Enzymes are used in Beverages
Some
in the food industry regard enzymes as nuisances -- substances that must be
deactivated or destroyed to create an acceptable product. However, for others,
particularly in the beverage industry, enzymes and the reactions they catalyze
are indispensable.
In
beverages, as in other food products, enzymes may occur naturally or their
presence may be due to intentional formulation. Enzymes perform many functions
in beverages. They can help increase yields, form nutrients for the fermentation
process, facilitate processing, and affect the color, flavor and clarity of the
finished product.
Enzymes
are biological catalysts based mainly on protein. Because they act as catalysts,
the molecules remain unchanged at the completion of the reaction. The exact
mechanism by which they perform their function is unknown, although science has
developed a number of theories. And although the enzymes can theoretically be
recovered, in most food and beverage processes they are merely deactivated by
heat upon the completion of the desired reaction because of the expense that
would be incurred if the processor tried to recover them .
Enzymes are typically
named for the reactions they catalyze. They fall into six major categories ,
oxidoreductases,
hydrolases, lysases, transferases, ligases and isomerases.
Of these types,
hydrolases play the
most important role in the beverage industry.
Each category contains
several types of enzymes;
esterases, glycosidases and peptidases are all
hydrolases,
for example. These may be known by a common name and by scientific nomenclature
that describes the reaction they catalyze.
Beta-1-4-glucan 4-glucanhydrolase
is generally referred to as cellulase.
Many industrial enzyme preparations contain a mixture of different types of
enzymes. The combination of main and side activities gives a particular
preparation its unique functionality. Enzyme isolation and purification increase
the cost.
‘’Some glucoamylases may
contain low levels of protease.
That might be a good thing if
you were making distilled spirits, but in beer it might affect the foam
stability."
Most enzymes catalyze
highly specific reactions. For example,
alpha-amylase (alpha-1-4-glucan
glucanhydrolase)
attacks the alpha bonds between the glucose portions of starch , resulting in
the formation of glucose. Not all enzymes show the same degree of specificity,
however. Some proteases,
such as papain,
hydrolyze random peptide bonds in proteins.
"If an acid protease is
used during beverage processing to prevent post-bottling haze, it should be
added after the other enzymatic reactions are complete,That's because proteases
can hydrolyze other enzymes present, as all enzymes are proteins."
A number of factors
affect enzyme activity. These include temperature, pH, concentration, contact
time with the substrate, trace metals, salt and salt ions , and oxidizing agents.
Enzymes are assayed in
terms of their activity, expressed as "units." This refers to the amount of
substrate catalyzed. Throughout the industry , a wide range of different
techniques are used, so anyone attempting to make a direct comparison must know
the exact method used.
As mentioned, enzymes in
beverages can occur naturally in the ingredients used to formulate the beverage.
Most fruits contain low levels of pectinase , and the malting process produces
significant levels of amylase. In other cases, a product designer can add an
enzyme preparation to achieve a specific goal or to supplement or standardize
naturally occurring enzymes.
Enzymes
play a crucial role in the production of beer and other types of malted liquor,
such as whiskey. In these products, enzymes provide three major functions: the
formation of sugars to be used during fermentation; viscosity control; and, in
beer, "chill-proofing."
The starting material for
beer and whiskey is malted grain. In beer , the grain used is generally barley,
although other grains such as corn can augment the barley. Germinating the
barley produces a mixture of enzymes, primarily alpha- and beta-amylases. These
break down the starch into fermentable sugars such as glucose, maltose and
maltotriose.
Modern brewers often
supplement these naturally occurring enzymes, especially when grains other than
barley are used. The additional enzymes can help make up for the lack of
amylases
in the other grains and increase the level of fermentable sugars. For example,
adding amyloglucosidase,
which is not found in either the barley or the fermenting yeast , can break down
certain dextrins that remain unaffected by the
alpha- and beta-amylases.
Added enzymes can also standardize the enzymatic conversion of starch, reducing
variation in the process and the finished product.
"There are differences in
the types of enzymes used in brewing versus those used for the production of
distilled spirits.Distilled spirits generally use a heat-stable bacterial
alpha-amylase,
but brewing rarely will. Often in brewing , malt is the primary source of enzyme,
followed by perhaps a
glucoamylase if it's a
light beer."
The efficiency of the
enzymatic conversion depends on the process, so you need to gelatinize the
starch to present a suitable substrate for enzyme action.
The next process where
enzymes play a role is the breakdown
of the beta-glucans and pentosans.
Left intact, these compounds
absorb fairly high levels of water, increasing the viscosity and adversely
influencing processing. The beta-glucans in particular tend to produce excessive
gumminess.
