Food Chem Final Exam

dextrans

- composed of glucose connected by 1,6-𝛂-glucosidic-linkages - complex CHOs found in bacteria and yeasts

amylose

- linear - found in molecular weights in the thousands up to 150,000

examples of emulsions

- oil in water (mayo, salad dressing)

dielectric constant

- very high in water= excellent solvent - refers to the ability of a solvent to operate ions

specific heat constants of relevant substances

- water= 1.0 - milk= 0.9 - vegetable oil= 0.47 - air= 0.24 water is more capable of transferring than are or oil

gelatinization

A. heating starch in water breaks hydrogen bonds in the starch granules 1) water into the granule, causing swelling 2) viscosity increases as water becomes bound; amount of free water outside is reduced 3) get more swelling 4) amylose migrates out of the granule because it is shorter 5) amylopectin continues to swell (can't move out because it is so big) B. most starches can be heated to 100 C with little or no rupture of starch granules C. keep heating--> rupture of granules= pasting

functional properties of starch

A. slight solubility B. Hydrolysis to smaller polymers; starch heated without water-> dextrinization, a chemical change; like browning C. swelling of starch - with cold water, swelling is reversible - with hot water, swelling is irreversible D. Thickening action in foods - required heating with water-> gelatinization, a physical change these properties relate to the behavior of starches in sols and gels

simple carbohydrates

monosaccharides: glucose, fructose, and galactose disaccharides: monosaccharide+glucose

crystalline structure

organized solids that form crystals - fudge - small crystals dissolve more easily the large ones, so small crystals shift more quickly, tending to coalesce into large crystals, the eventual result is a grainy texture

cellulose

- a complex carbohydrate composed of glucose units joined together by 1,4-β-glucosidic-linkages

factors affecting freezing point

- a solute or ionizing substance (sugar and salt) added to water will lower the freezing point - a solute reduces vapor pressure which reduces the freezing point - IOW the temperature must get lower for freezing to occur

carbohydrates: facts about linkages

- alpha, beta designations denote the orientation of the chiral carbon hydroxyl group - down= 𝛂 - up= β - 1, 4-𝛂-glycosidic linkages are planar - 1, 6-β-glycosidic linkages cause branching - 𝛂-glycosidic linkages are digestible - β-glycosidic linkage are not (usually)

1. factors affecting the boiling point

- boiling occurs when vapor pressure exceeds atmospheric pressure - altitude decreases atmospheric pressure, thus decreases boiling point - boiling point decreases 1°C for every 960 ft above sea level/decreases 1°F for every 500ft above sea level - at higher altitude, atm p decreases; less heat is needed to overcome atm p; water boils at a lower temp

amorphous candies

- candies that aggregate in a random manner; amorphous glass candies are hard and brittle -- occurs with higher sugar concentrations (>90%) and/or greater interfering substances -- if soft, chewy product is desired, boil to 120°C -- if firmer product is desired, boil to 125°C (higher temp will release more water) - greater viscosity prevents crystal aggregation, which is why these are amorphous - examples: sucks, caramels, toffee, brittles, marshmallows, gum drops, butterscotch, taffy

crystalline candies

- candies with organized crystalline structure and some liquid (mother liquid) 1) dissolve sugar (>100°C) have to use a thermometer to get right temp. 2) concentrate sugar, racing boiling point 3) carefully cool to supersaturation 4) at ~45°C, stir, agitate -- increases # of crystals -- decease size of crystals

dextrins

- composed of glucose ad linked by 1,4-𝛂-glycosidic-linkages - in dextrin, the n is <20; in amylose, the n is in the hundredths

sweeteners: syrups+

- corn syrup= mixture of CHOs resulting from hydrolysis - HFCS= more fructose - molasses= byproduct of sugar production - honey= best source of fructose naturally

amylopectin

- dendritic (branched) - found in molecular weights in the millions

monosaccharides

- differ in # of carbons in ring structure; orientation of hydroxyl groups on ring - triodes, pentoses, hexoses... - are classifies as D or L depending on their orientation at C5 - are all reducing sugars: contain a free or potentially free carbonyl group when the ring is broken (aldehyde or ketone)

states of water: solid/liquid

- for ice to melt into liquid water requires the absorption of 79.7 kcal - for water to freeze into ice it requires the loss of 80 kcal (heat of fusion) -- ice expands and makes it less dense then water = ice floats -- implication= when water freezes.. when ice melts

