Improved safety: for the product, for operators and for the environment

Microbiological Principles, in other words: what you would never like to find in the end product.

The air that surrounds us contains a variety of small, solid or liquid particles that compose the atmospheric aerosol. Due to sedimentation, it is practically impossible to find particles larger than 10μm. The human eye moreover, is not able to perceive particles with a diameter inferior to 30μm; it is therefore impossible to visibly judge the contamination of the air. It is also important to consider that the particles with a dimension inferior to 1μm do not sediment and that the microbes have dimensions that vary from 0,3 to 1μm; air is thereby an excellent vehicle of microbial contamination. The micro-contamination conveyed is therefore a very high risk factor in beverage productions, in particular as concerns cold fill products, as a microbic contamination at this stage of the production process is an almost certain source of contamination.

Bacteria

Bacteria are unicellular prokaryote organisms and have a very simple internal structure (no nuclear membrane, no membrane organelle) if compared to those of other living organisms. Their reproduction (bacterial growth) is the outcome of the division of every single cell into two parts exactly identical to the initial one, via a mechanism named fission. If the growth conditions are optimum, a bacteria cell is able to multiply every 20 minutes, so a single bacteria may originate almost 70 billion cells in 12 hours. The factors that influence reproduction include the quantity of nutrients available, humidity, pH, level of oxygen, and the presence of substances able to inhibit growth.
The substances which the majority of bacteria require are carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, magnesium, potassium, sodium, calcium and iron. The microorganisms grow by metabolizing certain food components such as carbohydrates and proteins. Temperature, pH and presence of water play a significant role in controlling the reproduction speed of the bacteria. In general, a large number of these microorganisms grow better in a neutral environment and require a certain minimum quantity of water. The temperature range that guarantees an optimum growth is influenced by the microorganism family; more or less, also for the more thermo-resistant bacteria, the reproduction stops at temperatures exceeding 70-80° C. The oxygen required for an optimum growth varies significantly from one species of bacteria to the other. Some microorganisms call for the presence of free oxygen in order to survive and multiply (aerobes) whereas others are not able to survive in presence of oxygen (anaerobes). If the temperature, the pH and the presence of humidity in substrata are favorable, the bacteria start to reproduce and to grow significantly until the source of the nutrition or the surrounding conditions do not change, for example, due to a lowering of the pH.

It is possible to recognize 4 main phases of the microbic development. The first phase (latency period or lag phase) is at growth rate zero. The cells start to adapt to the new conditions and the product within which they are inserted. Often, the nutritional use of diverse substrata occurs by means of specific enzymes that typically are not constitutional and must be appropriately developed by the bacteria. In the exponential phase (log phase) each cell of the microbial population enjoys in the same measure the reproduction conditions so that within the same time span (generation time) each one produces a copy of itself. The exponential phase lasts for a brief period due to the limitation of the nutritional resources available and the accumulation of toxic products generated by the same micro- organisms. The maximum obtained by the curve depends on the quantity of nutritional factor available. The growth stops, in fact, when the nutrient finishes or when the system becomes intoxicated.

At the end of this stationary period, in which the number of cells remain almost constant, in the absence of external interventions, the culture deteriorates; the speed of inactivation and death rate of the microorganisms prevails over growth. Surrounding conditions being equal, the bacterial growth rate will be tied to the initial contamination present inside the product and the time of exposure left for the microorganisms to develop.

Moulds and Yeasts

Moulds are multicellular fungi that are reproduced by the formation of spores (single cells that can multiply so much so that in turn generate an organism). They are formed in vast quantities and are easily conveyable by air. When they land on food surfaces, if the conditions of the substrata are favorable, they can grow and reproduce. Moulds are able to grow only under certain conditions of acidity. In particular, we can note their growth in solutions with a pH around 3,5.

The yeasts are made up of single cells that can be easily distinguished from bacteria, as they are much bigger. Normally they are oval in shape and longer in length; some have no flagellum or other type of transfer organ.
The majority of yeasts do not live on the ground but adapt to an environment rich in sugars, they are in fact very useful within the food field as regards the fermentation transformations of foodstuffs (e.g alcoholic fermentation for the production of wine, beer and bread). Yeasts, on the contrary to moulds, do not reproduce across spores. Yeasts are for the majority, gas producers, as when they develop, they produce gas.

Contamination Control

Contamination control is of primary importance, for the product, the container and the environment in which the filling operations are performed. The first rotary aseptic lines for PET containers introduced around the 1990’s, solved the environmental contamination control problems by installing the machine inside a controlled room, the so called "Clean Room". Afterwards, the so-called "Microbiological Isolator" was introduced and integrated on the machines as a contamination controlled environment pressurized by HEPA filtered air. Fundamental features of the environment contamination control is a correct filtration of the air inside the controlled environments, the management of the pressures of the various environments to control the path of possible particles, a correct management of the air flows, a correct sampling of the environment, the quality control and a correct management of the COP and SOP cycles.

Microbiological Isolator

The microbiological isolator is an environment contamination control system and is part of the aseptic system, in the process areas (sterilization, rinsing, filling and capping) as well as in the bottle and caps conveying areas. A good design of the machine safeguards are an integral part of the isolator as they must ensure easy cleaning, they must not have any stagnant spots where possible contamination may hide, all access hatches must be airtight. A contamination controlled system must also manage the air filtration operations, direct sterile air towards the various machines, maintain the overpressures set in the various environments and intake the air from the machines. The microbiological isolator is fitted with: intervention gloves, sterile object transfer box and material discharge container to facilitate operations during production, perform sampling activities and resolve any possible jams without having to open the actual isolator. Said systems reduce the major contamination risk factor to zero in an aseptic system, that is, direct operator intervention inside the sterile environment. The volumes to be controlled are reduced to a minimum as the isolator is installed directly on the base frames of the filling and container handling machines; the times required to sterilize the environments are therefore minimized and subsequently this leads to a reduction in sterilizing agent consumption.

Air Filtration

The air filtration of the treatment and filling environments of an aseptic line, is performed in three consecutive stages. The filters used are classified on the basis of different parameters, the most important ones are:

• field of use (substances and conditions of use)
• nominal flow rate
• grade of resistance
• level of powders that may accumulate
• efficiency

Differential Pressures

A controlled environment may have a number of chambers with diverse contamination control requirements where the safeguarding of the product is the primary goal. In this case, all chambers must be kept at static pressure (overpressure) slightly above the atmospheric pressure, in order to avoid infiltrations from the outside. By placing the chamber in overpressure, the only way in for the air is across the HEPA terminal filters. The pressures in the chambers must remain stable in the long term so as the air can always flow from the cleaner environments towards the dirtier ones. When toxic or unpleasant substances are in the controlled areas (e.g chemical sterilization cycles), for safety and environmental protection reasons, it is recommendable to reduce the differential pressures as far as possible.
This is why normally there are special air intake areas where the overpressure as compared to the external environment is maintained. Air is expelled by means of controlled vents and these operate continuously and constantly.