Lesson 2.1 Flashcards
chemical and physical properties of food, and carbs (55 cards)
1
Q
Foods
A
mixtures of chemicals that interact to produce sensory, chemical, and physical characteristics and their behavior under different conditions
can be simple (e.g. sugar) or complex (e.g. milk, muscle foods)
2
Q
Food colloidal disperions
A
particles of one substance distributed (dispersed phase) in another substance (continuous phase) without dissolving
continuous phase always has a higher concentration
3
Q
4 kinds of dispersions
A
- sol: solid (large molecules) in liquid
- gel: liquid in solid
- foam: gas in liquid/solid
- emulsion: liquid in liquid/solid
4
Q
Examples of sol dispersions
A
starches, proteins, some plant polysaccharides in water
5
Q
Examples of gel dispersions
A
starch paste, pectin (jams, jellies), proteins (tofu, gelatin)
6
Q
Examples of foam dispersions
foam and solid foam
A
- foam: whipped egg white, cake frosting (air beaten into egg white)
- solid foam: meringue (when whipped egg white is cooked), ice cream, bread
ice cream is also an emulsion!
7
Q
Examples of emulsions
emulsion and solid emulsion
A
- emulsion: milk, mayonaise, salad dressing
- solid emulsion: butter, margarine
- milk and mayo are O/W emulsions
- mayo is emulsified by egg yolk (doesn’t separate easily)
- margarine and butter are W/O emulsions, with oil being in its solid form of fat (under refridgerator or low ambient temp)
8
Q
Regular vs low fat mayonaise
A
low fat mayo (O/W) has less calories and fat but more sodium to compensate (and enhance flavor)
add oil (rate & order important!) to stabilize
9
Q
Emulsifier in low fat mayonaise
A
- oil is dispersed in vinegar (water) with egg yolk as the emulsifier
- egg yolk surrounds oil droplets, which immobilizes them (can’t flow like liquid would)
- immobilized oil droplets are scattered so water in vinegar can’t flow
10
Q
What’s the difference between a gel and solid emulsion?
A
- liquid entrapped in a solid 3D structure (large molecules)
- immiscible mixture (i.e. not homogenous) stabilized by an emulsifier
11
Q
Dispersion(s) in marshmallows
A
- gelatine in water
- gel (liquid in solid) entraps air bubbles
- solid foam (gas in solid)
12
Q
2 categories of food components
influence chemical properties of food systems
A
macro and micro
- carbs, fat, protein, water
- organic acids, pigments/colorants, vitamins and minerals, flavor constituents/aroma compounds
13
Q
Proximate analysis
A
quantifying the amount of carbs, fat, protein, water, and ash to determine chemical composition of food
allows us to reverse engineer what food is made of
14
Q
Carbohydrates
A
- organic compounds
- found mainly in foods from plant sources (e.g. fruits, vegetables, grain products, legumes)
- body’s main source of energy
- digestible carbohydrates = 4 Cal/gram
- contributes 50% of daily caloric intake
- recommended in the form of complex carbohydrates like starch
15
Q
2 kinds of carbohydrates
A
- simple: mono (one molecule sugar) and disaccharides (two molecule sugar)
- complex: polysaccharides
complex carbs are large molecules that consist of a string of monosaccharides
16
Q
How is the sweetness of simple carbohydrates determined?
A
by their molecular structure and interaction with sensory receptors in the tongue
complex carbohydrates cannot interact with taste buds, thus have no specific taste
17
Q
3 kinds of monosaccharides
simple carbohydrate
A
- fructose
- glucose
- galactose
- aka simple sugars, not chemically bonded to other sugar molecules
- isomers = same chemical formula (made of C,H, and O) but different arrangement of atoms = different sweetness index
18
Q
Disaccharides
simple carbohydrate
A
- union of two monosaccharide molecules
- can be split apart by enzymes or by boiling with dilute acids
19
Q
3 most important disaccharides in food
A
- sucrose (table sugar)
- lactose (milk sugar)
- maltose (malt sugar)
20
Q
Order of monosaccharides and disaccharides based on sweetness index
A
- fructose (140)
- sucrose (100) - gold standard!
