EFFECT OF SOLAR DRYING ON THE QUALITY AND ACCEPTABILITY OF JACKFRUIT LEATHER
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ISSN: 1579-4377
EFFECT OF SOLAR DRYING ON THE QUALITY AND ACCEPTABILITY
OF JACKFRUIT LEATHER
S. Okilya , I. M. Mukisa* and A.N. Kaaya
Department of Food Science and Technology, Makerere University, P.O.Box 7062, Kampala, Uganda.
ivanmukisa@agric.mak.ac.ug
ABSTRACT
This study investigated the applicability of solar drying, a popular method in the tropics, in
processing of jackfruit leather. The effect of solar drying on the quality and consumer acceptability
of jackfruit leather was compared to cabinet and convection oven drying methods commonly used in
the preparation of good quality fruit leathers. Results show that the moisture content of solar dried
leather (18.50 %) was not significantly different (p>0.05) from that of cabinet dried leather (18.85
%). However, the moisture content of the leather dried using these methods was significantly higher
than the oven dried leather (14.79 %). Solar dried leather had significantly lower color readings
compared to cabinet dried leather. The color loss in oven dried leather was not significantly different
from solar dried leather (p> 0.05). Instrumental results of texture showed that all the leathers were
not significantly different (p> 0.05). Solar dried leather was disliked and received significantly
lower scores (p< 0.05) on all sensory attributes evaluated. Although solar drying can be used to
produce jackfruit leather in a relatively short time, other studies maybe needed to improve its
sensorial quality.
KEYWORDS
Jackfruit; Fruit leather; Solar drying; Physicochemical properties; Sensory evaluation.I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
INTRODUCTION
The Jackfruit (Artocarpus heterophyllus lam), which is believed to have originated from India is
largely cultivated throughout many countries in the Middle East such as India, Burma, Ceylon,
Malaya and Southern China [1 - 3]. This fruit also grows in African countries such as Uganda and
Kenya; as well in Brazil, Jamaica and the Bahamas [2]. The interior of the fruit contains large
fleshy banana flavoured sweet bulbs which may be crispy or soft and yellow to brownish when ripe
[2]. Jackfruit pulp is rich in vitamins A, B and C and minerals such as calcium and iron [2 - 4]. .
The pulp is a source of energy and is also reported to have laxative effects as a result of its dietary
fiber content [1, 5]. .
The Pulp of ripe jackfruit can be eaten fresh, made into various local delicacies including
chutney, jam, jelly or can be preserved as candies and fruit leather among others [2, 6]. In Uganda,
however, jackfruit is mainly eaten in its fresh form. In this form, the fruit is not very easy to eat due
to difficulties in separating edible bulbs from the rind [7]. The fruit also exudes copious amounts of
sticky white latex which is not only sticky on the hands but also permanently stains clothing [2]. The
fruit’s bulky nature also makes it difficult to transport and store. Although it is available almost all
year round, there are peak seasons during which the fruit mainly rots away in gardens or in the
market due to its perishability nature. With post harvest losses of fruits and vegetables in Uganda as
high as 30-40%, this invariably results in loss of potential income and nourishment [8]. . There is
therefore a need to diversify utilization and reduce loss of jackfruit through processing into a variety
of convenient and shelf stable acceptable products like leathers.
Fruit leather refers to fruit puree or a mixture of fruit juice concentrate and other ingredients
which are cooked, dried on a non-sticky surface and rolled [9, 10]. A variety of fruits can be used to
produce leathers [11]. Leathers have been developed from fruits such as guava, paw paws, jackfruits
and durian [3, 6, 12 - 16]. Fruit leathers are mainly eaten as snacks [17]. They can, however, also
be made into beverages by blending with water or into sauces [11, 13]. Fruit leathers can also be
used as ingredients in products such as biscuits and breakfast cereals [16]. Though mainly popular in
North America, fruit leathers have been developed in different parts of the world including Africa
[13].
