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

560 Part 5: Fruits, Vegetables, and Cereals

Unsaturated

carbonyl compounds

Polymer

H+

Diketose-amino compound

Monoketose-

amino compound

–H 2 O

Deoxyosones + other

carbonyl compounds

N-containing

compounds

Aldose-amino compound

Unsaturated osones

Aldosylamino Furfurals

compounds

MELANOIDINS

Copolymer Polymer

Figure 28.1.Mechanism of browning reaction.

and crushed apple juice and concentrates. The most popular

type of apple juice is the one that has been clarified and fil-

tered before pasteurization and bottling. Natural juice is a juice

that comes from the press. Up to 2% of ascorbic acid can

be added before pasteurization and bottling in order to pre-

serve the color. Crushed apple juice is produced by passing

coarsely ground apples through a pulper and desecrator before

pasteurization.

Juice concentrates can be two types: frozen, when the Brix

is about 42◦, or regular (commercial) concentrate with a Brix

of 70◦or more. Regardless of the type of apple product that is

to be produced, the quality of the apple juice is directly related

to the quality of the raw material used in its production. Only

sound ripe fruits should be used in the processing of apple juice.

“Windfalls” or apples that are fallen and picked from the ground,

should not be used for the juice due to the risk of contamination

by pathogens such asE. coliO157:H7,C. parvum,Penicillium

expansium(producing the mycotoxin patulin) and also the risk of

pronounced musty or earthy off-flavor of the juice. Overmature

apples are very difficult to process, whereas immature apples

give a starchy and astringent juice with poor flavor.

The processing of apple juice starts with washing and sorting

of the fruit in order to remove soil and other foreign material as

well as decayed fruits. Any damaged or decayed fruit should be

removed or trimmed in order to keep down the level of patulin in

the finished juice. Patulin is an indicator, which tells if the juice

was produced from windfalls or spoiled apples. The acceptable

level of patulin in most countries is less than 50 ppb. Patulin

is carcinogenic and teratogenic. Various methods are currently

used to reduce the levels of patulin in apple juice, namely, char-

coal treatment, chemical preservation (sulfur dioxide), gamma

irradiation, fermentation, and trimming of fungus-infected ap-

ples. A recent study shows that pressing followed by centrifuga-

tion resulted in an average toxin reduction of 89%. Total toxin

reduction using filtration, enzyme treatment, and fining were 70,

73, and 77%, respectively, in the finished juice. (Bissessur et al.

2001). Patulin reduction was due to the binding of the toxin to

solid substrates such as the filter cake, pellet, and sediment.

Prior to pressing, apples are ground using disintegrators, ham-

mers, or grating mills. The effectiveness of the pressing oper-

ation depends on the maturity level of the fruits, as more ma-

ture fruits are often difficult to press. A wide range of presses

is used in juice extraction including hydraulic, pneumatic, and

screw/basket type. The vertical hydraulic is a batch-type press

and requires no press aid. The main disadvantage is that the

press is labor intensive and produces juice with low solids con-

tent. Hydraulic presses are the oldest type of press and are still

used worldwide. The newer versions are automated and require