Development Of A Non-Thermal Hurdle Technology For Cold Pasteurization Of Apple Cider - A Focus On Microfiltration

The effectiveness of a combined microfiltration (MF) and ultraviolet (UV) process on reduction microbial in apple cider was evaluated against pertinent pathogens and spoilage bacteria. MF using 0.8 [MICRO SIGN]m and 1.4 [MICRO SIGN]m pore size ceramic membranes was performed at 10 °C and a transmembrane pressure (TMP) of 155 kPa. The subsequent UV treatment was conducted at a low dose of 1.75 mJ/cm2. The combined MF and UV process achieved more than 5 log reduction of Escherichia coli, Cryptosporidium parvum and Alicyclobacillus acidoterrestris, for both membrane pore sizes. MF with 0.8 [MICRO SIGN]m pore size performed better than 1.4 [MICRO SIGN]m pore size on the removal of E. coli and A. acidoterrestris. The developed non-thermal hurdle treatment has the potential to significantly reduce pathogenic and spoilage organisms in apple cider, and help juice processors improve the safety and quality of their products. An optimization study concluded that a cross-flow velocity of 5.5 m/s and a TMP of 159 kPa are the optimal conditions for obtaining a high flux and low flux decline in cold MF of apple cider. A subsequent study was conducted to evaluate the effect of apple cider characteristics and membrane pore size on MF flux, under optimal MF conditions. Four membrane pore sizes were studied: 0.2, 0.45, 0.8 and 1.4 [MICRO SIGN]m. MF using pore sizes of 0.2 [MICRO SIGN]m and 0.45 [MICRO SIGN]m on one hand, and 0.8 [MICRO SIGN]m and 1.4 [MICRO SIGN]m on the other hand, resulted in similar particle sizes and turbidity of the MF juice, and similar flux behaviors. In order to clarify the role of pectin in fouling during MF of iii apple cider, pectin was added to a clarified base juice, at levels similar to those naturally occurring in apple cider. As pectin concentration increased, MF flux decreased, due to a large extent to the increase in viscosity with increasing pectin concentration. The MF flux for apple juice with added pectin was much higher than for untreated apple cider at the same pore size and a similar pectin concentration. This suggested that besides pectin concentration, the interaction of pectin with other juice components such as proteins and polyphenols and the formation of haze particles also have a significant contribution to fouling. Depectinization of apple cider improved MF flux using a 0.45 [MICRO SIGN]m membrane pore size, but had an adverse effect on the flux for 0.8 [MICRO SIGN]m and 1.4 [MICRO SIGN]m pore sizes. This could be explained by the different fouling mechanisms for different membrane pore sizes. Fouling for MF with 0.2 [MICRO SIGN]m and 0.45 [MICRO SIGN]m pore sizes is dominated by surface fouling and cake layer formation, while fouling for MF with 0.8 [MICRO SIGN]m and 1.4 [MICRO SIGN]m is dominated by pore constriction and pore blocking. It was proposed that the fouling mechanism depends on the relative size of membrane pores and the particles suspended in the feed, and there is a critical pore size where fouling transitions from the dominance of surface fouling and cake layer formation to the dominance of pore constriction and pore blocking. The conclusions of this work will help clarify some of the fundamental questions related to MF of apple cider, and at the same time offer some practical solutions for optimization and maximization of performance during MF of apple cider. i