A piece by the European Food Safety Authority on Listeria issues with blanched and frozen vegetables shows the importance of Listeria control in the post-processing environment. Also shows that the 100/gm level for Listeria may have issues. This comes after a long, ongoing "multi‐country outbreak of Listeria monocytogenes ST6 that caused 53 cases and 10 deaths over the period 2015–2018, was linked in 2018 to frozen vegetables."
We have known both of these items for some time. With blanched vegetables, we are never sure the consumer is going to properly handle and cook the vegetables. Therefore, low levels of Listeria can be problematic even if the product will not support growth during frozen storage.
In the US, as part of the Preventive Controls for Human Foods regulation, this is controlled as part of the Sanitation Preventive Controls if that product is considered ready-to-eat. And we have a zero-tolerance policy.
European Food Safety Authority
EFSA Journal
https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2020.6092
The public health risk posed by Listeria monocytogenes in frozen fruit and vegetables including herbs, blanched during processing
EFSA Panel on Biological Hazards (BIOHAZ) Konstantinos Koutsoumanis Avelino Alvarez‐Ordóñez Declan Bolton Sara Bover‐Cid Marianne Chemaly Robert Davies … See all authors
First published:20 April 2020 https://doi.org/10.2903/j.efsa.2020.6092
Abstract
A multi‐country outbreak of Listeria monocytogenes ST6 linked to blanched frozen vegetables (bfV) took place in the EU (2015–2018). Evidence of food‐borne outbreaks shows that L. monocytogenes is the most relevant pathogen associated with bfV. The probability of illness per serving of uncooked bfV, for the elderly (65–74 years old) population, is up to 3,600 times greater than cooked bfV and very likely lower than any of the evaluated ready‐to‐eat food categories. The main factors affecting contamination and growth of L. monocytogenes in bfV during processing are the hygiene of the raw materials and process water; the hygienic conditions of the food processing environment (FPE); and the time/Temperature (t/T) combinations used for storage and processing (e.g. blanching, cooling). Relevant factors after processing are the intrinsic characteristics of the bfV, the t/T combinations used for thawing and storage and subsequent cooking conditions, unless eaten uncooked. Analysis of the possible control options suggests that application of a complete HACCP plan is either not possible or would not further enhance food safety. Instead, specific prerequisite programmes (PRP) and operational PRP activities should be applied such as cleaning and disinfection of the FPE, water control, t/T control and product information and consumer awareness. The occurrence of low levels of L. monocytogenes at the end of the production process (e.g. < 10 CFU/g) would be compatible with the limit of 100 CFU/g at the moment of consumption if any labelling recommendations are strictly followed (i.e. 24 h at 5°C). Under reasonably foreseeable conditions of use (i.e. 48 h at 12°C), L. monocytogenes levels need to be considerably lower (not detected in 25 g). Routine monitoring programmes for L. monocytogenes should be designed following a risk‐based approach and regularly revised based on trend analysis, being FPE monitoring a key activity in the frozen vegetable industry.
Summary
Following a request from the European Commission, the Scientific Panel on Biological Hazards (BIOHAZ) was asked to provide a scientific opinion on the public health risk posed by Listeria monocytogenes and, if considered relevant by EFSA, other pathogens that may contaminate fruit, vegetables and herbs (FVH) which are processed (e.g. blanched) prior to being placed on the market frozen. It was clarified that fruit and herbs are out of scope of the assessment, as these are typically not blanched while some or all groups of vegetables may be blanched. These will be referred to as blanched frozen vegetables (bfV).
