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Food Chemistry > Whole Course > Flashcards

Whole Course Flashcards

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1
Q

T/F glucose binds strongly to water

A

true- but not to ice aka anti-freeze effect

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2
Q

what happens when non-polar molecules come in a water solution?

A

they come together because the total disruption of hydrogen bonds is less than when they are separate. the free energy will be lower!

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3
Q

does heating increase the solubility of protein in water solution?

A

yes and no. polar side chains can interact with water OR the unfolded chains aggregate instead.

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4
Q

what is water activity, aw?

A

how much water is available/ realtive water pressure: aw=p/p0 where p is the partial pressure of water vapour above the sample and p0 the water pressure above pure water above same temperature. it is a measure of the energy status of the water in a system. “the intensity with which water associates with other compounds “

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5
Q

what is the equilibrium relative humidity above the food

A

aw = ERH/100 where 0 is bone dry and 1 pure water. it enables us to predict which food will gain or lose water when exposed to air at a specific relative humidity

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6
Q

with what instrument can you measure aw?

A

hydrometer

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7
Q

what should you think about if you want to lower the migration of water in foods?

A

have the same aw for all the components in the food (wasa, fruit cake). this does not mean they have the same moisture content!

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8
Q

what is the relationship between water content and aw called?

A

moisture sorption isotherm

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9
Q

water holding capacity - what are the three layers?

A

vicinical water (not a solvent, hindered mobility, cannot form ice crystals at -40), multilayer water(swelling of macromolecules, not frozen at -40) and bulk water (can act as solvent and reduces viscosity, can freeze)

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10
Q

how does sucrose affect aw?

A

it binds water so tightly so it keeps the aw low - good conservative!

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11
Q

at which aw can bacteria and mold exist?

A

typically over 0.8 but some is below. but not under 0.6-0.5

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12
Q

T/F most reactions rates increase with increased aw. and most rates correlates better with aw than water content.

A

true. ex. oxidation, enzyme activity, maillard react.

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13
Q

what is amorphous structure?

A

glass structure - low molecular mobility => improved stability!

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14
Q

what is glass transition?

A

the temperature at which the food is between amorphous state and rubbery state. it’s wanted to have a tg above -25°C

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15
Q

what can increase the tg in a food?

A

adding oligo or polysaccharides

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16
Q

how can you improve glass stability?

A

reduce aw and water content

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17
Q

what defines a monosaccharide

A

3-8 carbons, “-ose”, never branched, all buy one carbon carries a hydroxyl group

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18
Q

what is monosacharide isomerization

A

aldoses and ketoses with the same number of carbons have isomers

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19
Q

how is a glycoside formed

A

hemiacetal+alcohol. typically formed enzymatically. it is stable and

20
Q

how can you determine glucose

A

oxidation of the carbonyl group

21
Q

what is created when reducing sugars

A

hydrogenation of sugars will convert ketoses or aldoses to alcohol. ex. glucose to sorbitol

22
Q

name 3 common oligosaccharides

A

maltose (mild sweetener, degradation product from starch), lactose and sucrose(disaccharide of glucose and fructose).

23
Q

name some functions of polysaccharides

A

energy storage(starch, glycogen), structure in plants(cellulose), colonic health(dietary fibers), texture and stability in foods (starch and gums)

24
Q

what is the difference between homo- and heteropolysaccharides

A

one vs. different monosaccharides

25
Q

what is starch

A

a homopolymer of glucose common in maize and potato and wheat. most common are amylose (linear) and amylopectin (largest molecule in nature, highly branched)

26
Q

what is the typical structure of amylopectin

A

it is very branched in a tree with sunfeather branches

27
Q

how can amylose be gelatinisated

A

by heat around 55-70 °C

28
Q

what is retrogradation

A

starch chains are re-associated. bread crust

29
Q

what is a dietary fibre

A

a carbohydrate with 10 or more monomeric units. not absorbed by our bodies

30
Q

what is cellulose

A

straight and stiff, insoluble

31
Q

what is beta-glucan

A

linked glucose units. soluble beta-glucan is highly viscous and promotes good physiological effect such as low cholesterol and blood glc.

32
Q

what is inulin

A

an energy reserve in ex.onions. mainly linear and prebiotic (food for probiotics) fat replacer

33
Q

what is pectin

A

linear polymer, in primary cell wall and middle lamella (holds cells together). solubilized during cooking. can form gels

34
Q

how can you form gels with seaweed

A

alginates- in brown algae form gels in presence of Ca+ . agar and carageenans in red algae are linear chains of galactose that can form gels without Ca+

35
Q

what are some positive and negative effects of Browning reactions?

A

+aroma, antioxidative, colour, antimicrobial, taste and - nutrient loss, toxicity, miscolouring and burned taste

36
Q

what is caramelization

A

a non-enzymatic reaction that dehydrate sugars. in temperatures above 100. generate color(HMF) and taste

37
Q

what is the maillard reaction

A

a complex series of reactions with a reducing sugar and an amine at high temperature. it is favoured at low water content and results in colour and aroma. the main things that affect the maillard reaction is time and temperature

38
Q

what is the first step in the maillard reaction

A

the sugar is condensed with an amino compound to form a glycosylamine/Schiff base and ultimately the generation of amadori compound

39
Q

what is the second step of the maillard reaction

A

the amadori compound reacts dependent on ph. in acidic conditions it leaves a 3-deoxyaldoketose which loses water and reacts just like in caramelization. in neutral or basic conditions a large number of cyclic compounds are formed such as maltol, isomaltol and sotolon. these give flavours. in reality both happens.

40
Q

what is the strecker degradation

A

generates the most important flavour compound. when alpha-dicarbonyl reacts with amino acids during heating. smell of bread and cake. and pyrazines to chocolate and rost meat

41
Q

what gives color in the maillard reaction

A

95% of all molecules entering maillard reaction end up as melanoidin polymers that give colour. ex pyrroles and pyridines

42
Q

tell some down sides of maillard reaction

A

mutagenic amine compounds are formed and acrylamide - formed by glucose and asparagine (asn) in strecker reac. in temp around 140-180 and is cancerogenous. typically in potato foods

43
Q

how to control and inhibit maillard reaction?

A

can be inhibited by sulfite and reaction can be controlled by lowering the ph, temp. and aw

44
Q

what is strecker degradation of ascorbic acid

A

it will brown on it’s own in aq. solution above 98 °C. increases with higher on and at ph 7 it happens at temp 25. formed in fruit juice. non-enzymatic

45
Q

what is enzymatic browning

A

PPO oxidation of monophenol into melanins and happens in fruit and potato. lower activity in lower pH

Food Chemistry (4 decks)

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