Module 5 - Exploiting microorganisms Flashcards
What two microbes are involved in the production of cheese?
Lactobilli reduces the pH of milk, creating a suitable environment for Rennet (chymosin) to function
Rennet protease cleaves surface glycopeptides from soluble casein molecules in milk
Cleavage of the negatively-charged side chains in kappa-casein forms para-kappa casein which allows for coagulation - the formation of hard cheese
Milk ripening
Surface ripening - the use of ripening at the surface of the food (ie mould on top of the camembert cheese)
Invasive ripening - the use of ripening within the food (ie mould within Roquefort cheese)
Ales
Top fermenters (Saccharomyces cerevisiae) cause yeast to rise to the surface
Ferment (between 20 and 25ºC) in just a few days
Ales tend to have heavier bodies, more alcohol, a darker hue and are cloudier than lagers
Lagers
Involves bottom fermenters (Saccharomyces carlsbergensis) causing yeast to settle at the bottom
Ferment anywhere from one to three months at a much colder temperature than ales (7 to 15ºC)
Lagers have a cleaner taste and appearance and have a lighter body than ales
Lagern means “to store” in German.
Flavour development: what compounds affect the flavour of alcohols?
Esters and fusel alcohols
Esters in flavour development
The most important aroma compounds in beer (ales) which also give a “fruity” character to beer, less desirable in lagers.
Fusel alcohols in flavour development
Group of long-chain alcohols that contribute to beer flavour directly or indirectly as ester precursors
Strong flavours (“alcoholic” or “solvent-like“ aroma) in beer (ales) and lager
Citric acid in beverages
Widely used in the preparation of food and sugar confectionery, soft drinks and beverages, detergent/cleaning industry, and as a stabiliser in medicines
Originally obtained from lemons, produced from a fungus since the 1940s, production worldwide is around 2.4 million tonnes p.a (expected to be close to 3 million tonnes by 2026)
Citric acid production
Citric acid produced from the tricarboxylic acid (TCA) cycle
Normal conditions - little if any citric acid is formed, however, with low Mn and Fe concentrations, citric acid is induced
Sugars purified by precipitation or ion exchange and stainless steel bioreactor used to avoid iron
Non-starch polysaccharides
High content of arabinoglucans increases viscosity in the gut, reducing absorption
A particular problem in the poultry industry
We can reduce viscosity by including ß-glucanase with the feed
Enables other cereals with high glucan content to be included with the feed e.g. barley
Phytate and phytase
Phytate (organic phosphate) cannot be degraded by monogastric stomachs
Phytase is produced by microbes to liberate phosphate from phytic acid, reducing phosphate supplementation by 40%
Food-bourne diseases
Two-thirds of all food poisoning outbreaks involve bacteria (the rest are caused by viruses, parasites, fungi and chemicals)
~ 600 million (1 in 10 people in the world) fall ill after eating contaminated food, >420 000 deaths every year (WHO)
Major disease in developing countries and most cases in children under 5 (40% of foodborne disease burden - for 125,000 deaths per year)
Food-bourne disease outbreak
Caused by many potential risk factors:
- Globalization and mass transport and production of processed foods (ie fast foods)
- Change in population (ageing, malnutrition, etc)
- New strains arising, (ie antibiotic resistance)
- Changes in food production/supply
Listeriosis: the process of infection
Fresh, raw vegetables (especially salads), unpasteurised milk, cheese, ice cream, uncooked fish (including smoked) & meats
Growth: When shredded but not cooked or treated with preservatives, plant saps (sugars etc) released, aiding Listeria growth (which grows at 4°C)
Contaminated water, manure added to soil directly contaminates vegetables, and indirectly contaminate milk
- Rare but has high mortality rates (20-30%)
Listeriosis: the process of infection
Rarely affect healthy adults unless a large dose, very young, elderly, sick and pregnant women are most susceptible
- Causes fever, fatigue, nausea, vomiting, and diarrhoea
- More serious symptoms can result in meningitis (brain infections) and septicemia (bacteria in the bloodstream)
Pregnant women: can result in miscarriage, stillbirth, or meningitis in the newborn
Mycotoxins: what are they, what do they produce, and what was its infection first called?
Toxic fungal metabolites that accumulate in cereal grains, nuts and other foodstuffs, particularly in storage
They produce aflatoxins, highly toxic and carcinogenic which affect man and livestock
First called Turkey X disease in the 1960s in the UK killed >100,000 turkeys due to contaminated groundnuts from Brazil
Aflatoxins: symptoms and testing
Symptoms:
Short-term:
* Abdominal pain and diarrhoea
* Headaches
* Convulsion (seizures)
* Emesis
Long-term:
* Cancer
* Liver/kidney failure
* Brain damage
Testing:
All cereals and nuts must be tested and contain <20ppb if given to humans and must contain <100ppb if given to livestock
Ergot poisoning: what does it do, what microbe causes it, and what are the symptoms of it?
Sporadic throughout history, occasional epidemics
Caused by claviceps purpurea
Causes severe joint pain, hallucinations, seizures, (Gangrene of the fingers, toes, nose and ears in severe cases)
Genetic manipulation: the definition
Involves the direct manipulation of genes
Genetically modified organism
GMO - an organism whose genetic material has been altered using genetic engineering techniques
Agrobacterium: what do they do and what use do they have in plants?
Live in the soil naturally and enter plants through wounds near the base of shoots
By using tumour-inducing (Ti) plasmids, they can use their T-DNA in it to biosynthesis plant growth hormones and octopine (an opine) - an amino acid that can only be utilised by the bacteria
Agrobacterium: the infection process
Wounded plants release acetosyringone and VirA and VirG detect this which begins the movement towards the wound
Once near the wound, a pillar made of VirB and held to the bacterium by VirD4 is made between itself and the plant which allows transport from the bacteria, including VirF, VirE2, and T-DNA supported and moved by VirD2
Plants: how do they detect an infection?
Flagellin (the protein compartment of flagella) is highly conserved and remains the same wherever it is found so essentially all plant cells have a receptor (leucine-rich repeat (LRR)) for flagellin to detect it
If the receptors are triggered, an MKK4/5 cascade is triggered where, eventually, VIP1 is phosphorylated and moves to the nucleus for pathogenesis-related protein (PRPs) transcription.
