CHANGES IN PECTIN CONTENT AND AVERAGE MOLECULAR WEIGHT OF PECTIN DURING MATURATION OF THE MANGO "KAEW"

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CHANGES IN PECTIN CONTENT AND AVERAGE MOLECULAR
WEIGHT OF PECTIN DURING MATURATION OF THE MANGO
“KAEW”*

Warunee VARANYANOND,1 Jun NAOHARA,2
Karuna WONGKRAJANG1
and Masatoshi MANABE3







ABSTRACT


Water soluble pectin (WSP) in an alcohol insoluble solid (AIS) of mango
“Kaew”, which is exclusively used in processing, increased with maturation.
Hydrochloric acid soluble pectin (HSP) decreased. Ammonium oxalate soluble pectin
(ASP) did not exhibit a regular pattern. Average molecular weight (MW) of all soluble
pectins decreased as the mangoes matured to the overripe stages. Between the half-ripe
and ripe stages, average MW decreased significantly in both WSP and ASP. Average
MW values for HSP declined gradually as maturation proceeded.

Key words: mango, pectin, molecular weight, maturation


Mango (Mangifera indica L.) is native to the Indo-Myanmar region where it has
been cultivated for over 4000 years (Mendoza & Wills, 1984). Thailand is considered
the origin of many mango cultivars that are commercially produced and marketed as
ripe, mature-green and immature-green fruits. The total mango production of Thailand
was about 1.2 million metric tons in 1995, and the largest producing area were in the
northern and northeastern parts of the country. Although more than 100 mango
cultivars have been observed in Thailand, only some of these are grown commercially
such as “Nam DoK Mai”, “Nang Klangwan”, “Khieo Sawoei” and “Kaew”. The
greatest amount of the fresh fruit produced was Kaew, accounting for about 31% of the
total volume, followed by Khieo Sawoei (14.7%). Kaew is mainly used in processing,
and its products are juice, mango in syrup, sweetened-dried and pickled mango. The
quality of the mango fruit changes during maturation. The color turns from green to








*Food Sci. Technol. Res., 5(4), 362-364, 1999
1 Institute of Food Research and Product Development, Kasetsart University, Bangkok, 10900, Thailand.
2 Research Institute of Technology, Okayama University of Science, Okayama-shi, Okayama, 700-0005, Japan
3 Faculty of Home Economics, Tokushima Bunri University, Tokushima-shi Tokushima, 770-8055, Japan

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yellow, the pulp texture becomes soft, and the sugar-acid ratio increases. Softening of
the fruit texture during maturation in the tissues is modified due to the degradation of
polysaccharides such as cellulose, hemicellulose and pectin (Roe & Bruemmer, 1981;
Kratchanova et al., 1991). The enzyme activity of polygalacturonase (PG),
pectinesterase (PE) and cellulase in mango has been studied (Roe & Bruemmer, 1981;
El-Zoghbi, 1994; Ashraf et al., 1981; King et al., 1988), and these activities change
during the ripening of the fruit. However, there is no enzyme information available on
mangoes cultivated in Thailand. Therefore, understanding the characteristics of pectins
and related pectolytic enzymes in fresh mango grown in that contry is very important
for the optimal production, processing and marketing of the fruit.

The objective of the present work was to document the changes in soluble
pectins, pectin molecules, and distribution of molecular weights for pectins of Kaew
mango during maturation.
MATERIALS AND METHODS

Materials Kaew mangoes were obtained from the local markets in Bangkok,
Thailand, during April and May in 1996 and 1998. The four stages of maturity of the
fruits used for this study were mature-green with a fully green peel color; half-ripe with
peel of green and a little yellow; ripe with peel pale green and yellow; and overripe with
fully yellow peel.

Extraction and analysis of soluble pectins Preparations of alcohol insoluble
solids (AIS) were made from the sliced fruit flesh by heating with 95% ethanol (EtOH).
After filtration through a cotton cloth, 70% EtOH was added to the residue, which was
kept overnight at room temperature. This procedure was repeated three times. Then,
95% EtOH was added to the mixture followed by the addition of acetone. The AIS was
dried at 40o C under vacuum.

Water soluble pectin (WSP), ammonium oxalate soluble pectin (ASP), and
hydrochloric acid soluble pectin (HSP) were extracted successively from AIS according
to the method of McColloch (1952). Extraction of pectin from AIS was carried out
twice. The amount of uronic acid in pectin was determined using the carbazole sulfuric
acid method described by Bitter and Muir (1962), and expressed as anhydrogalacturonic
acid.

Molecular weight of pectin Molecular weight (MW) distribution patterns were
obtained by high performance gel filtration (HPGF) chromatography as described

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previously (Naohara & Manabe, 1994). Average molecular weights of pectins were
calculated according to the method of Cazes (1966). The HPGF chromatography
system included a Waters U6K injector, a Waters model 510 pump, a Waters model 401
differential refractometer, Waters ultrahydrogel linear columns heated with a Sugai
model U620 heater and a Waters 805 data module. The mobile phase was 1 % acetic
acid and the flow rate was 1 ml/min. These operations were repeated 3 times.
RESULTS AND DISCUSSION

Changes in soluble pectins during maturation AIS contents in mango Kaew
flesh were as follows: mature; 4.11 %, half-ripe; 3.08 % ripe; 2.24 % and overripe; 2.15
% AIS of ripe and overripe fruits was thus approximately half that of mature fruit.

