CARPATHIAN JOURNAL OF FOOD SCIENCE AND TECHNOLOGY

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35

THE EFFECT OF DIFFERENT FRYING CONDITIONS ON THE COLOR

PARAMETERS OF PURPLE SWEET POTATO (Ipomoea batatas Poiret)

SLICES

Rahmat Fadhil1*, Diswandi Nurba2, Kiki Ikhwanto2

1 Department of Agricultural Engineering, Syiah Kuala University, Jalan Teungku Hasan Krueng Kalee

No.3 Darussalam 23111, Banda Aceh, Indonesia

2 Laboratory of Postharvest Technology, Syiah Kuala University, Darussalam 23111, Banda Aceh, Indonesia

* rahmat.fadhil@unsyiah.ac.id

Article history:

Received :

26 April 2016

Accepted :

6 June 2017

ABSTRACT

The aim of the research was to analyze of the surface color measurement to

the pre-frying and post-frying purple sweet potato (Ipomea batatas Poiret)

slices by using a combining device i.e. the digital camera and the graphic

software. It is believe that such analysis method able to observe colors and

an average in a value of L*a*b* units of food ingredient surfaces. The

digital images of purple sweet potato slices could be displayed on the

computer screen or printed on a certain piece of paper their colors and

structures can be analyzed. To do so, the method of digital image

application is used, namely a digital camera Canon Ixus 145 without using

the camera light and with the distance focus of 10 cm from the object.

Following that, the resulted images, were plotted against colors on the

Adobe Photoshop CS5. The results show that the use of the Adobe

Photoshop CS5 software is extremely helpful in measuring colors of purple

sweet potato chips due to the fact that it could bring a consistency when

defining colors of pre-frying and post-frying slices with the system model

of L*a*b* units. Overall, this study found that there is no difference in

colors between pre-frying purple sweet potatoes and the post-frying ones in

various treatments by the variance analysis and continued to the Duncan

Multiple Range Test (DMRT) at a confidence level of 95 percent (p<0.05),

except those in a fractional number of treatments.

Keywords:

Color;

Purple sweet potato;

L*a*b* model;

Frying;

Adobe Photoshop CS5.

1. Introduction A food visual appearance is still a primary

consideration for consumers to assess and

decide to buy a food product. The food color is

relatively one important parameter for

consumers to select foods that would be

consumed. This, at once, becomes a decision in

accepting those food ingredients, whether it is

proper to be accepted by consumers. The visual

on colors sometimes is more preferred by

consumers rather than observation on other

quality parameters and it provides a clue

regarding chemical changes in food ingredients

(Winarno, 2002). The digital image is a

process aiming to manipulate and analyze color

images in which involves many visual

perceptions and supported by a computer. The

image processing aims to see the detail of image

qualities in order to be interpreted easily by

humans or machines (Wijaya et al., 2007).

Overall, there are three measurement

models of a color space, those are the RGB

(red, green, blue) model (for televisions,

computer screens, scanners, and digital

cameras), the CYMK (cyan, magenta, yellow,

black) model (for printing industries) and the

CIE Lab model or also called as the L*a*b*

color m o d e l (used in laboratories of

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

36

color

measurement) (Fernandez et al., 2005). The

color model most commonly used is the L*a*b*

color model since it has a homogenous color

distribution (Leon et al., 2005, Zhang et al.,

2010). The homogeneity of color perceptions

carries an appropriate guarantee of color

differences and is essential for the process of

segmentation (Dong & Xie, 2005). This color

space is able to depict all colors that could be

seen by human eyes and is often used as a

reference of color spaces (Yam & Papadakis,

2004).

The color measurement of food ingredients

in L*a*b units is an international standard of a

color measurement developed by the

Commission Internationale d’Eclairage (CIE)

in 1976. The L*a*b color model comprises 3

components, those are the L* dimension as

luminance (color brightness) whose the value

ranges from 0 to 100, in which 0 is for black

and 100 is for white; the a* dimension

describing the color types of green-red, in

which a negative indicates a green color and

the reverse indicates a red color; and the b*

dimension for the color types of blue-yellow, in

which a negative indicates a green color and

the reverse indicates a yellow color. The a* and

b* dimensions are color dimensions opposite to

each other ranging from -120 to +120. The

L*a*b is an independent device that provides

consistent colors regardless of the inputs or

outputs. It is specifically devices of digital

cameras, scanners, monitors, and printers

(Widiasri, 2013; Lukinac et al., 2009; Yam and

Papadakis, 2004).

