Đề tài Sanitation in dairy plant

cult to clean areas and to compensate for the natural dilution that may occur because of the presence of condensation or residual rinse water from cleaning. Temperature: Sanitation in dairy plant Page 18 The growth rate of the microorganisms and the death rate due to chemical application will increase as temperature elevates. A higher temperature generally lowers surface tension, increases pH, decreases viscosity, and creates other changes that may help bactericidal action. An exception is the iodophors that vaporize above 50°C. These chemicals are more aggressive to surfaces, especially elastomers and gasketing materials, as the temperature rises. Thus, chemical sanitizers should be applied at ambient temperatures, ideally 21 to 38°C. Generally, the degree of sanitation greatly exceeds the growth rate of the bacteria, so that the final effect of increasing temperature is to enhance the rate of destruction of the microorganisms. Concentration: Increased sanitizer concentration enhances the rate of destruction of the microorganisms. pH: The activity of antimicrobial agents occurring as different species within a pH range may be dramatically influenced by relatively small changes in the pH of the medium. Chlorine and iodine compounds generally decrease in effectiveness with an increase in pH. Desired Sanitizer Properties The ideal sanitizer should have the following properties: ● Microbial destruction properties of uniform, broad-spectrum activity against vegetative bacteria, yeasts, and molds to produce rapid kill. ● Environmental resistance (effective in the presence of organic matter [soil load], detergent and soap residues, and water hardness and pH variability) ● Good cleaning properties ● Nontoxic and nonirritating properties ● Water solubility in all proportions ● Acceptability of odor or no odor ● Stability in concentrated and use dilution ● Ease of use Sanitation in dairy plant Page 19 ● Ready availability ● Inexpensive ● Ease of measurement in use solution A standard chemical sanitizer cannot be effectively utilized for all sanitizing requirements. The chemical selected as a sanitizer should pass the Chambers test (also referred to as the sanitizer efficiency test):Sanitizers should produce 99.999% kill of75 million to 125 million Escherichia coli and Staphylococcus aureus within 30 seconds after application at 20°C.The pH at which the compound is applied can influence the effectiveness of the sanitizer. Chemical sanitizers are normally divided according to the agent that kills the microorganisms. Chemical sanitizers are often used in dairy plant such as:  Chlorine Compounds,  Iodine Compounds,  Bromine Compounds,  NH4 + ,  Acid Sanitizers,  Peroxy Acid Sanitizers,  Acid Anionic Sanitizers,  Hydrogen Peroxide,  Ozone Ozone, a molecule comprised of three oxygen atoms, is naturally occurring in the earth’s upper atmosphere. It acts as a powerful and nonselective oxidant and disinfectant,(which indicates that it will attack any organic material that it contacts) and may control microbial and chemical hazards. Common by-products of ozonation are molecular oxygen, acids, aldehydes, and ketones. This sanitizer does not cause a harmful residue or contaminated flavor. This sanitizer is a more powerful disinfectant than chlorine. It has been used safely and effectively in water treatment and is approved in the United States as Generally Regarded as Safe (GRAS) for treatment of bottled water and has been applied in the food Industry in Europe during the past. It has a broad spectrum of germicidal activity. Generally, ozone is a more effective bactericide and virucide than chlorine and chlorine dioxide. Ozone is being evaluated as a chlorine substitute. Because it oxidizes rapidly, it poses less environmental impact than some compounds. Sanitation in dairy plant Page 20 Ozone is expensive, unstable, corrosive, temperature sensitive, very reactive, and should be generated as needed at the site of application. It is produced commercially through the incorporation of an ozone generator that uses electricity to generate the gas and ozone. The ozone is used as a gas or is contacted with water for application. A high voltage, alternating electric discharge is passed through a gas stream (dry air or oxygen). To control the electrical discharge and maintain a corona, a dielectric space or discharge gap is formed using a dielectric material such as ceramic or glass. A grounded electrode that is usually produced from stainless steel acts as a boundary to the discharge space. The most common shape for ozone generators is a cylinder, which is the most space- efficient, economic form .Care must be taken to ventilate the equipment properly as released ozone can be irritating to workers. Ozone is very unstable at a high as well as at a low pH. Ozone