Sudarsan Mukhopadhyay - Academia.edu (original) (raw)
Papers by Sudarsan Mukhopadhyay
Journal of Food Composition and Analysis, Aug 1, 2007
LC-DAD-ESI/MS was used to identify 23 flavonoids in the extract of Mexican oregano (Lippia graveo... more LC-DAD-ESI/MS was used to identify 23 flavonoids in the extract of Mexican oregano (Lippia graveolens H.B.K.), a spice and herb, used in the USA and Mexico. The identification of luteolin-7-O-glucoside, apigenin 7-O-glucoside, phloridzin, taxifolin, eriodictyol, scutellarein, luteolin, quercetin, naringenin, pinocembrin and galangin was confirmed by direct comparison with standards. Identification of 6-hydroxyluteolin, two 6-hydroxyluteolin 7-O-glycosides, three pentahydroxyflavanone hexosides, scutellarein 7-O-hexoside, 3-hydroxyphloretin hexoside, and three other flavones, was made by detailed analysis of their UV and mass spectral data. The identification of the flavonoid glycosides was further confirmed through detection of their aglycones following hydrolysis of the samples. The concentration of the identified flavonoids in three samples was also estimated. This is the first report of detection of over 20 flavonoids, including chalcones, in this plant material.
Journal of Food Safety
The microbial safety of produce continues to be a real concern. The objective of this study was t... more The microbial safety of produce continues to be a real concern. The objective of this study was to investigate the efficacy of high intensity short time pulsed light (PL) application on survival of Salmonella in packaged cherry tomato. Treatment effects on reduction of native microbiota and quality were also evaluated. Stem scars of cherry tomatoes, inoculated with a three serotypes cocktail of Salmonella enterica, was treated with PL for up to 60 s. Polyethylene (PE) films of 25.4, 50.8 and 76.2 μm thickness were used for packaging treatment. A10 s treatment equivalent to a fluence dose of 10.5 J/cm2 was considered optimum. Both packaged and direct PL treatments provided >1 log reduction of the pathogen in 10 s (10.5 J/cm2). Direct treatment for 10 s resulted in 1.9 ± 0.17 log CFU/g reduction of Salmonella. For packaged tomatoes, log reductions decreased with increasing film thickness but not significantly (p < .05). Also, no significant difference in PL decontamination effic...
Food Science and Technology
Assessment of pathogen survival is important for food safety. Listeria monocytogenes causes signi... more Assessment of pathogen survival is important for food safety. Listeria monocytogenes causes significant produce and food contamination worldwide. The objective of this research was to assess survival and reduction of L. monocytogenes on postharvest carrot and tomato subjected to low-dose radiation at different storage temperatures and times. Radiation levels of 0, 0.25, 0.50, 0.75, and 1 kGy were applied on produce inoculated with L. monocytogenes. Gamma radiation reduced Listeria populations by 5.9 logs on carrot and 3.9 logs on tomato at 3 days of storage (5 °C), while reductions were 4.4 and 4.0 logs on carrot and tomato, respectively; at 7 storage days (5 °C). At 20 °C, Listeria reductions were 2.8 logs on carrot and 4.2 logs on tomato (3 storage days) and pathogen decreases were 2.2 logs on carrot and 2.9 logs on tomato (7 storage days). Although pathogen reductions by radiation treatment varied with storage temperatures and days, the linear decreases were significant as the dosage increased from 0.25 to 1.0 kGy, implying that treatments were efficacious for pathogen inactivation. As low dose gamma radiation (1 kGy) showed substantial reduction of Listeria monocytogenes on fresh carrot and tomato, thus, use of low dose low dose gamma radiation can improve the post-harvest safety of carrot and tomato.
