Enzymes in Food Processing

Though it is necessary to control some undesirable changes brought about by some enzymes in
foods, there are, however, a number of processes that require the action of enzymes. Processes like
baking, manufacture of confectionery, meat tenderization, clarification of finit juices and wines,
development of flavour, etc., require the use of enzymes. Large quantities of commercial, partially
purified enzymes obtained from suitable plant, animal and microbial sources are used in the food
industry.
There are a number of advantages of using enzymes in food processing. They are natural non-toxic
substances that catalyze a given reaction without causing unwanted side reactions. They are active
under mild conditions of temperature and pH, active at low concentrations and the reactions they
catalyze can be easily controlled. Finally, they can be inactivated when a given reaction has
proceeded to the desired extent.
Some commonly used enzymes in food industries are the carbohydrases, proteases, Lipases and
some oxidizing enzymes.
Carbohydrases
Amongst carbohydrases, α-and β-amylases which bring about hydrolytic cleavage of amylum or
starch, invertase which hydrolyzes sucrose into glucose and fructose, pectinases which hydrolyze
pectic substances, cellulases which bring about the hydrolysis of cellulose, and glucose isomerase
which isomerizes glucose to fructose, are some of the enzymes used in food industries.
Amylases are very important in baking and in the manufacture of glucose syrups. There are two
amylases: α- and β-amylases, α-amylase hydrolyzes the α-1, 4 bonds of amylase and amylopectin
in a random manner liberating maltose. β-amylase also hydrolyzes the a-1, 4 bonds in starch
fractions but it acts in an orderly way removing successive maltose units form the nonreducing
end. The α- and β-amylases do not hydrotyze α-1, 6 linkages which occur in amylopectin. The
enzyme amylo α-1, 6 glucosidase can hydrolyze these bonds. By the combined action of α- and β-
amylases in flour used in bread-making, dextrins and maltose are formed and tjiis provides the
fermentable sugar for the yeast cells. These enzymic reactions continue in the baking process till
the enzyme activity is destroyed as the oven temperature rises. The type and extent of changes due
to carbohydrases in the flour determine the softness, crust colour, volume and texture of the baked
products.
Enzyme preparations, consisting of α- and β-amylases, amylo-1, 6-glucosidase, and glucoamylase
from microbial sources, can carry out the hydrolysis of starch paste to near completion and are
used in the preparation of glucose or glucose syrups (chocolate syrup). By the combined action of
acid and enzyme hydrolysis, sugar syrups of the required flavour and consistency can be obtained.
Amylases also find use in brewing industry in the conversion of starch to maltose for fermentation.
They are also used for the removal of starch turbidity in jellies to increase sparkling properties.
Invertase is the enzyme that hydrolyzes sucrose to glucose and fructose. While sucrose is
dextrorotatory (positive optical rotation), the mixture of equimolar amounts of glucose and
fructose is levorotatory (negative optical rotation) due to the highly levorotatory property of
fructose. This product of hydrolysis is called invert sugar and the enzyme is thus named invertase.
Invert sugar is much sweeter than sucrose and is widely used in the confectionery industry.
Pectic enzymes play an important part in fruit ripening, maintaining the viscosity of processed
foods and in textural changes. They also find use in the food industry. The haziness noticed in fruit
juices and wines is due to pectic substances. While in some cases, as in fruit juices, the haziness is
desirable, in other cases it is objectionable. When clarified fruit juices are required, the colloidal
pectic substances can be hydrolyzed by the enzyme pectinase when the cloud-forming particles
settle down. Clear juices can be obtained by decantation or centrifugation. Similarly, wines can be
clarified using pectinases. If, on the other hand, cloudiness is required in juices, the pectinase is to
be destroyed by pre-heating the juice, before it is processed. Pectinases are also used in the
digestion of mucilagenous material in coffee manufacture.
Glucose isomerase converts glucose to fructose. Corn syrup treated with this enzyme gives high-
fructose syrup, which is 50 per cent more sweet than sucrose. High fructose syrup is used in the
manufacture of aerated drinks.
Proteases
Proteases are enzymes that cleave a protein molecule by the hydrolysis of peptide bonds. They
find important uses in many food industries, such as baking, meat tenderization, cheese
manufacture and beer manufacture.
