san xuat enzym trong trai cay

Enzymes in Fruit Juice Production and Fruit Processing
5.1.2.1 Introduction
The first application of enzymes in the fruit juice industry was the use of pectinases for
apple juice clarification in the 1930s [500]. The fast clarification of juice after breakdown
of pectin by pectinases and the decrease in juice viscosity resulted in a shorter process
and greatly improved the quality of industrial apple juice. Later, pectinases were applied
to depectinization of red-berry juice. The use of pectinases and amylases to degrade
apple pectin and starch during the hot clarification stage prevents post-bottling haze
formation, and thus concentration of the juice by a factor of six has become possible.
This results in a smaller storage volume, cheaper transportation, and better concentrate
stability without spoilage. Treatment of apple pulp with pectinases and hemicellulases
was introduced later: by lowering the viscosity of the pulp, the press capacity and the
yield were significantly improved. Depectinization of juice with pectinases with high
arabanase activity improved product quality further by preventing araban haze forma-
tion after concentration of the juice. In the production of clear and stable red-berry juice
or concentrate, hot maceration with enzymes ensures a higher juice yield and a better
112 5 Industrial Enzymes
color extraction [501]. Nowadays, enzyme suppliers provide fruit juice producers with
tailor-made enzyme preparations optimally blended on the basis of fruit composition
for improved quality and stability of finished products, together with shorter process
duration and larger plant capacity. In association with new equipment and processing
technologies, industrial enzymes allow processors to add value to raw material for food
and feed and to reduce waste quantity. Industrial processes are very diverse and
numerous. Here the most common are described, but differences still exist depending
on the company and plant.
5.1.2.2 Biochemistry of Fruit Cell Walls
The pulp of fruits and vegetables is composed of cells. They are surrounded by a cell
wall, which resists internal pressure and external shock (Fig. 34). Polysaccharides
constitute 90–100 % of the structural polymers of walls of growing plant cells, known as
primary cell walls. Secondary cell walls develop from primary cell walls during cell
growth. Cell wall composition depends on fruit species and evolves in dependence on

agronomic and climatic conditions, fruit ripeness, the type and duration of storage of
the fruit (cell growth and cell senescence). The composition of plant cell walls has been
widely studied, and numerous models of the three-dimensional structure have been
proposed [502–504]. Three major independent domains are distinguished: the xylo-
glucan network, the pectin matrix, and the structural proteins. The cellulose–xyloglu-
can network is embedded in the pectin matrix. Pectin is the major structural
polysaccharide component of fruit lamellas and cell walls. Three pectic polysaccharides
are present in all primary cell walls: homogalacturonan and rhamnogalacturonans I and
II [505] (Fig. 35). Recent models divide pectin into so-called smooth regions of
Fig. 34 Fruit cells (fc) and middle lamellae (ml) connecting the cell walls
Fig. 35 Model of pectin smooth regions (SR) and hairy
regions (HR) model [506]. Ara ¼ arabinose, Gal ¼ galactose,
GalA ¼ galacturonic acid, Rha ¼ rhamnose, Xyl ¼ xylose
5.1 Enzymes in Food Applications 113
unbranched homogalacturonan (60–90 %) and hairy regions of highly branched
rhamnogalacturonan I (10–40 %) [507], [508]. Homogalacturonan is a homopolymer
of (1!4)-a-D-galactosyluronic acid residues, capable of forming gels. Carboxyl groups
of the galactosyluronic acid residues of primary cell wall homogalacturonan can be
methyl-esterified at the C-6 position and acetyl-esterified at the C-2 or C-3 position.
Helical chains of homogalacturonan that are less than 50 % methyl-esterified can form
a gel-like structure and condense by cross-linking with calcium ions, which are present
in primary cell walls. Degree of methylation, molecular weight, and pectin content are
specific to fruit species (Table 10).
Table 10. Fruit pectin composition
Fruit
Apple
Blackcurrant
Grape
Orange peel
Pear

