Effectiveness of inactivation of foodborne pathogens during simulated home pan frying of steak, hamburger or meat strips

In order to evaluate the effect of simulated home pan frying of raw meat and meat preparations of different animal species on the thermal inactivation of pathogens, the heat resistance (D-value) of three strains of Campylobacter jejuni, Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes and two strains of generic E. coli was validated in BHI and adjusted BHI (i.e. pH5.6 and 1.5% NaCl) at 60°C. The D-values were obtained of the linear phase of the survivor curves created in GInaFiT, a freeware tool to fit models to experimental data. The obtained D-values corresponded to those previously published in literature and confirmed L. monocytogenes to be the most heat resistant pathogen among them. Heat treatment in adjusted BHI significantly increased heat-resistance of E. coli O157:H7 and generic E. coli. Subsequently, the thermal inactivation of L. monocytogenes, Salmonella spp., C. jejuni and E. coli O157:H7 was evaluated using a standardized procedure simulating commonly used home pan frying of various types of meat including steaks or filets, hamburgers and meat strips from various animal species such as pork, beef, chicken, lamb and some turkey, horse, kangaroo and crocodile meat. Corresponding F70-values were calculated based upon measured core time/temperature profiles. It was noted that a core temperature of 70 °C was not always achieved and, moreover, a heat treatment equivalent to 2 min at 70 °C was also not always obtained. This was in particular noted in hamburgers although the meat was visually judged well done. On several occasions, residual survivors of the initial inoculated (4 logCFU/g) food borne pathogens could be recovered either by enumeration (limit of detection 1 logCFU/g) or by the presence/absence testing per 25 g. Pan frying of hamburgers yielded the highest number of surviving pathogenic bacteria (46%), followed by well-done filets and steaks (13%) and meat strips (12%). Taking only steaks (beef, horse, kangaroo, crocodile and turkey) into account, residual detection of pathogens occurred for all levels of doneness: 18% for well-done, 71% for medium and even 90% for rare steaks. Numbers of L. monocytogenes recovered after heat treatment ranged from <1 logCFU/g to 2.6 logCFU/g. Although, the prevalence of pathogens in meat might be low, and the numbers present in case of natural contamination are probably lower than the current used inoculum of 4 logCFU/g, consumers could still be exposed to surviving food borne pathogens in case of these commonly used pan frying of raw meat and meat preparations at consumer's home.publisher: Elsevier articletitle: Effectiveness of inactivation of foodborne pathogens during simulated home pan frying of steak, hamburger or meat strips journaltitle: International Journal of Food Microbiology articlelink: http://dx.doi.org/10.1016/j.ijfoodmicro.2015.04.014 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved.status: publishe

Microbiological analysis of strawberries for the presence of Salmonella spp. and VTEC in primary production, processing and trade in Belgium

Introduction: Fresh produce are an important component of a healthy diet, yet the last decades an increase was observed in the number of foodborne outbreaks associated with the consumption of fresh produce. Outbreaks included leafy vegetables, sprouted seeds, soft red fruit and melons. Since strawberries are an important fruit in Belgium and little information is available about microbial risks and how to control these risks, strawberries were sampled during primary production (6 farms: 3 open field cultivation and 3 hydroponic cultivation), processing (1 company) and trade (2 companies). Materials and methods: At farm level, samples were taken of strawberries, water, hands and substrate/soil during 4 visits, whereas at the processing level, wash water, strawberries (fresh, cut and in fruit salad), hands and contact surfaces were sampled during 6 visits. In the case of the trading companies 41 batches of strawberries were sampled. The samples were distributed over strawberry batches coming from Belgium/The Netherlands (20), Spain (13) and Egypt (8). Hands and contact surfaces were analysed for E. coli and Enterobacteriaceae by using a petrifilm and VRBL agar respectively. Strawberries, water and substrate/soil were analysed for E. coli and the presence or absence of Salmonella spp. and Verocytotoxin producing E. coli (VTEC) by the use of a petrifilm and the GeneDisc Cycler (Multiplex PCR). Results and Discussion: In general, no Salmonella spp. (0/201; 95% CI 0,00 – 1,88) or VTEC (0/201; 95% CI 0,00 – 1,88) was detected in any of the strawberry samples analysed nor at the level of processing and trade, nor in primary production. Neither was E. coli detected (< 10/g) as a hygiene indicator in any of the strawberry samples at processing or trade level. In primary production, E. coli was present in 2 strawberry samples (1,0 x 101 and 9,8 x 102 cfu/g). Generic E. coli were enumerated in 4/57 hand samples (2,0 ± 1,5 log cfu/25 cm²), 44/78 samples of irrigation water (1,5 ± 1,1 log cfu/100 ml), 4/24 soil samples (2,5 ± 0,5 log cfu/1000 cm²) and 7/24 substrate samples (1,8 ± 1,3 log cfu/g). Salmonella was not isolated from any of the environmental samples in primary production. On the other hand, 11/78 samples of irrigation water and 2/24 substrate samples were PCR-positive for VTEC, meaning that stx1 and/or stx2 and eae genes were detected. VTEC isolates from this irrigation waters or substrate samples were obtained in 4 out of 13 PCR-positive samples and confirmed as E. coli O26 (2 x water, 2 x substrate; the 4 isolates from these samples being obtained at one time interval from one farm). After further statistical analysis, it was found that there was a higher probability to find VTEC PCR signals in water in primary production if water sources can receive surface run-off water, are not disinfected or are located adjacent to farm animals. In addition, elevated E. coli numbers are an indicator for the presence of PCR VTEC signals (respectively 0/16, 3/13 en 8/15 samples with 1-10, 10-100 and ≥ 100 E. coli cfu/100 ml, respectively, showed PCR VTEC positive signals)

