11. Microbes and Food Flashcards
1
Q
How are microbes used in the dairy industry? 2
A
- Microbes are involved in many dairy products
2. Lactobacili cause separation and acidification of milk
2
Q
How are microbes used in the creation of curds? 6
A
- Rennet (chymosin) is a protease that removes surface glycopeptides from soluble casein micelles in milk
- Micelles are very small, which hydrophilic charged amino acid tails,which repel each other
- Enzyme removes surface charge
- Treated casein (paracasein) removes charged peptide side chain from k(kapa)-casein
- Without charge, ca2+ forms bridge between particles and particles coagulate
- This gives us curds
3
Q
How is rennet produced? 6.
A
- Lactobacili is added to pasteurised milk to acidify it, as rennet works best under acidic conditions
- Unpasteurised milk contains bacteria naturally
- Rennet was originally extracted from the stomachs of calves, found there as it makes mother’s milk easier to digest
- About 90% of all hard cheese is made using recombinant calf chymosin from Aspergillus niger.
- The protein has been cloned and expressed in this filamentous fungus
- No animals harmed but animal protein expressed, suitable for vegetarians?
4
Q
How is cheese produced? 6
A
- Precuring at warm temperature, milk acidified by lactobacili
- Colouring added if desired, then coagulation by rennet
- Whey separated and flavour added eg. salt if desired
- Compression of the curd
- Aging/maturation which is microbe based, they secrete enzymes and flavour compounds
- Cheese is finished
5
Q
Describe the surface ripening process that occurs in cheeses such as camembert. 4
A
- Surface of rounds inoculated with Penicllium camemberti mold
- Mycelium spreads across outside
- Secretes proteases, lipases etc. which breakdown inside, partially liquefying and making it soft
- Fungi also secrete flavour comppund
6
Q
Describe the invasive ripening process that happens in cheeses such as roquefort. 4
A
- Ripened by growth anda ctivity of mold, in this case penicillium roqueforti
- Cheese is inoculated right into round with fungal spores
- Mycelium produced which produces lipases, proteases and flavour compounds
- Grows throughout mass rather than surface only
7
Q
How are microbes involved in brewing ales? 5
A
- Top fermenters (s. cerevisiae), yeast rises to surface
- Ferment in a few days - whole proess is eight weeks
- Ales ferment between 20 and 25 degrees
- Ales tend to have heavier bodies, more alcohol, a darker hue and are cloudier than lagers
- New strains don’t necessarily give more alcohol
8
Q
how are microbes involved in brewing lagers? 6
A
- Bottom fermenters (s. carlsbergensis), yeast settles at bottom
- Ferment between one and three months
- Ferment at colder temp than ales, 17-15 degrees
- Lager means ‘to store’ in German
- Lagers have a cleaner taste and appearence and have a lighter body than ales
- The bacteria accumulate alcohol under microeriphilic conditions
9
Q
What is the role of microbes in making bread? 3
A
- Still fermentation to stop alcohol getting in
- In bread you want co2 rather than alcohol
- Different strains
10
Q
Hoew does flavour development work in lagers and ales? 6
A
- Esters are volatile acids, the most important aroma compounds in beer (ales). They are less desirable in lager
- Give fruity character to ale.
- Fusels alcohols are a group of long chain alcohols
- contribute directly to beer flavours, indirectly as ester precursors
- Strong flavours (alcoholic or solvent-like aroma) in ales and lager
- The smell is not alcohol, its fusels alcohol
11
Q
How are microbes involved in citric acid? 6
A
- Widely used in the preparation of food and sugar confectionery
- Of all citric acid used: 21% in food and confectionery, 45% in soft drinks, 19% in cleaning industry, 8% as stabiliser in medicines
- it lowers the pH of the substance you put it into
- Originally taken from lemons and limes
- 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
- Production worldwide is about 450 000tones p.a
12
Q
How is citric acid produced? 6
A
- produced form tca cycle
- under normal conditions, little, if any, citirc acid is formed
- induced under low/no manganese and iron conditions
- sugars purified precipitation or ion exchange to remove and metals present
- stainless steel bioreactor used to avoid iron
- with no manganese/iron, in certain strains, krebs stalls after citric acid cycle and next step is blocked as cofactors are absent
13
Q
What are non-starch polysaccharides? 5
A
- Animals, particularly poultry, can’t digest these, so enzymes must be added to feed to do it for them
- High content of arabinoglucans increases viscosity in gut, reducing nutrient absorption
- Adding beta glucanase from microbes reduces viscosity
- enables other cereals with high glucan content to be included in feed eg, barley
- With the enzyme, poultry weigh about 20% more
14
Q
What are phytate and phytase? 6
A
- In plant based animal feeds, inorganic phosphate is phytate
- can’t be degraded by monogastric animals eg. pigs
- Traditionally, feeds were supplemented with phosphate but this leads to ollution of ground water, rivers, lakes and algal blooming
- addition of microbial phytase liberates phosphate from phytic acid
- this reduces need for phosphate supplementation by 40%
- each molecule of phytic acid contains 6 molecules of phosphate
15
Q
how is microbial fermentation involved in chocolate? 3
A
- Chocolate requires microbial fermentation
- Coagulated polysaccharide is fermented, leaving bean
- also confer flavour compounds to bean
