1. intro to food microbiology...microorganisms and foods microorganisms of concern include: •...
TRANSCRIPT
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Introduction to Food MicrobiologyAndreia Bianchini, Ph.D.Associate Professor
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Microorganisms and Foods
Raw foods normally contain microorganisms!!!
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Microorganisms and FoodsMicroorganisms of concern include:
• Molds• Yeast• Bacteria• Viruses
Source: mpg.de
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Molds
• Multicellular, tubular filaments
• Reproduce by fruiting bodies (spores)
• Larger than bacteria and yeasts
• Widely distributed in nature (soil, air)
• Survive on many substances
• Given right conditions will grow on almost any food
• More tolerant to cold than heat
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Yeasts• Unicellular, usually egg‐shaped• Smaller than molds, larger than bacteria• Reproduction by budding• Widely found in nature• Associated with liquid foods with sugar and acid
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Bacteria• Most important and troublesome• May produce and release enzymes or toxins into the foods• Single cell, microscopic• Several shapes and forms
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Viruses• Small infectious agent that replicates only inside of living cells• While not inside a cell, it exists as a viral particle (virions):
– Genetic material– Protein coat– Envelope of lipids, in some cases
• A virion is 1/100 the size of a bacterium
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Reproduction of Bacterial Cells
• Reproduction by division (fission)
• Referred as “growth”
• Under optimum conditions a cell divides every 20‐30 minutes
http://www.leavingcertbiology.net
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Reproduction of Bacterial Cells
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Sporeforming Bacteria
• Bacterial spores are resistant to heat, cold and chemical agents• Vegetative cells are less heat resistant
2012 Pearson Education, Inc.
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Sporeforming Bacteria
2013 Department of Microbiology, Institute of Biology, Faculty of Science, Eötvös Loránd University, Budapest.
Kathryn Cross, Institute of Food ResearchDon Albrecht, AlbrechtGFX
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Bacterial Growth
Nutritional Requirements
Moisture
Oxygen Requirements
Temperature
pH
Water Activity
Factors Affecting Bacterial Growth and Survival
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Nutritional Requirements
• Carbon source • Nitrogen sources• Sulfur and phosphorus• Trace elements (i.e. copper, zinc, cobalt)• Vitamins (i.e. folic acid, vitamin B‐12)
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Moisture
© 2010 Nature Education http://kmbiology.weebly.com
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Oxygen Requirements• Aerobes• Anaerobes• Facultative anaerobes
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Temperature
https://courses.lumenlearning.com/microbiology/
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Thermal death curve of microorganisms at a certain temperature:
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Temperature
60 °CD value = 132 s
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Thermal death curve of microorganisms at different temperatures:
60 °CD value = 132 s
75 °CD value = 9 s
55 °CD value = 1110 s
67 °CD value = 60 s
Temperature
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pH
• It refers to the degree of acidity or alkalinity
• Organisms have a most favorable pH range for growth– Yeast and mold: lower pH– Bacteria: neutral pH
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Water Activity (aw)• Water availability is important for bacterial growth• Influenced by water‐binding capacity of ingredients• Most foods:
– Aw > 0.95 which support bacterial growth
https://muse.union.edu
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Microorganisms Minimal aw for Growth Molds 0.75Yeasts 0.88
Clostridium botulinum 0.93Salmonella 0.93
Staphylococcus aureus 0.85
Water Activity (aw)
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Sources of Foodborne Organisms
Soil
Water
Modern Farmer Media, 2017
http://www.crystalclearwater.co
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Characteristics and behavior:• The Good,• The Bad, and• The Ugly
Microorganisms
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• We add them to foods • Ferment foods to make flavors and textures we like
– Examples: yogurt, cheese, sour cream, pickles and bread
The Good
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• Properties of fermented foods:‐ Enhanced preservation‐ Enhanced nutritional value‐ Enhanced functionality‐ Enhanced organoleptic properties‐ Increased economic value
The Good
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• Change food and cause them to “go bad” or spoil
The Bad
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• Can make us sick ‐ pathogens • Illness can range from mild to life‐threatening• Bacterial foodborne illnesses:
– Salmonella spp.– Campylobacter spp.– Bacillus cereus– Staphylococcus aureus– Clostridium botulinum– Clostridium perfringens– Escherichia coli– Listeria monocytogenes