Pineapple
Strawberry
Pectin, wt %
0.5–1.6
1.0–1.2
0.1–0.4
3.5–5.5
0.7–0.9
0.04–0.1
0.5–0.7
Methylation wt %
80–92
50–80
50–65
65
50–70
22–40
20–60
114 5 Industrial Enzymes
These characteristics must be taken into consideration in choosing the right
pectinase balance for best fruit processing. During ripening, the protopectin in primary
cell wall is slowly transformed into soluble pectin by the action of endogenous
pectinases present in the fruit. The decrease in molecular weight is due to pectin
depolymerases, and the decrease in degree esterification mainly to pectin methylester-
ase. However, these activities are very low. Homogalacturonan contains chains of up to
about 200 galacturonic acid units, 100 nm long, with some rhamnose. A xylogalactur-
onan subunit (XGalA), substituted with xylose at the C-3 position of the galacturonic
acid residue, has been identified as part of the galacturonan backbone. It can be methyl-
esterified. Rhamnogalacturonan I (RGI) has a backbone of up to 100 repeats of the
disaccharide rhamnose-galactose. The side chain can vary in size from a single glycosyl

residue to 50 or more glycosyl residues [505]. In general, about half of the rhamnosyl
units of RGI have sidechains, but this can vary with cell type and physiological state.
[509].
Arabinans are mostly 5-linked arabinofuranosyl units forming helical chains, but
arabinosyl units can be interconnected at each free O-2, O-3, and O-5 position to form a
diverse group of branched arabinans [510]. The RGI of primary cell walls is branched
with (1!5)-a-L-arabinan, (1!3)- or (1!2)-a-L-arabinosyl residues, and arabinogalac-
tan (AG) type II with a (1!3),(1!6)-b-D-galactan backbone, with (1!3)-a-L-arabinosyl
residues [512, 511]. Other macromolecules such as cellulose, xyloglucan, and arabi-
nogalactan proteins (AGP) are associated with the plasma membrane [513]. Rhamno-
galacturonan II (RGII) is a low molecular weight (ca. 4.8 kdalton) complex
polysaccharide with a backbone of nine (1!4)-a-D-galactosyluronic acid residues
and four side chains attached to O-2 or O-3 of the backbone.
The side chains are composed of twelve different sugars [514] — apiose, 2-O-methyl-
l-fucose, 2-O-methyl-D-xylose, aceric acid (3-C-carboxy-5-deoxy-l-xylose), Kdo (3-deoxy-
D-manno-octulosonic acid), Dha (3-deoxy-D-lyxo-heptulosaric acid) — bound in more
than 20 different linkages. The two main hemicelluloses of all primary cell walls are
xyloglucan and arabinoxylan. Hemicelluloses bind tightly via hydrogen bonds to the
surface of cellulose linking or cross-linking microfibrils to create a cellulose–hemi-
cellulose network. Interconnections with the pectic polysaccharides are of primary
importance for the integrity of the pectin network. Cellulose is a (1!4)-b-D-glucan
which accounts for about 20–30 % of the dry matter of most primary cell walls and is
particularly abundant in secondary cell walls. In 1993-1994, VINCKEN and VORAGEN
demonstrated that xyloglucan was a key structure of apple cell walls for the degradation
of cell-wall-embedded cellulose (around 57 % of the apple cell-wall matrix) [515]. The
cellulose–xyloglucan network determines the strength of the cell wall and is embedded
in an independent pectin matrix, hemicelluloses, and proteins. In apples the xyloglucan
fraction makes up about 24 % of the total amount of sugar. About 5 wt % of some
primary cell walls is made up of the hydroxyprolin-rich structural glycoprotein extensin,
which binds some polysaccharides together. Fractions of the different macromolecules

in fruit are given in Table 11.
Starch is present in unripe apples in amyloplasts. This is the largest biological
molecule, with a molecular weight of 10
5
–10
9
dalton. Starch is composed of two
components: amylose and amylopectin [516]. Amylose, the minor component, is a
Table 11. Fruit cell wall composition in g/kg fresh matter
5.1 Enzymes in Food Applications 115
Fruit EIR Pectin Hemicellulose Cellulose Lignin Protein Total
Apple
Pear
Mango
20
15
25
272
281
408
169
148
91
349
267
236
2
69
27
76

