Non-destructive detection of moisture content for Ginkgo biloba fruit with terahertz spectrum and image: A preliminary study

Ginkgo biloba fruit is a typical recalcitrant seed, which is apt to dehydrate and harden, thus losing its activity, edibility and medicinal value during storage. The non-destructive detection method was investigated for monitoring moisture content (MC) variation of Ginkgo biloba fruit based on the sensitivity of terahertz (THz) wave to liquid water. The THz spectra and images of intact Ginkgo biloba seeds and their slices with different MC were collected. The influence of MC on THz wave was analyzed through the time domain spectra and frequency signal of absorption coefficients. The seed with higher MC achieved lower amplitude of time domain spectrum and longer flight time because of strong absorption of MC to THz radiation. The exponential equations were developed between MC and absorbance coefficients at characteristic frequencies of 1.68, 2.66, 2.79 and 3.02 THz with determination coefficients (R2) of 0.99 and root mean square error of cross validation (RMSECV) of 0.3–0.4 %, respectively. In addition, the gap between seed kernel and shell appeared because the seed kernel shrank due to water loss with the decrease of MC, and the model between the gap ratio and MC was established by THz image with R2 of 0.95 and RMSECV of 4.06 %, respectively. The results indicated that THz spectroscopy and image provided a new method for monitoring MC of Ginkgo biloba seed.