L2 FOOD COMPONENTS AND THEIR CHEMISTRY Flashcards
What are all the physical properties of food?
shape,colour,,size,surface condition,texture
What are the microbiological properties?
Microbial Load.Microbiological load refers to food safety. Any food product should not exceed its legally defined limits of microorganisms.
What are the sensory properties and explain them?
Flavor is a combination of taste and smell.
Aroma is detection of volatile components (smell)
The taste of a food is a combination of five major tastes—salt, sweet, sour, bitter, and umami
Texture refers to those qualities of a food that can be felt with the fingers, tongue, palate, or teeth.
Appearance includes its size, shape, color, structure, transparency or turbidity, dullness or gloss, and degree of wholeness or
damage.
What are Carbohydrates?
The term carbohydrate often means any food that is particularly rich in the complex carbohydrate starch (such as cereals, bread, and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts).
Two types based on functional groups – ketoses and aldoses
What are the classification of carbohydrates with eg?
Monosaccharide 1 unit (glucose,fructose,galactose)
Monosaccharides are water-soluble crystalline compounds. They are aliphatic aldehydes or ketones which contain one carbonyl group and one or more hydroxyl groups.
Disaccharide 2 unit (sucrose lactose)
Oligosaccharide 3-20 units
Polysaccahrides >20 (chitin,cellulose)
Which monosaccharides are hexoses and which are pentoses?
Hexoses:Glucose,Frucotse,Galactose
Pentoses:Arabinose,Xylose
What are the 2 types of polysaccharides(give eg) and explain the bond of the bond that joins the monomers.
Polysaccharides containing all the same monosaccharides are called homopolysaccharides (e.g., starch, cellulose and glycogen are formed from only glucose), whereas those which contain more than one type of monomer are known as heteropolysaccharides (e.g., pectin, hemicellulose and gums).
Glycosidic Bond
• Formed between the free carbonyl group of one monosaccharide and a hydroxyl group of another monosaccharide
What are the 5 functions of carbohydrates and explaiun.
Macronutrient- calories provider Sweeteners and preservatives Body and mouthfeel Fermentation Preservatives
Carbohydrates are energy provider and are counted as macronutrient. Each gram of carbohydrate provides 4 Cal of energy. Three macronutrients are lipids, proteins and carbohydrates.
The most obvious sensory property of sugars such as glucose, fructose, and sucrose is their sweetness, which varies depending on the specific sugar. Lactose (milk sugar) is the least sweet, whereas fructose is the sweetest sugar. Sugars are used as sweeteners in candies and many other food products.
Sugars contribute body and “mouthfeel” to foods. In other words, the addition of sugar makes a food more viscous or gives it a less runny consistency.
If sugar is replaced by a non-nutritive or high intensity sweetener such as aspartame or saccharin, the consistency of the food will be watery and
thin.
They are also metabolized by microorganisms.
This property is important in bread making, where sugar is fermented by yeast cells. The yeast feeds on the sugar, producing carbon dioxide,
which is the leavening agent and causes bread dough to rise before and during baking
At high concentrations, sugars prevent growth of microorganisms, because they reduce the water activity of food to a level below which bacterial growth cannot be supported. Sugars can, therefore, be used as preservatives. Examples of foods preserved in this manner include jams and jellies.
What are reducing sugars?
Sugars that contain a free carbonyl group are known as reducing sugars.
All monosaccharides are reducing sugars.
Disaccharides are reducing sugars only if they contain a free carbonyl group.
Involved in Maillard Reaction.
Which disaccharides are reducing sugars and which are not?
Sucrose is not a reducing sugar because it does not contain a free carbonyl group. The carbonyl groups of glucose and fructose are both involved in the glycosidic bond and are, therefore, not free to take part in other reactions. Maltose, on the other hand, has one carbonyl group involved in the glycosidic bond, and the other carbonyl group is free; thus, maltose is a reducing sugar.
What is sugar inversion?
During the digestive process the sucrose molecule is broken down into the two monosaccharides, glucosee and fructose, which can be easily absorbed.Invert sugar: An equimolar mixture of glucose and fructose, formed by hydrolysis of sucrose, either by acid and heat, or by enzymes such as invertase or sucrase.
Sucrose+ water= hydrolysis = Glucose + Fructose
This is called sugar inversion.(Convert to Monosaccharides)
Sugar inversion is specific to sucrose.
Explain Enzymatic and Non-enzymatic Brownings
Enzymatic Browning
non-desirable oxidation reaction that occurs in foods mainly fruits and vegetables.