82
127
868
847
889
Pineapple 13
Strawberry 12
Raspberry 20
163
411
168
267
66
89
210
232
177
85
11
73
94
255
277
819
975
784
Cherry
Papaya
13
26

396
364
49
165
130
124
169
4
244
127
988
784
*Ethanol-insoluble residue.
(1!4)-a-D-glucan and has a linear structure. Various degrees of polymerization have
been ascribed to this fraction, with chain lengths in the range of 100–1000 glucose
units. Amylopectin contains a-(1!6) and a-(1!4) glucose linkages. Amylopectin
exhibits branching at the 1!6 position, and its degree of polymerization is far higher
than that of amylose. The ratio amylose/amylopectin can vary in natural starches in the
general range 1/3 to 1/4.
5.1.2.3 Cell-Wall-Degrading Enzymes
Pectinases Progress in enzymology has been so fast that certain activities are not yet
described in the International Enzyme Classification (E.C. no.). Many microorganisms
produce enzymes that degrade fruit cell walls. Commercial pectinases for the fruit juice
industry come from selected strains of Aspergillus sp. Enzymes are produced during
fungal growth, purified, and concentrated. Pectinases are defined and classified on the
basis of their action toward pectin (Fig. 36). Pectin lyase (PL, E.C. 4.2.2.10) is a pectin
Fig. 36 Fruit pectin and pectin-degrading enzymes.
Ara ¼ arabinose, Gal ¼ galactose, GalA ¼ galacturonic acid,
OMe ¼ methyl ester, OAc ¼ ethyl ester, Rha ¼ rhamnose, Xyl ¼ xylose.
116 5 Industrial Enzymes

depolymerase of the endo type which has a great affinity for long, highly methylated
chains and acts by b-elimination of methylated a-1,4 homogalacturonan with the
formation of C4-C5 unsaturated oligo-uronides [517]. Pectin methylesterase (PME,
E.C. 3.1.1.11) removes methoxyl groups from pectin, and at the same time decreases
the affinity of PL for this substrate. This results in the formation of methanol and less
highly methylated pectin. PME from Aspergillus has a strong affinity for highly meth-
oxylated pectin such as apple pectin and acts according to a multichain mechanism [518].
Demethylation with PME generates free carboxylic acid groups and the pectin becomes
negatively charged. Polygalacturonase (PG, E.C. 3.2.1.15) exists in two forms: endo-PG
and exo-PG. Both types act only on pectin with a degree of esterification of less than
50–60 %. Endo-PG acts randomly on the a-1,4-polygalacturonic backbone and results in a
pronounced decrease in viscosity. Exo-PG acts at the nonreducing end of the chain. Exo-
PG releases small fragments from the chain and does not significantly reduce the
viscosity.
Seven endo-PGs, two exo-PGs, and seven PL isoenzymes from Aspergillus niger have
been described [519], [520]. Different enzymes acting on rhamnogalacturonan I
were identified and purified from Aspergillus sp. [521]. RGase A was identified as a
hydrolase that splits the a-D-GalAp-(1!2)-a-L-Rhap linkage of RGI, while RGase B
appeared to be a lyase that splits the a-l-Rhap-(1!4)-a-D-GalAp linkage by b-elimina-
tion. Two novel enzymes were also identified: a rhamnogalacturonan rhamnohydrolase
and a rhamnogalacturonan galacturonohydrolase. As an accessory enzyme for the
RGases, rhamnogalacturonan acetyl esterase (RGAE) was also described. Although the
structure of RGII substrate has been described, enzymes able to hydrolyze it are still
unknown and have not been described yet (2003).
Arabanases are pectinases, since they remove arabinose covalently bound to the
homogalacturonan backbone. Three enzymes have been described: an endo-arabinanase
(a-1!5; ABFA) and two arabinofuranosidases, namely, exo-arabinofuranosidase A
(a-1!2;a-1!3) (ABFA) and exo-arabinofuranosidase B (a-1!3;a-1!5; ABFB; E.C.
3.2.1.55). All three are produced by Aspergillus niger [522]. High activities are required for
apple and pear processing. In general, pectinase activity and ratio of the different