is most effective at a pH range of 6.0 to 8.5. As water temperature increases, the solubility of ozone decreases. It dissipates almost immediately at 40°C. Ozone is a broad-spectrum germicide which is effective against food pathogens, yeasts, and molds, and viruses and protozoa. It has been used to sanitize dairy equipment and to disinfect water, including pools, spas, and cooling towers and for algae control in water and wastewater treatment plants. It is not tolerant of organic soil. The probable mode of action of ozone is through the attack on the cell membrane, rupturing and killing the cell. Another application is to release gaseous ozone in cold storage rooms to control molds and eliminate ethylene, which can accelerate ripening in fruits and vegetables. Ozone is more stable in the gas phase and in an aqueous phase. The use of ozone presents safety issues. It is a powerful irritant to the respiratory tract and a cellular poison that interferes with the ability of lungs to fight infectious agents. Ozone, as chlorine dioxide, has been found to produce brominated organic compounds that are alleged potential carcinogens. Furthermore, there is a high capital cost associated with the use of ozone including the need for generators at point of use as well as the energy costs to operate them. Also, ozone is corrosive to soft metals and mild steel as well as rubber and some plastics. Sanitation in dairy plant Page 21 Table 1: Specific Areas or Conditions where Particular Sanitizers are Recommended 2.6. Enzymatic cleaning It is known that monocomponent enzymes can be used for biofilm removal. The heterogenicity of the biofilm matrix limits the potential of these enzymes for use in effective cleaning. The proteinase samples, e.g. chemotrypsin were shown to be effective Sanitation in dairy plant Page 22 in reducing and inactivating pure-culture biofilms, but when milk residues were present no effect of the proteinases could be observed. The different enzymatic cleaning procedures tested were also shown to be ineffective in inhibiting growth and metabolic activities of bacterial strains isolated from dairies. Based on the varying results obtained for removal and inactivation of microbes on surfaces by enzyme preparates, one possibility could therefore be to combine various types of enzymes to attain efficient cleaning. The use of enzymes is also limited due to the lack of techniques for quantitative evaluation of the enzymatic effects and the accessibility of the different enzymatic activities. The results showed that the resazurin-based fluorometric assay tested during that part of the project performed at the Faculty of Veterinary Medicine at the University of Helsinki can be used for estimating the enzymatic activities on process surfaces. This method can be recommended especially when a rapid, high-throughput capacity system is needed (Mikkola, 1999; Augustin, 2000). Table 2: Optimal Cleaning Guides for Dairy Processing Equipment 3. Equipment Cleaning is generally accomplished by manual labor with basic supplies and equipment or by the use of mechanized equipment that applies the cleaning medium (usually water),cleaning compound, and sanitizer. The cleaning crew should be provided with the tools and equipment needed to accomplish the cleanup with minimal effort and time. Storage space should be provided for chemicals, tools, and portable equipment. Sanitation in dairy plant Page 23 3.1. Mechanical Abrasives Although abrasives such as steel, wool, and copper chore balls, can effectively remove soil when manual labor is used, these cleaning aids should not be used on any surface that has direct contact with food. Small pieces of these scouring pads may become embedded in the construction material of the equipment and cause pit corrosion (especially on stainless steel) or may be picked up by the food, resulting in consumer complaints and even consumer damage suits. Wiping cloths should not be used as a substitute for abrasives or for general purposes because they spread molds and bacteria. If cloths are necessary, they should be boiled and sanitized before use. 3.2. Water Hoses Hoses should be long enough to reach all areas to be cleaned, but should be no longer than required. For rapid and effective cleanup, it is important to have hoses equipped with nozzles designed to produce a spray that will cover the areas being cleaned. Nozzles with rapid-type connectors should be provided for each hose. Fan-type nozzles give better coverage for large surfaces in a minimum amount of time. Debris lodged in deep cracks or crevices is dislodged most effectively through small, straight jets. Bent type nozzles are beneficial for cleaning, around and under equipment. For a combination of washing and brushing, a sprayhead brush is needed. Cleanup hoses, unless connected to steam lines, should have an automatic shut off valve on the operator’s end to conserve water, reduce splashing, and facilitate exchange of nozzles. Hoses should be removed from food production areas after cleanup, and it is necessary to clean, sanitize, and store them on hooks off of the floor. This precaution is especially important in the control of Listeria monocytogenes. 