MIDTERM 1 REVIEW

Question 1

objective vs sensory evaluation

Answer 1

objective: quantitative, unbiased, uses instruments

sensory: subjective, human experience, qualitative

Question 2

objective measurements

Answer 2

physical measurements:
- mass (g), volume, (L), density (g/L), specific gravity
- moisture: pressing, wettability
- texture: tensile strength, puncture strength, torque % sag
- color: standardized systems

chemical measurements:
- pH, nutrient analysis, sugar concentration, saltiness

Question 3

physiology of sensory evaluations

Answer 3

olfactory receptor neurons (10 mil)
- volatile/aromatic compounds

taste receptors (10 thous)
- sweet, salty, sour, bitter, umami
- umami: amino acid, savory

other flavors
- astringency, coolness, heat, glucosinolates

subthreshold levels

Question 4

affect of salt, acid, sugar

Answer 4

salt
- inc sweetness
- dec sourness

acid
- increase saltiness

sugar
- decrease saltiness
- decrease bitterness

Question 5

types of sensory tests

Answer 5

1. single sample (acceptability)
2. descriptive (scoring of attributes)
3. affective (preference)
4. difference test
   a. paired comparison which has greater amt of characteristic
   b. duo-trio (which sample of two is diff from control)
   c. triangle test (3 samples, which is diff)

Question 6

proteins in food

Answer 6

foam, thickening, structure

Question 7

protein stcuture

Answer 7

contains amino group (NH3), carboxyl group (COOH… carbonyl + OH + R); held together by peptide bonds

• primary: sequence of a chain of AA
• secondary: sequence of AA linked by hydrogen bonds (pleated sheets; alpha helix)
• tertiary: attractions present between alpha helices and pleated sheets
• quaternary: protein consisting of more than one AA chain

***secondary protein structure:
- necessary for function
- lowers thermodynamic state
- prevents aggregation

Question 8

types of proteins

Answer 8

globular protein (varying solubility)
- enzymes
- hormones
- transport proteins

fibrous proteins (insoluble in water)
- structural proteins (ex: collagen)

conjugated proteins
- bound to lipids
- carbs
- metals
- phosphorous
- (ex: lipoprotein)

*** what type of protein would you expect rennin to be?

Question 9

denaturation & coagulation in food science

Answer 9

1) heating/beating leads to denaturation
- tertiary structure lost
- inc viscosity, dec solubility
- dec water holding capacity
- inactivate enzymes

2. (continued) heating/beating leads to coagulation
   - R groups: crosslink: aggregation

Question 10

coagulation: isoelectric point

Answer 10

• point at which protein carries no electrical charge
• protein is least soluble at isoelectric point

*** (1) a positive charge on each molecule keeps them apart (2) when molecule loses charge they clump together

Question 11

hydrolysis

Answer 11

• heat of pH to break peptide bonds
• inc solubility
• dec thickening
• meat tenderizing

Question 12

egg structure

Answer 12

• yolk, germinal disc, vitelline membrane
• chalaza, air cell
• thick albumen, thin albumen
• inner membrane, outer membrane, cuticula

Question 13

egg formation

Answer 13

1. development of ovum in ovary
2. possible fertilization
3. egg white develops as it moves through oviduct
4. shell forms in oviduct
5. bloom (cuticula) forms
6. intestine merges and egg is laid through same pathway feces are excreted

Question 14

egg nutrition

Answer 14

white
- *3.2 g protein
- trace amount of fat

yolk
- 2.4 g protein
- *4.6 g fat (half saturated)

*overall
- 186 mg cholesterol in large egg
- fat soluble vitamins
- B12
- minerals
- sometimes omega 3s

Question 15

proteins in egg albumin

Answer 15

*ovalbumin: 54% of protein
conalbumin: binds metals if uncooked
ovamucoid: inhibits trypsin if uncooked
lysozymes: breakdown bacteria
ovamucin: thick albumin
avinid: binds biotin if uncooked