International Journal of Food Microbiology
Food Research International, 2020
The aim of this study was to examine the efficacy of lauric arginate (LAE, 1000 ppm-3000 ppm) as ... more The aim of this study was to examine the efficacy of lauric arginate (LAE, 1000 ppm-3000 ppm) as an assisting tool to reduce starved Listeria monocytogenes population in ground beef following sous-vide processing at different temperatures (55-62.5°C). Ground beef mixed with LAE was vacuum sealed and a laboratory water bath was used for sous-vide cooking. Loglinear and Weibull models were fit to the survival microbial population and the D and Z-values were determined at 55-62.5°C. Calculated D-values ranged from 33.62 to 3.22 min at temperature 55-62.5°C. LAE at higher concentration is an effective antimicrobial to increase the inactivation of the pathogen in sous-vide cooking. With the addition of LAE, D-values at 55 and 62.5°C determined by the Loglinear model decreased from 31.86 to 2.28 min (LAE 1000 ppm) and 16.71 to 0.56 min (LAE 3000 ppm), respectively; whereas the D-values at 55 to 62.5°C determined by the Weibull model were 44.26 and 2.09 min (LAE 1000 ppm) and 22.71 and 1.60 min (LAE 3000 ppm), respectively. This study shows that sous-vide processing of ground beef supplemented with higher concentration of LAE effectively inactivates L. monocytogenes and thus, helps increase the microbiological safety and product quality.
Current Opinion in Food Science, 2018
The role of emerging technologies to ensure the microbial safety of fresh produce, milk and eggs †
International Journal of Food Science & Technology, 2017
SummaryIncreased consumption of produce by consumers has been attributed to perceived health bene... more SummaryIncreased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to un...
Food Control, 2019
Periodic outbreaks of foodborne pathogens have resulted in food safety concerns, due to health im... more Periodic outbreaks of foodborne pathogens have resulted in food safety concerns, due to health implications and cost consequences. Occurrence of Listeria monocytogenes in foods and listeriosis have been reported in developed countries; however, documentation of listeriosis in South Africa is limited. In 2017-2018, Listeria was reported on polony (processed deli meat) and listeriosis was observed in South Africa (L. monocytogenes sequence type 6 (ST-6) was identified as the causal agent for listeriosis). Due to its potential effects, we conducted cost estimates to assess the implications of listeriosis outbreak with respect to illnesses, hospitalizations and deaths, and productivity losses. Cost estimates were computed on publicly available data by using USDA-ERS cost computation model for Listeria. Listeriosis had significant impacts, as mortality of 204 individuals with confirmed listeriosis cases was reported, with infants having the highest percent of fatalities (42%). The cost valuation of fatality cases was over US$ 260 million. Hospitalization costs associated with one-month recovery from listeriosis were estimated at US$ 10.4 million. Productivity losses attributed to listeriosis for humans and export value losses for food processors were in excess of US$ 15 million. Increase of food safety measures in South Africa could reduce foodborne disease outbreaks. Pre-emptive pathogen detection, sanitary procedures and bacterial inactivation can enhance control of L. monocytogenes in food processing environments.
Food Microbiology, 2019
Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H... more Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H7, microbial loads and apparent quality of spinach leaves †
Frontiers in Sustainable Food Systems, 2018
Cantaloupes, honeydew melons and watermelons inoculated with Salmonella cocktail at 4.5, 3.8, and... more Cantaloupes, honeydew melons and watermelons inoculated with Salmonella cocktail at 4.5, 3.8, and 3.2 log 10 CFU/cm 2 , respectively, were sanitized with 200 ppm chlorine before rinds removal, cutting, and juice preparation. Efficacy of 200 ppm chlorine in reducing transfer of Salmonella, aerobic mesophilic bacteria, yeast and mold, and Pseudomonas from the melon surfaces to freshly prepared fruit juice was investigated including the effect of waiting period before refrigeration of the juices. The melon juice filtrates were refrigerated immediately or stored at room temperature (∼22 • C) for 3 and 5 h before refrigeration. Average Salmonella bacteria recovered in fresh melon juice prepared from unwashed whole cantaloupes, watermelon and honeydew melons was 1.4, 0.5, and 0.4 log 10 CFU/ml, respectively. Juices from unwashed inoculated melons had the highest bacterial populations and storage at an abusive temperature of 10 • C led to proliferation. Holding these juices at room temperature for 5 h before refrigeration allowed Salmonella bacteria to increase by 0.5-0.8 log in cantaloupe juice and 0.3-0.5 log in watermelon and honeydew juices. No Salmonella bacteria was determined in fresh juices prepared from melons washed with chlorinated water. The results of this study showed that washing melons with 200 ppm chlorine before juice preparation and immediately refrigerating the juice will minimize the chances of Salmonella proliferation.
