2. GENETİCALLY MODİFİED FOODS
2.1.Introduction
Generally, this term refers to food crops that have been altered using a variety of
molecular biology techniques in order to provide them with either new or enhanced
characteristics. Examples of such enhancements of modifications are herbicide
tolerance, pesticide resistance, greater nutritional content or increased tolerance of cold
temperatures. Genetically modified organisms (GMOs) can also be referred to as
transgenic organisms. Transgenic simply means that the organism's genes come from
more than one source.
The idea of enhancing desired traits in food crops is not new. Upon
domestication of many plants, farmers used the process of artificial selection to grow
plants with desired qualities. However this method can be time consuming and it is very
difficult to introduce new traits into a specific population. In contrast, using genetic
engineering, scientists can take the gene that controls the trait from one organism and
insert it into another organism that does not have the gene. This creates an organism
with the desired characteristic quickly and easily. A common example of genetic
engineering is the insertion of Bacillus thuringiensis genes into corn to make Bt corn.
Bacillus thuringiensis is a bacterium that naturally produces a protein that is lethal to
insect larvae. By transferring the genes that encode this protein into corn, scientists have
created a type of corn that produces its own pesticides, making it resistant to insects
such as the European corn borer.
Transferring the gene
Taking a gene from one organism and inserting it into another is essentially a
process of cutting the gene which codes for the trait of interest from the foreign
organism and pasting this gene into the genome of the organism that you want to alter.
Insertion of B. thuringiensis genes into corn as an example. In order to cut out
the gene of interest in the bacteria, its total DNA is isolated. Special enzymes, called
restriction endonucleases, act as scissors to cut out the desired gene. These enzymes are
sensitive to the DNA sequence and will only cut DNA at specific spots. There are many
1
different enzymes that cut in different places, so the enzyme used depends on the
sequence of DNA surrounding the desired gene.
Once the gene is cut out, scientists must make an "expression cassette." This
consists of additional DNA surrounding the gene so that the corn cell knows where the
gene of interest begins and ends. The part that tells the corn cell where the gene begins
is called the promoter and the end, the terminator. Once the expression cassette has been
made, it is inserted into a plasmid. The plasmid is a parasitic circle of DNA present in
bacteria. By putting the cassette into a plasmid, millions of copies of it can be made.
These copies are then introduced into the host cell and get inserted into the genome.
Cells which have successfully incorporated the foreign gene into their genome are then
expanded in cell culture and used to generate new plants.
General schematic of GM crop production
2
The ethics of GM Foods
GM foods have been the subject of much controversy. Advocates feel that GM
foods will help provide food to the world's continually expanding population. Since the
number of people on earth keeps increasing (over 6 billion, and expected to double
within 50 years), and the amount of land suitable for farming remains constant, more
food must be grown in the same amount of space. Genetic engineering can make plants
that will give farmers better yields through several different methods.
Crops can be harmed or destroyed by many different factors. Insects, weeds,
disease, cold temperatures and drought can all adversely affect plants resulting in lower
yields for the farmer. Genetic engineering techniques can be used to introduce genes,
creating plants that are resistant or tolerant to these factors. Bt corn is an example of the
introduction of a pest resistance gene. The weed-killer can be sprayed over the entire
crop, killing all plants except the transgenic crop intended to be grown. Scientists have
also taken a gene from a cold-water fish and introduced it into potatoes to protect the
seedlings against sudden frost. These methods all create plants that are more likely to
survive and be healthy, thereby increasing the production of farmer's fields.
Genetic modification can also be used to change the properties of the crop,
adding nutrients, making them taste better, or reducing the growing time. A good
example of adding nutrients to food is the development of "golden" rice. Many
countries in the world rely on rice as their primary food source. Unfortunately, rice is
missing many essential vitamins and minerals, so people whose diet is based on rice are
often malnourished. One of the most severe consequences of this is blindness caused by
vitamin A deficiency. Researchers at the Swiss Federal Institute of Technology Institute
for Plant Sciences genetically engineered rice, making it high in vitamin A.
Golden rice is a controversial subject in its own right. Its development was a
breakthrough for biotechnology as it was the first time 3 genes were introduced
simultaneously (generally, only one gene is transferred at a time). Mammals make
vitamin A from beta-carotene, which is not found in polished white rice. A precursor to
beta-carotene (geranyl geranyl diphosphate, or GGPP) is present, but three additional
chemical reactions must be carried out to transform GGPP into beta-carotene. The gene
3
transfer was successful, resulting in rice that is high in beta-carotene and is actually
yellow coloured. On the surface, this seems like the solution to vitamin A deficiency.
Enzymes required for Vitamin A metabolism
Opponents of genetic modification have many criticisms against this new
technology. First of all there are multiple environmental concerns. GM foods can cause
harm to other organisms unintentionally. For example, a study published in Nature on
Bt corn found that the pollen caused high mortality rates in monarch butterfly
caterpillars, even though the caterpillars don't eat corn. If the Bt corn pollen is blown
onto neighbouring milkweed plants (the caterpillars food source) the caterpillars could
eat the pollen and die. The results of this study are under debate, since the experiments
were not done in the field, but in a laboratory, and new studies suggest that the original
may be flawed. Researchers at the University of Guelph performed a study and found
that under natural conditions, Bt corn does not pose a risk to the monarch butterfly.
Similarly, if pollen is blown onto neighbouring plants, the plants could
crossbreed and the introduced gene could be transferred to non-target plants. This is a
concern if a herbicide resistant crop were to breed with a weed and transfer the
herbicide resistance gene. This would create a weed that is unharmed by the chemicals
used to kill it.
4
Along with environmental concerns, there are also worries about the effects that
GM foods can have on humans. There are concerns that introducing a new gene into a
food could cause an allergic reaction in some people.
2.1.1. Macronutrients Of Foods - Fats, Oils, Fatty Acids, Triglycerides Chemical Structure
Lipids consist of numerous fatlike chemical compounds that are insoluble in
water but soluble in organic solvents. Lipid compounds include monoglycerides,
diglycerides, triglycerides, phosphatides, cerebrosides, sterols, terpenes, fatty alcohols,
and fatty acids. Dietary fats supply energy, carry fat-soluble vitamins (A, D, E, K), and
are a source of antioxidants and bioactive compounds. Fats are also incorporated as
structural components of the brain and cell membranes.