Soaking in the sodium bicarbonate

(NaHCO3) solution aims for crisping and would

produce the CO2 gas. As the concentration of

NaHCO3 improves, more gas will be generated

in food ingredients when the frying process is conducted. This gas builds some pores in the food ingredients. Due to a large number of pores in the ingredients, their mass becomes lower and will be friable to loads or outer forces exposed to them. As more pores are

built, the texture of chips produced will be much crispier (Shinta et al., 1995; Putranto et

al., 2013). The NaHCO3 is one of cake

improvers and a firming agent of fried foods in the form of white powder. As the concentration of NaHCO3 and the frying

temperature increase, the hardness value of chips will decline (Winarno, 2002).

2.Materials and methods

2.1. Tools and material

The tools used in this study were knifes,

peel removers, stoves, pans, plastic washbasins,

food jars, plastic bags, manual chip slicers,

digital scales, thermometers, a digital camera

Canon Ixus 145 (DIGIC 4, 16.0 MP, 28-224

mm, 8x optical, 16x zoom plus, 1600 max. ISO

value, ½.3 type CCD, 2.7- i nch LCD), and the

Adobe Photoshop CS5 program (Adobe System,

2010).

The main material used in this research was

the purple sweet potato obtained from famers in

the Sare area, Aceh Besar Regency, Aceh

Province, Indonesia. Purple sweet potatoes used

in this study were cropped in approximately 4-5

months of age after planting. In addition,

supporting materials included in this research

were sodium bicarbonate (NaHCO3), salt

(NaCl), water, and Bimoli brand cooking oil

produced by PT. Salim Ivomas Pratama Tbk.

2.2. Research procedures

The fresh purple sweet potatoes were washed

to get rid of any dirt, then they were weighed

in 500 grams and sliced in various thicknesses of

1 mm, 2 mm, and 3 mm. After slicing, each of

them were weighed before soaking in a

solution of 2% salt and 1 L of water within

10 minutes. Following that, the next soaking

used a solution of NaHCO3 at concentrations of 1

gram/liter water, 3 grams/liter water, and 5

grams/liter water within 30 minutes respectively

in order to enable chips to be crispy. Then, the

analysis of pre-frying purple sweet potatoes was

conducted.

The purple sweet potato slices were fried

on the stove at the temperatures ranging from

145oC to 150

oC for 2-3 minutes. The volume of

cooking oil was 2 L for 500 grams of sweet

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

37

potato s l i c e s from various thicknesses and

NaHCO3 concentrations. The cooking oil

was replaced in each completed frying so as

each treatment was conducted with the new

cooking oil. A thermometer was inserted

directly into the oil in order to keep the

temperature range desired. Since the

temperature stability of frying purple sweet

potato chips would determine colors and

crispness of chips produced, the chips from

each treatment, after frying, were weighed

and putted into jars. Finally, the color

measurement of post-frying sweet potato

slices was carried out.

2.3. The color measurement

The method of digital image taking was

conducted with a Canon Ixus 145 digital

camera having a resolution of 16 megapixels

without the camera light and with the focus

distance of 10 cm from objects in light rooms.

The digital image taking was performed in two

times of repetitions in each treatment of

ingredients. The digital images obtained were

saved in the SanDisk Ultra 30 MB/s memory

card at a capacity of 8 GB in the PNG (Portable

Network Graphics) format. Those images, then,

were transferred to a PC to be plotted against

colors on Adobe Photoshop CS5, thereby

obtaining the RGB (Red, Green, Blue) values at

a color intensity ranging from 0 to 225 (Magdić

and Dobričević, 2007; Lukinac et al., 2009).

Hue angles were obtained using the method

described by Precil (1953), that is:

Where R0, G0 and B0 indicate the color

parameters of sweet potato slices. The

calculation of R, G, and B values were shown

by the 0o

(red), 60o

(yellow), 120o

(green), 180o

(cyan), 240o

(blue), 300o

(magenta) degrees.

The average values of each color of purple

sweet potato slices were presented as the final

result of the color determination plotted along

R, G, B axises (Figure 1).

Figure 1. The graphic representation of color spaces along R, G and B axis (White, 2003).

