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Hot water treatment effective but affects bean sprout quality

Picture: Mung bean sprouts. Copyright: Flickr / Crispin Semmens
Picture: Mung bean sprouts. Copyright: Flickr / Crispin Semmens

Hot water treatment is an effective decontamination technique for raw mung bean sprouts but commercial feasibility could be affected by physical quality of the product, according to research.  

It was compared with chemical sanitizers with respect to effectiveness in enhancing microbiological quality of raw mung bean sprouts and to evaluate the physical and quality of hot water treated sprouts during storage.

Results showed that hot water treatment had a significant undesirable impact on the color and firmness after treatment or during storage, exhibiting that treated products had a shorter shelf life than untreated control.

Researchers said the temperature of 70 °C was too high to retain physical quality.

Treatment techniques

Hot water treatment reduced the microbial population by 4.19, 4.35, 4.81 and 4.37 log CFU/g in E.coli O157:H7, Listeria monocytogenes, Salmonella spp. and natural microflora.

Chemical sanitizer treatments using AEW, ASC, CPC, ozonated water and TSP resulted in less than 2-log reduction in the same bacterial strains.

Treatment time and concentrations of chemical sanitizers and the temperature of hot water used were selected based on their effectiveness which has been established in other studies.

Decontamination methods including acidic electrolyzed water (AEW), acidified sodium chlorite (ASC), cetylpyridinium chloride (CPC), trisodium phosphate (TSP) and hot water were evaluated for their efficacy against inoculated pathogens and natural mircoflora on mung bean sprouts.

On average, the total plate count for uninoculated raw mung bean sprouts was 9 log CFU/g.

The uninoculated bean sprouts were treated with various sanitizers and hot water to inactivate natural microflora.

Log reductions in different pathogens

ASC (1200 ppm) and CPC (2%) delivered 1.75- and 1.68-log reductions, which were significantly (P < 0.05) different from water treatment (0.75-log reduction). Efficacies of AEW (free chlorine 75 ppm) and TSP (10%) were not significantly (P > 0.05) different from water treatment.

Hot water treatment gave the highest reduction of 4.37 log CFU/g which was significantly higher than all tested chemical sanitizers. Ozonated water (2 ppm) treatment was the least effective with a reduction of only 0.41 log CFU/g.

Efficacy of sanitizers and hot water against E. coli O157:H7, L. monocytogenes and Salmonella spp. on bean sprouts were also compared.

AEW, ASC, CPC and TSP treatments for 180 seconds resulted in 0.98-, 1.69-, 1.06- and 0.67-log reductions of E. coli O157:H7, respectively, showing that these sanitizer treatments were more effective than water treatment and ASC and CPC were better than AEW and TSP.

Among the chemical sanitizers, ozonated water treatment for 180 seconds led to a reduction of 0.30 log CFU/g which was not significantly different from that of water treatment.

Hot water treatment for 20 seconds resulted in the highest reduction of 4.19 log CFU/g which was significantly higher than those of the chemical sanitizers.

For L. monocytogenes, AEW, ASC, CPC, ozonated water and TSP treatments resulted in significantly higher reduction in the total cell count compared to water treatment, achieving 0.77-, 1.40-, 0.86-, 0.92- and 0.90-log reductions.

Treatments with AEW, ASC, CPC and TSP led to 0.95-, 1.78-, 1.16-, and 0.73-log reductions in the population of Salmonella spp., showing better efficacy than water treatment.

Hot water caused the highest reduction of 4.81 log in the total cell count of Salmonella which was significantly greater than those caused by chemical sanitizers.

Ozonated water delivered a 0.29 log reduction in the population of Salmonella spp. which was not significantly different (P > 0.05) from water treatments.

ASC and CPC were more effective than AEW, ozonated water and TSP on the inactivation of foodborne pathogens and natural microflora on bean sprouts but the treatments resulted in significantly lower log reduction than hot water treatment

All media used were supplemented with 100μg/ml nalidixic acid so that pathogens isolated from inoculated bean sprouts were relatively free from other background bacterial contaminants.

Source: Food Control: Volume 42, August 2014, Pages 270–276

Online ahead of print DOI: 10.1016/j.foodcont.2014.02.013

“Comparison of the efficacy of various sanitizers and hot water treatment in inactivating inoculated foodborne pathogens and natural microflora on mung bean sprouts”

Authors: Li Kai Phua, Shan Yu Neo, Gek Hoon Khoo, Hyun-Gyun Yuk,

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