Absorption kinetics of oxygen scavengers

The oxygen (O-2) absorption kinetics of six commercial O-2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N-2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O-2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O-2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or -1.5 degreesC, and scavenger capacity on the O-2 absorption rate were determined. In addition, the effect of placing scavengers within over-wrapped trays within bags, was examined. Rates of O-2 absorption varied by factors of up to 2 between individual O-2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O-2 half-life when compared with those at higher temperatures, e.g. O-2 half-lives of 7.1 and 1.0 h at -1.5 and 25 degreesC, respectively, were obtained for one scavenger type. Shorter O-2 half-lives were obtained in air than in N-2 atmospheres at the same temperature, e.g. 02 half-lives of 1.0 and 3.3 h in air and N-2 at 25 degreesC, respectively, were obtained for one scavenger type. The O-2 absorption reactions were of first order for both high and low initial O-2 concentrations. However, O-2 concentration was the primary limiting factor for O-2 absorption in atmospheres having O-2 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 O-2 half-lives, indicating that the O-2 permeable film acts as an O-2 barrier when pack atmosphere has low O-2 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 O-2 absorption rate, storage temperature, and pack atmosphere (air/N-2/CO2).