Common Fatty Acids
Chemical Names and Descriptions of some Common Fatty Acids
Carbon Double
Common Name
Scientific Name
Atoms Bonds
Butyric acid
4
0
butanoic acid
Caproic Acid
6
0
hexanoic acid
Caprylic Acid
8
0
octanoic acid
Capric Acid
10
0
decanoic acid
Lauric Acid
12
0
dodecanoic acid
Myristic Acid
14
0
tetradecanoic acid
Palmitic Acid
16
0
hexadecanoic acid
Palmitoleic Acid
16
1
9-hexadecenoic acid
Stearic Acid
18
0
octadecanoic acid
Oleic Acid
18
1
9-octadecenoic acid
Vaccenic Acid
18
1
11-octadecenoic acid
Linoleic Acid
18
2
9,12-octadecadienoic acid
Alpha-Linolenic
Acid
18
3
9,12,15-octadecatrienoic acid
(ALA)
Gamma-Linolenic Acid
18
3
6,9,12-octadecatrienoic acid
(GLA)
Sources
butterfat
butterfat
coconut oil
coconut oil
coconut oil
palm kernel oil
palm oil
animal fats
animal fats
olive oil
butterfat
safflower oil
flaxseed (linseed)
oil
borage oil
peanutoil,
fish oil
fish oil
liver fats
Arachidic Acid
20
0
eicosanoic acid
Gadoleic Acid
Arachidonic Acid (AA)
20
20
1
4
9-eicosenoic acid
5,8,11,14-eicosatetraenoic acid
EPA
20
5
5,8,11,14,17-eicosapentaenoic acid fish oil
5
Behenic acid
Erucic acid
22
22
0
1
DHA
22
6
Lignoceric acid
24
0
docosanoic acid
13-docosenoic acid
4,7,10,13,16,19-docosahexaenoic
acid
tetracosanoic acid
rapeseed oil
rapeseed oil
fish oil
Small
amounts
in most fats
Fatty acids consist of the elements carbon (C), hydrogen (H) and oxygen (O)
arranged as a carbon chain skeleton with a carboxyl group (-COOH) at one end.
Saturated fatty acids (SFAs) have all the hydrogen that the carbon atoms can hold, and
therefore, have no double bonds between the carbons. Monounsaturated fatty acids
(MUFAs) have only one double bond. Polyunsaturated fatty acids (PUFAs) have more
than one double bond.
Butyric Acid
Butyric acid (butanoic acid) is one of the saturated short-chain fatty acids
responsible for the characteristic flavor of butter. This image is a detailed structural
formula explicitly showing four bonds for every carbon atom and can also be
represented as the equivalent line formulas:
CH3CH2CH2COOH or CH3(CH2)2COOH
The numbers at the beginning of the scientific names indicate the locations of
the double bonds. By convention, the carbon of the carboxyl group is carbon number
one. Greek numeric prefixes such as di, tri, tetra, penta, hexa, etc., are used as
multipliers and to describe the length of carbon chains containing more than four atoms.
Thus, "9,12-octadecadienoic acid" indicates that there is an 18-carbon chain (octa deca)
with two double bonds (di en) located at carbons 9 and 12, with carbon 1 constituting a
carboxyl group (oic acid) . The structural formula corresponds to:
6
CH3CH2CH2CH2CH2CH=CHCH2CH=CHCH2CH2CH2CH2CH2CH2CH2COOH
9,12-octadecadienoic acid (Linoleic Acid)
which would be abbreviated as:
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Fatty acids are frequently represented by a notation such as C18:2 that indicates
that the fatty acid consists of an 18-carbon chain and 2 double bonds. Although this
could refer to any of several possible fatty acid isomers with this chemical composition,
it implies the naturally-occurring fatty acid with these characteristics, i.e., linoleic acid.
When two double bonds are separated by one single bond they are said to be
"conjugated". The term "conjugated linoleic acid" (CLA) refers to several C18:2
linoleic acid variants such as 9,11-CLA and 10,12-CLA which correspond to 9,11octadecadienoic acid and 10,12-octadecadienoic acid.
2.1.2 Fatty Acid Configurations
2.1.2.1
Trans Fats
Double bonds bind carbon atoms tightly and prevent rotation of the carbon
atoms along the bond axis. This gives rise to configurational isomers which are
arrangements of atoms that can only be changed by breaking the bonds.
Cis-9-octadecenoic acid
(Oleic acid)
Trans-9-octadecenoic acid
(Elaidic acid)
7
These three-dimensional molecular projections show the Cis and Trans
configurational isomers of 9-octadecenoic acid with the hydrogen atoms shown in blue.
The Latin prefixes Cis and Trans describe the orientation of the hydrogen atoms with
respect to the double bond. Cis means "on the same side" and Trans means "across" or
"on the other side". Naturally occurring fatty acids generally have the Cis configuration.
The natural form of 9-octadecenoic acid (oleic acid) found in olive oil has a "V" shape
due to the Cis configuration at position 9. The Trans configuration (elaidic acid) looks
more like a straight line.
Cis
Trans
Configuration Configuration
2.1.2.2
Omega-3 and Omega-6 Fatty Acids
Omega-3 (ω3) and omega-6 (ω6) fatty acids are unsaturated "Essential Fatty
Acids" (EFAs) that need to be included in the diet because the human metabolism
cannot create them from other fatty acids. Since these fatty acids are polyunsaturated,
the terms n-3 PUFAs and n-6 PUFAs are applied to omega-3 and omega-6 fatty acids,
respectively. These fatty acids use the Greek alphabet (α,β,γ,...,ω) to identify the
location of the double bonds. The "alpha" carbon is the carbon closest to the carboxyl
group (carbon number 2), and the "omega" is the last carbon of the chain because
omega is the last letter of the Greek alphabet. Linoleic acid is an omega-6 fatty acid
because it has a double bond six carbons away from the "omega" carbon. Similarly,
alpha-linolenic acid is an omega-3 fatty acid because it has a double bond three carbons
away from the "omega" carbon. By subtracting the highest double-bond locant in the
scientific name from the number of carbons in the fatty acid we can obtain its
classification. For arachidonic acid, we subtract 14 from 20 to obtain 6; therefore, it is
an omega-6 fatty acid. This type of terminology is sometimes applied to oleic acid
which is an omega-9 fatty acid.
8
In these simplified structural formulas of unsaturated fatty acids, each angle
represents a carbon atom. Notice that all the double bonds have the Cis configuration.