"Adding
glucanase during
malting can aid with poor malt quality, decrease viscosity and filtration times,
increase yields and achieve faster run-off times,"
Enzymes also serve an
important function for those looking for a sparkling, clear beer, especially
those designed to be served at lower temperatures.
The beta-glucans can
cause some of what the industry refers to as haze, but most of this problem
comes from protein precipitation. "Chill-haze" is caused by the hydrogen bonding
of protein and tannin , and it is reversible. These two compounds can also form
a complex that does not
redissolve when the temperature rises. To solve this problem, papain is added
after brewing. Other processes such as filtration and protein flocculation have
been used to remove
protein.
"Papain works the best
and is the least expensive enzyme for chill-proofing.There are physical means to
remove some of the chill haze, such as silica gel filtration, but those methods
are fairly capital intensive."
Wine-making
generally relies on the naturally occurring enzymes present in the grape or
formed as a product of fermentation. These influence the color and flavor of the
finished product. Still, added enzymes could help in several areas.
Added
pectinase can aid in
pressing and clarification. It would be particularly helpful during any type of
elevated heating during the mash process, since higher temperatures at this
stage mean increased levels of
pectin
in the juice. This excess pectin not only affects the finished product, but also
influences the viscosity during processing. Pectinase can accelerate the release
of pigments from the grape skin, as well .
Sweet wines, such as
sauternes, depend on grapes treated with Botrytis cincerea (a mold that causes
the grapes to dehydrate, thus concentrating the sugar). This organism produces a
glucan polymer that can interfere with filtering. Therefore , it has become
common to use a specific glucanase to break down this molecule prior to
filtration.
Green
tea leaves must undergo a fermentation step to create the colors, flavors and
astringency associated with black tea. This fermentation is actually an
enzymatic degradation of various compounds. Naturally occurring
polyphenoloxidase and peroxidase cause most of the desired chemical changes, but
other enzymatic reactions probably help develop the flavor by creating aldehydes
and terpenes. In addition, catalase affects the level of peroxide available for
the peroxidase to act on.
This enzymatic activity
creates the need for another traditional step: "firing". When the reaction has
proceeded to the required level, the leaves are heated to approximately 190
degrees F to inactivate the enzymes.
As always , science has
found ways to improve on nature. The caffeine and polyphenols in tea complex to
form insoluble complexes in cold conditions, creating the "tea cream" seen in
iced tea. Enzymatically modifying this complex with tannase increases the cold
water solubility of tea solids and produces a clear tea beverage.
Those who want chocolate
milk or hot cocoa also rely on enzymes. In addition to a microbial fermentation
when processing the cocoa bean, both native enzymes and enzymes produced by the
yeast and bacteria provide several functions. They help break down the membrane
between the bean and pod. They may help generate reducing sugars inside the bean
that give the roasted product its characteristic
flavor. Proteases
create flavor
precursors , and polyphenoloxidase
helps develop the color.
The
juice industry relies heavily on enzymes to extract juice from fruits and
prepare a finished product. For non-citrus juices, such as apple, grape and
berry, processors add enzymes at the beginning of the mash stage to help extract
juice.
The cell walls of fruits
consist of cellulose,
hemicelluloses, pectin and proteins. Pectin is the major structural
polysaccharide. Adding the appropriate enzymes to break down these structures
makes it possible to extract a larger amount of juice, to facilitate pressing,
and to produce a clear juice.
"Juice processors sell
juice based on Brix (percent soluble solids).Adding low levels of enzymes --
0.01% to 0.03% -- can result in significant yield increases of approximately 20
% to 25%."
Adding cellulase,
hemicellulase and pectinase during or prior to pressing helps release the juice
contained within the cell walls, increasing yield. It can also save wear and
tear on pressing equipment and reduce energy requirements, especially when juice
is extracted from a fruit with a very firm structure, such as cranberries. Some
enzymatic processes allow the entire fruit to be liquefied.
"This method produces a
lot of soluble fiber and suspended solids, as well.It allows you to extract as
much as possible."
The most prevalent
enzymes used in juice processing are pectinases: primarily pectin methyl
esterase (PME) and polygalacturonase (PG) , although some pectinases may be used.
The PME first removes the methyl groups from the pectin molecule. The activity
required varies from fruit to fruit because different fruits have different
levels of methoxylation. Once this step is completed, the PG can break down the
main pectin chain by catalyzing hydrolysis. Pectin lyase can also split the
pectin polymer.
