Effect of drying methods on nutritional value of some vegetables

Abstract

Leafy vegetables, in addition to protein, contain a wide variety of substances and in particular significant amounts of vitamins, minerals and lipids. As all vegetables are not available in abundance throughout the year, it can be preserved in dried form and can be used throughout the year. In this experiment three green leafy vegetables coriander, curry leaves, mint and bitter gourd are used to study effective drying method for retention of nutrients. These vegetables were dried by five different methods of drying as Oven at 60 o C, Oven at 90 o C, Red light dry, Sun dry, Shade dry. After completion of drying decrease in dry weight, relative water content was also determined. Dried vegetable samples were grinded used for analyses of β carotene, Ascorbic acid content and water soluble reducing sugar. Large variation in nutritional value of vegetables by different methods of drying was observed.

Full text

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Effect of drying methods on nutritional value of some vegetables
Naikwade Pratap Vyankatrao
Department of Botany,
Nya. Tyatyasaheb Aathalye Arts, Ved. S. R. Sapre Commerce and
Vid. Dadasaheb Pitre Science College, Devrukh 415804, Maharashtra, India.
Corresponding author e mail: naikwade.pratap@gmail.com
Keywords:
Abstract
ascorbic acid, β carotene,
drying, nutrient,
vegetables
Leafy vegetables, in addition to protein, contain a wide variety of substances and in
particular significant amounts of vitamins, minerals and lipids. As all vegetables are
not available in abundance throughout the year, it can be preserved in dried form
and can be used throughout the year. In this experiment three green leafy vegetables
coriander, curry leaves, mint and bitter gourd are used to study effective drying
method for retention of nutrients. These vegetables were dried by five different
methods of drying as Oven at 60oC, Oven at 90oC, Red light dry, Sun dry, Shade
dry. After completion of drying decrease in dry weight, relative water content was
also determined. Dried vegetable samples were grinded used for analyses of β
carotene, Ascorbic acid content and water soluble reducing sugar. Large variation in
nutritional value of vegetables by different methods of drying was observed.
INTRODUCTION:
Green Leafy Vegetables (GLVs) occupy an
important place among the food crops as these
provide adequate amounts of vitamins and minerals
for humans. Begum and Pareira (1977) analyzed
thirty two varieties of edible green leaves easily
available in South India for their beta-carotene
content in different seasons of the year. Preservation
of these vegetables can prevent huge wastage and
makes them available in the lean season at
remunerative prices (Lakshmi and Vimala, 2000).
Vegetables have a unique place in diet
because of their color, flavor, nutrient content and
health benefits (Peter et al., 2010). They serve as
rich sources of β carotene, ascorbic acid, iron, zinc,
folate and dietary fiber (Negi and Roy 2000). Some
experiments carried out exhibited that green leafy
vegetables contains considerable amount of protein,
β carotene, ascorbic acid and can be enhanced by
application of organic manures (Naikwade et
al.,2011, Mogle et al.,2013, Naikwade 2014a,
Naikwade 2014b). Average intake of green leafy
vegetables in the Indian population is much less
than the recommended daily allowance; therefore,
the people suffer from deficiency diseases.
The rainfall in India is seasonal, as a result
bulky amount of vegetables are available in the
rainy season and under the favorable conditions
during winter, all of which are not properly utilized.
Some the low cost methods of praservation of
vegetables include blanching, improved traditional
techniques (Naikwade et al.,2012a, Naikwade et
al.,2012b) etc. GLV‟s are highly perishable due to
their high water activity, therefore methods
involving removal of this moisture helps in their
preservation. During the dry months of the year,
there is wide spread acute shortage of vegetables
throughout the country and the cost will be
increased beyond the purchasing limit of a poor
citizen. To satisfy the needs of the people surplus
vegetables must be conserved for use when
required.
The ideal less expensive and quite simplest
method of conservation of vegetables is to drive of
the surplus moisture in the fresh material and forage
crops through sum of hot and dry natural air
(Chatterjee and Malti, 1978). The dried powder of
vegetables is used to check malnutrition in India.
Dried vegetable powder is added to the meals and
served in government schools in Delhi under the
Mid Day Meal Scheme. In West Bengal, small-
scale trials of adding leaf powders of drumstick,
fenugreek, curry leaf etc in badi, papad, sauce and
soup powder keep up the quality and taste.
However, there is limited information
comparing the quality of leafy vegetables by
different drying methods. Coriander, mint, curry
leaves are rich in iron, β carotene, ascorbic acid ,
chlorophyll and are mainly used spices in India.