DHA (docosahexaenoic acid) and AA (arachidonic acid) are both crucial to the
optimal development of the brain and eyes. The importance of DHA and AA in infant
nutrition is well established, and both substances are routinely added to infant formulas.
Excessive amounts of omega-6 polyunsaturated fatty acids and a very high omega6/omega-3 ratio have been linked with pathogenesis of many diseases, including
cardiovascular disease, cancer, and inflammatory and autoimmune diseases. The ratio of
omega-6 to omega-3 in modern diets is approximately 15:1, whereas ratios of 2:1 to 4:1
have been associated with reduced mortality from cardiovascular disease, suppressed
inflammation in patients with rheumatoid arthritis, and decreased risk of breast cancer.
2.1.2.3
Triglycerides
Triglycerides are the main constituents of vegetable oils and animal fats.
Triglycerides have lower densities than water (they float on water), and at normal room
temperatures may be solid or liquid. When solid, they are called "fats" or "butters" and
when liquid they are called "oils". A triglyceride, also called triacylglycerol (TAG), is a
chemical compound formed from one molecule of glycerol and three fatty acids.
9
Oleic Acid
Glycerol or Glycerin
Glycerol is a trihydric alcohol (containing three -OH hydroxyl groups) that can
combine with up to three fatty acids to form monoglycerides, diglycerides, and
triglycerides. Fatty acids may combine with any of the three hydroxyl groups to create a
wide diversity of compounds. Monoglycerides, diglycerides, and triglycerides are
classified as esters which are compounds created by the reaction between acids and
alcohols that release water (H2O) as a by-product.
C18:1
C18:1
C16:0
C18:0
C18:0
C18:0
The triglyceride structural formula on the left is typical of olive oil. It consists of
two radicals of oleic acid and one of palmitic acid attached to glycerol (the vertical
carbon chain). The small squares represent the fatty acid components of the glyceride
molecules. The picture on the right shows the three-dimensional molecular structure of
10
tristearin, a triglyceride with three stearic acid radicals. Oxygen atoms are shown in red,
carbon atoms as dark gray, and hydrogen atoms as blue. Tristearin is found as a minor
component in many natural fats.
Soap is made traditionally by heating an alkali like sodium hydroxide (NaOH)
with animal fat. The chemical reaction (hydrolysis) produces glycerol and soap, which
consists of the sodium salts of the fatty acids, e.g., sodium stearate (CH3(CH2)16C(O)ONa+).
C18:1
C16:0
1,3-diglyceride
C16:0
1-monoglyceride
A diglyceride, or diacylglycerol (DAG), has two fatty acid radicals and exists in
the 1,2 form and the 1,3 form depending on how the fatty acids are attached to the
glycerol molecule. A monoglyceride, or monoacylglycerol (MAG), has only one fatty
acid radical per molecule of glycerol. The fatty acid may be attached to carbon 1 or 2 of
the glycerol molecule.
All esters of glycerol and fatty acids are metabolized in the same way.
Monoglycerides, diglycerides, and triglycerides all have 9 Calories per gram, but some
nutrition labels hide the calories of mono- and diglycerides under the contention that
"fat" consists only of triglycerides.
Artificial fats and fat substitutes have become more common as manufacturers
target people who through misinformation have acquired aversions to fats or who would
like to diet without reducing food intake. Olestra is an artificial fat created from sucrose
(a carbohydrate) and up to eight fatty acids. In the olestra chemical structure, sucrose
takes the place of glycerol. The olestra molecule is too large to be metabolized and
passes through the body unchanged, but because it acts as a lipid, it can cause depletion
11
of fat-soluble vitamins. Polyglycerol fatty acid esters (glyceran fatty acid esters) are
mixtures of the esters of fatty acids with polyglycerol. These compounds have the
general structure R-(OCH2-CH(OR)-CH2O)n-R, where R represents fatty acids and the
average value of n is about 3. Polyglycerol fatty acid esters are almost completely
metabolized like fats, so they are not calorie-free. The polymerized glycerol moiety is
not digested and is excreted primarily in the urine. The main purpose of these
compounds is to create products that are technically "fat free" and whose calories and
fatty acid compositions are not reported on the Nutrition Facts of food labels.
Fatty acid composition of some common edible fats and oils
Percent by weight of total fatty acids
Mono
Poly
unsaturated unsaturated
Saturated
Oil or Fat
Unsat
./Sat. Capric Lauric
Acid
ratio Acid
C10:0 C12:0
Myristic Palmitic Stearic Oleic
Acid
Acid
Acid
Acid
C14:0
C16:0
C18:0
C18:1
Linoleic
Alpha
Acid
Linolenic
(ω6)
Acid (ω3)
C18:3
C18:2
Almond Oil
9.7
-
-
-
7
2
69
17
-
Beef Tallow
0.9
-
-
3
24
19
43
3
1
Butterfat (cow)
0.5
3
3
11
27
12
29
2
1
Butterfat (goat)
0.5
7
3
9
25
12
27
3
1
Butterfat (human) 1.0
2
5
8
25
8
35
9
1
Canola Oil
15.7 -
-
-
4
2
62
22
10
Cocoa Butter
0.6
-
-
-
25
38
32
3
-
Cod Liver Oil
2.9
-
-
8
17
-
22
5
-
Coconut Oil
0.1
6
47
18
9
3
6
2
-
Corn Oil
6.7
-
-
-
11
2
28
58
1
Cottonseed Oil
2.8
-
-
1
22
3
19
54
1
Flaxseed Oil
9.0
-
-
-
3
7
21
16
53
Grape seed Oil
7.3
-
-
-
8
4
15
73
-
Lard (Pork fat)
1.2
-
-
2
26
14
44
10
-
12
Olive Oil
4.6
-
-
-
13
3
71
10
1
Palm Oil
1.0
-
-
1
45
4
40
10
-
Palm Olein
1.3
-
-
1
37
4
46
11
-
Palm Kernel Oil
0.2
4
48
16
8
3
15
2
-
Peanut Oil
4.0
-
-
-
11
2
48
32
-
Safflower Oil
10.1 -
-
-
7
2
13
78
-
Sesame Oil
6.6
-
-
-
9
4
41
45
-
Soybean Oil
5.7
-
-
-
11
4
24
54
7
Sunflower Oil
7.3
-
-
-
7
5
19
68
1
Walnut Oil
5.3
-
-
-
11
5
28
51
5
Percentages may not add to 100% due to rounding and other constituents not
listed.
