Industry outlook: Malaysia (2°30 N, 112°30 E) is
a tropical country where various fruits are cultivated. Some of these fruits
are native to this country while others are introduced elsewhere due to its
high commercial potential. Various fruits are cultivated in Malaysia as shown
in Table 1. The cultivated area for local fruit planting is
currently recorded at 298,429 ha with production at 1,767,800 metric tonne per
The per capita consumption of fruit in Malaysia is estimated at 48.82 kg for
year 2010 (Hassan, 2007).
Eleven local fruits namely the starfruit, dragon fruit, pineapple, rambutan,
durian, pomelo, papaya, mango, mangosteen, jack fruit and guava have been identified
as the new export earners for Malaysia to date. These fruits, which are known
as the exotic fruits in the West, are fast gaining popularity worldwide with
an estimated market worth of over USD10 billion annually (http://biz.thestar.com.my/news/story.asp?file=/
2010/8/3/business/6781157). Europe is currently the main tropical fruit
importer making up to almost 50% of the market share. The Food and Agriculture
Organisation of the United Nations (FAO) has also categorized mango, pineapple,
papaya and avocado as the fourth world major tropical fruits. Malaysia is already
producing some of these major tropical fruits in this list. Figure
1 shows some examples of fruits currently cultivated in Malaysia.
|| Typical tropical fruits planted in Malaysia
|*Source: Department of Agriculture, 2010 statistics
Fruit drying: In general, fruits can be preserved easily and drying
is known as one of the oldest preservation techniques known to mankind. Tropical
fruits generally have short shelf life of few days to a week depending on the
maturity and storage conditions. During peak harvesting period spoilage of fruits
occurs due to over fruiting which results in excessive production.
Fruits can normally be dehydrated by various methods and processed into various
forms of products. Hot air drying is the most common method used but other methods
such as freeze drying, heat pump drying, vacuum drying and microwave drying
can be used as an alternative drying option.
|| Examples of tropical fruits cultivated in Malaysia
||Drying studies of Malaysian fruits
The finished products can be obtained in several forms such as chips, cubes,
bars, powder, foam mat and leather. Fruits can also be pre-treated and subject
to osmotic dehydration prior to thermal drying (Law and Mujumdar,
2008). During drying, nutrients degrade in fruits and careful selection
of drying parameters is thus required to optimize the retention of these compounds.
Texture, colour, flavour and microbiological attributes are equally important
in the processing of fruit products (Hii et al., 2008).
Drying studies: Research and development works have been carried out
by local research agencies and universities to improve planting, harvesting
and processing of Malaysian fruits. Fruits can be consumed either in fresh or
processed form i.e., dried, candied, canned, fried and pickled. This study aims
to compile and review some selected drying studies that had been carried out
by researchers for Malaysian fruits (Table 2) and to further
explore the potential of drying other fruits that are planted locally.
DRYING OF MALAYSIAN FRUITS
Durian: Durian (Durio zibethinus) is the most popular and widely consumed
fruit in Malaysia. This fruit is also widely planted in South East Asian countries
and is known as the king of fruits. Typically, durian has a strong odour which
could be unpleasant to some consumers especially those not from Asian countries.
|| Drying conditions used for durian
The fruit has a thorn-covered husk and is usually consumed fresh. The fruit
pulp is the only edible portion from the fruit. Traditionally, the fruit pulps
can be processed into fermented durian (tempoyak) or durian cake (lempok). Drying
studies have been carried out using heated air (Radziah
et al., 2007a), spray and freeze drying (Man
et al., 1999; Chin et al., 2010).
Table 3 shows the drying conditions used in their studies.
Man et al. (1999) reported that freeze drying
was better than spray drying and gave higher aroma scores, better colour (more
yellowish, higher b value) and appearance. The better aroma score was due to
better retention of the flavour volatiles during freeze drying. However, the
bulk density was higher as compared to freeze drying due to the smaller particle
size which contributed to tighter packing of the cell structures. Glucose syrup
solid was found to be the most suitable encapsulating agent in spray drying.