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The demand for fresh and dehydrated curry
leaves, mint and coriander has considerably
increased over the last two decades. Bitter gourd is
treated as remedy for diabetes. This study has been
undertaken to investigate the effect of different
drying methods on the nutritional quality of three
leafy vegetables and bitter gourd. A comparative
evaluation of the effectiveness of the drying
vegetables as preservation techniques is also
described.
MATERIALS AND METHODS
Experimental site and Materials
Field experiment was carried out in the
Research lab located in the Botanical garden of Dr.
Babasaheb Ambedkar Marathwada University,
Aurangabad during the period from 2 May to 10
May 2011. Three green leafy vegetables coriander,
curry leaves, mint and bitter gourd, were collected
from local Aurangabad vegetable market early in
the morning. The vegetables were washed with
water and debris and mud was removed.
Treatments -
Vegetables were dried by five different
treatments i.e. Oven at 60oC, Oven at 90oC, Red
light dry, Sun dry, Shade dry. Temperatures of two
different ovens were set at 60oC and 90oC
respectively. Vegetables were kept in these ovens.
For Sun light drying, vegetables were kept in a
wooden tray and set aside in Sun light. For Red
light dry treatment red colored glass was set on
vegetable tray and kept in Sunlight. Sun light rays
were converted into red light while passing through
red colored glass and hence drying of vegetables
under red light became possible. For shade drying
vegetables were arranged on wooden racks and kept
in room.
Method -
Bitter gourd was cut into circular slices of
thickness 2-3 mm. The initial amount 300 gm each
of bitter gourd slices, coriander, mint and 220 gm of
curry leaves were kept for drying in different
treatments and decrease in weight was noted every
24 hours till it gives constant weight. In all cases the
materials were uniformly spread. After completion
of drying decrease in dry weight, relative water
content was also determined. The dried samples
were grinded and passed through 0.5 mm sieve to
get equal size and packed in air tight polythene bags
for analyses of nutrient uptake.
The loss of water from vegetables during
drying at various stages was measured after every
24 hrs. by calculating relative water content
(R.W.C.) as described by Harris and Thaine (1975)
using following equations,
R.W.C. = (Wt –Wd / Ws-Wd) ×100
Where,
Wt is the sample weight at time„t‟
Ws is the saturation or initial weight, and
Wd is the dry weight.
Nutrient Analyses -
The amount of β-carotene (Pro- vitamin A)
was estimated by following Knuckles et al. (1972).
Ascorbic acid was estimated by titration method
given by Sadasivam and Manickam (1992). Water
soluble reducing sugar (WSRS) determined with the
help of Folin-Wu tubes (Oser, 1979).
Statistical analysis -
All the results were statistically analyzed by
calculating Standard Deviation (S.D.) and
Coefficient of variation (C.V.) by following
Mungikar (1997).
RESULTS AND DISCUSSION:
Decrease in weight and relative water content
a) Mint
Mint took less time for drying as compared to other
vegetables. The Minimum days for complete drying
were taken by Oven at 90oC treatment i.e.3 days
followed in order by Oven at 60oC, Sun drying, Red
light drying and maximum in Shade drying i.e. 8
days. Relative Water Content (RWC) of mint is
shown in Fig. 1.
b) Coriander
For coriander, the Minimum days for
complete drying were taken by Oven at 90oC
treatment i.e.3 days followed in order by Oven at
60oC, Sun drying, Red light drying and maximum in
Shade drying i.e. 9 days(Table 2). Relative water
content was decreased from 100 to 0 (Fig 2).
c) Curry Leaves
For curry leaves, the Minimum days for
complete drying were taken by Oven at 90oC
treatment i.e.3 days followed in order by Oven at
60oC, Sun drying, Red light drying and maximum in
Shade drying i.e. 9 days. Relative water content was
decreased from 100 to 0 (Fig 3).
d) Bitter gourd
ANALYSIS
Decrease in weight
During experiment all the vegetables were
weighed and decrease in weight was determined
after every 24 hrs. (1day), till constant weight. For
bitter gourd, the Minimum days for complete drying
were taken by Oven at 90oC treatment i.e.4 days
followed in order by Oven at 60oC, Sun drying, Red
light drying and maximum in Shade drying i.e. 9

