Enzymes - Food Science & Human Nutrition
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Transcript Enzymes - Food Science & Human Nutrition
Enzymes
Enzymes – General properties
All enzymes are proteins that function as biological
catalysts
◦ They are essential for reactions to occur in living (and dying) cells
◦ They can have a dramatic impact on the quality deterioration of
many foods
◦ They can be used to perform positive reactions in food and
beverage processing (also textile, leather and pharmaceutical
industry)
Have specific ability to convert a particular substance into a particular
product
Very rapid action
Only need small amount
Can easily control them by adjusting their environment, e.g. pH, T,
concentration…..
They are all natural and non-toxic
Enzymes – General properties
Enzymes have one (or more) active sites in their structure that
have great specificity for certain substrates (bind only to these)
and catalyze their transformation into specific products
E
E-S
E-S#
E+P
Change in
environment
Enzymes – General properties
Lactose
Sucrose
Enzymes – General properties
The reason enzymes are able to speed up chemical reactions so much comes from
their ability to bind to their substrates with very high specificity and significantly
lower the activation energy (Ea) of the reaction converting a substrate to a product
Speed up reactions by 103-1011 compared to other catalysts; 108-1020 compared to
uncatalyzed reactions
A
Free energy
No enzyme
Ea
A
C
E
Enzyme
E-S
E+S
C
Ea
E+P
Progress of reaction
EA
Enzymes – General properties
There are six main types/groups of enzymes classified based
on their chemical reaction mechanism
1. Oxidoreductases
Catalyze oxidations or reductions of substrates
Some important food reaction examples:
Lipid oxidation – lipoxygenase (adds an oxygen on
fatty acids)
Browning – polyphenol oxidase (oxidizes phenols in
food)
2. Transferases
Catalyze a shift of a chemical group from a donor to
acceptor substrate
Not so important in foods
Enzymes – General properties
3. Hydrolases
Catalyze the hydrolysis (with help of water) of substrates
(i.e. breaking of bonds)
By far the most important enzymes with respect to food
quality and use in food processing
Some important food reaction examples:
Texture, protein modification – proteases (cleave the
peptide bond)
Texture, carbohydrate modification – e.g. amylases
(cleave glycosidic bonds) and pectinases (act on several
groups/bonds)
Hydrolytic rancidity, fat crystallization modification –
lipases (cleave ester bonds)
Enzymes – General properties
4. Lyases
Catalyze the removal or addition of chemical groups to
substrates
Not so important in foods
5. Isomerases
Catalyze intramolecular rearrangements
An important food reaction example:
Sweetness (Glu Fru) – glucose isomerase (converts
aldose to ketose)
6. Ligases
Catalyze combinations of substrates
Not so important in foods
Enzymes – General properties
Factors affecting enzyme activity
1. Enzyme and substrate concentration
◦ When substrate concentration is kept constant the enzyme reaction
is proportional to the amount of enzyme (i.e. doubling enzyme will
double the speed of the reaction) up to a certain limit
Here you start to have more
enzyme than substrate and rate
starts to level off
There is no added benefit for a
food operation to have too much
enzyme ($$$).
