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Food Chemistry > Proteins > Flashcards

Proteins Flashcards

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1
Q

what’s the typical length of a peptide?

A

100-300 AAs

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2
Q

which is the dominant amino acid form at diff pH

A

+ at low (NH3+,COOH) and - at high pH (NH2,COO-)

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3
Q

what is Nisin

A

a polypeptide produced by Streptococcus lactis that have antibiotic properties to gram positive bacteria. allowed in cheese manufacturing

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4
Q

name the 3 secondary protein structure

A

alpha helix, beta sheet and beta bend

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5
Q

anti-parallell or parallell beta sheet, which is most stable?

A

anti-parallell because the hydrogen bond H-O between the peptides are stronger

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6
Q

which intermolecular bonds can exist in the polypeptide chain

A

hydrogen bond, ionic bond, van der Waals and disulphide actually covalent

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7
Q

at which temp do proteins normally denature?

A

alpha helix proteins around 60-75 and beta sheet proteins 75-85

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8
Q

what is the Kjeldahl method

A

analyse total nitrogen to get protein content. ammonium gas

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9
Q

what is the Lowry method

A

detects soluble proteins through dilutions with basic reagent and then see absorbance

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10
Q

what happens to proteins when thermal treatment above 115

A

thiols etc are formed from aa with sulfide group. give rise to flavours

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11
Q

what happens with proteins when thermal treatment above 200

A

maillard reaction and isomerisation from L to D form. our digestive proteins cannot recognize these so loss of nutrition

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12
Q

in what way are the nutritional value lost when dehydroalanine is created

A

when heating under alkaline conditions it can form and cross link with Cys and Lys to create a non bioavaliable product (LAL)

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13
Q

what is furosine

A

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

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14
Q

what happens when severe heating above 300

A

possible formation of toxic products that ate mutagenic, such as “heterocyclic aromatic amines”. lipid oxidation, maillard and strecker

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15
Q

what can happen when heating meat with added nitrous acid

A

in slightly acidic conditions nitrosamines can be formed

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16
Q

at which pH is typically the isoelectric point

A

5.2-5.4

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17
Q

what is salting in

A

reduced interaction between ionic groups on the protein gives improved solubility. the more hydrophilic regions the bigger the effect

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18
Q

what is salting out

A

disrupted water structure as the salt starts compete with proteins for the water. cause clumping and reduced solubility

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19
Q

which are the 2 most common wheat proteins

A

glutenin and gliadin which together form gluten

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20
Q

what’s the model for the gluten structure

A

when glutenin and gliadin is mixed they form disulphide bonds

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21
Q

what happens when water is added to the gluten network

A

water loops are created in the beta sheet structure that facilitate for S-S bonds and hydrophobic interactions

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22
Q

what can be added to speed up the fermentation process in the dough

A

ascorbic acid is oxidized to DHAA which catalyzed the oxidation of glutathionine to it’s dimeric form.

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23
Q

what’s the effect of a reducing agent in gluten structure

A

smaller peptide chains to make a more compact dough

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24
Q

what’s the Chorleywood bread process CBP

A

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

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25
Q

what is the effect of lipids in gluten networks

A

polar lipids keep the gas that is produced during fermentation still in bread due to it’s emulsifying properties

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26
Q

whats the 2 Most abundant proteins in milk and how many many subclasses do they have

A

whey and casein. 4 each. alpha beta kappa casein and lactoglobulin, albumins and immunoglobin

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27
Q

how is fat in milk

A

exists in fat globules

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28
Q

what micelles are created in milk

A

casein micelles. K-casein on surface with negative charge and hydrophilic. hydrophobic core. nano-clusters with colloidal calcium phosphate

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29
Q

what are the properties of casein

A

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

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30
Q

what happens when the milk is heated

A

calcium and phosphate go out in the milk serum from micelle. this is unwanted.

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31
Q

describe the whey protein

A

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

32
Q

what happens when heat treatment milk or ferment it

A

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

33
Q

what is plasmin

A

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

34
Q

what are the negative and positive effects of plasmin on milk

A

(-) 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

35
Q

what’s the typical pasteurisation temperature and what happens over 140

A

around 72-95. above 140 maillard reaction takes place and you get UHT milk

36
Q

how can you control that the milk have been pasteurisation

A

the ALP test that is inactivated in 75 ° so milk turn blue if not pasteurisation

37
Q

what protein us important for coagulation of cheese

A

alpha(S1)-casein

38
Q

what protein us important for coagulation of cheese

A

alpha(S1)-casein

39
Q

how long time can maturation of cheese take

A

up to 3 years to make it hard

40
Q

what happens when the milk coagulates and what prevents this reaction

A

it’s an irreversible aggregation where casein micelle is strongly bound together. GMP on micelles are negative so the micelles repeal each other

41
Q

enzymatic coagulation?