- glucose (70-80)
- galactose (60)
- maltose (20)
- lactose (10-20)
21
Q
Sucrose
disaccharide
A
hydrolyzed into 1:1 ratio of glucose and fructose (invert sugar) by enzyme (invertase) or with acid
hydrolyization (broken down by adding water)
sucrose + water > glucose + fructose
22
Q
Invert sugar
when sucrose is hydrolyzed
A
- substitutes part of sucrose in candy making
- hygroscopic (affinity for moisture)
attracts water from the atmosphere
- influences state of water in food systems
- hygroscopicity prevents chewy candies, sticky lollipops from crystallizing (drying out, becoming brittle)
23
Q
Which foods is sucrose found in?
A
variety of fruits, grasses, and roots
* peaches, tangerines, pineapples (6-9%)
* mangoes (12%)
* commercial white sugar (>=99.5%)
24
Q
Honey
A
- made from nectar collected by honey bees in the form of sucrose
- hydrolyzed into 40:60 ratio of glucose and fructose by enzyme (invertase) in the bee’s saliva
25
Why is the ratio of glucose and fructose in honey 40:60 and not 1:1 like in sucrose?
## Footnote
hydrolization
another enzyme (glucose oxidase) secreted into nectar collected by bees converts some glucose into gluconic acid and hydrogen peroxide
## Footnote
act as preservatives in nectar, which is why honey has a long shelf-life
26
Lactose (milk sugar)
## Footnote
disaccharide
* consist of glucose and galactose (forming units)
* fermented by **lactid acid bacteria** (e.g. yogurt, cheese) and converted into lactic acid (acidulant and preservative)
27
What explains lactose intolerance?
lactose hydrolyzed by the enzyme lactase becomes **lactose-hydrolyzed milk**
## Footnote
broken down into glucose and galactose (higher S.I.), which explains why lactose-free (lactaid) milk is sweeter than regular milk
28
Maltose (malt sugar)
## Footnote
disaccharide
* consist of 2 molecules of glucose
* starch amylose (not sweet) hydrolyzed with enzyme (amylase) or acid
29
High fructose syrup processing
## Footnote
2 steps
1. maltose hydrolyzed with enzyme maltase into 1:1 glucose ratio
2. glucose hydrolyzed with enzyme glucose isomerase into HFS (isomerization)
## Footnote
90% fructose so used as sweetening agent in food (less calories)
30
7 functional properties of simple carbohydrates
## Footnote
mono and disaccharides
1. **sweetening power**
2. serve as reactants in non-enzymatic browning
3. crystallization
4. viscosity/body and mouthfeel
5. fermented by microorganisms
6. antimicrobial agents
7. humectancy (water/moisture retention)
## Footnote
viscosity = resistance to flow or thickness
31
Sweetening power
## Footnote
sweetness index (s.i.)
**sweetness is not correlated to calories**
e.g. fructose and lactose are both 4 cal/gram but fructose is 7x sweeter
## Footnote
i.e. only need 1/7 fructose for equivalent sweetening power to lactose so 1/7 less caloric intake
32
Crystallization
sugars can be crystallized from solution when water is evaporated
## Footnote
* e.g. table sugar (sucrose) from sugar cane juice
* sugars are soluble (as syrup) in water as temperature of water increases
33
Caramelization
## Footnote
reactant in non-enzymatic browning
reaction of sugars (reducing and non-reducing) when heated at high temperatures (200°C)
## Footnote
* produces caramel and butterscotch flavors (aroma compounds) and brown pigments (color) of caramel candies and toffies
* caramelizing sucrose produces color in cola beverages
34
Maillard browning
## Footnote
reactant to non-enzymatic browning
reducing sugars react with amino (nitrogen-lending) compounds (e.g. amino acids, proteins)
## Footnote
* reducing sugars (e.g. glucose, fructose, galactase, lactose) contain a free OH next to O in the ring structure
* sucrose is non-reducing (but can be hydrolyzed to glucose and fructose with high temp or acid)
35
2 products of Maillard browning reaction
1. low molecular weight intermediate compounds (desirable and undesirable aroma/flavors)
2. high molecular weight polymers (melanoidins or brown-black pigments)
## Footnote
e.g. toast, roasted coffee, potato chips, bread, sunless tanning lotions
36
Ripening
## Footnote
e.g. chocolates with liquid centers
* enzyme invertase is added to the crystallized firm center
* sucrose is inverted into a mixture of sucrose, glucose, and fructose
## Footnote
mixture **doesn't crystallize easily** (unlike sucrose alone) = **soft centers**
37
Polysaccharides
## Footnote
complex carbohydrates
* high molecular weight polymers or long chains of monosaccharide units (cellulose, starch = polymers of glucose)
* form part of cellular structure and firmness of tissues (e.g. cellulose, pectins, gums)
* energy reserve of animals and starch (e.g. glycogen, starch)
38
Sources of polysaccharides
* plants
* seaweed
* plant exudates
* microbial products
39
How do polysaccharides differ from simple sugars?
