Download Types, Characteristics and Growth of Microbes in Foods

Types, Characteristics and
Growth of Microbes in Foods
Lecture Two
Discussion
• What are microorganisms?
• Types of microbes?
• How are they related to hygiene and food
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How Microorganisms Relate To Food
• Three types of microorganisms occur in
foods.
– Beneficial,
– Pathogenic, or
– Spoilage
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Beneficial microorganisms
• Include microbes that
– may produce new foods or food ingredients
through fermentation(s) (e.g., yeasts and lactic
acid bacteria) and
– Probiotics : microorganisms that provide health
benefits when consumed
egs of Health benefits of probiotics?
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Spoilage microorganisms
• Organisms whose growth and actions can
cause food to deteriorate and develop
unpleasant changes in food such as
– taste
– Flavour/odour,
– texture, or
– colour degradation
Example???
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Pathogenic microorganisms
• They can cause human illness
• Two types of pathogenic microorganisms that
grow in or are carried by foods:
– intoxication
– Infection
Differentiate between these
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Intoxicating Vs Infectious Microbes
• Intoxication results from microorganisms growing
and producing toxin (which causes the illness) in a
food.
• Infectious microorganisms may cause illness by the
production of enterotoxins in the gastrointestinal
tract or adhesion to and/or invasion of the tissues.
– An infection is an illness that results from
ingestion of a disease-causing microorganism
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Sanitation and Food contamination
• A major challenge of sanitarian is to
– protect the raw materials, production area and other
involved locations general microbial contamination
• The microorganisms most common to food are
– bacteria and
– Fungi/moulds
– Virus
Find common examples of each
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Microorganisms Common to Food
• The fungi, consist of two major microorganisms:
– molds (which are multicellular) and
– yeasts (which are usually unicellular).
• Bacteria are unicellular.
Viruses, although transmitted more from person to person
than via food, should also be mentioned because they may
contaminate food as a consequence of poor employee
hygiene
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Growth of Microorganisms
How do bacteria grow?
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Microbial Growth Kinetics
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Microbial Growth Kinetics
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Food Spoilage
• Spoilage is usually equated with the decomposition and
putrefaction that results from microorganisms
• Its defined spoilage as an undesirable change in the
flavour, odour, texture, or colour of food caused by
growth of microorganisms and ultimately the action of
their enzymes
• Food is considered spoiled when it becomes unfit for
human consumption
• Manifestation of food spoilage could be
– physical or
– chemical
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Physical Changes
• The physical changes caused by microorganisms
usually are more apparent than the chemical
changes.
• Microbial spoilage usually results in an obvious
change in physical characteristics such as colour,
body, thickening, odour, and flavour
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Physical Changes
• Food spoilage is normally classified as being either
aerobic or anaerobic, depending on
– the spoilage conditions,
– the principal microorganisms (bacteria, moulds, or yeasts)
• Aerobic spoilage of foods from moulds is normally
limited to the food surface, where oxygen is available.
– Example: Moulded surfaces of food such as meats and
cheeses (during aging) can be trimmed off, and the
remainder is generally acceptable for consumption.
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Physical Changes
• Anaerobic spoilage occurs within
– the interior of food products or
– in sealed containers,
where oxygen is either absent or present in limited quantities
• Spoilage is caused by
– facultative and anaerobic bacteria,
– expressed through souring, putrefaction, or taint
Souring occurs from the accumulation of organic acids during
the bacterial enzymatic degradation of complex molecules
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Chemical Changes
• Through the activity of endogenous hydrolytic
enzymes that are present in foodstuffs (and the
action of enzymes that microorganisms produce),
proteins, lipids, carbohydrates, and other complex
molecules are degraded into smaller and simpler
compounds
• Initially, the endogenous enzymes are responsible for
the degradation of complex molecules. As microbial
load and activity increase, degradation subsequently
occurs
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Chemical Changes
• These enzymes hydrolyze the complex molecules into simpler
compounds, which are subsequently utilized as nutrient
sources for supporting microbial growth and activity
• Oxygen availability determines the end products of microbial
action.
• Availability of oxygen permits hydrolysis of proteins into end
products such as simple peptides and amino acids
• Under anaerobic conditions, proteins may be degraded to a
variety of sulfur-containing compounds, which are odorous
and generally obnoxious
• Others include Lipid oxidation, energy utilization or
fermentation
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Microbial Destruction
• Microorganisms are considered dead when
– they cannot multiply, even after being in a suitable
growth medium under favourable environmental
conditions.
• Death differs from dormancy, especially
among bacterial spores.
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Ways of Microbial Destruction
• Heat treatment
• Chemicals
• Radiation
• Pulsed Light
• Electronic Pasteurization
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Microbial Growth Control
• Most methods used to kill microorganisms may be
applied in a milder treatment to inhibit microbial
growth
• Sub-lethal heating, irradiation, or treatment with
toxic chemicals frequently causes injury to
microorganisms and impaired growth without death
• Injury is reflected through an increased lag phase,
less resistance to environmental conditions, and
greater sensitivity to other inhibitory conditions
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Microbial Growth Control
• Synergistic combinations of inhibitory agents, such as
irradiation plus heat and heat plus chemicals, can
increase microbial sensitivity to inhibitory conditions
• Injured cells appear to require synthesis of some
essential cell materials (that is, ribonucleic acid or
enzymes) before recovery is accomplished
• Microbial growth is inhibited through maintenance
of hygienic conditions to reduce debris available to
support bacterial proliferation
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Microbial Growth Control
• Frequently used methods in controlling microbial
growth include:
– Refrigeration
– Use of chemicals
– Dehydration and
– Fermentation
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Microbial Load Determination
• Various methods are available for determining microbial
growth and activity in foods.
• The choice of method depends on the
– information required,
– food product being tested, and
– the characteristics of the microbe(s).
• One of the most important factors in obtaining accurate
and precise results is the collection of representative
samples. Because of the large numbers and variability of
microorganisms present, microbial analyses are less
accurate and precise and, therefore, more subjective than
are chemical methods of analysis. However, these results
need to be interpreted.
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ASSIGNMENT
a. What are i) biofilms ii) mycotoxins and what are
their role in food hygiene and sanitation?
b. Define the following, giving relevant examples
1.
2.
3.
4.
Chemical poisoning
Food toxicoinfection
Psychosomatic food illness
Food infection
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