Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2005
Publication Date: 9/27/2005
Citation: Lu, R., Srivastava, A., Beaudry, R. 2005. A new bioyield tester for measuring apple fruit firmness. Applied Engineering in Agriculture. 21(5):893-900. Interpretive Summary: Firmness is an important quality attribute for apple fruit and other types of fresh produce. Currently, the fruit industry relies on a destructive sampling technique to measure fruit firmness. The Magness-Taylor (MT) firmness tester makes use of a round steel probe to measure the force required to penetrate the fruit flesh. Once MT firmness measurements are completed, the fruit have to be discarded. The industry is looking for a nondestructive technique that can reliably measure fruit firmness without degrading fruit quality. The objective of this research was to evaluate a specially designed portable firmness tester that is based on measuring the bioyield force of apple fruit. Bioyield is the phenomenon that indicates the initial fracture of the cell structure of the fruit and at this point no visible damage is observed on the surface of the fruit with the negligible browning of the fruit tissues under the skin. Bioyield force and MT firmness were measured on Delicious and Golden Delicious apples that were kept under different environmental conditions. There was a relatively good correlation (r) between MT firmness and bioyield measurements with the r-values ranging between 0.75 and 0.84 and the standard errors, a measure of variability about the average value, between 4.0 and 5.5 N. When all data were pooled, the correlation was 0.87 with a standard error of 5.0 N. Bioyield measurements in individual fruit were 41 to 47% more variable than MT firmness measurements, but the bioyield probe was only about half the size of the standard MT probe. For apples from cold storage environment, bioyield force and MT firmness showed a similar pattern of changes over time. However, when apples were kept at room temperature, MT firmness measurements were more sensitive to storage time and/or fruit condition than bioyield measurements. These results indicate that the bioyield tester can be used to measure and monitor fruit firmness. Since fruit from testing are not damaged or degraded, the procedure reduces economic losses to the fruit industry and provides a better means for quality tracking of apple fruit during growth, harvesting, and postharvest handling.
Technical Abstract: Nondestructive sensing of fruit firmness provides the producer and retailer with a means for assessing and/or assuring the quality and consistency of apples delivered to the market. The objective of this research was to evaluate a newly developed bioyield tester for measuring fruit firmness and its measurement variability within individual fruit in respect to the standard destructive Magness-Taylor (MT) firmness tester. A specially designed bioyield probe was coupled to a handheld digital force gauge that was mounted on a tabletop motor driven stand. Bioyield force and MT firmness were measured on Delicious apples over various periods of time when they were kept at either cold storage (5 C) or room temperature (24 C), designated as Cold Storage and Room Storage, respectively. Bioyield force and MT firmness were also measured on Golden Delicious apples treated with and without 1-MCP, a new chemical that inhibits ethylene action. The correlation between MT firmness and bioyield force ranged from 0.62 to 0.74 with the standard error (SE) between 5.2 and 6.7 N when all test data were used in the regression analyses. With removal of about 5% extreme data points, the correlation was improved, ranging from 0.75 to 0.82 and the SE between 4.0 and 5.5 N. The correlation coefficient was 0.87 with the SE of 5.0 N for the pooled Delicious data with the removal of 5% extreme data. For Cold Storage Delicious apples, a consistent pattern of changes in bioyield force and MT firmness was observed, each decreasing by 20% over a period of 32 days. For Room Storage Delicious apples, MT firmness appeared more sensitive to storage time than the bioyield force. MT firmness decreased by 18% for the Room Storage I group of apples over 21 days and about 17% for the Room Storage II over a period of 33 days. However, the corresponding decreases in bioyield force for the Room Storage I and II groups were 12% and 6%, respectively. A similar pattern of changes in bioyield force was observed from the same fruit monitored over 24 and 16 days under cold and room storage conditions, respectively. Bioyield force measurements within individual apples were approximately 41 to 47% more variable than MT firmness (9.0-9.7% versus 6.1-6.8%, as measured by the coefficient of variation). Since bruises resulting from bioyield tests are minimal and do not cause degradation to apple fruit, the bioyield tester can be used as a nondestructive means for assessing and monitoring fruit firmness during growth, harvesting and postharvest operations.