Direct sun drying, solar drying convection oven drying and electric cabinet drying are some
of the drying methods that can be used in processing fruit leathers [9, 11, 18, 11, 19]. Both cabinet
and convection oven dryers are reported to produce quality leather although cabinet dried leather is
more acceptable [11, 15]. Direct sun drying has also been used to produce acceptable guava leather
[14]. There are, however, no available studies on the use of solar drying in producing fruit leather.
Despite its reliance on climatic conditions, solar drying is increasingly becoming a popular
method of drying fruits in tropical countries such as Uganda [20]. Solar drying is cheap compared to
other advanced methods of drying since it mainly relies on energy from the sun, requires low or no
electric power and the dryers are relatively cheap and easy to construct [3, 21]. This makes it
suitable for use in rural areas with limited electrification and frequent load shedding commonly
practiced in Uganda. The use of such a low cost processing technology can help fruit growers to
increase their income by encouraging full utilization of locally available produce as raw material.
Therefore the objective of this study was to assess the effect of solar drying on the quality
and acceptability of jackfruit leather. Colour, texture and moisture content were evaluated since they
are the most important quality parameters of fruit leathers that are usually affected by drying [10].
Since electric cabinet driers and convection oven driers are known to produce high quality leathers,
they were used to provide a benchmark for evaluating the applicability of solar drying in production
of jackfruit leather.
102I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
MATERIALS AND METHODS
Raw materials
Fresh ripe whole jackfruits (Artocarpus heterophyllus lam) were purchased from Nakasero market in
Kampala. The variety with thin, fibrous, and mushy edible pulp was used. This type was selected
because it is more readily available in Uganda.
Sample preparation
The fruits were cut in half longitudinally and the sticky central cores carved out using a sharp knife.
Bulbs were scooped out by hand and the ends of the bulbs were cut to remove the seeds. The bulbs
were chilled prior to further processing so as to retard enzymatic softening as well as microbial
growth. The pulp was blended using a kitchen blender (Braun, type; 3 205K600, Germany) and the
mixture put in a pan where it was concentrated for 15 minutes in a water bath at 70˚C. The
concentration step evaporates off some water, which reduces the drying time [3, 11]. The
concentrates were allowed to cool to room temperature by natural convection prior to further
processing. The concentrates were then formed into sheets using fabricated stainless steel metallic
trays (20 cm long x 20 cm wide x 3 mm thick) lined with wax paper.
Drying the sheets
The sheets were dried in a solar dryer, convection oven dryer and electric cabinet dryer. Solar drying
was carried out in a green house solar dryer for three days (average temperature of 36.7°C).
Convection oven drying (Gallenkamp oven, size 2, SG93/08/850, United Kingdom) was done at
50°C for 18 hours [3]. Drying in the cabinet dryer (ABM Carbolite, type; 4EKF63A-2,
Greiffenberger, Germany) was done at 65˚C for 6 hours with an air velocity; 1.7 m/s per square
meter tray area [19]. After drying the sheets were rolled and packed in water proof food grade
polythene bags at room temperature prior to subsequent analyses. The sheets were dried in
quadruplicates for each method and two experimental runs were performed.
Physico-chemical analyses
Moisture content of the fresh pulp, concentrated pulp, and dried leather was determined according to
AOAC methods [22]. Colour was determined for the fresh samples, concentrated samples and the
dry jackfruit leather using a Lovibond Tintometer (Lovibond tintometer, L322/92E, Salisbury,
England). Leather texture was measured with a penetrometer (Matest Treviolo Penetrometer, B057-
10/ZG/0001, Italy). In this method, jackfruit leather samples of uniform thickness were held against
a stationary, hard surface and the pointed fixed tip of the penetrometer was forced into the leather
samples at a constant force of 1.962 N. The extent of penetration into the leathers were taken in
terms of degrees (˚) and then converted to mm (1˚= 0.01mm). Higher values indicate increase in
softness of the leather. Determinations were carried out in quadruplicates.
Sensory evaluation
Sensory evaluation, using a 9 point hedonic scale (1=dislike extremely, 5= neither like nor dislike,
9=like extremely), was carried out by 60 untrained panelists selected among students of the
Department of Food Science and Technology, Makerere University following standard procedures
[23]. Panelists were presented with three samples (each for the three different treatments) and
commercial bottled water for cleansing the palate. Evaluations were carried out in well lit booths.
