Samenvatting
Summary Food chemistry WUR
- Instelling
- Wageningen University (WUR)
In deze 'samenvatting' van 70 pagina's heb ik alle learning outcomes van Food Chemistry (WUR) uitgewerkt.
[Meer zien]Voorbeeld 10 van de 70 pagina's
Voorbeeld 10 van de 70 pagina's
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Door: bramdebruin1 • 4 jaar geleden
Voorbeeld van de inhoud
SAMENVATTING FOOD CHEMISTRYINHOUDSOPGAVE
1. Carbohydrates ...................................................................................................................................... 1
2. Proteins .............................................................................................................................................. 26
3. Lipids .................................................................................................................................................. 38
4. Phenolic compounds .......................................................................................................................... 51
5. Enzymes ............................................................................................................................................. 63
1. CARBOHYDRATES
1.2.1
o Know and recognize aldose/ketose, hexose/pentose, pyranose/furanose, /
Aldose: =O is connected to C1
Ketose: =O is connected to C2
Hexose: A monosaccharide with six carbon atoms in the main chain
Pentose: A monosaccharide with five carbon atoms in the main chain
, Pyranose: A six membered ring
Furanose: A five membered ring
: The OH group on the anomeric carbon points up
: The OH group on the anomeric carbon points down.
o Know that D/L-enantiomers are mirror images
D-enatiomer: The secondary hydroxyl group is on the right in the Fisher projection
L-enantiomer: The secondary hydroxyl group is on the left position in the Fisher projection.
o Know and recognize the anomeric carbon in a saccharide
During the formation of a cyclic compound from an aldose or ketose, a new chiral centre is
formed: the anomeric carbon. The anomeric carbon is the carbon atom between two oxygen
atoms: next to the oxygen atom in the ring and connected to another O-atom
o Understand what a reducing sugar is
When the monosaccharide is in the open form, the carbonyl group (C=O) can be oxidized by
for instance Cu2+ ions. In other words, the sugar molecule reduces the CU2+ ion. Therefore,
such a sugar is called a reducing sugar.
o Know the importance of a reducing sugar for reactions
All monosaccharides are reding sugars. Reducing sugars are very reactive at elevated
temperature. They can give rise to two different types of browning reactions: Caramelization
and the Maillard reaction.
o Know what muta-rotation is and the effect it has on the optic rotation
Since reducing sugars can open the ring structure, they convert from on anomeric form into
the other anomeric form via the open chain form. This conversion from one form to another is
called muta-rotation . Via mutarotation the form can change into the form and pyranose
could change into a furanose and vice versa. Mutarotation is temperature dependent.
,o Recognize the general structure of a monosaccharide
Monosaccharides are the simplest unit of carbohydrates. They're composed of carbon,
hydrogen, and oxygen atoms, and they cannot be broken down further since they are already
in their simplest form
o Recognize the difference between the structures of the different
monosaccharides
Glucose
Glucose can be obtained by hydrolysis of starch and is used as a milk
sweetener in foods.
Fructose
Fructose has a high sweetening capacity; it causes less dental caries
than glucose and saccharose and also is more suitable as a diet sugar
for diabetics. The many possibilities of tautomerism (= the
phenomenon that an organic compound can occur in several forms
with different structures that easily convert into one another) are
probably the reason that it is difficult for fructose to crystallize.
, o Know and recognize the general structure of uronic acid
Uronic acids are monosaccharides of which the primary hydroxyl group at C6 is oxidized to a
carboxylic group (CH2OH → COOH). These acids obtain their name by replacing the ending -
ose by the ending -uronic acid. Characteristic for these uronic acids is the fact that the
glycosidic linkage (=linkage between two monosaccharides) is relatively strong, as a result of
which the polymers such as pectin and alginate are quite stable.
o Understand the effect of pH on the charge of uronic acid
Since urnonic acids have a carboxylic acid group they also can have a negative charge
depending on the pH of the food product. In general, at low pH the carboxylic group is
uncharged (COOH) and at pH above 4 the group becomes negatively charged (COO-)
1.2.2
o Know, recognize and be able to draw glycoside linkages
Monosaccharides can be linked to each other via glyosidic linkages and consequently form
oligosaccharides and polysaccharides.