3.3. Brushes Brushes used for manual or mechanical cleaning should fit the contour of the surface being cleaned. Those equipped with spray heads between the bristles are satisfactory for cleaning screens and other surfaces in small operations where a combination of water spray and brushing is necessary. Bristles should be as harsh as possible without creating surface damage. Rotary hydraulic and power-driven brushes for cleaning pipes aid in cleaning lines that transport liquids and heat exchanger tubes. Brushes are manufactured from a variety of materials horse-hair, hog bristles, fiber, and nylon but are usually nylon. Bassine, a coarse-textured fiber, is suitable for heavy- duty scrubbing. Palmetto fiber brushes are less coarse and are effective for scrubbing with medium soil, such as metal equipment and walls. Tampico brushes are fine fibered and well adapted for cleaning light soil that requires only gentle brushing pressure. All Sanitation in dairy plant Page 24 nylon brushes have strong and flexible fibers that are uniform in diameter, durable, and do not absorb water. Most power-driven brushes are equipped with nylon bristles. Brushes made of absorbent materials should not be used. 3.4. Scrapers, Sponges, and Squeegees Sometimes scrapers are needed to remove tenacious deposits, especially in small operations. Sponges and squeegees are most effectively used for cleaning product storage tanks when the operation has insufficient volume to justify mechanized cleaning. 3.5. High-Pressure Water Pumps High-pressure water pumps may be portable or stationary, depending on the volume and needs of the individual plant. Portable units are usually smaller than centralized installations. The capacity of portable units is from 40 to 75 L/minute, with operating pressures of up to 41.5 kg/cm2. Portable units may include solution tanks for mixing of cleaning compounds and sanitizers. Stationary units have capacities ranging from 55 to 475 L/min. Piston-type pumps deliver up to 300 L/min, and multistage turbines have capacities of up to 475 L/min, with operating pressures of upto 61.5 kg/cm2.The capacity and pressure of these units vary from one manufacturer to another. In a centralized unit, the high-pressure water is piped throughout the plant, and outlets are placed for convenient access to areas to be cleaned. The pipes, fittings, and hoses must be capable of withstanding the water pressure, and all of the equipment should be made of corrosion-resistant materials. The choice of a stationary or portable unit depends on the desired volume of high-pressure water and the ease with which a portable unit can be moved close to areas being cleaned. Other uses of high-pressure water in the plant can also determine whether a stationary unit is warranted. High-pressure, high-volume water pumps have been used primarily when supplementary hot, high-pressure water is desired. Because this equipment uses a large volume of water and cleaning compounds, it is frequently considered inefficient. This concept has been applied to portable and centralized high-pressure, low-volume equipment that blends cleaning compounds for dispensing in areas to be cleaned. With a lower volume and water temperature, it is a more efficient approach that can effectively clean areas that are difficult to reach and penetrate. 3.6. Low-Pressure, High-Temperature Spray Units This equipment may be portable or stationary. The portable units generally consist of a lightweight hose, adjustable nozzles, steam-heated detergent tank, and pump. Operating pressures are generally less than 35 kg/cm2. Stationary units may operate at the main hot Sanitation in dairy plant Page 25 water supply pressure or may use a pump. These units are used because no free steam or environment fogging is present, splashing during the cleaning operation is minimal, soaking operations are impractical and hand brushing is difficult and time-consuming, and the detergent stream is easily directed onto the soiled surface. 3.7. High-Pressure Hot-Water Units This equipment utilizes steam at 3.5 to 8.5 kg/cm2 and unheated water at any pressure above 1 kg/cm2. These units convert the high-velocity energy of steam into pressure in the delivery line. The cleaning compound is simultaneously drawn from the tank and mixed in desired proportions with hot water. Pressure at the nozzle is a function of the steam pressure in the line; for example, at 40kg of steam pressure, the jet pressure is approximately 14 kg/cm2. This equipment is easy to operate and maintain but has the same inefficiency as the high-pressure, high-volume water pumps. 