Food Structure


Phenolic components within cell walls are the greatest limitation to biodegradation of plants, but the location and types of compounds within specific walls are poorly understood . Leaf blades of warm-season (Coastal and Coastcross-1 bermuda grasses and sudangrass) and cool-season grasses (orchardgrass and tall fescue) and leaflets of legumes (alfalfa and lespedeza) were evaluated before and after incubation with rumen microorganisms for 7 days to determine cell types and wall structures most resistant to biodegradation. UV absorption microspectrophotometry was used to characterize aromatics within selected undegraded cell types, which had been shown in digestion studies to vary in biodegradability, from representative plants of each of the three groups (Coastal bermudagrass, orchardgrass, tall fescue, and alfalfa). The most recalcitrant tissues {mestome sheath in grasses and xylem in legumes) had the greatest absorption, but spectra varied for the different plants. Spectra for the grasses, but not alfalfa, suggested a strong contribution from phenolic esters. Spectra of sclerenchyma were similar for the grasses and suggested a strong ester component. For partially digested tissues such as epidermis and parenchyma bundle sheath, UV absorption maxima and shoulders occurred in tissues that were partially or non-degraded; in contrast, absorption did not occur or was considerably less in tissues showing complete degradation. UV absorption microspectrophotometry is useful for characterization of phenolic compounds within cell types that differ in digestibility.

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