Question 16

egg grading and inspection

Answer 16

with age
- inc air cell, inc pH
- thinning of albumin
- vitelline membrane breakdown

candling
- air cell size, yolk stabalility

grading (voluntary
- AA grade (small air cell), A grade, B grade (large air cell)

inspection (required)
- wholesome, unaltered, truthfully labeled
- USDA Poultry Division
- restricted aggs: cracked, dirty, greenish whites

Question 17

egg safety

Answer 17

salmonella enteriditis
- from ovary (yolk), from intestine (shell)

prevention
- cooking to 160 deg and refrigerate
- pasteurization: heating to high temp without denaturing proteins (required for eggs out of shell)

Question 18

egg color

Answer 18

• egg yolk color due to carotenoids (provitamin A): lutein, zeaxanthin, carotene
• color is largely influenced by diet

Question 19

egg emulsifying

Answer 19

yolk proteins act as emulsifiers
- lecithin (contains phosphatidylcholine)
- lysolecithin

phospholipids: P and NP regions (P, hydrophilic head)

substitutes: mucilaginous polysaccharides (flax seed)
- egg white + synthetic yolk
- other proteins or starches

Question 20

egg binding and thickening

Answer 20

thickening via denaturation and coagulation
- ex: custard

coagulation is influenced by
- the source of protein (yolk, whole egg, white)
- rate of heating (tempering eggs)
- other added ingredients (custard)

Question 21

foam formation

Answer 21

uses: leavening, texture, structure

1. beating causes proteins to denature and introduces air
2. proteins rest of surface of liquid
   a. hydrophilic groups: face into air
   b. hydrophobic groups: bind to water

foamy > soft peaks > firm peaks > over beaten
- protein most stable at soft peaks
- coagulation occurs when over beaten
- syneresis (loss of water) when over beaten

Question 22

foam stability

Answer 22

increases when:
- liquids have lower vapor pressure
- liquids have lower surface tension
- proteins solidify at the surface of air bubble

other factors impacting stability:
- temperature of eggs/equipment
- using copper equipment
- additional ingredients (fat, sugar, liquid, salt, acid, amount of thin & thick white albumin)

Question 23

heating foams

Answer 23

1. air cells expand
2. egg proteins coagulate (ovalbumin unaffected by agitation)
3. firm, stable structure created (covalent bonds)

Question 24

food processing methods

Answer 24

mechanical (hand mixer)
- generated by creaming, beating, mixing
- transformed into a modest amount of heat energy
- thermal denaturation of egg white and other proteins

chemical (ceviche; acid cooking meat)
- hydrolysis using acids and water
- fermentation using enzymes and microbes
- dehydration in drying ovens
- oxidation in drying ovens
oxidation when food is air dried

electromagnetic/radient (microwave)
- radiant thermal processing (fire, broiling, sun)
- UV sterilization
- gamma irradiation
- microwaves for heating/cooking food

Question 25

food heating methods

Answer 25

microwave - rapid vibration of water, fat, or sugar molecules creating friction between dipoles (and generating heat within the food) - magnetron tube generates microwave - remainder of food heated via conduction induction - cooktop creates changing MF that interacts with iron in cookware to induce electric current and generate MF that heats pan - food heated via conduction (contact with hot surface) conduction (transferring heat) - energy transferred from heat source to metal molecules in pan - thermal heat eventually transferred to food in pan - requires time, energy is lost in heating pan and air (cast iron & al are best pans) - water, fat, and air can also conduct hear (ex: sous vide) convection (oven) - accelerate air circulation - shorten baking time - promote browning mass transfer (frying) - movement of food into/out of food being heated - frying temp must be controlled - frying can cause loss of water into oil and loss of water-soluble vitamins

