Myung-Sub Chung

Use of Organic Acids to Inactivate Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on Organic Fresh Apples and Lettuce

UNLABELLED This study was undertaken to investigate the antimicrobial effect of organic acids against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on whole red organic apples and lettuce. Several studies have been conducted to evaluate organic acids as sanitizers. However, no studies have compared antimicrobial effects of various organic acids on organic fresh produce, including evaluation of color changes of produce. Apples and lettuce were inoculated with a cocktail of 3 strains each of 3 foodborne pathogens provided above and treated with 1% and 2% organic acids (propionic, acetic, lactic, malic, and citric acid) for 0, 0.5, 1, 5, and 10 min. With increasing treatment time and acid concentration, organic acid treatments showed significant reduction compared to the control treatment (distilled water), and differences in antimicrobial effects between organic acids were observed. After 10 min of treatment with 1% and 2% organic acids in apples, propionic (0.92 to 2.75 log reduction), acetic (0.52 to 2.78 log reduction), lactic (1.69 to >3.42 log reduction), malic (1.48 to >3.42 log reduction), and citric acid (1.52 to >3.42 log reduction) exhibited significant (P < 0.05) antibacterial effects against 3 foodborne pathogens compared to the control treatment. In lettuce, propionic (0.93 to 1.52 log reduction), acetic (1.13 to 1.74 log reduction), lactic (1.87 to 2.54 log reduction), malic (2.32 to 2.98 log reduction), and citric acid (1.85 to 2.86 log reduction) showed significant (P < 0.05) effects compared to the control treatment. Changes in sample color subjected to organic acids treatment were not significant during storage. PRACTICAL APPLICATION It is suggested that organic acids have a potential as sanitizers for organic fresh produce. These data may help the organic produce industry provide safe fresh produce for consumers.

Combined effects of ultrasound and surfactants to reduce Bacillus cereus spores on lettuce and carrots.

This study was performed to compare the effectiveness of ultrasound treatment singly and in combination with surfactants as an alternative method to conventional sanitizers containing chlorine for reducing numbers of Bacillus cereus spores on fresh produce. A cocktail of three strains of B. cereus (10876, ATCC 13061, and W-1) spores was inoculated onto iceberg lettuce and then treated with ultrasound for 0, 5, 10, 20 and 60 min. Five minutes was found to be an adequate ultrasound (40 kHz, 30 W/L) treatment time which also caused no damage to lettuce leaf surfaces as observed through a field-emission scanning electron microscope (FE-SEM). Iceberg lettuce and carrots were inoculated with a cocktail of three strains of B. cereus spores and treated with combinations of ultrasound and various concentrations (0.03 to 0.3%) of surfactant (Tween 20, 40, 60, 80 and Span 20, 80, 85) solutions for 5 min. The efficacy of the combination of ultrasound and surfactant increased depending on the hydrophile-lipophile balance (HLB). The most effective treatment for reducing levels of B. cereus spores was the combination of ultrasound and 0.1% Tween 20, yielding reductions of 2.49 and 2.22 log CFU/g on lettuce and carrots, respectively, without causing deterioration of quality. These reductions were 1 log greater than those obtained by immersion in 200 ppm chlorine for 5 min. Further research for elimination of B. cereus spores involving study of spore adhesion and removal mechanisms from food surfaces is needed, as well as devising an industrial-scale ultrasound system for the food industry.

A facile and sensitive immunoassay for the detection of alpha-fetoprotein using gold-coated magnetic nanoparticle clusters and dynamic light scattering

A facile and sensitive immunoassay protocol for the detection of alpha-fetoprotein (AFP) was developed using gold-coated iron oxide magnetic nanoclusters and dynamic light scattering (DLS) methods. The increase in the average particle size due to AFP-mediated aggregation was measured using DLS, and the detection limit was better than 0.01 ng mL(-1).

