Preface   Safety is a matter of concern for human. Unsafe food has posed considerable health problems from time immemorial and many food safety problems encountered today are not new. The governments all over the world are doing their best to improve the safety of food supply. However the occurrence of food borne diseases remains a significant health issue in both developed and developing countries. This book is presented with a view to provide the students on the various importance of clean milk production, handling and processing to public health. We have tried to give in a nutshell the importance of adopting various practices for a holistic approach towards safe market milk and milk products. The description of spoilage and pathogenic organism will help the students to think in terms of investigating food contamination and thus their preventive and control measures. The experiments given in the laboratory manual are meant to teach the students in the microbiological aspect and safety of food.

Veterinary public health deals with the contributions of veterinary medicine to public health. It is concerned, in the first instance, with the control and elimination of zoonoses and also with the following areas of activity:     ·    Food hygiene (production, processing and distribution of foods of animal origin)     ·    Environmental contamination and degradation by animal wastes and animal products     ·    Comparative medicine (eg. Studies in animals on naturally appearing cancer, cardiovascular disease, metabolic and other disorders encountered in humans)     ·    Laboratory animal medicine     ·    Education and training in VPH and communication with the public     ·    Reproduction biology     ·    Aspects of mental and societal health     ·    Emergency veterinary functions in natural disasters and other catastrophes.

Life forms are composed of one of two basic cell types : Eukaryotic or Prokaryotic. Generally, eukaryotic cells are larger and more complex than the prokaryotic cells and possess a membrane-enclosed nucleus; eukaryotic means ‘true nucleus’ (eu=true; karyon = nucleus). All plants, animals, fungi, protozoa and algae are composed of eukaryotic cells. Only the microorganisms classes as bacteria and the archaea are prokaryotic cells. Prokaryotic cells have no nuclear membrane and therefore lack a true nucleus. The latin prefix pro means ‘early’ and in this instance suggests the somewhat primitive nuclear structure found in bacterial cells. Eukaryotic microorganism are sometimes simply referred to as eukaryotes, and the prokaryotic microbes as prokaryotes.

The term growth as applied to higher organisms such as animals commonly is concerned with increase in protoplasmic mass and does apply to reproduction or to increase in number. In microbiology the term refers to increase in the number of organisms. Bacteria increase in number by a process of simple binary fission. Each cell increase in size and redivide into two similar cells. Each of the divide cells may in turn divide to become two cells. Each division produces what is termed as new generation of cells, theoretically there are 2,4,8,16,32,64,128,256 cells in the 2,3,4,5,6,7,8,& 9th generation, this is known as logarithmic growth – the population doubles with each successive generation. Under favourable conditions, bacteria produce generation within 15min. Under unfavourable conditions 24 hours of more may be needed for each generation. Generation time for E.coli is 17 to 20 minutes.

The sources of contamination of milk on the farm can broadly be categorized as     a)    Interior of the Udder     b)    Exterior of the Udder. The interior reflects the health of the animal, while the exterior depends on the farm condition, equipment, persons, water etc. a) Interior of the Udder The animal by itself is one of the most significant contributors of microorganism in milk. The bacteria in the udder usually enter from the teat opening and get distributed internally by their own growth and physical movement. In the normal healthy udder, the types encountered in milk are most predominantly Micrococci, followed by Streptococci, Corynebacterium and others. Most of the bacteria are excreted in fore milk.

The Concept of ‘Clean Milk’ Production Although milk is nature’s most ideal and perfect single food both for the newborn and the mature human beings, the possibility of it being a source of biological and chemical hazards cannot be excluded. In view of the immense dietary importance of milk, the need for production of safe, clean and wholesome milk is emphasized. The term ‘clean milk’ does not mean milk in which all visible dirt is absent or milk from which it has been removed; rather it does denote raw milk from healthy animals, that has been produced and handled under hygienic conditions; that contains only small number of harmless bacteria and that possesses a good keeping quality without being treated by heat. In other words, the unhygienic production of milk may lead to inferior keeping quality as a result of rapid microbial multiplication under favourable storage conditions apart from serving as a potential health hazard. These microorganisms cause the milk to sour quickly, putrefy and develop undesirable flavours, colour defects, ropiness and bitterness. On the other hand, the pathogenic microorganisms, which may gain entry through various sources, may cause many diseases to the consumers.