pectinases can vary in different commercial preparations.
Hemicellulases Hemicellulases are enzymes that hydrolyze arabinogalactans, galac-
tans, xyloglucans, and xylans. Arabinanases are classified as pectinases when they act on
pectin side arabinans. They are also classified as hemicellulases when acting on
arabinogalactans or arabinoxylans. Aspergillus sp. produces enzymes that hydrolyse
arabino-(1!4)-b-D-galactans type I and arabino-(1!3)-(1!6)-b-D-galactans type II
[512], [523], [524].
The exo-(1!3)-b-D-galactanase is able to release galactose and (1!6)-b-D-galacto-
biose. Aspergillus enzyme is able to bypass a branch point in a b-(1!3) backbone. The
action of this enzyme is enhanced by the presence of ABFB. Xylanases hydrolyse the
(1!4)-b-D-xylans in synergy with ABFs [525].
Amylases In fruit juice industry, fungal acid amylase and amyloglucosidase are used
to process fruits which contain starch. This is the case for unripe apples at harvest time.
5.1 Enzymes in Food Applications 117
Aspergillus niger produces acid a-amylase and amyloglucosidase [526]. These exogenous
enzymes are applied after starch gelatinization (occurring above 75 8C) for preventing
post-bottling haze formation (starch retrogradation). Acid endoamylase (AA) acts on
amylose and amylopectin. It produces dextrins, which are substrates for glucoamylase
or amyloglucosidase (AG) a-1!4,1!6 exo-hydrolase, which release glucose from the
non-reducing end of the chain.
5.1.2.4 Apple Processing
After oranges, apples are the most important raw material worldwide for the production
of clear juice and clear concentrate. In 2004/2005 1.3 10
6
t of apple juice was produced
[528]. The major producers of apple juice are China, Poland, and Argentina [527].
5.1.2.4.1 Apple Pulp Maceration
The current trend is to process apple juice from table varieties having defects or not sold
for table consumption (Golden Delicious, Granny Smith, Jonagold, Red Delicious).
Apples processed in the crop period are easily pressed with a relatively high yield. They

