An adaptation of the American Oil Chemists' Society Official Method Cd 8-53 for determining peroxides in fats and oils using a 0.5-g sample is described. Comparisons of the Official Method and the small-scale method were performed by analyzing soybean oil samples spiked with t-butyl hydroperoxide and autoxidized soybean oil samples. A linear relationship between the Official Method and the small-scale method was obtained with an R 2 of 0.998. The small-scale method is sensitive, precise, and suitable for small sample sizes and uses only about 10% of the chemicals necessary for the Official Method.

The objective of this study was to measure and compare differences in oxidized products of oil extracted from unoxidized and oxidized walnuts using five different extraction methods: (i) mechanical pressing, or solvent extraction with (ii) hexane, (iii) methylene chloride, (iv) chloroform/methanol, or (v) supercritical carbon dioxide (SC-CO 2 ). Of the extraction methods evaluated, only chloroform/methanol and methylene chloride provided reasonable results for all parameters measured (total lipid yield, FA profile, PV, conjugated dienes, FFA content, and volatile content); however, chloroform/methanol extracted significantly greater levels of volatile compounds. The SC-CO 2 extraction with purified gas was simple and accurate for all data except collection of volatile compounds, as these materials are lost during the lipid extraction. Pressing was neither quantitative nor qualitative, and hexane extraction retrieved significantly lower levels of volatiles than the other methods, except for SC-CO 2 .

Supercritical carbon dioxide (SC‐CO2) was used to partially defat walnuts, and the oxidative stability of the extracted walnut oils was assessed. The SC‐CO2‐extracted oils were less stable during accelerated storage in the dark than was pressed walnut oil, as determined by PV, headspace analysis by solid‐phase microextraction, and sensory methods. The SC‐CO2‐extracted oils, however, exhibited greater photo‐oxidative stability than did pressed walnut oil by all of these methods, possibly because of the presence of chlorophyll in the pressed oil. Oxidative stability indices and tocopherol contents were significantly lower in the SC‐CO2‐extracted oils than in pressed oil.

English walnuts are popular because of their good taste, high n-3 FA content, and reported hypocholesterolemic effects. However, walnuts have a high fat content (~70% w/w) that is highly polyunsaturated, which contributes to oxidative instability. The objectives of this study were: (i) to use supercritical carbon dioxide (SC-CO 2 ) extraction to decrease the total fat content of walnuts, and (ii) to determine the effects of SC-CO 2 lipid extraction on the oxidative stability, flavor, and textural characteristics of the reduced-fat walnuts. The fat content of English walnut pieces was reduced by 25 and 40% with a pilot-scale SC-CO 2 extraction system. Full-fat, 25-, and 40%-reduced-fat walnuts were stored at 25 and 40°C for 8 wk. FA profiles were similar for residual oil in all treatments, and the profiles did not change with storage. PV and volatile compounds were significantly greater (P < 0.05) in full-fat walnuts than in reduced-fat walnuts at both storage temperatures. A trained sensory panel judged the reduced-fat walnuts to be less astringent and to have less walnut and rancid flavors. Fullfat walnuts had greater hardness than reduced-fat walnuts by both sensory and instrumental texture profile analyses. In general, reducing the relative fat contents of walnuts by 25% improved oxidative stability and maintained a high level of consumer acceptance.