Chemical and Physical Properties of Food Flashcards
What is a colloidal dispersion?
In Colloidal Dispersions, the particles of one substance are distributed, dispersed, in another substance without dissolving.
What are the terms given to each of the substances within a colloidal dispersion?
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.
Dispersed phase: solid
Continuous phase: liquid
Name of dispersion?
Give examples.
sol
Examples:
starches, proteins and some plant polysaccharides in water
Dispersed phase: liquid
Continuous phase: liquid
Name of dispersion?
Give examples.
emulsion
Examples: milk, mayonnaise
Dispersed phase: liquid
Continuous phase: solid
Name of dispersion?
Give examples.
solid emulsion
Examples: butter, margarine
Dispersed phase: [liquid]
Continuous phase: solid
Name of dispersion?
Give examples.
gel
Examples: starch, gelatin, pectin
Dispersed phase: gas
Continuous phase: liquid
Name of dispersion?
Give examples.
foam
Examples: beaten egg white, whipped cake frostings
Dispersed phase: gas
Continuous phase: solid
Name of dispersion?
Give examples.
solid foam
Examples: meringue, ice cream, bread
What is a sol?
A suspension of large molecules dispersed in a liquid, generally water.
What is an emulsion?
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).
Compare the dispersions of homogenized milk and skim milk.
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.
What is a solid emulsion?
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.
What is a gel?
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.
What is chemical composition?
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.
What is proximate analysis?
Quantifying the amount of Carbohydrate, Fat, Protein, Water and Ash.
What are the major food components of food systems?
Carbohydrates, fats, proteins and water.
These are the compounds are found in largest amounts in foods.
What are minor food components of food systems?
Organic acids, pigments, aroma compounds, vitamins and minerals
What are the two groups of food components in food systems?
Major and minor
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?
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.
What are the main monosaccharides found in foods?
Glucose, fructose and galactose
(simple carbohydrates)
What is one of the main functions of simple carbohydrates?
Ability to impart a sweetness sensation; however, sugars vary in their sweetening power.
How are disaccharides formed?
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.
How can disaccharides be split into their component parts?
They can be split into their component monosaccharides by enzymes or by boiling with dilute acids.
What are the most important disaccarides in foods?
Sucrose, lactose and maltose.
These disaccharides differ from one another in solubility, sweetness, and other properties.
How is table sugar obtained?
From sugar-cane or sugar-beet
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
How is invert sugar produced?
By hydrolyzing sucrose with the enzyme invertase or with acid, to produce a mixture of glucose + fructose (1:1).
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.
What are the primary sugars in honey?
What ratio do they occur?
Glucose and fructose in a 40:60 ratio
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.
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.
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
How is lactose formed?
By linking glucose and galactose together.
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.
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.
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
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.
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.
What are the primary sugars in maltose?
Two glucose units linked together
How is maltose obtained?
When starch (eg corn starch) is hydrolysed by the enzyme amylase or by heating with dilute acid.
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).
What is the composition of HFCS 42?
HFCS has 42% fructose, 52% glucose and 6% starch.
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.
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.
How is the sweetness of carbohydrates determined?
By their molecular structure and interaction with sensory receptors on the tongue.
Simple sugars vary in their sweetness
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
What is the basis of many hard candy products?
Production of hot supersaturated sugar solutions with controlled crystallization during cooling
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.
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.)
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.
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.
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.
What happens to sugars exposed to high temperatures?
They caramelize!
What do reducing sugars react with in order to produce flavours and colours in food?
Proteins and amino compounds
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.
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.
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.
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!
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.
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.
What are the characteristics and functional properties of agar?
- extracted from seaweed (kelp)
- used as a thickener agent
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.
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.
Where are polysaccharides used in food products generally sourced?
From plant or seaweed sources; a few are from microbial origin.
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.
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.
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.
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.
What is gluten?
Gluten, a protein in wheat flour, traps air bubbles in bread making.
Bread was prepared and photo was taken by Morgan Reid, LFS, UBC. This bread was prepared using a 250-year old sourdough culture
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.
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.
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).
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.
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.
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.
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.
