Abstract
Simple SummaryPreviously, we found that starch ruminal degradation kinetics between raw and steam flaked corn were significantly different, but the mechanism is still ambiguous. Currently, we have demonstrated that γ-zein protein, encapsulating the starch granules into the hydrophobic starch–protein matrix, and starch granule characteristics were dramatically different between raw and steam flaked corns. Along with the totally different abundance and procedures of starch hydrolyzing bacteria attached to the two grain types, we concluded that γ-zein protein content and starch granule morphology of corn grain determined starch ruminal degradation kinetics through altering the abundance and procedure of starch hydrolyzing bacteria attached to corn grain in rumen. The current study investigated differences of γ-zein protein contents and starch granule characteristics between raw and steam flaked corns and their influences on ruminal starch hydrolyzing bacteria (SHB) attached to corn grain. Two types of raw (Corn1 and Corn2) and their steam-flaked products (SFCorn1 and SFCorn2) were applied to explore physiochemical structures and SHB attachment. SDS-PAGE was conducted to detect γ-zein protein patterns, scanning electron microscope, and small angle X-ray scattering were performed to obtain starch granule morphology, while crystallinity, DQ starch, and DAPI staining were applied to quantify SHB. The steam flaking process destroyed γ-zein proteins and gelatinized starch granules. The median particle size of Corn1 and Corn2 starch granules increased from 17.8 and 18.0 μm to 30.8 and 26.0 μm, but crystallinity decreased from 22.0 and 25.0% to 9.9 and 16.9%, respectively. The percentage of SHB attached to Corn1 residues decreased (p = 0.01) after 4 h incubation, but SHB attached to SFCorn1 residues increased (p = 0.03) after 12 h incubation. Thus, the differences of γ-zein proteins and starch granule physiochemical structures between raw and steam flaked corn played an important role in improving the rate and extent of starch ruminal degradation through altering the process of SHB attached to corn.
Highlights
The differences of γ-zein proteins and starch granule physiochemical structures between raw and steam flaked corn played an important role in improving the rate and extent of starch ruminal degradation through altering the process of starch hydrolyzing bacteria (SHB) attached to corn
Starch granule is the basic unit of starch in corn endosperm and embedded in the starch–protein matrix [1,2,3], which influences the starch digestion by microbes
Naguleswaran et al [6] found that different granule morphology and crystallinity of triticale, wheat, and corn led to variance of the rate and extent of starch hydrolyzing, indicating that the natural characteristics of starch granules control starch amylolysis
Summary
Starch granule is the basic unit of starch in corn endosperm and embedded in the starch–protein matrix [1,2,3], which influences the starch digestion by microbes. The destruction of the starch–protein matrix makes the starch granules accessible to amylolytic digestion by ruminal bacteria. (2011) found that the ensiling process destroyed the corn starch–protein matrix and contributed to greater access to starch granules [2]. In addition to the starch–protein matrix, granule morphology and size, the degree of granule crystallinity and extent of granule damage influence starch digestibility [5]. Naguleswaran et al [6] found that different granule morphology and crystallinity of triticale, wheat, and corn led to variance of the rate and extent of starch hydrolyzing, indicating that the natural characteristics of starch granules control starch amylolysis
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