We compared the firmness and force relaxation characteristics of tomato flesh harvested at six maturity stages and stored intact or as 7-mm slices for 0 to 20 days. Three measurements were made on outer pericarp and columella tissue. A 4-mm cylindrical probe provided more consistent firmness measurements (lower percent CV) than a 6.4-mm spherical probe at harvest, and distances of 3 mm were more consistent than 1 mm. Following loading, stress relaxation was recorded for 10 s. Stored tomato samples were tested only with the 4-mm cylindrical probe and distance of 3 mm. Firmness was taken as the maximum force (Fmax) in the loading portion, usually occurring at 3 mm. Fmax of freshly harvested tomatoes ranged from 15 to 2 N for mature green and red tomatoes, respectively. Fmax was closely correlated to area, slope, and force at first peak, i.e., all four parameters measured the same physical property, and was moderately correlated (R > 0.9) to forces at specific relaxation times. Tomatoes stored intact generally had lower CVs than that of those sliced before storage, although there was little difference in average firmness (Fmax) between the two at a given storage time. A three-parameter model was developed to fit the relaxation curves. There was little correlation between Fmax and the three relaxation characteristics (R = 0.6 to 0.0), i.e., the relaxation characteristcs measured different physical properties than did Fmax. The responses of the relaxation characteristcs over storage time were dependent on the initial maturity of the tomatoes, but their values usually differed significantly between tomatoes stored intact or sliced, with tomatoes sliced before storage generally having higher values.
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