11. Microbes and Food

Question 1

How are microbes used in the dairy industry? 2

Answer 1

1. Microbes are involved in many dairy products

2. Lactobacili cause separation and acidification of milk

Question 2

How are microbes used in the creation of curds? 6

Answer 2

1. Rennet (chymosin) is a protease that removes surface glycopeptides from soluble casein micelles in milk
2. Micelles are very small, which hydrophilic charged amino acid tails,which repel each other
3. Enzyme removes surface charge
4. Treated casein (paracasein) removes charged peptide side chain from k(kapa)-casein
5. Without charge, ca2+ forms bridge between particles and particles coagulate
6. This gives us curds

Question 3

How is rennet produced? 6.

Answer 3

1. Lactobacili is added to pasteurised milk to acidify it, as rennet works best under acidic conditions
2. Unpasteurised milk contains bacteria naturally
3. Rennet was originally extracted from the stomachs of calves, found there as it makes mother’s milk easier to digest
4. About 90% of all hard cheese is made using recombinant calf chymosin from Aspergillus niger.
5. The protein has been cloned and expressed in this filamentous fungus
6. No animals harmed but animal protein expressed, suitable for vegetarians?

Question 4

How is cheese produced? 6

Answer 4

1. Precuring at warm temperature, milk acidified by lactobacili
2. Colouring added if desired, then coagulation by rennet
3. Whey separated and flavour added eg. salt if desired
4. Compression of the curd
5. Aging/maturation which is microbe based, they secrete enzymes and flavour compounds
6. Cheese is finished

Question 5

Describe the surface ripening process that occurs in cheeses such as camembert. 4

Answer 5

1. Surface of rounds inoculated with Penicllium camemberti mold
2. Mycelium spreads across outside
3. Secretes proteases, lipases etc. which breakdown inside, partially liquefying and making it soft
4. Fungi also secrete flavour comppund

Question 6

Describe the invasive ripening process that happens in cheeses such as roquefort. 4

Answer 6

1. Ripened by growth anda ctivity of mold, in this case penicillium roqueforti
2. Cheese is inoculated right into round with fungal spores
3. Mycelium produced which produces lipases, proteases and flavour compounds
4. Grows throughout mass rather than surface only

Question 7

How are microbes involved in brewing ales? 5

Answer 7

1. Top fermenters (s. cerevisiae), yeast rises to surface
2. Ferment in a few days - whole proess is eight weeks
3. Ales ferment between 20 and 25 degrees
4. Ales tend to have heavier bodies, more alcohol, a darker hue and are cloudier than lagers
5. New strains don’t necessarily give more alcohol

Question 8

how are microbes involved in brewing lagers? 6

Answer 8

1. Bottom fermenters (s. carlsbergensis), yeast settles at bottom
2. Ferment between one and three months
3. Ferment at colder temp than ales, 17-15 degrees
4. Lager means ‘to store’ in German
5. Lagers have a cleaner taste and appearence and have a lighter body than ales
6. The bacteria accumulate alcohol under microeriphilic conditions

Question 9

What is the role of microbes in making bread? 3

Answer 9

1. Still fermentation to stop alcohol getting in
2. In bread you want co2 rather than alcohol
3. Different strains

Question 10

Hoew does flavour development work in lagers and ales? 6

Answer 10

1. Esters are volatile acids, the most important aroma compounds in beer (ales). They are less desirable in lager
2. Give fruity character to ale.
3. Fusels alcohols are a group of long chain alcohols
4. contribute directly to beer flavours, indirectly as ester precursors
5. Strong flavours (alcoholic or solvent-like aroma) in ales and lager
6. The smell is not alcohol, its fusels alcohol

Question 11

How are microbes involved in citric acid? 6

Answer 11

1. Widely used in the preparation of food and sugar confectionery
2. Of all citric acid used: 21% in food and confectionery, 45% in soft drinks, 19% in cleaning industry, 8% as stabiliser in medicines
3. it lowers the pH of the substance you put it into
4. Originally taken from lemons and limes
5. Produced by Aspergillus niger since 1940s, a stain of filamentous fungi which secretes large amounts of citric acid under the right conditions. almost exclusively produced this way now
6. Production worldwide is about 450 000tones p.a

Question 12

How is citric acid produced? 6

Answer 12

1. produced form tca cycle
2. under normal conditions, little, if any, citirc acid is formed
3. induced under low/no manganese and iron conditions
4. sugars purified precipitation or ion exchange to remove and metals present
5. stainless steel bioreactor used to avoid iron
6. with no manganese/iron, in certain strains, krebs stalls after citric acid cycle and next step is blocked as cofactors are absent

Question 13

What are non-starch polysaccharides? 5

Answer 13

1. Animals, particularly poultry, can’t digest these, so enzymes must be added to feed to do it for them
2. High content of arabinoglucans increases viscosity in gut, reducing nutrient absorption
3. Adding beta glucanase from microbes reduces viscosity
4. enables other cereals with high glucan content to be included in feed eg, barley
5. With the enzyme, poultry weigh about 20% more