The panelists were also requested to complete a questionnaire that required demographic
information as well as their attitudes towards jackfruit consumption.
2.6 Statistical analysis
103I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
The means for the physico-chemical and sensory evaluation data were subjected to One-way
analysis of variance and Tukey’s test to check for significant differences (p< 0.05) using S-plus for
Windows (version 8.0.4).
RESULTS AND DISCUSSION
Effects of solar drying on the physicochemical properties of jackfruit leather
Table 1 shows the physicochemical properties of the jackfruit leather dried using a solar dryer, a
convection oven dryer and a cabinet dryer. Results showed that solar drying significantly reduced
the moisture content and colour readings of the jackfruit leather compared to oven drying and
cabinet drying respectively. There were no significant differences in the texture of the leathers
produced using the three drying methods.
Table 1: Effect of drying methods on physicochemical properties of jackfruit leather
Physical Property Drying method
Cabinet drying Oven drying Solar drying
(65 ºC, 6 hrs) (50 ºC, 18 hrs) (36.7 ºC, 72 hrs)
Moisture (%) 18.85 ± (1.199)a 14.79 ± (2.614)b 18.50± (1.164)a
Texture (mm) 1.02 ± (0.045)a 0.76 ± (0.087) a 0.94± (0.121)a
Colour (yellow-orange) 1.85 ± (0.207)a 0.80 ±(0.635)b 0.61± (0.445)b
Values are means ± (standard deviation ) of 8 determinations. Means within a row with the same letters are not
significantly different (p > 0.05). The means for moisture content of the fresh (73.4 %) and concentrated samples (69.9
%) were significantly different (p< 0.05).The means for colour readings of the fresh (3.21) and concentrated samples
(2.58) were not significantly different (p > 0.05).
Moisture content
The moisture content of the fresh (73.4 %) and concentrated fruit samples (69.9 %) was
significantly different (p< 0.05). The moisture content for the fresh sample falls within the range (72
- 77.2 %) earlier reported [1, 2]. The results showed that all the three drying methods significantly
reduced the moisture content of the leathers compared to the fresh fruit. The reduction in moisture
content in solar dried leather was not significantly different (p > 0.05) from that of cabinet dried
leather although it was significantly different (p < 0.05) from the oven dried leather. When higher
temperatures and longer drying times are used, leather with lower moisture content is obtained [15].
The moisture content of oven dried leather was lower than that of the solar and cabinet dried
leathers probably because oven drying was carried out at relatively high temperatures (50 ºC) and a
relatively long drying period (18 hours). Despite solar dried leather having been dried for a longer
time (72 hours) than oven dried leather, it lost less moisture. This is probably because the average
drying temperatures in the solar dryer (36.7 °C) were lower (Fig. 1) than those used in the oven
dryer (50 ºC). Cabinet and solar drying had similar effects on moisture content removal. Use of low
and high drying temperatures with short and long drying periods respectively may result into a
product with similar moisture content [4].
104I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
Figure 1: Variation of temperatures in the solar dryer chamber.
The values of moisture content obtained for all the dried leathers fall within the range of 12 -
25 % which is safe for storage of dried products [24]. Fruit products with moisture content of 13 -
25 % have water activity less than 0.8 [25]. Below this value, most microbial growth, especially
bacterial, is impeded with the exception of xerophillic moulds and osmophillic yeasts which can
thrive at water activity of 0.61 [26]. This suggests that all the leathers produced were generally
microbiologically stable. The spoilage of these leathers could most likely result from the action of
xerophillic moulds and osmophillic yeasts [11]. Although the water activity (< 0.8) associated with
the moisture levels attained ( 0.05) from both the convection
and cabinet dried leathers. The texture of fruit leathers is generally affected by their moisture
content and drying temperatures [15]. High temperatures and long drying times are associated with
lower moisture content and harder texture. Differences in texture of leathers could also be due to
variations in genetic make up of the fruit, rate of water absorption from the surroundings and protein
content of the fruit among others [12]. The texture of fruit leather is also affected by the addition of
sugar, which is sometimes done in order to improve the flavour of the leather [11, 14].