Enzyme Responsible for this reaction is polyphenol oxidase.In the presence of PPO enzyme changes substances known as phenolic compounds through oxidation to quinones.
Non Enzymatic Browning
Maillard Reaction and Caramelization.
What is Caramelization?
Browning reaction that can occur with any kind of sugar.
As sugar is heated, water leaves its molecule in the form of Hydrogen and Oxygen. The new molecules have a higher concentration of carbon, creating the distinctive caramel colour.
Sucrose, galactose, and glucose all caramelize at 170°C.
Fructose on the other hand, caramelizes at 110°C
In the first step of caramelization, water evaporates from the sugar. Next, the sugar starts to break down into smaller compounds. Sucrose, for example — also known as table sugar — breaks down into glucose and fructose. From here, like in the Maillard reaction, there’s a condensation process. During this step, the individual sugar compounds react with one another to form hundreds of complicated aromatic compounds. These compounds are what give caramelized foods their signature sweet and nutty taste.
What does sucrose break down to in Caramelization?
Sucrose breaks down into glucose and fructose first. Then it breaks down further into acetic acid which is sour,maltitol has a caramel taste,furan gives a nutty taste.
Explain Maillard Reaction
The marriage of high heat, amino acids, and sugar is responsible for the Maillard reaction. Although it doesn’t seem as if foods such as bread or meat would have sugar in them, even the most savory foods have these naturally occurring carbohydrates.
In the first stage of the reaction, a reducing sugar, such a glucose, condenses with a compound that contains a free amino group, and a chain of amino acids that make up a protein. From there, the sugar-amino acid reaction forms the Amadori rearrangement product, the beginning of a series of more complicated organic reactions.
The product is then the beginning of a series of more complicated reactions.
Show an example reaction between glucose and a amino group.
LOOK IT UP LMAO.
What are the factors that favour Maillard reaction?
High sugar content • High protein concentration • High temperatures • High pH • Low water content
How does sugar crystallization occur?
Water evaporates, increasing the concentration of sugar in the solvent. When sugar reaches a certain concentration, crystallization occurs.Crystallization from a supersaturated solution begins when particles enter the solution (anything even dust)
The size of the crystals depends on how many particles are present and how quickly the crystals grow around them
Why does sugar dissolve in water?
Sugars form molecular solutions due to
hydrogen-bond interchange. When sugar is placed
in water, the water molecules form hydrogen
bonds with the sugar molecules, thus hydrating
them.
How can a supersaturated solution be obtained?
Solubility increases with temperature; thus, a hot
sucrose solution may contain more solute than a
cold one. If a hot saturated sucrose solution is cooled
without disturbance, it will supercool, and a
supersaturated solution will be obtained.
A supersaturated solution contains more solute
than could normally be dissolved at that temperature.
It is unstable, and if stirred or disturbed, the
extra solute will rapidly crystallize out of solution.
What is sugar hydrolysis and give an eg?
Splitting of a compound into smaller parts by the addition of water
This reaction breaks down carbohydrates until they yield the sugars from which they are formed
Glucose syrup is a food syrup, made from the hydrolysis of starch. Glucose syrup is used in foods to soften texture, add volume, prevent crystallization of sugar, and enhance flavor.
Sucrose+ water= hydrolysis = Glucose + Fructose
What is a starch granule?
Starch granules– discrete, spherical aggregates of starch – contain
amylopectin (branched polysaccharaide) + amylose (unbranched polysaccharide)
The arrangement is relatively ordered – crystalline
What is starch gelatinisation?
Starch gelatinisation – when starch is heated with water to the gelatinization temperature, water molecules enter granules, bond between amylose and amylopectin loosened, amylose dissolves out into water, granules swell to produce
a starch paste – thick viscous liquid
Why is starch gelatinisation limited in bread baking?
During the bread baking process, gelatinization of the starch takes place during the oven stage. However, the extent of gelatinization is limited due to the limited amount of water that is present.
What is starch gelation?
Starch gelation – when starch paste is cooled, a solid gel with granules of amylopectin, in gel formed from a network of amylose polymers and water
Pastes from high amylopectin starches (e.g. glutinous rice – virtually no amylose) are non-gelling.(viscous)
Explain the structure of Amylose and Amylopectin in Starch.