solubility of simple sugars

- fructose > sucrose > glucose > lactose - with its greater solubility, fructose tends to make candies softer - with its low solubility, lactose tends to form crystals in a low temperature situation (gritty texture)

gelation

- gelatinized starch mixtures can be sol or gel dispersions -- hot pastes have flow properties, so they are sols: starch is the dispersed phase and water is the continuous phase -- many pasted become gels as they cool - why? amylose molecules outside granules can move around, then form hydrogen bonds to form the continuous phase - so gelation requires heat to release enough amylose, but not so much to break granules - requiere amylose to form hydrogen bonds - agitating will break bonds-> so add butter and flavorings immediately after removing from heat and allow to cool undisturbed - egg proteins must be coagulated to de-activate amylase (breaks down amylose)

retrogradation

- gradual re-arrangement of amylose molecules during storage -- aggregate in an orderly fashion -- is this desirable? yes can be in the textural and nutritional factors of food

sweeteners: sugar

- granulated sugar, table sugar: from sugar cane or beats - confectioner's sugar: pulverized sucrose + 1-3% constacrcdh to prevent caking - brown sugar: higher pH, higher moisture, higher impurities, the darker, the more flavor, clumpy unless you press, brownulated= granulated brown sugar (flows) - jaggery and other formulations

effects of ingredients on gelatinization: acid+heat

- hydrolyzes some starch; the smaller molecules move more freely - viscosity decreases - quicker heating yields a thicker product; why? less time for the acid to hydrolyze the starch, resulting in smaller chains of starch - adding acid after gelatinization avoids the thinning

effects of ingredients on gelatinization: sugar

- impedes swelling, delays rupture - competes for water - increases gelatinization temperature - increases translucence - reduces gel strength

hygroscopicity

- increased with temperature - good to preserve freshness; bad texture effects in highly humid environments

chemical structure

- large complex CHOs that consist of carrying amounts of amylose and amylopectin - most starches contain more amylopectin than amylose - roots and tuber starches are about 80% amylopectin - cereal starches are about 75% amylopectin (corn, wheat, rice; oats, barley) - way starches are developed to be 100% amylopectin - molecules within each layer are held together by hydrogen bonding -- innermost layer is the hilum, around which other layers form - layer are held to each other by hydrogen bonding as well - starch granules when seen using X-ray diffraction and polarized light exhibit birefringence= refraction of light in two slightly different directions

emulsions

- liquid dispersed within another liquid with which it is immiscible (doesn't mix) - requires energy for the continuous phase to stretch to encompass the dispersed phase - create emulsion by shaking; unstable - stability is increased by presence of an emulsifying agent; contains both polar and non-polar groups, so can interact with both phases - can be permanent, semi-permanent, temporary (even permanent emulsions can be broken)

amylopectin

- molecules that are extremely large and may have a molecular weight of a million or more - the branching of amylopectin results in a molecule with little solubility; like amylose, it also does not contribute sweetness to food flavors

facts about chain length

- mono- and di-saccahrides are sweet - longer chain polysaccharides are not - types of saccharides contribute texture and thickening ability - straighter chains are more soluble? - branched chains are less soluble? -- neither, amylose or amylopectin is THAT soluble -- the more the branching, the lower the boiling point

preparation/troubleshooting with amorphous candies

- most errors occur in cooking 1. problem: high viscosity--> are pockets, so hard to get accurate thermometer reading - solution: don't trap air 2. problem: heating too slowly--> more timer for breakdown of sugar molecules--> too much browning (too much inversion) - solution: don't heat too slowly 3. problem: uneven heating - solution:

troubleshooting with sugar

- most errors occur in cooling 1. problem: improper temp when heating leads to large crystals - solution: add water and redo 2. problem: humid, rainy day makes sugar more hygroscopic, increase water --> softer product - solution: boil to 1°F more than recipe calls for 3. problem: boiling too slowly--> too much inversion 4. problem: too little beating

sweeteners: alternatives

- polyols: sorbitol is hygroscopic but mannitol is not - why does xylitol give a cooling sensation? -- xylitol is an endothermic reaction, absorbing heat and resulting in a cool feeling - artificial sweeteners: splenda, sweet n low, stevia, equal

frozen desserts

- represent solutions, foams, emulsions, and suspensions - must endure thawing and refreezing because of customer transport - crystals that form without agitation tend to grown larger -- fat helps limit crystal growth (creamy mouthfeel) -- stabilizers help coat ice crystals to limit the growth

evaluation of amorphous candies

- should be of good color: light, golden brown, uniform, pulling taffy incorporates air (foam)--> lighter in color - flavor: not scorched - texture: varies with each type of candy

effects of ingredients on gelatinization:: high sugar+acid

- slows gelatinization - why? acid typically speeds up gelatinization but the sugar competes with the starch for the water and impedes on the process and slows it down

sugar altering freezing and boiling point

- sugars are non ionizing, non-volatile (tendency to go through gas) molecular solutes

what do simple sugars provide?

