Killing activity of microwaves in milk

Estimation of Bacteriophage MS2 Inactivation Parameters During Microwave Heating of Frozen Strawberries

Frozen berries have been repeatedly linked to acute gastroenteritis caused by norovirus, the most common cause of foodborne illness in the United States. Many guidelines recommend that frozen berries be microwaved for at least 2 min, but it is unclear if this thermal treatment is effective at inactivating norovirus. The objective of this study was to model the effect of microwave heating at varying power levels on the survival of bacteriophage MS2, a norovirus surrogate, when inoculated onto frozen strawberries. Bacteriophage MS2 was inoculated onto the surface of frozen strawberries with a starting concentration of approximately 10 log PFU/g. Samples (either 3 or 5 whole strawberries) were heated in a 1300-Watt domestic research microwave oven (frequency of 2450 MHz) at power levels of 30, 50, 70, and 100% (full power), for times ranging from 15 to 300 s to determine inactivation. Temperatures at berry surfaces were monitored during heating using fiberoptic thermometry. All experiments were conducted in triplicate. The primary model for thermal inactivation was a log-linear model of logN vs. time. The secondary model was for a D-value decreasing linearly with temperature and an added term that was path-dependent on the thermal history. Parameters in the model were estimated using dynamic temperature history at the surface of the berry, via nonlinear regression using all data simultaneously. The root mean square error was ∼0.5 PFU/g out of a total 6-log reduction. Log reductions of 1.1 ± 0.4, 1.5 ± 0.5, 3.1 ± 0.1, and 3.8 ± 0.2 log PFU/g were observed for 30, 50, 70, and 100% microwave power levels when three berries were heated for 60 s. D-values were 21.4 ± 1.95 s and 10.6 ± 1.1 s at 10 and 60°C, respectively. This work demonstrates an approach to estimate inactivation parameters for viruses from dynamic temperature data during microwave heating. These findings will be useful in predicting the safety effect of microwave heating of berries in the home or food service.

Recent advances in sterilization and disinfection technology: A review

Sterilization and disinfection of pollutants and microorganisms have been extensively studied in order to address the problem of environmental contamination, which is a crucial issue for public health and economics. Various form of hazardous materials/pollutants including microorganisms and harmful gases are released into the environment that enter into the human body either through inhalation, adsorption or ingestion. The human death rate rises due to various respiratory ailments, strokes, lung cancer, and heart disorders related with these pollutants. Hence, it is essential to control the environmental pollution by applying economical and effective sterilization and disinfections techniques to save life. In general, numerous forms of traditional physical and chemical sterilization and disinfection treatments, such as dry and moist heat, radiation, filtration, ethylene oxide, ozone, hydrogen peroxide, etc. are known along with advanced techniques. In this review we summarized both advanced and conventional techniques of sterilization and disinfection along with their uses and mode of action. This review gives the knowledge about the advantages, disadvantages of both the methods comparatively. Despite, the effective solution given by the advanced sterilization and disinfection technology, joint technologies of sterilization and disinfection has proven to be more effective innovation to protect the indoor and outdoor environments.

Effect of hydrolysis and microwave treatment on the antibacterial activity of native bovine milk lactoferrin against Cronobacter sakazakii

Bovine lactoferrin (bLF) is an iron-binding glycoprotein used in functional and therapeutic products due to its biological properties, the most important being its antimicrobial activity. In this study, hydrolysates of bovine lactoferrin (bLFH) obtained with pepsin, chymosin and microbial rennet were assayed against Cronobacter sakazakii (10⁴ CFU/mL) in different media: phosphate buffered saline (PBS), bovine skim milk and whey, and reconstituted powdered infant formula (PIFM). The results obtained have shown that hydrolysis of bLF enhances its antibacterial activity against C. sakazakii. The three types of bLFH dissolved in PBS reduced C. sakazakii growth from a concentration of 0.1 mg/mL and inhibited it completely above 0.5 mg/mL, after 4 and 8 h of incubation at 37 °C. The three bLFH (1 and 2 mg/mL) did not show any antibacterial activity in skim milk, whey and reconstituted PIFM after 8 h of incubation at 37 °C. However, C. sakazakii growth was completely inhibited in whey when pepsin and chymosin bLFH (2 mg/mL) were combined with undigested bLF (2 mg/mL), after 8 h of incubation at 37 °C. On the other hand, the combination of any of the three hydrolysates with bLF showed very low activity in skim milk and practically no activity in reconstituted PIFM. Furthermore, the effect of temperature after reconstitution (4, 23 and 37 °C), on the antibacterial activity of bLF (2.5 and 5 mg/mL) in reconstituted PIFM contaminated with C. sakazakii (10-10² CFU/mL) was also investigated. bLF at 5 mg/mL significantly reduced (p < .05) the proliferation of C. sakazakii in reconstituted PIFM at 37 °C until 2 h. C. sakazakii did not grow at 4 °C for 6 days in reconstituted PIFM with or without bLF. The effect of microwave heating (450, 550 and 650 W for 5, 10 and 15 s) on the antibacterial activity and stability of bLF (2.5 mg/mL) in reconstituted PIFM contaminated with C. sakazakii (10-10² CFU/mL) was also studied. The antibacterial activity of bLF was maintained after treatments at 450 and 550 W for 5 s, which kept 94 and 89% of bLF immunoreactivity, respectively. Moreover, microwave treatments of reconstituted PIFM with or without bLF, at 650 W for 5 s, and at 450, 550 and 650 W for 10 and 15 s, completely inactivated C. sakazakii.

