Effect of organic acids,hydrogen peroxide and mild heat on inactivation of Escherichia coli O157:H7 on baby spinach

Minimally processed baby spinach contaminated with Escherichia coli O157:H7 has been associated with multiple outbreaks of foodborne illnesses recently. Chlorinated water is widely used to wash vegetables commercially, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. This study was conducted to determine the effects of organic acids and hydrogen peroxide alone and in binary combinations with or without mild heat (40 and 50 °C) on the inactivation of Escherichia coli O157:H7 on baby spinach. Baby spinach leaves were dip-inoculated with E. coli O157:H7 to a level of 6 log CFU/g and stored at 4 °C for 24 h before treatment. Individual washing solutions (1% and 2% lactic acid [LA], citric acid [CA], malic acid [MA], tartaric acid [TA], acetic acid [AA], hydrogen peroxide [H₂O₂] as well as binary combinations of LA, CA, MA and H₂O₂ at final concentrations of 1% were used to decontaminate spinach leaves at 22, 40 or 50 °C for 2–5 min to test their efficacy in reducing E. coli O157:H7. Chlorinated water (200 ppm free chlorine) decreased the population of E. coli O157:H7 on baby spinach by only 1.2–1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% LA at 40 °C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7 which is significantly higher than chlorine washing. Washing with LA + CA or LA + HP at 40 °C for 5 min was equally effective against E. coli O157:H7, resulting in a 2.7 log reduction of E. coli O157:H7. The application of mild heat significantly enhanced the efficacy of washing solutions on the inactivation of E. coli O157:H7. There was, however, no significant difference between treatments at 40 °C for 5 min and 50 °C for 2 min. The results suggested that the use of organic acids in combination with mild heat can be a potential intervention to control E. coli O157:H7 on spinach.     

The influence of pre-wash chopping and storage conditions of parsley on the efficacy of disinfection against S. Typhimurium

Initial chopping of parsley before washing for subsequent processing into ready-to-eat foods later in the day is common in some restaurants. The aim was to evaluate the influence of pre-wash chopping on the S. Typhimurium decontamination by common washing and disinfection methods including the use of vinegar (4%, v/v, acetic acid), 0.25 g/l sodium dichloroisocyanurate (NaDCC), and water combined with manual agitation. This study demonstrated limited efficiency of applied methods and that holding pre-wash chopped leaves at 30 °C reduced the effectiveness of all washing solutions. Scanning electron microscopy (SEM) imaging indicated initiation of biofilm formation after 24 h at 5 °C with noticeable adhesion of cells to inaccessible folds of the vein on the leaf surface. NaDCC was shown to be the most effective solution achieving log reductions of 1.92–3.12 on intact parsley leaves. The latter being on those held at 5 °C for 4 h; However, its effectiveness was reduced by 0.73–0.93 and 1.19 log cfu/g on chopped leaves at 5 °C and on both intact and chopped leaves at 30 °C, respectively. In conclusion, strict temperature control and avoiding pre-wash chopping are highly recommended during handling of parsley for the optimal elimination of pathogenic microorganisms.     

Development of carrot parenchyma softening during heating detected in vivo by dynamic mechanical analysis

Dynamic mechanical analysis was employed to explore the development of carrot parenchyma softening during heating in the range of 30–90 °C. Results indicated that compared with raw carrots the toughness of carrots at 60 °C decreased significantly (P < 0.05) at 0.5 °C/min while there was no significant deference (P > 0.05) at 2 °C/min. Samples at 0.5 °C/min finally obtained the lower toughness. Besides, both loss tangent (LT) and two negative peaks on the temperature–slope plot were heating rate dependent. At 0.5 °C/min, distinct increases of LT started at about 48 °C while at about 67 °C at 2 °C/min. With increasing rate, LT effect decreased obviously. Increasing rates caused a shift of both peaks from low temperatures (49–60 °C) to high ones (67–75 °C). Values of both peaks were significantly higher (P < 0.05) at 0.5 °C/min than at 2 °C/min. Furthermore, the microstructure of samples at 0.5 °C/min was more rigid and irregular shrinkage, accompanied by more small pores as well as bigger cracks in comparison to that at 2 °C/min. And cell walls of samples at 0.5 °C/min seemed to thinner. Therefore, the development of carrot parenchyma softening during heating was both temperature and heating rate dependent. We suggested that the breakdown of pore proteins and middle lamella in cell walls induced the dramatic loss of cell turgidity and the subsequent changes of elastic modulus, collectively causing tissue softening.     

