starch crystallinity structure had type-B pattern with low crystallinity which was ranged 20.6-30.4 %. Based on the viscoelastisity profile of its cold paste, yam starch had strong resistance to high friction up to =107 rad/s. of the sweep test frequency Fractionation of yam starch was achieved by dry sieving Retsch Siever with 400 and 500 meshes, and was resulted in unperfectly separated of the size fractions. The fractionation was provided a significantly different on average value among the fractions for all cultivars with the range of average of 20.89- 27.93 μm as smaller fraction, 22.41-28.82 μm as medium size fraction and 25.00- 34.80 μm as large size fraction. Based on the average value of the fraction, the larger the granule size contributed to the increase of amylose and phosphorus content and reduced starch crystallinity. The difference in the granule size fraction was not enough to produce any significant effect of size on gelatinization character. In the paste formation, the starches showed type-B profile and higher paste stability could be found in the bigger granule size. The viscoelastisity character showed that the value of storage modulus (G') was increase as the granule size increase which was lead to the stronger gel formation of the paste from small granule
Keyword: yam starch, size fractionation, pasta profile, gelatinization, viscoelastisity