Novel approaches to improve the intrinsic microbiological safety of powdered infant milk formula

Human milk is recognised as the best form of nutrition for infants. However; in instances where breast-feeding is not possible, unsuitable or inadequate, infant milk formulae are used as breast milk substitutes. These formulae are designed to provide infants with optimum nutrition for normal growth and development and are available in either powdered or liquid forms. Powdered infant formula is widely used for convenience and economic reasons. However; current manufacturing processes are not capable of producing a sterile powdered infant formula. Due to their immature immune systems and permeable gastro-intestinal tracts, infants can be more susceptible to infection via foodborne pathogenic bacteria than other age-groups. Consumption of powdered infant formula contaminated by pathogenic microbes can be a cause of serious illness. In this review paper, we discuss the current manufacturing practices present in the infant formula industry, the pathogens of greatest concern, Cronobacter and Salmonella and methods of improving the intrinsic safety of powdered infant formula via the addition of antimicrobials such as: bioactive peptides; organic acids; probiotics and prebiotics.

Microwave Heating Inactivates Shiga Toxin (Stx2) in Reconstituted Fat-Free Milk and Adversely Affects the Nutritional Value of Cell Culture Medium

Microwave exposure is a convenient and widely used method for defrosting, heating, and cooking numerous foods. Microwave cooking is also reported to kill pathogenic microorganisms that often contaminate food. In this study, we tested whether microwaves would inactivate the toxicity of Shiga toxin 2 (Stx2) added to 5% reconstituted fat-free milk administered to monkey kidney Vero cells. Heating of milk spiked with Stx2 in a microwave oven using a 10% duty cycle (cycle period of 30 s) for a total of 165 kJ energy or thermal heating (pasteurization), widely used to kill pathogenic bacteria, did not destroy the biological effect of the toxin in the Vero cells. However, conventional heating of milk to 95 °C for 5 min or at an increased microwave energy of 198 kJ reduced the Stx2 activity. Gel electrophoresis showed that exposure of the protein toxin to high-energy microwaves resulted in the degradation of its original structure. In addition, two independent assays showed that exposure of the cell culture medium to microwave energy of 198 kJ completely destroyed the nutritional value of the culture medium used to grow the Vero cells, possibly by damaging susceptible essential nutrients present in the medium. These observations suggest that microwave heating has the potential to destroy the Shiga toxin in liquid food.

Enterobacter sakazakii: an emerging problem in paediatric nutrition

Recently there has been considerable concern related to the presence of bacteria, in particular Enterobacter sakazakii, in powdered infant formula milk. E. sakazakii, a member of the family Enterobacteriaceae, is an emerging opportunistic pathogen that has been associated with cases of meningitis, necrotizing enterocolitis and sepsis in premature and full-term infants. Feeding with powdered infant formula has been epidemiologically implicated in several clinical cases. Powdered infant formula is not a sterile product; good hygienic practice is, therefore, necessary in its reconstitution to reduce the risk of infection. The ingestion of raised numbers of E. sakazakii resulting from storage at room temperature after reconstitution is highlighted as well as the uncertain routes of E. sakazakii product contamination.

