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4) Food Commodities > 1. Milk and Dairy (Part II) > Flashcards

1. Milk and Dairy (Part II) Flashcards

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1
Q

what is the equation for density?

A

d = m / v

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2
Q

what is the units for density?

A

kg/m^3

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3
Q

what is the density of milk used for?

A

to estimate solids content

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4
Q

what does the density of a material depend on?

A

temperature and composition of material

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5
Q

milk with higher fat content tend to have ____ densities

A) higher
B) lower

A

lower

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6
Q

as you increases the temperature, density ____

A) increases
B) decreases

A

decreases

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7
Q

how is skim milk produced?

A

by removing fat

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8
Q

how is dehydrated milk produced?

A

removing H2O to obtain a dried product

usually done by spray drying

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9
Q

how is reconstituted milk produced?

A

when H2O is added to dehydrated milk to regenerate the milk emulsion

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10
Q

how is filled milk produced?

A

when other fat besides fat from cow milk is added into cow milk

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11
Q

how is toned milk produced?

A

when a high fat milk product (eg. buffalo milk) is diluted down with H2O or skimmed milk to lower the fat content

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12
Q

how is lactose-free milk produced?

A

milk is treated with enzyme lactase to break down the lactose

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13
Q

how is low-sodium milk produced?

A

by ion exchange chromatography

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14
Q

how is flavoured milk produced?

A

by adding flavour extracts

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15
Q

how is half and half produced?

A

by adding milk and cream in equal proportions

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16
Q

how is canned milk (evaporated and sweetened condensed milk) produced?

A

Moisture content is reduced by at least 60% by heat treatment

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17
Q

what reaction is responsible for the increase in thickness, color and flavour in canned milk?

A

carmelization and maillard reaction

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18
Q

what is condensed milk?

A

type of evaporated milk with sweetener added to a concentration of 15%

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19
Q

what are dehydrated milk product produced with?

A

can be produced with whole, skim, cream and butter milk

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20
Q

what is the same or different between different dried milk products produced from different milks?

A

different total solids, protein and fat

same water level

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21
Q

what is the importance of cream production?

A

b/c cream forms a good starting material for formation of other dairy products (eg. ice cream)

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22
Q

what are uses of cream?

A
  1. direct consumption

2. production of butter and ice cream

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23
Q

describe the production of cream.

A
  1. cream is separated from milk (gravity or centrifugal)

2. milk is left almost completely defatted

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24
Q

what kind of emulsion is butter?

A

water-in-oil

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25
Q

what is butter?

A
  • an emulsion of water-in-oil
  • has a continuous phase of liquid milk fat which are trapped water droplets, crystallized fat grains and air bubbles
  • phase inversion (water in oil) is achieved with hydrophilic emulsifiers
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26
Q

what are the 3 types of butter?

A
  1. butter from sour (fermented) cream: produces cultured cream butter
  2. butter from non-soured sweet cream: produces sweet cream butter
  3. butter from sweet cream, which is soured in a later step: produces soured butter
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27
Q

what are the types of butter based on?

A

the types of creams used to produce them

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28
Q

what is churning?

A

high speed agitation of cream or other milk types to rid the fat phase of moisture, which incorporates air into the cream as bubbles (forming whipped cream)

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29
Q

if you continue agitation after formation of whipped cream, what happens?

A
  • whipped cream becomes coarser

- eventually, the fat forms semi-solid butter granules, which separates from the liquid phase (butter milk)

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30
Q

what does the speed and duration of churning affect?

A
  1. how much moisture is expelled

2. how many crystals are formed to produce the butter

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31
Q

what are the steps of ice cream production?

A
  1. ice cream mix is pasteurized
  2. high pressure homogenization
  3. mix is aged in vats to increase viscosity, then rapidly cooled while air is mixed into it
  4. semi-solid ice cream is pumped out of freezer into packaging vessels to be hardened
  5. storage and transportation
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32
Q

what is “overrun” in ice cream production?

what equation is used to calculated %overrun?

A

the increase in volume caused by whipping air into the product

%overrun = (vol ice cream - vol of mix) / vol of mix) *100%

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33
Q

how is ghee produced?