Innovative Food Science & Emerging Technologies, 2016
UV-assisted TiO 2 photocatalysis (TUV) is an emerging non-thermal technology that has shown to ef... more UV-assisted TiO 2 photocatalysis (TUV) is an emerging non-thermal technology that has shown to efficiently inactivate food-borne pathogens. While TUV processing has been a wellestablished technique for water and wastewater treatment, its application in the food industry is minimal. The basic working principle underlying TUV technology is the photocatalytic production of reactive oxygen species (ROS) that carry out redox reactions with species adsorbed on the TiO 2 surface. Studies have confirmed that severe cell damage including destruction of the cytoplasmic membrane, super-coiled plasmid DNA and genomic DNA, and internal organelles occurred when bacteria were exposed to TUV. Recently, TUV has been explored for its applications in surface disinfection and post-harvest disease control of fresh produce, pasteurization of beverages, and anti-microbial food packaging. Although the novel developments in the technology are promising, more research is needed to achieve the practical application of this technology. The intent of this article is to provide an overview of the principles of TUV, the mechanism of microbial inactivation by TUV, and the recent findings on utilization of TUV for microbiological safety of foods and also, to present the prospective opportunities for TUV in the food industry.
Journal of food protection, Aug 1, 2016
Surface structure and biochemical characteristics of bacteria and produce play a major role in ho... more Surface structure and biochemical characteristics of bacteria and produce play a major role in how and where bacteria attach, complicating decontamination treatments. Whole cantaloupe rind surfaces were inoculated with Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes at 10(7) CFU/ml. Average population size of Salmonella, Escherichia coli O157:H7, and L. monocytogenes recovered after surface inoculation was 4.8 ± 0.12, 5.1 ± 0.14, and 3.6 ± 0.13 log CFU/cm(2), respectively. Inoculated melons were stored at 5 and 22°C for 7 days before washing treatment interventions. Intervention treatments used were (i) water (H2O) at 22°C, (ii) H2O at 80°C, (iii) 3% hydrogen peroxide (H2O2) at 22°C, and (iv) a combination of 3% H2O2 and H2O at 80°C for 300 s. The strength of pathogen attachment (SR value) at days 0, 3, and 7 of storage was determined, and then the efficacy of the intervention treatments to detach, kill, and reduce transfer of bacteria to fresh-cut pieces during fre...
Food Control, 2016
Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has bee... more Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has been shown to have antimicrobial activity against foodborne pathogens. The objective of this study was to assess the effect of a high-ellagic acid commercial pomegranate on the heat resistance of Escherichia coli O104:H4 in ground chicken. A full 2 4 factorial design was used, consisting of temperature treatment with four levels (55.0, 57.5, 60.0, and 62.5 C) and pomegranate with four levels (0.0, 1.0, 2.0, and 3.0 wt/wt. % containing 70% ellagic acid). Experiments were conducted twice, providing a total of 32 survival curves. A threeparameter Weibull primary model was used to describe survival kinetics. Secondary models were then developed to estimate the shape parameter b (i.e., curvature representing susceptibility of cells to stress), scale parameter g (i.e., time to reach the first decimal reduction) and the 5.0-log lethality time t 5.0 (i.e., time to reach a 5.0-log reduction), all as polynomial functions of temperature and pomegranate powder concentration. The positive effect of pomegranate concentration on both b and g demonstrated that the phenolic-rich pomegranate powder causes E. coli O104:H4 cells to become more susceptible to heat, increasing the steepness and concavity of the isothermal survival curves. It was estimated that the 5.0-log reduction time would reach a minimum at a pomegranate powder concentration of 1%, producing a 50% decrease in lethality time, in comparison to that without added pomegranate powder. Nonetheless, a mixed-effect omnibus regression further confirmed that the greatest difference in the thermal resistance of E. coli O104:H4 happened between tests with and without pomegranate powder. In fact, adding more than 1.0% pomegranate powder, at a constant temperature, resulted only in a marginal decrease in thermal resistance. Meat processors can use the model to design lethality treatments in order to achieve specific reductions of E. coli O104:H4 in ground chicken.
Journal of Dairy Science, 2016
In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (W... more In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100 g (WPC34) and 76.8 g of protein/100 g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35°C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log 10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35°C but at least 18 mo at lower temperatures, which should extend the market for these products.