Evaluation of electrolyzed water as cleaning and disinfection agent on stainless steel as a model surface in the dairy industry

In the dairy industry, cleaning and disinfection of surfaces are important issues and development of innovative strategies may improve food safety. This study was aimed to optimize the combined effect of alkaline electrolyzed water (AEW) and neutral electrolyzed water (NEW) as alternative cleaning and disinfection procedure on stainless steel plates (SSP) with and without electropolishing. NEW at 10 ppm total available chlorine (TAC), achieved a ˃5 log CFU/mL reduction of milk spoilage bacterial suspension, grown in trypticase soy broth (8.7 log CFU/mL of each bacterial strain: Pseudomonas aeruginosa, Enterococcus faecalis and Micrococcus luteus) contacted for 30 s. An optimal design of experiments was used to assess the combined effect of cleaning with AEW, followed by disinfection with NEW (40 ppm TAC, contact time 3 min). Tested factors were contact time (10, 20 and 30 min), concentration of AEW (100, 200 and 300 mg NaOH/L), temperature (30, 40 and 50 °C), and surface type (304-2B SSP with or without electropolishing), using sixteen treatments with two replicates. The response variable was bacterial cells removal (log CFU/cm²). All main effects, two factors interactions and a quadratic term significantly influenced cells removal, and were modeled using a second order polynomial. Best cleaning procedures were significantly affected by surface roughness; electropolished SSP required 10 min, 100 mg/L AEW at 30 °C, whereas SSP without modification required 30 min, 300 mg/L AEW at 30 °C. From confirmatory tests cells removed were 3.90 ± 0.25 log CFU/cm² for electropolished SSP, and 3.20 ± 0.20 log CFU/cm² for SSP without modification. NEW is non-corrosive, and can be advantageously used for environmentally friendly cleaning and disinfection processes.     

Temperature increase of foods in car trunk and the potential hazard for microbial growth

This study assessed the potential microbial hazard posed by temperature increases on refrigerated and frozen food stored in car trunk exposed to sunlight. The internal temperatures in the trunk and of food items (egg, milk, tofu, fresh meat, and frozen meat) stored in it during summer were measured at 10 min intervals for up to 3 h (12:00 PM to 15:00 PM). Trunk temperature steadily increased from 32.3 °C up to 41.5 °C, with longer exposure times. Food temperature also increased substantially during this period, reaching 33.5 °C (frozen meat), 35.3 °C (milk), 35.6 °C (tofu), 37.0 °C (egg), and 38.4 °C (fresh meat). Cloud cover and solar radiation affected car and food temperature, with lower cover and higher radiation associated with higher food temperatures (7.1 °C higher in the car trunk when compared to a situation of extensive cloud cover and low radiation, and 6.9 °C higher for eggs, 5.9 °C for milk, 5.0 °C for tofu, and 7.4 °C and 5.5 °C for fresh and frozen meat, respectively). The temperature of refrigerated foods (egg, milk, and fresh meat) reached 20 °C within 40 min (tofu: 60 min) and 30 °C within 90–110 min (tofu: 130 min). The temperature of frozen meat reached to danger zone (5–60 °C), which is associated with bacterial growth, after 90 min. Consumers should therefore realize the importance of time–temperature control, particularly in warm and sunny weather. Purchased foods should be transferred to a refrigerated environment as fast as possible, and the car trunk should be avoided. The present results can be used for consumer education, contributing to the recognition of the importance of food safety.     

Effects of chlorine treatment and packaging on the quality and shelf-life of modified atmosphere (MA) packaged coleslaw mix

The effects of an anti-microbial washing treatment combined with modified atmosphere packaging (MAP) on the quality and storage life of dry coleslaw were determined. The anti-microbial treatment consisted of washing for 5 min with agitation in a chlorine solution (100 ppm available chlorine). The coleslaw mix was packaged within two micro-perforated OPP films, PA-160, and PA-210 and stored at 4 and 8 °C for nine days. Chlorine treatment had large beneficial effects on quality, particularly at 4 °C. It significantly reduced respiration rate, resulting in significantly lower CO₂ and higher O₂ concentrations at both 4 and 8 °C compared with water washed coleslaw. Washing with chlorine was found to significantly improve sensory scores, particularly at 4 °C with better acceptability of appearance, colour and aroma. Microbial loads were significantly reduced by the use of chlorine and these reductions were substantially greater at 4 °C. Chlorine had no effect on tissue pH. Overall, chlorine washing had significant effects on the quality and storage life of MA packaged dry coleslaw mix of the treatments studied, the most effective was chlorine washing combined with storage in PA-160 film at 4 °C.     