Application of biobased materials for packing short, medium and long shelf life food products

The possible application of several multilayered biobased materials for packing different food products, ranging from short to long shelf life products, was investigated. Several transparent and metalized cellulose based film, a cellulose/PLA based film, a xylan based film and PLA trays with a PLA based film, a PLA/cellulose based film and a PLA/paper based film as topfilm were examined. The investigated food products were tomatoes, steak, French fries, ham sausage, filet de saxe (a raw cured pork meat product) grated cheese, tortillachips, rice cakes, dry biscuits and potato flakes all packed under air or modified atmosphere (MAP). The food products were stored at refrigerated (4°C) or room temperature and analyzed at certain points during their shelf life. For the short shelf life products, microbiological analysis (total plate count, lactic acid bacteria and yeast and moulds), gas composition of the headspace, color, aw and pH were followed and those quality parameters were each time compared with their evolution in the conventionally packaged food products. For the medium shelf life products also hydrolytic and oxidative lipid rancidity were monitored. For the long shelf life products no microbiological analysis were performed. Furthermore, sensory characteristics of the different food products were evaluated. From the storage experiments it could be concluded that most investigated biobased materials are good functional substitutes for the conventional packaging materials currently used. For example, the oxygen and carbon dioxide concentrations followed the same trend as in the reference film and the concentrations remained below the maximum limit or above the minimal limit during the entire shelf life of the food products

Survival of Salmonella and E. coli O157 on strawberries and basil during storage at different temperatures

Limited information about the survival of Salmonella and E. coli O157 on strawberries and basil is available. As strawberries and basil are often consumed raw, they can pose a potential risk of foodborne illness for consumers. Therefore, the survival of both pathogens was assessed during one week storage at cold and ambient temperatures. Strawberries (100 ± 5 g in a perforated box) and basil leaves (25 g in a closed tray), were inoculated with a mix of 2 strains of E. coli O157 or Salmonella (Thompson and Typhimurium) to obtain an initial inoculum of 104 – 105 cfu/g. Strawberries’ samples were stored at 4°C, 10°C, 15°C, and 22°C and basil leaves at 7°C, 15°C and 22°C for 7 days (or less if visual spoilage occurred before or the pathogens dropped below the detection limit i.e. 50 cfu/g). For each temperature/time condition 2 independent storage experiments were performed (study A and B) (with triplicate sampling at defined time points). Samples were analysed by plating on Chromocult agar (+ 50 µg/ml nalidixic acid; E. coli O157) and XLD (Salmonella). In addition, the visual quality was assessed during storage. No growth of E. coli O157 or Salmonella was observed in case of strawberries stored at 4°C, 10°C, 15°C and 22°C. E. coli O157 and Salmonella survived during 7 days at 4°C but with a decrease of 2,5 to 3,8 log units being observed and a final recovery rate from 2 and 5 out of 6 samples respectively. At 10°C, no E. coli O157 was detected anymore after 6 days (0/6), in contrast to Salmonella which could be detected after 7 days in 5/6 samples with a similar decrease as for 4°C (2,5 to 3,9 log units). The numbers of pathogens dropped below the detection limit after 4 and 5 days at 15°C for E. coli O157 and Salmonella in study A respectively, while in study B a reduction of 3,0 to 4,0 log units was observed after 6 days, which was the end of shelf life due to the growth of molds. Storage of strawberries at 22°C resulted in growth of molds from day 2 (A) or 3 (B) whereby a reduction of pathogens was noticed of 1 to 2 log units after 2 days. In contrast, reduction of pathogens below the detection limit was not yet reached after 7 days storage of basil at different temperatures and only at 22°C some samples needed to be discarded due to the growth of molds and quality defects. Storage of basil leaves for 7 days at 7°C resulted in a decline of maximum 1,8 log cfu/g for both pathogens. Similar results were obtained at 15°C for Salmonella, whereas no decline was observed in case of E. coli O157. Also at 22°C restricted increase/decrease (≤ 1 log cfu/g) was observed for both pathogens after 7 days. Thus, avoiding contamination in particular at cultivation (and (post-)harvest) is important as both pathogens survive during storage, washing has only a limited effect and both strawberries and basil are consumed after minimal processing, excluding an inactivation treatment