Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Food Science and Human Nutrition

First Advisor

Pamela J. White


During the past several years, walnuts have gained popularity because of their good taste, high n-3 fatty acid content, and reported hypocholesterolemic effects. Two negative components of walnut consumption are the relatively high fat content of this commodity (~70%), and the lack of oxidative stability caused by the high level of fat and its polyunsaturated nature. The objectives of this study were to: (1) use supercritical carbon dioxide (SC-CO 2) extraction to decrease the total lipid content of walnuts, thus improving dietary fat content, and (2) determine the effects of SC-CO2 lipid extraction on the oxidative stability, flavor and textural characteristics of the partially defatted walnuts initially after extraction and during storage. The relative lipid content of English walnut pieces was reduced by 25 and 40% using a pilot-scale SC-CO2 extraction system. Fullfat, 25 and 40% partially defatted walnuts were stored at 25°C and 40°C for 8 weeks. Oxidative stabilities of walnut oils, a by product walnut defatting, were also determined under accelerated conditions, and compared with a commercially prepared pressed walnut oil. Fatty acid profiles were not different for partially defatted and full-fat walnuts or SC-CO2 and pressed walnut oils. Peroxide values and volatile compounds were significantly greater in full-fat walnuts than in partially defatted walnuts at both storage temperatures. Partially defatted walnuts were less astringent, and had less painty and rancid flavors, as judged by a trained sensory panel. Full-fat walnuts were determined by both sensory and instrumental texture profile analysis to have greater hardness than partially defatted walnuts. Consumer acceptance hedonic scores of 25% reduced fat walnuts were not significantly different than full-fat walnut scores (6.5 and 7.0, respectively). The SC-CO2 extracted oils were less stable during accelerated storage in the dark than was pressed walnut oil, as determined by peroxide value, volatile analysis and sensory methods. Photo-oxidative stability was greater in the SC-CO2 extracted oils than pressed oil, probably because of the presence of chlorophyll in the pressed walnut oil. In general, reducing the relative fat contents of walnuts by 25 and 40% improved the oxidative stability while maintaining desirable flavor characteristics.



Digital Repository @ Iowa State University,

Copyright Owner

Tammy Dawn Crowe



Proquest ID


File Format


File Size

147 pages