Date: Aug 26, 2010 Author: Ramsey Kropp Source: Company Data
Microbial contamination of food and beverage products is a potentially catastrophic occurrence resulting in foodborne illness or food spoilage. The same nutritive properties that render cheese and dairy products such a valuable food also provide an ideal growth medium for microbes if contamination occurs. Although production and distribution of food is tightly regulated there is little secondary inspection of these products in the U.S., so outbreaks of foodborne illness are typically only detected after consumers become sick. An outbreak can lead to costly product recalls, regulatory fines, negative consumer sentiment, loss of brand value, idling production facilities, and civil or potentially criminal legal proceedings. Microbial contamination also leads to product quality issues and spoilage, resulting in loss of product, decreased shelf life, and unhappy customers.
Microbial Contamination
Microbes are the most successful life on earth, whether measured by total mass, number of species, or number of cells. There are more bacterial cells in an individual human than there are human cells. Microbes are found in almost every known environment and most pose no risk or are beneficial; many are necessary to prepare the foods and beverages we consume.
As evidence of the importance of microbes, some of the world's best microbiologists are in the brewing, baking, and cheese-making industries. Prevention of foodborne illness or food spoilage requires carefully balanced microbial control via removing harmful bacteria from production equipment and process ingredient streams, whilst not adversely affecting food quality or preventing the growth of desired microbes. A modern, well-run production facility will employ multiple techniques to prevent contamination in every step of their process. Table 1 contains a partial list of microbes of concern in cheese production.
Harmful microbes can generally be grouped into four groups: bacteria, fungi, protists, and viruses. Table 2 contains a partial list of pathogens present in untreated domestic wastewater and the categories in which they fall. Bacteria and fungi are most worrisome in cheese production, as they are most responsible for spoilage and foodborne illness. These organisms can use the chemical energy of affected food products to multiply and spread, one viable cell can become billions within a single day if growth conditions are ideal.
Both protists and viruses can be worrisome and highly dangerous pathogens in humans but are less likely to cause spoilage due to their life cycle. Viruses are only capable of reproducing when they hijack the cellular machinery of another living organism, while protists can only reproduce in aquatic environments or in a host. Neither viruses nor protists can directly use food energy for growth, and therefore they do not cause spoilage.
Microbes have remarkable mechanisms by which they can protect themselves and ensure their survival. Some bacteria are capable of forming a biofilm consisting of a slimy mass of extracellular material that protects the individual cells from damage by light, oxygen, disinfecting chemicals and other environmental harms. Microbes that colonize existing biofilms gain equivalent protection from efforts to inactivate them.
Many bacteria and protists have the ability to enter a dormant cystic state when environmental conditions are unfavorable. Cysts are much more resistant to damage than the active state. They can survive extremes in temperature, large doses of radiation (including UV light), high salinity, severe dryness, and remain viable for incredible periods of time.
Routes of Microbial Contamination
Most cheese plants will contain at least some level of microbial contamination even with rigorous and appropriate control measures in place. Microbes can elude detection and inactivation; for example, even the tiny gap between the threads of a screw and the threads in the hole can harbor thousands of bacteria. Many artisanal cheeses gain their unique characteristics from the natural microbes present where they are produced, but large-scale production requires greater consistency than artisanal methods typically provide. A well designed and rigorously applied hygiene plan is required to prevent the low-level natural microbial background from reaching levels that affect quality or safety.
In addition to the microbes already present, there are many paths through which microbes can enter a production facility. Cheese production requires water, milk, and other ingredients, along with production equipment, production and packaging materials, personnel, and ventilation. Each of these has the potential to introduce microbes into the production area. Microbe control procedures should identify the risk of contamination from every potential source and take steps to prevent it. As an example, the casing of a groundwater well that has corroded near the soil surface can admit untreated wastewater or farm runoff in the event of flooding or significant rainfall. As opposed to municipal water supplies, water from wells is often untreated; instead the well is regularly tested for the presence of coliform bacteria. Contamination in this case would occur without warning and the water could test clean until the next storm. Microbial treatment of source water can provide additional protection from unforeseen contamination.
