The Measurement of Soluble Solids Content in Snake Fruit (Salacca Edulis Reinw) cv. Pondoh Using A Portable Spectrometer

Abstract

In this research we reported the use of near infrared spectroscopy for nondestructive soluble solids content (SSC) measurement in intact snake fruit (Salacca edulis Reinw) cv. Pondoh. The spectra of 100 samples were acquired in the range of 300-1040 nm using an available, low cost portable spectrometer (VISNIR USB4000). The spectrometer used an array of linear CCD as a detector. The LS-1 Tungsten Halogen lamp is used as light source. This system is also equipped with a fiber optic. Snake fruits were placed on the sample holder and the spectra were measured using 100 ms of integration time and 50 scans for averaging. The spectra were acquired in two different positions in the middle of fruit. The total scanning time was 10 s for each fruit. The SSC of snake fruits were measured destructively following the spectra measurement using a digital refractometer. A portion of snake fruit flesh with associated with the point of spectra measurement was cut and juiced. Then the juice of snake fruit was placed on a digital refractometer. The SSC was quantified in Brix value. The trial free version of The Unscrambler V.9.1 was used as chemometrics tools to extract the useful information from the spectra. The calibration model was developed using Partial Least Squares Regression 1 (PLSR1) for three types of spectra, original, smoothing and second derivative spectra. The calibration model was evaluated using some parameters such as coefficient of determination (R2), standard error of prediction (SEP), bias between actual and predicted SSC value and ratio prediction to deviation (RPD) parameter. The possibility of using near infrared spectroscopy to measure SSC of intact snake fruit nondestructively was successfully demonstrated. The best calibration model with 3.32 of RPD value could be obtained.