Gloss Evaluation of Curved-surface Fruits and Vegetables

Gloss measurements are used to evaluate the quality and appearance of a product, especially in cases where esthetic appearance is of importance. Most commercial glossmeters are designed for measuring products of flat surface and therefore are not suitable for food products because of their uneven, curved surface. A new generation of commercial glossmeters is recently available for confined areas, curved surfaces, and surfaces that are not uniform. This article provides a brief review of gloss measurement principles and methods for fresh fruits and vegetables. It reports on the gloss measurement of apples and other fresh products using a commercial glossmeter and a specially designed spectrometer-based gloss measurement prototype integrated with imaging and automatic sample positioning capabilities. Results showed that the prototype had a nonlinear relationship with standard gloss measurements. With the new setup, the gloss of apples was measured with the repeatability for 90% of the measurements being better than 16%, calculated as the ratio of the difference between maximum and minimum gloss values to the mean value in percent. Further research is needed to simplify the imaging/mechanical configuration and improve the coordinate calculation algorithm to achieve more accurate, repeatable gloss measurements.