FOOD MICROBIOLOGY for HND food spoilageage

Microbial spoilage of food

1. FOOD MICROBIOLOGY

2. Food microbiology is the study of the microorganisms that inhibit, create, or contaminate food. This includes the study of microorganisms causing food spoilage; as well as, pathogens that may cause disease especially if food is improperly cooked or stored. Humans obtain food from animals and plants, and these must be healthy. Generally, foods when fresh are free of microorganisms (bacteria, fungi, viruses etc ), while food surfaces may have a low load of microorganisms. Food spoilage is complicated by the fact that food begins to deteriorate shortly after harvesting, gathering on slaughtering.

3. Why do we study food microbiology? Food Microbiologists study the interactions between food , microorganisms and their environment to ensure food safety, quality, and value. They study methods to preserve foods and prevent them from spoiling the food production chain. FOOD SPOILAGE Food spoilage is defined as damage or injury to food rendering it unsuitable for human consumption. Food must be considered spoiled if it is contaminated with any pathogenic microorganisms or poisonous agents, e.g. Pesticides, heavy metals etc. In most cases, there does not need to be an evident sign of spoilage. The food might look normal and only after eating it or by careful bacteriological and /or toxicological investigation, one is able to realize the defect. Food decay or decomposition is implied when the term ‘spoiled’ is used.

4. CAUSES OF FOOD SPOILAGE Food spoilage is ascribed to various causes;- Growth and activity of microorganisms:- Bacteria, yeast and moulds are the key microorganisms that cause food spoilage. They produce various enzymes that digest the various constituents of food. Enzymes activity: This refers to the action of enzymes inherently found in animal or plant tissues. These enzymes digest the various food components after the death of plant or animal. Chemical reactions: - These are the chemical reactions which occur in plant or animal tissues, but not catalyzed by enzymes e.g. Oxidation of fats – causing rancidity. Vermin: vermin includes; weevils, ants, rats, cockroaches, mice, birds, larval stages of some insects. Physical changes - These include those changes which are caused by freezing, burning, drying, pressure etc.  

5. MICROBIAL SPOILAGE OF FOODS

6. Bacteria, yeasts, and molds are the major causes of food spoilage. They produce various enzymes that digest various chemical constituents of food. Molds are the major cause of spoilage of foods with reduced water activity e.g. cereals and cereal products, meats etc. Bacteria are involved in spoilage of food with relatively high water activity eg milk and milk products, meat etc. PRIMARY SOURCES OF MICROOGANISMS IN FOODS   There are eight primary environmental sources of microorganism in foods, namely ; Soil and water: - The two environments are placed together because many of bacteria and fungi that inhabit both have a lot in common. Soil organisms may enter the atmosphere by the action of the wind and later enter water bodies when it rains. They also enter water, when rain water flows over soil into bodies of water. This common cycling results in soil and aquatic organisms being one and the same to a large degree.

7. Plants and plant products It may be assumed that many or most microorganisms found in the soil and water will contaminate plants. Only a relatively small number of the microorganisms find the plant environment suitable for their over – all well – being. Those that persist on plant products do so by virtue of a capacity to adhere to plant surfaces so that they are not easily washed away and because they are able to obtain their nutritional requirements from these surfaces. Notable among these are the lactic acid bacteria and yeasts. Others are; Corynebacteria , Pseudomonas and fungal pathogens . Food utensils When vegetables are harvested in containers and utensils, some or all of the surface organisms on the products contaminate contact surfaces. The cutting block in a meat market along with cutting knives and grinders are contaminated from initial sample, and this process leads to a buildup of organisms – this ensures a constant level of contamination by meat-borne organisms.  

8. Gastro – intestinal tract – of man and animals This biota becomes a water source when polluted water is used to wash raw food products. The intestinal biota consists of e.g. Salmonellae . Any or all of the Enterobacteriaceae may be expected in faecal waste, along with intestinal pathogens, including some protozoa e.g. E . histolytica , Giardia , lambria , Toxoplasma gondii , Cryptosporidium pavum , Cyclospora cayetanensis . Food handlers : The microorganism on the hands and outer garments of food handlers generally reflect the environment and habits of individuals. The organisms may be those from soil, water, dust and other environmental sources. Additional sources are the organism found in nasal cavities, the mouth, and on the skin and those from the gastro intestinal tract that may enter food through poor personal hygiene practices . Animal hides and skins; In the case of milk cows, the type of organism found in raw milk can be a reflection of the biota of the udder when proper milking procedures are not followed in milking and of the general environment of such animals. From both the udder and skin, organisms can contaminate the general environment, milk containers and the hands of handlers.  

