Absorption kinetics of oxygen scavengers

Abstract

The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or −1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over‐wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half‐life when compared with those at higher temperatures, e.g. O2 half‐lives of 7.1 and 1.0 h at −1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half‐lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half‐lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over‐wrapped trays within bags had up to 12 times longer O2 half‐lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2).