RESULTS

Definition of the possible niches of contamination and microbiological analysis

The handles of the seven different knives have been opened with a saw. As an example, two of the opened handles and the respective blades are reported in Figure 1 and 2. In both photos it possible to observe the presence of soil. The two knives shown have been chosen as an example of light and heavy contamination.

The presence of soil poses a question on the probability that this inner space, protected from the current sanitizing procedures, could represent a niche for the growth of microorganisms and a source of cross-contamination.

The results of the microbiological analysis showed that viable microorganisms and spores were present. The extent of contamination varied between the knives maybe also with respect to the length of utilization and the kind of use in the processing line.

This step gave a first estimation of the contamination level within the blade, but, the mean value obtained, was considered insufficient to define the target lethality of a sanitizing cycle. For this reason the target value of 7 log units inactivation has been chosen with reference to the definition of sanitization given by the EHEDG Glossary.

This value has been chosen as a very conservative value, because a recent Opinion on the sanitization of knives posed the question about if 3 log units of E. coli inactivation would be considered an acceptable level of hygiene.

The D/z-values, when available, help to determine which the most resistant pathogen of concern is, for a specific food and production process. Log linear inactivation models are among the first mathematical models used in food microbiology. Due to its broad applicability, the D/z-concept is most appropriate to obtain an estimation of the performance of an inactivation process.

It is usually difficult to choose the correct inactivation parameters between those present in international literature, furthermore the inactivation parameters are refereed to foods. To avoid lethality underestimation, the E. coli 95% upper prediction levels of D-values reported by van Asselt and Zwietering (2006) have been chosen as reference values.

Quantification of lethality on the blade

In Figure 4 the temperature profiles of the blades for the four target temperatures are shown. The correspondent inactivation obtained is shown in Figure 5 (for E. coli 95% upper prediction levels of D-values reported by van Asselt and Zwietering – 2006)

The times needed to reach 7 log inactivation of E. coli, were:

-          For 70 ºC cabinet target temperature: 26 minutes 20 seconds

-          For 75 ºC cabinet target temperature: 12 minutes 40 seconds

-          For 80 ºC cabinet target temperature: 8 minutes 5 seconds

-          For 85 ºC cabinet target temperature: 7 minutes

Quantification of lethality in the coldest point

Figure X – Comparison, at 85 ºC cabinet target temperature, for XL knives, between blade and core (coldest point) values.  In continuous lines, temperature profiles, and, in dotted lines, log inactivation values (for E. coli 95% upper prediction levels of D-values reported by van Asselt and Zwietering – 2006).

The times needed to reach 7 log inactivation of E. coli, for XL knives, at 85 ºC cabinet target temperature were:

-          Blade: 7 minutes (knife surface sanitization)

-          Knife coldest point: 10 minutes (whole knife sanitization)

Discussion

The totality of the inactivation parameters found in literature and entered in the spreadsheet refers to food products or model systems simulating foods. As stated by many authors, the main difficult in applying the D and z concept is the choice of the inactivation parameters for the estimation of the lethality of the heating process. In our case this choice was even more difficult.

The first assumption of this study was to use those data obtained in food to evaluate the effect in a knife. The leading theory is that the blade of the knife is a simplest model if compared to food. For the contamination found inside the handle the assumption is that the microorganisms could encounter conditions similar to those of a food product. The Authors are aware that some deviations can occur, and for this reason the most conservative values found were considered in the estimation of the lethality of the sanitizing process.

The assumption of a log-linear inactivation kinetic of microorganisms is only one of the possible cases of inactivation patterns of microorganism. However, in many cases, the survival curves of heated bacteria do not present a log linear relation: a concave or u pward concavity of curves has frequently been observed (Cerf, 1977).

The notion that microbial inactivation follows a first order kinetics has frequently been challenged during the ye ars

. There is now enough evidence that a log linear isothermal survival curve of bacterial cells is the exception rather than the rule (van Boekel, 2002).

In this study, this approach has been chosen for two main reasons:

-          simplicity of the use;

-          the most commonly accepted way to quantify the effect of a sanitization process in the food industry

CONCLUSIONS

The temperature profiles and the inactivation curves shown in this paper were obtained in pilot equipment. In industrial washing systems, the time-temperature slope will depend on the amount of power supplied and, consequently, the time to reach the inactivation target will be shorter for a higher power input.

