Introduction to Microbes

Micro-organisms are a problem in foods because they can cause food spoilageor foodborne disease.

Introduction to Microbes

Micro-organisms may be present in the raw ingredients of the food

or may be introduced to the food during preparation, from the food handlers or the food production environment.

Introduction to Microbes

Microorganisms are tiny, mostly one-celledorganisms capable of rapid reproductionunder proper growth conditions.

Those microorganisms important in the food industry include the bacteria, viruses,yeasts, molds, and protozoans.

Food Microbiology-useful microbes

Many microbes are helpful and serve useful functions such as causing breads to rise, fermenting sugars to alcohol, assisting in the production of cheese from milk, and decaying organic matter to replenishnutrients in the soil.

Food Microbiology-spoilage microbes

Microorganisms can also cause foods to spoil and make them inedible. Spoilage organisms cost the food industry millions of dollars each year.

Food Microbiology-harmful microbes

Microorganisms can also be harmful. These are called pathogens and cause between 24 to 81 million cases of foodborne illness in the U.S. each year.

Bacterial cell

Bacteria are single-celled microorganisms found in nearly all natural environments. Outward appearances of the cell such as size, shape, and arrangement are referred to as morphology.

Morphological types are grouped into the general categories of spherical (the cocci), cylindrical (the rods) and spiral. The cocci may be further grouped by their tendencies to cluster.

Diplococci attach in pairs, streptococci in chains, staphylococci bunch like grapes, and sarcinaeproduce a cuboidal arrangement.

Morphology of Bacteria

There are thousands of different kinds of bacteria. Some differ only slightly and it takes a highly

trained person to identify them. There are also groups which differ greatly in

growth habits and appearance and are quite easily identified.

But regardless of minor differences, most bacteria can be classified according to the five basic cell shapes illustrated.

Staphylococcus aureus

Bacillus cereus Bacillus subtilis

Vibrio parahaemolytices

Bacterial cell

Bacterial cells have definite characteristic structures such as the cell wall, cytoplasm, and nuclear structures.

Some also possess hair like appendages for mobility called flagella, fimbriae which aid in attachment, plus cytoplasmic and membranous inclusions for regulating life processes.

VirusesViruses are extremely small parasites. They

require living cells of plants, animals, or bacteria for growth.

The virus(virion) is mainly a packet of genetic material which must be reproduced by the host.

Viruses contains either RNA OR DNA enclosed in a protein coat usually referred to as a nucleocapsid. Nucleic acid might be single or double stranded

Yeast and mold

Yeast and mold are fungi which do not contain chlorophyls. They range in size from single-celled organisms to large mushrooms. Although some are multi celled, they are not differentiated into roots, stems and leaves.

The true fungi produce masses of filamentous hyphae which form the mycelium.

Depending on the organism, they may reproduce by fission, by budding as in the case of yeasts, or by means of spores borne on fruiting structures depending on the organism

Protozoa

Protozoa are single-celled organisms suchas the amoeba which can cause disease inhumans and animals. They possess cell structure similar to higher, more complex organisms.

Reproduction

. Bacteria and similar organisms reproduce by binary fission, a splitting of a single cell into two. The control center for the bacterial cell is the nuclear structure. Within it is the genetic material which is duplicated and transferred to daughter cells during reproduction. These daughter cells can again divide to produce four cells from the original one.

Generation time The time it takes for a new cell to produce a

new generation of daughter cells is called generation time.

Under optimum growth conditions, certain organisms can have a generation time of 15 minutes. In four hours over 65,000 cells could be produced from a single microorganism

GrowthMicroorganisms, like other living organisms, are dependent on

their environment to provide for their basic needs. Adverse conditions can alter their growth rate or kill them.

Growth of microorganisms can be manipulated by controlling: Nutrients available Oxygen Water Temperature Acidity and pH Light Chemicals

Nutrients

Nutrients such as carbohydrates, fats, proteins, vitamins, minerals and water, required by, man are also needed by microorganisms to grow.

Microbes differ in their abilities to use substrates as nutrient sources. Their enzyme systems are made available according to their genetic code.

Oxygen Requirements

Microbes also differ in their needs for freeoxygen. Aerobic organisms must grow in the presence of

free oxygen and anaerobic organisms must grow in the absence of free oxygen.

