Kathiravan Krishnamurthy

Inactivation of Staphylococcus aureus by pulsed UV-light sterilization.

Pulsed UV light is a novel technology to inactivate pathogenic and spoilage microorganisms in a short time. The efficacy of pulsed UV light (5.6 J/cm2 per pulse) for the inactivation of Staphylococcus aureus as suspended or agar seeded cells was investigated. A 12-, 24-, or 48-ml cell suspension in buffer was treated under pulsed UV light for up to 30 s, and 0.1 ml of sample was surface plated on Baird-Parker agar and incubated at 37 degrees C for 24 h to determine log reductions. Also, 0.1 ml of cell suspension in peptone water was surface plated on Baird-Parker agar plates, and the plates were treated under pulsed UV light for up to 30 s. The treated and untreated plates were incubated in the conditions described above. A 7- to 8-log CFU/ml reduction was observed for suspended and agar-seeded cells treated for 5 s or longer. In the case of suspended cells, the sample depth, time, treatment, and interaction were significant (P < 0.05). In the case of agar-seeded cells, the treatment time was significant (P < 0.05). Our results clearly indicate that pulsed UV technology has potential for the inactivation of pathogenic microorganisms.

Use of Pulsed Ultraviolet Light to Reduce the Allergenic Potency of Soybean Extracts

Pulsed ultraviolet light (PUV), a non-thermal food processing technology, is reported to be able to inactivate enzymes and reduce allergen levels from peanut extracts. The objective of this study was to determine if PUV would reduce the allergen levels and allergenic potency of soy extracts. Soy extracts were treated with PUV at various times (2, 4 and 6 min), centrifuged, and analyzed by SDS-PAGE and an indirect ELISA for IgE binding or allergenic potency. Results showed that PUV treatment led to an increase in sample temperature/weight loss but a decrease in the levels of soy allergens (i.e., glycinin and ?-conglycinin) as shown in SDS-PAGE. Allergens were reduced probably through aggregation which increased with treatment time. IgE binding was reduced as well in the following order: 20%, 44% and 50% reductions in absorbance values at 2, 4, 6 min, respectively (the latter two were not significantly different (p < 0.05%) from each other). It was concluded that PUV was capable of reducing the allergenic potency of soy extracts, and that the optimal PUV treatment time was 4 min. Clinical data is still needed before PUV can find an application in the development of less allergenic soybean beverages and products.

EFFECT OF PACKAGING MATERIALS ON INACTIVATION OF PATHOGENIC MICROORGANISMS ON MEAT DURING IRRADIATION

The effects of packaging materials, low-dose irradiation, and subsequent storage on inactivation of pathogen were studied. UV-sterilized meat surfaces were inoculated with approximately 5 to 6 log10 CFU/cm2 E. coli O157:H7 or approximately 6 to 7 log10 CFU/cm2 Salmonella Typhimurium, wrapped in plastic sheets of polyethylene, polylactic acid (PLA), polynylon, polypropylene, or low-density polyethylene (LDPE), sealed and vacuum packaged, and subjected to irradiation doses ranging from 0.5 to 2.0 kGy in a60 Co irradiator. Samples were analyzed for remaining bacterial populations immediately after irradiation and after 7 days of refrigerated storage (4°C). For S. Typhimurium, both the effect of packaging material and storage period were significant as compared to untreated samples (p < 0.05). Higher log10 reductions were observed following irradiation at all doses after refrigerated storage period than for day 0 samples. In general, irradiation resulted in higher log10 reduction of E. coli O157:H7 than S. Typhimurium at the same dose. The following conditions demonstrated maximum log10 reductions in this study: 2.0 kGy irradiation dose, 7-day refrigerated storage at 4°C, LDPE plastic for E. coli O157:H7, and PLA plastic for S. Typhimurium. However, there were no significant differences between the mechanical strength of irradiated and unirradiated plastics (p > 0.05).

Combining sanitizers and nonthermal processing technologies to improve fresh-cut produce safety

Abstract Fresh and fresh-cut produce are often consumed raw and are an important part of a healthy, balanced diet. In recent years, the consumption of fresh produce has been associated with outbreaks of Escherichia coli O157:H7, hepatitis A virus (HAV), and human norovirus (NoV), for example. Methods for improving fresh and fresh-cut produce safety would have tremendous benefit both for consumers, in terms of health and safety, and for the industry. This chapter addresses the development of combinations of chemical sanitizers (chlorine, ozone, chlorine dioxide) and nonthermal processing technologies that have potential commercial applications, such as the use of ultrasound to dislodge pathogens from fresh produce surfaces, and the use of energy-independent ClO2 technologies developed for forward military deployments to disinfect produce or food contact and handling surfaces.

Heat and Steam Treatments

Heat-based processes have been used for centuries for food preservation and still remain the most widely used preservation technique in food manufacturing. However, thermal processing treatments are not as efficacious in the destruction of pathogenic microorganisms at low water activities compared to moist environments. Several dry-heat processes have been applied to low-moisture foods and include drying, hot air and baking, air impingement, dry roasting, and oil roasting. These applications require higher temperatures and longer heat times to obtain equivalent lethality to moist-heat processes. Moist-heat processes, which include blanching, moist-air impingement, and controlled condensation steam, are very effective at inactivating microorganisms because the added moisture significantly reduces microbial thermal resistance. However, an increased moisture content of the product can reduce the shelf life, often resulting in the necessity for the (energy consuming) re-drying of product to remove the added moisture. Lastly, extrusion has been shown to be an effective process for microbial inactivation.