In particular, EFSA was asked to provide an estimation of the public health impact of L. monocytogenes contamination, and if considered relevant also of other pathogens in bfV, compared with other known pathogen–food combinations (Term of Reference 1; ToR1). Based on the number of human cases involved in the food‐borne outbreaks (FBOs) in the European Union (EU) (2005–2018), L. monocytogenes is the most relevant pathogen in bfV for public health. Therefore, the public health impact of L. monocytogenes contamination of bfV was compared with the better‐known risk of food‐borne illness associated with ready‐to‐eat (RTE) foods such as RTE meat products, dairy products and/or fishery products. Comparison was done using data on strong FBOs at EU/EEA level from 2008 to 2018 related to L. monocytogenes for the whole population. The ‘dairy’ food category was responsible for five outbreaks by L. monocytogenes involving 47 cases, while ‘fish and seafood’ and ‘meat and meat products’ caused nine and 16 outbreaks involving 63 and 190 cases, respectively. Cases linked to bfV were reported only in 2018 and involved 46 persons (all hospitalised) and five deaths. Also, a quantitative microbiological risk assessment (QMRA) model was used to estimate the listeriosis risk associated with the consumption of bfV by the elderly population of the age group 65–74 years old. The bfV were separated into two subcategories to encompass the range of consumer habits in relation to the mode of use/consumption; namely those consumed uncooked or cooked (i.e. boiled, fried or microwave heated). The estimated individual risk, i.e. the probability of illness per serving, is lower for bfV than for any of the RTE food subcategories evaluated, i.e. cold‐smoked fish, hot‐smoked fish, gravad fish, cooked meat, sausage, pâté and soft and semi‐soft cheese. It is up to 3,600 times greater for bfV consumed uncooked rather than cooked and judged to be very unlikely (5–10%) to be higher for bfV consumed uncooked than for soft and semi‐soft cheese. The estimated public health impact, i.e. the annual number of cases for elderly females in the EU, taken as an example, is less than two cases per year, which is, considering also the uncertainty, lower than any of the evaluated RTE food categories. The public health impact of bfV is dominated by the proportion of total servings consumed uncooked.
The main risk factors of contamination and growth of L. monocytogenes in bfV from processing until consumption were assessed in ToR 2. The production steps considered started from the receipt of the raw material at the processing plant, while the consumption steps included storage after thawing, food preparation and consumption habits. The main factors that may increase the contamination and/or growth of L. monocytogenes in bfV during processing are: (i) the hygiene status of the incoming raw materials; (ii) the hygienic conditions of the food processing environment (FPE), including food contact surfaces (FCSs) and non‐FCSs; (iii) the microbiological quality of the process water; and (iv) the time/Temperature (t/T) combinations used for storage, washing, blanching, cooling and freezing. Blanching (depending on t/T applied in the process) and water disinfection (to maintain the microbiological quality of process water) can reduce the contamination of L. monocytogenes in bfV at processing level. The main factors affecting contamination and/or growth of L. monocytogenes in bfV after processing are: (i) the intrinsic characteristics of the bfV (e.g. pH, aw, nutrients, presence of antimicrobial compounds and natural microbiota); (ii) the t/T profiles during thawing and storage; and (iii) the cooking conditions applied, including the cooking method and equipment.
In ToR 3, recommendations were requested on possible control options that may be implemented by food business operators (FBOp) during the production process of bfV. Control options are based on prerequisite programmes (PRPs), including good hygiene practises (GHP), good manufacturing practices (GMP) and operational PRPs (oPRPs), as well as procedures based on the hazard analysis and critical control points (HACCP) principles. Analysis of the hazards and activities of the target FBOp suggest that PRPs are sufficient to reduce contamination and the application of a complete HACCP plan is either not possible or would not further enhance food safety. In total, 11 PRP categories were identified, which, if implemented together, are very likely (95–99%) to reduce the probability of contamination of bfV by L. monocytogenes. Hygienic design of equipment, cleaning and disinfection of the processing environment and water control are of utmost importance to reduce the probability of introduction, survival and growth of L. monocytogenes. Additionally, t/T combinations applied during washing, blanching, cooling and freezing must be controlled to prevent the potential for any surviving L. monocytogenes to grow. Four different oPRPs are suggested as control measures and linked to seven different processing stages including: (i) equipment and processing environment (oPRP1: cleaning and disinfection); (ii) processing steps where water is used (oPRP2: water control); (iii) washing (oPRP3: t/T control); (iv) blanching (also oPRP3: t/T control); (v) cooling (also oPRP3: t/T control); (vi) freezing (also oPRP3: t/T control); and (vii) consumer practices (oPRP4: product information and consumer awareness). Additional control measures which the aim to reduce or eliminate L. monocytogenes in the product or on food process surfaces have been identified. However, not all of these measures are commercially available. In addition, their efficacy is not yet fully validated in industrial settings.