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days. Changes in Relative water content are shown
in Fig 4. At the end of drying, the weight of all
dried vegetables was higher in shade drying
treatment compared to Sun drying which indicated
higher solid loss during Sun drying. Joshi and
Mehta (2010) also proved that shade dried samples
show more moisture than sun dried samples. Negi
and Roy (2000) had reported that sun drying of
leafy vegetables seemed to present a disadvantage
of more solid losses during drying. Gupta and Nath
(1984) have also reported higher dehydration ratio
in sun-dried samples.
Nutrient Content
i) β carotene content:
β carotene is often considered as pro-
vitamin A, as its one molecule gets converted into
two molecules of vitamin A after consumption by
human beings (Mertz, 1967). After drying by
different methods, the β carotene content and %
overall retention in vegetables was calculated and is
mentioned in Table 1.
The β carotene was highest in fresh mint
followed by coriander, curry leaves and bitter
gourd. The values are comparable to those reported
earlier (West, et al., 1988; Simpson, 1983). After
drying the highest carotene content in mint was
found by Shade drying and lowest in Sun drying.
Variation of β carotene content was observed when
mint dried by various methods (C.V.37.19). Overall
retention of β carotene was maximum in Shade
drying while minimum in Sun drying. After drying,
the highest carotene content in coriander was found
by Shade drying and lowest in Sun drying. Large
variation of β carotene content was observed when
coriander dried by various methods (C.V. 63.22).
In case of curry leaves, after drying the
uppermost carotene content was found by Oven at
60oC and smallest in Sun drying. Variation of β
carotene content was observed when curry leaves
dried by various methods (C.V.53.36). After drying,
the peak carotene content in bitter gourd was found
by Oven at 90oC and least in Sun drying. Large
variation of β carotene content was observed when
bitter gourd dried by various methods (C.V. 65.52).
While comparing each other, highest
retention of β carotene was found by Shade drying
in case of mint and coriander; on the other hand in
case of curry leaves and bitter gourd, highest
retention of β carotene was found by means of Oven
at 60oC, Oven at 90oC respectively. However in all
vegetables lowest retention of β carotene was found
by Sun drying. Devadas et al. (1978) revealed that
sun drying of green leafy vegetables and their
subsequent storage for 1 year resulted in 10–60%
retention of β carotene. Loss of β carotene by Sun
drying can be minimized by using red colored glass
under Sunlight.
Vitamin A (β carotene) is very sensitive to
light. Retention of β carotene after sun drying
ranged between 18.32 and 39.84%. Kowsalya et al.
(2001) reported β carotene retention after sun
drying from 17.7 to 32.4%. In the earliest study by
Amandeep Kaur et al., (2008), β carotene retention
after drying in mint ranged from 26.08 to 65.59 %.
In the present study, β carotene retention after
drying in mint varied between 39.84% and 65.31%.
Statistical analysis indicates that there are enormous
variations in β carotene content as a result of
various treatments.
ii) Ascorbic acid content:
In fresh samples of vegetables, ascorbic
acid content was highest in coriander followed by
mint, curry leaves and bitter gourd (Table 2). There
was reduction in ascorbic acid content after drying.
After drying the highest amount of ascorbic acid in
mint was found in Oven at 90oC and lowest in Red
light drying. Variation of ascorbic acid content was
observed when mint dried by various methods (C.V.
50.98). After drying, the maximum ascorbic acid
content in coriander was found by Oven at 60oC and
minimum in Sun drying. In case of curry leaves,
after drying the topmost ascorbic acid content was
found by Oven at 90oC and smallest in Shade
drying. The highest ascorbic acid content in bitter
gourd was found by Oven at 90oC and least in Sun
drying. While comparing each other, highest
retention of ascorbic acid was found by Oven at
90oC in case of mint, curry leaves and bitter gourd
except coriander in which highest retention of
ascorbic acid was found in Oven at 60oC. The
lowest retention of ascorbic acid was found by Sun
drying in case of coriander and bitter gourd
nevertheless, lowest retention of ascorbic acid was
found by Red light drying and shade drying in case
of mint and curry leaves respectively.
Lakshmi and Vimala (2000) reported that
retention of ascorbic acid ranged from 15 to 31% in
sun-dried leafy vegetables. Thus, in the present
study, retention of ascorbic acid ranged from 25 to
38% which is more than previous reported values.
All drying methods significantly cause loss of
vitamin C (Kiremire et al.,2010) and this could be
attributed to the fact that vitamin C is highly prone
to oxidative destruction in the presence of heat,
light, oxygen, enzymes, moisture and metal ions
(Russell and MacDowell 1989).

