RESEARCH ARTICLE

Effect of Solar Drying on Physico-chemical and AntioxidantProperties of Mango, Banana and Papaya

Ghan Shyam Abrol • Devina Vaidya •

Ambika Sharma • Surabhi Sharma

Received: 20 November 2012 / Revised: 16 September 2013 / Accepted: 22 October 2013 / Published online: 7 February 2014

� The National Academy of Sciences, India 2014

Abstract Fruits play an important role in human nutri-

tion, but due to their high perishable nature they cannot be

stored for longer period. As drying is the ancient method of

preservation, therefore, solar tunnel drying is done to

evaluate the effect of drying on physico-chemical and

antioxidant activity of mango, banana and papaya fruits.

Fruits viz. mango and papaya were cut into slices while

banana were made into rings (thickness of 1 ± 0.1 cm) and

kept at a temperature of 60 ± 2 �C for 6 h under solar

tunnel drier. During drying the removal of moisture content

increased the physico-chemical properties viz. total soluble

solids, acidity, reducing and total sugars of all the fruits.

The antioxidant compounds, total phenols and total

carotenoids were increased while heat sensitive vit-C

decreased. However, the antioxidant activity, after drying,

was increased in mango from 68.6 to 86.3 %, in papaya

from 64.1 to 80.4 % and in banana from 59.5 to 73.2 %,

respectively. Thus, solar tunnel drying is an inexpensive

method of preserving the fruits efficiently and effectively

for longer period of time.

Keywords Mango � Banana � Papaya � Solar drying �Total phenols and total carotenoids

Introduction

Fruits play an important role in human nutrition because

they contain constituents that have health benefits and anti-

disease factors, such as antioxidants. Phenolic antioxidants

are gaining continuing attention due to their efficacy in

counteracting free radicals, linked with various diseases

[1, 2]. Plants phenolics are considered comparatively more

stable and are available as active phytochemicals for uses

in different food products to protect them from oxidation

and enhancing the shelf-life. Mango, banana and papaya

are the rich source of antioxidant compounds viz. ascorbic

acid, total phenols and total carotenoids. All these com-

pounds are sensitive to fruit ripening and declined during

storage, but solar drying of these fruits can store these

compounds for a longer duration. The process of drying is

one the oldest methods for food preservation, and drying is

a complex process involving heat and mass transfer phe-

nomena, which occurs frequently in most of the food

processing industries [3, 4]. Drying brings substantial

reduction in weight and volume, which minimizes pack-

aging, storage and transportation costs [5, 6]. Moreover,

products with a low moisture content can be stored at

ambient temperatures for longer periods of time due to a

considerable decrease in the water activity of the material

that reduced microbiological activity and minimized

physical and chemical changes [7, 8]. Physico-chemical

properties such as total soluble solids (TSS), rehydration

ratio, moisture content, acidity, reducing sugars and total

sugars are important parameters of dried fruits which

reflect the quality of final product. However, the drying

process may lead to changes in physico-chemical and

functional components. Therefore, the main objective of

this study was to determine the effect of solar tunnel drying

on the physico-chemical and antioxidant properties of

G. S. Abrol (&) � D. Vaidya � S. Sharma

Department of Food Science and Technology, Dr Y S Parmar

University of Horticulture and Forestry, Nauni, Solan 173230,

India

e-mail: ghanshyamabrol@gmail.com

A. Sharma

Department of Biotechnology, Jaypee University of Information

Technology, Waknaghat 173234, India

123

Natl. Acad. Sci. Lett. (January–February 2014) 37(1):51–57

DOI 10.1007/s40009-013-0196-1

mango, banana and papaya fruits, as these ranked as most

liked fruits in the Indian community and further there is no

report on effect of solar tunnel drying on antioxidant

activities of these fruits.

Materials and Methods

Fruit Samples

Fresh fruit samples were obtained from local market. The

fresh fruit samples were washed in tap water, and all

inedible parts were removed manually by using a steel

knife. Bruised or wounded fruits were discarded. For the

dehydration process, mangoes and papaya were cut into

slices while bananas were made into rings (thickness of

1 ± 0.1 cm) (Fig.1). All these were kept under solar tunnel

drier at a temperature of 60 ± 2 �C for 6 h. The dried

samples of fruits were immediately vacuum packed in high

density polyethylene bags and stored at ambient conditions.

Each experiment was carried out in triplicate.