9. Air and dust – The organisms found in air and dust, include most of gram positive bacteria, and among the fungi, a number of molds may be expected to occur in air and dust, along with some yeasts.

10. FACTORS AFFECTING MICROBIAL GROWTH IN FOOD   The factors affecting microbial growth fall into two categories; the Intrinsic factors and the Extrinsic factors. THE INTRINSIC FACTORS 1) Hydrogen ion concentration (pH) Most bacteria grow best at neutral or weakly alkaline pH, usually 6.6 – 7.5. Few bacteria may grow at pH below 4.0. Some bacteria can grow within a pH of 4.5 and 9.0 e.g. Salmonella . Bacteria tend to be more fastidious in their relationships to pH than molds and yeasts, with the pathogenic bacteria being most fastidious. Molds grow at pH of 1.5 – 11.0, while yeast grows at pH range of 1.5 – 8.5.

11. Fruits , soft drinks, vinegar and wines all have pH values all of which fall below the point at which bacteria normally grow. The excellent keeping quality of these products is due in great part to pH. It is a common observation that fruits generally undergo mold and yeast spoilage, and this is due to the capacity of these organisms to grow at pH values of less than 3.5. Most of the meats and sea foods have a final ultimate pH of about 5.6 and above. This makes these products to be susceptible to bacteria as well as mold and yeast spoilage.

12. Microorganisms that are able to grow in acid environment are called acidophilic microorganism. These microorganisms are able to grow at pH of around 2.0. Yeasts and molds grow under acid conditions. Other microorganisms such as V ibrio cholerae are sensitive to acids and prefer alkaline conditions. Most bacteria are killed in Strong acids or strong alkaline environment except the Mycobacteria.

13. 2) Moisture content One of the oldest methods of preserving foods is by drying or dessication . The preservation of food by drying is a direct consequence of removal or binding of moisture, without which microorganisms do not grow. It is generally accepted that the water requirement of microorganisms should be described in terms of water activity. Water activity (A w ) is a measurement of the amount of free water in a food medium. The amount of free water in food is important for growth of microorganisms. If there is lack of this free water, microorganism will not grow.

14. The A w of most fresh foods is above 0.99. In general bacteria require high levels of Aw for growth than fungi, with gram negative bacteria having higher requirements than the gram –positive bacteria. Most spoilage bacteria do not grow below A w = 0.91, whereas spoilage molds can grow at A w = 0.80. With respect to food- poisoning bacteria, Staphylococcus aureus can grow at Aw =0.86, whereas C lostridium botulinum does not grow at Aw below 0.94.

15. 3) Nutrient content of the food In order to grow and function normally microorganism of importance in the foods require the following; Water -Proteins Carbohydrate Lipids Nitrogen Sulphur Phosphorous Vitamins Minerals e.g. Ca 2+ , Fe 2+ Foods such as milk, meat, and eggs are rich in nutrients that are required by microorganism. These foods are therefore susceptible to microbial spoilage.

16. 4) Antimicrobial constituents (substances) The resistance of some foods against attacks by microorganisms is due to presence of naturally occurring substances that posses and express antimicrobial activity. Some plant species are known to contain essential oils that posses antimicrobial activity e.g. Allicin in garlic. Cow’s milk contains several antimicrobial substances, including lactoferrin , conglutinin , and the lactoperoxidase system. Milk casein is known to be antimicrobial under certain conditions. Lysozyme in Eggs is known to exhibit some antimicrobial activity.

17. 5) Biological structures The natural covering of some foods provides excellent protection against the entry and subsequent damage by spoilage organisms. For example, Eggs have shell and inner membranes that prevent yolk and egg white from infection.