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iii) Water Soluble Reducing Sugar content:
Total reducing sugar was determined of
different vegetables on dry matter basis (Table 3). In
mint, highest percentage of total reducing sugar was
found through Shade drying and lowest in Oven at
90oC. In coriander, maximum reducing sugar
percentage was found by Red light drying and
minimum in Shade drying (3.50). In case of curry
leaves, highest percentage of total reducing sugar was
found through Sun drying and lowest in Oven at 90oC.
The uppermost percentage of total reducing sugar in
bitter gourd was found by Oven at 60oC and smallest
in Oven at 90oC.
From the point of view of preservation of
total reducing sugar effective treatment for mint is
shade drying, for coriander Red light drying, for curry
leaves sun drying and for bitter gourd drying in oven
at 60oC are efficient. Statistical analysis indicates that
there are satisfactory variations in β carotene content
as a result of various treatments.
iv) Nitrogen and Crude Protein
Nitrogen and crude protein percentage of
different dried vegetables was estimated (Table 4). In
mint, maximum percentage of nitrogen was found
through Oven at 60oC and lowest in Shade drying.
Same pattern was followed in case of crude protein.
In coriander, highest nitrogen and crude
protein percentage was found by Oven at 60oC
followed in order by, Sun drying, Oven at 90oC, Shade
drying and minimum in Red light drying. In case of
curry leaves, maximum percentage of nitrogen and
crude protein was found through Oven at 60oC. In
bitter gourd, the highest percentage of nitrogen and
crude protein was found by Shade drying and smallest
in Oven at 90oC. From these observations it can be
concluded that highest percentage of crude protein
was found by Oven at 60oC in all vegetables. Earlier
experiments (Awogbemi and Ogunleye 2009) also
showed that protein percentage decrease day by day
while drying.
From these results it get cleared that drying
methods are useful for preservation of vegetables in
tropical India. Preservation of these green leafy
vegetables can prevent huge wastage and makes them
available in the lean season at remunerative prices
(Lakshmi and Vimala, 2000). Dehydration is a simple
and economical method of preservation of these
vegetables (Mandhyan et al. 1988). Dehydrated
vegetables are simple to use and have a longer shelf
life than fresh vegetables (Chauhan and Sharma,
1993). Use of sun drying can be increased by realizing
the pollution-free nature and renewable energy source
of Sun (Pande et al. 2000).
All vegetables were dried quickly by Oven at
90oC within 3-4 days, while it took 9 days for
complete drying in shade. The β carotene was highest
in fresh mint followed by coriander, curry leaves and
bitter gourd. Ascorbic acid content in fresh sample
was the highest in coriander followed by mint, curry
leaves and bitter gourd. Maximum β carotene retention
was observed in Shade drying. The highest retention
of ascorbic acid was found by Oven at 90oC. Drying in
oven at 60oC results in maximum preservation of
nitrogen and crude protein in all vegetables. A
particular method could cause least losses of one
nutrient but show the highest loss for another. One
method is suitable for particular vegetable but not
effective for other vegetable. Therefore the author
feels that an ideal method or combination of methods
has to be developed to protect the plant nutrients at
optimum level to use the seasonal and surplus
vegetable. Finally it can be suggested that drying in
oven at 60oC and Red light drying these two
treatments cause minimum loss in nutrients and can be
used for drying of vegetable competently.
Table 1. Effect of different drying methods on Beta carotene content and % retention
Mint
Coriander
Curry
Leaves
Bitter gourd
Treatment
mg/100
gm
%
Retention
mg/100
gm
%
Retention
mg/100
gm
%
Retention
mg/100
gm
%
Retention
Fresh
6.40
100
3.76
100
3.57
100
2.93
100
Oven 600C
3.12
48.75
1.20
31.91
1.86
52.10
0.66
25.19
Oven 900C
2.73
42.66
1.62
43.09
1.69
47.34
1.71
65.27
Red Light
3.94
61.56
1.00
26.60
1.06
29.69
1.13
43.13
Sun Dry
2.55
39.84
0.84
22.34
0.97
27.17
0.48
18.32
Shade Dry
4.18
65.31
1.74
46.28
1.49
41.74
1.62
61.83
Mean
3.82
1.69
1.77
1.42
S.D.
1.42
1.07
0.95
0.89
C.V.
37.19
63.22
53.36
65.52