3.8. Steam Guns Various brands of steam guns are available that mix steam with water and/or cleaning compounds by aspiration. The most satisfactory units are those that use sufficient water and are properly adjusted to prevent a steam fog around the nozzle. Although this equipment has applications, it is a high-energy-consuming method of cleaning. It also reduces safety through fog formation and increases moisture condensation, sometimes resulting in mold growth on walls and ceilings, and increased potential for the growth of L.monocytogenes. High-pressure, low-volume equipment is generally as effective as steam guns if appropriate cleaning compounds are incorporated. 3.9. Portable High-Pressure, Low-Volume Cleaning Equipment A portable high-pressure, low-volume unit contains an air- or motor-driven high- pressure pump, a storage container for the cleaning compound, and a high-pressure delivery line and nozzle (Figure 6).The self-contained pump provides the required pressure to the delivery line, and the nozzle regulates pressure and volume. This portable unit simultaneously meters the predetermined amount of cleaning compound from the storage container and mixes it in the desired proportion of water as the pump delivers the desired pressure. The ideal high-pressure, low-volume unit delivers the cleaning solution at approximately 55ºC with 20 to 85 kg/cm2 pressure and 8 to 12 L/minute, depending on equipment specifications and nozzle design. However, low-pressure, medium-pressure (boosted pressure),and high-pressure equipment exists. Although high pressure is effective in removing heavy soils, it can create too much atomization. Therefore, the food industry has evolved primarily to medium (boosted) pressure. The high-pressure cleaning Sanitation in dairy plant Page 26 principle is based on automation of the cleaning compound through a high-pressure spray nozzle. The high-pressure spray provides the cleaning medium for application of the cleaning compound. The velocity, or force, of the cleaning solution against the surface is the major factor that contributes to cleaning effectiveness. High- pressure, low-volume equipment is necessary to reduce water and cleaning compound consumption. This equipment conserves water and cleaning compounds, and it is less hazardous than high-pressure, high-volume equipment because the low volume results in reduced force as distance from the nozzle increases. Portable high-pressure, low-volume equipment is relatively inexpensive and quickly connected to existing utilities. Some suppliers of cleaning compounds provide these units at little or no rent to customers who agree to purchase their products exclusively. These units do require more labor than does centralized equipment because transportation throughout the cleaning operation is necessary and because less automation can be provided without a centralized system. Portable equipment is not as durable and can require an excessive amount of maintenance. High-temperature sprays tend to bake the soil to the surface being cleaned, providing the optimum temperature for microbial growth. This hydraulic cleaning equipment is beneficial for small plants because the portable units can be moved through the facility. Portable equipment can be utilized for cleaning parts of equipment and building surfaces, and is especially effective for conveyors and processing equipment where soaking operations are impractical and hand brushing is difficult and time-consuming. It appears that this method of cleaning may receive more attention in the future because it may be more effective in the removal of L.monocyto- genes from areas that are difficult to clean with less labor-intensive equipment such as Figure 6 A portable high-pressure, low-volume cleaning unit that is used where a centralized system does not exist. Sanitation in dairy plant Page 27 foam-dispensing units. A trend exists toward centrally installed equipment because of the potential labor savings and reduced maintenance. 