Question 14

What are phytate and phytase? 6

Answer 14

1. In plant based animal feeds, inorganic phosphate is phytate
2. can’t be degraded by monogastric animals eg. pigs
3. Traditionally, feeds were supplemented with phosphate but this leads to ollution of ground water, rivers, lakes and algal blooming
4. addition of microbial phytase liberates phosphate from phytic acid
5. this reduces need for phosphate supplementation by 40%
6. each molecule of phytic acid contains 6 molecules of phosphate

Question 15

how is microbial fermentation involved in chocolate? 3

Answer 15

1. Chocolate requires microbial fermentation
2. Coagulated polysaccharide is fermented, leaving bean
3. also confer flavour compounds to bean

Question 16

How are microbes involved in food borne disease? 6

Answer 16

1. 2/3 of all food poisoning outbreaks involve bacteria
2. the rest are caused by viruses, parasites, fungi and chemicals
3. major disease in developing countries due to heat and lack of refrigeration and sanitation
4. 100million cases of acute diarrhea occur in children under five in asia and africa
5. 5 million are fatal due to contaminated food and water
6. bacteria use our food for energy

Question 17

Talk about food based illnesses and death in the UK. 5

Answer 17

1. 35000 hospitalisations and 300 deaths
2. seems relatively rare but only a fraction are reported
3. pyramid of reporting:
   pathogen exposure
   develop disease
   seek doctor
   specificaiton
   lab
   isolation
   report
4. salmonella, listeria, campylobacter and e. coli 0157 casue 75% of deaths
5. 46% viral, 21% bacterial, 2% parasite and 31% unknown

Question 18

What are the causes of food borne disease outbreaks? 6

Answer 18

1. Mass production and processing of foods, fast foods
2. Any contamination is easily spread due to huge scale eg. salmonella in manure fertiliser
3. Globalisation and mass transport of food, shipping can take weeks and requires refrigeration
4. Change in human population causing immunity decline eg. aging, malnutrition, AIDS
5. New, sometimes antibiotic resistant strains arising
6. Changes in food production/supply

Question 19

What are the high risk groups for food borne disease? 4

Answer 19

1. Pregnant women and young children - listeria
2. Infants due to immature immune system - e. coli and listeria
3. Elderly due to reduced immune system - salmonella, camplylobacter, listeria
4. HIV/AIDS, TB patients and other immunosupressed - all pathogens

Question 20

What are the most commonly contaminated foods? 6

Answer 20

1. Poultry - bacterial levels are very high so must be cooked all the way through
2. leafy greens, salad vegetables, due to fertiliser
3. pre-prepared is especially bad as chopping anf mixing spreads contamination
4. chopping releases sugars from plants, which bacteria can feed on
5. beef, dairy, fruit and nuts
6. vine, pork, finfish, eggs

Question 21

what is listeriosis? (listeria monocytogenes) 6

Answer 21

1. Found in fresh, raw veg, esp salad, unpasteurised milk, cheese and ice cream, raw meat
2. if uncooked and not treated with preservative, shredding releases plant saps for bacterial growth
3. Grows at 4 degrees so survives in the friddge
4. Contaminated water, manure added to soil directly contaminating veg and indirect contamination of milk are the main sources
5. 20-25 deaths per year in uk
6. more in other countries

Question 22

What are the symptoms of listeriosis? 6

Answer 22

1. rarely occurs in healthy adults, unless a high dose
2. Very young, elderly, sick and pregnant suffer
3. casues fever, fatigue, nausea, vomiting and diarrheoa
4. More serious symptoms include meningitis (brain infection) and septicemia (bacteria in the bloodstream)
5. In pregnant women, can cause miscarriage, stillbirth ad meningitis in newborn
6. Pregnant women and cattle must not eat unpasteurised food

Question 23

what are ‘the moulds’? 6

Answer 23

1. don;t generally harm you, but some produce mycotoxins
2. these are toxic fungal metabolics which accumulate in cereal grains, nuts and other foods in storage
3. one example is aflatoxins, highly toxic and carcinogenic. produced by aspergillus flavus and a. parasiticus
4. affects mean and livestock
5. Turkey X disease in 1960s killed 100000+ UK turkeys (50% of GB poultry)
6. Came from contaminated groundnuts from brazil

Question 24

What are the symptoms of being affected by mycotoxins? 6

Answer 24

1. short term include abdominal pain and diarrhoa.
2. Also headache and vomiting
3. convulsions
4. long term effects include cancer
5. liver and kidney failure
6. brain damage

Question 25

How do you test for the presence of mycotoxins? 3

Answer 25

1. every bit of cereal must be tested 2. if more than 20ppb in human food, or 100ppb in cattle/poultry food, its all burned 3. the mycotoxins were prevelent in the middle ages

Question 26

What is ergot poisoning? 6

Answer 26

1. Sporadic throughout history, with occasional epedemics 2. casued by claviceps purpurea, which has melanised plant structures you shouldn't eat 3. Causes st anthoy's fire (common name for poisoning) 4. symptoms include joint pain, hallucinations and seizures 5. Can close capillaries in extremeties and in severe cases casue gangrene in fingers, toes, nose and ears 6. May have been cause of hallucinations of witchcraft, causing salem witch trials of 1692.