Inactivation effect of newly developed low concentration electrolyzed water and other sanitizers against microorganisms on spinach

The efficacy of newly developed low concentration electrolyzed water (LcEW) was investigated to inactivate the pathogens on spinach leaves as a convenient and safe alternative sanitizer and it was compared to other sanitizers. Spinach leaves were inoculated with Escherichia coli O157:H7 and Listeria monocytogenes and dip treated with deionized water (DIW), LcEW, strong acid electrolyzed water (SAEW), aqueous ozone (AO), 1% citric acid (CA) and sodium hypochlorite solution (NaOCl) for 3 min at room temperature (23 ± 2 °C). For all pathogens, the similar pattern of microbial reduction on spinach was apparent with LcEW and SAEW washing. In the present study, it was found that LcEW inactivated, at maximum, 1.64–2.80 log cfu/g and DIW resulted in lowest reduction, 0.31–0.95 log cfu/g of background or pathogenic microflora present on spinach leaves compared to the unwashed control. The findings of this study indicate that LcEW and SAEW did not differ significantly (P > 0.05) in reducing background or pathogenic microflora on spinach and LcEW may be a promising sanitizer for washing vegetables without environmental pollution instead of using electrolyzed oxidizing (EO) water or SAEW.     

Determination of thermal inactivation kinetics of Listeria monocytogenes in chicken meats by isothermal and dynamic methods

The objective of this research is to determine the thermal inactivation kinetics of Listeria monocytogenes in chicken breast meat under both isothermal and dynamic conditions. A four-strain cocktail of L. monocytogenes was inoculated to chicken breast meat. Isothermal studies were performed by submerging samples under hot water maintained at constant temperatures ranging from 54 to 66 °C. The D values at each temperature were determined and used to calculate the z value, using log(D) = log(D₀) − T/z. Dynamic studies were conducted by submerging samples in a water bath with its temperature programmed to increase linearly from 30 to 65 °C at 1.25 °C/min or 1.73 °C/min. A method was developed to determine the kinetic parameters from linear heating temperature profiles.The thermal inactivation of L. monocytogenes in chicken breast meat followed the first-order kinetics. The z value determined from the isothermal studies was 4.95 °C, which is very close to the values reported in the literature. The dynamic method can also be used to determine the thermal inactivation kinetics of L. monocytogenes. The average z value (4.10 °C) determined by the dynamic method was slightly lower than that determined by the isothermal method. However, the parameters (D₀ and z) determined from both isothermal and dynamic methods can be used to estimate the survival of L. monocytogenes exposed to linear heating temperature profiles, with statistically equal accuracies.The dynamic method explored in this study can be used to determine the D₀ and z values of microorganisms that exhibit first-order kinetics and are exposed to linear heating temperature profiles. Compared to the isothermal method, the dynamic method requires few data points and is equally accurate.     

A highly sensitive method for quantifying gallocatechin gallate and its epimer using a catechin-specific peptide

We have developed a method for quantifying gallocatechin gallate (GCg) and epigallocatechin gallate (EGCg) using a catechin-binding peptide (part of the 67-kDa laminin receptor). Using micro titer plates, we investigated various conditions, including the quantifiable range of EGCg concentrations, the optimal concentration of the catechin-binding peptide, and the optimal reaction conditions. In this microplate assay, after each well was coated with bovine serum albumin, sample containing GCg and EGCg was added at pH 8.0, and allowed to stand at 37 °C for 2 h. After washing, biotinylated-peptide solution was added at 1 μg mL^?1 and allowed to react for 1 h at 37 °C. Each well was added with streptavidin–horseradish peroxidase conjugate, followed by chromogenic reaction for 25 min at room temperature. After the reaction, absorbance was measured at 405 nm. Our method is capable of quantifying EGCg in the range of approximately 0.1–2.0 mg L^?1 with a high degree of sensitivity and a high correlation (R² = 0.98) between EGCg concentration and absorbance. The method was specific to GCg and EGCg and seems capable of estimating GCg and EGCg contents in the presence of other catechin compounds. The method is simple and highly sensitive for quantitative GCg and EGCg measurement that requires no special equipment or operation and can measure multiple samples simultaneously.     