That is why we have to study the
ideal concentration to work at
Chemical kinetics
120
100
C
h
a
n
g
e
S
80
1st Order Reaction
v = k [S]
60
40
20
0
-20
0
5
10
15
20
Time
25
30
35
40
Enzymes – General properties
o Increasing the substrate concentration under
fixed enzyme concentration leads to a non-linear
increase in reaction velocity that can be explained
by the formation of the Enzyme-Substrate
complex:
k1
o
k2
E + S ↔ E-S ↔E + P
k-1
o This reaction curve is shared by most enzyme and
gives us very useful information on the activity of
the enzyme and the affinity for its substrate
o Vmax gives us the maximum velocity that the
enzyme can produce (under the conditions
tested) – the higher the faster
o Km (determined as ½ Vmax) tells us the affinity
of the enzyme for its substrate
o Vmax/Km = catalytic efficiency (higher number
means more efficient)
Enzymes – General properties
At low [S]
[E] and [S] determine rate
A
B
A
At high [S]
[E] determines rate
Enzymes – General properties
2. Temperature
◦ Enzyme reactions increase with
temperature up to a point and
then activity declines as the
enzyme becomes denatured
◦ Different enzymes have different
temperature optima's (the point
when max activity is)
◦ Important to determine this to be
able to predict what type of
thermal treatment you need in
processing to inactivate
undesirable enzymes
Enzymes – General properties
3. pH
◦ All enzymes have a certain narrow range of pH where they perform
best
Most active between 4.5-8
Some active at very low (e.g. pepsin) or high pH
◦ Extremes of pH can affect the enzyme by denaturing it (remember it is
a protein) or affecting the charge of critical amino acids in its active site
(or charge on the substrate)
◦ For this reason pH control of foods with undesirable enzymes is
important
Pepsin
Trypsin
Activity
1
pH
12
Enzymes – General properties
4. Water activity
◦ Water can influence an enzyme in many ways
It can be critical for the SP reaction (e.g. hydrolysis)
It can be critical to solubilize the substrate and product
It can be critical for the flexibility of the enzyme structure
◦ Water activity can be varied in foods to slow down enzymatic activity
Enzyme 1
Enzyme 2
Activity
0
aw
1
Enzymes – General properties
5. Inhibitors
◦ We can use chemical compounds to inhibit or slow down the
activity of enzymes
1. Competitive inhibitors
Compete with the substrate for the active site
Enzyme can only bind to either S (substrate) or I (inhibitor) at one time
2. Non-competitive inhibitors
Bind to enzyme at another site than active site
Enzyme can bind to both S and I at the same time
3. Un-competitive inhibitors
Can only bind to the E-S complex (the intermediate state)
Enzyme binds first to S and then can bind to I
◦ These can be reversible or irreversible
◦ Some food use for these but many have flavor, odor, color and
toxicity problems, plus can be very expensive
Enzymes – Important food enzymes
HYDROLASES
They all have in common that they break bonds with the help of
water
1. Glycoside hydrolases
A) Enzymes that hydrolyze starch (glycosidic bonds)
◦ -amylase
Hydrolyses -1-4 glycosidic bonds within starch
Results in dextrins, maltose and maltotriose
◦ -amylase
Hydrolyses -1-4 glycosidic bonds from the non-reducing end of starch
Results in maltose
◦ Glucoamylase
Hydrolyses -1-4 and -1-6 glycosidic bonds in starch
Can hydrolyze all the way to glucose
◦ Pullulunase
Hydrolyses -1-6 glycosidic bonds in starch
These enzymes are naturally present in the food or are found in
microorganisms added to the food
Enzymes – Important food enzymes
Food importance of the glycoside hydrolases
Corn syrup production
◦ Using a cocktail of enzymes
starch can be converted to a
glucose syrup (dextrose)
◦ Start with -amylase to break
amylose and amylopectin to
smaller units
◦ Then use glucoamylase to break
down to glucose
◦ If maltose is desired use amylase and pullulanase
Enzymes – Important food enzymes
Baking
◦ -amylases are important to “dextrinize” the disrupted starch granules
(rupture during milling) and the dextrins are then hydrolyzed to
maltose by -amylase gives fermentable sugar for yeast to produce
CO2 (essential for rising of the bread)
◦ On baking there is further action of the amylases on the gelatinized
starch plays an important role in the final texture and quality of
bread
◦ Amylases added to bakery products can minimize staling