Identification of proteins involved in osmotic stress response in Enterobacter sakazakii by proteomics

Enterobacter sakazakii is considered an opportunistic food-borne pathogen, causing rare but significant illness especially in neonates. It has been proposed that the organism is relatively resistant to osmotic and dry stress compared to other species of the Enterobacteriaceae group. To understand the mechanisms involved in osmotic stress response, 2-DE protein analysis coupled to MALDI-TOF MS was employed to investigate changes in the protein profiles of E. sakazakii cells in response to two different types of osmotic stress (physical desiccation and growth in hyperosmotic media). In total, 80 differentially expressed protein spots corresponding to 53 different protein species were identified. Affiliation of proteins to functional categories revealed that a considerable number of the differentially expressed proteins from desiccated and hyperosmotic grown samples belonged to the same functional category but were regulated in opposite directions. Our data show that the protein pattern of NaCl-grown cultures reflect more or less a general down-regulation of central metabolic pathways, whereas adaptation of (non-growing) cells in a desiccated state represents an accumulation of proteins that serve some structural or protective role. The most striking effects observed for both types of osmotic stress in E. sakazakii were a significant down-regulation of the motility apparatus and the formation of filamentous cells.

Susceptibility pattern among pathogenic species ofAspergillusto physical and chemical treatments

Physical treatments, like heating or irradiation, may reduce the viability or eradicate Aspergillus conidia, which in turn might help to prevent infections by members of this genus. Chemical treatments can also prevent infection resulting from contaminated hospital fabrics or surfaces. Our objectives were to study the kinetics of survival of the conidia of pathogenic Aspergillus species, like A. fumigatus, A. flavus and A. niger, during exposure to heating at 60 degrees C and microwave irradiation. In addition, we evaluated the susceptibility patterns of Aspergillus conidia to such chemical agents as cupric sulphate and sodium hypochlorite. Heating the conidia of A. flavus and A. niger at 60 degrees C for 45 min was found to be fungicidal (reduction > 104 conidia/ml), but was not with A. fumigatus conidia. Short periods of microwave irradiation (40 s) resulted in a significant reduction of the viability of the conidia of these three Aspergillus species as a result of lethal membrane lesions. All Aspergillus species were similarly susceptible to cupric sulphate and sodium hypochlorite. Therefore, heating, microwave and the chemical treatments tested impaired significantly the viability of Aspergillus conidia, supporting the use of these methods as preventive measures among patients at risk.

Enterobacter sakazakii: a coliform of increased concern to infant health

The first cases of neonatal meningitis believed to have been caused by Enterobacter sakazakii were reported in 1961. Prompted by several subsequent outbreaks of E. sakazakii infections in neonates and an increasing number of neonates in intensive care units being fed rehydrated powdered infant formula, considered to be a source of the pathogen, public health authorities and researchers are exploring ways to eliminate the bacterium or control its growth in dry infant formula, processing environments and formula preparation areas in hospitals. Reviewed here are advances in taxonomy and classification of E. sakazakii, methods of detecting, isolating and typing the bacterium, antibiotic resistance, clinical etiology and pathogenicity. Outbreaks of E. sakazakii infections in neonates and adults are summarized. Reports on the presence of E. sakazakii in clinical settings, the environment and foods and food processing facilities are reviewed. Tolerance of the pathogen to environmental stresses, its behavior in powdered and rehydrated infant formulae and hazard analysis and risk management are discussed. Research needs are presented.

A top-down proteomics approach for differentiating thermal resistant strains ofEnterobacter sakazakii

Thermal tolerance has been identified as an important factor relevant to the pathogenicity of Enterobacter sakazakii in human neonates. To identify a biomarker specific for this phenotypic trait, intact protein expression profiles of 12 strains of E. sakazakii were obtained using liquid chromatography mass spectrometry. Proteins were extracted from the bacterial cells, separated by reversed-phase liquid chromatography and mass analyzed. At the end of the chromatography run, the uncharged masses of the multiply charged proteins were determined via automated software routines. The resulting data provided an accurate mass expression profile of the proteins found in the individual strains. From the individual expression profiles, it was possible to identify unique proteins corresponding to strains with thermal resistance. One protein found only in the thermal tolerant strains was sequenced and identified as homologous to a hypothetical protein found in the thermal tolerant bacteria, Methylobacillus flagellatus KT. The protein sequence of this protein was then used to reverse-engineer PCR primers for the gene sequence associated with the protein. In all cases, only thermal tolerant strains of E. sakazakii produced amplified PCR products, demonstrating the specificity of this biomarker.

Experimental assessment of disinfection procedures for eradication of Aspergillus fumigatus in food

Aspergillus fumigatus spores in food may represent an infectious risk for neutropenic patients. We examined the efficiency of disinfection procedures applicable to foods for eradication of A fumigatus. Boiling and microwave treatment fully decontaminated an experimental spore suspension and naturally contaminated liquid foods (reconstituted dried food, herbal tea). Full decontamination of experimentally contaminated surfaces was only obtained with 70% ethanol or heating at 220°C for 15 minutes. Pepper was decontaminated when heated for 15 minutes at 220°C but not by microwaving. Fruit skin was partially decontaminated by 70% ethanol. We conclude that A fumigatus spores can be eradicated from food by heating to a temperature of at least 100°C. When foods cannot be exposed to high temperature or microwaving, ethanol only partially reduces the level of surface contamination.

