Research on the evolutionary of spectral features of the initial damaged parts of 'Red Delicious' apples

It is crucial for early detection of mechanical damage to improve the quality of commodity fruit. For the problem of low identification accuracy of damage detection models due to the small degree of damage and unclear damage features in the initial damage of fruit and vegetables, this research analyzed the evolution process of spectral information in the initial damage of (0-3 h) of 'Red Delicious' apples. Three sensitive bands of 650-734 nm, 850-970 nm, and 1255-1314 nm, were extracted, and the average spectral reflectance and spectral curve shape features tan theta of the sensitive bands were analyzed. The conclusion is as follows: (1) In the 650-734 nm band, spectral reflectance decreasing and then stabilizing, reflecting enzymatic browning development. More severe damage led to lower reflectance. Over time, tan theta decreased, with more severe damage showing faster reduction, reflecting changes in chlorophyll content in the peel. (2) In the 850-970 nm band, reflectance showed a decreasing-then-increasing trend, reflecting moisture content changes in the damaged area. More severe damage resulted in lower reflectance. Over time, tan theta initially rose, then decreased and stabilized. More severe damage led to greater tan theta. (3) In the 1255-1314 nm band, reflectance initially increased, then decreased and stabilized, reflecting temperature changes in the damaged area. More severe damage led to higher reflectance. Over time, tan theta first increased, then decreased, with more severe damage showing smaller tan theta. The study on the evolutionary pattern of the spectral features after the impact of 'Red Delicious' apples provides theoretical basis for more reliable detection of the initial minor damage of apples in the future.