The amounts of soluble pectins in AIS at each stage are compared in Table 1.
An increase in WSP was observed during maturation of the fruit: there was a striking
difference between ripe and overripe stages of mango samples in 1996 as shown in the
percentage of WSP to total pectin. In contrast to WSP, a decrease in HSP was shown
during maturation of the fruit. These same patterns were found on the mango samples
in 1998. Total pectin in fresh mango had a tendency to decrease. Tandon and Kalra
(1984) examined pectin changes during the development of the fruit. Water soluble
pectin increased up to ripening. Alkali soluble pectin (protopectin) increased for a
maximum at 70 days after fruit set but decreased thereafter. The effect of harvested
data on pectin content was studied on three mango cultivars (Saeed et al., 1975). Water
soluble pectin increased as the season advanced, but protopectin decreased. Our data
showed that water soluble pectin increased and hydrochloric acid soluble pectin
decreased in AIS of mango during ripening of the samples both in 1996 and 1998.

Ripening of the mango fruit is characterized by softening during its maturation.
Changes in the molecular weight of the pectin and average MW of soluble pectins at
each maturation stage of mango were examined (Fig. 1) The data in 1998 was the same
as that in 1996, therefore, the result in 1996 is indicated here. The average MW of WSP
declined with maturation of the fruit, and was remarkably changed between half-ripe
and ripe. The values of the MW of WSP at each stage were 110,000 at mature; half
ripe, 90,000; ripe, 30,000 and overripe, 30,000, respectively.

The average MW of ASP gradually decreased from the mature to the overripe
stage. The average MW of ASP at the mature stage was similar to that of WSP, but at
the overripe stage, it was greater than of WSP. The average MW of HSP decreased as

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the fruit matured, and was remarkably small compared to that of WSP and ASP. The
MW of HSP in the mature fruit was about 33,000, but at its lowest was about 5000 at
the overripe stage. This lower average MW of HSP, compared with that of WSP and
ASP, probably was due to the degradation of pectin molecule during extraction with
0.05 N hydrochloric acid at 85o C for 2 h. Nevertheless, the same experiment was done
on the pectin in mandarin orange. However, a remarkable decrease in average MW
could not be found at HSP (Naohara and Manabe, 1994). The resistance to acid
hydrolysis of mango pectin is believed to be weaker than that of satsuma mandarin
pectin. Krat-chanova et al. (1991) suggested that mango pectin is rather unstable when
thermally treated in an aqueous solution for a long period.

Table 1 Soluble pection content (mg) in mango (100 g) at different stages in the
mango “Kaew”

Stage of maturation

Soluble pectin (mg)


WSP
ASP
HSP
TP
Mature
106.8
111.0
316.5
534.3
Half-ripe
120.1
92.4
246.4
458.9
Ripe
170.2
130.0
145.6
445.8
Overripe
283.3
96.8
81.7
462.3

WSP: water soluble pectin, ASP: ammonium oxalate soluble pectin, HSP: hydrochloric
acid soluble pectin, and TP: total pectin.











Fig. 1. Average molecular weight of pectin at the mature, half-ripe, ripe, and overripe
stage of development (Kaew). A different letter (a-d) above each same pettern
bar indicate significant difference at the 5% level.

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Fig. 2. Molecular weight distriburion of soluble pectin in mango at the mature, half-ripe, ripe,
and overripe stage of development (Kaew).
100,000 >, 100,000 – 200,000
200,000 – 300,000 300,000 – 400,000 400,000 – 500,000

500,000 – 853,000 853,000 <


Pectin obtained from mango through acid extraction (pH 1.5. 85o C, 30 min.)
had a molecular mass that ranged from 72,000 to 83,000 (Kratchnova et al., 1991). The
same results of average MW of mango were also found in the average MW of satsuma
mandarin fruit pectin (Naohara & Manabe, 1994). As shown in Fig. 2, MW of soluble
pectin in mango ranged widely from 100,000 to 853,000. These results showed that the
ratio of the smallest MW fraction of mango pectin to the total pectin was at the highest
value in HSP.

Freestone peach had parallel development between PG activity and the
formation of WSP. This was characteristic of freestone peaches, and the molecular
weights of peach pectins ranged from about 100,000 to several million by application of
gel filtration (Pressey et al., 1971). MW is believed to distribute largely from small to
large amounts among the same extracted pectin. Some enzymes that degrade the tissue
components are well known in tropical fruits, and pectinesterase activity has been
investigated (Ashraf et al., 1981; King et al., 1988; El-Zoghbi, 1994). El-Zoghbi
showed that PE activity declined with fruit ripening, while PG activity increased with
ripening of four kinds in fruit including mango. These pectolytic enzymes would
degrade macromolecules of polyuronide to smaller pectin size.

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With the maturation of the mango Kaew, the amount of WSP increased and that
of HSP decreased; also, MW decreased in both WSP and HSP. Moreover, the average
MW of HSP was less than that of WSP and ASP. Pectolytic enzyme activity in the
mango fruit was not studied in this experiment. This paper indictes the importance of
studying the behaviors of pectin content, molecular weight and pectolytic enzyme
activity of pectin.
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