Colour
All samples produced leathers that were yellow-orange in colour. Similar results were reported for
jackfruit leather produced from unfertilized floral parts of the fruit [6]. All the drying methods
significantly reduced the Tintometer color readings of the leathers compared to the colour of the
fresh fruit. Both solar (0.61) and oven (0.80) dried leathers had significantly lower colour readings
105I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
compared to cabinet (1.85) dried leather (p< 0.05). All the leathers turned brown upon drying. Light
coloured fruit leather tends to darken upon drying [11]. Solar and oven dried leathers lost more of
the yellow-orange colour probably because of the longer drying time they under went. Fresh fruits
contain beta-carotene which is responsible for the bright orange and yellow orange colour [30].
Decrease in the yellow-orange colour occurred because these pigments are sensitive to temperatures
above 22˚C [31, 32]. The drying temperatures were above 22˚C in all the drying methods. Solar and
oven dried leathers lost more colour than cabinet dried leather probably because solar and oven
leathers were dried for rather longer times (72 hours and 18 hours respectively) compared to cabinet
drying (6 hours).
Browning of the leathers could have resulted from non enzymatic vitamin C oxidation and
enzymatic oxidation of polyphenols [28]. This is because the temperatures involved in all drying
methods were high enough to favour the occurrence of these two chemical reactions. Vitamin C
oxidation is favoured by presence of oxygen, pH 4.0, water activity less than 0.75 and temperatures
ranging from 30-50 °C [28]. Oxidation of polyphenols occurs at water activity less than 0.85 and
temperatures ranging from 10-80 °C [29, 33]. The loss of color as well as browning in the solar and
oven dried leathers can be minimised by using additives such as ascorbic acid (Che Man and Sin
1997) and sodium metabisulphite [6, 34].
Sensory evaluation
The results of sensory evaluation of the jackfruit leather prepared using the three different drying
methods are shown in Table 2. While cabinet and oven dried leathers were generally acceptable,
solar dried leather was generally disliked with all attributes having scores less than 5.
Drying method Sensory attributes
Aroma Colour Taste Texture Overall
acceptability
Cabinet drying 6.18±(1.846)a 6.52±(2.071)a 6.63±(1.859)a 6.07±(2.09)a 6.67±(1.847)a
Oven drying 5.63±(2.099)a 5.75±(2.297)a 5.97±(2.091)a 5.55±(2.12)a 6.20±(1.876)a
Solar drying 4.38±(2.026)b 4.20±(2.032)b 4.33±(2.039)b 4.43±(1.97)b 4.47±(2.021)b
Table 2: Acceptability scores of sensory attributes of jackfruit leather
Values are means ± (SD) with n = 60. Means within same column with the same letters are not significantly different (p
> 0.05). Scores 1=dislike extremely, 5= neither like nor dislike, 9=like extremely.
Aroma acceptability
The aroma of the solar dried leather was generally disliked and had significantly lower acceptability
scores compared to cabinet and oven leather dried leather (p < 0.05). The aroma for both cabinet and
oven dried leather was acceptable (scores > 5). Che Man and Sin produced jackfruit leather using a
cabinet dryer at 50˚C for 24 hours with acceptable aroma [6]. The aroma of products results from
volatile substances in the fresh food such as esters, ketones, terpenes, aldehydes and others [33, 35].
The loss of these volatiles leads to a decrease in aroma detection. High aroma acceptability scores
for cabinet and oven dried leathers could be attributed to the short drying times (6-18 hours) used as
opposed to 72 hours in solar drying. Longer drying times may allow for greater loss of volatiles.
Jain and Nema used direct sun drying to produce guava leathers of 15% moisture content with
acceptable aroma [14]. However, the drying time of the leather was not reported. The addition of
sugar to the guava leather could have enhanced the aroma of the guava leathers. Honey and or sugar
can be used to enhance the aroma of fruit leathers [11]. However, the mean score for flavour rating
106I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
decreases with increase in sugar content beyond a given optimum amount [14]. It is therefore
important to optimise the amount of sugar added for the purpose of enhancing flavour.
