Near Infrared Transmittance Method for Nondestructive Determination of Soluble Solids Content in Growing Tomato Fruits

In soilless culture, control of nutrient solution is very important for production of the high quality tomato fruits. The control will be efficient by taking the information of internal properties of growing fruits into account. Therefore, nondestructive measurement method for these properties is highly required. Nondestructive near infrared (NIR) methods have already been used effectively in many crops such as mango, apple, peach, however, no studies have been reported on growing tomato fruit. In addition, tomato fruit has a great variation in internal structure that consists of flesh and pulp. It causes ununiformity in texture and chemical compositions within a fruit and hence significantly affects NIR spectra. Therefore, specially assembled NIR instrument is required for accurate nondestructive determination of constituents in the fruit. Three halogen lamps as a light source of the instrument illuminated almost the whole fruit surface from the upper side. Then the spectrum of transmitted light through the bottom of the sample was measured by spectrometer. The performance of this instrument was investigated by developing calibration model for determination of the soluble solids content (SSC) in the whole fruit from the spectrum. This method successfully determined the SSC of tomato fruits with correlation coefficient between predicted and actual values (r) of 0.91, standard error of performance (SEP) of 0.73%, and bias of 0.17%.