Molecular spectroscopic features of protein in newly developed chickpea: Relationship with protein chemical profile and metabolism in the rumen and intestine of dairy cows

Abstract

The first aim of this study was to investigate the nutritional value of crude protein (CP) in CDC [Crop Development Centre (CDC), University of Saskatchewan] chickpea varieties (Frontier kabuli and Corinne desi) in comparison with a CDC barley variety in terms of: 1) CP chemical profile and subfractions; (2) in situ rumen degradation kinetics and intestinal digestibility of CP; 2) metabolizable protein (MP) supply to dairy cows; and (3) protein molecular structure characteristics using advanced molecular spectroscopy. The second aim was to quantify the relationship between protein molecular spectral characteristics and CP subfractions, in situ rumen CP degradation characteristics, intestinal digestibility of CP, and MP supply to dairy cows. Samples (n=4) of each variety, from two consecutive years were analyzed. Chickpeas had higher (P<0.01) CP content (21.71–22.11 vs 12.96% DM), with higher (P<0.05) soluble CP subfraction (59.07–70.27 vs 26.18% CP), and in situ soluble (23.44–25.85 vs 1.30% CP) and rumen degradable (RDP; 72.23–72.57 vs 58.48% CP) fractions than barley. The potentially slowly rumen degradable (D; 74.14–76.56 vs 93.31% CP) and undegradable (RUP; 27.43–27.66 vs 41.52% CP) fractions were lower (P<0.01) in the chickpeas than barley. The effective degradability ratio of N to organic matter (OM) (36.07–38.44gN/kg OM) of the chickpeas was higher than the optimal for achieving optimum microbial CP (MCP) synthesis. The truly digested MCP (64.94–66.43 vs. 41.43g/kg DM); MP (81.10–83.67 vs 61.0g/kg DM) feed milk value (1.64–1.70 vs 1.24) was higher in the chickpeas than barley grain. The chickpeas had higher (P<0.05) amide I and II peaks area and height, and α-helix and β-sheet peaks height than barley. Multivariate analysis showed that protein molecular spectral data of chickpeas can be distinguished from the barley. The two chickpeas did not differ in CP content, and any of the measured in situ degradation and molecular spectral characteristics of protein. The content of RUP was positively (r=0.94, P<0.01) and that of RDP was negatively (r=−0.94, P<0.01) correlated with amide I/II area ratio. The regression analysis showed that the content of CP (R2=0.91) D-fraction (R2=0.82), RDP (R2=0.77), RUP (R2=0.77), TDP (R2=0.98), MP (R2=0.80), and FMV (R2=0.80) can be predicted from amide II peak height. Despite extensive ruminal degradation, chickpea is a good source of MP for dairy cows, and molecular spectroscopy can be used to rapidly characterize feed protein molecular structures and predict their digestibility and nutritive value.