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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Cell Wall Biology and Utilization Research » Research » Publications at this Location » Publication #333974

Title: Short communication: Gelatinization and enzymatic hydrolysis characteristics relevant to digestion and analysis of glycogen granules isolated from ruminal protozoa

item Hall, Mary Beth
item Zeller, Wayne
item HOFFSTETTER, HEIKE - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2019
Publication Date: 5/5/2019
Citation: Hall, M., Zeller, W.E., Hoffstetter, H. 2019. Short communication: Gelatinization and enzymatic hydrolysis characteristics relevant to digestion and analysis of glycogen granules isolated from ruminal protozoa. Journal of Dairy Science.

Interpretive Summary: Rumen microbes digest much of the feed a cow consumes. In turn, they provide nutrients the cow uses to grow and make milk. Understanding the digestion characteristics of microbial products and factors that affect their analysis is essential to improving our predictions of nutrients available to the cow. Rumen microbes can ferment carbohydrates or store them as glycogen, which is similar to starch. Evaluation of protozoal glycogen showed that it needed to be gelatinized for complete analysis, but even ungelatinized glycogen was more rapidly digested by enzymes than were corn or wheat starch. Accordingly, for most accurate analysis, protozoal glycogen should be gelatinized, and it may be estimated as more digestible than plant starch in predictions of digestibility.

Technical Abstract: Digestion and analysis of rumen microbial products are influenced by the physicochemical and enzymatic hydrolysis characteristics of those products. The objective of this study was to describe the physical and chemical characteristics of isolated protozoal glycogen granules. The protozoal glycogen granules were determined to be 98.3% alpha-glucan by enzymatic-colorimetric starch analysis. Two-dimensional (2D) nuclear magnetic resonance (NMR) analysis of the protozoal glycogen granules showed the glycogen to consist of alpha-(1,4) and alpha-(1,6) linkages, with the alpha-(1,6) bonds that represent branch points accounting for approximately 9.1% of the linkages as determined by variable temperature 1H-NMR spectroscopy. The presence of (1,3)-interglucal linkages (alpha or beta) was not detected by 2D-NMR analysis. The granules underwent gelatinization, which commenced at 65°C, as compared to purified wheat and corn starches which initiated gelatinization at 50°C and 65°C, respectively. Treatment of ungelatinized samples with amyloglucosidase for 2 h at 39°C showed approximately 3-fold greater hydrolysis to glucose for protozoal glycogen (24.7% of dry matter [DM]), than for wheat (9.0% of DM) or corn (7.4% of DM) starches. After gelatinization at 85°C, protozoal glycogen again showed a greater extent of enzymatic hydrolysis (95.3% of DM) than the starch samples (89.4% of DM for both wheat and corn). Thus, it appears that native glycogen may be more readily digested by small intestinal enzymes than corn or wheat starch, and that protozoal glycogen samples should be gelatinized to allow accurate enzymatic analysis of the alpha-glucan they represent.