The objective of this study was to explore if microwave irradiation and moist autoclaving treatments could change nutritive values, nutrients availability and protein inherent spectral structural characteristics in tannin (var. Fatima) and non-tannin (var. Snowbird) faba beans. An in situ approach with four cannulated dry Holstein dairy cows was applied in this study. The results showed that beans heated with microwave and autoclaving had increased contents of ether extract and neutral detergent insoluble CP and reduced soluble CP, sugar and tannin concentrations when compared with the raw seeds. Heating reduced degradable nutrients in the rumen and increased intestinally absorbable nutrients, but it failed to improve digestibility in total tract. All the results showed heating with moisture and pressure would be stronger and severer than microwave irradiation. The variety of faba bean interacted with thermal treatment on total truly intestinally absorbed protein value which showed to be highest in the microwaved brown faba bean and lowest in the unheated Snowbird bean. The degraded protein balance (OEB) value was significantly decreased after both kinds of heating process, suggesting that heating treatments could mitigate loss of nitrogen from the rumen to a large extent. We further collected spectral data using mid-IR spectroscopy and found heat processed beans had varied peak height and area ratios compared with raw beans. However, multivariate results implied that heating process failed to completely change the whole molecular conformation in the protein amide region. Correlations were found between ADF/ADL and spectral features, and the OEB value was negatively related to protein secondary structural α-helix. In conclusion, both faba beans were more sensitive to autoclaving treatment than microwave irradiation in terms of nutrient availability in ruminants.
Keywords: Autoclave; Availability; Irradiation; Nutritive; Protein molecular structures.
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