Question 26

states of matter

Answer 26

solid (low energy state) - without flow under moderate stress - molecules move slowly, tightly packed - strong, non-covalent bonds - crystalline solids: organized structure; amorphous: non-organized (dynamic) liquid - flow properties - temp determines fluidity - weaker transitory non-covalent bonds - medium distance between molecules gas (high energy state) - large distances between molecules - constant & fast movement of molecules - increase in volume & pressure when heated other - vapor pressure: pressure when molecules in compound attempt to be gaseous rather than liquid - evaporation: escape of liquid molecules into surrounding atmosphere - surface tension: strength of bonds at surface of liquid, bonds broken during evaporation - interfacial tension: molecules at surface of liquid remain with the liquid and not intersperse with a second liquid

Question 27

dispersions

Answer 27

A. true solutions - unsaturated - saturated - supersaturated B. colloidal dispersions - emulsions - sol - gel - foam C. coarse suspensions

Question 28

emulsions

Answer 28

- emulsifying agent - emulsion stability - permanent vs temporary emulsion

Question 29

milk proteins

Answer 29

whey and casein *casein micelle: submicelle, calcium phosphate, k-casein peptide chain

Question 30

milk processing

Answer 30

1. pasteurization 2. homogenization 3. fermentation 4. other a. evaporated milk, condensed milk, dried milk, alternative milks

Question 31

milk processing examples (process + results)

Answer 31

fluid milk - pasteurized; often homogenized; sometimes fat removal - whole: 3.5%; reduced fat: 2%; lowfat: 1%; fat free raw milk - none; may be certified - many touted benefits; rare but real risks evaporated milk - 60% water removed, sterilized - 2x fat/pro; shelf stable condensed milk - 50% water removed, sugar added - browns easily; shelf stable; thick; sweet dried milk - evaporated then blown as fine spray - cheap; light; very shelf stable fermented milk - introduced microorganisms - thicker; tarter; lower lactose alternative milks - varies: usually mechanically pressed nut/bean OR lactose added - no lactose; vegan; varying nutrient values; often expensive

Question 32

milk gels

Answer 32

cheese - coagulation of casein or whey (ricotta) yogurt - fermentation creates lactic acid and coagulation of casein - whey protein coagulated via heat

Question 33

cheese production process

Answer 33

1. curd formation: add acid or rennet, apply heat, bacteria 2. curd cutting & drainage: increase SA to expel whey 3. salting: controls bacteria, dehydrates curd, increases flavor 4. pressing: expel whey, form shape 5. aging: develops characteristic flavor, mold, bacteria added a. enzymes lead to further breakdown of casein to AA, which increases flavor

Question 34

yogurt

Answer 34

1. production process (fermentation) a. heat to 180 deg or rolling boil b. cool to 115 deg c. whisk in bacteria d. heat for 8 hrs on low temp (108-112 deg) 2. varieties a. skyr, greek yogurt, plant-based yogurt

Question 35

other related products

Answer 35

1. tofu 2. vegan cheeses 3. nutritional yeast 4. kefir

Question 36

milk foams

Answer 36

A. stability from protein - agitation/beating or apply heat to denature proteins - proteins wrap around air bubbles to stabilize - hydrophilic: facing outward - hydrophobic: inward touching air bubbles B. milk vs egg whites C. Maximizing stability - concentration protein - add acid - use homogenized milk - start with cold milk - add fat, stabilizers, and sugar

Question 37

cream foams

Answer 37

stability from fat - agitation/beating create air bubbles - fat globules coagulate - air bubbles are suspended in fat maximize stability - concentrate fat - add acid - use non-homogenized cream - start with cold cream - add sugar at end

Question 38

icecream

Answer 38

- considered a foam-air dispersed in liquid - must contain at least 10% milk fat and 20% milk solids (proteins and lactose) - no more than 0.5% stabilizers (gels and gums) overrun - increase in volume due to incorporation of air - gelato vs icecream (cost effective)

Question 39

butter

Answer 39

further disruption of fat globules (stage IV) --> excess coalescing --> air cells collapse --> BUTTER!