The Ugly
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% from the total cases
% of cases hospitalized
% of deaths
Norovirus (viral) 58% 26% 11%
Salmonella non‐typhoidal 11 % 35% 28%
Clostridium perfringens 10 %
Campylobacter spp. 9 % 15% 6%
Staphylococcus aureus 3 %
E. coli O157 4%
Listeria monocytogenes 19%
Subtotal 91 %
Adapted from: CDC, 2011
The Ugly
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Listeria monocytogenes
• Widely spread in nature• Only this specie, it is associated with pathogenicity in humans • High mortality rates (around 20‐30%)• Capable of crossing the placenta barrier
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Listeria monocytogenes• Symptoms
– Flu‐like disease (headache, fever and gastroenteritis)– Could advance to septicemia or meningitis
• Incubation period– 2‐5 weeks
• Associated with different foods such as: – Meats (hams and sausages)– Dairy products (raw milk, pasteurized milk and cheeses)
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• Commonly found on the skin and in the nose of about 30% of individuals
• Some of them has been reported with antibiotic resistance
• Toxin producer bacteria– Usually case of intoxication
• Symptoms – Vomiting – Diarrhea
Staphylococcus aureus
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• It has been found in soil and food production environment • Sporeformer bacteria
– Spore survives the heat in some processing and may germinate in the food
– Ability to produce infection and intoxication – Toxin production:
o pH > 6 o aw > 0.94
Bacillus cereus
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• Diarrheal syndrome – Abdominal pain, diarrhea, nausea (moderate)– Incubation period between 10‐14 hours – Toxin produced in the intestines– Infection Doses: 107 cells/g of food – Usually from dairy and meat products
• Emetic syndrome – Vomiting and nausea – Incubation period: 1‐5 hours (very similar to an intoxication)– Toxin produced in the food (heat stable)– Infection Doses: 108cells/g of food – Usually from pasta and starchy food
Bacillus cereus
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• Anaerobic microorganism• 20 to 30% of the human population are carriers • Toxin producer (enterotoxin)• Symptoms
– Nausea– Abdominal pain – Diarrhea – Less commonly vomiting
• Self limiting in healthy individuals • Associated with:
– Meat and poultry dishes– Meat products
Clostridium perfringens
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• Anaerobic microorganism • Spore is heat resistant • Do not grow or produce toxin below pH 4.5
• Toxin (neurotoxin):– The most powerful toxin known by humans– 1 nanogram is enough to kill a human– Used for cosmetic purpose
Clostridium botulinum
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• Symptoms – Dryness of the mouth and throat – Double vision, fixed pupils and difficulty focusing– Nausea and vomiting – Progressive paralysis that induces cardiac and pulmonary
failure• Mortality rate: 30‐ 60% of the cases • Associated with:
– Domestic canning of meat, fruits and vegetables
Clostridium botulinum
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• Most of the strains are pathogenic for humans or animal • Can be classified in two groups:
– Salmonella Typhi: Typhoid fever – Salmonella non‐typhoidal: Gastroenteritis
o Around 1.4 million of cases per year in USA
Salmonella spp.
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• Non‐typhoidal Salmonella:– Incubation period: 2 to 28 days – Symptoms
o Diarrheao Cramps, chills, abdominal pain o Nausea and vomiting
– Durationo 2 or 3 days
‒ Associated with:o Mainly poultry and eggs products
Salmonella spp.
http://www.cdhd.ne.gov
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• Subcategories according to their virulence properties: – Enterotoxigenic E. coli (ETEC)
o Gastroenteritis (traveler’s diarrhea) – Enteropathogenic E. coli (EPEC)
o Infant diarrhea– Enterohemorrhagic E. coli (EHEC)
o Hemorrhagic colitis – Enteroinvasive E. coli (EIEC)
o Dysentery (similar to Shigella)– Enteroaggregative E. coli (EAEC)
o Persistent diarrhea, mainly in children
Escherichia coli
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• Escherichia coli (EHEC) O157:H7– Incubation time: ranges from 3‐8 days– Symptoms:
o Diarrhea and cramps, progressing to a severe bloody diarrheao Fever and vomitingo Complication may progress to Hemolytic Uremic Syndrome (HUS)o Renal failure in children
– Mortality rate ranges from 3 to 5% of the cases – Associated with:
o Ground meat o Raw milk and juiceso Produce, fruits and sprouts
Escherichia coli
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• Symptoms:– Cramps– Fever– Vomiting– Diarrhea
• Incubation: 2‐5 days• Duration: 2‐10 days• Associated with:
– Raw and undercooked poultry– Unpasteurized milk– Water
Campylobacter jejuni
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• Virus: single‐stranded RNA, non‐enveloped• Causes gastroenteritis• Incubation period
– 24 to 48 hours • Symptoms
– Nausea and vomiting– Diarrhea and cramping
• Duration– 1 or 2 days
• Associated with:– Leafy greens– Fresh fruits– Shellfish
Norovirus spp.
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Food Processing and Preservation
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Introduction to Food MicrobiologyAndreia Bianchini, Ph.D.Associate Professor