Facultative organisms can grow with or without oxygen, while microaerophilic organisms grow in the presence of small quantities of oxygen.

Water

Water is necessary for microbes to grow, but microbes cannot grow in pure water. A measurement of the availability of water is aw or water activity.

The Aw of pure water is 1.0 while that of a saturated salt solution is 0.75.

Most spoilage bacteria require a minimum aw of 0.90. Some bacteria can tolerate an aw above 0.75 as can some

yeasts and most molds. Most yeasts require 0.87 water activity. An aw of 0.85 or less suppresses the growth of

organisms of public health significance

Temperature

Microorganisms can grow in a wide range of temperatures. Since they depend on water as a solvent for nutrients, frozen water or boiling water inhibits their growth.

General terms are applied to organisms based on their growth at different temperatures. Most organisms grow best at or near room and body temperature. These are mesophiles. Those growing above 400 C (1050 F) are called thermophiles while those growing below 250 C(750 F) are calledpsychrotrophs.

Acidity

The nature of a solution based on its acidity or alkalinity is described as pH. The pH scale ranges from 0, strongly acidic, to 14, strongly basic. Neutral solutions are pH 7, the pH of pure water.

Most bacteria require near neutral conditions for optimal growth with minimums and maximums between 4 and 9.

Yeast and molds can grow below pH 4 upto pH 3.

Acidity

Many organisms change the pH of their substrate by producing by-products during growth. They can change conditions such that the environment can no longer support their growth.

Yeasts and molds are more tolerant of lower pH than the bacteria and may outgrow them under those conditions.

Light & Chemicals

Ultraviolet light and the presence of chemical inhibitors may also affect the growth of organisms. Many treatments such as hydrogen peroxide and chlorine can kill or injure microbes.

Under certain conditions those given a sublethal treatment are injured, but can recover.

Industrial importance of molds

Molds are important to the food industry. Among their many contributions are the flavor and colorthey add to cheeses and the making of soy sauce. They also play a role in the making of such chemicals as citric and lactic acid and many enzymes.

Molds can also cause problems in foods. Certain kinds can produce poisons called mycotoxins.Mycotoxins have only recently been discovered and little is known about what causes molds to produce them

Molds produce a stem consisting of several cells. Together, these cells form a "fruiting body." The fruiting body produces the spores, which detach and are carried by air currents and deposited to start new mold colonies whenever conditions are favorable

Mold spores are quite abundant in the air. So, any food allowed to stand in the open soon becomes contaminated with mold if adequate moisture is present. Some types of molds are also psychrophiles and can cause spoilage of refrigerated foods

Aspergillus flavus Aspergillus fumagitus

Penicillium citrinum

Yeasts

Yeasts are small, single-celled plants. They are members of the family fungi (singular, fungus), which also includes mushrooms. Fungi differ from other plants in that they have no chlorophyl.

Bacteria thrive on many different types of food. But most yeasts can live only on sugars and starches. From these, they produce carbon dioxide gas and alcohol. Thus, they have been useful to man for centuries in the production of certain foods and beverages.

They are responsible for the rising of bread dough and the fermentation of wines, whiskey, brandy and beer. They also play the initial role in the production of vinegar.

Unlike bacteria, which multiply by binary fission, yeasts reproduce by a method called budding.

Because they can grow under conditions of high salt or sugar content, they can cause the spoilage of certain foods in which bacteria would not grow. Examples are honey, jellies, maple syrup and sweetened condensed milk.

Foods produced by the bacterial fermentation process, such as pickles and sauerkraut, can also be spoiled by yeasts which interfere with the normal fermentative process.

Saccharomyces cerevisiae

What is Food Spoilage

Spoilage is a natural phenomenon; it occurs at varying rates depending on the storage temperature, kind of food involved, kind of microorganisms present, packaging materials used, food additives used and method of preservation.

Food spoilage

Food spoilage is defined as any change in the organoleptic qualities (flavour, appearance, odour or texture) of the food that makes the food unacceptable to the consumer.

. A spoiled food is not necessarily unsafe to eat, but unpalatable to the consumer. Foods are attacked in a variety of ways that are harmful to the quality of the food.

Foods are organic and provide adequate nutrients for the growth of a wide range of chemoorganotrophic organisms.

