Module 8. Cleaning and sanitization

Lesson 36

36.1 Introduction

Cleaning and sanitization are the two processes employed in dairy industry to ensure hygiene and product safety. Cleaning refers to the removal of soil from the surface of the equipment, while sanitization implies destruction of all pathogenic and almost all non-pathogenic organisms. Cleaning and sanitization are complimentary processes. Either of these operations alone does not help to achieve the desired result to make the equipment/other surface free from soil and viable organisms.

There are three commonly used classifications for the level of cleanliness: physically clean, chemically clean and microbiologically clean. A physically clean surface is visually cleaned to a satisfactory standard. This normally pertains to nonfood contact areas such as floor cleaning in warehouse areas and yards within the food processing zone. A chemically clean standard is applied to all applications within the food processing area. The plant is cleaned to a standard at which anything in contact with the cleaned surface faces no contamination. A microbiologically clean standard is required for all direct and indirect food contact surfaces. This standard involves a reduction in total viable colonies to an acceptable level, which varies from country to country. Detergents are used in conjunction with disinfectants/ sanitizers to achieve a microbiologically clean surface.

36.2 Dairy Soil

During the course of processing, milk constituents deposit on the surface of equipment. These deposits are typically known as ‘dairy soil’ and consist of milk or milk product residues, which may be more or less modified by the agents that come in contact with it, such as the processing treatment, water or cleaning materials previously used, dust, dirt or other foreign matters. The accumulated dairy soil comprises largely of fat, protein (precipitated, coagulated and baked-on by heat), insoluble calcium salts from water and/or detergent and bacteria. Dairy soils are composed of 42.0 - 67.0% ash, 3.6 - 18.0% fat, 4.5 - 44.0% protein and 2.7-8.7% moisture. Continued deposition of the soil leads to accumulation of larger and harder particles that are known as milk stones.

36.3 Cleaning

Cleaning reverses the soiling process and requires a supply of energy usually in the form of mechanical and/or heat energy. While water does most of the cleaning, cleaning compounds or detergents reduce the energy required for soil removal. A detergent is a substance that either alone or in a mixture, reduces the work requirement of a cleaning process. All cleaning protocols involve wetting of soiled surface by bringing the cleaning solution into intimate contact with the soil to be removed followed by displacement of the soil from the surface by solution, emulsification, saponification, peptization and/or mechanical action. The soil removed from the surface is then dispersed or removed in the solution by scattering, deflocculation or emulsification and finally, the surface is rinsed to prevent re-deposition of the dispersed soil on the cleaned surface. Cleaning may be done by manual means, mechanically or by cleaning-in-place.

36.4 Detergents

Detergents assist the processes of washing and cleaning. A good detergent should be highly penetrable, be able to dissolve calcium salts deposited over the surface and keep them remain in solution to check re-deposition, possess moderate foam generation capacity, be non-corrosiveness and have a high bactericidal effect. It should also have the ability to soften water used for washing, good wetting power to assist the water to penetrate the greasy surface besides deflocculating and rinsing properties. It must also be non-corrosive and non-toxic. Although in general detergents are alkaline, acid detergents have to be employed to remove milk stones. Modern detergents are usually mixtures of more than one cleaning compounds. Detergents for use in the dairy industry can be divided into the following four general classes:

36.4.1 Alkaline detergents

Alkalis form the bulk of most dairy detergent compounds. The alkalis commonly used are soda, ash, caustic, soda, sodium bicarbonate, sodium metasilicate and trisodium phosphate. Soda ash, trisodium phosphate and sodium metasilicate in the ratio 12:5:3 make a very useful mixture for general cleaning in the dairy. For cleaning of aluminium or aluminium alloy equipment, a mild mixture containing trisodium phosphate, sodium bicarbonate and sodium metasilicate, in the proportion 2:2:1 is used. One part of these mixtures should be dissolved in 200 parts of water. A very good detergent for washing bottles is a mixture of 5-10% calgon (sodium hexametaphosphate) with sufficient caustic soda to give 1.5% alkalinity.