Physico-chemical Analysis

Rehydration of Fruit Samples

Rehydration experiments were carried out in distilled water

at 45 �C [9]. Fruit samples (10 g) were added to 100 mL of

water and mixed thoroughly. The samples were allowed to

rehydrate for 5 h, and the rehydration temperature was kept

constant using a water bath with adjustable temperature

control. After rehydration period, the excess water was

drained out.

Total Soluble Solids (TSS)

TSS of fresh and dried samples (after rehydration) were

measured using Erma hand Refractometer. The results

were expressed as degree Brix (�B). The readings were

corrected by applying the correction factor for the tem-

perature variation [10].

Rehydration Ratio (Rr)

Rr was expressed as a ratio of water absorbed by the dried

sample (Wr) to the weight of the dried sample (Wd) [10].

Rr ¼Wr=Wd

Titratable Acidity

Titratable acidity was estimated by titrating a known vol-

ume of the sample against standard 0.1 N NaOH solution

by using phenolphthalein as an indicator up to the end point

(pink colour). The titratable acidity was expressed as per

cent malic acid [10].

Fig. 1 Dried fruit samples of mango, banana and papaya

Titratable acidity (%) ¼Titre � Normality of alkali� volume made up � equivalent weight of acid

Vol:=wt: of sample taken � volume of aliquot taken � 1000� 100

52 G. S. Abrol et al.

123

Reducing and Total Sugars

A known weight of sample (25 g) was taken in a 250 mL

volumetric flask and 100 mL water was added to it. Solu-

tion was neutralized with 1 N NaOH and 2 mL of 45 %

lead acetate was added to it and kept for 10 min. Excess of

lead acetate was removed from the sample by using 2 mL

of 22 % potassium oxalate in 250 mL volumetric flask.

After diluting it up to the mark, the solution was filtered

and clear filtrate was taken to estimate reducing sugars by

titrating against a known quantity of Fehling’s A and

Fehling’s B solution using methylene blue as an indicator

[11]. Reducing sugars were estimated as per cent and

calculated as given below:

Total sugars were estimated by adding 5 g of citric acid

to 50 mL calibrated sample solution and heating it for

10 min. For complete inversion of sugars, neutralizing with

NaOH and making volume 250 mL in volumetric flask was

done. The total sugars were estimated as per cent and

calculated as given as under:

% Sucrose = (% total invert sugars - % reducing

sugars) 9 0.95

% Total sugars = (% reducing sugars ? % sucrose)

Quantitative Analysis of Antioxidant Compounds

Ascorbic Acid

Ascorbic acid content was determined as per standard

AOAC method [9] using 2,6-dichlorophenol indophenol

dye. The sample extracted in 3 % m-phosphoric acid was

titrated with the dye to an end point of pink colour. Results

were expressed as mg per 100 g of sample and calculated

by using the following formula:

Total Phenolics

The amounts of total phenolics in the fruits were

determined with the Folin–Ciocalteu reagent according

to the method of Bray and Thorpe [12] using catechol

as a standard. 1 g of sample was taken and grinded

with 10 mL of 80 per cent ethanol in pestle and mortar,

and centrifuged for 20 min at 1,000 rpm and filtered.

Filtrate was evaporated in oven up to dryness and dried

extract was dissolved in 5 mL distilled water.

0.2–2.0 mL aliquot was taken in separate test tubes and

volume was made up to 3 mL. Then 0.5 mL Folin-Ci-

ocalteu reagent was added. After 3 min 2 mL of

Na2CO3 (20 %) was added and mixed. Test tubes were

placed in boiling water bath for 1 min and then cooled.

Optical density of the sample was recorded at 650 nm

with the help of Spectronic-20. The concentration was

determined as per the standard procedure from the

standard curve. The standard curve was prepared using

different concentrations (8–32 lg/mL) of catechol and

results were expressed as mg per 100 g on fresh weight

basis.

Total Carotenoids

A known weight of sample was macerated with acetone in

pestle and mortar and extract was decanted into a conical

flask. Extraction was continued till the residue became

colourless. All extracts were combined and transferred into

a separating funnel. 10–15 mL of petroleum ether was

added to transfer the red pigments into the petroleum ether

and 5 % sodium sulphate was added to it. Again petroleum

ether was added to transfer all colour into it and then

separated out from separating funnel into 50 mL

Reducing sugars (%) =Factor � Dilution

Titre value � Weight of sample taken� 100

Total sugars as invert sugars ð%Þ ¼ Factor � Dilution

Titre � Weight of sample taken� 100

Ascorbic acid (mg=100 g) ¼ Titre � Dye factor � volume made up

Aliquot of extract taken � Weight of sample taken� 100

Physico-chemical and Antioxidant Properties 53

123

volumetric flask and volume was made up to 25 mL by

petroleum ether. The colour intensity (optical density)

was measured in Spectronic-20 at 452 nm using 3 %

acetone in petroleum ether as blank. The results were

expressed in terms of b-carotene as mg/100 g of the

sample [9].

