Oxidative Profile of Powdered Fruit Smoothies Collected in the Dehydration Chamber and the Cyclone during Pulse Spray Drying

Pulse Spray Drying (PSD) technology is proposed for powdering fruit smoothies (apple, orange and banana) with whey protein. A PSD pilot system with two successive powder collectors located in the dehydration chamber and cyclone was tested. The objective was to determine whether rehydrated smoothies from fine and coarse powders (FP and CP) exhibit a different oxidative profile. Both powders were characterized (granulometry, flowability, discolouration, wet properties and water solubility). Proximate composition and oxidative profile (colour changes, oxidation indexes, antioxidant vitamins and antioxidant status) were determined in the ready-to-eat (undried and rehydrated) smoothies. Due to its lower flowability, CP exited the drying chamber more slowly, where temperatures are highest. CP and FP showed differences for D (4,3) particle size, Carr Index, Hausner ratio, moisture content, water activity and CIELab colour, but not for water absorption and solubility. The ready-to-eat smoothies from both powders reached similar oxidation levels assessed by molecular markers such as 5-(Hydroxymethyl)furfural, available Lysine, L-ascorbic and dehydroascorbic acids or α-tocopherol. In contrast, product oxidation assessed by other indexes involving a large group of oxidizable compounds such as colour, lipid oxidation and, above all, antioxidant status, reflected that CP oxidizes more than FP during PSD. This different oxidative profile did not affect their rehydration properties, although both powders might present a different tendency towards oxidative deterioration during shelf-life. Thus, rehydrated smoothies might exhibit different quality traits.