Comparison of New Zealand (South Island) and Australian (Tasmanian) walnut cultivars : an organoleptic and biochemical study : A thesis submitted in partial fulfilment of the requirements for the Degree of Master at Lincoln University

Abstract

Seven different cultivars of walnuts (Juglans regia L.) grown in Australia (Tasmania) were compared with 6 cultivars grown in New Zealand (Canterbury). A preliminary assessment of the physical attributes and taste of all the nuts was carried out by members of the New Zealand Walnut Industry Group. The overall assessment scores of the Tasmanian walnuts was 73 (out of 100) compared to 65 for walnuts grown in Canterbury. While most of the attributes between the two groups of nuts were similar, the overall crackout score of the Tasmanian nuts received a perfect score of 20 while the Canterbury walnuts scored a mean of 14 for all of the six cultivars. The two groups of walnuts were then subjected to organoleptic assessment using 59 untrained tasters. The tasters recorded their impressions of the taste and after taste of all the nuts using a five point hedonic scale. The overall taste and after taste scores for the Tasmanian and Canterbury walnuts were very similar but individual cultivars Earnscleugh, Vina and Fernette achieved higher scores for taste when compared with all of the other cultivars evaluated while Fernette grown in Tasmania was given the highest overall score for the attribute after taste. Overall the cultivar Fernette grown in Tasmania had the best mean scores for both taste (3.5) and after taste (3.5) which were significantly greater than all of the other cultivars. All the walnuts were subjected to general proximate analysis, individual fatty acid analysis, tocopherol and phytosterol profile, and total and free phenolic analysis. There were no conclusive differences between Australian and New Zealand grown walnuts when comparing the proximate analysis, fatty acid profile, tocopherol profile, phytosterol profile or phenolic analysis. This is the first time the total and free phenolic content of New Zealand and Australian walnut cultivars has been reported. The free phenolic levels ranged from 10.9 to16.6 mg gallic acid equivalents(GAE)/g dry weight(DW) of walnut kernel, for cultivars Kirwee and Howard respectively. The total phenolic level ranged from 14.0 to 24.7 mg GAE/g DW of walnut kernel, for cultivars Serr (New Zealand) and Vina (New Zealand), respectively. There were no unusual observations or statistical differences when comparing the organoleptic and biochemical parameters between the different walnut cultivars. A correlation between the organoleptic and biochemical results was performed which showed no statistically significant correlations between any of the parameters determined.