o Know the definition of a disaccharide
A disaccharide is made out of two monosaccharides
, o Understand the systematic name of oligosaccharides
In addition to their trivial name (e.g. saccharose), most oligosaccharides also have a
systematic name. For example the systematic name for saccharose is O--D-glucopyranosyl-
(1-2)--D-fructofuranoside. From this systematic name is clear that
- Saccharose contains two sugars, fructose and glucose
- The sugars are 1-2 linked (C1 of glucose is linked to C2 of fructose)
- Glucose is in the -form and fructose in the -form
o Know the monomeric units of saccharose, lactose and maltose
Saccharose: Glucose + Fructose
Lactose: Galactose + Glucose
Maltose: Glucose + Glucose
o Know what an invert sugar is
Invert sugar is obtained from saccharose by hydrolysis to a 1:1 mixture of glucose and fructose
1.2.3
o Understand the words oligo-, tri-, and tetrasaccharide
Disaccharide: When two monosaccharides are linked the sugar molecule is a disaccharide
Trisaccharide: A saccharide consists of three linked monosaccharides
Tetrasaccharide: A saccharide that consists of four linked monosaccharides
Oligosaccharides: compounds that are composed of 2 to 20 monosaccharides
o Recognize the raffinose family oligosaccharides/-galacto-oligoscaccharides (monomeric
units)
The -galacto-oligoscaccharides, also referred to as
raffinose family oligosaccharides (RFO), naturally
occur in foods such as legumes, tubers and seeds.
These include: raffinose, stachyose and verbascose.
Raffinose is a trisaccharide, stachyose is a
tetrasaccharide and verbascose is a pentasaccharide.
These oligosaccharides can be regarded as a
saccharose molecule which is elongated at the
glucose site with one, two or three -(1-6)-galactosyl
residues. These sugars have no reducing properties. Raffinose
,o Recognize lactose-oligo (GOS, transagalactosyl-oligo)
The lactose-oligosaccharides also belong to the non digestible oligosaccharides (NDO’s). This
group includes lactulose and transgalactosyl-oligosaccharides (GOS). GOS naturally occur in
small quantities in human milk, besides many other types of oligosaccharides.
o Recognize malto-oligosaccharides
The malto-oligosaccharides are formed during the acidic or enzymatic hydrolysis of starch to
starch syrup. -amylase, -amylase, glucoamylases and pullulanes are used in the enzymatic
hydrolysis of starch. The most important malto-oligosaccharides are maltose (disaccharide),
maltotriose (trisaccharide) and maltotetraose (tetrsaccharide)
o Recognize fructo-oligosaccharides (FOS)
Fructo-oligosaccharides (FOS) are present in natural products, such as honey, and in vegetable
raw materials like bananas, asparagus, onions, garlic and wheat.
o Know what starch syrups are
Acid hydrolysis produces starch syrups, with DE-values varying between 20 and 68. The DE
value of glucose is 100 and the DE of starch is 0.
o Know what Dextrose Equivalent is and be able to make calculations with it
During starch degradation for every glycosidic linkage that is cleaved one reducing end is
formed. The degree of starch degradation is usually expressed as “Dextrose Equivalent” (DE).
DE =100* (Concentration of reducing sugards (g/L)/Concentration of total sugars (g/L))
DE = 100* (number of reducing ends/total number of glycosidic units)
o Be able to explain what happens with the Dextrose Equivalent during hydrolysis.
During hydrolysis the amount of reducing ends increases, this means that the amount of
reducing sugars increase to, which causes that the DE increases as well.
,1.2.4
o Recognize N-glycosides (glycosylamines) and know how they are formed
N-Glycosides, also called glycosylamines, are widely distributed in nature. They are formed in
food whenever reducing sugars occur together with proteins, peptides, amino acids or
amines.
