Effect of heat processing methods on the protein molecular structure, physicochemical, and nutritional characteristics of faba bean (low and normal tannin) grown in western Canada

This study aimed to determine the heat processing impact on the protein molecular structure (amide I, amide II, alpha-helix, and beta-sheet), and the nutritional characteristics (nutrient profiles, rumen degradation, intestinal digestion, and true protein supply) of faba bean grown in western Canada. Low tannin (LT) and normal tannin (NT) faba bean varieties were used for the present study, where varieties (n = 3) for each tannin level were used as a replicate. Based on previously published studies, sample groups were either heated with steam pressure at 121 degrees C for 30 minute (min) using a medium steam sterilizer or with microwave irradiation for 3 min in a conventional microwave with a power of 900 W and irradiation frequency of 2450 MHz. All seed was ground using a roller mill before heating. Heat-induced molecular structure changes were determined with Fourier Transformed Infrared spectroscopy (FTIR) while nutrient profiles, including dry matter (DM), crude protein (CP), soluble crude protein (SCP), and starch were obtained with traditional chemical analyses. An in situ rumen degradation study and a modified three-step in vitro technique was performed to analyze the degradation parameters and intestinal digestibility of feed nutrients in faba bean. Results showed that the peak area ratio of amide Ito amide II was lower in normal tannin faba bean types (1.835 vs. 2.073 absorbance units (AU), P < 0.0001) compared to low tannin faba bean types with both heat treatments, while the peak height ratio of alpha-helix to beta-sheet was higher in normal tannin types (1.249 vs. 1.090 AU, P < 0.0001) relative to low tannin types. Additionally, steam pressure reduced the SCP (45 vs. avg. 188 g/kg DM, P < 0.01), and increased the intestinal digestibility of crude protein (dIDP, 0.89 vs. avg. 0.79, P = 0.03) compared to other treatments. The truly absorbed protein supply in the small intestine was higher with steam pressure (DVE, 180 vs. 130 and 117 g/kg DM, P < 0.01) relative to the control and microwave irradiation, respectively. The feed milk value was higher with steam pressure (FMV, 3.65 vs. 2.65 and 2.38 kg milk/kg DM feed, P < 0.01) compared to the control and microwave irradiation, respectively. In the present study, steam pressure reduced the soluble crude protein and the effective degraded crude protein, increasing the truly digested protein in the small intestine more than microwave irradiation. These results suggest that steam pressure toasting of faba bean was a better treatment to improve protein degradability and supply in dairy cattle compared to microwave irradiation.