Taste acceptability
Solar dried leather had the lowest acceptability for taste and was generally disliked (score < 5).
Oven dried and cabinet dried leathers had comparable scores which were significantly greater than
those for solar dried leather. The taste of leather is contributed by the amount of sugars contained in
the fresh pulp. Increase in the amount of sugar beyond optimum amounts may, however, reduce the
taste ratings thus requiring optimization [14]. Sweetness rating may also depend on the type of the
fruit and may also vary during storage [13]. However, guava leather and pawpaw leather were
shown to maintain acceptable sweetness ratings within a study period of two months [12]. Besides
sugar and honey, other ingredients such as leaf oregano and garlic-salt among others could be used
to improve the taste of solar dried leather [11]. It is important to note that taste may also be
influenced by and may correlate with aroma [35]. Therefore, enhancing aroma may also improve
taste acceptability.
Colour acceptability
Solar dried leather had the lowest acceptability scores for colour and was generally disliked (score <
5). Oven and cabinet-dried leathers had comparable scores. It is clear from the data that colour
acceptability ratings of the leathers decreased with increase in drying time although the oven and
cabinet-dried leathers were not significantly different (p> 0.05). Drying above 22˚C leads to loss of
yellow-orange carotenoid pigments responsible for colour of the fresh fruits [31, 32]. The colour of
solar dried leather was not acceptable compared to oven and cabinet-dried leathers. This is probably
because solar-dried leather was dried for a longer time (72 hours) and thus lost more of its yellow-
orange color and underwent more browning reactions. However, it is important to note that
according to colour readings as determined by the instrumental method, cabinet dried leather
retained more colour than solar and oven dried leathers while solar and oven dried leather were not
significantly different. Colour acceptability for solar dried leather could be improved by preventing
browning reactions, minimizing carotenoid degradation or addition of colour additives.
Texture acceptability
The highest acceptability rating for texture was observed for cabinet dried leather followed by oven
dried leather while solar dried leather received the lowest rating (Table 2). The acceptability for
texture of oven and cabinet leathers were not significantly different (p> 0.05). It is important to note
that there were also no significant differences in the texture readings as determined by the
instrumental method. It is worth noting that the texture of fruit leathers can be evaluated in several
ways. The human mouth is more complex at evaluating texture as opposed to a penetrometer which
might measure just one aspect of texture [10, 36]. This illustrates the importance of sensory methods
in quality assessment of leather texture. The texture of fruit leather can be improved by adding
malto-dextrin, coconut oil or chopped nuts [9, 11].
Overall acceptability
Results showed that overall acceptability of the leathers (Table 2) was highest for both cabinet
(6.67) and oven (6.20) and lowest for solar dried leathers (4.47). The overall acceptability of oven
107I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
and cabinet dried leather were not significantly different (p> 0.05) although both of them were
significantly different (p< 0.05) from solar died leather. The results obtained are similar to those
obtained for all the other sensory attributes rated. It is reported that the acceptability of fruits and
vegetables is influenced by their aroma [37]. In this study, however, the results of overall
acceptability were significantly (p< 0.05) positively correlated with the acceptability of all the
sensory attributes tested (Table 4). For solar dried leather, aroma (r = 0.688) and colour (r = 0.636)
were more positively correlated with overall acceptability followed by texture (r = 0.575). This
shows the importance of enhancing these attributes in further studies on solar dried leather.
Consumer questionnaire
Results of demographic characteristics and attitudes of panelists towards jackfruit are presented in
Table 3. A total of 60 panelists aged 18-30 years participated in the study. The gender of the
respondents was equally represented (1:1). All were students from the Department of Food Science
and Technology Makerere University. Most of the consumers (70 %) eat jackfruit occasionally. The
majority of the consumers (57 %) reported that they eat the thin fibrous and mushy variety of
jackfruit. This variety is also known to have a very sweet taste and a strong odour. It was not
established whether this variety is more commonly consumed due to its attributes being more
superior or due to it being more readily available on the market. When asked what drives them into
eating jackfruit, the majority of panelists (60 %) noted that they eat the fruit because of its sweet
taste.