Accordingly, the values of X, Y, Z could

be calculated using an

equation from the Commission on Illumination

(CIE) (White, 2003) as follows:

X = 0,607R+0,174G+0,201B

Y = 0,299R+0,587G+0,114B

Z = 0.066G+1.117B

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

38

Subsequently, by using the system of

Hunter-Lab, the values of a* and b* that would

be plotted into the L*a*b* (Hunter-Lab, 2008)

units were gained; therefore digital images of

purple sweet potato chips were obtained.

L* = 25(100Y/100)1/3-16

a* = 500[(X/98.071)1/3-(Y/100)]1/3

b* = 200[(Y/100)1/3-

(Z/118.225)]1/3

2.4. The experiment design

This research used the Randomized

Completely Design with 3 treatments and 2

repetitions. Factors that were tested included

the purple sweet potato thicknesses of 1 mm, 2

mm, and 3 mm as well as the sodium

bicarbonate (NaHCO3) concentrations of 1

gram/liter, 3 grams/liter and 5 grams/liter.

Hence, there were 9 combinations of the

treatment and 2 repetitions so as the total was

18 experimental units. Data obtained, then, was

subjected to Analysis of Variance (ANOVA)

using a SAS software, version 9.1.3 (SAS

Institute Inc., 2006) and was tested further by

the Duncan Multiple Range Test (DMRT) at

the uncertainty of 5% (Gomez and Gomez,

1984; Sastrosupadi, 2000; Steel and Torie,

1980).

3.Results and discussions

There are several reasons to select the

Adobe Photoshop as a color measurement

method. Firstly, this software has numerous

features of picture editing and an analysis

capability comparable to other more expensive

softwares. Secondly, this software also

provides a more advance capability to manage

colors and create consistent colors rather than

other graphic softwares. Furthermore, it is

available in many computer laboratories and

also supported by the manufacturer and users

(Yam et al., 2004).

The average values of pre-frying and post-

frying color measurements from various

treatments and thicknesses of purples sweet

potato slices were obtained using the Adobe

Photoshop CS5. The L*, a*, and b* values

from purple sweet potato slices could be seen

in Table 1. The L* average values of purple

sweet potato slices gained range from 48.01

(the lowest) to 74.10 (the highest). The former

was obtained from a treatment of 3 grams/1 L

water NaHCO3 concentration and a slice

thickness of 2 mm (K2S2) and the latter was

obtained from a treatment of 5 grams/1 L water

NaHCO3 concentration and a slice thickness of

3 mm (K3S3). Whereas, the a* average values

of purple sweet potato slices gained range from

-8.28 (the lowest) to 27.04 (the highest). The

former was obtained from a treatment of 3

grams/1 L water NaHCO3 concentration and a

slice thickness of 3 mm (K2S3) and the latter

was obtained from a treatment of 1 gram/1 L

water NaHCO3 concentration (K1S1) and a

slice thickness of 1 mm (K1S1). Whilst, the b*

average values of purple sweet potato slices

gained range from 3.59 (the lowest) to 64.49

(the highest). The former was obtained from a

treatment of 3 gram/1 L water NaHCO3

concentration and a slice thickness of 1 mm

(K2S1) and the latter was obtained from a

treatment of 5 grams/1 L water NaHCO3

concentration and a slice thickness of 1 mm

(K3S1).

This color measurement is extremely

important in food industries since a large

amount of information, nowadays, could be

received from measurements at the level of

pixels that would enable better

characterizations of food color images. The

measurement in identifying food colors

commonly used is the one with the model of

L*a*b* units, due to the homogenous

distributions so as the results resemble colors

perceived by humans (Leon et al., 2006;

Papadakis et al., 2000; Segnini et al., 1999).

In brief, the results show that there is no

significant difference among colors created

from the treatment of various NaHCO3

concentrations and the different thicknesses of

purple sweet potato slices (L*: K1S1, K2S1,

K3S1; a*: K1S1, K2S1, K1S2, K2S2, K3S2,

K1S3, K2S3, K3S3; b*: K1S1, K2S1, K2S2,

K3S2, K1S3, K2S3, K3S3).

