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United States Department of Agriculture

Agricultural Research Service

Title: Moisture-dependent Color Characteristics of Walnuts

item Khir, Ragab
item Pan, Zhongli - John
item Atungulu, Griffiths
item Thompson, James
item Zheng, Xia

Submitted to: Proceedings for CIGR World Congress Meetings
Publication Type: Proceedings
Publication Acceptance Date: 6/13/2010
Publication Date: 6/13/2010
Citation: Khir, R., Pan, Z., Atungulu, G.G., Thompson, J.F., Zheng, X. 2010. Moisture-dependent Color Characteristics of Walnuts. Proceedings for CIGR World Congress Meetings.

Interpretive Summary: The manuscript reports an investigation of the relationship between the color characteristics of the shell and nut moisture content of individual walnuts. In addition, regression models are developed for predicting the walnut moisture based on shell color, which can be used for walnut sorting prior to drying.

Technical Abstract: Characterization of the relationship between the shell color of walnuts and their moisture content (MC) at harvest can provide valuable information to perform walnut sorting before the drying process. The objective of this study was to investigate the relationship between the color characteristics of the shell of walnuts and their MC. Measurements were carried out for three walnut varieties, Tulare, Howard and Chandler. Samples of walnuts were collected from the harvester at the first and second harvest with and without ethephon treatment. The walnuts were sorted into two categories, namely with and without hulls. The CIE L, a, and b color indices, were measured to determine the shell color of aforementioned categories, and total color difference, hue angle and chroma values were calculated. The results indicated that there is a huge variability on MC among individual walnuts. The MC of walnuts with hulls at harvest was much higher than that of walnuts without hulls. On average, the walnuts with hull had MC of 32.99 % compared to 13.86% of walnuts without hulls. The presence of hulls was a major factor affecting the shell color of walnuts. The L* and 'E values highly correlated with MC for both walnuts with and without hulls. Regression models were developed based on the correlations between MC and L* and 'E values. Although the a* and b* indices did not change with MC the a* values of walnuts with hulls were higher than those of walnuts without hulls. There was an overlap among b* values for walnuts with and without hulls. The obtained results revealed the potential of using the relationship between color indices and walnut MC to sort walnuts before drying process, which is essential to avoid overdrying, increase drying capacity, reduce energy use and obtain high quality walnut products.

Last Modified: 10/16/2017
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