Effects of mildly heated,slightly acidic electrolyzed water on the disinfection and physicochemical properties of sliced carrot

The efficacy of mildly heated, slightly acidic electrolyzed water (mildly heated SlAEW) at 45 °C for disinfection and maintenance of sliced carrot quality was studied. Mildly heated SlAEW (23 mg/L available chlorine, pH at 5.5) was used to treat the carrots, followed by rinsing with tap water (TW) for 2 min at 4 °C, and its effectiveness as a disinfectant was evaluated. The physicochemical properties of the carrots were determined and a comparison was made between treatments with SlAEW at room temperature (18 °C), TW at 18 °C and mildly heated TW at 45 °C. Results show that total aerobic bacteria, mold and yeast populations were significantly lower after mildly heated SlAEW treatment. Mildly heated SlAEW treatment reduced the total aerobic bacteria by 2.2 log₁₀ CFU/g and molds and yeasts by >1.9 log₁₀ CFU/g compared with TW treatment. Color indices of hue and chroma of sample surfaces were not affected by mildly heated SlAEW treatment and there were insignificant differences in hardness or the ascorbic acid and β-carotene contents of sliced carrots. The use of mildly heated SlAEW is suggested as an effective disinfection method for fresh cut carrots with low available chlorine.     

Effects of Quillaja saponaria extract and Nα-lauroyl-l-arginine ethyl ester on reducing selected foodborne pathogens in vitro and maintaining quality of fresh-cut endive (Cichorium endivia L.) at pilot plant scale

The aim of the present study was to evaluate the applicability of Quillaja saponaria extract (QSE) and N^α-lauroyl-l-arginine ethyl ester (LAE) as antimicrobial wash water additives in fresh-cut lettuce processing. Antibacterial activities of LAE and QSE against selected strains of the foodborne pathogens Salmonella enterica, Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes were examined in vitro. Minimum inhibitory concentrations determined by broth microdilution assay demonstrated that LAE exhibited a strong antimicrobial activity with MICs between 4 and 32 μg/mL against all tested strains, whereas QSE showed a weaker antimicrobial activity with MICs >512 μg/mL. On a pilot-plant scale, the effects of warm water washing at 45 °C for 120 s with and without 40 mg/L QSE or 100 mg/L LAE as well as cold water washing at 4 °C for 120 s with QSE or LAE, respectively, of shredded endive (Cichorium endivia L.) were investigated regarding microbiological and sensory quality as well as physiological properties. Samples were analyzed for headspace O₂ and CO₂ levels, phenylalanine-ammonia-lyase activity and contents of nitrite and nitrate during nine days of cold storage at 4 °C. By analogy to its antimicrobial effect against the foodborne pathogens in vitro, LAE allowed up to 4 log₁₀ cfu/mL reduction of the microbial load in the washing water of the pilot plant, and might therefore reduce cross-contamination while saving water. The addition of LAE to warm washing water impaired sensory properties of fresh-cut endive during storage, which was predicted by chlorophyll fluorescence imaging analyses. QSE treatment combined with warm water washing best retained sensory appearance throughout our study, being possibly suitable for the production of premium products.     

High pressure processing pretreatment enhanced the thermosonication inactivation of Alicyclobacillus acidoterrestris spores in orange juice

