Date Available

12-12-2023

Year of Publication

2023

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Agriculture, Food and Environment

Department/School/Program

Animal and Food Sciences

First Advisor

Dr. Rachel Schendel

Second Advisor

Dr. David Harmon

Abstract

Hemp (Cannabis sativa L.) is used in the United States as a source of CBD oil, fiber, and grain. While hempseeds are consumed whole or as dehulled hemp hearts, hempseed oil is also a desirable seed oil in human nutrition. The process of collecting hempseed oil leaves behind hempseed cakes that are abundant in protein and fiber. Feeding of hempseed cakes to animals, including ruminants, has only initially been explored. Extraction of CBD from hemp inflorescences generates organic waste that may find a second purpose as a fiber feed for cattle. Little is known about the exact fiber composition of hempseed or hemp inflorescences. Certain polymers are expected in the cell wall of dicotyledonous plants like hemp such as cellulose, xyloglucans, xylans, mannans, pectins, and lignin. Structural variation in the exact degree of branching and substitution types exist between plant species and tissue types, and these differences have impacts on interactions within the wall.

To characterize the cell wall polysaccharides of hempseeds, water-insoluble and water-soluble cell wall material was isolated from the ground and defatted, whole hempseeds (2SO4) hydrolysis and methanolysis, were employed to release monosaccharides which were separated and detected with HPAEC-PAD. Linkage types in the polysaccharides were determined by the generation and analysis of partially methylated alditol acetates (PMAAs) with GC-MS and GC-FID. Targeted enzymatic screenings were conducted to release xyloglucan oligosaccharides and pectic arabinans and galactans which were consequently analyzed with HPAEC-PAD/MS and HPAEC-PAD, respectively. Acetyl bromide soluble lignin was determined spectrophotometrically. Then, insoluble cell wall material was used as substrate in an experiment using the ANKOM DaisyII system to evaluate in vitro true digestibility (IVTD) with rumen inoculum. Intact and CBD-extracted inflorescences from two hemp cultivars were analyzed for their monosaccharide composition with Saeman hydrolysis and methanolysis, and their linkage types were assessed via the generation and analysis of PMAAs.

The analyses revealed an abundance of cellulose and xylans in the hempseed cell wall. Mannans, pectins, and xyloglucans were also identified. Xyloglucans in the hempseed cell wall were less substituted in the insoluble material than in the water-soluble material. Arabinans from hempseeds were both branched and linear, and the ABSL content of the hempseeds was 17.0 ± 1.0%. Fermentation of the insoluble hempseed cell wall material yielded an IVTD of 36.02 ± 2.91% after 48 hours. Analysis of hemp inflorescences revealed the same polysaccharide components, but a much smaller proportion of xylans and a larger proportion of arabinans. While co-extraction with supercritical CO2 and ethanol may have removed some pectins, it seems that cultivar has a greater impact on the polysaccharide profile of hemp inflorescences than the CBD extraction process. While resistant to microbial digestion, hempseed is fiber-rich and warrants further research in vivo to investigate its integration into ruminant diets and an exploration of the fiber impact on the human gut microbiome.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.442

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