## Footnote
i.e. monosaccharides
usually insoluble in water and tasteless
40
Applications of polysaccharides in food
* thickening
* suspending solids
* stabilizers or gelling agents
41
Kinds of polysaccharides
* pectin
* agar
* alginates
* gum arabic/acacia
* carrageenan
* xanthan gum
* starch
* cellulose, hemicellulose
## Footnote
and guar gum extracted from guar beans
42
Pectins
## Footnote
polysaccharides
* from plant tissues
* help maintain **particles in suspension** in orange juice and unclarified apple juice
* contribute to **viscosity** of ketchup and tomato paste
* affects the overall mouthfeel of foods
* used as **gelling agents** for jams and jellies
43
Alginates
## Footnote
polysaccharide
* extracted from seaweed
* **suspending and thickening agents** once purified
## Footnote
e.g. salad dressings, puddings, pie fillings, ice cream, sherbet, icings
44
Carrageenan (Irish moss extract)
* extracted from seaweed
* **suspending agent and stabilizer** in dairy products
## Footnote
e.g. cocoa particles in chocolate milk; stabilizer in in ice cream
45
Xanthan gum
## Footnote
polysaccharide
* extracted from bacteria (Xanthomonas campestris)
* used for the control of **viscosity** and as a **suspending agent** (e.g. salad dressings)
* provide "loaf structure" in wheat-free bread
46
Gum arabic/acacia
## Footnote
polysaccharide
* plant exudate from sap (in bark) of acacia trees
* thickening agent in candies
47
Starch
## Footnote
polysaccharide
* polymer of glucose (> 500 glucose molecules)
* linked by **a-1, 4**
* digestible once gelatinized (can be broken down by enzyme)
* present in plant materials as starch granules
## Footnote
**starch granules** consist of densely packed starch molecules
48
2 parts of starch molecules
1. linear amylose
2. branched amylopectin
## Footnote
normal corn starch has **1:3** amylose:amylopectin
49
Amylose molecules
## Footnote
in starch molecules
linear chain of glucose molecules that
* orient parallel to each other
* move close enough together to bond (Hydrogen bonds)
* contribute to **gel formation**
## Footnote
more amylose = more jelly-like structure
50
Amylopectin molecules
## Footnote
in starch molecules
* gives **viscosity** to the cooked paste
* sidechains and bulky shape keep molecules from bonding together
## Footnote
more amylopectin = more viscous
51
Starch gelatinization
## Footnote
e.g. cooking pasta
when starch is **heated in water**, starch granules swell and eventually burst
* bonds joining amylose and amylopectin are weakened
* allowing water molecules to move in and form H-bonds
## Footnote
* i.e. starch granules absorb water and release amylose and amylopectin
* heat accelerates gelatinization
52
Starch retrogradation
## Footnote
e.g. refridgerating cooked pasta
* linear amylose chains orient back into crystalline zones (intermolecular H-bonding)
* form aggregates, resulting in syneresis (loss) of water
## Footnote
accelerated by refridgeration temperatures and partially reversed by heating
53
Outcomes of starch retrogradation
* loss of water-holding capacity
* toughening of food
* gritty texture
## Footnote
e.g. stale bread, gritty starch puddings
54
Cellulose
## Footnote
polysaccharide
* most abundant of all carbohydrate polymers
* plant cell wall material
* linear chain of glucose units linked by **b-1, 4**
* indigestible (part of dietary fiber component of food)
## Footnote
cannot be broken down by an enzyme
55
3 functional properties of polysaccharides
1. stabilizers/thickeners/viscosity
2. gelling agents/gelatinization (L/S)
3. fat replacers
## Footnote
* keep compounds, mixtures, or solutions from changing state
* act as **thickening agents** by increasing the viscosity of the continuous phase
