Abstract
The differences of the nutritive values among the varieties of sweet potato were examined with the digestion trial with pigs and by the in-vitro method using the intestinal fluid of pigs in Experiment 1, and the influences of the processing methods of sweet potato, potato and cassava on the nutritive values were studied with the in-vitro method in Experiment 2.
Four sweet potato varieties, Kyukei 20 and Kyukei 40 bred for use as food and Kyushu 82 and Kogane-sengan bred for use as material for starch, were used for digestion trials after drying in oven. Eight piglets weighing approx. 40kg were used for the in-vivo digestion trial. Once a day, they were given 1200g of either a basal feed or an experimental diet which was prepared by mixing the ovendried sweet potato from each variety with the basal diet in a 1:1 weight ratio. The digestibilities of crude protein (CP) and energy were determined by the chromic oxide method. Digestible energy (DE, kcal/g in dry matter) determined with the in-vitro method for Kyukei 20, Kyukei 40, Kyushu 82 and Kogane-sengan was 3.22, 3.23, 3.63 and 3.49, respectively, the latter two being significantly higher than the former two (P<0.05) A similar relationships was found in DE determined with pigs, but it was not significant (P>0.05); DE with pigs was 3.67, 3.70, 3.87 and 3.82, respectively. The DE of the varieties of sweet potato for starch tended to be higher than that for food use. A close correlation (r=0.99) found in DE between the in-vitro method and the in-vivo method indicates that the in-vitro method gives a good estimate of DE in pigs. Digestible crude protein (% in dry matter) determined with pigs was -0.1, -0.4, 2.3 and 1.7, respectively.
Sweet potato (Kogane-sengan) and potato (Dejima) were freeze-dried, sun-dried, oven-dried or boiled and used for the determination of in-vitro DE in order to estimate DE for pigs. In sweet potato, the estimated DE was 3.66, 3.71, 3.81 and 3.90, respectively, and that in potato was 2.60, 2.75, 2.95 and 3.92, respectively. DE of potato was significantly (P<0.05) improved by boiling. The DE values of boiled sweet potato and those of potato were comparable to those of corn which was 3.87. The estimated DE of cassava with oven-drying was 3.85, which was higher than that of sun-dried one amounting to 3.69 (P<0.05).