In ToR 3, recommendations were requested on routine monitoring for L. monocytogenes in the bfV processing environment and final product. This was carried out by critically appraising available guidelines for the industry. It was clarified that sampling and monitoring recommendations have the purpose to verify that the food safety management system (FSMS) implemented by the FBOp is well designed and has the appropriate control measures. Environmental monitoring (EM) can be used to validate or verify specific PRPs or as a strategy to monitor the environment for unhygienic conditions. An EM program should establish the sampling strategies and microbiological methods for L. monocytogenes detection most appropriate for maximising the identification of sources and routes of L. monocytogenes contamination in the FPE. Well‐established routine EM programmes should be designed on a risk‐based approach, considering the nature and size of the food operation and reflecting aspects related to the raw materials, the production processes and the final product application, but they also need to be regularly revised based on trend analysis. To establish a routine monitoring program, the FBOp should consider the following criteria: (i) the identification of the sampling points; (ii) the target microorganisms; (iii) the sample size; (iv) the frequency of testing; and (v) the selection of sampling, detection and quantification methods. It is not possible to give specific advice regarding the sampling sites that should be selected or the number of samples and frequency of sampling because these must be chosen on a case‐by‐case basis and established on a risk‐based approach and trend analysis. Sampling, detection and enumeration methods should follow validated methods. Subtyping of L. monocytogenes isolates by molecular methods (such as whole genome sequencing; WGS) is necessary to establish whether the isolates belong to a persistent clone.
It was clarified that, if the FBO decides to establish an intermediate level of L. monocytogenes concentrations in bfV at the end of the production process (i.e. performance objective; PO) compatible with the food safety objective (FSO) of 100 CFU/g at the moment of consumption without cooking, the PO would need to be estimated considering reasonably foreseen storage conditions (e.g. 48 h 12°C). This was mainly inferred from a study that considered the potential growth of L. monocytogenes in different bfV during storage for a maximum of 120 h at 5 to 12°C. It was concluded that the occurrence of relatively low levels of L. monocytogenes at the end of the production process, e.g. < 10 CFU/g (detection limit of the quantification method), would be compatible with that limit of 100 CFU/g as long as any labelling recommendations given are strictly followed (i.e. 24 h at 5°C). However, considering reasonably foreseeable conditions of use by the consumers beyond the labelling instructions (i.e. 48 h at 12°C), levels need to be considerably lower, even below the detection sensitivity of the current available standard analytical procedure/methods (not detected in 25 g) for those vegetables that best support pathogen growth. Microbiological criteria, set by the risk manager, can be used as a tool to verify that the threshold of the L. monocytogenes concentration in bfV at the end of production (compatible with the limit) is not exceeded. Sampling plans should be designed to take into consideration the expected heterogeneity of the contamination, the specificity and the sensitivity of the analytical methodology as well as the statistical confidence required for acceptance or rejection of non‐compliant lots. The impact of possible food safety criteria (FSC) on public health and/or on product compliance would be useful information to support risks managers’ decisions in this respect.
Consumer education and standardised label information are recommended to promote better understanding by consumers. It is also recommended to raise the awareness of the public health risks associated with the consumption of uncooked bfV, particularly by susceptible population groups. It is also recommended to perform subtyping of L. monocytogenes isolates detected during the routine monitoring program in FPE by molecular methods (e.g. WGS) and to improve collection and reporting of data on human listeriosis, including underlying conditions.
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