Lycopene quantification in intact watermelon (Citrullus lanatus) using on-line near infrared spectroscopy

Fruits and vegetables are main source of natural antioxidant components. Antioxidants give protection against harmful free radicals and reduce rate of cancer and heart disease. The most efficient carotenoid antioxidant is lycopene. Lycopene is a natural pigment which protects the body by neutralizing the negative effects of oxidants. Red flesh watermelon is, togheter with tomato, the main food sources of lycopene as the plentiful carotenoid. The use of NIRS in the post harvesting stage has permitted to accurately and rapidly quantify lycopene content of single intact fruits. 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 4000-10000 cm-1 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 concentration, determined using HPLC (JASCO, Japan) as reference method, were 17.6-150.7 mg/kg of fresh pulp. The PLS model for watermelon could predict lycopene concentration with R2 of 0.877 and SECV of 15.68 mg/kg. External validation have confirmed predictive ability with R2 of 0.805 and SECV of 16.19 mg/kg for lycopene. This method can be reliably used for fast and reliable quantification of lycopene concentration in each intact single watermelon, providing an important issue for agri-food product valorisation using NIR technology.