Oxygen scavengers independent of transition metal catalysts

#This invention relates to compositions for reducing the oxygen concentration present in an atmosphere or liquid (often referred to as oxygen scavenging). In one particular application, the compositions are used in or in association with food packaging.

#A wide variety of foods and other materials are susceptible to loss in quality during storage under atmospheric levels of oxygen. The damage can arise from chemical oxidation of the product, from microbial growth, and from attack by vermin—much of which may be avoided by reducing the oxygen availability in the environment of the materials. In the field of packaging, relatively low-oxygen atmospheres have traditionally been generated by vacuum packing and inert gas flushing. Such methods are not, however, generally applicable for various reasons. For example:

#soft porous foods such as cakes cannot be subjected to strong vacuum;

#FIG. 1: Photoreduction of 2-methyl-9,10-anthraquinone (0.075M in ethyl cellulose, heat sealed between two layers of PVDC-coated polypropylene). Spectra show the photoreduction of the sample under xenon lamp irradiation (0, 30, 90, 180, 300 and 600 seconds) and detail the decline of the peak at 327 nm, with a corresponding increase in the peak at 375 nm, as irradiation time increases.

#FIG. 2: Photoreduction of 2-methyl-9,10-anthraquinone (0.075M in ethyl cellulose, heat sealed between EVOH barrier laminate and SURLYN1601) under xenon lamp irradiation (0, 30, 90, 180, 300 and 600 seconds). The peak at 327 nm decreased with increasing irradiation time, while the peak at 375 nm increased until approx. 300s irradiation, when it began to decrease.

#FIG. 3: Reoxidation of reduced species in air after storage for 106 days under nitrogen. The reoxidation involves the gradual loss of the peak at 375 nm with a corresponding increase in the peak at 327 nm. The three spectra shown above correspond to the film sample reduced, and then after 1 day and 21 days left to oxidise.

#9,10-Anthraquinone, 0.05 g, and ethyl cellulose (degree of substitution, 2.5), 1.5 g, were dissolved in ethyl acetate, 12 ml. The solution was cast onto plastic coated glass to give a film 10-15μ thick when the solvent had evaporated. A sample of the film was placed in a nitrogen flushed spectrophotometric cuvette and the absorbance at 252. nm and 264. nm was measured.

#While still in the cuvette under nitrogen, the sample was irradiated for 20 seconds with light from a xenon lamp using a Suntest CPS instrument, and the ratio of absorbance at 254.8 to that at 264.3 measured. The sample was exposed to air for a total of 10 days to allow reoxidation of the anthrahydroquinone and/or the semi-quinone, which would result in the absorbance ratio returning towards its initial value. The results in Table 1 show that photoreduction occurs on irradiation, followed by reoxidation upon exposure to air. Slight shifts in Amax occurred with reduction and oxidation. 1 TABLE 1 Absorbance Ratio Treatment 254.3/264.3 252.4/264.3 252.8/264.3 None 2.10 Irradiated (20s) 0.93 3 days in air 1.44 6 days in air 1.49 10 days in air 1.50

#2-methyl-9,10-anthraquinone (hereinafter referred to 2-methylanthraquinone or MeAq), 0.0167 g, was dissolved in ethyl acetate, 9 ml, together with ethyl cellulose, 1.15 g, and a film was cast as in Example 1. The film was 20-30 μm thick. A strip of this film was placed between two layers of the PVDC-coated polypropylene, and the two outer layers were heat sealed together to form a flat package containing the ethyl cellulose layer with essentially no headspace.