Milk Pasteurization by Pulsed UV-light Treatment

Staphylococcus aureus is a pathogen of concern in milk and milk products. Pulsed UV-light is a novel technology that can be used to inactivate this pathogen in a very short time. Efficacy of pulsed UV-light was investigated for inactivation of S. aureus in milk. A surface response model was used to design the experiments. 12, 30, and 48 ml of cell suspension in milk was treated under pulsed UV-light for 30, 105, and 180 seconds. 0.1 ml of treated and untreated samples was spiral plated on Baird-Parker agar and incubated at 37oC for 24 h. The colonies were then enumerated and log10 reduction was calculated. The log10 reduction obtained varied from 0.16 to 8.55 log10 CFU/ml demonstrating the ability of pulsed UV-light to inactivate Staphylococcus aureus. The effect of treatment time, time*distance interaction, and time*volume interaction were found to be significant (p<0.05). Maximum log10 reductions were obtained for (i) 8 cm sample distance from UV-strobe, 30 ml sample volume, and 180 sec treatment time combination and (ii) 10.5 cm sample distance from UV-strobe, 12 ml sample volume, and 180 sec treatment time combination.

Investigation of Staphylococcus aureus Inactivation by Pulsed UV-light and Infrared Heating Using Micro-spectrometry and Transmission Electron Microscopy

Pulsed UV-light and infrared heat treated S. aureus cells were analyzed using transmission electron microscopy to identify the damages caused during the treatment. A five second treatment of S. aureus with pulsed UV-light resulted in complete inactivation of S. aureus even after enrichment. The temperature increase during the pulsed UV-light treatment was 2oC. S. aureus was treated using six ceramic infrared lamps with the power of 500 W. A 5 ml of S. aureus cells in phosphate buffer was treated at 700oC lamp temperature for 20 min. The microscopic observation clearly indicated that there was cell wall damage, cytoplasmic membrane shrinkage, cellular content leakage, and mesosome disintegration for both pulsed UV-light and infrared treatments. The structural damage of S. aureus during pulsed UV-light treatment might be caused by the constant disturbances of the intermittent pulses. Temperature increase might be the cause of the cellular damage by infrared heat treatment. FTIR microspectrometry was successfully used to classify the pulsed UV-light and infrared heat treated S. aureus by discriminant analysis. Further investigation on identification of key absorption bands may result in a better assessment of the chemical and structural changes during pulsed UV-light and infrared heating.

Best Practices for Assessing, Managing, and Communicating Food Allergen Risks: An Introduction

The public health issues associated with food allergens can only be tackled by taking an integrative approach that involves all sectors of the food industry and engages all who are involved in the manufacture, preparation, and service of foods. Significant advances have been made over the past two decades in our understanding of food allergens and in the development of control measures to minimize the public health risks associated with them (e.g., issuance of allergen labeling regulations, development of guidelines for managing allergens in food production and foodservice operations, and establishment of policies in communities and schools to manage food allergies). However, broad and successful implementation of allergen controls has yet to be achieved. Many gaps still exist, including the lack of hazard analysis and risk management approaches tailored to the needs of specific types of operations, absence of detailed documentation on best practices, insufficient dissemination of available information and resources to stakeholders, and shortage of tools and programs to train staff. This book is designed to address many of these gaps by highlighting best practices for the assessment, management, and communication of food allergen risks at various stages of the food chain, including manufacture of packaged food, serving meals in restaurants and other foodservice establishments, and preparation of food at home. The information presented also provides valuable resources for stakeholders to develop structured, risk-based training programs. This chapter provides an overview of current efforts to address public health issues associated with food allergens and the challenges that remain.

Infrared Heat Treatment for Inactivation of Staphylococcus aureus

The efficacy of infrared heating for inactivation of Staphylococcus aureus, a pathogenic microorganism, in milk was studied to investigate the potential of this technology for milk pasteurization. S. aureus population was reduced from 0.10 to 8.41 log10 CFU/ml, depending upon the treatment conditions. The effects of infrared lamp temperature (536, 619oC), volume of the treated milk sample (3, 5, and 7 ml), and treatment time (1, 2, and 4 min) were found to be statistically significant (p 4 min) indicated that there was no growth observed following enrichment in most cases for treatment at a 619oC lamp temperature. The results demonstrated that infrared heating has an excellent potential for effective inactivation of S. aureus in milk. Further optimization of the process may result in a commercially successful milk pasteurization method.

Effect of Packaging Materials on Inactivation of Pathogenic Microorganisms on Meat during Irradiation

Beef surface samples were inoculated with E. coli O157:H7 or Salmonella Typhimurium, wrapped with five selected plastics i.e., polylactic acid (PLA), low density polyethylene (LDPE), polypropylene, polynylon, and polyethylene and vacuum packaged. Following vacuum packaging, the samples were subjected to various irradiation doses (0.5, 1.0, and 2.0 kGy) in a 60Co irradiator. The resulting microbiological samples were analyzed for microbial reduction immediately after irradiation and after seven-days of refrigerated storage. Also, the packaging materials’ mechanical strength was analyzed. The change in the mechanical strength was not significant among all the packaging materials used (p>0.05). However, the effect of packaging material, storage, and irradiation dose were significant (p<0.05) for reducing both E. coli O157:H7 and Salmonella Typhimurium on beef surfaces. Polylactic acid plastic and LDPE plastic exhibited higher log10 reductions for Salmonella Typhimurium and E. coli O157:H7 respectively for both immediate and 7 day refrigerated storage analysis. Generally, the storage samples (Day-7) exhibited higher log10 reductions than the immediate analysis samples (Day-0). Also, E. coli O157:H7 demonstrated higher log10 reductions than Salmonella Typhimurium.