are stored at low temperature in controlled atmosphere for several months and
processed according to market demand. During storage, the insoluble protopectin
is slowly transformed into soluble pectin by endogenous apple pectinases (protopecti-
nase type), and starch is slowly degraded by endogenous apple amylases into glucose
and consumed during post-harvest metabolism. Soluble pectin content can increase
from 0.5 up to 5 g per kilogram of over-ripe apple [529]. Apples become difficult to press
unless macerated with pectinases (Fig. 37). In the traditional process, enzymes are used
at two different stages (Fig. 38). Application of commercial pectinases from Aspergillus
sp. in apple mash is necessary because activity of endogenous enzymes is too low to
cause an immediate noticeable effect. Because apple pectin is highly methylated,
commercial enzyme preparations must contain a high concentration of pectinlyase or
pectin methylesterase in association with polygalacturonase and arabanase, together
with side activities such as rhamnogalacturonase and xylogalacturonase. Rapidase
Press (DSM), Rapidase Smart (DSM), Pectinex UltraSP (Novozymes), and Rohapect
MA+ (AB Enzymes) pectinases sold for apple pulp maceration contain enzymes
necessary to obtain a good pressability and high yield throughout the entire season.
Fig. 37 Effect of pectinases on percentage apple juice yield during the processing season
118 5 Industrial Enzymes
Fig. 38 Production of apple concentrate
Commercial products contain more or less the enzyme activities described below, but
with different ratios from non-GM and GM organisms.
Pulp enzyming results in a fast decrease in pulp viscosity, a large volume of free-run
juice, and fast pressing. The yield is over 90 % with hydraulic press and pomace
leaching, compared to 75–80 % maximum without enzyme treatment.
5.1.2.4.2 Apple Juice Depectinization
Pectin is the main cause of juice turbidity. One liter of juice with 13 % dry matter can
contain 2–5 g of pectin after pressing, depending on the ripeness of the fruit. Pectinase
dosage is determined in the laboratory by performing the alcohol test. Acidified ethanol
(2 volumes of ethanol containing 0.5 % HCl þ 1 volume of apple juice) is used to
precipitate residual pectin with a molecular weight of up to 3000 dalton. It is important

to use acidified ethanol; otherwise, precipitation of organic acids or calcium pectate
occurs because of the pH change after mixing ethanol with the juice, and thus a a false
positive result is obtained. Pectinlyase or pectin methylesterase plus polygalacturonase
and arabanase are the most important enzymes. Arabinose represents 55 % of neutral
sugars in hairy regions of apple pectin. Arabanase activity prevents haze formation after
juice concentration. The juice clarification is carried out after enzymatic depectiniza-
tion [530]. The first stage consists of destabilization of the cloud by PL, which has no
Fig. 39 Apple juice depectinization
5.1 Enzymes in Food Applications 119
visible effect but results in a strong decrease in the viscosity of the juice (Fig. 39). PL cuts
pectin at random, and cutting 1–2 % of the linkages is enough to reduce apple juice
viscosity by 50 %. PG becomes active only after the action of PME. Because of its high
molecular weight, PG cannot hydrolyze pectin with a degree of methylation greater
than 50–60 % due to steric hindrance. At this stage, PL is no longer active and pectin
hydrolysis is due to the system PME/PG. The second stage is cloud flocculation. The
sedimentation necessary for the clarification of apple juice occurs only after enzymatic
degradation of pectin and starch. The cloud is composed of proteins that are positively
charged at the pH of the juice (3.5–4.0) since their isoelectric point lies between pH 4.0
and 5.0. These proteins are bound to hemicelluloses that are surrounded by pectin as a
negatively charged protective colloid layer. Pectinases such as Rapidase C80 Max
(DSM), Pectinex C80 Max (Novozymes), and Rohapect DAL (AB Enzymes) partially
hydrolyze the pectin gel, and thus results in the electrostatic aggregation of oppositely
charged particles (positive proteins and negative tannins and pectin), flocculation of the
cloud, and then clarification of the juice [530]. The optimal pH for this mechanism is
3.6. The alcohol test shows whether juice depectinization is complete.
At the beginning of the processing season, unripe apples contain 5–7 g of starch per
liter of juice. At this point, the iodine test gives a dark blue color and starch can be
precipitated with iodine. Starch is present as granules 2–13 mm in size, composed of 30 %
amylose and 70 % amylopectin chains. The latter can fix 20 wt % iodine. Apples contain
endogenous amylases, but the process is too short and activities are too low to degrade the