These enzymatic reactions
to the pectin molecule not only increase yield, they clarify the juice. The
cloud consists of small particles made up of pectin/protein complexes suspended
in the juice. These create
a haze. Adding enzymes that help break down the pectin changes two things. First
, the viscosity of the juice decreases. Second , the enzymes cause ions to form,
resulting in electrostatic aggregation which increases the size of the particles.
The combination of decreased viscosity and increased particle size causes a floc
that settles out , and the clarified juice can be removed.
Amylase
and amyloglucosidase may also be required to break down any starch present in
the fruit. Starch becomes a problem when using immature fruit, such as green
apples. If not broken down, the starch can form large polymers in the juice that
create a haze.
For some juices,
particularly orange juice and fruit nectars, a cloud is a desirable attribute.
In these cases, any naturally occurring or added pectolytic enzymes must be
inactivated by heat. However , these juices may need reductions in viscosity. In
these products a controlled breakdown of pectin is sometimes done using
polygalacturonase or pectin lyase.
Enzymes
in fruit juice also affect the color and flavor of the juice. Many of the
naturally occurring enzymes help to form esters, aldehydes and alcohols -- all
important flavor volatiles in fruit.
Enzymes can affect the
anthocyanins, the major pigment in berry and grape juices.The correct level of
enzymes helps preserve the color. However, excess dosages can reduce or break
down color.
Enzymes have
been used in the debittering
of citrus juice, particularly grapefruit juice. The major bitter compound is a
flavonone, naringin. Adding a combination of enzymes containing alpha-rhamnosidase
and beta-glucosidase breaks the molecule down to nariginin and prunin, reducing
the bitterness. However, the enzymes are not yet approved in the United States.
Limonin, another bitter citrus compound, may also be present in citrus fruits.
This , too, can be enzymatically broken down. Neither of these processes are
fully commercialized.
The other class of beverages that can benefit from the addition of enzymes includes milk and other fluid dairy products. The enzymatic process of interest is the hydrolysis of lactose.
For the lactose-intolerant,
the lactose in milk can pose serious medical problems. These people cannot
produce enough beta-galactosidase in their digestive system to break down this
sugar. Lactase, a beta-galactosidase,
catalyzes the hydrolysis of the beta-D-galactoside linkage of lactose,
converting it into glucose and galactose. Lactase is produced commercially
through the controlled fermentation of certain microorganisms, including
Kluyveromyces lactis and Aspergillus oryae. Although some oral preparations of
this enzyme are on the market, the milk itself can be treated, resulting in a
low-lactose or lactose-free product.
"To treat milk, the
lactase is injected directly into the pasteurized milk. During the storage time,
the lactose is hydrolyzed to glucose and galactose. The yeast-derived lactase
operates well under neutral pH conditions and at temperatures between 3 to 25
degrees.If the consumer wishes to enjoy a lactose-containing product then the
enzyme of choice is lactase derived from Aspergillus oryae. The enzyme is
ingested, generally in tablet form, and works in the digestive system to
hydrolyze the lactose."
Enzyme
selection depends not only on the reaction required, but on processing factors,
as well. Heat renders enzymes inactive through denaturation. The exact
temperature varies with the enzyme and is an important consideration when
choosing the correct enzyme for a specific process. Fungal enzymes tend to be
less stable under high heat than bacterial ones. It's important to choose an
enzyme that withstands normal process temperatures yet can be inactivated
without resorting to excessive heat.
"All enzymes operate
within a particular range,but there are some very discrete differences in terms
of the pH optimum as well as the temperature optimum. For example, in one class
of heat-stable alpha-amylase the temperature optimum would be 195 degrees F, but
another one would have an optimum of 205 degrees F. Others might be more pH
tolerant."
"The action pattern may
be different.In brewing, the viscosity of the mash can vary depending on the
enzyme used. That can influence the production set-up; you could get build up if
one type doesn't flow as fast. Every plant is unique in design and where one may
have a bottleneck, another doesn't. There are enzymes on the market that can
solve those kinds of problems."
The time of the process
plays a large role in determining the enzyme type and the appropriate
concentration. The longer the time the substrate is exposed to an enzyme, the
lower the dose needed to achieve the same end point.
Enzymes also have an
optimum pH range for activity. For many, this falls in the neutral range.
However , enzymes used in fruit juice processing have a lower pH optima and have
to be acid-tolerant since most juices have a pH between 3 and 4.
"Temperature is the most
important factor affecting enzyme performance, as the reaction rate doubles for
every 18 degrees F up to its optimum temperature.But there are many factors that
influence performance. That's one reason why we feel it's important to work
closely with the customer. We can suggest when to add the enzyme, the dosage
rates, and the time of reaction based on the customer's process and equipment to
get the best performance from the enzymes they use."
|
|