The main constituents of wheat flour are starch and protein. In the baking industry, to obtain a
product of required volume, texture, flavour and better storage properties, it is necessary that both
starch and the protein gluten of wheat flour undergo some degradative changes. The required
changes in the properties of gluten in the preparation of bakery products are brought about by the
use of proteases from fungal sources.
A number of proteolytic enzymes from plant, animal and microbial sources are employed in
tendering meat. The enzymes hydrolyze one or more of the muscle components of meat resulting
in increased tenderness. The enzymes commonly used in tenderizing meat are trypsin, papain,
bromelin and ficin, and also other enzymes from fungal sources.
Rennin is the major proteolytic enzyme of the fourth stomach of the suckling calf. This enzyme
plays an important role in the production of cheese. The casein of milk is an aggregate of many
caseins. Rennin cleaves one peptide bond of one of the caseins (K-casein), resulting in the curdling
of milk. Curdling of milk by rennin yields a firm curd, which is the initial step in the manufacture
of cheese.
One of the problems in the production of beer is haze in beer. This could be due to the proliferation
of the infecting micro-organisms in beer or to the combination of proteins and tannins in the beer.
Proteolytic enzymes can successfully prevent the latter type of haze. By reducing the size of the
protein molecules by partial hydrolysis, the protein-tannin reaction is eliminated. The enzymes
papain, pepsin, ficin, bromelin and bacterial proteases are used to prevent beer haziness, the most
commonly used enzyme being papain.
Lipases
Lipases are enzymes that hydrolyze ester linkages in glycerides. The fatty acids produced from the
hydrolysis of triglycerides can lead to characteristic off-flavour in foods. Lipases are also involved
in the manufacture of cheese. During cheese ripening there is extensive hydrolysis of butter fat
resulting in the formation of various fatty acids responsible for the characteristic flavour of cheese.
For the production of milk with a slightly cured flavour for use in milk chocolate, lipases are used.
Oxidoreductases
In addition to hydrolytic enzymes discussed above, a number of oxidoreductases are of importance
in food science. Some of the important ones are the following:
Glucose oxidase: Glucose oxidase is an enzyme which oxidizes glucose to gluconic acid in
presence of oxygen, and in the process hydrogen peroxide is formed. The commercial preparation
of glucose oxidase contains catalase which quickly decomposes hydrogen peroxide to water.
Glucose oxidase is commercially used to remove traces of glucose and oxygen in a variety of food
products, such as beer, cheese, carbonated beverages, dried eggs, fruit pies, wines, etc., to prevent
deterioration during storage by oxidation and/or browning.
Glucose Oxidase
Glucose gluconic acid +H2O2
Catalase
2H2O2-------------------------------- > 2H2O + O2

Peroxidases: Peroxidases are enzymes which oxidize H2O2 or organic peroxides (e.g. methyl
hydrogen peroxide) in the presence of an oxidizable substance.
AH2 +ROOH ------------------- > A+H2O + R-OH
where AH2 is the hydrogen donor or oxidizable substance and ROOH is a peroxide. This enzyme
is quite heat stable. About 50 per cent of enzyme activity remains even after the enzyme is heated
at 85°C for over 30 min. Because of this property the activity of this enzyme is used to detect
effectiveness of blanching. The loss of peroxidase activity in a blanched food product is taken to
indicate the inactivation of the deteriorative enzymes.
Ascorbic oxidase: Ascorbic acid gets easily oxidized in the presence of ascorbic oxidase. It also
gets oxidized by atmospheric oxygen without the involvement of the enzyme. The enzymic
oxidation reactions are significant in the processing and storage of citrus fruit juices and
concentrates, and vegetable products. The oxidation results in a browning reaction and loss of
vitamin C activity.
Lipoxygenases: These enzymes bring about the oxidation of essential fatty acids resulting in the
development of off-flavour. The intermediate products of lipoxygenase action on lipids damage
vitamins and proteins in foods. Lipoxygenases are present in legumes like soyabean, mung bean,
green beans and peas, and in cereals such as wheat, oats, barley and corn. The off-flavour and
odour noticed sometimes in foods are due to the action of lipoxygenases on lipids present in them.
Lipoxygenases are used in some countries in the production of bread. The enzyme brings about
bleaching by oxidation of the natural pigments of the flour to produce a very white crumb.
A number of enzymes other than those mentioned above are also of importance in food science.
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