Charles Nkufi Tango

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.

Synergetic effect of combined fumaric acid and slightly acidic electrolysed water on the inactivation of food-borne pathogens and extending the shelf life of fresh beef.

To evaluate synergetic effect of slight acidic electrolysed water (SAEW) and fumaric acid (FA) on inactivation of total viable count (TVC) and Staphylococcus aureus, Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella Typhimurium in fresh beef and to study shelf life and sensory quality of beef.

Fumaric Acid and Slightly Acidic Electrolyzed Water Inactivate Gram Positive and Gram Negative Foodborne Pathogens

Sanitizing effectiveness of slightly acidic electrolyzed water (SAEW) and fumaric acid (FA) at different dipping temperatures (25–60 °C), times (1–5 min), and concentrations (5–30 ppm for SAEW and 0.125%–0.5% for FA) on pure cultures of two Gram positive pathogens Staphylococcus aureus (SA) and Listeria monocytogenes (LM) and two Gram negative pathogens Escherichia coli O157:H7 (EC) and Salmonella Typhimurium (ST) was evaluated. FA (0.25%) showed the strongest sanitizing effect, demonstrating complete inactivation of EC, ST, and LM, while SA was reduced by 3.95–5.76 log CFU/mL at 25–60 °C, respectively, after 1 min of treatment. For SAEW, the complete inactivation was obtained when available chlorine concentration was increased to 20 ppm at 40 °C for 3 and 5 min. Moreover, Gram positive pathogens have been shown to resist to all treatment trends more than Gram negative pathogens throughout this experiment. Regardless of the different dipping temperatures, concentrations, and times, FA treatment was more effective than treatment with SAEW for reduction of foodborne pathogens. This study demonstrated that application of FA in food systems may be useful as a method for inactivation of foodborne pathogens.

Modeling of Bacillus cereus growth in brown rice submitted to a combination of ultrasonication and slightly acidic electrolyzed water treatment.

The combined effects of ultrasonication and slight acidic electrolyzed water were investigated to improve the microbial safety of brown rice against Bacillus cereus infection and to evaluate the growth kinetics of these bacteria during storage of untreated and treated rice at various temperatures (5, 10, 15, 20, 25, 30, and 35°C). The results indicate that this combination treatment was bactericidal against B. cereus, resulting in an approximately 3.29-log reduction. Although B. cereus can be efficiently reduced by treatment, temperature abuse during storage can allow B. cereus to recover and grow. A primary growth model (Baranyi and Roberts equation) was fitted to the raw growth data from untreated (control) and treated samples to estimate growth rate, lag time, and maximum population density, with a low standard error of the residuals (≤0.140) and high adjusted coefficient of determination (>0.990). The growth curves obtained from the Baranyi and Roberts model indicated that B. cereus grew more slowly on treated brown rice than on untreated brown rice. Secondary models predicting the square root of the maximum growth rate and the natural logarithm of the lag time as a function of temperature were satisfactory (bias factor = 0.993 to 1.013; accuracy factor = 1.290 to 1.352; standard error of prediction = 18.828 to 36.615%). Inactivation results and the model developed and validated in this study provided reliable and valuable growth kinetics information for quantitative microbiological risk assessment studies of B. cereus on brown rice.

Development and evaluation of chitosan and its derivative for the shelf life extension of beef meat under refrigeration storage

The current study was aimed to study the shelf life of beef meat at refrigeration storage using novel chitosan derivative (Ch-D). Chitosan was modified with antimicrobial monomethyl fumaric acid (MFA). The chemical structure of the resulting material was characterized by FT-IR and HR-XRD. The results confirmed the successful synthesis of conjugate sample. For the shelf life study, following lots were used: control (distilled water), chitosan 0.5%, Ch-D 0.5%. The samples were kept at 4 °C for 16 days and analyzed at 4-day intervals. Ch-D treatment significantly reduced the total viable counts, enterobacteriaceae, lactic acid bacteria, psychrotrophic bacteria, and yeasts–moulds when compared with the chitosan and control during refrigeration storage. The peroxide value (PV) for Ch-D was 0.19 0.04 meq O2 kg 1 fat and chitosan was 0.21 0.07 meq O2 kg 1 fat and showed no significant difference (P < 0.05) at the end of the storage. Thiobarbituric acid reactive substance (TBARs) value for Ch-D was 0.48 0.02 mg MDA kg 1 and chitosan was 0.57 0.09 mg MDA kg , while the carbonyl contents for Ch-D was 3.16 0.23 nM mg 1 protein and chitosan was 3.11 0.16 nM mg 1 protein at 16 days of storage. Values for Ch-D and chitosan treatments were significantly lower (P < 0.05) for all the quality attributes as compared with the control throughout storage. At the end of storage, Ch-D treatment showed a significant increase (P < 0.05) in lightness (L = 41.54 0.09) and yellowness (b* = 2.23 0.04). The redness for control was high (a* = 6.12 0.09) as compared with the treated samples. Based primarily on microbial counts, Ch-D treatment extended the shelf life of beef meat by about 8 days, maintaining acceptable quality attributes.