4. Sanitation methods 4.1. Regulation and process of cleaning and disinfecting The design of modern dairy equipment allows cleaning and disinfecting to take place without the equipment having to be taken apart, i.e, cleaning-in-place (CIP). This means that the processing equipment must be made of materials (eg, stainless steel) that are resistant to the corroding effects of the cleaning agents. The processing equipment must also be designed in such way that all surfaces in contact with the product can be cleaned. Careful cleaning in dairy plant is very important because milk components are excellent substrates for microorganisms. This does not alone apply to the parts in contact with the product, but also to the external parts and rooms etc… 4.1.1. The effectiveness of the cleaning is determined by the following four factors:  The chemical factor is determined by the cleaning agent and the concentration in which it is used. The cleaning agent is chosen according to the type of pollution to be removed, in this way: Table 3: The cleaning agent is chosen according to the type of pollution to be removed The functions of the cleaning agents are: - To loosen the pollution - To keep the impurities dissolved in the cleaning solutions to prevent them from precipitation on the cleaned surfaces Sanitation in dairy plant Page 28 - To prevent sedimentation of lactic salts. Guiding concentrations: Acid (HNO3) 0.8-1.2%, and lye (NaOH) 0.8-1.5%.  The mechanical factor is determined by the speed of the liquid over the surfaces. The faster the liquid moves, the more efficient the cleaning will be. It is important that the movement of the liquid is turbulent, i.e. that the liquid parts continuously change place mutually. Consequently, the pump speeds are considerably higher during CIP than during production. The cleaning turbines in the tanks make up an effective mechanical factory, but partial blockings of the turbines may appear. In consequence, the turbines should be inspected regularly.  The thermal factor (the temperature) is very important. Within chemistry it is said that the reaction speed is doubled if the temperature is increased by 10 0 C. However, a too high temperature also presents disadvantages, as residues of proteins and lactic salts are precipitated at too high temperatures, and the solubility of the salts in the water is reduced. Guiding temperatures: Lye solution 70 – 750C and acid solution 60 – 650C.  The time factor is important to the softening and solution part of the pollution. In the program survey, approximate periods for the single steps in the programs are indicated. The indicated periods should only be regarded as a broad guidance, as there may be considerable differences between the single routes, both as regards equipment to be cleaned and the fouling degree. 4.1.2. Disinfection The purpose of a disinfection is to kill the largest possible number of bacteria to avoid an infection of the products. Heat in the form of steam or especially hot water is the most used form of disinfection. The central CIP plant includes programs for sterilisation with hot water, and the return temperature is set to 85 – 900C. Cleaning of dairy equipment is carried out as follows: 4.1.2.1. Pre-rinse The processing equipment is rinsed with cold or warm water. The object is to remove any possible product residue before cleaning. The rinsing water containing the product residue should be led to suitable reception facilities in order to minimise pollution. 4.1.2.2. Cleaning with sodium hydroxide Sanitation in dairy plant Page 29 The process equipment is cleaned by means of circulation of a hot sodium hydroxide cleaning solution. Today, special cleaning agents are commonly used instead of sodium hydroxide. After cleaning, the cleaning solution is collected and re-used. Re-use should not take place before the concentration of the returning solution (%) has been checked and adjusted accordingly. 4.1.2.3. Intermediate rinse Any remaining cleaning solution is flushed out with either collected rinse water or fresh water. 4.1.2.4. Cleaning with nitric acid The process equipment is cleaned by means of circulation of a hot nitric acid cleaning solution. Today, special cleaning agents are commonly used instead of nitric acid. After cleaning, the cleaning solution is collected and reused. Re-use should not take place before the concentration of the returning solution (%) has been checked and adjusted accordingly. 4.1.2.5. Final rinse Any remaining cleaning solution is flushed out with either cold or hot water. Chemical free water is collected and used for pre-rinse. 4.1.2.6. Disinfection This is carried out immediately before the product plant is put into operation. Disinfection can be carried out thermally or chemically. The CIP plant is normally designed to allow for disinfection by circulation of either hot water at 90-95°C or a solution of e.g. hydrogen peroxide. Today special agents for disinfection is widely used in place of hydrogen peroxide. Disinfection must always be followed by a rinse with clean and drinkable water. 4.1.3. Cleaning Methods 4.1.3.1. Cleaning agents: The following cleaning agents can be used for CIP-cleaning.  Lye, NaOH, Sodium hydroxide: - 30% concentrated solution.  Acid, HNO3,Nitric acid: Sanitation in dairy plant Page 30 - 30% concentrated solution. - 62% concentrated solution. Hydrochloric acid, (HCl), and/or chlorine-containing cleaning agents, (Cl ), must never be used. 4.1.4. General maintenance of CIP plant:  Daily check: Cont