Freeze drying versus Spray drying to obtain Grapefruit IntegroPectin powder

Background: IntegroPectin is a new family of citrus pectins of broad biological activity obtained via hydrodynamic cavitation of citrus biowaste carried out in water only. These pectins have already been isolated by freeze drying, a time-consuming and expensive procedure difficult to be scaled up. Since recently the spray drying technique has been greatly appreciated for food and pharmaceutical applications, this work proposes a comparison between Grapefruit IntegroPectin powders isolated via spray drying (SD) and via freeze drying (FD). Methods: A mini Spray Dryer B-290 with B-295 inert loop (Büchi) and a FreeZone 2.5 Liter freeze dry system (Labconco) were used. Dried powders comparison was carried out in terms of total phenolic content (Folin-Ciocalteu), amount of the most representative flavonoids (HPLC-DAD analysis), radical scavenging activity (DPPH assay), total protein content (Bradford assay) and pH on the re-dissolved powders. Results and discussion: the optimized SD process led to a very high yield (>95%) referred to the fully quantitative yield of FD process and resulted extremely quick and thus advantageous (30-50 min/100 mL of water extract versus 3 days/30 mL, respectively). The two resulting IntegroPectin powders displayed analogous Naringin and Hesperidin content and similar pH in water solution (≈4-5). The total phenolic content and the antioxidant power of the SD IntegroPectin were slightly higher than those of the FD powder. Instead, in the SD sample the protein content resulted nearly 4 times lower than the FD one, probably due to denaturation which might occur at the relatively high temperature required for the SD process. This could be favourable to achieve long-term protection of the biophenols contained in the powder. Conclusions: considering the broad-spectrum potentiality of these new pectins from citrus waste, the spray drying technique results effective, convenient and easily scalable with less technical effort and costs than the freeze drying process.