Commodity conditioning to reduce impact bruising

This paper proposes tools for managing bruise threshold in apples, pears, and potatoes by controlling temperature, relative turgor, and strain rate. It includes information on the effects of these three factors on tissue failure stress and failure strain; and an equation for estimating bruise threshold based on these failure properties, Poisson's ratio, and specimen mass and radius of curvature. In general, higher temperature and/or lower relative turgor (within limits) in potato tubers and some pear cultivars resulted in improved bruise threshold, while in apples, lower relative turgor improved bruise threshold but temperature had little effect. While some of this information has been available qualitatively or quantitatively for quasi-static loading, this work quantifies the relationships among these variables for impact loading. The theory of elasticity-based equation predicts that impact bruise threshold is directly proportional to tissue failure stress, to the 4th power of tissue failure strain, the 3rd power of radius of curvature, and inversely proportional to specimen mass. Preliminary validation work predicted apple and potato bruise thresholds within 23% of experimental values or better for assumed values of Poisson's ratio. The relationship is already proving valuable in screening of new cultivars. (C) 2001 Elsevier Science B.V. All rights reserved.