The spoilage of high acid fruit juices and nectars by Alicyclobacillus acidoterrestris is a major concern to juice manufacturers around the world since it is difficult to detect. In this study, thermosonication (ultrasound and heat, TS) and thermal inactivation of A. acidoterrestris spores in pretreated orange juice were carried out and resistance parameters were estimated. First, the effect of TS acoustic energy density (AED, 0.3–20.2 W/mL) on the inactivation at 75 °C was investigated. Then, the influence of TS temperature (70–78 °C) on the spore inactivation (AED = 20.2 W/mL) was studied. Next, we explored the effect of high pressure processing (HPP) pretreatment of juice on the 20.2 W/mL TS inactivation at the best temperature (78 °C). Lastly, the thermal inactivation of spores in juice heat shocked + 1 min sonicated vs. untreated juice was also investigated.Results of TS showed higher spore inactivation for higher AED (D_75°C-value of 49 min for 20.2 W/mL vs. 217 min for 0.33 W/mL). Lower D-values were obtained at higher temperatures (D_78°C-value of 28 min vs. D_70°C-value of 139 min at 20.2 W/mL). The TS D_78°C-value (at 20.2 W/mL) decreased further from 28 min to 14 min when the orange juice was previously submitted to 600 MPa for 15 min. Thermal treatment alone at 78 °C resulted in almost no spore inactivation, whereas the heat shock + ultrasound pretreatment of juice enhanced the thermal inactivation of spores (D_85°C-value decreased from 69 to 29 min). To conclude, HPP-assisted TS provided the best method for spore inactivation, indicating the benefit of high pressure and power ultrasound technology in addition to heat. TS required at least 8 °C lower temperatures than thermal treatments to achieve the same spore inactivation, which could enhance juice quality and energy savings.     

Selection of a decontamination treatment for fresh Tuber aestivum and Tuber melanosporum truffles packaged in modified atmospheres

The objective of this study was to develop a surface disinfection method which, combined with modified atmosphere packaging (MAP), prolonged the shelf-life of Tuber aestivum and Tuber melanosporum truffles. T. aestivum was washed with sodium hypochlorite (500 ppm chlorine), hydrogen peroxide (5%) and ethanol (70%) alone or in combination with ultrasound (35 Hz) for 10 min at 4 °C. Dipping in ethanol 70% with ultrasound was found to be the most effective treatment, achieving 4 logarithmic reductions for pseudomonads, reductions greater than 2 logarithmic units for Enterobacteriaceae, lactic acid bacteria and molds and 1.5 logarithmic reductions for yeasts. Finally, both truffle species were decontaminated with the selected treatment, packaged with a microperforated film and stored at 4 °C for 28 days. In this situation the microbial counts and the sensory quality were maintained throughout storage and the shelf-life of both truffle species were prolonged to 28 days.     

Effects of integrated treatment of nonthermal UV-C light and different antimicrobial wash on Salmonella enterica on plum tomatoes

The aim of this study was to evaluate inactivation of inoculated Salmonella enterica on whole tomato surface exploiting integration of nonthermal ultraviolet light (UV-C) treatment with antimicrobial wash. The effect of combined treatment on background microflora (aerobic mesophilic, and yeast and mold), during storage at ambient temperature (22 °C) for 21 days was also determined. A bacterial cocktail containing three serotypes of S. enterica (S. Newport H1275, S. Stanley H0558, and S. Montevideo G4639) was used based on their association with produce-related outbreaks. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve cell population of about 10⁷ CFU/tomato. An inoculated tomato was initially treated with a low (0.6 kJ/m²) dose of UV-C light (253.7 nm) followed by immersion in selected sanitizing solution (700 ml) to wash under mild agitation (ca. 250 rpm) for 2 min at room temperature (22 °C). Inactivation efficacy of combined treatments varied widely depending on the sanitizer property. Combined UV-C plus aqueous ozone (1 ppm) provided 3.13 ± 0.47 log CFU/fruit Salmonella reduction which was significantly lower (p < 0.05) compared to the rest of the combination treatments; whereas the treatment of UV-C followed by immersion in a novel antimicrobial preparation ‘HEN’, formulated mixing hydrogen peroxide, EDTA and nisin provided the best log reduction (4.71 ± 0.25 log CFU/fruit). Organic acids (1%) or their binary mixtures, hydrogen peroxide (3%), and HEN provided greater than 4.0 log reductions for UV-C treated tomatoes. Treatments were effective in controlling native microbial loads as the total aerobic mesophilic organisms and the population of yeast and mold remained significantly (p < 0.05) low during storage compared to control. Findings from this study provide safe and effective post harvest intervention strategies for produce industry as an alternative to current chlorine based wash. These results may also help researchers design future decontamination studies.     

