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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Healthy Processed Foods Research » Research » Publications at this Location » Publication #274194
Title: Moisture-dependent color characteristics of walnuts

Author
item KHIR, RAGAB - Suez Canal University
item ATUNGULU, GRIFFITHS - University Of California
item Pan, Zhongli
item THOMPSON, JAMES - University Of California
item ZHENG, XIA - University Of California

Submitted to: International Journal of Food Properties
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2012
Publication Date: 11/21/2012
Citation: Khir, R., Atungulu, G., Pan, Z., Thompson, J., Zheng, X. 2012. Moisture-dependent color characteristics of walnuts. International Journal of Food Properties. 17(4):877-890.

Interpretive Summary: This research is aimed to characterize the shell color of walnuts based on their moisture content (MC) at harvest for different varieties under different harvesting conditions. The obtained results indicated the feasibility of performing of walnut sorting before the drying process. The sorting method should be implemented in industry for increasing the walnut drying capacity, reduce energy use and improve quality of walnut products.

Technical Abstract: Characterizing the shell color of walnuts based on their moisture content (MC) at harvest can provide valuable information for performing walnut sorting before drying. 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. The walnuts were sorted into two categories, namely with and without hulls at harvest. The CIE L*, a*, and b* color indices were measured to quantify the shell color of aforementioned categories after hull removal, and total color difference, hue angle (h*) and chroma (C*) values were calculated. The results indicated 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 32.9% compared to 13.86% of walnuts without hulls. The presence of hulls was a major factor affecting the color of walnut shell. The L* and 'E values are highly correlated with MC for both walnuts with and without hulls. Although the a* and b* indices did not change much with MC for each category, 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 hue angle and chroma relationships with MC were non-linear within the same category of walnuts either with or without hulls. The obtained results revealed the potential of using the relationship between color indices especially L* and 'E and walnut MC to sort walnuts before drying, which is essential to avoid overdrying, increase drying capacity, reduce energy use and obtain high quality walnut products.