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.
The majority of the beverages on the market due to their level of sugar and water content represent a perfect habitat for the growth of microorganisms.
Moulds, yeasts and bacteria are the main types of microorganisms that may cause contamination and alteration of a product; not necessarily dangerous for humans. The microbic contamination may arise at any level of the production chain, from the harvest or production of the ingredients to the end package. The transmission occurs normally by contact with a non-sterile entity, that could be solid, liquid or gaseous.
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.
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.
|Lactobacillus brevis||Cryptococcus albidus||Aspergillus niger|
|Lactobacillus buchneri||Debaryomyces hansenii||Botrytis cinerea|
|Lactobacillus paracasei||Picha anomala||Byssochlamys fulva|
|Lactobacillus paralens||Picha membranaefaciens||Byssochlamys nivea|
|Lactobacillus plantarum||Rhodotorula glutinis||Geotrichum candidum|
|Lactococcus lactis||Saccharomyces cerevisiae||Neosartorya fischeri|
|Leucaonostoc mesenteroides||Torulaspora delbrueckii||Penicillum citrinum|
|Enterobacter cloacae||Zygosaccharomyces bailii||Penicillum expansum|
|Gluconobacter oxydans||Zygosaccharomyces florentinus||Talaromyces flavus|
|Alicyclobacillus acidocaldarius||Zygosaccharomyces microellipsoides|
|Alicyclobacillus acidoterrestris||Zygosaccharomyces rouxii|
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:
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