FIRMNESS MEASUREMENT OF TOMATO SLICES - SAMPLE VARIATION

Authors: Abbott, Judith; WU, TIANXIA - USDA/FAS/ICD

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Firmness is important to quality of fresh tomatoes; its measurement is important in postharvest studies to develop procedures for preparation and handling of freshcut tomato slices. Firmness varies greatly between and within individual tomatoes. This study was conducted to determine appropriate sample sizes and locations to measure firmness of freshcut tomato slices to optimize the statistical power of treatment comparisons. We tested columella and pericarp tissues on slices from upper, central, and lower portions of tomatoes at the turning stage of maturity, the stage showing maximum variability. Columellar tissues were firmer and more variable than pericarp. We recommend that firmness values of columella and pericarp be reported separately. The upper slice was less variable than the equatorial or lower slice, but firmness values for the equatorial slice can better represent the whole fruit. Averaging multiple test sites within a particular slice and tissue type is recommended. A sample size of about 15 tomatoes per experimental unit is recommended for detecting differences in firmness between treatments (assuming adequate replications of the treatments) and increasing that to 20 generally improves sensitivity. Our results indicate the importance of controlling the origin of samples tissue type and within-fruit location when making firmness measurements on sliced tomatoes. These results can be used as guidelines, but should be evaluated for the specific tomatoes to be tested, the instrumentation, and the differences that will be considered significant. This information should benefit postharvest physiologists and food scientists involved evaluation of tomatoes, particularly for freshcut slices.

Technical Abstract: Firmness is an important quality attribute of fresh tomatoes. Because firmness varies greatly between and within individual tomatoes, it is important to have an adequate sample to optimize the statistical power of treatment comparisons, regardless of measurement method. The purpose of this study was to determine sample size and other statistical recommendations for measuring firmness of freshcut tomato slices. We tested columella and pericarp (junction of outer wall and interlocular ray) on slices taken from upper, central, and lower portions of tomatoes at the turning stage of maturity. Columellar tissues were firmer and more variable than pericarp. We recommend that firmness of columella and pericarp be reported separately. The upper slice was less variable than the equatorial or lower slice, but firmness of the equatorial slice was most similar to the mean of the three slices and so can better represent the whole fruit. Averaging multiple test sites (within a slice and tissue type) is recommended because it reduces the portion of total variance due to variability within a slice. A sample size of about 15 tomatoes per experimental unit is recommended (assuming adequate replication of the experimental units) and increasing that to 20 generally improves the sensitivity of the comparison. Our results indicate the importance of controlling the origin of samples tissue type and within - fruit location when making firmness measurements on sliced tomatoes. These results can be used as guidelines, but should be evaluated in terms of variability of specific tomatoes to be tested, instrumentation, and differences that will be considered significant.