Review of sensor technologies for realtime process control of ethylene in citrus degreening

Abstract

Over 50% of Florida citrus marketed as fresh fruit is
degreened as the fruit has matured to a level above internal grade standards while the peel retains a high chlorophyl level. Accurate control and monitoring of ethylene in citrus degreening is essential since >10 ppm ethylene has been shown to enhance decay. To maintain citrus fruit quality, it would be advantageous to monitor and control ethylene levels as well as the standard parameters of temperature, humidity, and fresh air exchange in the degreening process. Three sensor techniques were evaluated for ethylene sensing; metal oxide semiconductor (MOS), non-dispersive infra-red (NDIR), and chemical luminescence (CL). The units were calibrated using gas chromatography equipped with a flame ionization detector (GC-FID). A linear relationship between the standard GC-FID laboratory procedure for the NDIR and CL sensing techniques was found. The CL unit was adapted for multiple location sampling.