Increasing theturbidity up to 2400 Nephelometric Turbidity Units (NTU) negatively
impacted the effectiveness of the treatment resulting in
lower log reductions. Nonetheless, this evaluation was performed
using a laminar flow rate, while a turbulent flow regime is a condition
required by the FDA to ensure the safety of the UV treated
juices (FDA, 2013). Murakami et al. (2006) evaluated the same effect
in a model apple juice solution with turbidities between 0.5
and 858 NTU and treated with UV doses ranging from 2 to
36 mJ cm2
. A significant effect of SIS on the UV inactivation of
E. coli K-12 was also observed and explained by the seeming
layering of light penetration, which causes the portion of the
product closest to the UV-light source to be sterilized effectively,
while the farther portion may not be equally treated. However, the
effect of turbulence was not evaluated and the extrapolation of the
results for juices with higher solids content has some limitations.
Similarly, very little information has been published regarding the
change in color of apple juice (browning) due to enzymatic reactions
on the efficiency of UV light treatments. Koutchma et al. (2004)
studied this effect adding caramel (from a commercial carbonated
beverage), to a model solution and found that increasing the absorbance
of the solution resulted in lower inactivation levels of E. coli K-
12. However, caramel is not naturally found in apple juice, the results
of the study were not related to the actual time after apple pressing
and corresponding color change during juice manufacturing, and its
impact on the productivity of the UV system was not assessed.
This study aims to address some of the existing gaps in the
literature regarding the influence of the presence of insoluble solids
and the darkening of apple juice after apple pressing on the
effectiveness of the UV treatment of cloudy apple juice when using
a commercial-scale processing reactor. The elucidation of this information
will contribute to understand how these variables may
affect the inactivation of E. coli and the productivity of UV light
systems when treating apple juice and similar liquid products.