starch. When the juice is heated to 75–80 8C, starch changes from an insoluble form to a
soluble form (gelatinization with water). If no amylase is added, these molecules can
subsequently undergo retrogradation and form large aggregates that are difficult to
hydrolyze and clog filters. The addition of fungal amylase and amyloglucosidase results in
the hydrolysis of soluble starch into glucose monomers. Retrogradation and post-bottling
haze formation are prevented, and clarification and filterability are improved. Prepara-
tions such as Hazyme DCL (DSM) and AMG (Novozymes) contain a-amylase and
amyloglucosidase from Aspergillus niger. The dosage is determined by the iodine test. The
third stage is clarification with finings and sheet filtration, which is being replaced by
micro- or ultrafiltration (UF). Inorganic membranes have cut-offs from 20 000 to
500 000 dalton. Insoluble particles and soluble undegraded molecules such as parts
of RGI, RGII, proteins including enzymes, and polyphenols, remain to a greater or lesser
extent in the retentate, depending on the cut-off of the filtration membrane. Recently, it
120 5 Industrial Enzymes
was found that undegraded RGI, RGII, and dextrins can foul UF membranes. Rapidase
UF (DSM) and Novoferm 43 (Novozymes) contain rhamnogalacturonases and other side
activities to improve ultrafiltration flow rate.
In conclusion, apple juice is easily produced after pulp maceration and juice depecti-
nization with enzymes, with possible concentration of up to 708 brix (percentage by weight
of soluble solids in a syrup at 68 8F), without risk of gel or haze formation. A few producers
make ‘‘natural’’ or cloudy apple juice, e.g., in Germany and the USA. Until now, they did
not add enzymes, because the existing commercial pectinases induce fast clarification of
the juice. DSM sells a purified pectin methylesterase without pectin depolymerase activity.
It can be used in the cloudy-juice process at the maceration stage to improve the yield, and
also in the French cider process with calcium for defecation with flotation techniques.
5.1.2.5 Red-Berry Processing
The production of clear juice and concentrate from blackcurrant, raspberry, or
strawberry requires enzymatic maceration and depectinization [531], [532]. Clarifica-
tion, filtration, and concentration are difficult because these juices have high pectin
content (typical content of residual low molecular weight pectin of 7 g L

1
compared to
0.5 g L
1
in apple juice). It is assumed that pectin hairy regions remain as soluble colloid
in the juice and hemicelluloses tend to bind to phenolics and proteins during
processing and storage. The result is the formation of irreversibly linked brown
complexes that enzymes can no longer break down. An additional problem is related
to the frequent contamination of red berries, mainly strawberry and raspberry, with
Botrytis cinerea. This parasitic fungus, growing on rotten berries, secretes a b-1,3-1,6-
linked glucan into the berries with a molecular weight of ca. 10
6
dalton [533]. This gum
reduces the filterability and the clarity of the juice. It is possible to hydrolyze this glucan
with b-glucanases with Filtrase (DSM)Glucanex (Novozymes).
Single-Stage Red-Berries Process The single-stage process consists of simultaneous
blackcurrant or blackberry maceration and depectinization (Fig. 40). Pectinases are
used to improve juice and color extraction while retaining the organoleptic properties of
the fruit. However, the extracted color is sometimes partly destabilized by anthocya-
nases (side activities of pectinases) or by oxidation. Oxidation can be chemical or
enzymatic, due to the endogenous polyphenol oxidase (PPO) of the fruit, and is
catalyzed by metal ions. It is therefore recommended that the pulp be heated to
90 8C to inhibit fruit oxidases prior to maceration with enzymes. Some red berries are
very acidid (pH 2.6–2.8) and have high contents of phenolics and anthocyanins, which
are inhibitors of pectinases. Hence, red-berry processing requires commercial pecti-
nases that are especially stable under these conditions. This is the case for Klerzyme 150
(DSM), Klerzyme Intense (DSM), and Pectinex BEXXL (Novozymes).
Two-Stage Red-Berries Process The two-stage process consists of enzymatic macera-
tion of fruit pulp, followed by a second addition of enzyme for juice depectinization at
low temperature. Raspberries or gooseberries are heated to 90 8C for at least two