- sweetness - solubility - hygroscopicity: ability to attract water - alteration of freezing and boiling points - triggering color changes (carmelization and Maillard browning) - hydrolization from action by heat, enzymes, or acids - triggering crystal formation - ripening (flavor and texture change from degradation products during storage) - texture changes (increased viscosity, increased volume and increased mouthfeel - stabilization of foams - tenderizing of starch-thickened products

coarse suspensions

- tend to separate from the influence of gravity -- particles settle to the bottom soon after agitation -- can reform over and over - no effect on freezing or boiling points - usually solid in liquid (ex. flour and water; oatmeal and water)

glass transitions

- the glassy state is achieved with cold temperature and low water activity; an increase in temp or water activity decreases stiffness/viscosity, resulting in a more elastic, rubbery texture - occurs over a range of temperature despite the existence of a s specific temp for the transition for each food solid -- resorption of water on surface alters the texture of the solids, proving unwanted bonding of cells--> problems in storage

monosaccharides: glucose, fructose, galactose

- these are all C6H12O6 - glucose is the most common monosaccharides - fructose is found in fruits and honey - galactose is found in lactose - two monosaccharides condense to form a disaccharide

examples of Maillard reaction

- toast - caramel poor from milk and sugar - color of beer, chocolate, roast meat, coffee, and maple syrup - color of dried and condensed milk

colloidal dispersions

- two phase system sontaiibng medium-sized particles - the continuous phase surrounds the dispersed (discontinuous) phase, and can react with each other - the dispersed phase is isolated in the continuous phase - the phases can be any state of mater and can change with temperature - no effect on freezing and boiling points

implication of boiling point

- water boils easier, but is less effective - foods must cook longer at higher altitudes - proportions of ingredients might need to be modified= need more water to keep it all from boiling away

bound water

- water bound to other substances no longer exhibits typical water properties (does not flow, does not act as a solvent, and does not freeze) - implication: bound water changes texture of foods (ex. water no longer flows in the gelatinization of starch or denaturation of protein)

factors affecting ice crystallization

- water: forms crystals - sucrose: sweetens, lowers freezing point product melts easier - fat: inhibits crystal growth, improves texture - nonfat-milk solids: limit crystal size - emulsifiers: promotes dispersion of fat in mix, stabilizes foam - stabilizers: viscosity of stabilizers prevent crystal growth; gelatin, vegetable gums: agar, carrageenan, guar, xanthin (think of dairy free ice creams) - agitation: reduces crystal size and incorporates air to increase volume (called overrun) - rapid drop in temperature: helps form small rather than large ice crystals

how do you know which the continuous phase and which is the dispersed phase?

-- viscosity (stickiness) is increased either way -- depends on the nature of the emulsifying agent; if agent is more hydrophilic, reduces surface tension of water more, enabling the water to coalesce more than oil= oil-in-water emulsion - food industry will utilize the hydrophilic/lipophilic balance scale to choose emulsifiers

triggering color changes: non-enzymatic browning

1) carmelization occurs when sugars are heated to melting (170°C) but before charring or burning -- heating breaks ring structures ad created acids and aldehydes with greater reactivity -- sucrose must be inverted to glucose and fructose = inverted sugar -- oligosaccharides formed - halt the caramelization process by adding boiling water instead of cold water because the energy difference will be too big and the mixture will splatter

how to calculate the change in freezing point

1. one molecule son a solute depresses freezing point of 1 L of water by 1.86°C 2. the gram molecular weight of sugar is 342 g 3. sugar weight in g / 342 g x 1.86°C= new freezing point in °C per liter

process starches undergo

A. Gelatinization B. Pasting C. Gelation D. retrogradation

paste formation

A. as heat continues to rise-> slurry becomes translucent->loss of birefringence-> but starch (amylopectin) continues to swell B. as heat continues to rise, granules hit their maximum volume and begin to implode-> viscosity then decreases C. evaluation: you want a thickened starch paste to be smooth and translucent-> but unmodified starched tend to become stringy/mucilaginous

maltodextrin

a breakdown product of starch hydrolysis and is used as a thickener by the food industry - also contributes to acceptable mouthfeel - n is usually 3-17 glucose units

isotherm

a plot of the uptake (resorption) and loss (desperation) of water (at constant temp) - record of water activity for a given food - hysteresis

