Proteins Flashcards
what’s the typical length of a peptide?
100-300 AAs
which is the dominant amino acid form at diff pH
+ at low (NH3+,COOH) and - at high pH (NH2,COO-)
what is Nisin
a polypeptide produced by Streptococcus lactis that have antibiotic properties to gram positive bacteria. allowed in cheese manufacturing
name the 3 secondary protein structure
alpha helix, beta sheet and beta bend
anti-parallell or parallell beta sheet, which is most stable?
anti-parallell because the hydrogen bond H-O between the peptides are stronger
which intermolecular bonds can exist in the polypeptide chain
hydrogen bond, ionic bond, van der Waals and disulphide actually covalent
at which temp do proteins normally denature?
alpha helix proteins around 60-75 and beta sheet proteins 75-85
what is the Kjeldahl method
analyse total nitrogen to get protein content. ammonium gas
what is the Lowry method
detects soluble proteins through dilutions with basic reagent and then see absorbance
what happens to proteins when thermal treatment above 115
thiols etc are formed from aa with sulfide group. give rise to flavours
what happens with proteins when thermal treatment above 200
maillard reaction and isomerisation from L to D form. our digestive proteins cannot recognize these so loss of nutrition
in what way are the nutritional value lost when dehydroalanine is created
when heating under alkaline conditions it can form and cross link with Cys and Lys to create a non bioavaliable product (LAL)
what is furosine
when extended heating, fructose and side chains of Lys and Arg create furosine. this become a measure of extent of heat treatment and is unwanted but not toxic
what happens when severe heating above 300
possible formation of toxic products that ate mutagenic, such as “heterocyclic aromatic amines”. lipid oxidation, maillard and strecker
what can happen when heating meat with added nitrous acid
in slightly acidic conditions nitrosamines can be formed
at which pH is typically the isoelectric point
5.2-5.4
what is salting in
reduced interaction between ionic groups on the protein gives improved solubility. the more hydrophilic regions the bigger the effect
what is salting out
disrupted water structure as the salt starts compete with proteins for the water. cause clumping and reduced solubility
which are the 2 most common wheat proteins
glutenin and gliadin which together form gluten
what’s the model for the gluten structure
when glutenin and gliadin is mixed they form disulphide bonds
what happens when water is added to the gluten network
water loops are created in the beta sheet structure that facilitate for S-S bonds and hydrophobic interactions
what can be added to speed up the fermentation process in the dough
ascorbic acid is oxidized to DHAA which catalyzed the oxidation of glutathionine to it’s dimeric form.
what’s the effect of a reducing agent in gluten structure
smaller peptide chains to make a more compact dough
what’s the Chorleywood bread process CBP
method for large bakeries that reduce the dough prep/fermentation time with 60 %. addition of ascorbic acid and fat. less protein content in the weat flour. the aroma and maillard reaction is reduced
what is the effect of lipids in gluten networks
polar lipids keep the gas that is produced during fermentation still in bread due to it’s emulsifying properties
whats the 2 Most abundant proteins in milk and how many many subclasses do they have
whey and casein. 4 each. alpha beta kappa casein and lactoglobulin, albumins and immunoglobin
how is fat in milk
exists in fat globules
what micelles are created in milk
casein micelles. K-casein on surface with negative charge and hydrophilic. hydrophobic core. nano-clusters with colloidal calcium phosphate
what are the properties of casein
80% of milk protein and bind 50% of the total Ca. heat resistance 140°C 4 sec. all of them have hydrophobic and hydrophilic part. k-casein is one of the smallest and is different in the way that it doesn’t have P-ser group donut cannot bind CaP
what happens when the milk is heated
calcium and phosphate go out in the milk serum from micelle. this is unwanted.
describe the whey protein
it’s globular and 20% of proteins in milk. heat sensitive and becomes the skin on milk after boiling. b-lactoglobulin is important for vitamin transport. when heated the s-s bond breaks
what happens when heat treatment milk or ferment it
the reactive SH group in b-lactoglobulin is exposed and can interact with other b-lactoglobulins or k-casein on micelles. make it more viscous to yoghurt
what is plasmin
the main proteolytic enzyme in milk that can degrade casein. in pastorisation the plasminogen is degraded and cannot activate plasmon. higher amount in older cows
what are the negative and positive effects of plasmin on milk
(-) lower quality of cheese, degradation if b-casein give bitter taste, greater loss of whey (+) in some cheeses you want the bitter taste like cheddar and swiss
what’s the typical pasteurisation temperature and what happens over 140
around 72-95. above 140 maillard reaction takes place and you get UHT milk
how can you control that the milk have been pasteurisation
the ALP test that is inactivated in 75 ° so milk turn blue if not pasteurisation
what protein us important for coagulation of cheese
alpha(S1)-casein
what protein us important for coagulation of cheese
alpha(S1)-casein
how long time can maturation of cheese take
up to 3 years to make it hard
what happens when the milk coagulates and what prevents this reaction
it’s an irreversible aggregation where casein micelle is strongly bound together. GMP on micelles are negative so the micelles repeal each other
enzymatic coagulation?
rennet produced by cells in stomach. most chymosin in calves and more pepsin in adults. the chymosin cleave bond on k-casein which make it less hydrophilic and the micelles can aggregate. the cut of part is the GMP. a gel is formed when the micelles curdling around fat globules. syneresis
acidic coagulation of milk
HCl bends the k-casein so that the micelles can come together
How does lactic acid bacteria work in milk
They lower the pH which helps with the fermentation and affects the milk coagulation and gel firmness. Also kill some bacteria and give cheese texture and taste
Describe in basic way how to make cheese
Raw milk is patsteurated. Rennet is added to coagulate the cheese (curding) It is cutted nd stirred and whey is lost. then it is milled and, salted and pressed. then it is left for ripening
Why do they salt the cheese
for better taste, reduce water content, impact the consistence and on starter bacteria Culture.
