A novel instrument to delineate varietal and harvest effects on blueberry fruit texture during storage

Firmness is an important quality index for blueberries. It is the major factor that determines consumer acceptability, storability and resistance to injury and diseases during storage and fresh marketing. Blueberry cultivars vary in their firmness, with southern highbush cultivars usually softer than Rabbiteye blueberries. In this study, varietal and harvest effects on blueberry firmness were measured by the Firmtech II and laser air-puff instruments. This was the first time that the laser air-puff, a non-contact food firmness tester, had been used for firmness testing of small fruit, such as blueberry.

Two southern highbush cultivars (Sweet Crisp and Emerald) and two Rabbiteye cultivars (Vernon and Savory) were used for varietal effect measurement, while a Rabbiteye cultivar (Premier) that was both machine and hand harvested was used for harvest effect observation. Fifty berry samples per replicate and four replicates were tested by two instruments at harvest and after 7, 14, or 21 days of storage. The laser air-puff tester successfully delineated the difference in firmness due to cultivar characteristics and harvest methods, as well as the firmness loss over 21 days of postharvest cold storage (4 °C). The firmness index derived from the laser air-puff tester achieved a significant correlation with the firmness values measured by the Firmtech (R(2)=0.80). A new texture index, springiness, was developed from the laser air-puff, which largely reflects the varietal differences in elasticity of fruit.

This study demonstrated the efficacy of the laser air-puff instrument for blueberry firmness measurement. This non-contact instrument not only provides an alternative method of firmness measurement, but also offers a new index for fruit elasticity evaluation and better texture evaluation for blueberries.