A shearing technique measuring resistance properties of plant stems

A shearing technique was developed to measure fracturing properties of plant stems. Shearing force measurements assess the amount of energy required to fragment plant tissue as an indication of resistance to particle breakdown during mastication. The objective of this study was to develop a rapid and inexpensive method of accurately measuring the shearing properties of forage stems. Shearing properties of alfalfa stems were measured by shearing 20 main stems from each of 24 cultivars. Stems were dried and divided into three 16 cm segments, top, middle and bottom. Each segment was sheared between two nodes at the approximate mid-point using an Ottawa Texture Measurement System with a Warner-Bratzler blade (dull grade) lowered at 1.35 mm s−1. Instrument repeatability was determined using a homogenous material (plastic coffee stirrers) with mechanical and textural properties similar to those of a plant stem. The shearing technique provided a repeatable and rapid measurement of shearing force (coefficient of variation for plastic stirrers, 4.2%). For alfalfa stems harvested at similar physiological maturity, shearing forces for each shearing location on the stem differed (P < 0.001) among cultivars. At all shearing locations, shearing force varied considerably between cultivars; however, variations among shearing locations were similar. Shearing force was significantly correlated with diameter, weight, linear density and, to a lesser extent, with the cell wall chemical constituents of the stem.