Food Research International, 2015
We have received with great satisfaction that our article “Modelling the effect of pH, sodium chl... more We have received with great satisfaction that our article “Modelling the effect of pH, sodium chloride and sodium pyrophosphate on the thermal resistance of Escherichia coli O157:H7 in ground beef” (Food Research International, 69:289–304; 2015) has awaken interest in another predictive microbiology research group. Henceforth, we respond to each of the queries raised by Davey and Chandrakash in their Letter to the Editor, dated May 7, 2015.
Journal of dairy science, 2011
High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria... more High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria such as Bacillus anthracis (BA), but is lethal to its vegetative cells. Crossflow microfiltration (MF) using ceramic membranes with a pore size of 1.4 μm has been shown to reject most microorganisms from skim milk; and, in combination with pasteurization, has been shown to extend its shelf life. The objectives of this study were to evaluate MF for its efficiency in removing spores of the attenuated Sterne strain of BA from milk; to evaluate the combined efficiency of MF using a 0.8-μm ceramic membrane, followed by pasteurization (72°C, 18.6s); and to monitor any residual BA in the permeates when stored at temperatures of 4, 10, and 25°C for up to 28 d. In each trial, 95 L of raw skim milk was inoculated with about 6.5 log(10) BA spores/mL of milk. It was then microfiltered in total recycle mode at 50°C using ceramic membranes with pore sizes of either 0.8 μm or 1.4 μm, at crossflow velo...
Food Research International, 2015
The objective of this study was to assess the combined effects of temperature, pH, sodium chlorid... more The objective of this study was to assess the combined effects of temperature, pH, sodium chloride (NaCl), and sodium pyrophosphate (SPP) on the heat resistance of Escherichia coli O157:H7 in minced beef meat. A fractional factorial design consisted of four internal temperatures (55.0, 57.5, 60.0 and 62.5°C), five concentrations of NaCl (0.0, 1.5, 3.0, 4.5 and 6.0 wt/wt.%) and SPP (0.0, 0.1, 0.15, 0.2 and 0.3 wt/wt.%), and five levels of pH (4.0, 5.0, 6.0, 7.0 and 8.0). The 38 variable combinations were replicated twice to provide a total of 76 survivor curves, which were modelled by a modified three-parameter Weibull function as primary model. The polynomial secondary models, developed to estimate the time to achieve a 3-log and a 5-log reduction, enabled the estimation of critical pH, NaCl and SPP concentrations, which are values at which the thermo-tolerance of E. coli O157:H7 reaches it maximum. The addition up to a certain critical concentration of NaCl (~2.7-4.7%) or SPP (~0.16%) acts independently to increase the heat resistance of E. coli O157:H7. Beyond such critical concentrations, the thermo-resistance of E. coli O157:H7 will progressively diminish. A similar pattern was found for pH with a critical value between 6.0 and 6.7, depending upon temperature and NaCl concentration. A mixed-effects omnibus regression model further revealed that the acidity of the matrix and NaCl concentration had a greater impact on the inactivation kinetics of E. coli O157:H7 in minced beef than SPP, and both are responsible for the concavity/convexity of the curves. When pH, SPP or NaCl concentration is far above or below from its critical value, the temperatures needed to reduce E. coli O157:H7 up to a certain log level are much lower than those required when any other environmental condition is at its critical value. Meat processors can use the model to design lethality treatments in order to achieve specific log reductions of E. coli O157:H7 in ready-to-eat beef products.
Journal of Food Protection, 2014
The risk of non-O157 Shiga toxin–producing Escherichia coli strains has become a growing public h... more The risk of non-O157 Shiga toxin–producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and...
Synthesis, 2000
A simple and convenient four-step synthesis of 4-hydroxy-2-trifluoromethylthiophene (1) a novel b... more A simple and convenient four-step synthesis of 4-hydroxy-2-trifluoromethylthiophene (1) a novel bioisostere of α,α,α-trifluoro-m-cresol is reported. The key step is the condensation between ethyl 3-methoxy-4,4,4-trifluorocrotonate and methyl thioglycolate to form methyl 3-hydroxy-5-trifluoromethylthiophene-2-carboxylate (6). Hydrolysis of the ester followed by decarboxylation furnishes 1. Multi-hundred gram quantities of 1 have been obtained utilizing the present procedure.