Preparation and handling of powdered infant formula: a commentary by the ESPGHAN Committee on Nutrition

Powdered infant formulae are not sterile and may contain pathogenic bacteria. In addition, milk products are excellent media for bacterial proliferation. Multiplication of Enterobacter sakazakii in prepared formula feeds can cause devastating sepsis, particularly in the first 2 months of life. In approximately 50 published case reports of severe infection, there are high rates of meningitis, brain abscesses and necrotizing enterocolitis, with an overall mortality from 33% to 80%. Breast feeding provides effective protection against infection, one of the many reasons why it deserves continued promotion and support. To minimize the risk of infection in infants not fully breastfed, recommendations are made for preparation and handling of powdered formulae for children younger than 2 months of age. In the home setting, powdered infant formulae should be freshly prepared for each feed. Any milk remaining should be discarded rather than used in the following feed. Infant feeds should never be kept warm in bottle heaters or thermoses. In hospitals and other institutions written guidelines for preparation and handling of infant formulae should be established and their implementation monitored. If formula needs to be prepared in advance, it should be prepared on a daily basis and kept at 4 degrees C or below. Manufacturers of infant formulae should make every effort to minimize bacterial contamination of powdered products.

Thermal inactivation of Enterobacter sakazakii in rehydrated infant formula

The presence of low levels of Enterobacter sakazakii in dried infant formula have been linked to outbreaks of meningitis, septicemia, and necrotizing enterocolitis in neonates, particularly those who are premature or immunocompromised. In the current study, the ability of 12 strains of E. sakazakii to survive heating in rehydrated infant formula was determined at 58 degrees C with a submerged coil apparatus. The observed D58-values ranged from 30.5 to 591.9 s, with the strains appearing to fall into two distinct heat resistance phenotypes. The z-value of the most heat-resistant strain was 5.6 degrees C. When dried infant formula containing this strain was rehydrated with water preequilibrated to various temperatures, a more than 4-log reduction in E. sakazakii levels was achieved by preparing the formula with water at 70 degrees C or greater.

Lethal effect of microwaves on spores of Bacillus spp

Strains representing four types of common heat-resistant spores of Bacillus spp., B. cereus CCRC 14655, B. coagulans CCRC10606, B. licheniformis CCRC14693, and B. subtilis CCRC14199, were heated with microwaves at different power levels and under different conditions in salt solutions, starch solutions, and containers. The results of this study showed that B. licheniformis spores had the highest microwave tolerance at a power level of 100% for different incubation times. B. coagulans spores showed the lowest microwave tolerance in salt solutions with water activity values of 0.6, 0.7, 0.8, and 0.9, and B. licheniformis spores were the most resistant in the tested salt solutions at different incubation times. An analysis of the effect of the viscosity of the medium revealed that the bacteria had the lowest microwave resistance in a medium containing <0.8% starch in solution. The microwave resistance levels of the test microorganisms were the lower in glass containers than in polypropylene containers and aluminum foil-enclosed pouches. Of the four species of bacilli, B. licheniformis had the highest microwave tolerance (P < 0.05) under all conditions.

Outbreak of necrotizing enterocolitis associated with Enterobacter sakazakii in powdered milk formula

We describe an outbreak of necrotizing enterocolitis (NEC) that occurred in the neonatal intensive care unit of our hospital. A total of 12 neonates developed NEC in June-July 1998. For two of them, twin brothers, the NEC turned out to be fatal. Enterobacter sakazakii, a known contaminant of powdered milk formula, was isolated from a stomach aspirate, anal swab, and/or blood sample for 6 of the 12 neonates. A review of feeding procedures revealed that 10 of the 12 patients were fed orally with the same brand of powdered milk formula. E. sakazakii was isolated from the implicated prepared formula milk as well as from several unopened cans of a single batch. Molecular typing by arbitrarily primed PCR (AP-PCR) confirmed, although partially, strain similarity between milk and patient isolates. No further cases of NEC were observed after the use of the contaminated milk formula was stopped. With this outbreak we show that intrinsic microbiological contamination of powdered milk formula can be a possible contributive factor in the development of NEC, a condition encountered almost exclusively in formula-fed premature infants. The use of sterilized liquid milk formula in neonatal care could prevent problems with intrinsic and extrinsic contamination of powdered milk formula.