Modeling high protein liquid beverage fouling during pilot scale ultra-high temperature (UHT) processing

Abstract

Ultra-high temperature (UHT) processing is where liquid foods are sterilized at temperatures at or near 135°C. Because of the relatively high temperature, UHT processes are known for developing severe foulants on heat exchange surfaces. Furthermore, there is ambiguity (and commercial variation) in the exact process temperature when UHT processing. Therefore, it was the goal of this research to quantify the effects of process temperature changes on fouling rates in a pilot UHT system. The research performed evaluated fouling when processing 20% (wt./wt.) reconstituted non-fat dry milk as a model high protein beverage. The variables of interest were process temperature (127, 132 and 138°C) and run time. Each thermal process was designed to maintain equivalent thermal processing of a model microbe (F0=7.5) by adjusting the hold tube length at each temperature. After a defined run time, foulant from the pilot system was extracted into a sodium hydroxide solution. Compositional changes in this solution were indirectly associated with the pickup of foulant from the pilot system. Statistical differences (α=0.05) in fouling rates were observes as a function of process temperature using 4 foulant indicators (active alkali, electrical conductivity, protein content and color). The temperature dependence of fouling rate fit significantly to Arrhenius models (r2 range 0.95–0.99) with activation energies ranging from 116.6 to 154.5 kJmol−1. Results provide evidence that reduction in process temperatures can significantly decrease fouling rates, therefore increasing product run times.