Establishing quality parameters for Australian walnuts

Abstract

Australian walnuts are perceived to be of high quality; however, there has been no systematic process to describe walnut quality in Australia. A set of standard parameters could provide credible evidence for any claim of 'superior quality', as well as increasing the value of the industry by producing more nuts of the desired quality. A first step in the production of high quality walnuts is to develop a better understanding of what 'quality' represents and how that quality can be achieved. A project involving six walnut producers selected from different growing regions of Australia, aimed to identify factors that may influence walnut quality. Nuts were assessed at harvest for physical attributes (size, weight, kernel colour, shell and kernel defects) and at harvest and various times during postharvest storage for hedonistic qualities (texture, taste, rancidity, aftertaste). Tests for free fatty acids and peroxide value were conducted independently and approximately 3, 6 and 9 months after harvest. All peroxide values were below 2 and all free fatty acid values below or close to 0.2 indicating that the initial high quality had not deteriorated. Storage up to 6 months appears to have no adverse effect on walnut quality if the nuts remain in-shell. Some decline in walnut quality was evident by 9 months, suggesting that storage beyond that period may become an issue. Participants now have some baseline information for developing benchmarks for Australian walnut quality and a basis from which to further develop and establish walnut quality parameters.