Efficacy of UV-TiO2 photocatalysis technology for inactivation of Escherichia coli K12 on the surface of blueberries and a model agar matrix and the influence of surface characteristics

Abstract

Surface disinfection of fresh blueberries is an important food safety challenge due to the delicate texture and short shelf life of these small fruits. A newly designed water-assisted photocatalytic reactor was developed for disinfection of fruits with a delicate texture and complex surface characteristics. Efficacy of UV-TiO2 photocatalysis was evaluated in comparison with UV alone for inactivation of Escherichia coli K12 (as a surrogate for Escherichia coli O157:H7) inoculated onto the surface of the blueberry skin, calyx, and an experimentally prepared agar matrix that was used as a model matrix. Influence of surface characteristics such as surface hydrophobicity and surface free energy on bacterial adhesion were also investigated. The initial bacterial population on all surfaces was approximately 7.0 log CFU/g. UV-TiO2 photocatalysis (4.5 mW/cm2) for 30 s achieved comparatively higher bacterial reductions of 5.3 log and 4.6 log CFU/g on blueberry skin and agar matrix surfaces, respectively, than 4.5 log and 3.4 log CFU/g reductions for UV alone (6.0 mW/cm2). Total phenolic and total anthocyanin contents of fruits were significantly increased after both UV-TiO2 and UV treatments, compared with water washed control fruits. UV-TiO2 photocatalysis technology is a non-chemical and residue-free method with reduced water usage for surface disinfection of fresh blueberries.