◦ Need to add -amylases to some flours (what harvested in dry
climates)
Brewing
◦ High level of amylases in barley malt (no need to add more)
◦ During mashing (milled barley malt and water at 50C) amylases
hydrolyze starch to give maltose for yeast to utilize and produce CO2
and ethanol
Enzymes – Important food enzymes
B) Invertase
◦ An enzyme that hydrolyzes the glycosidic bond between
glucose and fructose in sucrose
Results in invert sugar (free glu and fru)
Popular in the confectionary industry because invert sugar
is sweeter than sucrose and has less tendency to
crystallize
Popular in soft candy fillings
C) Lactase
◦ An enzyme that hydrolyses the glycosidic bond between
galactose and glucose in lactose
Increases sweetness and solubility of the sugar
Done in the dairy industry to minimize crystallinization in
ice cream and to produce lactose free products
Enzymes – Important food enzymes
2. Pectinases
Occur widely in fruits and vegetables and are responsible
for the degradation of pectic substances
◦ Pectin methyl esterase
Hydrolyze the methyl ester linkages of pectin
Causes loss of cloud in citrus juice (big problem)
CO O C H
CO O H
3
O
CO O C H
O
O
CO O C H
O
O
CO O H
3
O
PME
3
O
O
CO O C H
O
3
O
O
O
O
O
O
O
O
O
O
O
O
CO O C H 3
CO O H
O
Ca
C O O C H
C O O H
3
O
C O O C H
O
3
O
O
O
O
O
O
O
O
C O O H
3
O
O
C O O C H
O
O
3
O
O
O
90C for 1 min
O
O
O CO O C H 3
O
O
O
CO O H
O
CO O C H 3
O
O
O CO O H
Ca
C O O C H
CO O HO
O
O
O
O
O
CO O C H 3
OO
O
O
O
CO O C H 3
CO O H
O
O
O
O
O
Ca
O
CO O H
O
O
O
O
O
CO O C H 3
O
O
O
O
O
Converts colloidal pectin to non-colloidal pectin
We add this enzyme when clarity is desired (e.g. apple juice)
Enzymes – Important food enzymes
3. Proteases
◦ Enzymes that hydrolyze peptide bonds in proteins
A) Papain
◦ Found in papaya
◦ Broad pH (3-11) and temperature stability
For this reason very popular for a variety of food applications
1. Used as a meat tenderizer on inferior meat cuts (can also use slice of
pineapple on meat)
The enzyme makes its way into the muscle and hydrolyzes
primarily connective tissue proteins (collagen etc.) and softens
muscle
Have to use low amount to prevent liquefaction of muscle
If you mix raw papaya into Jell-O it will not form a gel
Other popular tenderizing enzymes are ficin (from figs),
bromelain (from pineapple) and microbial proteases
Enzymes – Important food enzymes
2. Papain can also be used to clear turbidity (chill haze) in beer
◦ When bottled or canned beer is kept below 10C (50F) a haze can form
Interactions of proteins/polypeptides and tannins in beer
◦ This can be prevented using chill-proofing
Protease (papain mostly used) added during post-fermentation
maturation to hydrolyze the proteins/polypeptides to prevent large
aggregates to form on cooling
Enzymes – Important food enzymes
B) Digestive proteases
◦ Trypsin & Chymotrypsin
Found in animal pancreas
Can cause quality problems in muscle foods if contamination
from intestines occurs (e.g. ground products) over-softening of
the meat
They are often used to make protein hydrolysates for the food,
beverage and the pharmaceutical industry
Most active at pH 7-9
◦ Pepsin
Very acidic activity optima (pH 1.8)
Somewhat limits its use
Used in cheese making, chillproofing and also in making protein
hydrolysates
animal and fertilizer use primarily, some for food use
Enzymes – Important food enzymes
◦ Chymosin (rennin)
Essential for the manufacture of good quality cheeses
Found in the fourth stomach of suckling calf's
Very expensive and “inhumane” to process now so it has been
engineered into a bacteria that mass produces it
Has a very specific activity
Hydrolyzes only one bond in к-casein, one of the many proteins that
make up the milk casein protein complex (к-, -, -casein)
This breaks up the casein complex (micelle) and it aggregates leading
to a clot, the first step in cheese production
Most other proteases can initiate a milk clot like chymosin but they
would continue the casein hydrolysis producing bitter peptides and
eventually breaking the clot
Enzymes – Important food enzymes
C) Microbial proteases
◦ Several fungal and bacterial proteases are used in the food industry
◦ Fungal proteases
Some have almost equal ability to form cheese cloths like chymosin
A protease cocktail from Aspergillus oryzae is used to partially break
down bread proteins (glutens) to reducing mixing time and making
