Food Biochemistry and Food Processing (2 edition)

BLBS102-c28 BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come

28 Biochemistry of Fruit Processing 561

HCNH 2

H OH

HO H

H OH

H O

CH 2 OH

HC

H OH

HO H

H OH

H O

CH 2 OH

NH 3 CH

H OH

HO H

H OH

H OH

CH 2 OH

NH 2

HC

O

HO H

H OH

H OH

CH 2 OH

–H

NH 2

CH 2 NH 2

H O

HO H

H OH

H OH

CH 2 ÖH

H 2 NCH 2 COH

HO H

H OH

H OH

CH 2 O

alpha-D-Glucopyranosylamine

1-Amino-1-deoxy-alpha-D-fructopyranose

+ H

H

Figure 28.2.Amadori rearrangement in amino sugars.

press aid such as up to 1–2% paper pulp or rice hulls or both

in order to reduce spillage and increase juice channel in the

mash. The apple mash has many natural enzymes. Pectinolytic

enzyme products contain the primary types of pectinases, pect-

inmethylesterase (PME), polygalacturonase (PG), pectin lyase,

and pectin transeliminase (PTE). PME deesterifies methylated

carboxylic acid moieties of pectin, liberating methanol from

the side chain, after which PG can hydrolyze the long pectin

chains (Fig. 28.3). Enzymatic mash treatment has been devel-

oped to improve the pressabiliy of the mash and, therefore the

throughput and yield. An amount of 80–120 mL of enzyme per

ton is added to the apple mash in order to break down the cell

structure. High-molecular weight constituents of cell walls, like

protopectin, are insoluble and inhibit the extraction of the juice

from the fruit and keep solid particles suspended in the juice.

Pectinase used in the apple juice processing is extracted from the

fungusAspergillus niger. Pectinase developed for apple mash

pretreatment acts mainly on the cell wall, breaking the structure

and freeing the juice. Also, the viscosity of the juice is lowered,

and it can emerge more easily from the mash. The high content of

pectin esterase (PE) causes the formation of deesterified pectin

fragments, which has a low water-binding capacity and reduces

the slipperiness. These pectins consist of chains of galacturonic

acid joined by alpha-glycoside linkage. In addition, polymers

of xylose, galactose, and arabinose (hemicelluloses) form a link

with the cellulose. The entire system forms a gel that retains the

juice in the mash. The extraction is easier, even if the pectins

are partially broken by pectinesterase. The pomace acts like a