Inactivation reference data used in this work has been chosen considering the “worst case” scenario. In industrial systems, the final user would be able to choose the best fitted parameters (reference microorganism and inactivation reference data) to meet with country or sector specific regulations, Sanitation Standard Operating Procedures, HACCP prerequisits and Food Safety Management standards (BRC, IFS, ISO 22000).

Industrial washing systems must be able to record data from the processes, to document that every batch has achieved the hygienic target.

Energy saving: this capacity of continuously monitoring and recording the inactivation performance, should be used to stop the energy input to the system as soon as the inactivation target is achieved.

 

Industrial equipment design

The design of the washing cabinet combines the mechanical effect of the tunnel and the “shower effect” characteristic of the washing cabinet currently commercialized.

The cleaning step is carried out mechanically. In fact, the pump energy is concentrated in spraying nozzles to create the effect of a soil removing curtain. A circular motion is applied to attack the knives from different sides and angles. In this way it is possible to remove the soil efficiently, achieving quickly the desired cleaning effect.

The disinfection step is obtained thorough heat transfer to the knives by means of hot water from an independent low pressure circuit, creating a “shower effect”.

Software calculates, through the predictive model based on inactivation parameters, the accumulation of lethal effect due to the temperature. Two independent temperature probes are incorporated. The temperature double checking is intended to ensure the reliability of the process. In case of unforeseen events the cycle starts from the beginning as a corrective measure in order to guarantee the targeted log inactivation.

Every day, more and more companies are sensitive to the environment. Mimasa has been aware of the importance of its preservation for years and that’s why we keep working to maximize the efficiency of our machines.

Furthermore, over the last years, the energetic costs have exponentially risen. That’s the reason why many industries are investing great efforts in optimizing the energetic consumption on their processes.

The self cleaning filtering system that Mimasa installs in most of its equipment is a clear example of how to optimize consumption. By separating the impurities outside the machine, the water is kept in the right conditions for longer. So, the final result is a high quality wash with less water and less chemical products, but above all less energy since less water needs to be heated, thus generating minimal environmental impact.

One of the most notorious examples is the disinfection through water atomizing, which reduces water and disinfectant consumption up to 15 times compared to the traditional systems.

In order to minimize energy consumption, some other options are already being offered together with all the equipment, such as the automatic rinse stop when no elements are passing through it or the isolation of the chassis to minimize heat loss.

And we keep working on developing systems that allow us to minimize the consumption and so reducing the energetic costs of our customers and the environmental impact.

Objectives

In this framework an effective and efficient system for the sanitization of knives is missing. In this perspective the aims of the present study are:

-          to develop a method able to guarantee the sanitization of knives and mesh gloves;

-          to reduce sanitizing process times with respect to those currently applied;

-          to optimize the energetic efficiency of sanitizing process;

-          to design a new washing machine including an expert system able to monitor the sanitizing performance based on the three previous aims.

Knives as a possible source of cross contamination in food processing

Tools such as knives, as well as hands and clothing, are primarily contaminated through contact with surfaces that are rich in bacteria, such as the skin of slaughtered animals, intestinal contents, abscesses and the incised surfaces of lymph nodes.

A number of bacterial pathogens able to cause food-borne diseases in humans can contaminate meat. Pathogens can be transferred to food from utensils that are not properly cleaned and disinfected. Since some pathogenic microorganisms can survive outside the human body for considerable periods of time, unsanitized utensils could be a direct or indirect source of food borne illnesses (Food Code, 2001a).

Searching niches of possible contamination

With the aim to detect if other parts of the knife than blade could be a niche of possible contamination, the handles of seven knives were opened with a saw. The knives, from different manufacturers belonged to different meat processing plants and were used for different periods in cutting and deboning operations. See figure 3 and 4 as the slightest and highest contamination.

Time temperature testing

Four target temperatures (70, 75, 80, 85ºC) were considered. Three knives of different size (Dick, boning knife narrow blade ergogrip 15AZ; Dick, boning knife wide blade ergogrip 18AZ; Dick butcher ergogrip 21AZ) were used to simulate the sanitizing cycle.

The three different knives are from now named S, M and XL depending on the size, being S the smallest one and XL the bigger one. The objective was to monitor the temperature of the blade and also to monitor the coldest spot of the handle of knife.

The temperature of the blade was considered equivalent to that of the cabinet. The cabinet, when closed, was completely sealed and the position of the probe was studied to give an accurate value of the cabinet temperature.