Journal of Food Composition and Analysis, Aug 1, 2007
LC-DAD-ESI/MS was used to identify 23 flavonoids in the extract of Mexican oregano (Lippia graveo... more LC-DAD-ESI/MS was used to identify 23 flavonoids in the extract of Mexican oregano (Lippia graveolens H.B.K.), a spice and herb, used in the USA and Mexico. The identification of luteolin-7-O-glucoside, apigenin 7-O-glucoside, phloridzin, taxifolin, eriodictyol, scutellarein, luteolin, quercetin, naringenin, pinocembrin and galangin was confirmed by direct comparison with standards. Identification of 6-hydroxyluteolin, two 6-hydroxyluteolin 7-O-glycosides, three pentahydroxyflavanone hexosides, scutellarein 7-O-hexoside, 3-hydroxyphloretin hexoside, and three other flavones, was made by detailed analysis of their UV and mass spectral data. The identification of the flavonoid glycosides was further confirmed through detection of their aglycones following hydrolysis of the samples. The concentration of the identified flavonoids in three samples was also estimated. This is the first report of detection of over 20 flavonoids, including chalcones, in this plant material.
Journal of Food Safety
The microbial safety of produce continues to be a real concern. The objective of this study was t... more The microbial safety of produce continues to be a real concern. The objective of this study was to investigate the efficacy of high intensity short time pulsed light (PL) application on survival of Salmonella in packaged cherry tomato. Treatment effects on reduction of native microbiota and quality were also evaluated. Stem scars of cherry tomatoes, inoculated with a three serotypes cocktail of Salmonella enterica, was treated with PL for up to 60 s. Polyethylene (PE) films of 25.4, 50.8 and 76.2 μm thickness were used for packaging treatment. A10 s treatment equivalent to a fluence dose of 10.5 J/cm2 was considered optimum. Both packaged and direct PL treatments provided >1 log reduction of the pathogen in 10 s (10.5 J/cm2). Direct treatment for 10 s resulted in 1.9 ± 0.17 log CFU/g reduction of Salmonella. For packaged tomatoes, log reductions decreased with increasing film thickness but not significantly (p < .05). Also, no significant difference in PL decontamination effic...
Food Science and Technology
Assessment of pathogen survival is important for food safety. Listeria monocytogenes causes signi... more Assessment of pathogen survival is important for food safety. Listeria monocytogenes causes significant produce and food contamination worldwide. The objective of this research was to assess survival and reduction of L. monocytogenes on postharvest carrot and tomato subjected to low-dose radiation at different storage temperatures and times. Radiation levels of 0, 0.25, 0.50, 0.75, and 1 kGy were applied on produce inoculated with L. monocytogenes. Gamma radiation reduced Listeria populations by 5.9 logs on carrot and 3.9 logs on tomato at 3 days of storage (5 °C), while reductions were 4.4 and 4.0 logs on carrot and tomato, respectively; at 7 storage days (5 °C). At 20 °C, Listeria reductions were 2.8 logs on carrot and 4.2 logs on tomato (3 storage days) and pathogen decreases were 2.2 logs on carrot and 2.9 logs on tomato (7 storage days). Although pathogen reductions by radiation treatment varied with storage temperatures and days, the linear decreases were significant as the dosage increased from 0.25 to 1.0 kGy, implying that treatments were efficacious for pathogen inactivation. As low dose gamma radiation (1 kGy) showed substantial reduction of Listeria monocytogenes on fresh carrot and tomato, thus, use of low dose low dose gamma radiation can improve the post-harvest safety of carrot and tomato.