N-glycosides are formed by coupling of the carbonyl group of the sugar residue to a primary
amino group of an amino acid, peptide or protein. This is followed by elimination of water and
the formed product (called an imine) cyclizes to an N-glycoside.
o Recognize O-glycosides and know how they are formed
O-glycosides are formed by substitution of the C1 hydroxyl group of a sugar unit with another
hydroxyl group present in a second compound.
1.2.5
o Know what degree of polymerization is
A degree of polymerization indicates the number of monosaccharides in a polysaccharide
o Be able to classify polysaccharides in homo/heteroglycans and linear/branched
Homoglycans: composed of one kind of monomer
Heteroglycans: composed of several kinds of monomers
Linear: Next to each other - •-•- •-•- •-•
, Branched: Also on upper or under side of a molecule - •- •- • -• - • -•
• •
o Know the differences in structure and properties between amylose and cellulose
Cellulose is present in plan cell walls and amylose is one of the components of starch. Both are
glucans (=polymer of glucose). In cellulose the glucose-units are coupled to each other by -
(1-4)-glucosidic linkages, in amylose however by -(1-4)glucosidic linkages. Cellullose is
insoluble and nondigestible for humans. By contrast, amylose is a soluble substance and one
of the most important calorie suppliers to humans. Do to their regular elongated chains,
cellulose molecules can arrange themselves well, as a result of which hydrogen bonds can be
formed between the chains and consequently insoluble micelles are formed. Amylose
molecules dissolve as coils or spirals, however, when a number of molecules or parts of a
molecule chain happen to touch each other, H-bonds can also be formed at the site of
contact. As a result, micelles can be formed and become insoluble (retrogradation) or form a
gel.
o Know what storage polysaccharides and plant cell wall polysaccharides are
Another approach is a classification according to the biological function of the
polysaccharides. The following groups have been defined:
Storage polysaccharides: Starch, dextrins and inulin in plants, glycogen in animals
Plant cell wall polysaccharides (incl. sea algae and algae): Cellulose, hemicellulose, pectin,
algin, carrageenan, agar, etc.
o Know the factors that influence the properties of polysaccharides
The properties of a polysaccharide are determined by the following factors:
- Kind of monosaccharide units from which the macromolecule is built up
- Conformation of this monosaccharide unit (a/b)
- Nature of the glycosidic linkage (for instance 1,4 or 1,6) and the arrangement of
these different linkages in the polymer
- Branching pattern
- Degree of polymerization
- Presence of charged groups (uronic acids)
- Substitution (methylation, acetylation or sulphation) of the monosaccharide units
1.3.1
o Know when crystallization takes place
The solubility of sugars is not unlimited. Solubility means the amount of sugar (dry matter)
that can be completely dissolved in a certain volume of water at a certain temperature. If this
solubility is exceeded, the solution becomes over-saturated and crystallization may occur.
Crystallization means that solid sugar particles are formed in the form of crystals (ordered
structures).
o Know that solubility depends on the kind of sugar and temperature
Lactose is the least soluble of the common sugars (fructose, Sorbitol, Xylitol, Glucose,
Saccharose and lactose). Fructose has the highest solubility (a 90% solution is possible)> A big
, advantage of the use of saccharose is that its solubility hardly depends on temperature. In
general, the solubility of sugars increases if the temperature increases.
1.3.2
o Know the influence of water activity on the reaction rates of lipid oxidation and enzymatic
browning
Food products with a high sugar concentration have a low water activity (or ERH (=equilibrium
relative humidity)). → ERH/100 = aw
The water activity influences the rate of chemical reactions and the growth of
microorganisms. A lowering of the water activity slows down the growth of micro-organisms,
reactions that are catalyzed by enzymes and non enzymatic browning. However, the
autoxidation of fat is accelerated during drying of foods. Foods with an aw value between 0,6
and 0,9 are to a large extent protected against microbial decay.
o Understand the effect of sugar on the water activity
In a sugar solution, the water molecules are bound in the water “jacket” of the sugar molecule
and as a result water is less free or loses the possibilities of free motion. When the
concentration of the sugar increases, more water is bound and less free water is present, so
the water activity decreases and reaches a minimum when the solution is saturated.
