Thermal processing extends the shelf life of fruit and vegetables products by inactivating microorganisms and enzymes. The effect of a pasteurization (P) treatment, 90 ± 2 °C for 35 s, provided by continuous semi-industrial microwave (MW) under different conditions (high power/short time and low power/long time) or conventional pasteurization (CP) on orange-colored smoothies and their changes throughout 45 days of storage at 5 °C were investigated. Results indicated that vitamin C and antioxidant capacity (FRAP) in CP decreased dramatically in comparison with the unheated and MWP smoothies. On the contrary, all heating treatments increased the contents of total phenolic compounds and carotenoids. Based on the sensory quality and microbial counts, the shelf life of all those heated smoothies reached 45 days. No Listeria monocytogenes growth was found and all microbial counts were below the European legal limits (2007). MWP as compared to the CP method led to a greater reduction of mesophilic bacteria after 45 days at 5 °C (3.7 log cfu g-1 for CP and 1.6 log cfu g-1 for MWP). The highest power and the shortest time MWP treatments (3600 W for 93 s), resulted into better preservation of FRAP and vitamin C.
Keywords: Beverage; Bioactive compounds; Heat treatment; Microbial counts; Quality attributes.