In India, the collection, transport and distribution of raw milk involves a number of agencies and persons at rural and urban level – village producers, milk collectors, halwais (Sweet-makers), milk vendors, dairies, producer-retailers and wholesale or retail markets. 1. Collection Usually, the milk collectors approach the small village producers to collect milk and the same is sold directly or indirectly (through agents) to a dairy (milk procurement centres) or halwais or city milk vendors or consumers. The producer – retailers themselves, in some cases, supply the milk to the above said parties. The production of milk in small, scattered holdings in village causes problems during its collection. It involves visits to many villages, some of which are not easily accessible for the purpose.

Starters are selected strains of micro-organisms deliberately added to milk during conversion into cheese, dahi, yoghurt and other fermented dairy products to bring about specific changes in the appearance, body, texture and flavour characteristics of the desired final products. Functions of Starters The primary function of almost all starter culture is to develop acid in the product. The secondary effects of acid production include coagulation, expulsion of moisture, texture formation and initiation of flavour production. In addition to these, the starters also help in imparting pleasant acid taste, conferring protection against potential pathogens and providing a longer shelf life to the product. These bacteria convert 1% of lactose in milk approximately to lactic acid with very little by-products such as acetic acid, ethanol, CO2 and normally with no substances causing taints and hence leading to a clean and wholesome milk souring.

Milk fermentation is process by which a change is produced in milk through the activity of microorganism. As milk leaves the udder it serves as a medium for the growth of many species and accordingly undergoes a series of changes, the processes producing these changes constitute the milk fermentation. Fermentation of organic compounds, especially in the lack of oxygen leads to the rapid break-down of ‘biopolymers’ to produce ‘anaerobic food chains’.

Bacteriophage is the term applied to bacterial viruses. Bacteriophage having the ability to lyse certain sensitive living cells. Phages are small particles, which can only be seen in the electron microscope after the application of suitable staining techniques. All phages have a head and most have a tail. The head may be isometric or prelate with a hexagonal outline. There are two types of phages virulent and temperate which enter a different relationship with the host, the lytic and lysogenic cycles respectively.

The significance of milk in human nutrition is now well established as it is considered as the best, ideal and complete food for all age groups. However, in spite of being so, milk can also serve as a potential vehicle for transmission of some diseases under certain circumstances. Moreover, by virtue of possessing almost all the essential nutritional factors, milk can also serve as an excellent culture and protective medium for certain microorganisms, which may include potential pathogens capable of causing serious health problems to the consumers. In this way, milk may serve not only as a vehicle of transmission of disease causing organisms, but it can also allow these pathogens to grow, multiply and produce certain toxic metabolites, thereby making itself an extremely vulnerable commodity from public health point of view.

According to International Dairy Federation(IDF),1980, Mastitis also called as ‘mammitis’ is defined as an inflammation of the udder, almost always of microbial origin and is the outcome of a local or a general infection. The common symptoms are related to inflammation, viz., swollen, hot, red, and painful udders. Mastitis can be classified based on symptoms or on the causative organism. A) Forms of mastitis based on symptoms     1.    Acute or clinical     2.    Sub-acute or subclinical     3.    Chronic.

Tuberculosis Tuberculosis has been recognized as one of the most important infectious diseases in the world because of its high global impact and its chronic debilitating character, particularly in the poor section of society. Milk-borne tuberculosis is directly or indirectly related to the consumption of raw milk from infected dairy herds.

