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

562 Part 5: Fruits, Vegetables, and Cereals

O

O

O O O

O O O

H 3 COOC HOOC H 3 COOC H^3 COOC

Pectin-methyl-esterase

___________________________________________________________

O

O O O

O O O

O

HOOC HOOC HOOC HOOC

_____________________________________________________

Polygalacturonase

HOH HOH

O

HOOC

(n)

O

O

O

O

O

O

O

O

H 3 COOC HOOC H 3 COOC H^3 COOC

_____________________________________________________Pectin-transeliminase

O

H 3 COOC

O O

O

HOOC H 3 COOC

O

O

H 3 COOC

HOH

O

O

HOOC

HOH

O

HOH HOH

O

H 3 COOC HOOC

(n) (n)

Figure 28.3.Diagrammatic representation of the site of action of various pectinolytic enzymes.

pressing aid, when used with mash predraining. The applica-

tion of enzyme treatment can increase the press throughput by

30–40% and the juice yield by over 20%. Mash pretreatment

also increases the flux rate of ultrafiltered apple juice by up to

50%. An important by-product of apple juice industry is pectin.

Therefore, overtreatment of mash with pectinolytic enzymes

could render the pomace unsuitable for the production of pectin.

Inactivation of the enzyme after reaching the appropriate level

of pectin degradation is an important step in the production of

apple juice. Residual pectic enzymes in apple juice concentrate

could cause setup problems, when used for making apple jelly.

There is a recent development in apple juice extraction with the

process of liquefaction. Liquefaction is a process of completely

breaking down the mash by using an enzyme preparation, tem-

perature, and time combination. The liquefied juice is extracted

from the residual solid by the use of decanter centrifuges and ro-

tary vacuum filters. It is a common practice, with the addition of

cellulose enzyme to the mash to further degrade the cellulose to

soluble solids, increasing the juice Brix nearly by 5◦. The com-

mercially available enzyme preparations contain more than 120

substrate specific enzyme components. Another popular extrac-

tion method is the countercurrent extraction method, developed

in South Africa and refined in Europe in the 1970s. The principle

of the system is as follows: the mash is heated, predrained, and

counterwashed with water and recycled hot juice. A 90–95%

recovery is possible when the throughput is about 3 tons per

hour. The main disadvantage of the system is the lower solu-

ble solids content of the obtained juice (6–8 vs. 11–12 from