3. factors affecting the boiling point

addition of solutes and ionizing substance lowers vapor pressure - implication: higher temp is needed to overcome Atm p and get a food to boil (+0.52°C per mole of solute) - sugar: many implications of foods - salt: ionizes so it does increase BP, but a food gets too salty too quickly, so the has limited use - colloids: have no appreciable effect of PB

induction

alternating electrical current produces a magnetic field that stimulates the iron in the pan - pans must contain iron! - works b/c iron is not a good conductor; therefore the current causes the metal to heat - food then heats by conduction

microwaves

assigned frequencies of 915-2459 megahertz - microwaves penetrate the food, causing the water dipoles to vibrate, resulting in friction and therefore heat within the food - no energy transfer at the surface of the food= no browning - must have food in the microwave oven so the waves can be absorbed by something - metal bounces the waves back

surface tension

attraction between molecules at the surface of a liquid

2. factors affecting the boiling point

changes in atmospheric pressure resulting from weather - barometric pressure decreases on cloudy days - implications: water boils at a lower temp on a cloudy day and you have to monitor temperature for food products that require specific temperatures (ex. candies and fudges)

reducing sugar

contain a free or potentially free carbonyl group when the ring is broken - maltose is a reducing sugar but sucrose is NOT

supersaturation

contains more solute than it "should" at a given temperature - supersaturation is possible when more solute is dissolved because of higher temp, then the solution is carefully cooled so the solute stays in solution

starch paste

cooled with no agitation= gel (requires amylose)-> aging/cutting= syneresis cooled with agitation/using waxy starches/presence of amylase= no gel

5. factors affecting the boiling point

cooling in a partial vacuum - simulates altitude - used by the food industry to broil certain foods since the lower temperature protect and color of foods

water activity: implications

crucial for food safety - water activity affects whether microorganisms thrive or not - dried foods at moisture levels of 125 or less are not susceptible to microbiological spoilage - and affects flow properties of liquids

energy to heat transfer: radiant

direct transfer of energy from source to food - broiling: from source above to surface of food - grilling: from source below to surface of food - microwaves: short electromagnetic waves penetrate food - infrared lamps: use longer waves to keep food warm

amorphous solids

disorganized structure - hard candies - can undergo glass transitions

texture is affected by: ripening

effects of storage - mother liquid: liquid in equilibrium with a crystalline candy - first few days of ripening improves texture while equilibrium is established - longer storage leads to aggregation into larger crystals--> glitter texture -- so food industry adds invertase enzyme to interfere with aggregation - final candy should be smooth, creamy, hold shape, not taste scorched

energy to heat transfer: mechanical

ex. creaming, beating, mixing - creaming: agitating fat and sugar to get a light and fluffy mixture - beating: rapid agitation of a wide range of substances (used for developing gluten in dough) - good for denaturing proteins

hysteresis

food absorbing water will have more water activity then food losing water

dispersions

foods are mixtures of greater than or equal to 2 substances - such diversions are defined by particle size: -- true solutions: ions/molecules are less than 1 nm; consist of solutes dissolved in solvents and can be ionic or molecular -- colloidal dispersion are particles that are between 1 micron and 1 millimicron (1 nm) -- coarse suspensions are particles greater than 1 micron

states of water: gas

for water to vaporize into steam requires the absorption of 539.4 kcal (heat of vaporization)

foams

gas in a continuous ohs, usually liquid (egg white foams) - such liquids have low surface tension and low vapor pressure - some solid matter in the foam increases stability - foams contribute to volume and fluffy texture

convection

heat transfer by circulation of hot air or liquid - circulation can be artificial: stirring, rotisserie - circulation can be from natural density change - promotes even cooking and good browning - saves time and energy -- decreases temp by ~25°F or reduce cooking time by ~30-40%

conduction

heat transfer by direct contact of substances - heat is transferred in a continuous and progressive fashion - need to stir to keep original food from burning before the more distant food gets hot - pans conduct heat differently; cast iron and aluminum conduct heat well but stainless steal heats unevenly - water is an excellent conductor, heating evenly; fats get hot faster, and can heat to a higher temperature