International Journal of Food Microbiology
Food Research International, 2020
The aim of this study was to examine the efficacy of lauric arginate (LAE, 1000 ppm-3000 ppm) as ... more The aim of this study was to examine the efficacy of lauric arginate (LAE, 1000 ppm-3000 ppm) as an assisting tool to reduce starved Listeria monocytogenes population in ground beef following sous-vide processing at different temperatures (55-62.5°C). Ground beef mixed with LAE was vacuum sealed and a laboratory water bath was used for sous-vide cooking. Loglinear and Weibull models were fit to the survival microbial population and the D and Z-values were determined at 55-62.5°C. Calculated D-values ranged from 33.62 to 3.22 min at temperature 55-62.5°C. LAE at higher concentration is an effective antimicrobial to increase the inactivation of the pathogen in sous-vide cooking. With the addition of LAE, D-values at 55 and 62.5°C determined by the Loglinear model decreased from 31.86 to 2.28 min (LAE 1000 ppm) and 16.71 to 0.56 min (LAE 3000 ppm), respectively; whereas the D-values at 55 to 62.5°C determined by the Weibull model were 44.26 and 2.09 min (LAE 1000 ppm) and 22.71 and 1.60 min (LAE 3000 ppm), respectively. This study shows that sous-vide processing of ground beef supplemented with higher concentration of LAE effectively inactivates L. monocytogenes and thus, helps increase the microbiological safety and product quality.
Current Opinion in Food Science, 2018
The role of emerging technologies to ensure the microbial safety of fresh produce, milk and eggs †
International Journal of Food Science & Technology, 2017
SummaryIncreased consumption of produce by consumers has been attributed to perceived health bene... more SummaryIncreased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to un...
Food Control, 2019
Periodic outbreaks of foodborne pathogens have resulted in food safety concerns, due to health im... more Periodic outbreaks of foodborne pathogens have resulted in food safety concerns, due to health implications and cost consequences. Occurrence of Listeria monocytogenes in foods and listeriosis have been reported in developed countries; however, documentation of listeriosis in South Africa is limited. In 2017-2018, Listeria was reported on polony (processed deli meat) and listeriosis was observed in South Africa (L. monocytogenes sequence type 6 (ST-6) was identified as the causal agent for listeriosis). Due to its potential effects, we conducted cost estimates to assess the implications of listeriosis outbreak with respect to illnesses, hospitalizations and deaths, and productivity losses. Cost estimates were computed on publicly available data by using USDA-ERS cost computation model for Listeria. Listeriosis had significant impacts, as mortality of 204 individuals with confirmed listeriosis cases was reported, with infants having the highest percent of fatalities (42%). The cost valuation of fatality cases was over US$ 260 million. Hospitalization costs associated with one-month recovery from listeriosis were estimated at US$ 10.4 million. Productivity losses attributed to listeriosis for humans and export value losses for food processors were in excess of US$ 15 million. Increase of food safety measures in South Africa could reduce foodborne disease outbreaks. Pre-emptive pathogen detection, sanitary procedures and bacterial inactivation can enhance control of L. monocytogenes in food processing environments.
Food Microbiology, 2019
Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H... more Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H7, microbial loads and apparent quality of spinach leaves †
Frontiers in Sustainable Food Systems, 2018
Cantaloupes, honeydew melons and watermelons inoculated with Salmonella cocktail at 4.5, 3.8, and... more Cantaloupes, honeydew melons and watermelons inoculated with Salmonella cocktail at 4.5, 3.8, and 3.2 log 10 CFU/cm 2 , respectively, were sanitized with 200 ppm chlorine before rinds removal, cutting, and juice preparation. Efficacy of 200 ppm chlorine in reducing transfer of Salmonella, aerobic mesophilic bacteria, yeast and mold, and Pseudomonas from the melon surfaces to freshly prepared fruit juice was investigated including the effect of waiting period before refrigeration of the juices. The melon juice filtrates were refrigerated immediately or stored at room temperature (∼22 • C) for 3 and 5 h before refrigeration. Average Salmonella bacteria recovered in fresh melon juice prepared from unwashed whole cantaloupes, watermelon and honeydew melons was 1.4, 0.5, and 0.4 log 10 CFU/ml, respectively. Juices from unwashed inoculated melons had the highest bacterial populations and storage at an abusive temperature of 10 • C led to proliferation. Holding these juices at room temperature for 5 h before refrigeration allowed Salmonella bacteria to increase by 0.5-0.8 log in cantaloupe juice and 0.3-0.5 log in watermelon and honeydew juices. No Salmonella bacteria was determined in fresh juices prepared from melons washed with chlorinated water. The results of this study showed that washing melons with 200 ppm chlorine before juice preparation and immediately refrigerating the juice will minimize the chances of Salmonella proliferation.
