Effect of Two Stage Drying Mode on the Quality Attributes ... · PDF fileEffect of Two Stage Drying Mode on the Quality Attributes of Dried Onion Slices ... Key words- response surface

Effect of Two Stage Drying Mode on the Quality Attributes of Dried Onion Slices

Namita J. Patil Assistant Professor, Department of Food Technology ,College of Technology,

Shivaji University, kolhapur

J.P. Pandey Professor Department of Post Harvest Process & Food Engineering,

College of Technology, G B P U A & T, Pantnagar

Sanjeev Kumar Garg Associate professor Department of Post Harvest Process & Food Engineering,

College of Agricultural Engineering, JNKVV, Jabalpur

Abstract-Effects of processing variables such temperature (during first stage), cut-off time and tempering period on quality attributes such as ascorbic acid, reducing sugar, total sugar, rehydration ratio, dehydration ratio and colour of dried onion slices was carried out to develop dried onion slices so as to reduce spoilage and post harvest losses of onion. Response Surface Methodology (RSM) was employed for the experimental design. Results showed that Ascorbic acid decreases with increase in temperature. There was increase in rehydration ratio by decreasing temperature and cut-off time. The full second order model was found inadequate in describing the reducing sugar, total sugar, dehydration ratio, L*, a* and b* due to lower values of R2 and F.

Key words- response surface methodology, onion , dehydration, ascorbic acid, rehydration ratio

I.INTRODUCTION

Onion (Allium cepa L.) is an important vegetable crop in the world. Onion is being extensively cultivated all over the world, especially in china, India, Netherlands, Pakistan, Bangladesh and Australia. India is the second largest producer of onion with an area of 554.15 (‘ooo ha) and production of 9.5 MT next to China[1]. About 35% to 40% produces lost due to lack of proper post harvest practices and management for onions in India. Thus, there is a need for processing it into stable products in order to minimize the losses during the postharvest handling and storage [5,12]. Onions are used for their flavor, aroma, and taste, being prepared domestically or forming raw materials for a variety of food manufacturing processes (dehydration, freezing, canning, and pickling). Onions were among the earliest vegetables to be produced, canned, dried, and frozen. Dehydration is the most important method for preservation of onions with an ultimate aim of improving storability by reducing its moisture content. Removal of water from onions prevents microbial growth and thus makes storage without refrigeration possible. The dried onion has become a standard ingredient used as flavour additive in a wide variety of processed foods such as ketchup, sauces, soups, salad dressings, sausage and meat products, potato chips, crackers and other snack items. The fundamental objective to create a shelf-stable product, in food drying is to dry a product but without affecting the desired quality attributes. The ascorbic acid, sugars, rehydration ratio and colour of the dried onion are considered the most important quality attributes affecting the degree of acceptability of the product by the consumer. The rehydration characteristics of a dried product are widely used as a quality index. Rehydration is a complex process and indicates the physical and chemical changes caused by drying and treatments preceding dehydration [4,7].Ascorbic acid is probably the most liable of all the vitamins contained in the foods. The loss was occurred because it is water soluble and is rapidly destroyed by heat, light and oxidation. Losses vary from 10 to 50 % during preparation of the food for drying due to washing, leaching and blanching. If vegetables were sulphited before drying, retention is increased [6]. Hence, the

International Journal of Latest Trends in Engineering and Technology (IJLTET)

Vol. 5 Issue 3 May 2015 149 ISSN: 2278-621X

present research work was carried out to investigate the effect of various process conditions such temperature (during first stage), cut-off time and tempering period on nutritional quality of onion slices using two stage drying.

II.MATERIALS AND METHODS

Fresh well-graded, dark pink colored, good quality onions were procured from local market, peeled and cut into slices of thickness 4 mm and pre-treated with 0.25 % KMS for 5 min [9].; 100 g of onion slices were taken as test sample. The Tray dryer (cabinet type) was used for drying studies of onion. Dryer consists of an air delivery system, air heating system, drying chamber with trays, temperature controller etc. The treated samples were spread uniformly in a single layer on the tray of drier. Drying of onion slices during first stage was carried out at 70, 80, 90 0C for 30, 50, 70 min, then these samples were tempered for a period of 0, 20 40 min and dried at 600C in second stage till attainment of final moisture content of 4 to 6 % (db). The dried samples were then packed in polythene bag to avoid moisture migration from atmosphere as these dried slices are hygroscopic in nature.