18. EXTRINSIC FACTORS   The extrinsic factors of foods are not substrate dependent. They are those properties of the storage environment that affect both the foods and their microorganisms. They are factors external to the food that affect microbial growth. They include : ( i ) Temperature of storage (ii) Presence and concentration of gases in the environment Relative humidity of food storage environment.

19. 1) Temperature of storage Microorganisms, individually and as a group, grow over a very wide range of temperatures. The lowest temperature at which a microorganism has been reported to grow is – 34 o C while the highest was in excess of 100 o C. Bacteria can therefore be grouped into three categories based on their temperature requirements for growth;- ( i ) Psychrophilic microorganisms These grow best at around 20 o C, but also down to-10 o C in unfrozen media. The psychrophilic bacteria can cause food spoilage at low temperatures. Several of the bacteria found in soil and water belong to this group.  

20. (ii) Mesophilic microorganisms These microorganisms grow best between 20 o C – 45 o C. With optimal between 30 o C – 40 o C. The optimum growth temperature is around 37 o C. Some of the mesophiles such as P seudomonas aeroginosa may grow at lower temperatures of between 5 o C – 45 o C.None of the mesophiles are able to grow at temperatures below 5 o C or above 45 o C. Most of the pathogenic bacteria belong to this category of microorganisms.   (iii) Thermophilic microorganisms These grow at temperatures above 45 o C, and often their optimum growth temperature is between 50 o C-70 o C. Growth of some bacteria may occur upto temperatures of 122 o C . Bacteria in this group are mainly spore formers and are of importance in the food industry especially in processed foods eg Bacillus,  

21. 2) Concentration of gases in the environment Carbon dioxide (CO 2 ) is the single most important atmospheric gas that is used to control growth of microorganisms in food. CO 2 along with oxygen (0 2 ) are the two most important gases in modified atmosphere packaged (MAP) foods. Various microorganisms require for growth, either high oxygen (aerobic microorganisms), low oxygen tension ( microaerobic microorganisms) or absence of oxygen (Anaerobic microorganisms). Some microorganisms (Facultative anaerobes) may grow either in high oxygen tension, or in the absence of oxygen .

22. Anaerobic or facultative aerobic spore formers are most likely to grow in canned foods. Microaerophilic bacteria are most likely to grow in vacuum packed foods, since they require low oxygen tension. Aerobic bacteria are likely to grow on the surface of raw meat. Aerobic molds are likely to grow in insufficiently dried or salted products.

23. 3) Relative humidity of food storage environment Relative humidity is defined as 100 X a w . This is the amount of moisture in the atmosphere or food environment. Foods with low water activity placed in high humidity environment take up water. This increases their Aw, and hence spoilage of the food occurs easily. For example, dry grains stored in an environment with high humidity will take-up water and undergo spoilage by molds.

24. MICROORGANISMS IMPORTANT IN FOOD industry

25. Bacteria that are important in food microbiology may be divided into groups according to the fermentation product, e.g. lactic acid bacteria , propionic acid bacteria , acetic acid bacteria . ... Microorganisms are essential for the production of foods such as cheese, yogurt, bread, beer, wine and other fermented foods . What microorganisms are used in food production ? Most commonly used microorganisms are yeast, bacteria , moulds , or a combination of these. A good example of microorganism usage in food production is the process of fermentation, which results in the production of organic acids, alcohols and esters.

26. Bacteria Bacteria are the largest group of unicellular microorganisms. The shapes of medically important bacteria are classified into - C occi , or spherical cells; -Bacilli , or cylindrical or rod shaped cells; -Spiral or curved forms. The pathogenic or disease causing bacteria are usually gram negative, however, three gram-positive rods are known to cause food intoxications :  Clostridium botulinum,C . perfringens,and Bacillus cereus Different strains of bacteria are also used in production of various food and dairy products. Strains of Streptococcus, Lactobacillus Bifidobacterium , Erwinia etc . are used in the production of fermented food and dairy products. Streptococcus thermophilus and Lactobacillus bulgaricus are used to produce yogurt .