Screening for bacteriocin-producing lactic acid bacteria from kurut,a traditional naturally-fermented yak milk from Qinghai–Tibet plateau

The objective of this study was to screen the bacteriocin-producing lactic acid bacteria (LAB) strains from kurut collected from six regions in Qinghai–Tibet Plateau. Upon the elimination of the effects of organic acids and hydrogen peroxide on tested microorganisms, 5 strains, among a total of 256 presumptive LAB strains screened, belonging to the species of Lactobacillus casei (strains T1, T11 and S9), Lactobacillus lactis (strain S2), and Leuconostoc lactis (strain T14), showed inhibition activities against both Staphylococcus aureus and Escherichia aerogenes. The inhibition activities were destroyed after treated with proteinase K, pepsin and trypsin separately, suggesting the proteinaceous nature of the antimicrobial compounds produced from the strains. The bacteriocins from strains T1 and T14 remained stable for 20 min at 121 °C and after 2 h of incubation at pH values between 3.0 and 11.0, compared with those from strains S2 and T11 that were stable during pH 3.0–6.0, and that from strain S9 stable between pH 3.0 and 9.0. Bacteriocins produced from strains S2, S9 and T11 were resistant to heating treatment at 100 °C for 20 min. Bacteriocins did not adhere to the surface of the producer cells. The results suggest that the extracellular bacteriocins produced from special LAB strains from kurut, of high antibacterial activity, as well as high thermal and pH stability, may be applied to dairy products manufactory to inhibit the growth of spoilage and pathogens during fermentation.     

Effect of pH,temperature and storage time on the stability of bovine myelin basic protein

Bovine central nervous system tissue (CNT) harboring highest levels of the infectious agent for prion diseases, has been banned from food and feed supplies. Effective detection of CNT in excessively processed meat and feedstuffs requires the assay based on a stable marker in CNT as the analyte. Myelin basic protein (MBP), the major central nervous system (CNS) myelin protein, was reported to be detectable up to 115 °C in the literature. This study further investigated the effects of pH, temperature and storage time on the stability of purified bovine MBP (18.5 kDa) in solutions. Purified MBP dissolved in 10 mM PBS was adjusted to pH 3.0, 7.2 and 10.5, respectively. Sample at each pH was subjected to three heat treatments, 100 °C, 121 °C, and 133 °C for 30 min. The unheated and 100 °C heated samples at pH 7.2 were stored at 4 °C for 19 days to study the storage stability of bovine MBP. The immunoreactivity of all samples was examined using indirect non-competitive enzyme-linked immunosorbent assay and immunoblotting with an anti-MBP monoclonal antibody. The protein degradation was observed by analyzing samples using SDS-PAGE. Results show that bovine MBP was most stable at pH 7.2 while the protein was least stable at pH 10.5. MBP started to degrade after heating at 121 °C for 30 min at pH 7.2. Storage up to 19 days at 4 °C did not significantly affect the immunoreactivity of unheated and heated samples. However, unheated MBP samples started to show degradation from day 8 of storage; while no degradation was observed in 100 °C heated samples over the storage time. This study demonstrated that bovine MBP can be a suitable marker for the detection of bovine CNT in highly processed food and feed supplies.     

Sensory quality and food safety of boneless chicken breast portions thawed rapidly by submersion in hot water

Boneless chicken breast portions were thawed by submersion in hot water (60 °C) and compared to refrigerator thawing. Thawing in hot water was significantly quicker (2–8.5 min) than refrigerator thawing (10–15.5 h). Thawing time in hot water increased with an increase in meat thickness. Sensory panelists could not distinguish a difference between hot water versus refrigerator thawed and subsequently grilled chicken breast portions. A model for Salmonella growth predicts that thawing chicken breast at the slowest rate in this study (0.5 °C/min) would result in a lower increase in the Salmonella concentration than that expected for room temperature storage for 4 h.     

Growth and inhibition by spices of growth from spores of enterotoxigenic Bacillus cereus in cooked rice