The localization of the coldest point inside the handle was obtained by an X ray CT analysis (Yokogawa medical systems ACPRO) (Figure 1). After localizing the coldest point, a hole was made on the handle to introduce a probe into it (Testo, sensor A NiCr-Ni Type K class 1) to register the inner temperature profile. The right positioning of the probe inside the handle was also controlled by X ray CT (Yokogawa medical systems ACPRO). The holes were sealed with cyanoacrylate glue (Figure 2).

All probes were connected to a data logger Testo (T4-177). For each target temperature and for each blade the correspondent time/temperature profile during sanitizing was obtained both for blade and coldest spot. Logged values were transferred to a PC spreadsheet program (Excel 2007 for Windows)

Quantification of lethality of heating against microorganisms

The same approach which has been used in food processing to design optimal time temperature treatment is here proposed as a method to quantify the effect in terms of inactivation in the sanitization of food utensils like knives.

In 1943, Katzin et al. (1943) defined the decimal reduction time that Ball and Olson (1957) symbolized by the letter D. Thus, the model appears in the familiar form:

logN_t = logN₀ – t/D

In this model, the classical D-value presents a simple biological significance: time that leads to a 10-fold reduction of surviving population at a constant reference temperature and is easily estimated from a simple linear regression.

The models are simple and have proven their value in heat processing over 80 years, although this may be due to systematic over-processing. This concept still governs canning process calculation.

A spreadsheet for the estimation of the log inactivation of some selected microorganisms has been created. The estimation of the log inactivation was based on the log-linear approach. The spreadsheet was created in order to work in Celsius degrees and to calculate the cumulative and the actual lethality of the process for each step conducted above 40ºC. The cooling was not included in the calculation of lethality.

In a first instance three microorganisms were chosen as target: Salmonella spp., Listeria monocytogenes and Escerichia coli. On the basis of an extended literature research, a little data base comprising the inactivation parameters D and z for three target microorganisms were added.

An extensive literature study was first conducted in order to widen the range of inactivation D and z values of foodborne pathogenic microorganisms. In this framework the recent work of Van Asselt and Zwietering (2006) was considered as basic source of inactivation parameters. In their study the authors collected a large quantity of D-values (n =4066) from literature for various pathogens and linear regression was applied to obtain average D-values (together with the 95% upper prediction level) and z-values. As reported by the authors, the 95% upper prediction levels of the D-values can be used as a (conservative) estimate of inactivation and can be used to give order of magnitude values in overall process evaluations. Furthermore the Authors conclude that even effects of shoulders disappear in the overall analysis.

For each target temperature four profiles were obtained during sanitizing cycle. Each profile was put in the spreadsheet to obtain the theoretical inactivation in terms of logarithm units.

One of the most demanding requirements to fulfil BRC, IFS and other regulations in slicing plants is the sticks disinfection, specially the cooked ones, before their entrance to the clean room.

Mimasa has developed a completely new system, based on water atomizing with disinfectant product. This technique has multiple advantages, although the most significant is the reduction of water and disinfectant consumption. The consumption is up to 15 times lower compared to the traditional spraying systems.

Furthermore, the water atomizing system guarantees a uniform distribution of the disinfectant through all the surfaces of the cold meat piece, including the creases around the clip area. Another clear advantage is the minimization of humidity at the entrance of the clean room.

Not only can be used with any sort of approved disinfectant, such as those dissolved in water or the pure ones (alcohol type), but they can also work with ozonyzed water or electrolyzed water, for instance.

In order to reduce consumption even more, the machine incorporates an automatic start system when a cold meat piece is detected and an automatic stop system after a programmable time with no product passing through it.

Its compact design allows placing it at the entrance of any line in the clean room, even just before the freezing tunnels.

Las exigencias higiénicas en los procesos productivos y en todos los elementos que intervienen en éstos, han aumentado de forma muy significativa a lo largo de los últimos años. La correcta combinación de los factores del Círculo de Sinner (efecto mecánico, temperatura, tiempo y producto químico) y un buen diseño de los equipos garantizan un óptimo resultado. En Mimasa ofrecemos contratos de garantía de higiene, medida objetivamente. Disponemos de equipos y tecnología para valorarla y ofrecemos la medición a través de microbiología y/o bioluminiscencia en función de los requerimientos de cada cliente.

Garantizamos sus cajas, moldes, bins, palets, etc. libres de E.Coli, Salmonella y Listeria y le registramos y guardamos el proceso en formato Excel.