Exploring Near-Infrared and Raman Spectroscopies for the Non-Destructive In-Situ Estimation of Sweetness in Half Watermelons

Watermelons are in high demand for their juicy texture and sweetness, which is linked to their soluble solids content (SSC). Traditionally, watermelons have been sold as whole fruits. However, the decline in the mean size of households and the very large size of the fruits, together with high prices, mainly at the beginning of the season, mean that supermarkets now sell them as half fruits. For consumers, it is important to know in advance that the fruits that they are purchasing are of a high quality, based not only on external flesh colour but also on sweetness. Near-infrared spectroscopy (NIRS) and Raman spectroscopy were used for the in situ determination of SSC in half watermelons while simulating supermarket conditions. A handheld linear variable filter (LVF) device and an all-in-one (AIO) Process Raman analyser were used for the NIRS and Raman analysis, respectively. The excellent results obtained—including residual predictive deviation for prediction (RPDp) values of 3.06 and 2.90 for NIRS and Raman, respectively—showed the viability of NIRS and Raman spectroscopies for the prediction of sweetness in half watermelons.