Jackfruit aroma, availability and colour were also noted to be important factors influencing
consumption of the fruit. The percentage of consumers who eat jackfruit for health reasons was
small (10%) possibly indicating the ignorance of consumers about its nutritional importance. A
small proportion (3%) like the fruit for its juice content. It is important to note that jackfruit is not
necessarily juicy. Only the mashed and over ripened type contains juice. Most consumers (87%)
indicated that they dislike jackfruit because of its sticky white gummy latex. This conforms to
earlier observations that utilization of jackfruits is limited by the exudation of the copious sticky
white latex [2]. This necessitates processing of the fruit to remove the latex thus improving its value
and acceptability. Jackfruit aroma was also noted to be important in influencing jackfruit
acceptability. A few consumers indicated that they dislike the fruit because of its satiety effect (7%)
and the soft texture (3 %). The undesirable satiety effect would probably a rise when too much of
the fresh ripe pulp is eaten. This condition may cause some discomfort. The soft texture is variety
dependant and is also often achieved when the fruit is left to ripen for a long time. A high
percentage of consumers (70 %) reported that they do not know about any jackfruit products
existing on the market. This conforms to our observation that apart from being consumed in fresh
form, there are no processed jackfruit products on the local market. There is therefore a need to
develop new and high quality jackfruit products to promote utilization of this fruit.
108I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
Table 3: Demographic characteristics of the consumer acceptability panel
Characteristic No. of Assessors/
(%)
Age (years)
18-30 60/ (100)
Sex
Male 30/ (50.0)
Female 30/ (50.0)
About how often do you eat jackfruit?
Occasionally (once in a while) 42/ (70.0)
Three times a month 8/ (13.0)
More than once a week 6/ (10.0)
Types of jackfruit eaten by consumers
Thin, fibrous, mushy edible pulp, very sweet and strong odour 34/ (56.7)
Thick, firm, often crisp and less fragrant pulp 20/ (33.3)
Others (moderate i.e. between hard and soft) 6/ (10.0)
What drives consumers into eating jackfruit
Sweet taste 36/(60.0)
Aroma 16/(26.7)
Availability 8/(13.3)
Colour 6/(10.0)
Health 6/(10.0)
Texture 4/(6.7)
Hunger 2/(3.3)
What consumers like about jackfruit
Sweet taste 54/ (90.0)
Colour 10/ (16.7)
Aroma 8/ (13.3)
Satiety effect 6/ (10.0)
Texture 4/ (6.7)
Juiciness 2/ (3.3)
What consumers disk like about jackfruit
Latex 52/ (87.0)
Aroma 20/ (33.3)
Satiety effect (makes one feel too full) 4/ (6.7)
Texture ( when too soft) 2/ (3.3)
Whether consumer know about any
jackfruit product on market
No 42/ (70.0)
Yes 18/ (30.0)
109I. M. Mukisa. et al. EJEAFChe, 9 (1), 2010. [101-111]
CONCLUSION
Although solar drying reduced moisture content to desired levels and had similar effects on texture
when compared to cabinet and oven drying, solar dried leather was generally not sensorially
acceptable. Solar dried leather was not acceptable because its long drying time and low temperature
encouraged greater loss of colour pigments and aroma compounds as well as browning reactions.
Although fruit leathers are not popular in Uganda, the fact that oven and cabinet dried jackfruit
leathers produced in this study were acceptable suggests that such products could be adopted when
introduced on the market. Therefore, further studies are still needed to improve the sensory quality
of solar-dried leather. Further studies are also needed to evaluate the nutrient retention, microbial
stability and shelf life of solar dried leathers in order to establish the suitability of solar drying in
processing of jack fruit leather.
ACKNOWLEDGMENTS
We thank Mr. Benjamin Ssentongo and Mrs. Jacqueline Lubega for the technical assistance and
advice. We are also grateful to the Department of Agricultural Engineering, Makerere University for
providing the solar dryer.
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