Why is there holes in cheese
The bacteria that is responsible for the ripening/fermentation give rise to Co2 gas. Also depends on the pressing step.
What is the “Crying of the cheese”
Amino acids in solution
What is the most tender meat
Meat with lots of fat and muscle. Not so much connective tissue
What affects the juiciness of meat
The water conent, pH (solubility) and the fat content
What affects the tenderness of meat
Connective tissue and structure, Sarcomer length (i.e. the degree of contraction), degree of proteolysis (tenderize with enzymes)
Whats the major difference between fish and meat proteins
Fish do not have as much connective tissue proteins such as collagen and elastin
Which proteins do meat manly consists of
Myofibrillar proteins (contractile,regulatory and structural), sacroplasma poteins (enzymes, myoglobin) and connective tissue proteins.
What is the thin filament
Actin that forms a double-stranded coil. one of the contractile proteins
What is the thick filament
Consists of myosin that forms two twisted alpha-helices. one of the contractile proteins. The ones inside the muscle fiber with heads
What is needed for muscle contraction
Ca2+ and ATP
What happens after slaughter to the meat
A lot of Ca is released and when ATP is used up the muscle contracts and stays that way since ATP is needed to release the action/myosin. This is called rigor and occurs around 10-30 h after slaughter
What is caracteristic about the type 1 fiber - slow fiber
Its dark/red because of myoglobin, which favour oxidation => gets rancid faster. Energy source is mainly fatty acids and require cellular respiration
What is caracteristic about type ll fiber - fast fiber
Energy source mainly creatine phosphate and glycogen. Produce lactic acid when O runs out. Low in myoglobin hence the white color.
How is collagen fibers built up
Cross linking between collagen. Needs vitamin C (Sea men disease). The numebr of cross links increse with age. The breaks can be broken by prolonged heating which can cause gelatnization
Describe the Post-rigor stage
The muscle gradually becomes more soft. The muscle proteins are hydrolysed by proteases such as calpain and cathepsin.
How should you handle the meat before rigor
Hanging result in less contraction. Electrical stimulation give such a Heavy contraction that myofibrils disrupt which make it easier for proteases to come in. Cold under 10 C result in strong contraction which give though meat.
Which method is best after rigor and cutting
vacuum packing to allow for proteolytic enzymes to work on the meat, low oxygen levels keep it fresh.
What two quality problems can happen to meat
PSE (pale, soft, exudative) Mainly affect pork, rapid decrease of pH, decreased water holding
DFD (Dark, firm, dry) Caused by empty energy stores before slaughter, high pH, bind hard to water so feels dry
How is salt affecting the water holding capacity in meat
When salt is added the isoelectric Point is moved which make peptide Surfaces more negative. This allows for water to migrate in = better water holding. The pH can also change this property, add phosphate or polyphosphate.
Why is fish more sensitive meat
It contains less glycogen than mammal muscle, so the drop in pH is smaller and therefore more easily attacked by bacteria.
Describe the morphology of fish muscle
Have Myomere (the flakes) and Myoseptum (the membrane separating the flakes
Give reasons for the high amount of polyunsaturated fatty acids in fish
They eat algae which are rich in them. It is needed for their cellular membranes not to freeze when its Cold.
In what ways are the fish muscle different in fat more than the PUFA.
The lipids are more evently dispered within the muscle. The dark has more fat, the fat is stored in the fish liver.
How is sea food muscle proteins different from mammal
18-22 %, low amount connective tissue, no tenderization needed. Proteins denature easily because they are heat sensitive (used to the Cold). Not only mysoin but also paramyosin.
What kind of fish is “Sill”
Herring, this needs to be under proteolytic work to become more tender, not like other fishes.
What generates the allergy in sea food
The parvalbumins, which can cause IgE-mediated immune reactions. Very stable even in heat and digestion.
What is meant by gaping in the fish filet?
The membranes separating the flakes (myoseptum) are cnnected via treads of connective tissue. When these break it creates gaps in the filet. happens when its affected by tension such as quickly frozen and rigor mortis.
Which are the Three main pigments in sea food?
- Astaxanthin: also antioxidant (red Salmon) 2. Heme-proteins (can turn from red to Brown during oxidation) 3. Melanin: black membrane in the gut lining and also formed when tyrosine is oxidized in shrimps, called melanosis (enzymatic browning). Can be prevented by using sulphites.
What mainly affect taste in fish?
In the degradation of ATP, deamination creates the compound IMP. This gives a sweet, meaty flavor. As autolysis is proceeded the inosine forms and then hypoxanthine which give a bitter taste.
What affects the odour of fish?
Amines are responsible for this caracteristic scent. Especially DMA and TMA (di- and trimethylamine)
What can happen to poorly refrigerated fish?
Fish containing a lot of free amino acids, especially histidine, in their muscle can yield histamine. Can cause skin rash.
