Frequency index as related to maturity stage of Montong durian
1998
Anupun Terdwongworakul | Wichet Srichonpet | Kittidet Poniyom | Anek Sukcharoen (Kasetsart Univ., Bangkok (Thailand). Kamphaengsaen Campus. Kasetsart University Development and Research Institute. National Agricultural Machinery Center)
Free vibration technique (tapping and measuring of acoustic sound) for determining the resonant frequency in fruits was implemented for durian. Frequency index based on the resonant frequency (f) and mass (m) of the fruit was the emphasized parameter to be employed for following the maturity of durian. In the research, 30 durians of variety MONTONG from 6 trees (5 fruits each tree) were taken as the samples for the measurement. Each fruit was tapped on the trees and the measurement of resonant frequency was made. At the same time the volume of each fruit was also recorded and converted to the mass by multiplying with the density of similarly matured durian on the same tree. The measurement was made on the trees at weekly interval. The period of measurement took place about 55 days after flowering until the whole lot of samples were properly mature for harvesing (about 132 days). The primary investigation showed that f*[2) was related to m*[2/3) exponentially in durian samples measured on the same day (the same stage of maturity). This implied that for durians with similar stage of maturity the bigger fruit would yield smaller magnitude of resonant frequency and the trend was of exponential fahion. The exponential relationship between f*[2) and m*[2/3) was affected by the stage of maturity in such that the group of more mature durians resulted in greater rate of the exponential relation. Having established such relationship the frequency index was proposed as 2/3 f*[2)ln(m) which could reflect the rate of exponential decay. The frequency index, 2/3 f*[2)ln(m) was found to decrease significantly with an increase in days after blossom. The trend was statistically consistent with different trees.
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