Determination of the content of water and rice bran in solid media used for mushroom cultivation using near-infrared spectroscopy

Near-infrared spectroscopy (NIR) was employed for the simultaneous determination of the water and rice bran content in solid media used for mushroom cultivation. The solid media were prepared by addition of water to a mixture of sawdust with rice bran and wheat bran. The medium packed in a polyethylene bag was placed in a near-infrared spectrophotometer. The reflected rays, in the wavelength range between 400 and 2500 nm, were measured at 2 nm intervals. To obtain a calibration equation for water content, a simple linear regression was carried out on the near-infrared spectral data at 1450 nm and on the water content of a calibration sample set (sample number, n=113) obtained using dry-weight method. The values of the simple correlation coefficient and the standard error of calibration were 0.995 and 1.33%, respectively. On the basis of the result of a multiple linear regression on the content of rice bran in the solid media, a calibration equation using the second-derivative reflectance data at the wavelengths of 672 and 2100 nm was obtained, with the values of the multiple correlation coefficient and standard error of 0.978 and 1.73%, respectively. To validate the calibration equations obtained, water and rice bran content in the prediction sample set (n=56) not used for formulating the calibration equations were calculated using the calibration equations, and compared with the values obtained using the dry-weight method based on the mixing ratio. For both the water and rice bran content, excellent agreement was observed between the results of the conventional method and those of NIR method. The simple correlation coefficient and standard error of prediction mere 0.995 and 1.33% for water content and 0.975 and 1.84% for rice bran content. The content of water and rice bran in the solid media could be analyzed simultaneously by NIR. The NIR procedure was simple, and the operation time required to determine the content was only 5 min. These results indicate that NIR may be a useful method for monitoring the content of water and rice bran in solid media used for mushroom cultivation.