The physical and chemical characteristics of a food and how it is stored determine its degree of susceptibility to microbial spoilage

Food spoilage

Food is considered spoiled when an undesirable change in the color, flavor, odor or texture has occurred. Foreign substances in food products make foods undesirable.

The onset of food spoilage is rather indefinite. It is a gradual process occurring because of poor sanitation, enzymatic or chemical reactions, improper temperature controls, microbial growth or physical abuse

Food Spoilage

Foods are classed into three categories based upon their water activity which is one of the factors that determines their susceptibility to microbial spoilage:

(i) Highly perishable foods (meats, fish, poultry, dairy products)(ii) Semi-perishable foods (potatoes and some vegetables)(iii) Stable foods (dried foods).

Types of food spoilageTypes of food spoilage fall into two major

categories, according to the cause of the spoilage:

microbial spoilage is caused by microorganisms and their products;

non-microbial spoilage can be caused by foreign material in the foodstuff or by enzymes that occur in the foodstuff naturally.

Conditions Necessary for Microbial Spoilage

Microbial spoilage is the major cause of food spoilage. It occurs as a result of contamination of food by microorganisms, provision of a suitable environment for their growth, and degradation of the foodstuffs.

To control microbial buildup, you must control the following:

The source of microorganisms - people, raw materials, equipment, air currents, dust and pests.

Food residues, which are required for bacterial growth.

Conditions Necessary for Microbial Spoilage

Moisture, which is required for growth; relative humidity should be monitored.

Time, during which food product is exposed to a given set of conditions that promote bacterial growth.

Temperature since, in general, temperature determines the generation time of microorganisms.

Enzymatic spoilage

Enzymes are chemicals produced by all living things. They help speed up or slow down chemical reactions, act as transports for foods, and are a normal constituent of foods. For instance, as a banana matures, the color changes from green to yellow to brown to black. The change is caused by the enzymes (chemicals) in the banana. The ripening, then softening, of other fruits such as apples, peaches and tomatoes is another example of enzymatic action.

Enzymatic spoilage

Enzymes can be inactivated by heat, which is the reason for blanching vegetables; or they can be inactivated by cold temperatures below 40 degrees F, which is the reason for placing vegetables under refrigeration. Think of green tomatoes in the refrigerator compared to tomatoes sitting on the window sill.

Enzymatic spoilage

Bacteria also produce enzymes that break down food and allow them to obtain nutrients through their cell walls. Therefore, lowering the temperature reduces the rate of enzyme action as well as the rate at which bacteria can multiply.

Refrigeration increases the time required to spoil food.

Enzymatic spoilage

As the number of bacteria increases, the amount of enzymes produced increases. Higher temperatures can cause increased enzymatic activity. With large numbers of bacteria and high temperatures, a food will spoil very rapidly.

When bacterial contamination is high and the storage temperature is low, a food will keep for a moderate period of time; when the bacterial contamination is low and the storage temperature high, food will keep for a moderate period of time.

However, if the contamination of bacteria is low and the storage temperature kept low, the food product will have the longest possible shelf life

Non-microbial spoilage

Food may spoil as a result of chemical changes within the food itself or by a reaction between the food and the packaging material

Oxidation of fats & oils rancidity Inclusion of foreign material in foods.

Washers, bolts, nuts and various other items have been found in canned foods

Non-microbial spoilage

Presence of hair, flies, roaches, and other pests or parts of pests have been found in food products

Problems with weevils in cornmeal and similar products. Other pests can drill through a plastic bag, an aluminum foil wrap, a paper cup or through chocolate and lay their eggs in the center of a peanut butter candy bar.

Sporulation

Under adverse conditions, certain bacteriacan protect the cells genetic material byproducing spores. These are extremelyresistant capsules of genetic materials.Though there are no discernible life processes

in the spore, under proper sporulationconditions, a viable, reproducing cell will germinate from it

SporesThere are certain basic differences between spores

and active or vegetative bacterial cells. Spores are not easily killed. In fact, conditions which will quickly kill active bacteria have little or no effect on spores. A temperature of 1800 F will kill bacterial cells within minutes, but bacterial spores can resist this temperature indefinitely. This is important to us in that all processing times for canned foods are calculated by using both the time and temperature required to kill bacterial spores.

