Impact of steam pressure toasting time on the alpha helix to beta sheet ratios, nutritional value, protein and carbohydrate subfractions, and rumen fermentation parameters of Faba bean seeds for dairy cattle

Abstract

The use of Faba bean (Vicia faba) seeds (FBS) as a potential feed ingredient for ruminants has been previously evaluated. However, the effects on nutrient supply and degradability linked to protein secondary structure ratios after different steam pressure toasting (SPT) times are scarce. This study aimed to determine the role of varying alpha-helix to beta-sheet ratios induced by SPT duration on the nutritional value of Snowbird FBS in dairy cattle. Fifteen samples (1 variety × 3 years × 5 treatments) were analyzed for protein secondary structures and nutrient composition. The dry matter (DM), crude protein (CP), starch, and neutral detergent fibre-assayed with a heat stable amylase and expressed inclusive of residual ash (aNDF) contents in raw seeds were 914, 286, 328, and 179 g/kg DM, respectively. The averaged DM, CP, starch, and aNDF in the SPT-processed seeds were 904, 292, 374, and 405 g/kg DM, respectively. Soluble crude protein was about five times higher in raw seeds (239 g/kg DM) compared to steam-pressure toasted seeds (avg. 51 g/kg DM) (P < 0.01). The total digestible nutrients (TDN1x) and energy values gradually decreased as SPT time increased (P < 0.01). Hence, the TDN1x in the raw seeds was 832 g/kg DM, while the values at 30, 60, 90, and 120 min were lower by 2.78, 3.87, 6.44, and 7.71 units, respectively. The NEL3x reduced from 2.03 in raw seeds to 1.82 Mcal/kg (P < 0.01). The effective degradability (ED) of nutrients decreased with SPT duration from 0 to 120 min. Hence, the EDDM reduced from 692 to 357 g/kg DM (P < 0.01), the EDCP from 224 to 67 g/kg DM (P < 0.01), and the EDST from 237 to 129 g/kg DM (P = 0.01). Steam pressure toasting from 30 and up to 60 min might be the optimal range for processing FBS (Snowbird var). These findings could be supported by a post-ruminal evaluation of the nutrients that escaped ruminal fermentation.