A
  1. simmer butter at low heat and gentle stirring
  2. butter liquifies to form a yellow colored liquid
  3. impurities and particles is skimmed off
  4. final product is a clear yellow liquid, called ghee
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34
Q

what is involved in the fermentation process of fermented dairy products?

what enzyme is mainly involved?

A

milk sugar –> lactic acid

due to lactic acid bacteria (LAB) mainly.

bacteria, yeasts and molds may also be involved

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35
Q

what is LAB?

A

lactic acid bacteria

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36
Q

what are primary LABs?

A 
lactobacillus
lactococcus
leuconostoc
pediococcus
streptococcus
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37
Q

what is affected by the types of microorganisms involved in fermentation?

A
  1. types of products produced

2. configuration of the lactic acid formed

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38
Q

what two pathways can fermentation proceed to? what do they produce?

A
  1. glycolytic pathway (to form ONLY lactic acid by homofermentation)
  2. or the pentose phosphate pathway (to form MULTIPLE products: eg. lactic acid, acetic acid, ethanol, CO2 by heterofermentation
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39
Q

what metabolic pathway in fermentation of dairy products uses homofermentation?

A

glycolytic pathway

forms only lactate

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40
Q

what metabolic pathway in fermentation of dairy products uses heterofermentation?

A

pentose phosphate pathway

forms more than one product

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41
Q

describe the steps in the heterofermentation

A
  1. glucose
  2. glucose-6-P
  3. xylulose-6-P
  4. 3 phosphoglycerate and acetyl-1-P

2 options to proceed:
A) 3-phosphoglycerate –> pyruvate –> lactate
B) acetyl-1-P –> acetaldehyde –> acetic acid and ethanol

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42
Q

what are the possible products of the heterofermentation pathway

A
  1. lactate

2. acetic acid + ethanol

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43
Q

what does the configuration of lactic acid formed in the fermentation of dairy products depend on?

A

depends on the type of microorganism involved

can produce enantiomers (D and L) in varying amounts

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44
Q

which enantiomer of lactic acid is formed in humans?

what can high intake of D-lactic acid result in?

A

L-lactic acid

Thus, high intake of D-lactic acid can result in high levels in the blood and hyperacidity of the urine

45
Q

which enantiomer of lactic acid should be limited? why?

A

D-lactic acid

because high intake can result in high levels in blood and hyperacidity of the urine

46
Q

what two enzymes can break down lactic acid?

A
  1. phosphorylase

2. lactase

47
Q

what does the break down of lactic acid by phosphorylase ultimately form?

A

DHAP and 3-phosphoglycerate

48
Q

describe the breakdown of lactic acid by phosphorylase

A
  1. lactic acid
  2. galactose-6-phosphate and glucose
  3. galactose-6-P goes through glycolysis to form DHAP + phosphoglycerate
49
Q

what does the break down of lactic acid by lactase ultimately form?

A

lactate (provides sour taste)

50
Q

describe the breakdown of lactic acid by lactase

A
  1. lactase
  2. glucose and galactose
  3. glucose-6-P
  4. pyruvate
  5. lactate
51
Q

what compound provides a sour taste in fermented dairy products?

A

lactate

52
Q

what are two methods that sour milk can be obtained by?

A
  1. spontaneous souring fermentation of milk

2. addition of lactic acid producing bacteria

53
Q

how is sour milk produced?

A
  • lactose is converted into lactate during fermentation

- lactate coagulates casein at pH4-5

54
Q

what are the characteristics of sour milk?

A

thick and sour tasting curdled milk

55
Q

what are the characteristics of butter milk?

A
  • thick
  • sour
  • more bubbly than regular milk
56
Q

what are the 2 types of buttermilk?

A
  1. natural

2. cultured

57
Q

how is natural buttermilk produced?

A

draining the liquid left after butter crystals are removed in the process of butter making

58
Q

how is cultured butter milk produced?

A

by adding bacterial cultures (especially streptococcus lactis) to pasteurized skim milk

59
Q

how is sour cream produced?

A
  1. add S. lactic to light cream

2. fermentation until concentration of lactic acid reaches 0.5%

60
Q

how is yogurt produced?

A
  1. add LAB starter culture (s. thermophilus and lactobacillus bulgaricus) to pasteurized homogenized milk
  2. incubation
  3. final product has pH4-4.2 with lactic acid
61
Q

how is yogurt treated after the process is done?

A
  1. the yogurt is heated or chilled to stop the fermentation process. If chilled, the bacteria remains active, thus the product is termed “active culture yogurt”
  2. gelatin or skim milk powder can be added to thicken yogurt
62
Q

what are characteristics of kefir?

A
  • sparkling, slightly alcoholic milk beverage
  • indigenous to turkestan
  • similar consistency to very thin yogurt
63
Q

what products does Kefir contain?

A
  • lactic acid
  • alcohol
  • CO2
  • some products of casein degradation resulting from proteolytic action of yeast
64
Q

how is kefir produced?

A

by fermentation of raw milk inocculated with yeast, such as torulau (responsible for alcoholic fermentation) and saccharomyus

65
Q

in kefir, what does yeast grow?

A

solid structures that are particles of clotted milk plus the kefir microflora

when wet, the structures look like small cauliflower heads

when dry, they look like brownish seeds

66
Q

what are the 3 basic steps of cheese making?

A
  1. curdling of milk
  2. removal of whey (separating from casein)
  3. ripening of curd in presence of special microflora
67
Q

what 4 factors can cheese be classified on?

A
  1. milk source
  2. mode of curd formation
  3. texture consistency or moisture content
  4. fat content
68
Q

what are the 3 modes of curd formation?

A
  1. acidification
  2. rennet/chymosin
  3. combination of both
69
Q

what are the overall cheese production steps?

A
  1. standardizing milk to have the right amount of fat and protein content, based on type of cheese you are making
  2. mix and blend
  3. pasteurization
  4. homogenization
  5. treat homogenized material with the agent (enzyme treatment or acidification)
  6. agitate with mild heat (causes protein and fat in milk to coagulate, resulting in loss of moisture from curds)
  7. curds are cut into cubes
  8. heating with stirring (changes hardness and texture of product)
70
Q

what are the steps of curd formation?

A
  1. milk is standardized to adjust fat and protein contents to desired levels
  2. additives are added
  3. pasteurization
  4. pasteurized milk is treated with agents (chymosin/rennet or acid)
71
Q

what are two ways of using acid coagulation to treat curds?

A
  1. starter culture (eg. lactic acid or propionic acid, bacteria, molds)
  2. adding acid (gamma gluconolactone)
72
Q

compare enzyme coagulation to heat acid coagulation methods

A

enzyme coagulation has lower recover of the protein in the curd than heat acid coagulation

73
Q

describe the process of cheese ripening

A
  1. curd is ripened until characteristic flavour, body and texture is achieved
  2. degradation of lactose, proteins and fat, such as bacteria and milk enzymes
74
Q

what factors affects the final product after cheese ripening?

A
  • microbial content
  • biochemical
  • composition of the curd
  • temp
  • humidity
75
Q

what are the main types of starter cultures used in cheese production?

A
  1. mesophillic cultures: optimum growth at 20-40degC
  2. thermophilic cultures: optimum growth up to 45degC
  3. mixed cultures: both cultures
76
Q

what are the important characteristics of starter cultures for cheese production?

A
  1. ability to produce lactic acid (during curd formation)
  2. ability to break down the protein (during ripening)
  3. ability to produce CO2 (in some cheeses)
77
Q

what kind of cheeses is rennet/chymosin NOT used in?

A

some fresh cheeses (Eg. cottage cheese) where curd formation is mainly induced by lactic acid

all other cheeses have curd formation induced by chymosin/rennet

78
Q

after rennet is added to milk, what happens to casein?

what reaction is this called?

A

chymosin cleaves kappa-casein between PHE105 and MET106 of kappa-casein to form:

  1. para-kappa casein
  2. glycomacropeptide

chymosin reaction

79
Q

in the chymosin reaction, what happens to glycomacropeptide and para-kappa casein?

A

glycomacropeptide is H2O soluble and remains in solution

para-kappa-casein precipitates in presence of Ca2+

without the protection of intact kappa-casein, casein micelles will coagulate and precipitate (Curd formation)

80
Q

where is rennet traditionally found?

A

4th stomach of young calves

81
Q

what is rennet often used with?

A

pepsins from bovine pancreas

82
Q

what are 3 types of substitutes for animal enzymes?