them more extensible
Some are added to help with flavor and texture development and
speeding up fermentation in fermented dairy products
Fungal proteases are also used to tenderize meat
◦ Bacterial proteases
Subtilisin from Bacillus subtilisin is popular and is used in combination
with papain in beer chillproofing
Enzymes – Important food enzymes
4. Lipases
◦ Enzymes that all hydrolyze ester bonds between fatty acids and a
glycerol molecule
Work at the water-oil interface
◦ Two classes
a) 1,3-lipases: preferentially hydrolyze ester bonds at SN1 and SN3
b) 2-lipases preferentially hydrolyze ester bonds at SN2
Enzymes – Important food enzymes
◦ Lipases have a dramatic impact on the quality of food products
A) Lead to hydrolytic rancidity
BAD when
Free fatty acids released in muscle foods and react to proteins to
denature them and give a tough texture (happens on freezing
muscle)
they are not inactivated in milk; release short chain fatty acids that
are very volatile and can also oxidize
GOOD when
Used in fermented products
Extremely important in ripening of cheeses and dry-sausages
Short chain fatty acids released from milk fat produces the
characteristic odor and flavor of these products (C:8 especially)
Enzymes – Important food enzymes
B) They can be used to modify the properties of lipids
Very popular application in the margarine industry to modify lipid crystal
structure to give different textures and melting points
Also used to produce mono and diglycerides for use as emulsifiers
A very unique reaction system must be used for these enzymes since they are
soluble in water but act on a lipid substrate
The enzyme is located
in the water droplet of
a water-in-oil emulsion
and acts on the oil
surrounding the water
droplet
Enzymes – Important food enzymes
ISOMERASES
They all catalyze the intramolecular
arrangement within a molecule
Glucose isomerase
◦ The most important for the food industry
◦ Catalyzes isomeric rearrangement of glucose to
fructose (converts an aldose to a ketose)
Gives a sweeter product than corn syrup
Corn
Syrup
Glu isomerase
pH 7
50-60C
Sweetness glu = 70; fru = 170; sucrose = 100
Product called high fructose corn syrup
Made from corn syrup (which is made by amylase
digestion of starch)
Enzymes are immobilized in large columns where
the reaction takes place – can reuse them
42% (HFCS) 52%
Enzymes – Important food enzymes
OXIDOREDUCTASES
Enzymes that catalyze the oxidation or
reduction of substrates
A) Lipoxygenase
◦ Found in a wide variety of plants
(primarily legumes) and have also been
identified in animal tissue (e.g. in the
skin of fish)
◦ Specific for the oxidation of fatty acids
that have a cis, cis penta-1,4-diene unit,
so there are three naturally occurring
fatty acids that can be substrates
Linoleic acid (2 double bonds)
Linolenic acid (3 double bonds)
Arachidonic acid (4 double bonds)
Enzymes – Important food enzymes
Importance of lipoxygenases in foods
◦ Desirable
The enzyme plays a role in bleaching of wheat and soybean flours
It contributes to the formation of S-S bonds in gluten in dough, thus one
does not have to add chemical oxidizers
◦ Undesirable
Lipid oxidation and reactions of its products
Breakdown products of hydroperoxides give off-flavors and odors
Oxidation products (the free radicals or hydroperoxide) can bind and/or
oxidize proteins to lead to textural problems
Lipid oxidation also leads to nutritional loss of essential polyunsaturated fatty
acids
Vitamins may also be oxidized by the oxidation products
Chlorophylls and carotenes can be bleached
Its action can be effectively delayed by using antioxidants
Enzymes – Important food enzymes
B) Polyphenol oxidase (PPO)
◦ Found in plants (fruits and
vegetables), animals (including
humans), insects and microbes
◦ Catalyzes the oxidation of phenolic
compounds (mono and/or
diphenols) in the presence of O2 to
give quinones which polymerize into
melanin pigments (desirable or
undesirable)
◦ Its activity can be inhibited by:
Removing O2
pH < 4.5 (lemon juice)
Ascorbic acid (vit-C) (again,
lemon juice)
Bi-sulfites
EDTA
Polymerizes Melanins
Undesirable browning of apples,
bananas, mushrooms, shrimp, lobster,
human freckles?
Up to 50% economic loss of tropical
fruit due to PPO activity
Desirable browning of tea, coffee,
cocoa, raisins, prunes, tobacco,
human tan, freckles?