3. Results and discussion
3.1. Effects of temperature, pressure and flow rate on lycopene yield
Table 1 shows the experimental design and the lycopene yields obtained under different testing conditions. A Box–Behnken model and three-dimension (3D) response surface (Fig. 1A–C) were also used for information. As can be seen, in general, the best results in terms of extraction yield were obtained working at the highest temperature and relatively high pressure and flow rate (31.25 lg/g on raw tomato skin in run four and 30.27 lg/g of raw tomato skin in run eight).The statistical model, representing the lycopene yield from tomato skin as a function of the independent variables within the region under investigation, can be expressed by the following quadratic equation: