Chemical and Physical Properties of Food Flashcards
1
Q
What is a colloidal dispersion?
A
In Colloidal Dispersions, the particles of one substance are distributed, dispersed, in another substance without dissolving.
2
Q
What are the terms given to each of the substances within a colloidal dispersion?
A
The substance that is dispersed within another is called the dispersed phase.
The substance that extends throughout the system and surrounds the dispersed phase is called the continuous phase.
3
Q
Dispersed phase: solid
Continuous phase: liquid
Name of dispersion?
Give examples.
A
sol
Examples:
starches, proteins and some plant polysaccharides in water
4
Q
Dispersed phase: liquid
Continuous phase: liquid
Name of dispersion?
Give examples.
A
emulsion
Examples: milk, mayonnaise
5
Q
Dispersed phase: liquid
Continuous phase: solid
Name of dispersion?
Give examples.
A
solid emulsion
Examples: butter, margarine
6
Q
Dispersed phase: [liquid]
Continuous phase: solid
Name of dispersion?
Give examples.
A
gel
Examples: starch, gelatin, pectin
7
Q
Dispersed phase: gas
Continuous phase: liquid
Name of dispersion?
Give examples.
A
foam
Examples: beaten egg white, whipped cake frostings
8
Q
Dispersed phase: gas
Continuous phase: solid
Name of dispersion?
Give examples.
A
solid foam
Examples: meringue, ice cream, bread
9
Q
What is a sol?
A
A suspension of large molecules dispersed in a liquid, generally water.
10
Q
What is an emulsion?
A
An emulsion is a suspension of liquid droplets (fat or water) within a liquid medium (fat or water). Food emulsions can be either oil in water (o/w) or water in oil (w/o).
11
Q
Compare the dispersions of homogenized milk and skim milk.
A
Homogenized milk is a dispersion of milk fat droplets in a liquid medium (skim milk portion of milk), while skim milk itself is a suspension of milk protein particles, the casein micelles, within a water-based medium.
12
Q
What is a solid emulsion?
A
A solid emulsion is a dispersion of liquid droplets within a solid phase.
Margarine and butter are examples of water in oil emulsions, in which the continuous phase is solid under refrigerator or low ambient temperatures.
13
Q
What is a gel?
A
A dispersion of water held within a continuous matrix of polysaccharides (starch gels) or proteins (gelatin gels).
Some scientists consider the water in gels to be a second continuous phase rather than a dispersed phase.
14
Q
What is chemical composition?
A
Foods are made of chemical components that are working together and making the food the way it is.
Chemical composition is determination of these compounds.
The chemical composition tables identifies the amounts of these compounds in each food.
15
Q
What is proximate analysis?
A
Quantifying the amount of Carbohydrate, Fat, Protein, Water and Ash.
16
Q
What are the major food components of food systems?
A
Carbohydrates, fats, proteins and water.
These are the compounds are found in largest amounts in foods.
17
Q
What are minor food components of food systems?
A
Organic acids, pigments, aroma compounds, vitamins and minerals
18
Q
What are the two groups of food components in food systems?
A
Major and minor
19
Q
What is the main source of energy for humans (generally), and what food sources do they occur in?
How many kilocalories per gram do they provide?
What is the AMDR?
What form should you aim to eat?
A
Carbohydrates occur in foods as sugars and starches and are the human body’s main source of energy.
Digestible carbohydrates contribute 4 Calories (kilocalories) of metabolized energy per gram.
Carbohydrates should contribute about 50% of our caloric intake per day; and most of the carbohydrates that we consume should be in the form of complex carbohydrates (polysaccharides) such as starch rather than as simple carbohydrates (monosaccharides and disaccharides) such as table sugar.
20
Q
What are the main monosaccharides found in foods?
A
Glucose, fructose and galactose
(simple carbohydrates)
21
Q
What is one of the main functions of simple carbohydrates?
A
Ability to impart a sweetness sensation; however, sugars vary in their sweetening power.
22
Q
How are disaccharides formed?
A
Disaccharides are formed by the union of two monosaccharide molecules by a bond called a glycosidic linkage (alpha or beta).
Disaccharides are also considered as “simple” carbohydrates.
23
Q
How can disaccharides be split into their component parts?
A
They can be split into their component monosaccharides by enzymes or by boiling with dilute acids.
24
Q
What are the most important disaccarides in foods?
A
Sucrose, lactose and maltose.
These disaccharides differ from one another in solubility, sweetness, and other properties.
25
How is table sugar obtained?
From sugar-cane or sugar-beet
26
Which monosaccharides compose pure sucrose?
Where can sucrose be naturally found?
Glucose and fructose
Sucrose can be found in a variety of fruits, grasses and roots
27
How is invert sugar produced?
By hydrolyzing sucrose with the enzyme invertase or with acid, to produce a mixture of glucose + fructose (1:1).
28
Why is invert sugar used in place of sucrose, particularly for carbonated beverages?
The use of invert sugar in place of sucrose is because of the inherently greater sweetening power per unit weight of the fructose containing sweetening systems.
29
What are the primary sugars in honey?
What ratio do they occur?
Glucose and fructose in a 40:60 ratio
30
Describe the processing done by bees on the nectar they collect.
Most of the nectar collected by the honey bee contains sucrose which is hydrolyzed by invertase in the saliva of the honey bee.
Some of the glucose is converted to gluconic acid and hydrogen peroxide by glucose oxidase, another enzyme secreted into the collected nectar by the honey bee.
The gluconic acid and hydrogen peroxide act as preservatives in the nectar.
*Honey also contains minute quantities of disaccharides and complex sugars.*
31
Discuss sweetness in relation to caloric contribution.
**It is important to note that sweetness has no relation to caloric contribution of a sweetening agent to the diet.**
Fructose and lactose each produce 4 Calories of metabolized energy per gram when digested and absorbed, but lactose is only one-seventh as sweet as fructose.
Thus for an equivalent sweetness intensity, less fructose would be required than lactose.
Conversely, a product sweetened with lactose could potentially contain seven times the caloric content compared to a product sweetened with fructose.
32
What is milk sugar, and where does it occur?
Lactose, occurs in the milk of all animals.
Cow's milk contains about 4-5%, whereas human milk contains 6-8% lactose
33
How is lactose formed?
By linking glucose and galactose together.
34
What does it mean to be lactose intolerant?
Lactose intolerant people are those who do not have the enzyme lactase necessary to digest (breakdown) lactose (milk sugar).
People who are lactose intolerant can suffer from minor cramps to extreme intestinal discomfort.
35
How is hydrolysis of lactose acheived, and what is the effect?
The hydrolysis of lactose found in dairy products into its component monosaccharides is catalyzed by the enzyme lactase.
Breaking down lactose substantially increases the sweetness.
36
What is the acidulant and preservative agent in yogurt and numerous cheeses?
Lactose can also be fermented by lactic acid-producing bacteria, into lactic acid
37
What processing is done to produce a lactose-free dairy product?
Lactose-free products have had the enzyme lactase (usually isolated from yeast) added to them.
## Footnote
*Alternatively, lactose intolerant individuals can take tablets containing the enzyme, prior to eating or drinking dairy or other food products with lactose or milk solids.*
38
39
What are the primary sugars in maltose?
Two glucose units linked together
40
How is maltose obtained?
When starch (eg corn starch) is hydrolysed by the enzyme amylase or by heating with dilute acid.
41
How is high fructose corn syrup produced from maltose?
Maltose can be further hydrolysed by the enzyme maltase into its component D-glucose units, which are then enzymatically isomerized by the enzyme glucose isomerase to produce a liquid syrup composed of 42% fructose, commercially known as high fructose corn syrup (HFCS 42).
42
What is the composition of HFCS 42?
HFCS has 42% fructose, 52% glucose and 6% starch.
43
How is HFCS 55 produced?
Subsequent technological improvements in which the HFCS 42 syrup is passed through an ion-exchange column that retains fructose, allow for the production of a 90% fructose syrup.
HFCS 90 is then blended with HFCS 42 to create HFCS 55, which has a sweetness profile similar to sucrose.
44
Why is HFCS preferentially used by the food industry?
The cost of these syrups is lower than the cost of sucrose or even invert sugar.
45
How is the sweetness of carbohydrates determined?
By their molecular structure and interaction with sensory receptors on the tongue.
## Footnote
*Simple sugars vary in their sweetness*
46
When do sugars produce **body** and **mouth feel**?
When they are incorporated into foods at concentrations high enough to affect the viscosity (resistance to flow) of the food product
47
What is the basis of many hard candy products?
Production of hot supersaturated sugar solutions with controlled crystallization during cooling
48
Why are sugars readily soluble in water?
Sugars are readily soluble in water because they contain many hydroxyl (OH) groups, which form hydrogen bonds with water.
49
What increases the solubility of sugars?
What is the property used to produce? Give examples.
Solubility of sugars increases as the temperature of water increases.
This property is used to produce syrups of varying concentrations for various uses
(e.g. pancake syrup, concentrated syrups for use in food processing, cooking or confections.)
50
What is the basis for production of table sugar?
Sugars can be **crystallized** from solution when water is **evaporated**.
Example: production of table sugar (sucrose) from the juice extracted from sugar cane and sugar beets.
51
How can sugars function as a preservative?
Sugars, in sufficiently high concentration, can be used to inhibit growth of undesirable microorganisms.
They function as a preservative by binding water needed by the microorganisms.
52
What is the basis for production of fermented foods?
Sugars are fermented by microorganisms with the concomitant production of acids and/or alcohol as well as flavouring compounds.
53
What happens to sugars exposed to high temperatures?
They caramelize!
54
What do reducing sugars react with in order to produce flavours and colours in food?
Proteins and amino compounds
55
How do simple sugars participate in browning reactions?
Another important property of the simple sugars is their ability to **serve as reactants in non-enzymatic** browning reactions, namely **caramelization** and the **Maillard** browning reaction.
56
Describe the caramelization browning reaction.
The **caramelization** reaction involves reaction of sugars (reducing and non-reducing sugars) when heated at high temperatures (200°C) to produce caramel and butterscotch flavours.
The brown pigments formed during the heating of sugars contributes to the colour of caramel candies and toffees.
*The pigments are not the same as the melanoidins formed during the Maillard reaction.*
57
When does the Maillard browning reaction occur?
When reducing sugars react with nitrogenous compounds such as amino acids, proteins or amines
The Maillard browning reaction is responsible for the formation of the brown pigments that appear on bread slices when they are toasted in the toaster.
58
What is a reducing sugar?
A reducing sugar contains a free aldehyde or ketone group.
Therefore, it will contain a “free” OH on the position next to the O in the ring structure.
*Recall: Tollen's Test from Chem 233!*
59
Give examples of reducing sugars.
Glucose, Fructose, Galactose and Lactose are examples of reducing sugars.
Sucrose does not have this "free" OH, therefore is not a reducing sugar.
60
Sucrose is not a reducing sugar, will invert sugar be considered as a reducing sugar?
Invert sugar is derived from the hydrolysis of sucrose and consists of glucose and fructose.
The invert sugars are both reducing sugars but sucrose is a non-reducing disaccharide and does not react in the carbonyl reactions which are used to determined reducing sugar capability. (Tollen's Test!)
Invert sugar is a reducing sugar.
61
What are the characteristics and functional properties of agar?
* extracted from seaweed (kelp)
* used as a thickener agent
62
During the Maillard reaction, many low molecular weight intermediate compounds are formed and these often are aroma and flavour compounds that contribute to the desirable or undesirable flavours produced in a food.
Give examples of both desirable and undesirable compounds, and describe why they form.
Examples of desirable compounds are the aroma and flavour of baked bread, toasted bread and roasted coffee, while undesirable aromas and flavours are those that form in skim milk powder during storage or during the browning of canned peaches during long-term storage.
The brown colours are high molecular weight pigments, melanoidins, formed as a result of polymerization of some of the low molecular weight intermediate fractions.
63
What are polysaccharides, how are they classified, and how do they differ from simple carbohydrates?
Polysaccharides are high molecular weight, long chains of monosaccharide units (i.e. glucose).
They are classified as the complex carbohydrates and differ from simple carbohydrates by being insoluble in water and generally tasteless.
64
Where are polysaccharides used in food products generally sourced?
From plant or seaweed sources; a few are from microbial origin.
65
How do polysaccharides affect the properties of food products?
They contribute to the thickness or viscosity and textural properties of food products.
66
What are the characteristics and functional properties of pectins?
* **structural polymers in plants (such as apples)**
* form the cementing material between individual plant cells
* pectin affects the texture of plant tissues
* **used in jams and jellies as gelling agents in the presence of sufficient sugar and acid**
* contribute to the viscosity of tomato paste and ketchup
* contribute to the mouth feel and maintenance of particles in suspension (e.g. orange juice, unclarified apple juice)
67
What are the characteristics and functional properties of alginates?
* extracted from certain types of seaweed
* used as gelling agents
* keep solids and liquids in suspension in fruit juices
68
What are the characteristics and functional properties of gum arabic or gum acacia?
* is a plant **exudate from the bark of the acacia trees**
* used as thickener and stabilizer in products like beer, soft drinks, ice cream
69
What are the characteristics and functional properties of carrageenan?
* extracted from certain types of seaweed (red algae)
* used as a suspending agent to keep cocoa particles in suspension in chocolate milk
70
What are the characteristics and functional properties of xanthan gum?
* produced by bacteria
* first isolated from rotting cabbage, now cultured in large fermentation tanks and purified
* used in salad dressings as a thickening agent, which enables the dressing to cling to the salad components
* used as a suspending agent to maintain pieces of onion, red pepper, spices in a stable suspension.
71
What are the characteristics and functional properties of cellulose and hemicellulose?
* are present in many plant tissues as supporting structures (e.g. the fibres in celery)
* are polymers of glucose that are indigestible
* along with pectin and the other carbohydrate gums form the indigestible portion of our carbohydrate intake that is known as dietary fibre
72
What are the characteristics and functional properties of starch?
* are polymers of glucose
* digestible when cooked (e.g. rice, potatoes, etc.)
* used as thickening, suspending and gelling agents
73
Why is starch bland?
The length and bulkiness of the starch molecule prevent it from interacting with our tongue receptors!
74
What is starch used for in food?
Mostly used as a thickening, suspending and gelling agent.
75
How does starch exist in food?
In foods such as cereals and tubers starch exists in the form of **starch granules**.
Starch molecules are tightly packed within starch granules.
The starch granule is not digestible, nor is it soluble in cold water unless it is heated.
76
What is amylose?
Starch molecules (**amylose**, a straight/linear chain starch molecule and **amylopectin**, a branched starch molecule) are tightly packed within starch granules.
77
What is amylopectin?
Starch molecules (**amylose**, a straight/linear chain starch molecule and **amylopectin**, a branched starch molecule) are tightly packed within starch granules.
78
79
What is gelatinization?
When starch is heated in water, it undergoes a phenomenon known as gelatinization.
The starch granules absorb water and swell-up as the water entering the granule begins to "loosen" the bonds between the starch molecules.
Hydrogen bonds form between the water and starch molecules.
The starch granule eventually "bursts", becoming soft and pliable.
80
Give examples of starch gelatinization.
This is the phenomenon that occurs when puddings are made or when flour is used as a thickening agent when making gravies.
Starch gelatinization is the phenomenon that leads to the conversion of hard, unchewable, raw rice kernels to the soft, easily chewed, cooked rice.
81
What is retrogradation?
Gelatinized starch can lose some of its water holding capacity upon cooling and/or during refrigerated storage.
This phenomenon involves the re-association of starch molecules, especially the amylose polymers, into an ordered structure.
The linear amylose molecules orient themselves in crystalline regions, leading to a squeezing out ("syneresis") of water and a loss of tenderness of the food (e.g. staling of bread) or the development of a gritty texture (e.g. starch based pudding stored in the refrigerator).
82
Where does bread stale quickest? At room temperature, the fridge, or the freezer?
Bread stales more quickly in the refrigerator than the freezer or at room temperature.
## Footnote
*Think about why.*
83
How may retrogradation be avoided?
To a certain extent through the use of **dextrins** and/or modified starches, thus reducing the tendency for alignment of linear amylose chains.
84
How are dextrins produced?
Starches can be partially hydrolysed by acids or enzymes to produce products of intermediate chain length (dextrins!) that have numerous uses in food products.
85
What are dextrins used in food products for?
To create foods that provide the sensation of containing fat but that are low in fat.
86
Can retrogradation be reversed?
Partially.
By heating the food.
(e.g. heating stale bread or buns in an oven or the microwave oven; however, once the product cools the starch quickly retrogrades again.)
87
How are the glucose monomers in cellulose or hemicellulose joined together?
By a beta, (ß)1- 4 link.
## Footnote
*Humans do not have the enzyme needed to break the beta link and therefore, cellulose is indigestible.*
88
Where is cellulose found?
Present in many plant tissues as supporting structures (e.g. the fibres in celery).
89
What makes up dietary fibre?
Along with pectin and the other carbohydrate gums, cellulose forms the indigestible portion of our carbohydrate intake.
90
What is the structure of xanthan gum?
Xanthan gum is a polysaccharide with a ß-D-glucose backbone like cellulose, but every second glucose unit is attached to a trisaccharide.
91
How is xanthan gum produced?
By the bacterium Xanthomonas campestris, which is found on cruciferous vegetables such as cabbage and cauliflower and causes black rot.
Nowadays, it is cultured in large fermentation tanks and purified.
92
How is xanthan gum used in food products?
In salad dressings as a thickening agent, which enables the dressing to cling to the salad components.
As a thickener for sauces, to prevent ice crystal formation in ice cream
Also as a low-calorie substitute for fat.
93
Where are Agar, Alginates & Carrageenan extracted from?
These polysaccharides are extracted from different types of seaweed (kelp).
94
What are agar, alginates, and carrageenan used for in food products?
**Thickening, gelling and suspending agents.**
For example, alginates keep solids and liquids in suspension in fruit juices and provide thickness to dietetic and regular salad dressings, puddings, pie fillings, ice cream, sherbet and icings.
Carrageenan is used as a suspending agent to keep cocoa particles in suspension in chocolate milk, and it is also used as a stabilizer in ice cream (stabilizing the colloidal dispersions).
95
What is Gum Arabic (Acacia Gum)?
What is it used for?
These gums are plant exudates from the bark of the acacia trees. It is used as thickener and stabilizer in products like beer, soft drinks, and ice cream.
96
What forms can lipids be found? What form makes up most of human dietary lipid consumption?
Lipids can be found in the form of triglycerides, phospholipids and sterols.
Most of the fats and oils we consume from food are in the form of triglycerides.
97
How does fat make food more palatable?
Fats act as a **lubricant** in food making the food easier to chew and swallow.
98
How is homogenization used?
Homogenization, or other high-energy mixing processes, may be used to disperse one liquid phase into another.
Nevertheless, after two liquid phases such as oil and water are mixed and then left to stand, the natural tendency is for the two phases to separate.
99
What is tenderizing power?
Fats have **tenderizing power** because they coat the flour particles (protein and starch) in baked goods, creating a flaky, lighter texture that makes them easy to tear apart.
Fats work best as shortening when the crystals are in the beta prime form, which produces a fine texture in the baked goods.
*Cakes will have a crumbly texture without the moistness given by fats.*
100
What is aeration?
Fats add air (gas) to batter and doughs; another function of fats in baked goods.
The fat surrounds the air molecules that are being incorporated into the batter.
They contribute to the formation of the dispersion by decreasing the viscosity in the batter, thus making it easier to flow and rise.
101
How do fats contribute to the overall flavour of food?
Fats and oils are carriers of many aroma constituents in foods that are usually fat-soluble.
102
When do fats and oils begin to smoke and vaporize?
Fats and oils can be heated to very high temperatures before they begin to smoke and vaporize.
Foods fried in hot fats and oils (deep fat frying) cook very fast because of the temperatures that can be attained.
103
What is a desirable characteristic of fats?
Fats gradually soften when heated.
This contributes to the desirable features such as chocolates that melt in your mouth and butter and margarines that are spreadable.
104
What are emulsifiers?
Compounds that promote the formation of emulsions, i.e., the dispersion of one phase in the form of small droplets, in the second continuous phase.
Emulsifiers are **amphiphillic** molecules that have a hydrophilic [water loving] portion and a hydrophobic [water hating] portion.
105
What lipid can act as an emulsifier?
Phospholipids
106
What is the structure of a phospholipid?
Phospholipids are structurally similar to triglycerides, except that only two fatty acids are linked to the glycerol (making it a diglyceride), and a charged group (negatively charged phosphoric acid esterified with positively charged choline group) is linked to the third position of glycerol.
107
What is lecithin and where is it found?
Lecithin is an example of a phospholipid.
Lecithin is a naturally occurring emulsifier commonly found in egg yolk and soybean oil.
108
Give examples of naturally occurring emulsifiers aside from lecithin.
Other naturally occurring emulsifiers include the proteins from milk, egg yolk or other foods.
## Footnote
*Sometimes, synthetic emulsifiers (e.g. "Polysorbate 60") are used to assist in forming food emulsions.*
109
What are stabilizers?
How are they used?
Give examples.
Compounds that increase the viscosity of the continuous phase, keeping the droplets suspended or dispersed and thus reducing the rate of creaming.
Some of the polysaccharides discussed earlier in this lesson are commonly used as stabilizers to thicken the continuous phase (water); some examples are “xanthan gum” and “propylene glycol alginate”.
110
How do emulsifiers work?
Emulsifiers assist in formation of an emulsion by orienting themselves at the interface between the two phases, with their hydrophilic and hydrophobic portions facing water and oil, respectively, thereby reducing the interfacial tension between oil and water phases.
This can also help to stabilize the emulsion by preventing the dispersed oil droplets or water droplets from coalescing together.
111
What are some other factors that may affect emulsion stability?
Droplet size, and the viscosity of the continuous phase.
Droplet size must be such that, the downward pull of gravity, is balanced by the upward forces of buoyancy.
*This will reduce the tendency for "creaming" (floating to the top) of the less dense (oil) phase.*
112
There are 20 different amino acids in proteins found in food systems and in the human body. What are the essential amino acids?
Nine of the amino acids cannot be synthesized by human tissues and must be obtained via food.
These essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine; histidine (essential for infants only).
113
What is the major function of milk homogenization?
Formation of a stable emulsion to prevent fat separation, such as that which occurs in non homogenized milk.
114
What are protein molecules made up of?
Long chains of hundreds or even thousands of amino acid units joined together by a peptide bond.
115
What are amino acids?
Monomers of proteins
Amino acids are a type of organic acid.
They are made up of an amino group (NH2) and a carboxyl group (COOH) attached to the same carbon atom.
116
Describe how protein acts as an emulsifier. Give an example.
Many proteins are amphiphillic molecules as they contain hydrophilic and hydrophobic portions (from amino acids) allowing them to act as emulsifiers.
One part of these amino acids is attracted to water, forming hydrogen bonds, while the other part avoids water and binds with oil.
Egg yolk and mustard proteins in mayonnaise function as emulsifiers.
117
How much protein is required by adults?
How any calories does a gram of protein provide?
Adults require 0.8 grams of protein per kilogram of body weight.
Proteins produce 4 Calories per gram when they are digested and the amino acids are metabolized for energy.
118
How do proteins in tissue systems such as meats and fish contribute to the texture of the products?
The difference between a tender steak and a tough steak can often be related to the types and relative abundance of various types of protein molecules within the muscle structure.
## Footnote
*Proteins from various sources (cereal grains, milk, meat, fish, legumes) can be used in various states of purity as food ingredients with differing functional properties.*
119
What is a foaming agent?
Proteins have the ability to trap air in bubbles and this leads to the formation of foams.
Egg white proteins function as foaming agents in the making of whipped egg whites. Whipping introduces air and denatures (unfolds) the protein molecules. The protein molecules then coagulate to form a fine film around the air pockets.
*Aquafaba may be used in place of egg white proteins, the result is the same.*
120
What is a solid foam and how is it formed?
Solid foams such as meringue are formed when the whipped egg whites are heated causing the protein to denature and form a more rigid three-dimensional structure, which won't collapse when the air escapes.
Bread and ice cream are also examples of solid foams.
121
What is gluten?
Gluten, a protein in wheat flour, traps air bubbles in bread making.
## Footnote
*Bread was prepared and photo was taken by Morgan Reid, LFS, UBC. This bread was prepared using a 250-year old sourdough culture*
122
What is gelatin and how does it form a gel?
Gelatin (from the animal protein: collagen) forms a gel by trapping large volumes of water within a semi rigid three dimensional protein matrix.
123
What leads to the formation of textures characteristic of cured meat?
Heating of meat proteins during the manufacture of luncheon meats, such as bologna and frankfurters, leads to gelation, and emulsion.
124
How can milk protein form a gel?
When it is acidified, such as in making of yogurt and cheese.
The gel holds water and has a smooth texture.
125
Describe the role of milk protein in a latte, in milk, and in cheese.
In latte (A): the milk protein traps air bubbles to form the foam structure.
In milk (B): casein, a milk protein, acts as an emulsifier preventing the fat globules to separate (cream) from the skim milk portion.
In cheese (C): casein forms a gel structure in the cheese curd.
126
Enzymes are proteins that function as biological catalysts. Give examples of enzymes used in food production.
In some cases enzymes are added to food as an ingredient (**invertase** in candy making)
Some enzymes are used to promote food-processing operations while others are causative agents in food spoilage (amylase can ruin a starch gel; lipases can cause lipolytic rancidity which is the release of free fatty acid from glycerides).
127
What is responsible for reactions associated with ripening of fruits and vegetables?
Enzymes in living tissue food systems
Those same enzymes will continue the ripening process after harvest and unless they are inactivated the enzymes will eventually cause spoilage of the product
(e.g. loss of crispness of stored apples; loss of sweetness of apples during storage; loss of colour in the skin of apples during storage).
128
What are heating processes in food processing generally designed to accomplish?
To inactivate enzymes and undesirable microorganisms in order to extend storage life of foods.
129
Where are enzymes used in food processing sourced?
Microorganisms, when added to food systems, to produce fermented foods, are essentially sources of desirable enzymes required to catalyse the desired chemical reactions needed to produce fermented food products (yogurt, sauerkraut, soy sauce).
Enzymes are also extracted from a variety of sources (plants, animal by-products, microorganisms) and purified for use as aids in food processing
(e.g. proteases used for milk coagulation during cheese making; pectinases to enhance juice recovery and for clarification of apple juice; invertase for conversion of sucrose to invert sugar; isomerase to produce high fructose corn syrup).
130
What is the basis for many food allergies?
Intolerance to certain proteins in foods
131
Why is water an extremely important component of food systems?
Water is related to all aspects of food ranging from our perception of quality, to the ability of microorganisms to be metabolically active in food systems.
132
What forms does water exist in food as?
Free water
Bound water
133
What is free water?
Some water may be present within intergranular spaces, within pores of the food matrix and as a thin film of water on the surface of many foods.
Free water can be found in tissue food systems and in dispersions.
Water that is free and not bound by food components generally retains its usual physical properties, can also function as a dispersing agent for colloidal substances, can function as a solvent and can be used by microorganisms.
134
What is bound water?
Some water can be **ad**sorbed on surfaces of macromolecules such as starches, pectins, proteins through forces such as van der Waals forces and hydrogen bond formation.
This water does not display all of its normal physical properties and it is not readily available for use by microorganisms and chemical or enzymatic reactions.
Another form of bound water is the water that is associated with food matrices as water of hydration.
135
How can sugars and salts be used to control or prevent growth of certain microorganisms in foods?
Sugars and salts (sodium chloride) can bind substantial amounts of water and are often added to foods for the purpose of decreasing the amount of free water in the food system.
136
What is water activity?
Water activity is a measurement that is frequently used in monitoring the availability of water (free water) in foods for the support of:
* microbial growth
* chemical reactions
* enzymatic reactions
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How is water activity measured?
Water activity can be measured as the ratio of the vapour pressure of water in the food to the vapour pressure of pure water, both measured at the same temperature.
Water activity can range from 0 (no free water) to 1.0 (all the water is free, such as in distilled water).
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How may water activity of foods be adjusted?
By physically removing water from foods during **concentration** and **dehydration** processing operations, also when the water in the food is **frozen** (the free water is in a solid state, in the form of ice crystals), or by adding substances that bind water thus lowering the proportion of water in the free form. The most commonly used **water-binding agents** are sugars and salt.
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What is pH?
pH is a measure of the acidity of a food.
Foods and beverages differ in pH because of their content of acids, which produce hydrogen ions.
We are able to detect these ions by using a hydrogen sensitive electrode in a device called a pH meter.
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What is moisture content and does it relate to water activity?
Measurement of the moisture content of a variety of food systems is a frequently conducted quality assurance measurement.
However, measurement of water content of foods does not indicate whether the water is bound or free.
*The data in the table shows that water content of foods cannot be used as a reliable indicator of the water activity.*
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Where are organic acids found and what do they do?
Fruits contain natural acids which give the fruits tartness and slow down bacterial spoilage.
Organic acids also impart flavour and acidity to food.
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Where is malic acid found?
Apples
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Where is citric acid found?
citrus fruits, tomatoes, strawberries.
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Where is tartaric acid found?
grapes
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Where is lactic acid found?
yogurt, cheese, olives, cottage cheese, sauerkraut.
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What are the major uses of organic acids?
To adjust pH or to acidify food, and to impart flavour.
A number of organic acids are also employed as antimicrobial agents.
Organic acids have a wide range of textural effects in food systems due to their reactions with proteins, starches, pectins, and other food constituents.
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How is pH important to the food industry?
An important pH for the food industry is pH 4.6; this is the borderline between an acidic food and a low acid food.
* acid foods have pH of 4.6 or less
* low-acid foods have pH greater than 4.6
**Acid foods will not support growth of disease causing microorganisms.**
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What is chlorophyll?
Chlorophyll, the green pigment in plants, is responsible for the green colour in apples, lettuce, celery and broccoli.
Chlorophyll a has a blue green hue (e.g. in the florets of fresh broccoli) while chlorophyll b has a yellow green hue (stems of broccoli).
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What are carotenoids?
Carotenoids, a diverse group of pigments, can be subclassified into carotenes and xanthophylls.
Carotenoids naturally produce red, orange and orange-yellow colours in many foods.
(e.g. tomatoes, carrots, pineapples, shrimp)
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What are Anthocyanidins and anthocyanins and how are they affected by changes in pH?
Anthocyanidin complexed with glucose or other sugars, the predominant colour pigments in blueberries, cherries, cranberries, plums and red cabbage.
The anthocyanins are particularly sensitive to changes in pH, showing marked changes in colour with pH changes in the food system.
The colour is most stable at low pH.
The colour loss is reversible, and the red hue will return upon acidification.
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What are the red pigments in blood and muscle?
Other pigments in food systems include hemoglobin and myoglobin (the red pigments in blood and muscle).
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What are some environmental changes that pigments are sensitive to?
(pH, presence or absence of oxygen, presence of metal ions, enzymatic degradation)
Thus colour changes often occur in fresh fruits, vegetables, meats and fish during storage, spoilage and as a result of processing and cooking.
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How is the complex aroma profile of foods detected?
When we inhale volatile constituents of foods that react with the receptors in the olfactory regions of our nasal passages.
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Describe the volatile and flavour constituents of aroma.
The volatile constituents that contribute to the aroma of foods are present in very low concentrations but are nonetheless very important constituents of foods.
The flavour constituents are either present as part of the food matrix (fresh strawberries) or are modified (cooking of strawberries) or created (roasting of coffee) during processing or cooking.
Any change in that specific mixture of volatile compounds or their concentrations will alter the aroma that we perceive.
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What are the water-soluble vitamins?
Vitamin C (ascorbic acid), thiamin, riboflavin, niacin, pyridoxine, vitamin B12, and folacin.
These vitamins are found within the water (aqueous) phase of foods.
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What are the fat-soluble vitamins?
vitamin A, vitamin D, vitamin E (& K)
found within the fat (oil) portion of foods
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How is vitamin C used as a food additive?
**Bleaching agent:** Hasten oxidation and aging processes as in flour whitening treatment (Ascorbic acid converts to its oxidizing from during mixing)
**Preservative:** Act as antioxidant to slow down rancidity and browning reactions
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How are tocopherols (vitamin E) used as a food additive?
**Preservative**: Antioxidant
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How are minerals (calcium, magnesium, sodium, potassium, iron, and zinc) associated with chemical properties and textural characteristics of food systems?
Are active participants in chemical and biochemical reactions that change properties of food
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Briefly explain the importance of carbohydrates, fats, proteins, and water in food systems.
Carbohydrates can have several functional properties in food, ranging from imparting sweetness to thickening capacity.
Fats can be saturated or unsaturated, which affects their physical state (solid versus liquid) and functional properties in food. These functional properties range from tenderizing to emulsifying capacity.
Proteins not only impart texture and act as enzymes, but also have other functional properties such as gel and foam formation.
Water in food is found in the free and bound form. Water activity is an important measurement of the amount of free water available for microbial, chemical and enzymatic reactions. Water activity can be controlled during processing of foods.
