Arai Nayuta, Miyake Masafumi, Yamamoto Kengo, Kajiwara Itsuro, Hosoya Naoki
Division of Mechanical Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo 135-8548, Japan.
Division of Human Mechanical Systems and Design, Hokkaido University, N13, W8, Kita-ku, Sapporo-shi 060-8628, Hokkaido, Japan.
Foods. 2021 Feb 3;10(2):323. doi: 10.3390/foods10020323.
Many methods based on acoustic vibration characteristics have been studied to indirectly assess fruit ripeness via fruit firmness. Among these, the frequency of the S vibration mode measured on the equator has been examined, but soft-flesh fruit do not show the S vibration mode. In this study, a Rayleigh wave is generated on a soft mango fruit using the impulse excitation force generated by a laser-induced plasma shock wave technique. Then, the flesh firmness of mangoes is assessed in a non-contact and non-destructive manner by observing the Rayleigh wave propagation velocity because it is correlated with the firmness (shear elasticity), density, and Poisson's ratio of an object. If the changes in the density and Poisson's ratio are small enough to be ignored during storage, then the Rayleigh wave propagation velocity is strongly correlated to fruit firmness. Here, we measure the Rayleigh wave propagation velocity and investigate the effect of storage time. Specifically, we investigate the changes in firmness caused by ripening. The Rayleigh wave propagation velocity on the equator of Kent mangoes tended to decrease by over 4% in 96 h. The Rayleigh wave measured on two different lines propagated independent distance and showed a different change rate of propagation velocity during 96-h storage. Furthermore, we consider the reliability of our method by investigating the interaction of a mango seed on the Rayleigh wave propagation velocity.
许多基于声学振动特性的方法已被研究，以通过果实硬度间接评估果实成熟度。其中，已对在赤道处测量的S振动模式的频率进行了研究，但软果肉果实并未表现出S振动模式。在本研究中，利用激光诱导等离子体冲击波技术产生的脉冲激发力，在软芒果果实上产生瑞利波。然后，通过观察瑞利波的传播速度，以非接触、无损的方式评估芒果的果肉硬度，因为它与物体的硬度（剪切弹性）、密度和泊松比相关。如果在储存过程中密度和泊松比的变化足够小，可以忽略不计，那么瑞利波的传播速度与果实硬度密切相关。在此，我们测量瑞利波的传播速度，并研究储存时间的影响。具体而言，我们研究成熟导致的硬度变化。肯特芒果赤道处的瑞利波传播速度在96小时内趋于下降超过4%。在两条不同直线上测量的瑞利波传播了不同的距离，并且在96小时的储存期间显示出不同的传播速度变化率。此外，我们通过研究芒果种子对瑞利波传播速度的影响来考虑我们方法的可靠性。
