QUANTIFICATION OF CAROTENOIDS IN INTACT WATERMELON (Citrullus lanatus) USING ON-LINE NEAR INFRARED SPECTROSCOPY

Fruit consumption is no longer merely a result of taste and personal preferences, but has been becoming a concern of health, due to the bioactive fruit nutrients content, including carotenoids, flavonoids, phenolic compounds and vitamins. Nowadays the major interest of carotenoids is principally related to their antioxidant action by scavenging oxygen radicals and reducing oxidative stress in the organism. A great interest has recently been focused on lycopene and beta-carotene, compounds responsible for red/orange colour in fruits and vegetables, due to their preventive activity against several pathologies, such as cardiovascular disease and some cancers types, such as prostate, gastrointestinal and epithelial. Red flesh watermelon is, together with tomato skin, the main food sources with lycopene as the most abundant carotenoid. Apart from this micronutrient, other carotenoids such as beta-carotene also are present in this fruit. In watermelon, lycopene and beta-carotene concentration increases consistently during ripening, up until the appearance of fully red flesh. The use of NIRS in the post harvesting stage has permitted to accurately and rapidly quantify lycopene and beta-carotene content of single intact fruits, simultaneously estimating also the soluble solids. 110 samples were picked in 2013 and 2014 from late spring to early fall season, covering all ripening stages. Each fruit was submitted to NIR radiation while transporting along the conveyor belt system at 3 different belt speeds (in the range 35-45 Hz) and at 6 different positions of fruits on the belt, in order to simulate when fruits randomly fall down on the belt from the collecting containers. 1650 spectra were collected in the 900-1700 nm with 5 nm interval using an on line diode array NIR instrument (NIROnLine, Buchi, Switzerland) and calibration/validation models were built with SX-Plus software (Buchi, Switzerland) on pretreated spectra (derivatives and SNV). External validation were performed with other new 35 samples. Calibration ranges of lycopene and beta-carotene concentration, determined using HPLC (JASCO, Japan) as reference method, were 17.6-150.7 mg/kg of fresh pulp and 1.5-15.1 mg/kg of fresh pulp, respectively. The PLS model for watermelon could predict lycopene concentration with R2 of 0.877 and SECV of 15.68 mg/kg, and -carotene concentration with R2 of 0.822 and SECV of 0.81 mg/kg. External validation have confirmed predictive ability with R2 of 0.805 and SECV of 16.19 mg/kg for lycopene and with R2 of 0.737 and SECV of 0.96 mg/kg for -carotene. Results for soluble solids prediction are satisfactory and consistent with those reported in literature. The significant linear correlations between spectral parameters and carotenoids concentration of samples suggest that this method can be reliably used for fast and reliable quantification of carotenoids concentration in each intact single watermelon, providing an important issue for agri-food product valorisation using NIR technology.