Development of sensor system for real-time measurement of respiration rate of fresh produce

Abstract

Monitoring respiration as rates of either O2 consumption or CO2 production is an important tool to optimise the design of packaging systems or to maintain optimal conditions inside storage systems for fruit and vegetables. Currently, respiration rates are mostly measured by gas chromatography or headspace gas analysers. Both these methods are manual and, for analysis, draw a considerable amount of gas from the system. Thus, they risk lowering the air pressure inside the storage and packaging volumes. In this study, a compact (free volume of 3.3 L) and modular respirometer based on a respiration measuring sphere (RMS88) was developed, which consisted of one O2 (0–25%) and two CO2 sensors (0–0.5% and 0–5%) for continuous real-time monitoring of gas concentrations and respiration rates of fresh produce. This system was tested under different conditions and respiration rates of strawberries were measured. At first, the system was tested without and with flushing of ambient air (every 6 h at 5 L/min) inside the respirometer at 10 °C. The system was further tested with strawberries stored under modified atmospheric conditions and flushing (every 5 h at 5 L/min) with stepwise reductions of O2 from 21% to 16%, 8%, 4%, 2%, and 1% O2 (balanced by nitrogen). Additionally, the developed system was tested under in-situ conditions for strawberries stored inside respirometer, kept in two separate controlled atmosphere (CA) metal chambers at 10 °C and 20 °C respectively. In addition, the respiratory quotient (RQ) of strawberries was calculated from the respective O2- and CO2-based respiration rates at all storage conditions. The modular respirometer proved to be a useful system for rapid, high accuracy and real-time measurement of respiration rates of fresh produce during time windows of several days.