Chin et al. (2010) reported the presence of
30 volatiles that were extracted from the fresh durian pulps. However, not all
compounds remained present in the freeze and sprayed dried durian. Four ester
volatiles (ethyl thioacetate, propyl butanoate, propyl 2-methylbutanoate and
propyl 3-methylbutanoate) were not detected in the freeze dried sample while
10 more volatile compounds were not detected in sprayed dried samples. Eight
new volatiles were even developed in the sprayed dried sample (5 aldehydes,
1 ketone, 1 furan and 1 pyrole). Freeze drying caused reduction of major aroma
volatiles ranged from 70.5-97.2% as compared to spray drying at 98-99%.
|| Drying conditions used for ciku
The unusual high loss of volatiles in freeze drying could have happened during
sample preparation prior to drying. Radziah et al.
(2007a) reported drying at temperatures lower than 50°C produced dried
product with better aesthetic quality. Drying at higher temperatures (80-90°C)
markedly decolourised and shrivelled the sample.
Ciku: Ciku (Manilkara zapota) or commonly known as sapodilla is not native to Asian countries but is believed to be originated from Mexico, Central America and the Caribbean. The fruit is quite similar to a smooth skin potato and inside its fresh looks pale yellow to brown colour. This fruit is consumed among Malaysian but not as popular as other fruits such as banana, mango and durian. Drying conditions used for ciku are presented in Table 4.
Leong and Shui (2002) reported that ciku has the highest
antioxidant capacity among tropical fruits. Chong et
al. (2009) and Chong and Law (2011) reported
drying studies of ciku using sun and intermittent drying, respectively.
Three drying periods (initial transient, constant and falling rate periods) were observed during sun drying. In terms of product quality, browning caused a decrease in L* and b* values but an increase in a* value which resulted in great colour change. This could be due to the prolong drying period which resulted in longer exposure time. For the same reason, retention of polyphenols was quite low (28%) as compared to fresh fruit. Texture analyses showed significant difference between the hardness and chewiness of dried ciku. Springiness of ciku was slightly lower and about 85% increase in cohesiveness was observed.
Studies using intermittent and dehumidified air drying were found able to reduce
the hardness and chewiness of dried ciku. Critical moisture content that contribute
to case hardening was identified at 0.15 g moisture/g dry matter. Drying profile
that used 5 h cold air-19 h hot air intermittently was found optimum for ciku
drying (Chong and Law, 2011).
Chempedak: Chempedak (Artocarpus integer) is native to South
East Asia and quite resemble to the appearance of jackfruit (Fig.
2). The fruit is oblong in shape and contains pulp coated seed which is
|| Drying conditions used for chempedak
||(a) Rambutan, (b) dokong and (c) langsat
The pulp is usually consumed fresh while the seed need to be boiled or cooked
in order to be consumable. The drying kinetics and product quality of chempedak
fruit were reported by Chong et al. (2008a, b).
Table 5 shows the experimental conditions used in their studies.
Fluctuating drying rates were reported during the sun drying process. However, both initial transient and falling periods were clearly observed during drying. Texture analyses showed that both hardness and chewiness were significantly higher than the fresh sample. The increase in hardness could be due to depolymerisation of cell wall constituents such as pectin, after exposure to heat during drying. The sun dried chempedak was observed darker due to enzymatic browning and this resulted in significant total colour change. Similar sample was subject to hot air drying and results showed occurrence of the initial transient and mostly falling rate period throughout drying. The logarithmic model was found able to predict the moisture reduction process. Similar observations were reported in sun drying in terms of colour and texture.
Dragon fruit: Dragon fruit or pitaya is a non-seasoning fruit native to Mexico, Central and South America. The fruit has red-skinned with white flesh, which is the type consumed widely but it can also be red-skinned with red flesh or yellow-skinned with white flesh. The flesh can be processed into juice and wine. This fruit has recently become popular among Malaysian and even to tourists.