o Understand the role of humectants in food
Humectants are additives with a high water-binding capacity. They can be uses lower the
water activity in foods. A number of carbohydrates also belongs to this group. In particular
invert sugar, starch syrups and sorbitol
1.3.3
o Know what the Brix ratio describes
Degrees Brix (symbol °Bx) is the sugar content of an aqueous solution. One degree Brix is 1
gram of sucrose in 100 grams of solution and represents the strength of the solution as
percentage by mass.
o Understand the role of sugar substitutes and intense sweeteners in food
Synthetic sweeteners show the same effect as sugar. It can neutralize a sour taste. Sugar
alcohols and synthetic sweeteners are also added for sweetening of foods, especially in diet
products (diabetics) and low-calorie products. Sugar substitutes are compounds that are
applied in a food as sugar (for their sweet taste) but that are converted in the human body
without the response of insulin.
o Know that sugars, sugar alcohols and intense sweeteners differ in relative sweetness
The relative sweetness of saccharose is 1. That of sugar substitutes is around 0,5/1 while this
relative sweetness of intense sweeteners is between 20 and even 700.
o Know the effect of temperature on the relative sweetness of sugars
The quality and intensity of the taste of sugars do not only depends on their chemical
structure, but also on the temperature, the pH and the presence of other components.
, The temperature dependency of the intensity is very clear in the case of D-fructose.
Sweetness is always compared with saccharose. In general, the relative sweetness decreases
when the temperature increases.
o Know the difference in sweetness and caloric value between sugar substitutes and intense
sweeteners
Important sugar substitutes are the sugar alcohols (sorbitol, xylitol and mannitol) and, to a
certain extent, fructose. These sugar substitutes have a caloric value of about half of that of
sugars. Sweeteners, such as saccharine, cyclamate, acesulfame and aspartame are natural or
synthetic compounds that have an intense sweet taste and have no or little caloric value.
o Know what a sugar alcohol is and how it is formed
Sugar alcohol (sorbitol, xylitol and mannitol). Sugar alcohols have a OH on every C. They can
industrially by hydrogenation of sugars. Sugar alcohols does not consist in a ring structure.
1.3.4
o Know what NDO’s are and what their prebiotic function is
NDO’s are non-digestible oligosaccharides. These oligosaccharides are not degraded by the
digestive enzymes of the gastrointestinal tract and consequently they arrive in the large
intestine undigested. In this way they can play a role as prebiotic. Prebiotics are defined as
compounds that cannot be digested by the human digestive tract (therefore they reach the
large intestine unchanged) and can stimulate the growth and/or activity of a specific set of
health promoting bacteria and such improve the wellbeing of the human/animal.
o Know what dietary fibers are
Dietary fiber includes all soluble and insoluble polysaccharides in a food, with the exception of
starch. All these compounds have in common that they are non-digestible polymers; they do
not have a function as energy source. The most important high fiber raw materials are cereals
and legumes. Dietary fibers would offer protection against a number of diseases of civilization
(diabetes, obesity, constipation etc.)
1.3.5
o Understand which properties of polysaccharides play a role in viscosity
The viscosity of a polymer solution depends on the size and the form of the molecules and the
conformation they will have in the solvent. The greater the freedom of rotation around the
glyosidic linkages in polysaccharides, the more flexible the chains will be. Very flexible
polysaccharide chains occur as random coil, of which the shape is determined by chance.
Linear polymers in solution rotate and bend and consequently take up a lot of space. They
often collide with each other, cause friction, use energy, and consequently give viscosity.
Linear polysaccharides give very viscous solutions, even in low concentrations. Viscosity
depends on the degree of polymerization (molecular weight) as well as the volume, form and
flexibility/stiffness of the dissolved polymer chain. A strongly branched polysaccharide
molecule takes up less space than a linear polysaccharide with the same molecule weight. The
result is that a strongly branched polysaccharide will collide less often and give a lower
viscosity than the linear polysaccharide with the same molecule weight.
Linear polysaccharide chains that contain a negative charge as a result of ionization of a
carboxyl group (pectin, alginate) or a sulphate ester (carrageenan) are shaped as stretched
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