Food and Beverage Industry
Microbial Treatment Technologies
Microbes of concern in the food, beverage, and dairy industries are found in three broad "environments": in water, on surfaces, and in the ambient air or atmosphere. Microbial control in each of these environments requires different treatment technologies. Unclean or untreated surfaces and crevices can serve as a reservoir
for growth, resulting in ongoing contamination and potentially tainted product. General plant hygiene and cleaning practices are a first line of defense against
microbial contamination.
Additionally, there are technologies nd techniques that can provide
further protection. Water and ingredient streams should be periodically checked for microbial contamination. Water heaters set at too low a temperature can harbor microbial growth. Surfaces should regularly be cleaned and treated to inhibit microbial growth. Air handling equipment and filtration elements should be regularly checked for cleanliness and potentially fitted with microbial control elements.
Water is an integral component in cheese production, including as an ingredient, as the working fluid in heating and cooling operations, for cleaning equipment, and for rinsing products and packages. Microbial contamination in water has the potential to affect the final product at multiple points, so particular care is warranted. Table 3 contains a list of several possible treatment technologies used for the disinfection of water.
Chemical
Of these water treatment technologies, thermal and chemical disinfection are the most widely used for the treatment of drinking and other potable waters. Chemical disinfection, almost exclusively as chlorination with hypochlorous acid or salts thereof, is widely used for municipal treatment, as it provides a long lasting residual disinfection (water is sterile to the tap). Chlorine generation is a massive industrial process, so costs are low relative to more advanced chemical treatments like ozone. Chlorine damages cellular structures through oxidation thereby inactivating to kill microorganisms. Sterilization with chlorine is surprisingly slow, requiring several hours or days of contact time at normal concentrations to be completely effective. This is acceptable where there is significant residence time in pipes or channels between the point of application and the point of consumption.
Chlorine is added to the water as one of many forms depending on the application and other requirements. It can be provided as powders, prills or pellets, in liquid solutions, and as a compressed gas. It can also be generated on site by electrochemical reactions in saltwater. Independent of form, dose control is key to successful chlorine application. The chlorine dose required to adequately sterilize water can vary widely with changes in dissolved or suspended organic material, the presence of dissolved or particulate metals, and the microbial load of the water stream.
Chlorine disinfection is strongly pH dependent; a high pH (basic water) converts the active hypochlorous acid to the less effective hypochlorite ion. Low pH causes the hypochlorous acid to revert to chlorine gas, which is emitted to the atmosphere. Sunlight, dissolved metallic species, and particulate inorganic material can also catalyze the destruction of hypochlorous acid. Chlorine is a powerful oxidizer and can cause corrosion of equipment at high concentrations. The same reactions that result in antimicrobial activity can also interfere with normal food chemistry, impacting product quality. Chlorine reacts with organic materials present in the water to form halocarbons and with proteins to form chloramines. Halocarbons and chloramines are health hazards and can affect taste, odor, or product quality when present as an ingredient. Additionally, there are reports of certain bacterial species (e.g. Mycobacteria), bacteria in biofilms, and spores being resistant to chlorine treatment 1.
M i c r o b i a l Control in Cheese Making
1P. A. Pelletier, G. C. du Moulin, and K. D. Stottmeier, "Mycobacteria in Public Water Supplies: Comparative Resistance to Chlorine," Microbiological Sciences 5, no. 5 (May 1988): 147--48.
Water Treatment for the
Food and Beverage Industry
There are disinfecting chemicals as alternatives to chlorine but they are used far less frequently due to cost, safety considerations, lack of familiarity, and/or their potential impact on product quality. Ozone (O3) is gaining more acceptance for use in pools but does not provide the strong residual disinfection of chlorine and must be generated on site. Chlorine dioxide is an exceptional disinfecting agent but is explosive at high concentrations. Preservatives (e.g., bactericides and bacteristats) as a food additive may have application in water disinfection, but are expensive and there is a paucity of research into their use in treating water.