Bacillus cereus is a pathogenic spore-forming bacterium implicated in cases of diarrheal and emetic type of foodborne illness. We previously found that enterotoxigenic B. cereus is widely present in retail spices. Here we analyzed the spore heat resistance of nine diarrheal strains isolated from spices. Seven had D_95°C values ranging from 0.64 to 3.53 min while two emetic strains had D_95°C values of 7.04 min and 6.64 min. The ability of selected strains to grow in cooked rice at temperatures 20 °C, 17 °C and 12 °C was determined as well as their toxin expression capability. After 48 h, B. cereus levels of 1.26 × 10⁷ and 3.8 × 10⁷ CFU/g were obtained in cooked rice maintained at 17 °C and 20 °C respectively. At 12 °C, counts did not reach 10⁴ CFU/g even after 48 h of incubation. The increase in the aerobic, mesophilic bacterial population (APC) and B. cereus population naturally present in 0.1% crushed pepper added to cooked rice was determined over a period of 48 h at 20 °C and 17 °C. Levels of B. cereus in pepper/rice samples reached a maximum of 1600 MPN/g at 20 °C while the APC was 2.4 × 10⁸/g at this temperature. When thyme, containing the same initial natural level of B. cereus, was added to rice in place of pepper, more than a five-fold greater level of B. cereus was detected at 20 °C. Since thyme contained initial APC of 2.5 log₁₀ less than pepper we conclude that the high APC functions in a competitive-exclusion manner, minimizing the growth of B. cereus and potentially other agents of foodborne illness. This is particularly relevant in instances of temperature abuse of foods and may explain the low incidence of foodborne illness due to B. cereus despite its widespread presence shown in previous surveys of market spices.     

Optimising sorting and washing of home-grown maize to reduce fumonisin contamination under laboratory-controlled conditions

Subsistence farming communities with low socio-economic status reliant on a mono cereal maize diet are exposed to fumonisin levels that exceed the provisional maximum tolerable daily intake of 2 μg kg^?1 body weight day^?1 recommended by the Joint FAO/WHO Expert Committee on Food Additives. In the rural Centane magisterial district, Eastern Cape Province, South Africa, it is customary during food preparation to sort visibly infected maize kernels from good maize kernels and to wash the good kernels prior to cooking. However, this customary practice seems not to sufficiently reduce the fumonisin levels. This is the first study to optimise the reduction of fumonisin mycotoxins in home-grown maize based on customary methods of a rural population under laboratory-controlled conditions. Maize obtained from subsistence farmers was analysed for the major naturally occurring fumonisins (FB₁, FB₂ and FB₃) by fluorescence HPLC. Large variations were observed in the unsorted and the experimental maize batches attributable to the non-homogeneous distribution of fumonisin contamination in maize kernels. Optimised hand-sorting of maize kernels by removing the visibly infected/damaged kernels (fumonisins, 53.7 ± 15.0 mg kg^?1, 2.5% by weight) reduced the mean fumonisins from 2.32 ± 1.16 mg kg^?1 to 0.68 ± 0.42 mg kg^?1. Hand washing of the sorted good maize kernels for a period of 10 min at 25 °C resulted in optimal reduction with no additional improvement for wash periods up to 15 h. The laboratory optimised sorting reduced the fumonisins by 71 ± 18% and an additional 13 ± 12% with the 10 min wash. Based on these results and on local practices and practicalities the protocol that would be recommended to subsistence farmers consists of the removal of the infected/damaged kernels from the maize followed by a 10 min ambient temperature water wash.     

Inactivation of Neosartorya fischeri and Paecilomyces variotii on paperboard packaging material by hydrogen peroxide and heat

This study reports on the influence of heat and hydrogen peroxide combination on the inactivation kinetics of two heat resistant molds: Neosartorya fischeri and Paecilomyces variotii. Spores of different ages (1 and 4 months) of these molds were prepared and D-values (the time required at certain temperature/hydrogen peroxide combination to inactivate 90% of the mold ascospores) were determined using thermal death tubes. D-values found for P. variotii ranged from 1.2 to 25.1 s after exposure to different combinations of heat (40 or 60 °C) and hydrogen peroxide (35 or 40% w/w) while for N. fischeri they varied from 2.7 to 14.3 s after exposure to the same hydrogen peroxide concentrations and higher temperatures (60 or 70 °C). The influence of temperature and hydrogen peroxide concentration on the d-values varied with the genus of mold and their ages. A synergistic effect of heat and hydrogen peroxide in reducing D-values of Paecilomyces variotti and N. fischeri has been observed. In addition to strict control of temperature, time and hydrogen concentration, hygienic storage and handling of laminated paperboard material must be considered to reduce the probability of package’s contamination. All these measures together will ensure package’s sterility that is imperative for the effectiveness of aseptic processing and consequently to ensure the microbiological stability of processed foods during shelf-life.