Assessment of Enterotoxin Production and Cross‐Contamination of Staphylococcus aureus between Food Processing Materials and Ready‐To‐Eat Cooked Fish Paste

This study evaluated Staphylococcus aureus growth and subsequent staphylococcal enterotoxin A production in tryptone soy broth and on ready-to-eat cooked fish paste at 12 to 37 °C, as well as cross-contamination between stainless steel, polyethylene, and latex glove at room temperature. A model was developed using Barany and Robertss growth model, which satisfactorily described the suitable growth of S. aureus with R(2)-adj from 0.94 to 0.99. Except at 12 °C, S. aureus cells in TSB presented a lag time lower (14.64 to 1.65 h), grew faster (0.08 to 0.31 log CFU/h) and produced SEA at lower cell density levels (5.65 to 6.44 log CFU/mL) compare to those inoculated on cooked fish paste with data of 16.920 to 1.985 h, 0.02 to 0.23 log CFU/h, and 6.19 to 7.11 log CFU/g, respectively. Staphylococcal enterotoxin type A (SEA) visual immunoassay test showed that primary SEA detection varied considerably among different storage temperature degrees and media. For example, it occurred only during exponential phase at 30 and 37 °C in TSB, but in cooked fish paste it took place at late exponential phase of S. aureus growth at 20 and 25 °C. The SEA detection test was negative on presence of S. aureus on cooked fish paste stored at 12 and 15 °C, although cell density reached level of 6.12 log CFU/g at 15 °C. Cross-contamination expressed as transfer rate of S. aureus from polyethylene surface to cooked fish paste surface was slower than that observed with steel surface to cooked fish paste under same conditions. These results provide helpful information for controlling S. aureus growth, SEA production and cross-contamination during processing of cooked fish paste.

Evaluation of nisin-loaded chitosan-monomethyl fumaric acid nanoparticles as a direct food additive

Nisin-loaded chitosan-monomethyl fumaric acid (CM-N) nanoparticles were evaluated as a novel, direct food additive. Chitosan (CS) was modified with monomethyl fumaric acid (MFA) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). CS-loaded nisin (CS-N) and CM-N nanoparticles were produced through ionic interactions between the positive amino group of CS and CS-MFA and negative tripolyphosphate ions. The resultant materials were characterized by TNBS assay, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and zeta potential analysis. CS-MFA was successfully synthesized with 8.38 ± 0.02% substitution of the amino groups, as confirmed by TNBS assay. The percentage yield of CS-N and CM-N nanoparticles was 81.64 and 76.83% and nisin encapsulation efficiency was 71.48 ± 0.48 and 60.32 ± 0.63%, respectively. The average particle size of CS-N and CM-N nanoparticles was 134.3 and 207.9 nm, while the zeta potential of CS-N and CM-N nanoparticles was +39.4 mV and +31.5 mV, respectively. Upon antibacterial activity against foodborne pathogens, CM-N significantly reduced bacterial counts compared to the other tested samples in orange juice after 48 h of incubation. Based on the preliminarily results, CM-N nanoparticles have shown impressive properties and can be used in the food industry as carriers and direct antimicrobial agents.

An experimental validated in silico model to assess Staphylococcus aureus growth kinetics on different pork products.

To gain an understanding of the growth kinetics of Staphylococcus aureus to ensure the safety of pork, and to develop a predictive growth model of Staph. aureus in raw pork, ham and sausage pork under specific storage time and temperature conditions.

Human microbiome restoration and safety

The human gut microbiome consists of many bacteria which are in symbiotic relationship with human beings. The gut microbial metabolism, as well as the microbial-host co-metabolism, has been found to greatly influence health and disease. Factors such as diet, antibiotic use and lifestyle have been associated with alterations in the gut microbial community and may result in several pathological conditions. For this reason, several strategies including fecal microbiota transplant and probiotic administration have been applied and proven to be feasible and effective in restoring the gut microbiota in humans. Yet, safety concerns such as potential health risks that may arise from such interventions and how these strategies are regulated need to be addressed. Also, it will be important to know if these microbiome restoration strategies can have a profound impact on health. This review provides an overview of our current knowledge of the microbiome restoration strategies and safety issues on how these strategies are regulated.

Development of Predictive Models for the Growth Kinetics of Listeria monocytogenes on Fresh Pork under Different Storage Temperatures

This study was conducted to develop a predictive model to estimate the growth of Listeria monocytogenes on fresh pork during storage at constant temperatures (5, 10, 15, 20, 25, 30, and 35°C). The Baranyi model was fitted to growth data (log CFU per gram) to calculate the specific growth rate (SGR) and lag time (LT) with a high coefficient of determination (R(2) > 0.98). As expected, SGR increased with a decline in LT with rising temperatures in all samples. Secondary models were then developed to describe the variation of SGR and LT as a function of temperature. Subsequently, the developed models were validated with additional independent growth data collected at 7, 17, 27, and 37°C and from published reports using proportion of relative errors and proportion of standard error of prediction. The proportion of relative errors of the SGR and LT models developed herein were 0.79 and 0.18, respectively. In addition, the standard error of prediction values of the SGR and LT of L. monocytogenes ranged from 25.7 to 33.1% and from 44.92 to 58.44%, respectively. These results suggest that the model developed in this study was capable of predicting the growth of L. monocytogenes under various isothermal conditions.