A

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

42
Q

acidic coagulation of milk

A

HCl bends the k-casein so that the micelles can come together

43
Q

How does lactic acid bacteria work in milk

A

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

44
Q

Describe in basic way how to make cheese

A

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

45
Q

Why do they salt the cheese

A

for better taste, reduce water content, impact the consistence and on starter bacteria Culture.

46
Q

Why is there holes in cheese

A

The bacteria that is responsible for the ripening/fermentation give rise to Co2 gas. Also depends on the pressing step.

47
Q

What is the “Crying of the cheese”

A

Amino acids in solution

48
Q

What is the most tender meat

A

Meat with lots of fat and muscle. Not so much connective tissue

49
Q

What affects the juiciness of meat

A

The water conent, pH (solubility) and the fat content

50
Q

What affects the tenderness of meat

A

Connective tissue and structure, Sarcomer length (i.e. the degree of contraction), degree of proteolysis (tenderize with enzymes)

51
Q

Whats the major difference between fish and meat proteins

A

Fish do not have as much connective tissue proteins such as collagen and elastin

52
Q

Which proteins do meat manly consists of

A

Myofibrillar proteins (contractile,regulatory and structural), sacroplasma poteins (enzymes, myoglobin) and connective tissue proteins.

53
Q

What is the thin filament

A

Actin that forms a double-stranded coil. one of the contractile proteins

54
Q

What is the thick filament

A

Consists of myosin that forms two twisted alpha-helices. one of the contractile proteins. The ones inside the muscle fiber with heads

55
Q

What is needed for muscle contraction

A

Ca2+ and ATP

56
Q

What happens after slaughter to the meat

A

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

57
Q

What is caracteristic about the type 1 fiber - slow fiber

A

Its dark/red because of myoglobin, which favour oxidation => gets rancid faster. Energy source is mainly fatty acids and require cellular respiration

58
Q

What is caracteristic about type ll fiber - fast fiber

A

Energy source mainly creatine phosphate and glycogen. Produce lactic acid when O runs out. Low in myoglobin hence the white color.

59
Q

How is collagen fibers built up

A

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

60
Q

Describe the Post-rigor stage

A

The muscle gradually becomes more soft. The muscle proteins are hydrolysed by proteases such as calpain and cathepsin.

61
Q

How should you handle the meat before rigor

A

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.

62
Q

Which method is best after rigor and cutting

A

vacuum packing to allow for proteolytic enzymes to work on the meat, low oxygen levels keep it fresh.

63
Q

What two quality problems can happen to meat

A

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

64
Q

How is salt affecting the water holding capacity in meat

A

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.

65
Q

Why is fish more sensitive meat

A

It contains less glycogen than mammal muscle, so the drop in pH is smaller and therefore more easily attacked by bacteria.

66
Q

Describe the morphology of fish muscle

A

Have Myomere (the flakes) and Myoseptum (the membrane separating the flakes

67
Q

Give reasons for the high amount of polyunsaturated fatty acids in fish

A

They eat algae which are rich in them. It is needed for their cellular membranes not to freeze when its Cold.

68
Q

In what ways are the fish muscle different in fat more than the PUFA.

A

The lipids are more evently dispered within the muscle. The dark has more fat, the fat is stored in the fish liver.

69
Q

How is sea food muscle proteins different from mammal

A

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.

70
Q

What kind of fish is “Sill”

A

Herring, this needs to be under proteolytic work to become more tender, not like other fishes.

71
Q

What generates the allergy in sea food

A

The parvalbumins, which can cause IgE-mediated immune reactions. Very stable even in heat and digestion.

72
Q

What is meant by gaping in the fish filet?

A

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.

73
Q

Which are the Three main pigments in sea food?

A
  1. 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.
74
Q

What mainly affect taste in fish?

A

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.

75
Q

What affects the odour of fish?

A

Amines are responsible for this caracteristic scent. Especially DMA and TMA (di- and trimethylamine)

76
Q

What can happen to poorly refrigerated fish?

A

Fish containing a lot of free amino acids, especially histidine, in their muscle can yield histamine. Can cause skin rash.

Food Chemistry (4 decks)

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