Authors

Abstract

The mechanical properties of walnuts play an influential role in the process of walnut shell-cracking. To determine the optimal mechanical properties of walnuts, the effect of moisture content (MC) on the mechanical properties of walnuts was investigated. The results showed that Rupture force (F), Rupture displacement (D), and Rupture energy (E) of walnuts decreased proportionally with a reduction in the MC. To select an optimal pre-treatment for enhancing the mechanical properties of walnuts prior to shell-cracking, the effects of radio frequency (RF) and hot air (HA) heating treatment to change the mechanical properties of the walnuts were examined. The results indicated that the heating treatments of walnuts could lead to a brittle and easily breakable shell, with the F decreasing from 231.99±34.31 N to 174.73±24.89 N, the D decreasing from 1.68±0.18 mm to 1.36±0.13 mm, and the E decreasing from 207.31±44.29 mJ to 119.47±25.99 mJ. The mechanical properties of walnut shells are optimized to the best condition with the application of either a 2-minute RF treatment, a 3-minute RF treatment, or an 8-minute HA treatment. Notably, RF heating is significantly more time-efficient compared to the HA treatment. Quality evaluation indicated that there were no significant (p > 0.05) changes in color values, hardness, and brittleness between the heat-treated walnut kernels and the untreated walnut kernels. Overall, the results obtained from this study demonstrate that RF heating treatment is an effective method for optimizing the mechanical properties of walnuts prior to shell-cracking, and the results may provide guidance for the design and improvement of walnuts shell-cracking processes.

Abstract in Chinese

核桃的力学性能是影响核桃破壳效果的重要因素。为了获取最优的力学性能，研究了含水率对核桃力学性能的影响。结果表明，核桃的破壳力、破壳位移和破壳能均随着含水率的降低而降低。为了确定核桃破壳之前最佳的预处理方法，研究了射频(RF)加热处理和热风(HA)加热处理对核桃力学性能的影响。结果表明，加热处理使核桃壳变脆易碎；其中，在RF 2min、RF 3min、HA 8min三种加热处理方法下，核桃的力学性能达到最优；并且与HA加热处理相比，RF加热处理大大缩短了加热时间。品质分析结果表明，加热处理后的核桃和未处理的核桃的颜色值、硬度和脆性没有显著变化（p>0.05）。本研究的结果表明，RF加热处理是优化核桃力学性能的有效方法，此研究结果可为核桃破壳工艺的设计和改进提供指导。