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3.4. In vitro protein digestibility (IVPD)
The results of IVPD of Hamra, Shahla and Baidha varieties as a function of fermentation time are presented in Table 5. IVPD progressively increased in the three varieties. Significant increases (P⩽0.05) in IVPD occurred in Hamra (79.4%), Shahla (74.6%) and Baidha (78.1%) at 24 h when compared to 75%, 69.6% and 74.6% for 0 h for the three varieties. In both Hamra and Baidha varieties there was no significant increase in IVPD after 18 h of fermentation, whereas Shahla showed a significant increase. These results clearly demonstrate that fermentation improved protein digestibility. Several workers have observed significant increase of IVPD by natural fermentation. Yousif and El-Tinay (2001) showed that natural fermentation of sorghum increased IVPD from 51.8% to 75.6%. Similarly, Chavan et al. (1988) reported significant increase in IVPD of sorghum, green grain and sorghum plus green grain blend within the first 24 h of fermentation. The improvement of protein digestibility after fermentation can be attributed to the reduction of antinutritional factors such as trypsin inhibitor and tannins.