Normally raw milk contains different levels of inhibitory substances, which restrict the normal development of bacteria and some times may even kill them. The degree of inhibitory activity varies considerably in milks of different species, viz, cow, buffalo, human. Maximum activity present in human milk, variations occur in the milks of individual animals and some times even at different milking or from different quarters of the udder of the same animal. There are two groups of antimicrobial substances present in milk:     1.    Inherent or naturally occurring substances in milk.      2.    Non- inherent compounds secreted into milk from other sources.

Dairy equipment and utensils with which milk and milk products come into contact are the main sources of contamination in the products. By the use of effective equipment cleaning and sterilization methods on routine basis, milk of high bacteriological quality can be consistently produced. In composite milk plant, a variety of equipment and utensils are used. The use of stainless steel for the fabrication of dairy utensils and equipment provide highly polished and hard smooth surface that can be cleaned readily, apart from showing resistance to corrosive action of detergents and bactericidal solutions. Utmost care is taken to avoid dents and scratches, which could be the possible focal points of subsequent contamination. To overcome all these problems aluminium and stainless steel vessels and equipment present an ideal situation.

Introduction Numerous characteristics of food determine its acceptability to consumers and to regulatory officials. Before accepting a food for consumption, it must be attractively presented, must have desirable odour and flavour characteristics and other qualities and must be free from potential pathogens or their toxic products. The ultimate nutritive qualities, flavour and appearance have been preserved and no harmful organisms or substances are present to affect the consumer adversely. If the quality of the product is good, its keeping quality is also likely to be substantial. Conversely, there are more chances of spoilage of an inferior quality food product during storage.

India Milk legislation and regulations are designed to prevent fraud and adulteration. But they now cover many factors that affect sanitation and public health. Milk generally is classified into grades according to the care with which it is produced.

Exercises   Sampling of Milk Ex.No: ......................................................................... Date:................. Sampling of Milk for Examination Careful and Accurate sampling of milk is of utmost importance in all analysis of milk. Milk should be uniform throughout in its composition and any sample of milk drawn out of it for analysis must necessarily be a true representative of the whole lot of milk. The factors disturbing the uniformity of the composition of milk are mainly the separation and partial churning of fat, others being freezing and souring of milk. Thorough mixing of milk must first be ensured either by stirring with a long handle dipper, if the container is big or by pouring from one vessel to another or by shaking gently. if the sample bottle has been allowed to stand for some time resulting in the separation of fat in the cream layer or lumps of fat appear, the bottle may be heated in a water bath upto 1000F to melt the fat before mixing. Under no circumstances milk should not be shaken violently since viscosity does not allow air bubbles to rise easily. Moreover agitation of milk tends to churn it with the result uneven distribution of fat occurs. Samples of milk should be examined as fresh as possible, since important changes in its physical conditions, chemical composition and bacteriological content may take place even within a short time. Sampling of Milk When Fat Has Separated When the fat separation is slight, i.e, when there is no visible separation of cream, pour the milk from one vessel to another several times immediately before each sample is drawn. Stirring milk with a plunger is less effective than pouring. When the fat separation is visible as a layer, pour the milk from one vessel to another for a greater number of times. When milk contains dried cream or hardened cream, warm it to 1050-1100 F for 5 to 10 minutes to allow the cream to melt, then vigorously agitate and immediately sample. When milk fat is partially churned due to transit or excessive agitation, etc., warm the milk to 1050-1100F long enough to melt the butter granules and then vigorously shake before sampling. Composition of frozen milk is very uneven in its liquid and frozen portions, the former containing most of the milk solids while the later most of the water. In such cases warm to melt the frozen portion, mix thoroughly and sample. In ordinary curdled milk the percentage of fat remains unchanged in amount but it is not evenly distributed throughout the milk. In such cases, add to the milk a strong solution of caustic soda or potash or strong ammonia water to the extent of 5-10 per cent of the volume of the milk used for sampling. Shake the alkali with the milk until the mixture becomes completely liquid, sa