Antioxidant Activity

Antioxidant activity (free radical scavenging activity) was

measured as per the method of Brand-Williams et al. [13].

DPPH (2,2-diphenyl-1-picrylhydrazyl) was used as a source

of free radical. A quantity of 3.9 mL of 6 9 10-5 mol/L

DPPH in methanol was put into a cuvette with 0.1 mL of

sample extract and the decrease in absorbance was measured

at 515 nm for 30 min or until the absorbance become steady.

Methanol was used as blank. The remaining DPPH con-

centration was calculated using the following equation:

Antioxidant activity (%Þ ¼AbðBÞ � AbðSÞ

AbðBÞ� 100

where Ab(B) = Absorbance of blank; Ab(S) = Absorbance

of sample.

Statistical Analysis

Results were expressed as mean values ± standard deviations.

Each analysis assay was done five times from the same sample

to determine reproducibility. The means for the physico-

chemical evaluation 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 Discussions

Physico-chemical Properties

The changes observed in physico-chemical properties of

fresh and dried fruits are show in Table 1. The different

parameters TSS, rehydration ratio, moisture content, acid-

ity, reducing sugars and total sugars reflects the quality of

mango, banana and papaya fruits after drying under solar

tunnel drier. TSS of fresh mango, banana and papaya fruit

was found to 17.73 ± 0.19, 23.20 ± 0.16 and

15.27 ± 0.19 �B, respectively. Loss of moisture and con-

centration effect resulted in increase in TSS of dried fruits

of mango, banana and papaya 60 ± 0.06, 64.60 ± 0.16

and 60.13 ± 0.09 �B, respectively. Moisture content of

mango (79.63 ± 0.45 %), banana (75.57 ± 0.009 %) and

papaya (94.17 ± 0.24 %) was found very high. After solar

drying rehydration ratio of dried mango, banana and

papaya was also estimated and found highest in papaya

(1:4.90%) and lowest in dried banana (1:3.14), which

shows the water absorption and reconstitution capacity of

dried fruits. Acidity, reducing sugars and total sugars was

increase after solar drying of fruits.

Among the three fruits the highest acidity was recorded

in papaya (0.217) followed by mango (0.207) and lowest in

banana (0.125) on fresh basis. The increase in acidity might

be due to removal of moisture content and hence concen-

tration effect resulted in increase in acidity. Further the

increase in acidity might have been due to formation of

acids because of inter-conversion of sugars and other

chemical reactions [14].

Table 1 Physico-chemical analysis of fresh and dried mango, banana and papaya fruits

Fruits TSS (�B) Rehydration ratio Moisture content (%) Acidity (% MA) Reducing sugars (%) Total sugars (%)

Fresh basis

Mango 17.73 ± 0.19b – 79.63 ± 0.45b 0.207 ± 0.014b 5.08 ± 0.14a 11.52 ± 0.37b

Banana 23.20 ± 0.16c – 75.57 ± 0.22a 0.125 ± 0.002a 7.23 ± 0.16c 19.22 ± 0.03c

Papaya 15.27 ± 0.19a – 94.17 ± 0.31c 0.215 ± 0.01c 6.15 ± 0.03b 8.17 ± 0.04a

After drying

Mango 60.00 ± 0.06d 3.93:1 – 0.958 ± 0.025e 26.47 ± 0.02d 42.64 ± 0.01d

Banana 64.60 ± 0.16e 3.14:1 – 0.990 ± 0.01f 38.33 ± 0.02e 45.96 ± 0.02e

Papaya 60.13 ± 0.09d 4.90:1 – 0.829 ± 0.013d 40.80 ± 0.65f 54.27 ± 0.25f

All data are the mean ± SD of five replicates. Mean followed by different letters in the same column differs significantly (p B 0.05)

b-carotene (mg=100 g) ¼ lg of carotene per mL � dilution as read from curve

Weight of sample � 1000� 100

54 G. S. Abrol et al.

123

Statistical analysis of the data showed a highly signifi-

cant difference in the reducing sugars and total sugars

content of dried slices of mango, banana and papaya. The

increase in the reducing sugar content might be due to the

conversion of total sugar into simple sugars and also con-

centration of fruit slices during drying process. Similar

increase in reducing sugars and total sugars were observed

in different fruits by various workers [15–21].

