Molecular basis of structural makeup of hulless barley in relation to rumen degradation kinetics and intestinal availability in dairy cattle: A novel approach

To date, no study has been done of molecular structures in relation to nutrient degradation kinetics and intestinal availability in dairy cattle. The objectives of this study were to (1) reveal molecular structures of hulless barley affected by structural alteration using molecular spectroscopy (diffuse reflectance infrared Fourier transform) as a novel approach, and (2) quantify structure features on a molecular basis in relation to digestive kinetics and nutritive value in the rumen and intestine in cattle. The modeled feeds in this study were 4 types of hulless barley (HB) cultivars modified in starch traits: (a) normal starch cultivar, (b) zero-amylose waxy, (c) waxy, and (d) high-amylose. The molecular structural features were determined using diffuse reflectance infrared Fourier transform spectroscopy in the mid-infrared region (ca. 4,000-800 cm−1) of the electromagnetic spectrum. The items assessed included infrared intensity attributed to protein amide I (ca. 1,715-1,575 cm−1), amide II (ca. 1,575-1,490 cm−1), α-helix (ca. 1,648-1,660 cm−1), β-sheet (ca. 1,625-1,640 cm−1), and their ratio, β-glucan (ca. 1,445-1,400 cm−1), total carbohydrates (CHO; ca. 1,188-820 cm−1) and their 3 major peaks, structural carbohydrates (ca. 1,277-1,190 cm−1), and ratios of amide I to II and amide I to CHO. The results show that (1) the zero-amylose waxy was the greatest in amide I and II peak areas, as well as in the ratio of protein amide I to CHO among HB; (2) α-helix-to-β-sheet ratio differed among HB: the high-amylose was the greatest, the zero-amylose waxy and waxy were the intermediate, and the normal starch was the lowest; (3) HB were similar in β-glucan and CHO molecular structural makeup; (4) altered starch HB cultivars were similar to each other, but were different from the normal starch cultivar in protein molecular makeup; and (5) the rate and extent of rumen degradation of starch and protein were highly related to the molecular structural makeup of HB. In conclusion, the molecular structural makeup on a molecular basis was related to rumen degradation kinetics and intestinal availability in dairy cattle. The alteration of starch structure in barley grain affects starch structure and the magnitude of protein and β-glucan contents, as well as the protein molecular structure of HB.