Fermentation Fermentation selects for the growth of one or

more bacteria which then inhibit the growth of harmful microbes. Often the product of these reactions alters the flavor and texture of some foods. Many of the foods you eat are made with microbes. Some of the flavors and textures of food can directly be attributed to the bacteria and the chemicals they produce as a result of feeding on our food. These foods include yogurt, cheese, buttermilk, sour cream, salami, coffee, olives, pickles, sauerkraut, soy sauce, alcoholic beverages, and vinegar.

What is yogurt?

Yogurt is a fermented milk product that can be made from any milk, even soy milk. A mixed culture of Lactobacillus acidophilus (or bulgaricus) and Streptococcus thermophiles(they work better together than they do separately) produce lactic acid which lowers the pH and makes it sour. The partial digestion of the milk (lactose) which occurs during fermentation makes the lactose easily digestible, which is good for lactose-intolerant people.

Yoghurt

Microbes Involved: Lactobacillus bulgaricus and/or

acidophilus & Streptococcus thermophilus

Role of microbes in yoghurt What they do The streptococcus produces lactic acid. Lactic acid lowers

the pH, thus changing the form of the milk proteins and causing the mixture to thicken.

The lactobacillus bacteria produce acetaldehyde, acetic acid, volatile fatty acids, ethanol, carbon dioxide and various other products which influence flavor and aroma.

If streptococci outgrow the lactobacilli, the result is a harsh, sour yogurt due to overproduction of lactic acid relative to flavor components. The ratio for proper taste is 1:1

Fruit and fruit flavors are pasteurized separately and added later.

Nutritional value of Yoghurt

Yogurt Facts a good source of calcium, riboflavin and protein. has a fine curd which makes it more easily digestible than sweet

milk. lactose is converted to lactic acid; this makes digestion easier on

lactose- intolerant people Lactobacillus acidophilus may synthesize Vitamin B in the intestine. cultured yogurts are higher in folic acid than other yogurts. lactic acid bacteria fight pathogenic organisms: Salmonella typhi

die, E. coli are unable to develop, and S. paratyphi and Corynebacteriae diphtheriae lose their pathogenic properties.

fermented milk cultures have been reported to help treat peptic ulcer, diarrhea, and dysentery.

Freshly prepared yogurt contains 10,000,000,000 (109) bactria per gram

Food Safety

Food safety is a very broad topic. Pesticides, herbicides, chemical additives, and spoilage are all of concern, but food scientists, food processors, and consumers focus most on microbiological quality.

Microorganisms pose a challenge to the food industry and most food processes are designed with microbial quality in mind.

Microorganisms are often too small to be seen with the unaided eye and have the ability to reproduce rapidly. Many of them produce toxins and can cause infections.

For all of these reasons, the microbiological quality of the food we eat is scrutinized closely.

Food-borne IllnessThe sickness resulting from eating food

contaminated with either bacterial toxins or by certain bacteria in the food, often resulting in vomiting, diarrhea and prostration.

Food-borne diseases are most often caused by several species of bacteria, although viruses, parasites, amoebas and other biological as well as chemical agents may be responsible.

Food-borne Illness

Food poisoning would include illness caused by naturally poisonous foods, like certain wild mushrooms, or from chemical contaminants in the food.

Food-borne illness

Today, food-borne illness is of serious concern. Its frequency is not known because a great majority of the cases go unreported. Reporting food-borne illness to public health authorities is not required in the United States.

Estimates claim as many as 200 million cases in the U.S. per year. Only a small percentage of these are hospitalized. Most are passed off as traveler's diarrhea, 24 hour flu, or upset stomach.

Pathogen Any microorganism that can cause

disease. Salmonella is always considered a

pathogenic microorganism. E. coli is considered an opportunistic

pathogen. It is not always pathogenic, but given the opportunity, it can cause food-borne illness

Common Bacterial Food-borne Pathogens

Bacillus cereus

Campylobacter jejuni

Clostridium botulinum

Clostridium perfringens

Listeria monocytogenes

Salmonella serovars

Staphylococcus aureus

Vibrio cholera

Vibrio vulnificus

Vibrio parahaemolyticus

Yersinia enterocolitica

Parasitic Diseases Amebiasis Ascaris, Round worms Cryptosporidiosis Cyclospora Cysticercosis Giardiasis Toxoplasmosis Trichinosis

Viral Diseases

Hepatitis A Virus Noro virus (formerly known as Norwalk

Virus Rotavirus Viral gastroenteritis