Where percentages vary, average values are used.
Fatty acid compositions depend on the sources of the oils. Canola oil is made
from selectively bred rapeseed plants that contain less than 2% erucic acid. Some crops
have produced canola oil with 76% oleic acid. The table lists the linoleic type of
safflower oil; oleic types of safflower oil have approximately 78% monounsaturated,
15% polyunsaturated, and 7% saturated fatty acids. Not shown in this table: Coconut
oil, also called copra oil, has 8% caprylic acid (C8:0). Cod liver oil has 7% palmitoleic
acid (C16:1), 17% C20 unsaturated fatty acids (10% EPA), and 11% C22 unsaturated
fatty acids (6% DHA). Peanut oil has approximately 5% of C22:0 and C24:0 fatty acids.
Palm olein is the liquid fraction obtained by the fractionation of palm oil after
crystallization at controlled temperatures. Cow butterfat has 4% butyric (C4:0) and 2%
caproic (C6:0) acids. Goat butterfat has 4% butyric (C4:0), 3% caproic (C6:0), and 3%
caprylic (C8:0) acids. Beef tallow, cow butterfat, human butterfat, and lard all have
about 3% palmitoleic acid (C16:1). Human depot fat, usually found in the abdomen of
men and around the thighs and hips of women, has a composition similar to lard.
2.1.2.3.1
The triglyceride profiles of these fats and oils
The percentages in the table above reflect the overall proportions of the fatty
acid radicals in the triglycerides. If we had 33 representative triglyceride molecules
containing 99 fatty acid radicals, the number of each fatty acid radical in these 33
molecules would be proportional to its percentage in the table. For example, 33
representative molecules of lard triglycerides would contain, on average, 26 radicals of
palmitic acid (C16:0), 14 radicals of stearic acid (C18:0), 44 radicals of oleic acid
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(C18:1), and 10 radicals of linoleic acid (C18:2). These fatty acid radicals would be
distributed randomly among the 33 triglyceride molecules. The typical lard triglyceride
molecule would have one or two radicals of oleic acid and one radical of palmitic acid.
Frequently, there would be triglycerides with one radical each of oleic, palmitic, and
stearic acids. Only rarely would one encounter triglycerides with only palmitic and
stearic acid radicals.
Triglyceride profile for lard.
Each square represents the fatty acid components of a representative triglyceride
molecule.
C16:0
C18:0
C16:0
C18:1
C18:0
C18:2
C18:0
C18:0
C16:0
C18:1
C18:1
C18:1
C16:1
C16:0
C18:1
C18:2
C16:0
C18:1
C18:1
C16:0
C18:1
C18:2
C16:0
C18:2
C18:1
C18:2
C18:1
C18:1
C18:1
C18:1
C16:0
C16:0
C18:0
C18:1
C18:0
C16:0
C18:2
C18:1
C18:0
C18:2
C18:1
C16:0
C18:1
C18:1
C18:1
C18:1
C16:0
C18:1
C16:1
C16:0
C18:1
C18:1
C16:0
C18:1
C16:0
C16:0
C18:0
C18:1
C18:2
C18:2
C18:1
C18:1
C18:1
C18:0
C18:1
C18:1
C18:1
C14:0
C18:0
C16:0
C16:0
C18:1
C18:0
C16:0
C18:1
C18:1
C16:0
C18:1
C18:0
C18:0
C16:0
C16:1
C18:1
C16:0
C18:1
C16:0
C16:0
C18:1
C16:0
C16:0
C20:1
C18:1
C18:0
C18:2
C18:1
C14:0
C18:1
C18:1
C18:1
This profile was constructed using a random distribution of the appropriate
percentages of the fatty acids in 33 representative triglyceride molecules. Red is used
for saturated, green for monounsaturated, and blue for polyunsaturated fatty acids.
Although the composition of the individual triglyceride molecules may vary, the
relative proportion of fatty acids remains constant. The profiles for canola oil or olive
oil would be mostly green and blue with very little red, whereas the profile for coconut
oil would be mostly red.
Metabolism of Fats
14
Metabolism of natural C20 Cis fatty acids produces powerful eicosanoids.
2.1.2.4
Proteins/Aminoacids
Proteins consist of amino acids which are characterized by the -CH(NH2)COOH
substructure. Nitrogen and two hydrogens comprise the amino group, -NH2, and the
acid entity is the carboxyl group, -COOH. Amino acids link to each when the carboxyl
group of one molecule reacts with the amino group of another molecule, creating a
peptide bond -C(=O)NH- and releasing a molecule of water (H2O). Amino acids are the
basic building blocks of enzymes, hormones, proteins, and body tissues. A peptide is a
compound consisting of 2 or more amino acids. Oligopeptides have 10 or fewer amino
acids. Polypeptides and proteins are chains of 10 or more amino acids, but peptides
consisting of more than 50 amino acids are classified as proteins.
In the animal kingdom, peptides and proteins regulate metabolism and provide
structural support. The cells and the organs of our body are controlled by peptide
hormones (see table below). Insufficient protein in the diet may prevent the body from
producing adequate levels of peptide hormones and structural proteins to sustain normal
bodily functions. Deficiency of good quality protein in the diet may contribute to
seemingly unrelated symptoms such as sexual dysfunction, blood pressure problems,
fatigue, obesity, diabetes, frequent infections, digestive problems, and bone mass loss
leading to osteoporosis. Severe restriction of dietary protein causes kwashiorkor which
is a form of malnutrition characterized by loss of muscle mass, growth failure, and
decreased immunity.
15
Allergies are generally caused by the effect of foreign proteins on our body.
Proteins that are ingested are broken down into smaller peptides and amino acids by
digestive enzymes called "proteases". Allergies to foods may be caused by the inability
of the body to digest specific proteins. Cooking denatures (inactivates) dietary proteins
and facilitates their digestion. Allergies or poisoning may also be caused by exposure to
proteins that bypass the digestive system by inhalation, absorption through mucous
tissues, or injection by bites or stings. Spider and snake venoms contain proteins that
have a variety of neurotoxic, proteolytic, and hemolytic effects.