Effect of various conditions on inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in fresh-cut lettuce using ultraviolet radiation

The effect of various conditions on inactivation of foodborne pathogens and quality of fresh-cut lettuce during ultraviolet (254 nm, UVC) radiation was investigated. Lettuce was inoculated with a cocktail of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes and treated at different temperatures (4 and 25 °C), distances between sample and lamp (10 and 50 cm), type of exposure (illuminated from one or two sides), UV intensities (1.36 to 6.80 mW/cm²), and exposure times (0.5 to 10 min), sequentially. UV treatment at 25 °C for 1 min achieved 1.45-, 1.35-, and 2.12-log reductions in surface-inoculated E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, whereas the reduction of these pathogens at 4 °C was 0.31, 0.57, and 1.16 log, respectively. UV radiation was most effective when distance from UV lamp to the sample was minimal (10 cm) and radiation area was maximal (two-sided exposure). All UV intensities significantly (P<0.05) reduced the three pathogens after 10 min exposure, but the effect of treatment was correlated with UV intensity and exposure time. Color values and texture parameters of lettuce subjected to UV treatment under the optimum conditions (25 °C, 10 cm between sample and lamp, two-sided exposure, 6.80 mW/cm²) were not significantly (P>0.05) different from those of nontreated samples up to 5 min exposure. However, these qualities significantly (P<0.05) changed at prolonged treatment time. These results suggest that UV radiation under optimized conditions could reduce foodborne pathogens without adversely affecting color quality properties of fresh-cut lettuce.

Inactivation of biofilm cells of foodborne pathogen by aerosolized sanitizers.

The objective of this study was to determine the effect of aerosolized sanitizers on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes biofilms. Biofilms were formed on a stainless steel and polyvinyl chloride (PVC) coupon by using a mixture of three strains each of three foodborne pathogens. Six day old biofilms on stainless steel and PVC coupons were treated with aerosolized sodium hypochlorite (SHC; 100 ppm) and peracetic acid (100, 200, and 400 ppm) in a model cabinet for 5, 10, 30, and 50 min. Treatment with 100 ppm PAA was more effective than the same concentration of SHC with increasing treatment time. Exposure to 100 ppm SHC and PAA for 50 min significantly (p<0.05) reduced biofilm cells of three foodborne pathogens (0.50 to 3.63 log CFU/coupon and 2.83 to more than 5.78 log CFU/coupon, respectively) compared to the control treatment. Exposure to 200 and 400 ppm PAA was more effective in reducing biofilm cells. Biofilm cells were reduced to below the detection limit (1.48 log CFU/coupon) between 10 and 30 min of exposure. The results of this study suggest that aerosolized sanitizers have a potential as a biofilm control method in the food industry.

Bacteriological quality of vegetables from organic and conventional production in different areas of Korea.

Foods grown in organic production systems have been described as representing an increased risk to public health compared with foods from conventional production. Leafy vegetables (spinach, romaine lettuce, and green sesame leaves) grown in organic and conventional systems were collected from various areas in Korea and examined using standard culture methods to compare the microbiological quality of the produce grown in the two agricultural systems. The 354 samples of these leafy vegetables were analyzed for levels of indicator bacteria (aerobic bacteria, coliforms, and Escherichia coli) and the prevalence of the pathogens Staphylococcus aureus, E. coli O157:H7, Listeria monocytogenes, Bacillus cereus, and Salmonella. Aerobic bacteria and coliforms were detected in all vegetable types, but nonpathogenic E. coli was below the limit of detection in all samples. B. cereus was the most prevalent pathogen, found on 7 (11.1%) of the 63 organic spinach samples. The prevalence of S. aureus was highest in organic sesame leaves; it was found on 5 (8.0%) of the 63 samples. The prevalence of L. monocytogenes was highest on organic romaine lettuce and spinach; it was found in 4 (6.4%) of 63 samples of each type of vegetable. E. coli O157:H7 found on only 1 (1.58%) of 55 conventional spinach samples. These results suggest that farming type at most only slightly affects the hygienic quality of leafy vegetables, and no effect was found for sample collection area. Salmonella was not isolated from any of the conventional or organic leafy vegetables. These results do not support the hypothesis that organic produce poses a substantially greater risk of pathogen contamination than does conventional produce.