27. Molds Molds are multicellular filamentous fungi whose growth on foods is usually readily recognized by their fuzzy or cottony appearance. Molds also find their use in manufacturing of different foods and food products. They are used in ripening of various types of food products as cheese (e.g. Roquefort,Camembert ). Molds are also grown as feed and food and are employed to produce ingredients such as enzymes like amylase used in making bread or citric acid used in soft drinks. Molds are major contributors in the ripening of many oriental foods. A species of Bothrytiscinerea , is used in rotting of grape for production of wine. Lactic fermentations using molds results in a unique Finnish fermented milk called viili .

28. Yeasts Yeasts have the ability to ferment sugars to ethanol and carbon-dioxide and hence they are extensively in food industry. The most commonly used yeast, the baker’s yeast is grown industrially. Saccharomyces carlsbergensis is most commonly used in fermentation of most beers. The other yeast strains of importance are Brettanomyces , Schizosaccharomyce ,, Candida, Cryptococcus, Debaryomyces , Zygosaccharomyces , Hanseniaspora , Saccharomyces Points to remember Bacteria, molds and yeast are the most important microorganisms that cause food spoilage and also find the maximum exploitation in production of food and food products. Different strains of bacteria and fungus are used for fermentation of dairy products for production of a wide variety of cultured milk products. Both bacteria and fungi are used in cheese production processes .

29. Lactic acid bacteria are used for coagulation of milk that can be processed to yield a wide variety of cheeses, including soft unripened , soft ripened, semisoft, hard, and very hard types . Microorganisms such as Lactobacillus and Bifidobacterium are used as in food and health industry. Spirulina , a cyanobacterium , also is a popular food source sold in specialty stores . Molds are used for rotting of grapes for production of different varieties of wines. Mushrooms ( Agaricusbisporus ) are one of the most important fungi used as a food source. Alcoholic beverages as beer are produced by fermentation of cereals and grains using different strains of yeasts.

30. Food enzymes produced by microorganisms

31. Microbial enzymes produced from industries are selected from different groups of microorganisms and they include bacteria, fungi and yeasts. Many enzymes are produced in industries but most predominant enzymes that are produced on large scale in industries include protease, α-amylase, glucose isomerase and glucamylase . Enzymes produced in industries with the help of microorganisms were found to exhibit good biological activity. Microbial source is preferred over plants and animals for production of enzymes mainly because of the following reasons: Enzymes can be produced on large scale and are economical. 2 ) The process of extraction and purification of enzymes from microbial sources is easier in comparison with plant and animal sources. 3 ) Microbial sources are capable of producing variety of enzymes in different environmental conditions in limited space and time period.

32. 4) Genetic manipulation is carried out to yield higher quantity of enzymes produced from microbial sources .

33. 1) Lipase Lipases are enzymes which catalyze the hydrolysis of long chain triglycerides. Lipase is naturally present in the stomach and pancreas of humans and other animal species in order to digest fats and lipids. Microbial lipases are produced by bacteria, fungi and yeast. Microbial enzymes contribute approximately 90 % of global lipase market. The enzyme lipase finds application in various industries including food, biofuel, detergents and animal feed industries . It is also being used in leather, textile and paper processing applications. In food and beverages industry, lipases find major application in dairy, baking, fruit juices, beer and wine industries.

34. 2) α- Amylases α- Amylases are starch degrading enzymes capable of hydrolyzing α-1, 4 glycosidic bonds of polysaccharides and results in the production of short chain dextrins . This enzyme finds wide applications in bakeries acting as an agent for flavor enhancement and anti-staling agent. These enzymes are widely distributed in all living organisms. α- Amylases finds wide applications in food industry like baking, brewing. It is widely used in baking industry for improving the bread quality . During the baking process, α- amylases are added to dough of bread and results in the conversion of starch to smaller dextrins which are subsequently fermented by yeast.

35. 3) Glucoamylases Glucoamylases are exo -acting enzymes which catalyzes the hydrolysis of polysaccharide starch from the non-reducing end . This enzyme is produced mainly by Aspergillus niger and Aspergillus awamori . But the one which is produced from Rhizopus oryzae is widely used for industrial applications It is widely used for the production of high glucose syrups as well as high fructose syrups. It also finds application in baking industry by improving flour quality, reduce staling of dough etc. It improves bread crust colour and improves quality of high fiber baked products. It converts the starch present in flour to maltose and fermentable sugars.