Thermal
Thermal disinfection is the oldest sterilization technology. Boiling water is sufficient to inactivate pathogens, although several hours of boiling may be necessary to treat bacterial endospores. High pressure autoclaves allow water to be heated above normal boiling (100˚C or 212˚F) and shorten sterilization times, but can require annual expensive safety testing (e.g. hydrostatic pressure tests) to ensure safe operation. Pasteurization heats the process flow to near boiling for a prescribed time and is the most widely used sterilization process in the food and beverage production industry. The lower temperature of pasteurization limits its effectiveness for destroying bacterial spores. Pasteurization is energy intensive due to the large specific heat capacity (energy required to heat a given volume a given temperature) of water and the need to cool the water
again prior to use. The high operational costs associated with pasteurization can be ameliorated with proper system design that utilizes efficient heat exchangers. Microbial growth can be accompanied by the release of toxins (e.g. Cyanotoxins in algal blooms), which persist even after the original microbial population is destroyed by pasteurization. These toxins are often implicated when there is an outbreak of foodborne illness of short duration unaccompanied by infection.
Ultraviolet Irradiation
Ultraviolet (UV) sterilization is a widely used technique to inactivate microbes. The inactivation is caused by damaging 240 to 270 nm wavelength. These microbes are not actually killed per se by exposure to UV, but rather they are rendered unable to reproduce and no longer infectious. The effectiveness of UV to inactivate a pathogen is proportional to the intensity of the UV light multiplied by the contact time typically given as mJ°øs/cm2 or mW/cm2). Water quality strongly affects the intensity of UV in an exponential manner.
For example, if 90% of UV light is absorbed in the first centimeter of water, then only 1% of the initial intensity reaches a distance of 2 cm. The transparency of water to ultraviolet light is affected by calcium, alkalinity, hardness, iron content, manganese content, dissolved organic material, and turbidity. The exponential loss of intensity to absorbance requires UV sterilizers to have either short optical paths or very high UV intensity to treat large flow rates.
Membrane Processes
Microbes, although small in relation to human scales, are not infinitesimal. Filtration can be highly effective for providing microbially pure water. Nearly all microbes except viruses can be removed by size exclusion filtration with a 0.2 μm filter element, viruses can be removed by a20 nm (0.02 μm) element, and an osmotic membrane can even remove dissolved salt and organic molecules. Filtration elements with small pore sizes rapidly clog in traditional filtration equipment, and so membrane cross-flow filtration is typically used (Figure 1). Membrane filtration equipment costs do not economically scale down for small cheesemaking operations. Damaged membranes can allow untreated water to bypass the filter element and result in contamination. Bacterial growth in either cross-flow or dead-end filtration can result in filters clogging and decreased production.
Food and Beverage Industry
A New Alternative
AquaMost's PECO technology combines aspects of both ultraviolet radiation and chemical disinfection in a single device. High intensity UV light and a small electric potential are used to activate a solid nanostructured catalyst to produce hydroxyl radical, a powerful oxidizing species capable of destroying cellular structures and breaking down organic chemicals. In water with even minimal salinity these hydroxyl radicals generate chlorine, providing an additional germicidal method of action. This generated chlorine is quickly converted into further hydroxyl radicals by the action of the UV, resulting in hydroxyl radical formation in the bulk water and preventing residual chlorine from being generated by the system. The generated radicals are substantially more oxidizing than chlorine, so shorter contact times are required to damage critical microbial structures.
These oxidizing species also breakdown organic contaminants and toxins, including emerging contaminants of concernthat traditional water treatment technologies are unable to remove. Successfully treated contaminants include pesticides, pharmaceuticals, hormones, endocrine disrupting compounds,plastic/polymer breakdown products, chlorinated solvents, and gasoline additives that can leach into groundwater sources.
AquaMost, Inc., a privately held corporation based in Madison, Wisconsin, is the developer of water treatment systems that use a patented triple-action technology that eliminates microbiological contamination such as bacteria, virus, mold, spores, yeast, and residual chemicals, including chlorine.
Dr. Ramsey Kropp is an environmental chemist with a focus in water and air treatment, particularly the removal of pathogens and contaminants employing nanomaterials and Advanced Oxidative Processes (AOPs) including photo- and photoelectro-catalytic heterogeneous catalysis, ozonolysis, UV sterilization, and electrostatic precipitation.