36.4.2 Water softeners

Hard water is not suitable for cleaning operations as some ingredients of the cleaning material precipitate the hard salts that adhere to equipment surfaces or settle at the bottom on standing. Hard water also causes spotting and promotes water-stone and milk-stone formation besides possessing soap-destroying and scale-forming properties. Replacing 5-10 parts of soda ash in the detergent mixture with an equivalent proportion of calgon takes care of the hardness in water.

36.4.3 Synthetic detergents

They have good surface-active and emulsifying properties and improve wetting or penetrating power by lowering the surface tension of water.

36.4.4 Acid cleaners

Acid cleaning agents are used in combination with alkaline agents to remove milk stone deposited on metal surface exposed to heat. Phosphoric acid, diluted with water (140 g in 45.3 kg) is very commonly used.

36.5 Selection of Detergents

The selection of detergents in a dairy plant is very important. There is no ‘universal detergent’ that could be applied to all situations. For example, sodium hydroxide-(caustic-soda)-based detergents, when in contact with aluminium, galvanized and other soft metal surfaces leads not only to rapid corrosion, but also to the release of hydrogen gas, which can form an explosive mixture with air. Electrical installations and moisture sensitive processes require minimal use of water and therefore, detergents which contain non-toxic and non-tainting alcohols would be needed. The chemical composition of the local water supply will also affect the selection of detergents. With hard water, when alkaline detergents are used at elevated temperatures, there is a chance of scale deposition on plant surfaces. The result is unattractive and, if it occurs on a direct or indirect food contact surface, it may become a source of physical and microbial contamination. Sequestering and dispersing materials are used in alkaline formulations to prevent scale deposition. Several factors specific to individual applications also affect detergent selection. Fermentative applications, for example, will generate carbon dioxide, which will rapidly break down sodium hydroxide to sodium carbonates. These will subsequently precipitate as process generated scale.

In response to these challenges, formulated detergents meant for specific use and based on acids, alkalis or neutral materials have come to the market. Acids are effective in dissolving mineral salts and in the hydrolysis of proteins, while caustic alkalis will break down carbonized deposits and saponify fats and oils. Neutral materials such as sequestrants and surfactants are used to prevent precipitation of water hardness salts in hot or alkaline solutions, and for wetting of soil, soil penetration, soil suspension and surface tension reduction respectively. Table 36.1 lists some of the ingredients found in modern formulated detergents along with their applications.

Table 36.1 Selected examples of ingredients in formulated detergents

Table 36.1a
Table 36.1b
Considering the environmental safety aspects of synthetic detergents, enzyme based cleaners which are biodegradable, less (or non-) toxic, non-corrosive, environmental friendly and with improved cleaning properties and stability in different formulations and sanitization are available in the market now. Proteases, amylases, lipases and cellulases make up the major portion of the market for industrial enzymes in cleaning applications to hydrolyse the respective biological material in dairy soils.

Selected Readings

Anon. 1992. Advances in detergent and cleaning-in-place system.
Anon. 1994. Revolutionary Cleaning Technology. Dairy Foods 95 (9) 110-111
Britz, T.J. and Robinson, R.K. 2008. Advanced Dairy Science and Technology. Blackwell Publishing Ltd., UK.
Dairy Processing Handbook. 2000. Alfa-Laval AB, Dairy and Food Egg. Division, Sweden. Chapter 21.
Hall, H.S. Tuszynski, W.B. 1984. Maintenance Systems for the Dairy Plant. FAO Animal Production and Health Paper 45. FAO Animal Production and Health Division. Food and Agriculture Organization of the United Nations. Rome.
Marriott, N.G. and Gravani, R.B. 2006. Principles of Food Sanitation. Fifth Edn. Food Science Text Series. Springer Publications. USA.

Last modified: Friday, 22 June 2012, 6:34 AM