Innovative Food Science & Emerging Technologies, 2016
UV-assisted TiO 2 photocatalysis (TUV) is an emerging non-thermal technology that has shown to ef... more UV-assisted TiO 2 photocatalysis (TUV) is an emerging non-thermal technology that has shown to efficiently inactivate food-borne pathogens. While TUV processing has been a wellestablished technique for water and wastewater treatment, its application in the food industry is minimal. The basic working principle underlying TUV technology is the photocatalytic production of reactive oxygen species (ROS) that carry out redox reactions with species adsorbed on the TiO 2 surface. Studies have confirmed that severe cell damage including destruction of the cytoplasmic membrane, super-coiled plasmid DNA and genomic DNA, and internal organelles occurred when bacteria were exposed to TUV. Recently, TUV has been explored for its applications in surface disinfection and post-harvest disease control of fresh produce, pasteurization of beverages, and anti-microbial food packaging. Although the novel developments in the technology are promising, more research is needed to achieve the practical application of this technology. The intent of this article is to provide an overview of the principles of TUV, the mechanism of microbial inactivation by TUV, and the recent findings on utilization of TUV for microbiological safety of foods and also, to present the prospective opportunities for TUV in the food industry.
Journal of food protection, Aug 1, 2016
Surface structure and biochemical characteristics of bacteria and produce play a major role in ho... more Surface structure and biochemical characteristics of bacteria and produce play a major role in how and where bacteria attach, complicating decontamination treatments. Whole cantaloupe rind surfaces were inoculated with Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes at 10(7) CFU/ml. Average population size of Salmonella, Escherichia coli O157:H7, and L. monocytogenes recovered after surface inoculation was 4.8 ± 0.12, 5.1 ± 0.14, and 3.6 ± 0.13 log CFU/cm(2), respectively. Inoculated melons were stored at 5 and 22°C for 7 days before washing treatment interventions. Intervention treatments used were (i) water (H2O) at 22°C, (ii) H2O at 80°C, (iii) 3% hydrogen peroxide (H2O2) at 22°C, and (iv) a combination of 3% H2O2 and H2O at 80°C for 300 s. The strength of pathogen attachment (SR value) at days 0, 3, and 7 of storage was determined, and then the efficacy of the intervention treatments to detach, kill, and reduce transfer of bacteria to fresh-cut pieces during fre...
Food Control, 2016
Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has bee... more Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has been shown to have antimicrobial activity against foodborne pathogens. The objective of this study was to assess the effect of a high-ellagic acid commercial pomegranate on the heat resistance of Escherichia coli O104:H4 in ground chicken. A full 2 4 factorial design was used, consisting of temperature treatment with four levels (55.0, 57.5, 60.0, and 62.5 C) and pomegranate with four levels (0.0, 1.0, 2.0, and 3.0 wt/wt. % containing 70% ellagic acid). Experiments were conducted twice, providing a total of 32 survival curves. A threeparameter Weibull primary model was used to describe survival kinetics. Secondary models were then developed to estimate the shape parameter b (i.e., curvature representing susceptibility of cells to stress), scale parameter g (i.e., time to reach the first decimal reduction) and the 5.0-log lethality time t 5.0 (i.e., time to reach a 5.0-log reduction), all as polynomial functions of temperature and pomegranate powder concentration. The positive effect of pomegranate concentration on both b and g demonstrated that the phenolic-rich pomegranate powder causes E. coli O104:H4 cells to become more susceptible to heat, increasing the steepness and concavity of the isothermal survival curves. It was estimated that the 5.0-log reduction time would reach a minimum at a pomegranate powder concentration of 1%, producing a 50% decrease in lethality time, in comparison to that without added pomegranate powder. Nonetheless, a mixed-effect omnibus regression further confirmed that the greatest difference in the thermal resistance of E. coli O104:H4 happened between tests with and without pomegranate powder. In fact, adding more than 1.0% pomegranate powder, at a constant temperature, resulted only in a marginal decrease in thermal resistance. Meat processors can use the model to design lethality treatments in order to achieve specific reductions of E. coli O104:H4 in ground chicken.
Journal of Dairy Science, 2016
In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (W... more In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100 g (WPC34) and 76.8 g of protein/100 g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35°C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log 10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35°C but at least 18 mo at lower temperatures, which should extend the market for these products.
