UV-C treatment of soymilk in coiled tube UV reactors for inactivation of Escherichia coli W1485 and Bacillus cereus endospores

Coiled tube UV reactors were used to investigate the influence of tube diameter (1.6 mmID, and 3.2 mmID) and Reynolds number (Re) to inactivate Escherichia coli W1485 and Bacillus cereus spores in raw soymilk (RSM). Four levels of Re (343, 686, 1029 and 1372) were tested in RSM inoculated separately with each bacterium and treated in the UV reactors at a constant residence time of 11.3 s with UV-C dose of 11.187 mJ/ cm2 at 253.7 nm. Inactivation efficiency of both microorganisms increased with Re. Maximumreductions of 5.6 log10 CFU/ml of E. coli and 3.29 log10 CFU/ml of B. cereus spores were achieved in the 1.6 mm ID UV reactor. Inactivation efficiency was higher in the 1.6 mm ID UV reactor than the 3.2 mm ID UV reactor for both the organisms. Effect of UV-C light on lipid oxidation of untreated RSM, measured as malondialdehyde and other reactive substances (MORS) content, was much higher (95 nmol/ml) than the UV-treated (58 nmol/ml) and thermally pasteurized (55 nmol/ml) RSM during the storage period of 7 days. The UV-C treatment can be effectively used for reducing E. coli cells and B. cereus spores in soymilk without compromising its quality

Impact of UV-C processing of raw cow milk treated in a continuous flow coiled tube ultraviolet reactor

Raw cow milk (RCM) was treated in a continuous flow coiled tube ultraviolet reactor at the Reynolds number (Re) of 713 for a residence time of 17 s with cumulative UV-C dose of 16.822 mJ/cm2.  SPC in RCM was reduced by 2.3logs at these conditions.  Sensory analysis of milk samples was conducted using triangle test.  UV-C treated RCM and untreated RCM was compared with the fresh RCM (control) using triangle test method of olfactory sensory analysis right after the UV treatment and during storage periods (1, 3, 7 d) at 4℃.  There were no significant differences among the odor of UV-light-treated, untreated, and control, right after the UV treatment.  Perceivable change in the odor of UV-treated and untreated RCM compared to the fresh RCM was observed on the 3rd and 7th days after treatment.  There was no significant difference between the malondialdehyde and other reactive substances (MORS) content in untreated and fresh milk right after the treatment and during storage.  Lipid oxidation products content of UV-treated RCM was significantly higher than that of the fresh or untreated RCM.Keywords: raw cow milk, ultraviolet processing, UV-C treatment, sensory test, lipid oxidation substance

Design of Dean flow Ultraviolet (UV) reactors and testing their efficacy for inactivation of Escherichia coli W 1485 and Bacillus cereus spores in milk

Consumer demand for fresher foods has necessitated the use of non-thermal technologies in processing milk. Two Dean Flow UV reactors (1/16 ID × 1/32 Thick & 1/8 ID × 1/32 Thick) were designed in the laboratory. The objective of this study was to examine the efficacy of designed UV reactors at four levels of Reynolds numbers (Re) on inactivation of Escherichia coli W 1485 cells and Bacillus cereus spores in raw cow milk (RCM), commercially processed skimmed cow milk (SCM) and raw soymilk (RSM). RCM, SCM and RSM were inoculated separately with E. coli W 1485 and B. cereus spores and were treated through the designed reactors for a residence time of 11.3 ± 0.1 s, equivalent to an UV dose of 0.05 J/ml in 1/16 ID reactor and 0.02 J/ml in 1/8 ID reactor. Four levels of Re were tested in the range of 181-1372. The influence of tube diameter (thickness of milk exposed to UV) and Re (indicator of turbulence) at constant residence time (11.3 ± 0.1 s) on inactivation of both the bacteria in both the UV reactors was analyzed using two-way ANOVA with proc GLM in SAS software. E. coli was inactivated to non-detectable levels (≥7.8 log10 CFU/ml) in SCM from the second level of Re (532.2) in 1/16 ID reactor. E. coli was also inactivated significantly (\u3e 5logs) in RSM at the highest Re (1372) but this was not achieved in the case of RCM (712.7). Increasing the residence time to 14.2 s or greater (17 s) (equal to UV dose of 0.06 and 0.08 J/ml) inactivated E. coli cells to non-detectable levels in RCM using 1/16 ID reactor at the highest level of Re (712.7). Reduction of E. coli cells were in the range of 0.45-7.78 logs whereas B. cereus spores were in range of 1.06- 3.29 logs in all types of milk used in this study. The interaction effect of tube diameter and Re was statistically significant for E. coli cells in RCM, and SCM; B. cereus spores in SCM, and RSM (p \u3c 0.05) whereas this was statistically non significant for E. coli cells in RSM and B. cereus spores in RCM (p \u3e 0.05). Main effects of Reynolds number, and tube diameter were statistically significant (p \u3c 0.05) on inactivation of B. cereus spores in RCM and E. coli cells in RSM. Inactivation efficiencies for both bacteria were higher in 1/16 ID reactor than 1/8 ID reactor. Using the 1/16 ID reactor at highest level of Re (RCM Re = 712.7, RSM Re = 1372), inactivation of standard plate count (SPC) present in RSM and RCM, and lipid oxidation during storage period (0, 1, 3 and 7 days) were measured. Inactivation of SPC in UV-treated RSM (3 logs) was lower than thermal pasteurization at 72°C for 20 s (7 logs). In case of RCM, the SPC was inactivated to 1.9 logs from 4.2 logs. Sensory evaluation (olfactory) of UV treated, untreated (milk passed through the 1/16 ID reactor while the UV lights turned off), and fresh RCM (control) suggested no change in flavor after treatment and upto 1 day after storage in refrigerated condition, but a perceivable change in the quality of UV treated and untreated cow milk were observed during the 3rd and 7th days when compared with fresh RCM (milked same day). RCM was treated with different UV dose levels (0.04, 0.05, 0.08, 0.12 and 0.16 J/ml) to examine the effect of UV light on malondialdehyde and other reactive substances using TBARS test kit. Reactive substances such as malondialdehyde content increased as the UV dose increased. The presence of malondialdehyde and other reactive substances were not significantly different (p \u3c 0.05) in both thermal and UV-pasteurized soymilk; whereas these substances were found to be higher in UV-treated RCM after 7 days of storage than the untreated milk stored for 7 days at 4 °C and the fresh RCM. The designed reactors 1/16 ID and 1/8 ID reactors were useful to inactivate bacteria present in milk. But, the inactivation efficiency was more in 1/16 ID reactor than 1/8 ID reactor