MARKET MILK

Module 8. Cleaning and sanitization

Lesson 37
DAIRY SANITIZERS AND THEIR PROPERTIES

37.1 Introduction

Sanitization involves destruction of pathogens and minimizing microflora. It is aimed at reducing microorganisms to a level acceptable by public health authorities. Sanitizers are classified as thermal, radiation or chemical.

37.2 Thermal Sanitizers

Thermal sanitizers are very effective, their efficacy depending on the extent of microbial contamination, humidity, pH, temperature and time.

37.2.1 Steam

Although steam is effective as a sanitizer, its application is limited because of its high cost. By-products of steam condensation can cause hurdles in the cleaning operations. It is also difficult to regulate and monitor contact temperature and time.

37.2.2 Hot water

Hot water as a sanitizer is relatively inexpensive, easy to apply and readily available. It is relatively non-corrosive and penetrates into cracks and crevices and can be effective over a broad range of microorganisms. However, the process requires come-up and cool-down time and is, therefore, slow. The energy costs are high. Safety aspects also need to be taken care of. The process also has the disadvantages of forming or contributing to film formations and shortening the life of certain equipment or parts such as gaskets.

Hot-water sanitization is commonly used through immersion (small parts, knives, etc.), spray (dishwashers) or circulating systems. The temperature-time combination required depends on the application. Some typical regulatory requirements for use of hot water in dishwashing and utensil sanitization applications specify immersion for at least 30 sec at 77°C for manual operations, a final rinse temperature of 74°C in single tank and single temperature machines and 82°C for other machines. The Grade A Pasteurized Milk Ordinance specifies a minimum of 77°C for 5 min.

37.3 Radiation

Radiation in the form of ultra violet, high-energy cathode or gamma rays destroys microorganisms rapidly. UV rays in the wavelength of 25 Angstrom units has been used extensively in the form of a sterilizing lamp to destroy undesirable organisms for foods on assembly lines, bakeries and other similar applications. UV radiations (contact time just more than 2 min) are very useful on surfaces that are heat sensitive such as flexible packing materials.

37.4 Chemical Sanitizers

Chemical sanitizers are also called low-temperature sanitizers. The ideal chemical sanitizer for food contact surface application should have a wide range of activity, destroy microorganisms rapidly, be stable under all types of conditions, be tolerant of a broad range of environmental conditions, be readily soluble and possess some detergency and be low in toxicity and corrosiveness, and be inexpensive. As no available sanitizer meets all of these criteria, it is important to evaluate the properties, advantages and disadvantages of available sanitizer for each specific application. The most commonly used chemical sanitizers in dairy industry are chlorine, iodine and quaternary ammonium compounds (QACs).

37.4.1 Chlorine-based sanitizers

Chlorine compounds are broad-spectrum germicides, which act on microbial membranes, inhibit cellular enzymes involved in glucose metabolism, have a lethal effect on DNA and oxidize cellular protein. Chlorine has activity at a low temperature, is relatively cheap, and leaves minimal residue or film on surfaces. It is non toxic, practically colourless, odourless and tasteless. Commonly used chlorine compounds include liquid chlorine, hypochlorites, inorganic chloramines and organic chloramines. The maximum allowable level for no-rinse applications is 200 ppm available chlorine, but recommended usage levels vary. For hypochlorites, an exposure time of 1 min at a minimum concentration of 50 ppm and a temperature of 24°C are recommended. For each 10°C drop in temperature, a recommended exposure time is doubled. For chloramines, the recommended combination is 200 ppm for one min.

The activity of chlorine is severely affected by factors such as pH, temperature and organic load. It is also relatively resistant to water hardness when compared to other sanitizers, especially the QACs. The major disadvantage of chlorine compounds is corrosiveness, particularly at higher temperatures, to many metal surfaces. Health and safety concerns include skin irritation and mucous membrane damage in confined areas. At low pH (below 4.0), the deadly mustard gas (Cl2) can form. Recent concerns also include use of chlorine as a drinking water disinfectant and as an antimicrobial agent in meat products, which may lead to the formation of potentially carcinogenic trihalomethanes (THMs) under appropriate conditions.

37.4.2 Iodine

Iodine sanitizers have been in use since the 1800s. The most active agent, but not too stable, is the dissociated free iodine most prevalent at low pH. Iodine sanitizers exist in many forms, usually with a surfactant as a carrier. These mixtures are called iodophors, which like chlorine compounds, have a very broad spectrum activity against bacteria, viruses, yeasts, molds and protozoans. Recent theories on bactericidal activity of iodine suggest cell wall damage and destruction of microbial enzyme activity although earlier it was thought that it is through direct halogenation of proteins. Generally recommended dosage for iodophors is 12.5 to 25 ppm for one min.

The degree to which iodophors are effective depends on properties of the surfactant used in the formulation. Iodophors are more resistant to organic matter and water hardness than chlorine. However, high pH leads to loss of activity. Iodine has limited solubility in water. It is limited to lower temperature applications, as it vaporizes at 48.8°C. Iodine can also cause staining on some surfaces such as plastics. Although iodine has a long history of use in wound treatment, ingestion of the gas poses toxicity risks in closed environments.

37.4.3 Quaternary ammonium compounds (QAC)

Quaternary ammonium compounds (QACs) are neutral disinfectants. QACs are a class of compounds, which have the general structure as depicted in Figure 37.1. The properties of these compounds depend upon the covalently bound alkyl (R) groups, which can be highly varied. The length of the carbon chain of R-group is directly related with sanitizer activity in QACs. Since QACs are positively charged cations, their mode of action is related to their attraction to negatively charged materials such as bacterial proteins.

Fig. 37.1 General structure of QACs

QACs are readily soluble and non-toxic, non-corrosive and surface active, very sensitive to organic matter (presence of milk solids improves their lethality) and do not affect sensory properties of the product. They are effective against bacteria, yeasts, mold and viruses. Some applications leave a residual antimicrobial film, though this is a disadvantage in the manufacture of cultured dairy products and cheese. QACs are more active against gram positive than gram-negative bacteria. They are not highly effective against bacteriophages. Their incompatibility with certain detergents makes thorough rinsing following cleaning operations essential. Many QAC formulations can cause foaming problems in CIP applications. QACs pose very little toxicity or safety risks under recommended usage and are commonly used as environmental fogs and as room deodorizers. These compounds are active and stable over a broad temperature range. Because they are surfactants, they possess some detergency and are, therefore, less affected by light soil than other sanitizers, though heavy soil decreases activity significantly. QACs are more active at alkaline pH. Most QACs are intolerant to hardness in water. This can be improved by the use of EDTA as a chelator.

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.