36. 4 ) Protease Proteases are enzymes which catalyze the hydrolysis of peptide bonds present in proteins and polypeptides. It represents 60% of industrial enzymes in the market. The major sources of proteases enzyme are animals, plants and microorganisms (both bacterial and fungal). These proteases are widely used in food industry for various applications such as brewing, tenderization of meat, coagulation of milk and as a digestive aid. In addition, proteases are also used to improve the flavor, nutritional value, solubility and digestibility of food proteins.

37. 4) Lactase (β- galactosidase ) The enzyme β- galactosidase catalyzes the hydrolysis of lactose. They belong to the family of hydrolase . The enzyme β- galactosidase can be obtained from numerous biological systems including plants, animals and microorganisms. The production β- galactosidase from microorganisms such as bacteria, fungi and yeast is being preferred as choice due to higher yield and thus relatively low cost of the enzyme.

38. 5) Phospholipase Phospholipases selectively break down phospholipids into fatty acids and other lipophilic substances . Phospholipases are widely used in food industry and the most important one is in the production of oils, dairy industry and in the manufacture of several bakery items. Phospholipases are also applied in cheese manufacture and bread manufacture.

39. Food microorganisms and diseases

40. Food Intoxication : It refers to the consumption of toxic chemicals liberated or produced by bacterial growth in food . These respective toxins results in variety of illness of the consumers. These toxins are not visible to naked eye but will change the chemical properties of the food . What is the difference between food infection and food intoxication? Foodborne infection is caused by the ingestion of food containing live bacteria which grow and establish themselves in the human intestinal tract. Foodborne intoxication is caused by ingesting food containing toxins formed by bacteria which resulted from the bacterial growth in the food item. Food poisoning : The illness resulting from eating food or drinking water containing poisonous substances including bacteria, viruses, pesticides, or toxins.

41. For a foodborne illness (poisoning) to occur, the following conditions must be present: The microorganism or its toxin must be present in food . The food must be suitable for the microorganism to grow . The temperature must be suitable for the microorganism to grow . Enough time must be given for the microorganism to grow (and to produce a toxin ). The food must be eaten.

42. The most common symptom associated with foodborne illnesses is diarrhea. Each pathogenic microorganism has its set of characteristic symptoms. The severity of the foodborne illness depends on the pathogenic microorganism or toxin ingested, the amount of food consumed (dose), and the health status of the individual. For individuals who have immunocompromised health conditions, or for the aged, children, or pregnant women, any foodborne illness may be life-threatening.

43. There are six groups of microorganisms that can cause food-borne illness. They are: bacteria viruses parasites protozoa fungi prions

44. Example of microbes that cause food poisoning 1) Vibrio cholerae V. cholerae has a free life cycle, it is ubiquitous in aquatic environments. It causes Cholera. Symptoms include diarrhea, running stomach, vomiting 2) Staphylococcus aureus Staphylococcal foodborne illness is one of the most common diseases acquired by S. aureus . Symptoms include nausea, vomit, abdominal cramps, salivation, diarrhea could be present or absent. The first three symptoms are the most common ones. 3) Bacillus cereus B. cereus is a ubiquitous microorganism in the environment, and it can easily contaminate any food production and processing system, due to the formation of endospores. Symptoms include nausea, abdominal cramps, watery diarrhea

45. PRINCIPLES OF FOOD PRESERVATION

46. A good method of food preservation is one that slows down or prevents altogether the action of the agents of spoilage. Also, during the process of food preservation, the food should not be damaged . T he principles of food preservation include the following: 1 ) Prevention or delay of microbial decomposition • By keeping out microorganisms (asepsis) • By removal of microorganisms (done by cleaning, trimming,filtration ) • By hindering the growth and activity of microorganisms (e.g. by low temperatures, drying, anaerobic conditions, or chemicals) • By killing the microorganisms (e.g. by heat or radiation)

47. 2) Prevention or delay of self decomposition of the food • By destruction or inactivation of food enzymes • By prevention or delay of chemical reactions (By using antioxidant)