A Comprehensive Analysis of Factors Influencing Firmness Characterization in Peach and Nectarine

Penetration test is the most direct and widely recognized standard method for assessing fruit firmness. Texture analyzers are increasingly employed for accurate fruit firmness measurement, offering advantages in reducing operator errors compared to the traditional manual test. The diverse options of texture analyzers provide flexibility for users, but also present challenges for standardizing firmness measurements. In addressing these issues, factors influencing firmness characterization, including peeling, probe size, penetration speed, penetration depth, and measurement parameters were analyzed for peach and nectarine. The results show that, compared to skin-off parameters, skin-on parameters exhibited absolute advantages for the nectarine cultivar. We also found the importance of probe size selection for accurate firmness detection for different cultivars, and it appears to be closely related to whether the fruits were peeled. The peach cultivar "HJ" is suitable for using a thicker probe (8 mm) after peeling, while the nectarine cultivar "ZNJH" is suitable for using a relatively thin probe (5 mm) with the skin on. The influence of speed is relatively low; however, a penetration speed of 5 mm/s is more recommended due to its better performance in capturing firmness differences. The force values at the steady phase of force-displacement curves perform best among all tested parameters. Penetration depths of 8 and 10 mm show no significant difference, suggesting that once the steady phase is reached, the influence of penetration depth is minimal.