Direct quantification of lycopene in products derived from thermally processed tomatoes: optothermal window as selective, sensitive and accurate method without the need for preparatory steps

The concept of the optothermal window (OW) is proposed as a reliable analytical tool to rapidly determine the concentration of lycopene in a large variety of commercial tomato products in an extremely simple way (the determination is achieved without the need for pretreatment of the sample). The OW is a relative technique as the information is deduced from the calibration curve that relates the OW data (i.e., the product of the absorption coefficient ß and the thermal diffusion length µ) with the lycopene concentration obtained from spectrophotometric measurements. The accuracy of the method has been ascertained with a high correlation coefficient (R = 0.98) between the OW data and results acquired from the same samples by means of the conventional extraction spectrophotometric method. The intrinsic precision of the OW method is quite high (better than 1%), whereas the repeatability of the determination (RSD = 0.4-9.5%, n = 3-10) is comparable to that of spectrophotometry.