Experimental design:

Response Surface Methodology (RSM) was employed for the experimental design. The RSM allows design of experiments with minimum number of experiments, without affecting the accuracy of results and determine the interactive effects of the variables on the responses [8]. It provides statistically acceptable results and can be used for optimization of the process [2,3]. Incomplete Composite Block (Box & Behnken) design was used to design the experiments with three variables, each to be examined at three levels. The three independent variables were high temperature during first stage (Td), cut-off time (tc) and tempering period (tp). The levels of temperature were 70,80 and 90oC for first stage, 30,50 and70 min for cut-off time and 0,20 and 40 min for tempering period. The experimental design resulted in 17 combinations on which experiments were performed (Table 1). Quality determination

For estimation of quality attributes such as ascorbic acid, reducing sugar and non reducing sugar of the dried onion slices standard methods were adopted. Ascorbic acid

Ascorbic acid in the sample was estimated by 2, 6- dichlorophenol-indophenol visual titration method [10].

Total Sugar and Reducing Sugar

Total sugar and reducing sugar content in the sample was estimated by Lane and Eynon method [10].

Colour Colour of sample was determined using the digital camera and Adobe Photoshop 7.0 .The sample was kept under the light source such that the light intensity over the food sample should be uniform. Digital camera (Sony -7.2 mega pixels) was used to capture the image. Adobe Photoshop 7.0 was used to obtain color parameter L*, a*, b*, the preferred color model for food research. L* is the luminance or lightness component, which ranges from 0 to 100, and a* (from green to red) and b* (from blue to yellow) are the two chromatic components, which range from -120 to +120. To convert Lightness, a and b values obtained from the Histogram window to L*, a*, b*, following formulas were used. . [13].

L*= (Lightness/250) ×100 ……….. (1)

a*= (240a/255) – 120 ……….. (2)

b*= (240b/255) – 120 ……….. (3)

Rehydration Ratio

For the rehydration ratio test, dehydrated samples (2 g each) were dipped in boiling water for 25 minutes and contents were then filtered through Wattman No.4 filter paper. The rehydrated onion sample was then weighed and the weight recorded as WR. The rehydration ratio (RR) was computed using the following equation. [10].



(RR) WD WR … (4)

Where, WR is weight of rehydrated onions, g, WD is weight of dehydrated onions, g.

Dehydration Ratio:

Dehydration ratio was calculated by taking the weights of sample before drying and the weight of sample after drying [9,11].

Dehydration ratio WDWB

= ... (5)

Where, WB is weight of onion sample before drying, g, WD is weight of onion sample after drying,g. Development of Second Order Models

A complete second order model (Eq. 6) was fitted to the data and adequacy of the model was tested considering R2 (the coefficient of multiple determination) and fisher’s F-test. The models were then used to interpret the effect of various parameters on the response. A second order response function for three independent variables has the following general form:

… (6)

Where,

0, ii, ij are constants Xi, Xj are variables (coded) The regression coefficients of complete second order model and their significance are reported in Table 3. The program provided the values of coefficients of model and related statistics in terms of lack of fit and p-value. The value of p represented the probability of significance. A high p-value indicated that the model had a significant lack of fit and therefore inadequate. The lower the values of p better the model. The models having p-value lower than 0.1 (indicating the lack of fit is insignificant at 90% confidence level) were accepted. The sign and magnitude of the coefficient explain the nature of the effect. Negative sign at linear level means decrease in response when the level of the predictor is increased while positive sign indicates increase in the response. Significant negative interaction suggests that the level of one of the predictors can be increased while that of other decreased for constant value of the response. Positive interaction means the response is minimum at center point and it increases with increase or decrease of both the variables from center point. Positive coefficient of a quadratic term indicated the minimum response at center value of the parameter and it increases with increase or decrease in parameter level. Negative coefficient of the quadratic term shows the maximum response at the centre value and it decreases with increase/decrease in parameter level.

