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Size and Moisture Distribution Characteristics of Walnuts and Their Components

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Abstract

The objective of this study was to determine the size characteristics and moisture content (MC) distributions of individual walnuts and their components, including hulls, shells, and kernels under different harvest conditions. Measurements were carried out for three walnut varieties, Tulare, Howard, and Chandler cultivated in California, USA. The samples for each variety were collected from the harvester at the first and second harvest of nuts treated with and without ethephon. The nuts were sorted into two categories as with hulls and without hulls before conducting dimension and MC measurements. The results showed that there was a wide range of size distribution for nuts with and without hulls and a huge variability in moisture content among individual nuts at harvest. The average MC of nuts with hulls was much higher than that of nuts without hulls for all tested varieties. The nuts with hulls had an average moisture content of 32.99% compared to 13.86% for nuts without hulls. Also, the shell moisture content was much higher than kernel moisture content. On average, the differences in moisture content between shell and kernel was 11.56% for nuts with hulls and 6.45% for nuts without hulls. There was no significant deference in hull MC between the first and second harvest for the studied varieties. Based on the regression analysis, it was observed that strong relationships exist between the MC of shells and kernels. The obtained results provide information for designing and developing new handling and processing equipments, especially for increased drying capacity, reduced energy use, and obtaining high-quality walnut products.

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Abbreviations

MC:

Moisture content (in percent)

SMC :

Shell moisture content

MCwb :

Moisture content, percentage of wb

Φ:

Sphericity

L :

Major diameter or length, in millimeters

W i :

Initial weight (in grams)

D 1 :

Intermediate diameter or width (in millimeters)

W d :

Dry weight (in grams)

D 2 :

Minor diameter or thickness (in millimeters)

W si :

Shell initial weight (in grams)

D g :

Geometric mean diameter (in millimeters)

W sd :

Shell dry weight (in grams)

h1 :

First harvest

W ki :

Kernel initial weight (in grams)

h2 :

Second harvest

W kd :

Kernel dry weight (in grams)

K mc :

Kernel moisture content

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Acknowledgments

The authors thank the California Walnut Board for its financial support and Cilker Orchards for their support with walnut samples. The research was conducted at the Western Regional Research Center of USDA-ARS and Department of Biological and Agricultural Engineering, University of California, Davis, USA.

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Authors and Affiliations

  1. Department of Biological and Agricultural Engineering, University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA

    Ragab Khir, Zhongli Pan, Griffiths G. Atungulu, James F. Thompson & Dongyan Shao

  2. Processed Foods Research Unit, USDA-ARS-WRRC, 800 Buchanan St, Albany, CA, 94710, USA

    Zhongli Pan

  3. Department of Agricultural Engineering, Faculty of Agriculture, Suez Canal University, Ismalia, Egypt

    Ragab Khir

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  1. Ragab Khir
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  2. Zhongli Pan
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  3. Griffiths G. Atungulu
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  4. James F. Thompson
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  5. Dongyan Shao
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Correspondence to Zhongli Pan.

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Khir, R., Pan, Z., Atungulu, G.G. et al. Size and Moisture Distribution Characteristics of Walnuts and Their Components. Food Bioprocess Technol 6, 771–782 (2013). https://doi.org/10.1007/s11947-011-0717-1

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  • DOI: https://doi.org/10.1007/s11947-011-0717-1

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