NEAR-INFRARED SPECTROMETRIC METHOD FOR NONDESTRUCTIVE DETERMINATION OF SOLUBLE SOLIDS CONTENT OF PEACHES

A nondestructive method for measuring the soluble solids (SS) content of peaches [Prunus persica (L.) Batsch] was developed using near-infra red (NIR) spectrometry. NIR transmittance in the 800 to 1050 nm region was measured for four cultivars of peaches ('Blake', 'Encore', 'Red H aven', and 'Winblo'), over a period of three seasons (1993 through 199 5). Each fruit was scanned on both halves keeping the suture away from the incident light be am. Soluble solids contents of flesh samples ta ken from corresponding scanned areas were determined using a refractom eter. Multiple linear regression models using two wavelengths were dev eloped with second derivative spectral data and laboratory measurement s of SS content. Multiple correlation coefficients (R) for individual cultivar calibrations within a single season ranged from 0.76 to 0.98 with standard error of calibration (SEC) values from 0.35% to 1.22%. S elected spectra and corresponding SS data in individual cultivar calib ration data sets were combined to create season and cultivar calibrati on data sets to cover the entire range of SS contents within the seaso n or within the cultivar. These combined calibrations resulted in R va lues of 0.92 to 0.97 with SEC values ranging from 0.37% to 0.79%. Simp le correlations of validations (r) ranged from 0.20 to 0.91 and the st andard error of prediction (SEP) ranged from 0.49 % to 1.63 % while th e bias varied from -0.01% to -2.62 %. Lower r values and higher SEP an d bias values resulted when individual cultivar calibrations were used to predict SS levels in other cultivar validation data sets. Cultivar calibrations, season calibrations and the overall calibration predict ed SS content of all validation data sets with a smaller bias and SEP and with higher r values. These results indicate that NIR spectrometry is suitable for rapid nondestructive determination of SS in peaches. Feasible applications of the method include packinghouse sorting of pe aches for sweetness and parent and progeny fruit quality assessment in peach breeding programs. Using this technique fruit may be sorted int o two or three sweetness classes. The technique may also potentially b e extended to other fruit.