Food Research International, 2015
We have received with great satisfaction that our article “Modelling the effect of pH, sodium chl... more We have received with great satisfaction that our article “Modelling the effect of pH, sodium chloride and sodium pyrophosphate on the thermal resistance of Escherichia coli O157:H7 in ground beef” (Food Research International, 69:289–304; 2015) has awaken interest in another predictive microbiology research group. Henceforth, we respond to each of the queries raised by Davey and Chandrakash in their Letter to the Editor, dated May 7, 2015.
Journal of dairy science, 2011
High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria... more High-temperature, short-time pasteurization of milk is ineffective against spore-forming bacteria such as Bacillus anthracis (BA), but is lethal to its vegetative cells. Crossflow microfiltration (MF) using ceramic membranes with a pore size of 1.4 μm has been shown to reject most microorganisms from skim milk; and, in combination with pasteurization, has been shown to extend its shelf life. The objectives of this study were to evaluate MF for its efficiency in removing spores of the attenuated Sterne strain of BA from milk; to evaluate the combined efficiency of MF using a 0.8-μm ceramic membrane, followed by pasteurization (72°C, 18.6s); and to monitor any residual BA in the permeates when stored at temperatures of 4, 10, and 25°C for up to 28 d. In each trial, 95 L of raw skim milk was inoculated with about 6.5 log(10) BA spores/mL of milk. It was then microfiltered in total recycle mode at 50°C using ceramic membranes with pore sizes of either 0.8 μm or 1.4 μm, at crossflow velo...
Food Research International, 2015
The objective of this study was to assess the combined effects of temperature, pH, sodium chlorid... more The objective of this study was to assess the combined effects of temperature, pH, sodium chloride (NaCl), and sodium pyrophosphate (SPP) on the heat resistance of Escherichia coli O157:H7 in minced beef meat. A fractional factorial design consisted of four internal temperatures (55.0, 57.5, 60.0 and 62.5°C), five concentrations of NaCl (0.0, 1.5, 3.0, 4.5 and 6.0 wt/wt.%) and SPP (0.0, 0.1, 0.15, 0.2 and 0.3 wt/wt.%), and five levels of pH (4.0, 5.0, 6.0, 7.0 and 8.0). The 38 variable combinations were replicated twice to provide a total of 76 survivor curves, which were modelled by a modified three-parameter Weibull function as primary model. The polynomial secondary models, developed to estimate the time to achieve a 3-log and a 5-log reduction, enabled the estimation of critical pH, NaCl and SPP concentrations, which are values at which the thermo-tolerance of E. coli O157:H7 reaches it maximum. The addition up to a certain critical concentration of NaCl (~2.7-4.7%) or SPP (~0.16%) acts independently to increase the heat resistance of E. coli O157:H7. Beyond such critical concentrations, the thermo-resistance of E. coli O157:H7 will progressively diminish. A similar pattern was found for pH with a critical value between 6.0 and 6.7, depending upon temperature and NaCl concentration. A mixed-effects omnibus regression model further revealed that the acidity of the matrix and NaCl concentration had a greater impact on the inactivation kinetics of E. coli O157:H7 in minced beef than SPP, and both are responsible for the concavity/convexity of the curves. When pH, SPP or NaCl concentration is far above or below from its critical value, the temperatures needed to reduce E. coli O157:H7 up to a certain log level are much lower than those required when any other environmental condition is at its critical value. Meat processors can use the model to design lethality treatments in order to achieve specific log reductions of E. coli O157:H7 in ready-to-eat beef products.
Journal of Food Protection, 2014
The risk of non-O157 Shiga toxin–producing Escherichia coli strains has become a growing public h... more The risk of non-O157 Shiga toxin–producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and...
Synthesis, 2000
A simple and convenient four-step synthesis of 4-hydroxy-2-trifluoromethylthiophene (1) a novel b... more A simple and convenient four-step synthesis of 4-hydroxy-2-trifluoromethylthiophene (1) a novel bioisostere of α,α,α-trifluoro-m-cresol is reported. The key step is the condensation between ethyl 3-methoxy-4,4,4-trifluorocrotonate and methyl thioglycolate to form methyl 3-hydroxy-5-trifluoromethylthiophene-2-carboxylate (6). Hydrolysis of the ester followed by decarboxylation furnishes 1. Multi-hundred gram quantities of 1 have been obtained utilizing the present procedure.