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United States Department of Agriculture

Agricultural Research Service

Research Project: New Sustainable Processing Technologies to Produce Healthy, Value-Added Foods from Specialty Crops and their Co-Products

Location: Healthy Processed Foods Research

Title: Characterization of physical and aerodynamic properties of walnuts

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

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2013
Publication Date: 10/1/2013
Citation: Khir, R., Pan, Z., Atungulu, G.G., Thompson, J.F. 2013. Characterization of physical and aerodynamic properties of walnuts. Transactions of the ASABE. 57(1):53-61.

Interpretive Summary: The information related to physical and aerodynamic properties of walnuts at harvest is important for developing new approaches and methods for handling, dehulling, sorting and drying operations. Such approaches and methods could be used to improve the current processing practices for reducing energy use and increasing processing efficiency as well as enhancing product quality. The research concluded that the significant difference in the smallest axial dimension of walnuts with hull and those without hull could be used for separating these two types of nuts with less than 2% sorting error. Additionally, using air with terminal velocity of 10 m/s could achieve a complete separation of walnuts without hull from those with hull. For dehulled walnuts and walnuts without hull at harvest, using pneumatic method based on terminal velocity will be an effective method to sort walnuts into different groups with desired moisture ranges. The implementation of the research findings should lead to a significant energy saving, reduced transportation and labor expenses, and improved drying efficiency and end product quality.

Technical Abstract: The objective of this research was to study the physical and aerodynamic properties of freshly harvested walnuts. Measurements were carried out for three walnut varieties, Tulare, Howard and Chandler cultivated in California, USA. The nuts treated with and without Ethephon were collected from mechanical harvesters. The nuts were sorted into two categories, those with hull and those without hull before measuring nut dimension, density, terminal velocity and moisture content (MC). For nuts with a hull at harvest, all measurements were conducted before and after manual removal of the hulls and were characterized as undehulled and dehulled nuts. The effect of water washing on the nut density and terminal velocity was also determined. The results revealed that three axial dimensions (L, D1 and D2) were in the range of 42.2 - 59.4, 36.4 - 54.4 and 35.86 - 51.4 mm, respectively for walnuts with hull and 30.7 - 44.4, 27.7 - 42.2 and 25.1 - 40.5 mm, respectively for walnuts without hull. The average densities for dehulled and undehulled walnuts were 553±110, 716±106 and 878±102 kg/m3, respectively. The corresponding average terminal velocities were 7.9±1.2, 10.1±1.4 and 14.1±1.7 m/s. It was found that strong relationships existed between the MC versus the density and terminal velocity of individual nuts. A terminal velocity of 10 m/s can separate the dehulled from undehulled walnuts, and then the in-shell walnuts can be further sorted into groups with different MCs based on desired terminal velocities. This separation can improve processing and energy efficiency in handling and drying operations. There was no significant effect of ethephon treatment and water washing on the nut density and terminal velocity.

Last Modified: 07/26/2017
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