rapid drops in temperature

how do you achieve the rapid temp drop? - surround ice cream container with salt/ice solution (1:8 or 1:6) - ice melting is an induction reaction (absorbs heat, endothermic) - salt dissolving in water is endothermic - the absorbed heat comes from the ice cream mixture and the ice/salt brine, which lowers freezing point

texture is affected by: invertase

interfere with the alignment of crystals into large aggregates - corn syrup (mixture of glucose, maltose, dextrins from hydrolysis of cornstarch) - HFCS (also contain fructose) - fat (cream, chocolate >50% fat, butter)

true solutions

ions/molecules < 1 nm - effect on freezing and boiling points whose solutions can be: unsaturated (more solutes can be added) , saturated, (full of solutes) and supersaturated

the water molecule is a dipole

it is electrically asymmetrical, with a positive end (hydrogens) and negative end (oxygen) - partial charges are capable of forming hydrogen bonds - boiling point is high because of strength of hydrogen bondsc

tendency to undergo browning

lactose>ribose>fructose>glucose

dextrinization

large molecules being broken down, once they are really small they are called dextrins

texture is affected by: acid

like cream of tartar, causing inversion - slowing boiling promotes more inversion - inversion promotes smoother texture because the mix of sugars results in less aggregation of crystals than one would expect

gel

liquid dispersed ina solid (baked custard, curd cheese) - does not flow, more bound water than liquid water

liquid: vapor pressure

liquids experience vapor pressure = tendency fro liquids to become gases

syneresis

loss of free liquid from a gel, usually negative, but needed in cheese production

liquids: evaporation

loss of molecules at the surface of liquid, without being surrounded by molecules being surrounded by molecules with their existence cross-linking, surface surface molecules escape from liquid - evaporation occurs when vapor pressure exceeds surface tension

What causes the filling of a lemon meringue pie to ooze out of the crust? how could it have been prevented

over hydrolysis during preparation of the filling, it could have been avoided by rapidly heating the starch and adding acid after gelatinization is complete so that the thinning caused by the hydrolysis will be avoided

complex carbohydrates

polysaccharides - animals: glycogen - plants: starch and fiber

effects of ingredients on gelatinization: fat or milk proteins

reduces gelatinization temperature

effects of ingredients on gelatinization: low sugar+acid

reduces gelatinization temperature but thinning occurs quickly

maillard browning

series of reactions in condensing a reducing sugar + and amine, resulting in surface color browning -- all monosaccharides are reducing sugars, but sucrose is not, so sucrose must first undergo inversion - heat and pH > 6.0 increase the Maillard reaction - add an amine ----> glycosamine

factors affecting freezing point: salt

since a molecule of salt (NaCl) ionizes into 2 ions, salt has twice as great an effect as sugar on freezing point - 1 gram molecular weight of salt (58 g) in a liter of water depresses the freezing point of the solution to 3.72°C - implication: melting ice on your driveway= salt lowers FP and ice will melty last a lower temp, and freezing or mention and iced desert

sols

solid dispersed in a liquid (gravy), keeps flow properties - these can interchange when conditions change (sol cools down into a gel and vice versa)

solubility and temperature

solubility is influenced by temperature - less solute can dissolve at a lower temp - therefore there is a limit to how much of a solute will dissolve at a given temperature

4. factors affecting the boiling point

steam pressure increases BP - steam created cannot escape, which increases Atm p - use a pressure saucepan or pressure canner important to increase temperature needed when canning low-acid foods

solids

substances that do not flow (low energy states where molecules are moving slowly; solids are in equilibrium with liquid) 1. amorphous 2. crystalline structure

liquids

substances that exhibit flow properties (molecules move more rapidly via absorption of heat)

gases

substances that move at great distances from each other (molecules are moving very quickly) - steam and CO2 are the functionally important gases in foods - gases can expand: heat (leavening action when baking bread) and pressure (fermentation by yeast)

liquids: interfacial tension

the surface tension of different liquids varies - therefore two different liquids next to each other ten not to mix - interfacial tension is important in considering emulsion (ex. oil and water)

water activity

vapor pressure of water in a sample/vapor pressure of pure water - foods with solutes will have vapor pressure lower than that of water - water content not the same as water activity - since vapor pressure is affected by temp, the temps of both substances must be the same when calculating water activity - by definition any food will have water activity < 1.0

to achieve gels of the same gel strength?

vary the amount of starch, depending on the type of starch