III.RESULTS and DISCUSSION

The measured quality parameters of dehydrated onion at each experimental run are reported in Table 2. Full second order model was fitted into ascorbic acid, reducing sugar, total sugar, rehydration ratio, dehydration ratio and colour and experimental conditions using multiple regression analysis and the results obtained are given in Table 3. Effect of processing parameters on Ascorbic acid

The ascorbic acid content in the dried onion ranged from 5.1 to 9.3 (mg/100 gm). The maximum ascorbic acid content was observed at 700C temperature, 50 min cut-off time and 40 min tempering period. Ascorbic Acid =8.48-1.537Td-0.3tc+0.162tp-0.475Tdtc-0.05Tdtp+0.075tctp-0.915Td2-0.09tc2-0.315tp2 ……….(6) The coefficient of determination (R2) for the regression model for ascorbic acid was 92.46%, which implies that the model account for 92.46% variability in data. Model was highly significant (p<0.05) with F as 9.53. Lack of fit was insignificant; therefore second order model was adequate in describing ascorbic acid content. Ascorbic acid was significantly affected by temperature (p< 0.01).With increase in the levels of temperature, the ascorbic acid

3

1i

2iii

3

1ijjiij

3

1i

2

1iii0 X XX X Y



decreases. No effect of cut-off time and tempering period on ascorbic acid was observed. Anova for total effect of individual parameters on ascorbic acid is given in Table 4.

Effect of processing parameters on Total Sugar and Reducing Sugar

The total sugar in the dried onion varied from 33.60 to 44.97%. The maximum total sugar was observed at 700C temperature, 50 min cut-off time and 40 min tempering period. The model was considered inadequate for describing the total sugar due to lower value of R2 and F (Table 3). The reducing sugar in the dried onion ranged from 24.51 to 12.20 %. The model is not adequate because the calculated F value (0.485) is lower than tabulated F value (6.71 at 1% and 3.68 at 5%) (Table 3). Effect of processing parameters on dehydration ratio

The dehydration ratio is one of the important parameter showing the bulk reduction in the weight of the onion. More the dehydration ratio betters the process of drying. It varied from 6.76 to 9.36. The maximum dehydration ratio was observed at 800C temperature, 70 min cut-off time and 0 min tempering period. The model was considered inadequate for describing the dehydration ratio due to lower value of R2 and F (Table 3). Effect of processing parameters on rehydration ratio

The rehydration ratio (RR) is quality index and higher the rehydration ratio betters the quality of the product. It varied from 4.35 to 5.71. The maximum rehydration ratio was observed at 700C temperature, 50 min cut-off time and 40 min tempering period. RR=5.354-0.313Td-0.087 tc +0.0462tp-0.17 Tdtc-0.062Tdtp-0.005 tctp-0.183 Td

2-0.220 tc2+0.051tp

2 ….(7)

The coefficient of determination (R2) for the regression model for rehydration ratio was 95.76%. Model was highly significant (p<0.05) with F as 17.57. Lack of fit was insignificant; therefore second order model was adequate in describing rehydration ratio. Rehydration ratio was significantly affected by temperature and cut-off time (p< 0.01). Therefore with increase in the levels of these, the rehydration ratio decreases. Effect of temperature was found highest as compared to that of cut-off time; however no effect of tempering period on rehydration ratio was observed. Anova for total effect of individual parameters on rehydration ratio is given Table 4. Effect of processing parameters on Colour

The colours of onion slices were measured in terms of L-value (brightness/darkness), a-value (redness/greenness), and b-value (yellowness/blueness). The L*, a*, and b* values of onion slices were range between 21.33 to 49.80, 4.75 to 14.91 and 1.27 to 7.66 respectively. Lack of fit is insignificant but model is considered inadequate for describing the L*, b*and a* due to lower value of R2 and F (Table 3).

IV.CONCLUSION

The effect of various process conditions such temperature (during first stage), cut-off time and tempering period on nutritional quality of onion slices using two stage drying was studied. Ascorbic acid content of onion decreased with increase in drying temperature. However Cut-off time and tempering period did not affect ascorbic acid significantly. There was increase in rehydration ratio by decreasing temperature and cut-off time. The effect of tempering period on rehydration ratio was not significant. The full second order model was found inadequate in describing the reducing sugar, total sugar, dehydration ratio, L*, a* and b* due to lower values of R2 and F.

REFERENCES [1] Anonymous 2010.India set for record onion produce http://beta.the hinhu.com/business/economy/article 437982.ece. [2] Box G E P, Hunter WG, Hunter J S 1978.Statistics for experiments. John Wiley and sons. Newyork . [3] Cochran W G, Cox G M1957..Experimental designs. John Wiley and sons.Newyork [4] Feng H, Tang J 1998. Microwave finish drying of diced apples in a spouted bed. J.Food Sci., 63: 679-683. [5] Gowda S J , Gupta C P ,Ojha T P 1986. Studies on dehydration of onion. Mysore J.Agric.Sci., 20: 186-194. [6] Harris R S ,Loesecke V 1960. Nutritional evaluation of food processing. John Wiley and Sons Pub., New York. [7] Lewicki P P (1998). Some remarks on rehydration of dried foods. J. Food Engg., 36: 81-87. [8] Myers R H 1971. Response surface methodology, Allyn and Bacon, Bosten. [9] Pawar,V.N., Singh,N.I., Dev,D.K., Kulkarni,D.N. and Ingale, U.M.(1988). Solar drying of white onion flakes. Indian Food Packer, Jan.-

Feb.:15-28.