Many structures of the body are formed from protein. Hair and nails are made of
keratins which are long protein chains containing a high percentage (15%-17%) of the
amino acid cysteine. Keratins are also components of animal claws, horns, feathers,
scales, and hooves. Collagen is the most common protein in the body and comprises
approximately 20-30% of all body proteins. It is found in tendons, ligaments, and many
tissues that serve structural or mechanical functions. Collagen consists of amino acid
sequences that coil into a triple helical structure to form very strong fibers. Glycine and
proline account for about 50% of the amino acids in collagen. Gelatin is produced by
boiling collagen for a long time until it becomes water soluble and gummy. Tooth
enamel and bones consist of a protein matrix (mostly collagen) with dispersed crystals
of minerals such as apatite, which is a phosphate of calcium. Muscle tissue consists of
approximately 65% actin and myosin, which are the contractile proteins that enable
muscle movement. Casein is a nutritive phosphorus-containing protein present in milk.
It makes up approximately 80% of the protein in milk and contains all the common
amino acids.
2.1.2.4.1
Amino Acids
Naturally occurring amino acids, their abbreviations, and structural formulas
*Essential amino acids
Ala = alanine
CH3CH(NH2)COOH
Arg = arginine
H2N-C(=NH)NHCH2CH2CH2CH(NH2)COOH
Asn = asparagine
H2N-C(=O)CH2CH(NH2)COOH
Asp = aspartic acid
HOOC-CH2CH(NH2)COOH
Cys = cysteine
Gln = glutamine
16
HS-CH2CH(NH2)COOH
H2N-C(=O)CH2CH2CH(NH2)COOH
Glu = glutamic acid
HOOC-CH2CH2CH(NH2)COOH
Gly = glycine
H2N-CH2COOH
His = histidine*
Ile = isoleucine*
CH3CH2CH(CH3)CH(NH2)COOH
Leu = leucine*
Lys = lysine*
CH3CH(CH3)CH2CH(NH2)COOH H2N-CH2CH2CH2CH2CH(NH2)COOH
Phe = phenylalanine*
Met = methionine*
CH3-S-CH2CH2CH(NH2)COOH
Pro = proline
Ser = serine
HOCH2CH(NH2)COOH
Trp = tryptophan*
Thr = threonine*
CH3CH(OH)CH(NH2)COOH
Tyr = tyrosine
Val = valine*
CH3CH(CH3)CH(NH2)COOH
The term "essential amino acid" refers to an amino acid that is required to meet
physiological needs and must be supplied in the diet. Arginine is synthesized by the
body, but at a rate that is insufficient to meet growth needs. Methionine is required in
large amounts to produce cysteine if the latter amino acid is not adequately supplied in
the diet. Similarly, phenylalanine can be converted to tyrosine, but is required in large
quantities when the diet is deficient in tyrosine. Tyrosine is essential for people with the
disease phenylketonuria (PKU) whose metabolism cannot convert phenylalanine to
tyrosine. Isoleucine, leucine, and valine are sometimes called "branched-chain amino
acids" because their carbon chains are branched.
2.1.2.4.1.1
Stereochemistry
17
In all twenty amino acids, except glycine, the carbon atom with the amino group
is attached to four different substituents. The tetrahedral bond angles of carbon and the
asymmetry of the attachments make it possible for amino acids to have two nonsuperimposable structures, the L and R forms, which are mirror images of each other.
Only L-amino acids are found in proteins. L-amino acids have the amino group to the
left when the carboxyl group is the top, as illustrated here. The wedge bonds are above
the display plane and the dotted bonds are below the display plane.
L-Alanine
2.1.2.4.1.2
Formation of a peptide from two amino acids
18
This illustration shows the reaction of two amino acids, where R and R' are any
functional groups from the table above. The blue circle shows the water (H2O) that is
released, and the red circle shows the resulting peptide bond (-C(=O)NH-).
The reverse reaction, i.e., the breakdown of peptide bonds into the component
amino acids, is achieved by hydrolysis. Many commercial food products use hydrolyzed
vegetable proteins as flavoring agents. Soy sauce is produced by hydrolyzing soybean
and wheat protein by fungal fermentation or by boiling with acid solutions.
Monosodium glutamate (MSG), a flavor enhancer, is a sodium salt of glutamic acid that
is found naturally in seaweed and fermented soy products.
2.1.2.4.1.3
Amino acid profiles of food proteins
The following table shows representative amino acid profiles of some common
foods and dietary protein supplements. The percentages are averages of several
commercial products. Casein and whey are milk proteins. Casein is the protein that
precipitates from milk when curdled with rennet; it is the basis for making cheese.
Whey is the watery part of milk that remains after the casein is separated.
Percentage (%) by weight of amino acid
Amino Acid
Alanine
Arginine
aspartic acid
Cysteine
glutamic acid
Glycine
histidine *
isoleucine *
leucine *
protein
egg white
6.6
5.6
8.9
2.5
13.5
3.6
2.2
6.0
8.5
beef
6.1
6.5
9.1
1.3
15.0
6.1
3.2
4.5
8.0
chicken
5.5
6.0
8.9
1.3
15.0
4.9
3.1
5.3
7.5
19
whey
5.2
2.5
10.9
2.2
16.8
2.2
2.0
6.0
9.5
casein
2.9
3.7
6.6
0.3
21.5
2.1
3.0
5.1
9.0
soy yeast
4.2 8.3
7.5 6.5
11.5 9.8
1.3 1.4
19.0 13.5
4.1 4.8
2.6 2.6
4.8 5.0
8.1 7.1
lysine *
methionine *
phenylalanine *
Proline
Serine
threonine *
tryptophan *
Tyrosine
valine *
6.2
3.6
6.0
3.8
7.3
4.4
1.4
2.7
7.0
8.4
2.6
3.9
4.8
3.9
4.0
0.7
3.2
5.0
8.5
2.8
4.0
4.1
3.4
4.2
1.2
3.4
5.0
8.8
1.9
2.3
6.6
5.4
6.9
2.2
2.7
6.0
3.8
2.7
5.1
10.7
5.6
4.3
1.3
5.6
6.6
6.2
1.3
5.2
5.1
5.2
3.8
1.3
3.8
5.0
6.9
1.5
4.7
4.0
5.1
5.8
1.6
5.0
6.2
* Essential amino acids
Egg white protein is considered to have one of the best amino acids profiles for
human nutrition. Plant proteins generally have lower content of some essential amino
acids such as lysine and methionine. Soy protein is one of the best plant proteins, but
nevertheless, the most prominent difference in this chart is the proportion of the
essential sulfur-containing amino acid methionine. Egg white protein has approximately
three times more methionine than is found in soy protein. The yeast information is for
"brewer's yeast" (Saccharomyces Cervisiae).
2.1.2.5
Carbonhydates / Sugars
Carbohydrates consist of the elements carbon (C), hydrogen (H) and oxygen (O)
with a ratio of hydrogen twice that of carbon and oxygen. Carbohydrates include sugars,
starches, cellulose and many other compounds found in living organisms. In their basic
form, carbohydrates are simple sugars or monosaccharides. These simple sugars can
combine with each other to form more complex carbohydrates. The combination of two
simple sugars is a disaccharide. Carbohydrates consisting of two to ten simple sugars
are called oligosaccharides, and those with a larger number are called polysaccharides.
2.1.2.5.1
Sugars
Sugars are white crystalline carbohydrates that are soluble in water and generally
have a sweet taste.
Monosaccharide classifications based on the number of carbons
20
Number
of
Carbons
Category
Name
Examples
4
Tetrose
Erythrose, Threose
5
Pentose
Arabinose, Ribose, Ribulose, Xylose, Xylulose, Lyxose
6
Hexose
Allose, Altrose, Fructose, Galactose, Glucose, Gulose, Idose,
Mannose, Sorbose, Talose, Tagatose
7
Heptose
Sedoheptulose
Many saccharide structures differ only in the orientation of the hydroxyl groups
(-OH). This slight structural difference makes a big difference in the biochemical
properties, organoleptic properties (e.g., taste), and in the physical properties such as
melting point and Specific Rotation (how polarized light is distorted). A chain-form
monosaccharide that has a carbonyl group (C=O) on an end carbon forming an aldehyde
group (-CHO) is classified as an aldose. When the carbonyl group is on an inner atom
forming a ketone, it is classified as a ketose.
2.1.2.5.1.1.Tetroses
D-Erythrose D-Threose
2.1.2.5.1.2.Pentoses
D-Ribose
DArabinose
D-Xylose
21
D-Lyxose
The ring form of ribose is a component of ribonucleic acid (RNA).
Deoxyribose, which is missing an oxygen at position 2, is a component of
deoxyribonucleic acid (DNA).
In nucleic acids, the hydroxyl group attached to carbon
number 1 is replaced with nucleotide bases.
Ribose
2.1.2.5.1.3.
Deoxyribose
Hexoses
D-Allose
D-Altrose
D-Glucose
D-Mannose
D-Gulose
D-Idose
D-Galactose D-Talose
Structures that have opposite configurations of a hydroxyl group at only one
position, such as glucose and mannose, are called epimers. Glucose, also called
dextrose, is the most widely distributed sugar in the plant and animal kingdoms and it is
the sugar present in blood as "blood sugar". The chain form of glucose is a polyhydric
aldehyde, meaning that it has multiple hydroxyl groups and an aldehyde group.
22
Fructose, also called levulose or "fruit sugar", is shown here in the chain and ring forms.
The relationship between the chain and the ring forms of the sugars is discussed below.
Fructose and glucose are the main carbohydrate constituents of honey.
D-Tagatose
D-Fructose Fructose
(a ketose)
2.1.2.5.1.4.
Galactose
Mannose
Heptoses
Sedoheptulose has the same structure as fructose, but it has one extra carbon.
D-Sedoheptulose
2.1.2.5.1.5.
Chain and Ring forms
Many simple sugars can exist in a chain form or a ring form, as illustrated by the
hexoses above. The ring form is favored in aqueous solutions, and the mechanism of
ring formation is similar for most sugars. The glucose ring form is created when the
oxygen on carbon number 5 links with the carbon comprising the carbonyl group
(carbon number 1) and transfers its hydrogen to the carbonyl oxygen to create a
hydroxyl group. The rearrangement produces alpha glucose when the hydroxyl group is
on the opposite side of the -CH2OH group, or beta glucose when the hydroxyl group is
on the same side as the -CH2OH group. Isomers, such as these, which differ only in
their configuration about their carbonyl carbon atom are called anomers. The little D in
the name derives from the fact that natural glucose is dextrorotary, i.e., it rotates
23
polarized light to the right, but it now denotes a specific configuration.
Monosaccharides forming a five-sided ring, like ribose, are called furanoses. Those
forming six-sided rings, like glucose, are called pyranoses.
D-Glucose
(an aldose)
2.1.2.5.1.6.
α-D-Glucose
β-D-Glucose
Stereochemistry
Saccharides with identical functional groups but with different spatial
configurations have different chemical and biological properties. Stereochemisty is the
study of the arrangement of atoms in three-dimensional space. Stereoisomers are
compounds in which the atoms are linked in the same order but differ in their spatial
arrangement. Compounds that are mirror images of each other but are not identical,
comparable to left and right shoes, are called enantiomers. The following structures
illustrate the difference between β-D-Glucose and β-L-Glucose. Identical molecules can
be made to correspond to each other by flipping and rotating. However, enantiomers
cannot be made to correspond to their mirror images by flipping and rotating. Glucose is
sometimes illustrated as a "chair form" because it is a more accurate representation of
the bond angles of the molecule.
β-D-Glucose
β-L-Glucose
24
β-D-Glucose
(chair form)
β-D-Glucose
2.1.2.5.1.7.
β-L-Glucose
Sugar Alcohols, Amino Sugars, and Uronic Acids
Sugars may be modified by natural or laboratory processes into compounds that
retain the basic configuration of saccharides, but have different functional groups. Sugar
alcohols, also known as polyols, polyhydric alcohols, or polyalcohols, are the
hydrogenated forms of the aldoses or ketoses. For example, glucitol, also known as
sorbitol, has the same linear structure as the chain form of glucose, but the aldehyde (CHO) group is replaced with a -CH2OH group. Other common sugar alcohols include
the monosaccharides erythritol and xylitol and the disaccharides lactitol and maltitol.
Sugar alcohols have about half the calories of sugars and are frequently used in lowcalorie or "sugar-free" products.
Amino sugars or aminosaccharides replace a hydroxyl group with an amino (NH2) group. Glucosamine is an amino sugar used to treat cartilage damage and reduce
the pain and progression of arthritis.
Uronic acids have a carboxyl group (-COOH) on the carbon that is not part of
the ring. Their names retain the root of the monosaccharides, but the -ose sugar suffix is
changed to -uronic acid. For example, galacturonic acid has the same configuration as
galactose, and the structure of glucuronic acid corresponds to glucose.
Glucitol or Sorbitol
(a sugar alcohol)
Glucosamine
Glucuronic acid
(an amino sugar) (a uronic acid
25
Disaccharide descriptions and components
Disaccharide Description
Component monosaccharides
sucrose
common table sugar
glucose + fructose
lactose
main sugar in milk
galactose + glucose
maltose
product of starch hydrolysis glucose + glucose
trehalose
found in fungi
Sucrose
glucose + glucose
Lactose
Maltose
Sucrose, also called saccharose, is ordinary table sugar refined from sugar cane
or sugar beets. It is the main ingredient in turbinado sugar, evaporated or dried cane
juice, brown sugar, and confectioner's sugar. Lactose has a molecular structure
consisting of galactose and glucose. It is of interest because it is associated with lactose
intolerance which is the intestinal distress caused by a deficiency of lactase, an
intestinal enzyme needed to absorb and digest lactose in milk. Undigested lactose
ferments in the colon and causes abdominal pain, bloating, gas, and diarrhea. Yogurt
does not cause these problems because lactose is consumed by the bacteria that
transform milk into yogurt.
Maltose consists of two α-D-glucose molecules with the alpha bond at carbon 1
of one molecule attached to the oxygen at carbon 4 of the second molecule. This is
called a 1α→4 glycosidic linkage. Trehalose has two α-D-glucose molecules connected
through carbon number one in a 1α→1 linkage. Cellobiose is a disaccharide consisting
of two β-D-glucose molecules that have a 1β→4 linkage as in cellulose. Cellobiose has
no taste, whereas maltose and trehalose are about one-third as sweet as sucrose.
2.1.2.5.1.8.
Polysaccharides are polymers of simple sugars
26
Many polysaccharides, unlike sugars, are insoluble in water. Dietary fiber
includes polysaccharides and oligosaccharides that are resistant to digestion and
absorption in the human small intestine but which are completely or partially fermented
by microorganisms in the large intestine. The polysaccharides described below play
important roles in nutrition, biology, or food preparation.
2.1.2.5.1.9.
Starch
Starch is the major form of stored carbohydrate in plants. Starch is composed of
a mixture of two substances: amylose, an essentially linear polysaccharide, and
amylopectin, a highly branched polysaccharide. Both forms of starch are polymers of αD-Glucose. Natural starches contain 10-20% amylose and 80-90% amylopectin.
Amylose forms a colloidal dispersion in hot water (which helps to thicken gravies)
whereas amylopectin is completely insoluble.
Amylose molecules consist typically of 200 to 20,000 glucose units which form
a helix as a result of the bond angles between the glucose units.
Amylose
Amylopectin differs from amylose in being highly branched. Short side chains
of about 30 glucose units are attached with 1α→6 linkages approximately every twenty
to thirty glucose units along the chain. Amylopectin molecules may contain up to two
million glucose units.
27
Amylopectin
The side branching chains are clustered together within the amylopectin molecule
Starches are transformed into many commercial products by hydrolysis using
acids or enzymes as catalysts. Hydrolysis is a chemical reaction in which water is used
to break long polysaccharide chains into smaller chains or into simple carbohydrates.
The resulting products are assigned a Dextrose Equivalent (DE) value which is related
to the degree of hydrolysis. A DE value of 100 corresponds to completely hydrolyzed
starch, which is pure glucose (dextrose). Maltodextrin is partially hydrolyzed starch that
is not sweet and has a DE value less than 20. Syrups, such as corn syrup made from
corn starch, have DE values from 20 to 91. Commercial dextrose has DE values from
92 to 99. Corn syrup solids are mildly sweet semi-crystalline or powdery amorphous
products with DEs from 20 to 36 made by drying corn syrup in a vacuum or in spray
driers. High fructose corn syrup (HFCS), commonly used to sweeten soft drinks, is
made by treating corn syrup with enzymes to convert a portion of the glucose into
fructose. Commercial HFCS contains from 42% to 55% fructose, with the remaining
percentage being mainly glucose. Modified starch is starch that has been changed by
mechanical processes or chemical treatments to stabilize starch gels made with hot
water. Without modification, gelled starch-water mixtures lose viscosity or become
28
rubbery after a few hours. Hydrogenated glucose syrup (HGS) is produced by
hydrolyzing starch, and then hydrogenating the resulting syrup to produce sugar
alcohols like maltitol and sorbitol, along with hydrogenated oligo- and polysaccharides.
Polydextrose (poly-D-glucose) is a synthetic, highly-branched polymer with many types
of glycosidic linkages created by heating dextrose with an acid catalyst and purifying
the resulting water-soluble polymer. Polydextrose is used as a bulking agent because it
is tasteless and is similar to fiber in terms of its resistance to digestion.
Relative sweetness of various carbohydrates
fructose
invert sugar*
HFCS (42% fructose)
sucrose
xylitol
tagatose
glucose
high-DE corn syrup
sorbitol
mannitol
trehalose
regular corn syrup
galactose
maltose
lactose
173
120
120
100
100
92
74
70
55
50
45
40
32
32
15
* invert sugar is a mixture of glucose and fructose found in fruits.
2.1.2.5.1.10. Glycogen
Glucose is stored as glycogen in animal tissues by the process of glycogenesis.
When glucose cannot be stored as glycogen or used immediately for energy, it is
converted to fat. Glycogen is a polymer of α-D-Glucose identical to amylopectin, but
the branches in glycogen tend to be shorter (about 13 glucose units) and more frequent.
The glucose chains are organized globularly like branches of a tree originating from a
pair of molecules of glycogenin, a protein with a molecular weight of 38,000 that acts as
a primer at the core of the structure. Glycogen is easily converted back to glucose to
provide energy.
29
Glycogen
2.1.2.5.1.11. Inulin
Some plants store carbohydrates in the form of inulin as an alternative, or in
addition, to starch. Inulins are polymers consisting of fructose units that typically have a
terminal glucose. Inulins have a sweet taste and are present in many vegetables and
fruits, including onions, leeks, garlic, bananas, asparagus, chicory, and Jerusalem
artichokes.
