The analysis of the fatty acid profile of New Zealand grown walnuts: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Science Honours at Lincoln University

Abstract

The proportions of oleic (C18: 1), linoleic (C18:2), and linolenic (C18:3) acids relative to one another in walnut oil, is important to the economic value of the walnut. Low linoleic and linolenic acid content may improve the shelf life and cooking qualities of the oil and the nut. But a higher linolenic acid level in the oil and nut, might be more desirable, because of the recent findings, that the consumption of linolenic acid and other polyunsaturated fatty acids, may be nutritionally beneficial to humans. Experiments on the suitability of walnuts for particular end uses may, therefore, require fatty acid profile analysis. Walnut oil was extracted from 14 different walnut cultivars sourced from 3 different sites and analysed by gas liquid chromatography. The fatty acid profiles of ten of these cultivars were compared, before and after storage. It was concluded that these ten different walnut cultivars had significantly different fatty acid profiles and bond ratios, but the three months storage had no consistent effect. The walnut cultivar 152 had a C18:3 content of 15.38% whereas the cultivar 143 had a C18:3 content of 9.95 %. The cultivar 152 had a C18: 1 content of 13.8 %, whereas the cultivar 143 had a Cl8: 1 content of 26.05 %. The cultivar 152 had a bond ratio of 182.46 which is higher than 143 which had a bond ratio of 165.77. The fatty acid profiles of walnuts sourced in California USA and Canterbury New Zealand were determined, with significant differences in the fatty acid composition and bond ratio being found. Hartley grown in California USA, had a C 18:2 content of 61.8 % and a C18: 1 content of 15.22 %. Hartley grown in Canterbury New Zealand, on the other hand, had C18:2 content of 58.75 % and a C18: 1 content of 18.41 %. The Canterbury grown Hartley had a bond ratio of 172.72, whereas the Hartley grown in California had a bond ratio of 175.35. The fatty acid profiles of three different cultivars from two different sites within Canterbury New Zealand were determined. It was found that the fatty acid composition of the walnuts, aid not differ significantly between sites. The fatty acid composition of ten walnut cultivars, sourced from the same site within Canterbury New Zealand, but from two different years was determined. No year to year main effect was found but, a significant interaction between the fatty acid composition or bond ratio and year was found. The cultivar 1199 had a C18:2 content in 1994 of 59.28 % and a C18:2 content in 1995 of 55.51 %. The cultivar Vina had a bond ratio of 177.5 in 1994 and a bond ratio of 173.2 in 1995. Blending of cultivars and environment selections may be needed to achieve a stable fatty acid profile for walnuts. If marketing requirements deem this to be essential, selective breeding may also modify walnut fatty acid profiles to suit particular needs.