minutes to increase color extraction and to destroy fruit polyphenol oxidase. The pulp is
then cooled to 20–25 8C for enzymatic maceration. After pressing, the extracted juice is
Fig. 40 Production of blackcurrant concentrate
5.1 Enzymes in Food Applications 121
depectinized with pectinases. The low processing temperature after heating prevents
aroma losses, and high-quality juices and concentrates can be produced. In the case of
strawberries, it is inappropriate to heat the pulp because it would create an unpressable
pure´e, aromas loss, and juice browning. Hence, strawberries are processed at ambient
temperature [532].
5.1.2.6 Tropical Fruit and Citrus Processing
Tropical Fruit Tropical fruit is mainly processed to pure´e and stored before further
processing to cloudy or clear juice. Fruit pure´e, cloudy or clear juice from apricot, peach,
kiwi, mango, guava, papaya, and banana are often processed without enzymes. The
main problem is viscosity, which can be decreased with pectinases [528]. Pectinases and
amylases can be later used for clear juice production.
122 5 Industrial Enzymes
Fig. 41 Citrus processing
Citrus Fruits The development of frozen concentrated orange juice started in 1940.
Orange juice is the most consumed fruit juice in the world. Citrus fruit processing
includes exploitation of all byproducts, among which pectin and essential oils are the
most significant (Fig. 41). Although in certain countries it is not permitted to use
enzymes in the production of premium orange juice, they can be used in other
applications. Enzymes can increase the yield of solids recovery during pulp washing,
facilitate the production of highly concentrated citrus base, improve recovery of
essential oil from peel, debitter juice, and clarify lemon juice [528]. An example of
citrus processing using enzymes is fruit peeling. The whole orange or grapefruit is
treated with pectinases for digestion of albedo (the white, inside part of the peel), which
binds flavedo (the orange or yellow, outside part of the peel). The fruit peel is scored and
whole fruits are treated with a 2 % pectinase solution by vacuum infusion technology.
After vacuum break, fruits are maintained at 40 8C for 15–60 min for albedo digestion

inside the fruit. Peeled fruits are then rinsed, cooled, and packed.
Another example is the production of clear lemon concentrate. Cloudy lemon juice
coming from the extractor contains particles composed of pectin and proteins remain-
ing in suspension and binding citral aroma (predominant lemon flavor). Clarification of
lemon juice was achieved in the past by addition of large amounts of bentonite or sulfur
dioxide. Today, clarification can be carried out with the very acidic pectinase Clarex
Citrus 12XL (DSM), which degrades the pectin part of the cloud. Enzymes are added to
the juice in amounts of 10 g hL
1
at 8–10 8C to avoid juice oxidation. The insoluble
solids are removed by filtration or ultrafiltration. The brilliant lemon juice can be
concentrated at 658 brix.
5.1.2.7 Conclusion
5.1 Enzymes in Food Applications 123
Nowadays, enzyme producers provide a wide range of pectinases for processing of fruit
to give various products such as puree, cloudy juice, clear juice, and concentrate. The
evolution of technology and processes including enzymes allow processors to obtain
higher juice yield (productivity) together with higher quality of finished products. The
use of specific pectinases adapted to the fruit process improves the shelf life of juices
and concentrates (stability of color and freedom from turbidity). Apart from juice
processing, the wide range and the high specificity of commercial enzymes open the
way to new processes and new types of fruit-derived products. The trend is to process
fruit under milder and more strictly controlled conditions to obtain new fruit products
with sensory characteristics closer to those of fresh fruit.
However, because processing technology evolves faster than regulation, it is neces-
sary to define food standard values and process references (equipment, process stages,
type of enzymes. . .). In Europe, a Code of Practice has been developed to maintain
quality and authenticity standards [534]. Members of Association of the Industry of
Juices and Nectars from fruits and vegetables (AIJN) in parallel with the Association of
Microbial Food Enzyme Producers (AMFEP) have established references for fruit juice

composition and enzyme specifications, in line with commercial standards and
regulations of different countries.