Antioxidant Compounds

Table 2 represent the antioxidant compounds (ascorbic

acid, total phenols and total carotenoids) present in fresh

and dried mango, banana and papaya. Ascorbic acid

decreased after drying in mango, banana and papaya from

34.67 ± 0.19 to 7.59 ± 0.10, 20.6 ± 0.16 to 5.32 ± 0.18

and 68 ± 2.16 to 15.13 ± 0.50, respectively. Ascorbic

acid, a water-soluble vitamin, is rapidly synthesized from

carbohydrates, and variations in ascorbic acid contents

occur due to the different species of plants, ripeness, place

of origin, storage conditions, processing and handling

[22, 23]. It is difficult to retain ascorbic acid during drying

because ascorbic acid is susceptible to heat [24–26].

Moreover, ascorbic acid and its oxidation product (dehydro

ascorbic acid), has many biological activities in the human

body due to its antioxidant properties [27, 28].

Carotenoids are yellow, orange, and red pigments present

in many fruits and vegetables. Several of these carotenoids

are precursors to vitamin A (b-carotene and b-cryptoxan-

thin). Due to their conjugated double bonds, b-carotene and

b-cryptoxanthin are both radical scavengers and quenchers of

singlet oxygen molecules v [29]. The highest total carote-

noids were found in dried mango (30.12 ± 0.14 mg/100 g)

followed by dried papaya (26.04 ± 0.10 mg/100 g).

Total phenols increased after solar drying in all the three

fruits viz. mango, banana and papaya (Fig.2). It might be

due to the formation of Maillard reaction products leading

to formation of new phenolic compounds from their pre-

cursor at high temperature [30, 31]. Moreover, it can be

presumed that bound phenolics with larger molecular

weight, in samples might have been liberated into simple

free forms by heat treatment leading to enhancing total

phenolic contents [32].

Antioxidant Activity

Figure 3 shows the antioxidant/free radical scavenging

activity of fresh and solar dried fruits mango, banana and

papaya. Dried fruits showed high antioxidant activity than

fresh fruits. In mango it increases from 68.6 to 86.3 %, in

papaya from 64.1 to 80.4 % and in banana from 59.5 to

73.2 %. This can be attributed due to the increase in

ascorbic acid, carotenoids and total phenolics after solar

drying, as antioxidant activity totally depends upon pig-

ments like carotenoids and anthocyanins [33], ascorbic acid

[34] and total phenolic content [35] in the product. DPPH is

stable free radical with characteristic absorption at 515 nm

and antioxidants react with DPPH radicals and converts it

into 2,2-diphenyl-1-picrylhydrazine. The degree of discol-

ouration indicates scavenging potential of the antioxidant

Table 2 Effect of solar drying on antioxidant compounds of mango,

banana and papaya fruits

Fruits Ascorbic acid

(mg/100 g)

Total carotenoids

(mg/100 g)

Fresh basis

Mango 34.67 ± 0.19b 6.32 ± 0.34b

Banana 20.6 ± 0.16a –

Papaya 68 ± 2.16c 5.03 ± 0.33a

After drying

Mango 7.59 ± 0.10e 30.12 ± 0.14d

Banana 5.32 ± 0.18d –

Papaya 15.13 ± 0.50f 26.04 ± 0.10c

All data are the mean ± SD of five replicates. Mean followed by

different letters in the same column differs significantly (p B 0.05)

Fig. 2 Effect of solar drying on total phenols (mg/100 g) of mango,

banana and papaya fruits

Fig. 3 Effect of solar drying on antioxidant activity (%) of mango,

papaya and banana fruits

Physico-chemical and Antioxidant Properties 55

123

extract, which is due to the hydrogen donation ability of

antioxidants [36].

Conclusion

Present study shows that the physico-chemical and anti-

oxidant properties of fresh and dried fruits (mango, banana

and papaya). Solar tunnel drying resulted in increase in

TSS, acidity, reducing sugars and total sugars. Further, the

drying of these fruits reduced the bulk and maintains the

quality without altering much in its functional properties.

The solar tunnel drying resulted in an increase in the total

phenols and total carotenoids and a decrease in ascorbic

acid, but at overall the antioxidant/free radical scavenging

activity is increased. Therefore, it can be concluded that the

solar tunnel drying is the least cost effective and safe

method of preserving the quality of fruits.

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