Comparison of Gross Protein Value and Metabolizable Energy of Dried Skim Milk and Dried Yoghurt

In order to compare the protein quality and metabolizable energy (M.E.) of dried yoghurt and dried skim milk three experiments were conducted. In the first experiment, drum dried skim milk, dried yoghurt prepared from drum dried skim milk and dried yoghurt prepared from fresh skim milk were used as test materials. The gross protein value (G.P.V.) of these test materials were 87, 99 and 133 respectively. These values were significantly different (p < 0.01). The results of the second experiment showed that the superiority of G.P.V of dried yoghurt to dried skim milk was not due to the possibility of the presence of some unidentified growth factors (U.G.F.) in the dried yoghurt. In the second experiment the G.P.V. of spray dried skim milk, dried yoghurt prepared from spray dried skim milk and spray dried skim milk plus dried whey were 94, 113 and 94 respectively. These values were significantly different (p < 0.01). Bioassay showed that the concentration of methionine was greater in dried yoghurt than in dried skim milk (p < 0.05) while there were no significant differences in the concentration of lysine. In the third experiment the M.E. of drum dried skim milk, dried yoghurt prepared from drum dried skim milk and dried yoghurt prepared from fresh skim milk were 2.723, 3.928 and 4.127 kcal./gm. respectively. These values were significantly different (p < 0.01). The percentage of gross energy as M.E. of these test ingredients were 62.1, 75.3 and 77.9 respectively which were also significantly different (p < 0.01). The results of these experiments suggest that the superiority of G.P.V. and M.E. of dried yoghurt as compared with dried skim milk could be due to increasing the availability of nutrients and decreasing the concentration of lactose in process of conversion of dried skim milk to dried yoghurt.