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Table 2. Effect of different drying methods on Ascorbic acid content and % retention
Mint
Coriander
Curry
Leaves
Bitter gourd
Treatment
mg/100
gm
%
Retention
mg/100
gm
%
Retention
mg/100
gm
%
Retention
mg/100
gm
%
Retention
Fresh
295
100
314
100
267
100
193
100
Oven 600C
179
60.53
182
58.01
82
30.77
64
33.31
Oven 900C
204
69.01
143
45.50
104
38.95
79
40.71
Red Light
82
27.85
107
34.12
75
28.09
68
35.16
Sun Dry
111
37.53
89
28.44
71
26.75
61
31.46
Shade Dry
93
31.48
93
29.57
68
25.41
75
38.86
Mean
160.48
157.71
111.24
89.90
S.D.
81.81
85.60
77.38
50.94
C.V.
50.98
55.33
69.57
56.66
Table 3. Effect of different drying methods on Water Soluble Reducing Sugar %
Treatment
Mint
Coriander
Curry leaves
Bitter gourd
Oven 600C
4.49
4.54
3.20
3.43
Oven 900C
3.99
3.86
2.75
2.57
Red Light
4.16
4.82
3.05
3.28
Sun Dry
4.31
4.04
3.55
2.70
Shade Dry
5.05
3.50
3.02
3.00
Mean
4.40
4.15
3.12
3.00
S.D.
0.41
0.53
0.29
0.37
C.V.
9.24
12.79
9.42
12.23
Fig 1. Relative water content of Mint

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Fig 2. Relative water content of Coriander
Fig 3. Relative water content of Curry leaves

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Fig 4. Relative water content of Bitter gourd
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