A
  1. coagulating enzymes from plants
  2. coagulating enzymes (Acid proteinases) from microorganisms
  3. recombinant chymosin
83
Q

what forces/interactions hold micelles together?

A
  1. hydrophobic interactions
  2. H bonds
  3. electrostatic interactions (via Ca2+ and Ca3(PO4)2 bridges between phosphoserine, phosphothreonine and glutamic acid residues
84
Q

how is casein micelle formation influenced by temperature?

A

the hydrophobic interactions that hold micelles together are weaker below 5degC

thus, increasing temperature = increases micelle formation.

Decreasing temp = decreases micelle formation

85
Q

should H+, Ca2+, citrate, phosphate and temperature be increased or decreased to form casein micelles?

A

H+, Ca2+ and temp should be INCREASED

citrate and phosphate should be DECREASED

86
Q

should H+, Ca2+, citrate, phosphate and temperature be increased or decreased to form soluble casein monomers?

A

H+, Ca2+ and temp should be DECREASED

citrate and phosphate should be INCREASED

87
Q

in casein micelle formation, what is the role of citrate and phosphate?

A

they are chelating agents due to their phosphoryl and carboxyl groups which bind w/ calcium

88
Q

in the coagulation process of casein, what happens when citrate and phosphate are removed?

A

removal will allow Ca2+ to interact in the coagulation process

89
Q

in cheese production, what is the starter culture for?

A

it produces lactic acid in curd to assist syneresis

90
Q

what is syneresis?

A

contraction of the coagulum for elimination of whey

91
Q

when does the production of lactic acid stop?

A

when all lactose in the cheese has been fermented

92
Q

how does lactic acid producing bacteria starter culture affect growth of other bacteria that may have survived pasteurization?

A

it surpasses their growth

93
Q

proteolysis involves proteases from… (3)

A
  1. milk (naturally present)
  2. bacteria in the starter culture
  3. rennet
94
Q

describe Co2 production in swiss cheese

A
  1. propionic acid bacteria in the starter culture converts lactic acid into propionic acid, acetic acid and CO2
  2. CO2 gas is dissolved in the moisture phase of the cheese
  3. when solution is saturated, gas is released and collects within pockets of the ripening curd. This forms holes in the ripened product
95
Q

why is Co2 sometimes injected into cheese milk?

A
  1. lower pH

2. shorten coagulation times

96
Q

what is saltpeter?

A
  • NaNO3 or KNO3

- added to cheese to control growth of undesirable bacteria and microorganisms to prevent quality defects in cheese

97
Q

how can saltpeter requirement be substantially reduced or eliminated?

A

if milk is pre-treated by processes, such as microfiltration

98
Q

why would calcium chloride be added to milk in cheese production?

A

to achieve a constant coagulation time and firmness of coagulum

99
Q

what happens when excess calcium chloride is added?

A

coagulum may be too hard and difficult to cut

100
Q

what is the function of adding disodium phosphate (Na2PO4)?

A

to increase elasticity of coagulum in the production of low fat cheese

101
Q

what does the color of cheese depend on?

A

color of milk fat

102
Q

what are examples of coloring agents used for cheese to correct seasonal variations?

A

carotene and oreleana

103
Q

how is green chlorophyll used as a coloring agent?

A

to obtain a pale color as a contrast to the blue mould in some cheeses

104
Q

after all free whey has been remove from the curd, what are the 2 ways that the curd is moulded?

A
  1. by transferring directly to a mould (for granular cheeses)
  2. pressing it into a block
105
Q

what occurs after the moulding of the curd?

A

moulds are placed in a pneumatic or hydraulic pressing system

pressure is applied to the curd to assist final whey expulsion and texture development

106
Q

adding salt to the curd causes what?

A
  1. more moisture to be expelled due to osmotic pressure and salting out effect on whey proteins
  2. change in consistency of the cheese
  3. changes in bacterial processes that occur during ripening
107
Q

what are 2 ways that salt is applied to cheese?

A

dry salting or brine salting

108
Q

the duration of salting of cheese depends on what?

A
  1. salt content typical of the type of cheese
  2. size of cheese (larger cheese = longer salting time)
  3. rate of salt penetration and absorption

4) Food Commodities (6 decks)

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