Estimated daily intakes of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) antioxidants in Korea

The study was conducted to establish the estimated daily intake (EDI) of antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) in Korea. The EDIs were obtained from two sources. One of the estimations was based on the analytical determination of BHA, BHT and TBHQ in 12 food categories (ten food categories for TBHQ) and on individual dietary intake data obtained from the National Health and Nutrition Survey in 1998 (n=11 525, age > 1 year). The other EDIs of BHA, BHT and TBHQ were based on the maximum permitted levels specified in national food standards in Korea and on individual dietary intake data obtained from the National Health and Nutrition Survey in 1998 (n=11 525, age > 1 year). To establish the EDIs based on the analytical determination and on individual dietary intake data, 133 food samples in 12 food categories were selected from the foods considered to be representative sources of BHA, BHT and TBHQ in the Korean diet. Selected samples were analysed by GC with FID. BHA was not detected in any of the samples analysed. BHT and TBHQ were detected in the samples, but the levels were significantly lower than their maximum limits. The EDIs1 of BHT, and TBHQ for average consumers were 0.0156−3, and 0.0012−3 mg kg−1 body weight bw day−1 and as a proportion of the ADI were 0.0052 and 0.0002%, respectively. For 95th percentile consumers, the EDIs of BHT and TBHQ were 0.0080 and 0.0006 mg kg−1 bw day−1, and as a proportion of the ADI were 2.67 and 0.09%, respectively. EDIs for BHA, BHT and TBHQ based on the maximum permitted levels and on individual dietary intake data were 0.04, 0.04 and 0.04 mg kg−1 bw day−1, respectively. The EDIs of BHA, BHT and TBHQ for average consumers ranged from 6.00 to 14.42% of the ADI of each antioxidant. According to these results, the EDIs of BHA, BHT and TBHQ in Korea were significantly lower than ADI of these antioxidants established by the JECFA.

Development of predictive models for the growth of Escherichia coli O157:H7 on cabbage in Korea.

Cabbage is the main material of coleslaw, a popular side dish in Korea as well as many other countries. In the present study, the combined effect of temperature (15, 25, and 35 °C) and relative humidity (60%, 70%, and 80%) on the growth of Escherichia coli O157:H7 on cabbage was investigated. The polynomial models for growth rate (GR), lag time (LT), and maximum population density (MPD) estimated from the Baranyi model were conducted with high coefficients of determination (R(2)> 0.98). Subsequently, performance and reliability of the models were assessed through external validation, employing three indices as bias factor (B(f)), accuracy factor (A(f)), and the standard error of prediction expressed in percentage (%SEP). The B(f), A(f), and %SEP values of the predictive models for GR were 1.008, 1.127 and 18.70%, while 1.033, 1.187 and 20.79% for LT and 0.960, 1.044 and 5.22% for MPD, respectively. The results demonstrated that the developed secondary models showed a good agreement between the observed and predicted values. Therefore, the established models can be suitable to estimate and control E. coli O157:H7 growth risk on cabbage at some steps from farm to table in Korea as a valuable tool.

Growth and predictive model of Bacillus cereus on blanched spinach with or without seasoning at various temperatures

The growth of Bacillus cereus on blanched spinach with or without seasoning at various temperatures (15, 20, 25, 30, and 35°C) was investigated. The number of B. cereus on blanched spinach stored at 35°C was significantly increased and resulted in maximum populations (7.8 log CFU/g) after 10 h. However, the growth rate of B. cereus on blanched spinach with seasoning stored at 35oC was lower than on blanched spinach without seasoning. The growth rate (GR) of B. cereus on blanched spinach stored at 15°C was lower than the other temperatures. The lag time (LT) of B. cereus on blanched spinach with seasoning was longer than blanched spinach without seasoning. Primary growth models of B. cereus on blanched spinach fit well to a modified Gompertz model (blanched spinach R2 =0.98; blanched spinach with seasoning R2 =0.96). These results might be used for developing safe storage guidelines for cooked vegetable at various temperatures.

Modeling the combined effect of temperature and relative humidity on Escherichia coli O157:H7 on lettuce

The effect of relative humidity (RH) and temperature on the microbial behavior of Escherichia coli O157:H7 on lettuce was investigated. Experimental data obtained under different combined conditions of RH (60, 70, and 80%) and temperature (15, 25, and 35°C) were fitted into the Logistic model with delay to estimate specific growth rate (SGR) with high coefficients of determination (R2s >0.98). The estimated SGR values were used to develop a Gamma-concept model. Then, several statistic characteristics were employed to verify the performance and reliability of the developed model, which demonstrated that the predictive model was not biased and had high accuracy in prediction. Besides, the analysis of relative importance of temperature and RH indicated that temperature is much more influential on the growth of E. coli O157:H7 on lettuce than the ambient RH changes.