[10] Ranganna S 1986. Hand book of analysis and quality control for fruit and vegetable products. 2nd edn. Tata McGraw hill publication Co. Ltd., New Delhi. p 112

[11] Sagar V R 2001. Preparation of onion powder by means of osmotic dehydration and its packaging and storage. J.Food Sci. and Tech., 38 (5):525-528.

[12] Sarsavadia P N, Sawhney R L, Pangavhane D R, Singh S P 1999. Drying behaviour of brined onion slices. J. Food Eng. 40(3): 219-226. [13] Spyridon E, Papadakis, Malek A, Kamdem R E,Yam K L 2000. A versatile and inexpensive technique for measuring color of foods. J. Food

Tech. 54(12): 48-51.

Table 1 Experimental design for experiments

Exp.

No.

Coded levels Real values

Td tc tp Td tc tp

1 -1 -1 0 70 30 202 1 -1 0 90 30 203 -1 1 0 70 70 204 1 1 0 90 70 205 -1 0 -1 70 50 06 1 0 -1 90 50 07 -1 0 1 70 50 408 1 0 1 90 50 409 0 -1 -1 80 30 010 0 1 -1 80 70 011 0 -1 1 80 30 4012 0 1 1 80 70 4013 0 0 0 80 50 2014 0 0 0 80 50 2015 0 0 0 80 50 2016 0 0 0 80 50 2017 0 0 0 80 50 20

Td=Temperature (OC) ,tc=Cut-off time (min) ,tp=Tempering period (min)



Table 2 Quality parameters of dehydrated onion slices

Exp

No.

Ascorbic

acid

(mg/100)

RS

(%)

TS

(%)RR DR

Colour

L* a* b*

1 8.9 18.12 33.89 5.21 7.27 49.5 8.00 4.41

2 6.7 18.66 41.19 4.92 7.01 21.33* 6.75 3.41

3 9.2 12.38 33.60* 5.32 7.60 49.8** 4.75* 3.33

4 5.1* 14.79 41.69 4.35* 6.76* 29.08 11.91 6.08

5 8.2 23.15 34.61 5.36 8.73 36.00 11.33 7.66**

6 5.3 16.34 42.48 4.86 8.82 43.41 12.66 5.83

7 9.3** 19.69 44.97** 5.71** 8.77 35.91 12.33 7.08

8 6.2 14.29 37.25 4.96 7.81 39.33 7.83 2.08

9 8.6 16.89 39.78 5.26 7.77 43.18 2.81 1.27*

10 7.9 23.58 36.11 5.15 9.36** 41.83 12.08 6.75

11 8.1 24.27 41.47 5.23 7.59 39.75 11.91 6.50

12 7.7 22.73 37.67 5.10 7.49 33.08 10.66 3.25

13 8.9 12.20* 40.19 5.25 7.00 22.75 7.50 2.16

14 7.6 24.51** 41.48 5.33 9.05 44.75 9.75 4.91

15 8.4 20.00 37.54 5.43 7.81 35.83 9.91 6.16

16 8.8 17.12 35.78 5.40 8.44 24.16 12.25 2.75

17 8.7 13.81 37.80 5.36 7.22 26.25 14.91** 3.66

** Maximum Value & * Minimum Value,

RS-Reducing sugar, TS- Total sugar, RR- Rehydration ratio, DR- Dehydration ratio



Tabl

e 3

Res

ults

of r

egre

ssio

n an

alys

is fo

r qua

lity

para

met

ers

A

scor

bic

Aci

d

Red

ucin

g

suga

r

Tot

al

suga

r

Reh

ydra

tion

ratio

Deh

ydra

tion

ratio

Col

our

L*

b*

a*

C

oeff

.P (%

)C

oeff

.P (%

)C

oeff

.P (%

)C

oeff

P (%

) C

oeff

P

(%)

Coe

ff

P (%)

Coe

ffP (%

)C

oeff

P (%)

Con

s8.