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

39

Table 1. The L*a*b* unit values of pre-frying and post-frying purple sweet potato slices

3S3

The notification of same words in each column shows that there is no statistically significant difference (P>0.05)

Descriptions:

K1S1 = the NaHCO3 concentration of 1 gram and the thickness of 1 mm K2S1 = the NaHCO3 concentration of 3 grams and the thickness of 1 mm K3S1 = the NaHCO3 concentration of 5 grams and the thickness of 1 mm K1S2 = the NaHCO3 concentration of 1 gram and the thickness of 2 mm K2S2 = the NaHCO3 concentration of 3 grams and the thickness of 2 mm K3S2 = the NaHCO3 concentration of 5 grams and the thickness of 2 mm K1S3 = the NaHCO3 concentration of 1 gram and the thickness of 3 mm K2S3 = the NaHCO3 concentration of 3 grams and the thickness of 3 mm K3S3 = the NaHCO3 concentration of 5 grams and the thickness of 3 mm

Initial K1S1 K2S1 K3S1 K1S2 K2S2 K3S2 K1S3 K2S3

K

L* Pre 62.73 + 3.48 a 66.66 + 5.15 a 63,39 + 2.48 a 65,5 0 + 7.19 a 67,8 7 + 2.50 a 70,5 4 + 1.30 a 70,33 + 11.73 a 68,69 + 7.39 74,1 0 + 3.59 a

Post 62,43 + 5.03 a 57.25 + 14.08 a 55,27 + 1.81 a 51,4 3 + 0.00 b 48,0 1 + 0.00 b 57,0 8 + 8.02 b 60,25 + 0.79 a 65,55 + 4.99 60,4 7 + 9.72 a

a* Pre 27,04 + 16.14 a 10,59 + 13.37 a 13,45 + 1.97 a 8,7 3 + 6.18 a 3,0 0 + 4.16 a 6,76 + 12.77 a 3,51 + 6.21 a 4,04 + 14.58 a -2,4 2 + 0.13 a

Post 7,41 + 4.76 a 6,31 + 10.87 a 6,26 + 1.44 b 2,84 + 11.15 a 6,2 5 + 2.25 a 3,0 9 + 2.97 a 5,97 + 4.37 a -8,28 + 8.45 a -3,5 4 + 7.96 a

b* Pre 12,44 + 1.86 a 3,59 + 1.05 a 8,56 + 5.55 a 11,6 4 + 0.13 a 5,8 4 + 8.46 a 13,1 6 + 4.68 a 12,50 + 4.37 a 11,22 + 1.35 a 10,8 7 + 1.08 a

Post 6,55 + 1.35 a 6,85 + 4.51 a 64,49 + 17.90 b 4,8 2 + 0.91 b 14,2 2 + 9.59 a 11,4 5 + 6.48 a 4,07 + 9.48 a 12,94 + 12.55 a 13,4 1 + 1.89 a

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

40

Figure 2. The graph of Pre-frying L*a*b values (Adopted from Konicaminolta, 2003)

Figure 3. The graph of Post-frying L*a*b values (Adopted from Konicaminolta, 2003)

Fadhil et al. Carpathian Journal of Food Science and Technology 2017, 9(2), 35-42

41

Hoever, several other treatments show a

significant difference between those of pre-

frying and post-frying (L*: K1S2, K2S2,

K3S2; a*: K3S1; b*: K3S1,

K1S2) (Table 1). Figure 2 and Figure 3

also show the different L*a*b* values gained.

Apparently, it is due to the inhomogeneous

color of those purple sweet potato slices

resulting in the different L*a*b* values of each

thickness and NaHCO3 concentration.

4.Conclusions

The use of the Adobe Photoshop CS5

software is very helpful in analyzing colors of

purple sweet potatoes as it could provide a

consistency in defining colors of pre-frying and

post-frying slices with the system model of

L*a*b* units. Overall, there is no significant

difference among several treatments of pre-

frying and post-frying purple sweet potatoes by

the Duncan Multiple Range Test (DMRT) at

the confidence level of 95 percent (P<0.05),

except in a fractional number of treatments.

Consumer decision on food products,

particularly is based on the visual perception

and this becomes commonly the only one

immediate decision of the food product

acceptance. This coverage eventually suggests

that an analysis model of this system could be

used in analyzing colors of a food product,

particularly in observing the color distribution

of food ingredient surfaces having the average

values within L*a*b* units. Later on, it is

necessary to conduct a further research, in

particular for the application on different food

ingredients and products.

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