Food Biochemistry and Food Processing (2 edition)

BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come

192 Part 2: Biotechnology and Enzymology

then serve as substrates for exocellulases to produce smaller

oligosaccharides (such as cellobiose and cellotetrose), and the

latter molecules are hydrolyzed further by cellobiases intoβ-d-

glucose units.

Cellulase is used in coffee processing to hydrolyze cellu-

lose during drying of the beans. They are also used extensively

in laundry detergents, in textile, pulp, and paper industries, as

digestive supplements in pharmaceutical applications, and to

facilitate in the biotransformation of feedstock into biofuels,

although this process is presently in its infancy. The enzyme is

marketed commercially asCelluclastby Novozymes and is used

to digest cellulose into fermentable sugars in the form of glucose

oligomers, cellobiose, and glucose, or to reduce the viscosity of

soluble cellulosic materials.

Invertases and Sucrases

Invertases, also known asβ-fructofuranosidases, are enzymes

that hydrolyze the disaccharide sucrose into its corresponding

monosaccharide units, fructose and glucose, that is,

Sucrose+H 2 O⇔Fructose+Glucose

Sucrases also spilt sucrose into equimolar mixtures of glu-

cose and fructose, the difference between the two being that

invertases split the O–C (fructose) bond, while sucrases break

the O–C (glucose) bond. The equimolar mixture of glucose and

fructose thus produced is known as invert sugar or artificial

honey. Invertase is produced for commercial use from the yeast

S. cerevisiaeorS. carlsbergensis, although bees also synthesize

the enzyme to make honey from nectar. The enzymes are also

present in bacteria (Bogs and Geider 2000), in the cell walls and

vacuoles of higher plants like carrots (Quiroz-Castaneda et al.

2009), tomatoes (Elliot et al. 1993), as well as in the seeds,

stems, roots, and tubers of several higher plants (Cooper and

Greenshields 1961, 1964).

Invertase is produced and marketed commercially under the

brand name Maxinvert by Novozymes and is used extensively in

the confectionery industry to make products such as chocolate-

covered berries and nuts, soft-centered candies, marshmallows,

and fudges. Invertase derived from yeast is also commercially

available from Enzeco for the inversion of sucrose into a mixture

of fructose and glucose.

Pectinases

Pectinase or pectic enzymes are a group of carbohydrases that

hydrolyze pectins, large and complex heteropolysaccharides

comprising of 1,4-α-d-galactosyluronic acid residues. Pectins

occur naturally in fruits and can contribute to the viscosity and

haziness of alcoholic and nonalcoholic beverages. Pectic en-

zymes act to break down pectins into smaller molecules to en-

hance their solubility. By this action, pectic enzymes clear hazes

in beverages that form from residual pectins in the juices and

also increase the yields of fruit juices. Members of the pecti-

nase family of enzymes include pectinesterase (also known as

pectyl hydrolase, pectin methyl esterase, or PME) and poly-

galacturonase. They are widespread in the cell walls of higher

plants (e.g., avocado, carrots, tomato), as well as in some bacte-

ria (e.g.,B. polymyxa,Closytidium multifermentans,andEr-

wina aroideae), fungi (e.g.,A. niger,Penicillium digitatum,

Geotricum candidum,andFusarium oxysporum), and yeasts

(e.g.,S. fragilis). PME catalyzes the hydrolysis of pectins via

the removal of methoxyl groups to form pectic acids, that is:

Pectin+H 2 O⇔Pectic acid+Methanol

Pectin lyase also known as pectolyase hydrolyzes pectins via

eliminative cleavage of (1,4)-α-d-galacturonan methyl esters

in pectins with 4-deoxy-6-O-methyl-α-d-galact-4-enuronosyl

residues at the nonreducing termini. Food-grade pectolyase is

produced on a commercial scale from fungi and is used to re-

move residual pectins in wines and ciders. The enzyme is also

used in combination with cellulase in plant cell culture to de-

grade plant cell walls to generate protoplasts.

Polygalacturonases (PGases) break down the glycosidic

bonds linking the galacturonic acid residues in the polymer,

and they may be either endo or exo in action. The endo-PGases

cleave the 1,4-α-d-galactosyluronic acid residues of pectins in

a random fashion, while the exo-PGases degrade pectins by ter-

minal action to produce galacturonic acid residues.

A variety of pectic enzymes are commercially available from

Novozymes for applications in the food industry. Examples in-

clude Pectinex (a mixture of pectinases produced fromA. niger)

for fruit and vegetable juice processing and the maceration of

plant tissues, Peelzym (produced fromA. aculeatus) for hands-

free peeling of citrus fruits, and NovoShape (produced fromA.

aculeatusandA. oryzae) for maintaining the shape and structure

of whole chunks or pieces of fruits in a finished product.

Fructosidases

Fructosidases, also known as inulases, are a group of enzymes

that catalyze the hydrolysis of inulin or fructans into simpler

components. Inulin is a linear polysaccharide naturally present in

plants. The linear chains consist of about 35 fructose molecules

linked together byβ-1,2-glycosidic bonds and terminating in a

glucose unit. Interest in this group of enzymes has been growing

in recent years because of their capacity to form industrial fruc-

tose from fructans. These enzymes are commonly found in plants

and are also produced by microorganisms such asAspergillus

sp.,S. fragilis,andS. marxianus. Fructosidases produce fructose

from inulin in high yield for commercial use (Singh et al. 2007,

Sirisansaneeyakul et al. 2007, Munoz-Guti ̃ ́errez et al. 2009).

Lipases

The term lipases is used to refer to a large group of hy-

drolytic enzymes that catalyze the breakdown of ester bonds

in biomolecules such as triglycerides (TGs), phospholipids,

cholesterol esters, and vitamin esters. On the basis of the nature

of their substrate molecules, lipases are classified into triacyl-

glycerol lipase (or true lipases), phospholipases, sterol esterase,

and retinyl-palmitate esterase. For TGs, arguably the most

abundant food lipids, lipases hydrolyze the ester bonds in TGs

to form free fatty acids and glycerol. Lipases belong to theα/β