Starch is a glucose polymer that contains two types of molecules, known as amylose and amylopectin. Starch is the most abundant constituent and most important reserve polysacchqride of cereals. On a molecular level, its major constituents are the glucose polymers ammylose (25 - 28 %) and amylopectin (72 - 75 %).
Amylose consists of some 500 to 6000 a-(1,4)-linked D-glucopyranosyl units.
amylopectin consists of linear chains of 10 to 100 a-(1,4)-linked D-glycopyranosyl units which are connected by a-(1,6)-linkages, forming a very large and highly branched polysaccharine of up to 3 million glucose units
Both are long chains of glucose molecules joined by α-1,4-glycosidic bonds; however, amylose is a linear chain, whereas amylopectin contains branches. The branches make amylopectin less soluble in water than amylose.
Draw Amylose and Amylopectin Structure.
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Explain the full steps of the gelatinization process
The gelatinization temperature is reached— approximately 140–160 F (60–71 C), depending upon the starch type, and is completed at 190–194 oF (88–90 C), or higher.
Water is able to penetrate further into the starch granule and swelling takes place. Sufficient water must be present to enter and enlarge the starch granule.
Diffusion of some amylose chains occurs as they leach out of the starch granules.
Granule swelling increases as the temperature increases. The larger starch granules are the first to swell.
• Swollen granules take up more space and the mixture thickens as the enlarged granules leach amylose and possibly amylopectin.
• The starch paste continues to become thicker, more viscous, and resistant to flow as it gelatinizes.
Give examples of lipids.
Examples of common lipids include butter, vegetable oil, cholesterol and other steroids, waxes, phospholipids, and fat-soluble vitamins
What is the smallest fatty acid?
butyric acid is the smallest fatty acid, having four carbon atoms, and it is found in butter.
What is a fatty acid?
Fatty acids are long hydrocarbon chains, with a methyl group (CH3) at one end of the chain and a carboxylic acid group (COOH) at the other.
What are the characteristics of unsaturated and saturated fatty acids?
Characteristics of saturated fatty acids/fats:
solid at room temperature with a high melting point.
Linear structure
Characteristics of unsaturated fatty acids/fats:
Liquid at room temp.
Low melting point
Give eg of monounsaturated, polyunsaturated and saturated fatty acids.
Oleic acid CH3(CH2)7CH=CH(CH2)7COOH
Unsaturated fatty acid
linoleic and linolenic acids, contain two or more double bonds
Palmitic acid CH3(CH2)14COOH
Saturated fatty acid
Explain cis or trans fatty acids.
The double bonds in fatty acids occur in either the cis or the trans configuration.
In the cis form, the hydrogen atoms attached to the carbon atoms of the double bond are located on the same side of the double bond.
In the trans configuration of the isomer, the hydrogen atoms are located on opposite sides of the double bond, across from one another.
Melting point: The trans double bonds have a higher melting point than the cis configurations
2) A cis double bond causes a kink (bend) in the chain.
Some other important points:
1) Almost all naturally occurring fats and oils that are used in food exist in the cis configuration.
2) Vaccenic acid is a naturally occurring trans-fatty acid found in small amounts in the fat of ruminants and in dairy products such as milk, butter, and yogurt.
Explain hydrogenation and its purpose.
Hydrogenation is the process of adding hydrogen to unsaturated fatty acids to reduce the number of double bonds. Hydrogenation of unsaturated fatty acid occurs when hydrogen gas is reacted with oil under controlled conditions of temperature and pressure and in the presence of a nickel, copper, or other catalyst. The reaction is carefully controlled and stopped when the desired extent of hydrogenation has been reached. As the reaction progresses, there is a gradual production of trans-fatty acids which increases the melting point of the fat or oil and creates a more solid product.
Purpose:
Increase melting point of fats
Increase fat stability by retarding rancidity of fats. Higher is the unsaturation of fats, faster is the rancidity process.
Improves oxidative stability
What are proteins?
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form in a biologically functional way.
What is protein denaturation?
Denaturation is the change in the secondary, tertiary, and/or quaternary structure of a protein. There is no change in the primary structure. In other words, denaturation does not involve breaking of peptide bonds. The protein unfolds, yet there is no change in its amino acid sequence.
What are some desirable denaturation reactions?
Heating beaten egg white foams to form meringues
Adding acid to milk to form cottage cheese
Inactivating enzymes by heating to slow down vegetable spoilage
What are some undesirable denaturation reactions?
Loss of protein functionality, specially in milk proteins, where denatured proteins due to heat processing conditions reduces its bioavailability to body.
