The effect of storage conditions on the stability of peroxide values of New Zealand grown walnuts

Storage stability of three locally grown and produced walnut oils (wild, grafted, kernelz and Cultivar 149) was determined by laboratory testing of their peroxide values. Oils were stored at high (60 o C) and moderate temperatures (room temperature, 24 o C), either in the dark or in the light. Different coloured bottles and three levels of vitamin E addition (no addition; 60 mg addition per bottle; 180 mg addition per bottle) were used to give information about the effects of anti-oxidants and light on the oxidative rancidity of walnut oil. Peroxide value (PV) was used as an objective measurement of oxidation. The results indicated the tested walnut oils had a reasonably long shelf life probably due to their naturally high contents of antioxidants. Differences among oil types and storage conditions in storage stability could be determined by laboratory methods. Further studies to select a cultivar with optimum oil qualities and comparisons to hedonic and UV absorbence changes in the oil would be useful.