Drying studies were carried out to dry dragon fruit using microwave (Nordin
et al., 2008) and spray drying (Taufik, 2009).
Table 6 shows the drying conditions used in these studies.
Nordin et al. (2008) reported that power density
of 19.02 W g-1 is not suitable as the sample would char at this power
|| Drying conditions used for dragon fruit
Tang and Cenkowski model was found able to fit the kinetics data during drying.
The time taken for significant colour changes to occur was found proportional
to the power output. The colour change also followed closely to the beginning
of the falling rate period. In terms of shrinkage, the samples shrank by more
than 70% with increasing power density. However, there was no increase in hardness
observed. The internal structure of the sample collapsed completely at the end
Taufik (2009) reported optimum condition of 180°C
by using 20% maltodextrin for the production of dragon fruit powder. At this
drying condition the retention of vitamin C was the highest among all drying
conditions. Solubility was determined at 90% in all the samples while sample
that was obtained at 180°C showed dissolubility rate of less than 40 sec.
Jackfruit: Jackfruit (Artocarpus heterophyllus) is native to
South East Asia and is commonly known as nangka locally. It is also the national
fruit of Bangladesh. The fruit can grow to as big as 90 cm long and weighs almost
36 kg. The edible part of the fruit is the golden yellowish flesh and it can
be also eaten unripe by cooking both the flesh and the seeds. Drying studies
have been reported by Radziah et al. (2007b)
and Pua et al. (2010) by using heated air and
drum drying, respectively.
Radziah et al. (2007b) reported limited degree
of shrinkage and browning at drying temperature of 35°C. Drying at 40-45°C
showed pronounced shrinkage and decolouration. The lower temperature also produced
dried jackfruit with higher degree of redness. Studies by Pua
et al. (2010) indicated that optimum drum condition for producing
the jackfruit powder was at 336 kPa steam and 1.2 rpm rotational speed. This
led to desirable quality attributes with the smaller colour change, lower moisture
and water activity and higher scores in sensory evaluation. Response surface
analyses indicated that both the drum speed and steam pressure affected the
drum temperature significantly during drying.
Banana: Banana, or locally known as pisang, is widely planted and consumed
in Malaysia. It is also one of the main traded fruits globally. The fruit is
native to many south East Asian countries and it can be eaten fresh, fried,
cooked and in some countries the banana heart (flower) is also consumed either
in raw or cooked form.
|| Drying conditions used for jackfruit
|| Drying conditions used for banana
Drying conditions used for banana are presented in Table 8.
Drying studies (Table 7) were carried out by Fadhel
et al. (2011) and Fernando et al. (2011)
by using solar drying and infrared drying, respectively. Both studies reported
fitting of various empirical models to predict the drying process. The effective
diffusivity values were found increase with temperature and infrared power due
to greater adsorption of energy on the product surface. Diffusivity values were
reported ranging from 1.85x10-9 to 7.02x10-9 m2 sec-1.
Fadhel et al. (2011) developed an indirect solar
dryer which consisted of a heat collector and a drying cabinet. The drying cabinet
consisted of three trays and it was observed that the top tray dried faster
as compared to the rest since this section was exposed to the heated air initially.
The Wang and Sing model was found able to predict the experimental moisture
Salak: Salak (Salacca glabrescens) is a native palm fruit in Indonesia and Malaysia. This fruit is commonly known as snake fruit by the locals as the fruit skin resembles the reptile skin. The fruit consists of three cloves in off white colour with a thin layer of transculent cuticular membrane on the surface.
Hot air and heat pump drying of salak fruit was carried out by Ong
and Law (2011) at 40-90 and 26- 37°C, respectively. Studies showed that
reduction of total ascorbic acid was due to combination of thermal and enzymatic
degradation. Degradation of phenolic compounds was mostly due to thermal effects.
Drying at temperature below 37°C produced final products with higher phenolic
content than hot air drying (T>40°C). It was suggested to implement intermittent
drying according to the different stage of drying to improve product quality.
