Whole Course Flashcards
T/F glucose binds strongly to water
true- but not to ice aka anti-freeze effect
what happens when non-polar molecules come in a water solution?
they come together because the total disruption of hydrogen bonds is less than when they are separate. the free energy will be lower!
does heating increase the solubility of protein in water solution?
yes and no. polar side chains can interact with water OR the unfolded chains aggregate instead.
what is water activity, aw?
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 “
what is the equilibrium relative humidity above the food
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
with what instrument can you measure aw?
hydrometer
what should you think about if you want to lower the migration of water in foods?
have the same aw for all the components in the food (wasa, fruit cake). this does not mean they have the same moisture content!
what is the relationship between water content and aw called?
moisture sorption isotherm
water holding capacity - what are the three layers?
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)
how does sucrose affect aw?
it binds water so tightly so it keeps the aw low - good conservative!
at which aw can bacteria and mold exist?
typically over 0.8 but some is below. but not under 0.6-0.5
T/F most reactions rates increase with increased aw. and most rates correlates better with aw than water content.
true. ex. oxidation, enzyme activity, maillard react.
what is amorphous structure?
glass structure - low molecular mobility => improved stability!
what is glass transition?
the temperature at which the food is between amorphous state and rubbery state. it’s wanted to have a tg above -25°C
what can increase the tg in a food?
adding oligo or polysaccharides
how can you improve glass stability?
reduce aw and water content
what defines a monosaccharide
3-8 carbons, “-ose”, never branched, all buy one carbon carries a hydroxyl group
what is monosacharide isomerization
aldoses and ketoses with the same number of carbons have isomers
how is a glycoside formed
hemiacetal+alcohol. typically formed enzymatically. it is stable and
how can you determine glucose
oxidation of the carbonyl group
what is created when reducing sugars
hydrogenation of sugars will convert ketoses or aldoses to alcohol. ex. glucose to sorbitol
name 3 common oligosaccharides
maltose (mild sweetener, degradation product from starch), lactose and sucrose(disaccharide of glucose and fructose).
name some functions of polysaccharides
energy storage(starch, glycogen), structure in plants(cellulose), colonic health(dietary fibers), texture and stability in foods (starch and gums)
what is the difference between homo- and heteropolysaccharides
one vs. different monosaccharides
what is starch
a homopolymer of glucose common in maize and potato and wheat. most common are amylose (linear) and amylopectin (largest molecule in nature, highly branched)
what is the typical structure of amylopectin
it is very branched in a tree with sunfeather branches
how can amylose be gelatinisated
by heat around 55-70 °C
what is retrogradation
starch chains are re-associated. bread crust
what is a dietary fibre
a carbohydrate with 10 or more monomeric units. not absorbed by our bodies
what is cellulose
straight and stiff, insoluble
what is beta-glucan
linked glucose units. soluble beta-glucan is highly viscous and promotes good physiological effect such as low cholesterol and blood glc.
what is inulin
an energy reserve in ex.onions. mainly linear and prebiotic (food for probiotics) fat replacer
what is pectin
linear polymer, in primary cell wall and middle lamella (holds cells together). solubilized during cooking. can form gels
how can you form gels with seaweed
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+
what are some positive and negative effects of Browning reactions?
+aroma, antioxidative, colour, antimicrobial, taste and - nutrient loss, toxicity, miscolouring and burned taste
what is caramelization
a non-enzymatic reaction that dehydrate sugars. in temperatures above 100. generate color(HMF) and taste
what is the maillard reaction
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
what is the first step in the maillard reaction
the sugar is condensed with an amino compound to form a glycosylamine/Schiff base and ultimately the generation of amadori compound
what is the second step of the maillard reaction
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.
what is the strecker degradation
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
what gives color in the maillard reaction
95% of all molecules entering maillard reaction end up as melanoidin polymers that give colour. ex pyrroles and pyridines
tell some down sides of maillard reaction
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
how to control and inhibit maillard reaction?
can be inhibited by sulfite and reaction can be controlled by lowering the ph, temp. and aw
what is strecker degradation of ascorbic acid
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
what is enzymatic browning
PPO oxidation of monophenol into melanins and happens in fruit and potato. lower activity in lower pH
