Spectroscopic profiling of soluble solids content and acidity of intact grape, lime, and star fruit

Purpose Visible and near infrared spectroscopy have been applied widely in fruits quality assessment especially on the measurement of soluble solids content (SSC) measured in o Brix and acidity measured in pH. Spectroscopy technique has been applied on three botanically different categories of fruits, that is: imported Californian table grape, Mandarin lime and star fruit. The purpose is to examine the ability of spectroscopy technique to quantify internal quality parameters with very narrow variability due to the characteristics of the raw material analyzed. This work also presents comparative study on peak wavelengths that can best be used to calibrate SSC and pH of different types of fruits. Design/methodology/approach The effective wavelengths chosen for calibration development are compared with those selected by other researchers in similar experiments. NIR wavelengths 910 nm (C−H band) and 950 nm (O−H band) are the most important wavelengths for the prediction of SSC for all examined fruits while wavelengths 922‐923 nm and 990‐995 nm for pH. Visible wavelength 605, 675 and 654 nm can efficiently improve the SSC and pH prediction for grape, lime and star fruit, respectively. Findings The best prediction for SSC has been achieved with R 2 =0.953 and RMSE=0.182 for grape, R 2 =0.918 and RMSE=0.109 for lime and R 2 =0.957 and RMSE=0.354 for star fruit. The best prediction for pH has been achieved with R 2 =0.763 and RMSE=0.110 for grape, R 2 =0.841 and RMSE=0.073 for lime and R 2 =0.862 and RMSE=0.261 for star fruit. Originality/value Currently, the spectroscopy research conducted for the measurement of fruits qualities is conducted through wide range spectrometer. However, the peak responses are only located at specific wavelengths. Hence, the selection of wavelengths related to SSC and pH will allow the design of low cost instruments for the prediction of these internal quality parameters.