Mango: Mango (Mangifera indica) is planted widely in many tropical
countries and has a long history of cultivation i.e., it has been cultivated
in India for over 4000 years. This fruit is very popular among Malaysians and
mango tree can be seen planted in the garden of many Malaysian houses.
Mango puree was encapsulated with gum Arabic and dried using a spray dryer
(Bachtiar and Sarmidi, 1997). Drying was carried out
using inlet temperatures of 160-220°C and outlet temperatures of 79-110°C,
respectively. Optimum condition was found at flowrate of 900 mL h-1
with inlet and outlet temperature at 200 and 134°C, respectively. The powder
was able to retain its nutritional value, colour and aroma at this setting.
However, in a pilot scale dryer different optimum condition was determined at
1200 mL h-1, inlet temperature of 160°C and outlet temperature
of 96°C. This could be due to several scale-up factors i.e., heat transfer
that were not considered during the execution of the laboratory works.
Starfruit: Starfruit (Averrhoa carambola) is believed to be originated
from Indochina, Malaysia and Indonesia. Malaysia is one of the biggest exporters
of start fruit in the world (Mokji and Abu Bakar, 2007).
The fruit when cut across the flesh resembles the shape of the star with five
edges. The whole fruit is edible including the waxy skin and it is also a very
good source of antioxidants (Shui and Leong, 2004).
Solar dryer was developed and tested with thermal heat storage by Vignesvaran
and Hii (2011). The thermal heat storage system was constructed from river
stone such that heat can be absorbed and released by the stone during day and
night time, respectively. The thermal storage system was able to prolong drying
for extra 10 h even during night time. Elasticity was found decreased with moisture
content due to hardening. Colour change due to browning was observed typically
caused by enzymatic browning.
Papaya: Papaya (Carica papaya) is one of the major fruits planted
and produced in Malaysia. It is usually consumed fresh but pickled and dried
papayas are also commonly found in the local market. Drying studies was carried
out by Zaki et al. (2007) using microwave-vacuum
dryer. Papaya samples were treated at various power levels (110-750 W) and pressure
(200-700 mmHg). However, product quality of the dried papaya was not reported.
Drying rates were found increased with microwave power intensity but system
pressure played no significant effect in moisture reduction. Only falling rate
period was observed throughout drying.
POTENTIAL OF OTHER FRUITS AND FUTURE WORKS
Based on the list in Table 1, there are still plenty of fruits that can be processed into dried fruit with high commercial potential. Fruits such as langsat, dokong and rambutan are often over produced during the harvesting season (Fig. 2). Farmers are not benefited from the over production due to the excessive supply which causes a sharp drop in the prices of these fruits. The flesh from these fruits has almost the same texture as longan, which is currently available in the market in dried form and is selling at a much higher price.
Besides commercial fruits, some rare fruits can also be found in Malaysia and
reported to have unique medicinal value i.e., high antioxidant activity. These
fruits are not planted widely due to lack of interest from estates and plantation.
It is usually grown in wild or planted in family owned orchard. Examples of
these fruits are such as cerapu, terap, cermai, pulasan, beruas, ceri, jentik-jentik
and durian nyekak. It was found that cerapu and jentik-Jentik had the highest
antioxidant capacity and the highest ß-carotene content, respectively,
among the rare fruits tested (Khoo, 2009). Preservation
of these fruits in dried form would enable these fruits to reach a wider segment
of the consumers especially those from the urban areas. The dried fruits can
also be branded with its high nutritional and antioxidant values which are well
accepted by consumers from the Americas and Europe.
Various studies have been carried out in the past to process Malaysia fruits into dried form and to increase its market value. Research and development works are constantly carried out by local research agencies and universities to develop new product and to improve the quality of the existing one. The potential of other local fruits should be further envisaged as overproduction would not benefit the farmers in the long run. Rare fruits are another area with great commercial potential as these fruits are known to have medicinal value, such as antioxidant, which is beneficial to human health.
The support given by the Faculty of Engineering, University of Nottingham, Malaysia Campus is acknowledged.