COMPARATIVE CELL WALL CONSTITUENT LEVELS OF TANNIN-FREE AND TANNIN-CONTAINING CULTIVARS OF FABABEANS (VICIA FABA L.)

A series of experiments has been carried out with tannin-free and tannin-containing cultivars of fababeans. The in vitro dry matter digestibility of the cotyledon portion of the two groups of fababeans was the same (88.2%) whereas the in vitro digestibility of the testa portion of the tannin-free cultivars was much higher (27.6%) than that of the tannin-containing cultivars (9.2%). The concentrations of certain cell wall constituents in the testae of tannin-free and tannin-containing cultivars were also different (P < 0.01); the respective average values for the two groups were: condensed tannins, 0.2 and 4.9%; lignin, 4.2 and 6.2%; acid detergent fiber, 72 and 66%; and cellulose, 67 and 60%. There was a negative correlation between the in vitro dry matter digestibility and the amount per unit weight of whole beans of either condensed tannin (r = −0.86, P < 0.01) or lignin (r = −0.89, P < 0.01). When expressed on a similar basis there was no correlation between levels of cellulose or acid detergent fiber and in vitro dry matter digestibility.