Prediction of Total Soluble Solid Content in Intact and Cut Melons and Watermelons Using near Infrared Spectroscopy

There is currently a growing tendency for fruit to be classified and marketed in accordance with quality criteria. One parameter used to evaluate quality in melons and watermelons is total soluble solid content, measured by invasive analytical methods which are incompatible with current quality-assurance requirements for individual pieces of fruit. Use of near infrared (NIR) reflectance spectroscopy as a nondestructive technique for measuring total soluble solid content could therefore be of considerable interest to the fruit and vegetable sector. The present study assesses the use of a NIR diode array spectrometer for estimating total soluble solid content (°Brix) in intact and cut melons and watermelons. NIR calibration models were developed using two sets for each fruit, a 2006 set (N = 158) and a 2007 set (N=415) for melon samples and a 2006 set (N=77) and 2007 set (N = 183) for watermelon samples, grown in El Ejido (Almeria, Spain). The predictive ability of the calibrations developed were greater for cut fruit (SECV= 0.60°Brix, r² = 0.88, RPD=2.94 in melons and SECV = 0.49 °Brix, r² = 0.85, RPD=2.50 in watermelons) than for intact fruit (SECV = 0.98°Brix, r² = 0.76; RPD=2.05 in melons and SECV= 0.93°Brix, r² = 0.65, RPD = 1.69 in watermelons). This study demonstrates the value of NIR spectroscopy for grading cut melons and watermelons, intact melons and possibly intact watermelon fruits into categories of high, medium and low levels of sweetness.