الفهرس 
Structure, Occurrence and Function of Pectic Substances
Occurrence and functionOnly 14 pages are availabe for public view
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Abstract
-SU-J-O-I-A-R-Y
One of the moat important contents of fruitsare the
pectin and the pectic substances, These substances beside
being structural components of the fruit, they play a
major role in holding the juice contained in the fruits.
Thus, the pectins have decisive role in the determining the
juice yield. Furthermore they have significant effects on
the properties of the resulting juice. In order to obtain
highest yield of the juice possible it has been found necessary
to break-down the pectin polymers present in the tissues
in the fruits. Such processes are carried out in the industry
using various pectic enzymes particularly those obtained
from microorganisms.
1- In the present investigation, screening studies were
carried out in 38 fungal cultures with respect to their
ability to produce polygalacturonase (PG). Pec.in methyl
esterase (PE) pectin lyase (PL). The scre~ning studies
were c~rried out on two media, one which containing
pectin and other containing sucrose as the sole sourcE
carbon.
2- With respect ~o PG enzyme, the highest enzymatic activities
were obtained on pectin containing media u~ing
Asp. niger DSM 823, Asp. aculeatus DSM 63261, Mucor
pusillua QM 346 and Asp. foetidus DSM 734.
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3- On sucrose containing media the activities of PG’s were
generally lower than those obtained in pectin containing
media. Highest activity were obtained from Mucor pus”:..lus
QM 346, ~· alliaceus DSM 913, Asp. ustus DSM 1149,
Asp. aculeatus DSM 6)261.
4- In case of pectin lyase (PL) the enzyme was detected on~y
on pectin containing media. Little or no activity was
detected in the presence sucrose as a carbon source.
5- With respect to pectin methyl esterase (PE) o~y very
few cultures namely:
Asp. phoeni~is DS.i!. 62068
Asp. alliaceus DSM 813
Asp. ni~er QM 731
Asp. niger DSM 63263
Fusarium oxysporum LC
~· terricola DSM 63305
Asp. oryzae DSM 1864
Aop. fumigatus DSM 819
Asp. ochraceus DSM 824
Rhizopus oryzae DSK 853
produced detectable amounts of this enzyme on pectin
containing media.
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6- Two organisms namely Asp. aculeatus DSM 6)21 Mucor pu
pusillus QM 346 were selected to study the production
physiology and biochemical properties of their polygalacturonase
activity.
7- Physiological studies on formation of polygalacturonase
by Asp. ~uleatus and 1tucor pueillus have shown that
the production of polygalacturonase is affected by culture
conditions:
(a) The pectin salt medium (PSM) was the best medium for
both cultures for production of polygalacturonase
activities. This medium was superior to wheat bran
medium and also to the medium containing a mixture
of wheat bran + pectin with respect to en~v~.e production.
(b) Vs.rioufl carbon sources were tet>teC: namely pectin,
pe:::tic acid, sucrose, glucose, galactose, lRcto::_,
a:-abir:ose, cellobiose ar:cl soluble s’arch. :;:t .. as
fcWJd ir. ss.se o:f Asp. acul:-~t~ the r.igh.ee• pr
enzymatic level were obtained wi tb pectin follc,. ’”by
cellob:! ose, pectic acid and soluble starer.. On
the other h!’\nd .,..ith Mucor pusillus the highest FG
activity were obtained using pectin and arabinose.
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(c) Various nitrogen sources were tested namLly potassium
nitrate, sodium nitrate, ammonium chloride, ammonium
citrate, ammonium sulphate, Gelatin, peptone, casein
hydrolyzate and urea. It was found that sodium
nitrate followed by potassium nitrate proved to be
the most favourable nitrogen source for PG production
by~· aculeatus, while ammonium citrate followed
by sodium nitrate supported highest levels of PG
production by Mucor pusillus.
(d) LevelR of enz,Jme formation under condi”tions of
shaken a.nd static cultures die not vary significantly.
High levels of the PG activities were formed
by both cultures under beth static and suake culture
conditions.
(e) The optimum pH values of the medium for proriuction
of PG activity was the range between 4-5 for As£.
~culeatus and in the range between 4-6 ~ucor pusillus.
(f) ’:’he optimum temperatures for production of h_. were
within the range between 28-J2°C and within the
range between 28-J7°C for cultures of Asp. aculeatus
and Mucor pusillue respectively.
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(g) It was found that J-4 days incubation period is
optimal for PG production from Asp. aculeatus wheareas
6 days were required for Mucor pusillus to
obtain high levels of enzyme under study.
(h) No marked difference could be detected within the
enzyme levels produced at 1 % and 2 % pectin concentration
in both cultures.
B- characterization of polygalacturonase actiVity formed by
both cultures has revealed the following properties:
(a) The polygalacturonase enzyme of Asp. aculeatus showed
maximum acti~ity at pH J, whereas pH 4.5 was the optimum
value for PG activity produced by Mucor pusillus.
(b) With respect to enzyme concentration li~ear activity
response was obtained with enzyme concentration up
to 0.15 mg protein/ml for the enzyme of Asp. aculeatus.
In case of the enzyme of Mucor pusillus the activi•y
increased at h~gher protein concentrations but not in
linear mar~er.
(c) A linear response of reaction rate for PG of Asp.
aculeatus was obtained with polygalaeturonic acid as
a substrate up to o.a % final concentration, but the
response to pectin was lower. In case of the PQ
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activity of Mucor pusillus ~ne reaction rate increased
with increasing substrate concentration for both
pectin and polygalacturonic acid up to 1.2 % final
concentration. However, the activity was lower than
in case of Asp. aculeatus.
(d) The optimum temperature for PG activity f~r Asp.
aculeatua was 60°C, and 50°C for the enzyme of ~ucor
pusillus.
(e) Polygal~cturonases by Asp. aculeatus and Mucor
pusillus were extremely sensitive to boiling.
9- Application of the enz)~ea of both cultures have shown
that the juice yield obtained from citrus fruit, lemon,
grapefruit and carrot could be increased as a result of
enz;,me application. !iarkec increases were also obtained
in total sugars and acidity of the resul”ting ~-dee.
10- Tl:.ese results r”Rve been discussed in view of pvssible
a;;:: cation of ;olygal’l.cturonases obtai!’:ed frorr: As-.
ac·uleat>ls a!10 Mucor pusillus in the juice industry f<’r
th~ purpose of yielc and quF<lity improvement of the resulting
juice obtained from different fruits.