Food microbiology Flashcards
Examples of Prokaryotic cells
bacteria cells
What are gram positive bacteria
Gram-positive are purple and have a thick peptidoglycan cell wall layer above cytoplasmic membrane
What are gram negative bacteria
Gram-negative are pink and have a thin peptidoglycan layer with an additional outer membrane composed of lipopolysaccharide
Properties of gram positive bacteria
It is heat resistant
Properties of gram negative bacteria
Gram-negative bacteria outer membrane can help it evade immune system & limit entry of antibodies & sanitizers
Which factors can increase risk of food contamination
biological layers such are biofilms which are resistant to cleaning sanitizers and tough, dormant resistant structures called endospores that are resistant to heat
What is mold able to form
Mold form long filaments called hyphae which further group together to form mycelium
How are proteins spoilt
Proteins are hydrolyzed into peptides causing bitter taste, foul-smelling amines, ammonia or sulfur containing volatiles such as hydrogen sulfide
How are lipids spoilt
Triglycerides are hydrolyzed into microbial lipase giving rise to free fatty acids causing hydrolytic rancidity
How are carbohydrates spoilt
Carbohydrates when broken down can be mushy, organic acids are produced, unsightly pigments are synthesized by accumulation of too many spoilage bacteria cells or production of dextran
What are low acid foods
Foods with pH higher than 4.5
What are the differences between yeast and mold and bacteria
Yeast & mold can grow at temperatures, pH and water conditions that may not be feasible for bacteria. It can also produce mycotoxins. Yeast is unicellular while mold is multicellular
What are bacteria that can tolerate higher levels of salt
halophiles
What are bacteria that can tolerate higher levels of sugar
osmophiles
What are strong odor attributed to
Enterobacter or Serratia species
What happens in Food intoxications
Microorganism produce toxins that are ingested by humans
What is Staphylococcus aureus
aerobic Gram-positive cocci, it is found due to unhygienic handling of food. It is heat stable
What is Clostridium botulinum
anaerobic Gram-positive bacilli. It is widely distributed in soils, water & environment. It forms heat-resistant spores & is a risk for low-acid canned foods as it thrives in neutral environment
What is Aspergillus flavus
It produces alfatoxins
What is salmonella
Salmonella are Gram-negative facultative anaerobes & are associated with under-processed meat & feces
What is Listeria monocytogenes
Gram-positive rod that is well known for being able to grow at low temperatures
What is Escherichia coli
Escherichia coli is a Gram-negative bacteria that is on-pathogenic & found in feces of humans & animals
What are Toxicoinfections
This happens when the pathogen grows to high numbers in the food, gets ingested, and then produces toxins in the human body
What are Bacillus cereus & clostridium penfringens
Gram-positive & are found in soil.
They produce heat resistant spores but do not grow well in low temperatures
Is processing at higher temperature for shorter periods better than lower temperatures for longer periods
higher temperature for shorter periods
Best temperature to grow microorganisms
10℃ to 35℃
What are the temperatures to keep hot and cold food
Best to keep hot food at above 60℃ & cold food below 5℃
What are extrinsic factors
Factors which affect the external environment of the food
What are intrinsic factors
Intrinsic factors are conditions within the food which affects the growth of microorganisms
What is fermentation
Fermentation is the metabolic process that takes place during desired microbial growth resulting in evident physical & chemical changes to food materials
What can fermentation produce
Organic acids, vitamins, anti microbial compounds, ammonia carbon dioxide, sugars
What are the 2 most common lactic acid bacteria used in fermenting yoghurt
Lactobacillus delbrueckii subsp. Bulgaricus & Streptococcus thermophilus
Why are 2 species used
Lactobacillus delbrueckii is able to grow quickly but is only able to lower the pH to about 5.5 after which the growth is inhibited by low pH. Streptococcus thermophilus grows slowly but can bring the pH down to 4.5
What species can bring down the bacteria slowly
Lactobacillus plantarum, Leuconostoc spp & Pediococcus spp
What are some examples used to produce alkaline fermented foods
Bacillus subtills Gram-positive ferments Natto while Rhizopus oligosporus mold ferments tempeh
What is used in the fermentation of bread dough
Saccharomyces cerevisiae.
What is alcoholic fermentation
sugars are converted into alcohol
What are some examples of metabodies
alcohol, organic acids & other anti-microbial compounds that can inhibit growth of other microorganisms
