14B-17

R. MAO¹, J. TANG¹, A. Buranasompob², B. G. Swanson², and J. D. Hansen³. (1) Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, (2) Department of Food Science and Human Nutrition, Washington State University, Pullman, WA 99164-6376, (3) Yakima Agricultural Research Laboratory, USDA-ARS, Wapato, WA 98951

JUSTIFICATION: International agreements and environmental regulations will likely force the US multi-billion dollar nut industry to abandon the use of methyl bromide fumigant for control of insect pests. Alternative phytosanitation and quarantine treatments are needed for domestic and international markets. New thermal treatments are being investigated because of the uncertain future of other chemical fumigants and increasing public concern over environmental and health issues. A delicate balance must be determined between killing insects and minimizing thermal impact on product quality. Our previous research indicated that short-time microwave or RF heating was an effective way to control insects infesting walnuts and almonds. However, nuts are vulnerable to becoming rancid. Information is needed regarding the effect of heat treatments on rancidity and shelf-life.

OBJECTIVES: Our objectives were to study the rancidity and the shelf-life of shelled walnuts and almonds as affected by short-time heat treatments.

METHODS: Shelled nuts were heated at 55°C for various times and stored at 35°C for 10 days to simulate the shelf-life at 4°C for approximately one year. Oil was pressed from the nuts and kept at -25°C until analysis. Free fatty acid, peroxide, p-anisidine, and 2-thiobarbituric acid values of the oil were used to characterize the rancidity and to correlate with sensory evaluation.

RESULTS: Any single test was not able to represent the rancidity. Overall evaluation of multiple test results revealed that heating at 55°C for 24h and storage at 35°C for 10 days had affected the rancidity slightly. The results suggest that the short-time heat treatments that are sufficient to kill insect pests did not affect the quality of the nuts and did not reduce the normal season-to-season shelf-life.

SIGNIFICANCE: This research provides information on the quality of walnuts and almonds as affected by short time heat treatments for control of insect pests.