On‐Line Sterilization of Cheese Whey Using Ultraviolet Radiation

Abstract

The effectiveness of ultraviolet radiation for on-line sterilization of cheese whey was investigated. The effects of flow rate and residence time on the performance of three UV reactors having different gap sizes (18, 13, and 6 mm) were studied. Six flow rates and six residence times were tested with the three UV reactors. The cheese whey used in this study had a very high turbidity (4317 NTU), very poor transmittance in the UV radiation germicidal range ( approximately 0%), and high percentage of large solid particles ( approximately 20% > 100 microm). Although the cheese whey physical characteristics showed low probability of sterilization using UV radiation, the study showed that UV radiation can be used on-line to sterilize cheese whey if the proper reactor gap size and the appropriate residence time are used. There were combined effects of the flow rate and gap size. The cell removal efficiency increased with increases in residence time and decreases in the UV reactor gap size. Removal efficiency of 100% was not achieved in this study with the first UV reactor (18-mm gap size), whereas 100% removal efficiency was achieved with the second (13-mm gap size) and third (6-mm gap size) UV reactors at residence times of 2.0 and 0.5 h, respectively. The microbial decay rates achieved in this study were 4.94, 7.62, and 20.9 h(-)(1) using the first, second, and third UV reactor, respectively. Residence times of 3.3, 2.1, and 0.8 h would be required to completely destruct a microbial population of 5.95 x 10(6) cells/mL using the first, second, and third UV reactors, respectively. Although cheese whey sterilization using UV radiation seems to be a good alternative to pasteurization, increases in cheese whey temperature resulted in lamp fouling. If online sterilization is to be used, the fouling problem should be investigated and a maintenance scheme for the UV reactor should be developed.

Reduced fouling and enhanced microbial inactivation during online sterilization of cheese whey using UV coil reactors in series

“…Cairns [44] proposed fouling to be a net process of loading and removal of UV absorbing organics and/or organics present in the liquid medium and suggested adsorption as one mechanism of fouling. While using cheese whey for online sterilization, Mahmoud and Ghaly [17] found a rubber like material on the quartz tube, which was morphologically homogeneous and consistent along whole lamp. They related lamp fouling to the increases in the cheese whey temperature.…”

“…McDonald et al [29] stated that liquid in the UV reactor must have sufficient residence time and turbulent mixing to achieve dose equilibrium. Mahmoud and Ghaly [17] while sterilizing cheese whey by UV found that the cell removal efficiency increased with increase in residence time (decrease in flow rate). The destruction efficiency in the single coil reactor increased from 60.77% at the flow rate of 5 mL/min (168 min residence time) to 99.98% at the flow rate of 30 mL/min (a 28 min residence time) and then decreased with increases in the flow rate reaching 46.2% at the flow rate of 70 mL/min (a 12 min residence time).…”

“…The outlet temperature reported in the literature for various UV reactors varied from 10 to 62.8°C [17,31,39,40]. According to environmental technology verification program conducted by EPA [41] on UV reactors produced by Trojan Technologies Incorporated (Canada), the temperature of the effluent will vary depending on the flow rate and the reactor geometry.…”

“…In order to save time while ensuring complete destruction of micro-organisms, continuous sterilization technique for cheese whey using UV-C radiations has been suggested by Mahmoud and Ghaly [17] and Singh and Ghaly [18].…”

“…Fouling (progressive decline in efficiency with time due to accumulation of deposits onto a transfer surface) has been found to be a major factor limiting the efficiency of conventional UV reactors mainly due to: (a) lack of mixing, and (b) high temperatures inside the reactors [17]. Dean flow (the double spiral motion produced by a gradual bend in a closed passage) has been used to reduce fouling [19,20] and provide effective means for heat and mass transfer enhancement [21] in helical and coiled tubes.…”