48

0.35

17

.528

84

.56

38.5

5827

.9

5.35

4 0.

05

7.90

4 26

.62

460.

815

88.1

93.

928

40.6

896

.646

41.9

7

Td

-1.5

37

0.0*

**

-1.1

56

52.9

71.

942

9.62

* -0

.313

0.0*

**

-0.2

47

34.2

118

1.07

025

.79

-0.6

3536

.79

0.93

875

.67

t c-0

.3

15.9

6 -0

.556

75

.95

-0.9

0639

.98

-0.0

873.

24**

0.

195

44.7

41.

1E-0

499

.93

0.47

849

.27

12.3

2628

.12

t p0.

162

42.2

2 0.

125

94.4

81.

048

33.4

5 0.

0462

20.2

2 -0

.377

16

.38

33.4

15

61.3

1-0

.325

63.7

41.

853

66.4

5

Tdt

c-0

.475

12

.15

0.46

8 85

.50.

196

89.4

3 -0

.17

0.81

***

-0.1

45

68.4

113

.876

74

.32

0.93

834

.85

17.6

8220

.47

Tdt

p-0

.05

85.8

1 0.

352

89.0

8-3

.897

2.96

**-0

.062

22.0

7 -0

.261

47

.14

3.98

0 86

.03

-0.7

9342

.38

8.49

736

.46

t ctp

0.07

5 78

.89

-2.0

59

43.2

6-0

.029

98.3

9 -0

.005

91.7

4 -0

.423

25

.62

7.07

6 81

.46

-2.1

835.

19*

27.6

6812

.37

Td2

-0.9

15

1.02

**

-2.5

23

33.0

10.

052

97.1

-0

.183

0.49

***

-0.1

32

70.3

836

.419

59

.79

0.80

040

.83

1.88

766

.16

t c2-0

.09

74.2

0.

980

69.6

3-1

.018

48.8

8 -0

.220

0.18

***

-0.6

12

10.9

658

.848

50

.53

-0.4

2065

.823

.095

15.4

t p2

-0.3

15

26.9

7 3.

360

20.6

11.

216

41.1

8 0.

051

29.0

9 0.

7616

5.

67*

104.

150

38.1

40.

935

33.8

22.

992

58.3

1

R2

(%)

92.4

6 38

.42

67.0

5 95

.76

67.6

9 35

.54

61.0

1 66

.42

F 9.

53

0.48

5 1.

58

17.5

7 1.

63

0.43

1.

22

1.19

LO

F N

s ns

ns

N

s ns

ns

ns

N

s

*

** ,

** ,

* Si

gnifi

cant

at 1

, 5 a

nd 1

0 %

leve

l of s

igni

fican

ce re

spec

tivel

y

ns=

Non

sign

ifica

nt,

s =si

gnifi

cant

, co

ns =

con

stan

t (m

in)

X1

=Tem

pera

ture

(0 C),

X2

= C

ut-o

ff ti

me

(min

) , X

3 =

Tem

perin

g pe

riod



TAB

LE 4

Ana

lysi

s of v

aria

nce

(AN

OV

A) f

or t

otal

eff

ect o

f ind

ivid

ual p

aram

eter

SOU

RC

E

A

scor

bic

Aci

dR

ehyd

ratio

nR

atio

DF

SS

MS

F-V

alue

D

FSS

M

S F-

Val

ue

Mod

el

9

24.9

66

2.77

49.

54**

9

1.36

6 0.

152

17.5

6***

Tem

pera

ture

(Td)

4 23

.349

5.

837

20.0

7***

4 1.

060

0.26

530

.66*

**

cut-o

ff ti

me(

t c)

4

1.67

9 0.

420

1.44

4

0.38

2 0.

096

11.0

5***

Tem

perin

g pe

riod

( t p)

4

0.66

2 0.

165

0.57

4

0.04

4 0.

011

1.27

Erro

r

7 2.

036

0.29

1

7 0.

060

0.00

9

Tot

al

16

16

***,

**

Sign

ifica

nt a

t 1, 5

% le

vel o

f sig

nific

ance

resp

ectiv

ely

F tab

= (

Mod

el –

6.71

(1%

) an

d 3.

68(5

%))

, Fta

b =

(leve

l-4.1

2 (5

%) a

nd 7

.85

(1%

)



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Effect of Two Stage Drying Mode on the Quality Attributes ... · PDF fileEffect of Two Stage Drying Mode on the Quality Attributes of Dried Onion Slices ... Key words- response surface