With increasing walnut production in California, walnuts are stored for longer times. It is increasingly important to optimize storage conditions to reduce quality degradation. We examined the effects of temperature (5, 15, and 25°C) and relative humidity (20%, 40%, and 60% in year 1 and 40%, 60%, and 80% in year 2) on the rate of quality degradation of Chandler, Howard, Tulare, and Vina walnuts. The effects of harvest timing (early vs late) and storage as shelled or in-shell product were investigated. Later harvested walnuts had darker kernel color, and walnuts stored as kernels (shelled) had higher rates of kernel darkening, peroxide formation, and free fatty acid development than walnuts stored in-shell. Temperature had a significant effect on quality with faster degradation at higher temperatures. There was a significant interaction between temperature and relative humidity effects on quality. The effects of relative humidity were often insignificant at storage temperatures of 5°C, but were apparent at 15°C after 12 months of storage and at 25°C after six months. Chandler walnuts were also evaluated by a trained taste panel after 6 and 12 months of storage. Principal component analysis was used to compare taste, texture, and aroma attributes evaluated by the taste panel to indicators of walnut quality including water activity, moisture content, free fatty acids, peroxide value, hexanal content, and kernel darkening. Temperature was found to significantly impact walnut oxidation and perceived rancidity, and relative humidity affected walnut textural quality.
|Advisor:||Mitcham, Elizabeth J.|
|Commitee:||Brown, Patrick J., Donis-Gonzalez, Irwin R.|
|School:||University of California, Davis|
|Department:||Horticulture and Agronomy|
|School Location:||United States -- California|
|Source:||MAI 82/8(E), Masters Abstracts International|
|Subjects:||Horticulture, Food Science|
|Keywords:||Free fatty acids, Peroxide value, Relative humidity, Walnut, After harvest quality, California, Temperature effects|
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