Inulin
n = approx. 35
2.1.2.5.1.12. Cellulose
Cellulose is a polymer of β-D-Glucose, which in contrast to starch, is oriented
with -CH2OH groups alternating above and below the plane of the cellulose molecule
thus producing long, unbranched chains. The absence of side chains allows cellulose
molecules to lie close together and form rigid structures. Cellulose is the major
30
structural material of plants. Wood is largely cellulose, and cotton is almost pure
cellulose. Cellulose can be hydrolyzed to its constituent glucose units by
microorganisms that inhabit the digestive tract of termites and ruminants. Cellulose may
be modified in the laboratory by treating it with nitric acid (HNO3) to replace all the
hydroxyl groups with nitrate groups (-ONO2) to produce cellulose nitrate (guncotton)
which is an explosive component of smokeless powder.
Cellulose
2.1.2.5.1.13. Chitin
Chitin is an unbranched polymer of N-Acetyl-D-glucosamine. It is found in
fungi and is the principal component of arthropod and lower animal exoskeletons, e.g.,
insect, crab, and shrimp shells. It may be regarded as a derivative of cellulose, in which
the hydroxyl groups of the second carbon of each glucose unit have been replaced with
acetamido (-NH(C=O)CH3) groups.
Chitin
2.1.2.5.1.14. Beta-Glucan
Beta-glucans consist of linear unbranched polysaccharides of β-D-Glucose like
cellulose, but with one 1β→3 linkage for every three or four 1β→4 linkages. Betaglucans form long cylindrical molecules containing up to about 250,000 glucose units.
Beta-glucans occur in the bran of grains such as barley and oats, and they are
recognized as being beneficial for reducing heart disease by lowering cholesterol and
31
reducing the glycemic response. They are used comercially to modify food texture and
as fat substitutes.
Beta-Glucan
2.1.2.5.1.15. Glycosaminoglycans
Glycosaminoglycans are found in the lubricating fluid of the joints and as
components of cartilage, synovial fluid, vitreous humor, bone, and heart valves.
Glycosaminoglycans are long unbranched polysaccharides containing repeating
disaccharide units that contain either of two amino sugar compounds -- Nacetylgalactosamine or N-acetylglucosamine, and a uronic acid such as glucuronate
(glucose where carbon six forms a carboxyl group). Glycosaminoglycans are negatively
charged, highly viscous molecules sometimes called mucopolysaccharides. The
physiologically most important glycosaminoglycans are hyaluronic acid, dermatan
sulfate, chondroitin sulfate, heparin, heparan sulfate, and keratan sulfate. Chondroitin
sulfate is composed of β-D-glucuronate linked to the third carbon of Nacetylgalactosamine-4-sulfate as illustrated here. Heparin is a complex mixture of linear
polysaccharides that have anticoagulant properties and vary in the degree of sulfation of
the saccharide units.
32
Chondroitin Sulfate
Heparin
2.1.2.5.1.16. Agar and Carrageenan
Agar is extracted from seaweed and is used in many foods as a gelling agent.
Agar is a polymer of agarobiose, a disaccharide composed of D-galactose and 3,6anhydro-L-galactose. Highly refined agar is used as a medium for culturing bacteria,
cellular tissues, and for DNA fingerprinting. Carrageenan is a generic term for several
polysaccharides also extracted from seaweed. Carrageenan compounds differ from agar
in that they have sulfate groups (-OSO3-) in place of some hydroxyl groups.
Carrageenan is also used for thickening, suspending, and gelling food products.
Agarobiose is the repeating disaccharide unit in agar.
2.1.2.5.1.17. Guar Gum
Guar is a legume that has been traditionally cultivated as livestock feed. Guar
gum is the ground endosperm of the seeds. Approximately 85% of guar gum is guaran,
a water soluble polysaccharide consisting of linear chains of mannose with 1β→4
linkages to which galactose units are attached with 1α→6 linkages. The ratio of
galactose to mannose is 1:2. Guar gum has five to eight times the thickening power of
starch and has many uses in the pharmaceutical industry, as a food stabilizer, and as a
source of dietary fiber.
33
Guaran is the principal polysaccharide in guar gum.
2.1.2.5.1.18. Pectin
Pectin is a polysaccharide that acts as a cementing material in the cell walls of
all plant tissues. The white portion of the rind of lemons and oranges contains
approximately 30% pectin. Pectin is the methylated ester of polygalacturonic acid,
which consists of chains of 300 to 1000 galacturonic acid units joined with 1α→4
linkages. The Degree of Esterification (DE) affects the gelling properties of pectin. The
structure shown here has three methyl ester forms (-COOCH3) for every two carboxyl
groups (-COOH), hence it is has a 60% degree of esterification, normally called a DE60 pectin. Pectin is an important ingredient of fruit preserves, jellies, and jams.
Pectin is a polymer of α-Galacturonic acid with a variable number of methyl ester
groups.
2.1.2.5.1.219. Xanthan Gum
Xanthan gum is a polysaccharide with a β-D-glucose backbone like cellulose,
but every second glucose unit is attached to a trisaccharide consisting of mannose,
34
glucuronic acid, and mannose. The mannose closest to the backbone has an acetic acid
ester on carbon 6, and the mannose at the end of the trisaccharide is linked through
carbons 6 and 4 to the second carbon of pyruvic acid. Xanthan Gum is produced by the
bacterium Xanthomonas campestris, which is found on cruciferous vegetables such as
cabbage and cauliflower. The negatively charged carboxyl groups on the side chains
cause the molecules to form very viscous fluids when mixed with water. Xanthan gum
is used as a thickener for sauces, to prevent ice crystal formation in ice cream, and as a
low-calorie substitute for fat. Xanthan gum is frequently mixed with guar gum because
the viscosity of the combination is greater than when either one is used alone.
The repeating unit of Xanthan Gum
2.1.2.5.1.20. Glucomannan
Glucomannan is a dietary fiber obtained from tubers of Amorphophallus konjac
cultivated in Asia. One gram of this soluble polysaccharide can absorb up to 200 ml of
water. Glucomannan creates very viscous solutions that when ingested with food retard
the absorption of nutrients. The polysaccharide consists of glucose (G) and mannose
(M) in a proportion of 5:8 joined by 1β→4 linkages. The basic polymeric repeating unit
has the pattern: GGMMGMMMMMGGM. Short side chains of 11-16 monosaccharides
occur at intervals of 50-60 units of the main chain attached by 1β→3 linkages. Also,
acetate groups on carbon 6 occur at every 9-19 units of the main chain. Hydrolysis of
35
the acetate groups favors the formation of intermolecular hydrogen bonds that are
responsible for the gelling action.
A portion (GGMM) of the glucomannan repeating unit.
The second glucose has an acetate group
36