259 

 

Journal homepage: www.fia.usv.ro/fiajournal 

Journal of Faculty of Food Engineering,  
Ştefan cel Mare University of Suceava, Romania  

Volume XV, Issue 3- 2016, pag. 259  - 265 

 

 

ANALYSIS OF PHYSICAL PARAMETERS OF NATURAL JUICES 

 

Mihaela JARCĂU1, *Maria POROCH-SERIŢAN1 
1Faculty of Food Engineering, Stefan cel Mare University of Suceava,   

AdressUniversitatii 13, 720229 Suceava, ROMANIA,  mihaela.jarcau @ fia.usv.ro,  mariap@ fia.usv.ro  

*Corresponding author 

Received August 7th 2016, accepted September 27th 2016 

 
Abstract: The purpose of this paper was to investigate the change in density, electrical conductivity, 

pH, refractive index, dry soluble solids, as well as the parameters specific to the color of natural juices 

stored at + 4°C and normal atmospheric pressure in two types of containers. The physical parameters 

were determined immediately after the obtaining of juice, at 2 days and 5 days of storage respectively. 

From the analysis of experimental results, there is an increase in density, in all samples, while the pH 

changes only slightly for the orange juice. Storage at temperatures of + 4°C reduces the risk of 

contamination and decreases speed of biochemical changes, but it is not sufficient to guarantee the 

nutritive and organoleptic qualities of the juice and its acceptability by the consumer. 

 

Keywords: electrical conductivity, pH, refractive index, color, juice. 
 

 

1. Introduction 
 

Physical and chemical analyzes of 

fruit and vegetables juices (density, 

electrical conductivity, pH, refractive 

index, dry soluble solids), and the 

parameters specific for the color, represent 

investigating methods of the beverage 

quality examined to storage at the 

temperature of 0 - +4°C and normal 

atmospheric pressure in various kinds of 

container on a period of up to five days. 

Knowing the physical parameters is very 

important in determining the optimum 

storage conditions of fruit and vegetables 

juices, the sizing of storage and the 

conditioning installations. Specific 

parameter values of fruit and vegetables 

juices and concentrates are useful in 

preparing thermal balance. 

Current requirements of consumers 

are turning to juices of superior quality that 

are cheap, with nutritional value, flavor, 

texture and a color corresponding to fresh 

fruits without chemical preservatives and 

yet wholesome and safe. 

Keeping juices at low temperatures 

is carried out in order to preserve them 

(prevents fermentations). Refrigeration is 

used to temperatures between -5ºC and 

+5ºC without changing the state of 

aggregation and the freezing temperatures 

are used between -10ºC and -30ºC [1-2]. 

Using artificial cold for the processing, 

storage and marketing of perishable foods is 

a method widely used in almost all branches 

of food industry. Due to its preservative and 

inhibitory action on agents that cause 

degradation, cold artificial processes used 

in refrigeration, freezing or freeze-drying 

[1]. Refrigeration operation comprises two 

phases, the actual refrigeration (cooling 

from the initial temperature to the storage 

temperature) and keeping the refrigeration. 

It has been found that by lowering the 

temperature of juice from 25 - 30ºC to 0ºC, 

the preservation period is increased to 

approximately 15 times [2]. 

http://www.fia.usv.ro/fiajournal
mailto:mariap@fia.usv.ro
mailto:mariap@fia.usv.ro


Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
260 

Fruits are particularly valuable for 

the content of carbohydrates, vitamins, 

minerals, pigments and other biologically 

active substances. Fruits have an alkalizing 

effect in the body (like vegetables) and they 

represent the food that influence the health 

of the organism and reduce the risk of 

chronic diseases. Fruits rich in 

carbohydrates are contraindicated for 

diabetics and overweight people, but also 

healthy people with normal weight should 

not consume excess. They are suitable for 

children and athletes who require 

immediate energy. Vegetables are an 

important source of vitamins, minerals, 

carbohydrates (~ 5% for leafy vegetables 

and 10 - 12% for root vegetables, melons, 

Solano fruiting), fiber (1 - 2%), and other 

biologically active substances [3]. 

Vegetable juices with pulp can be used to 

feed infants from the age of 4 months as 

excellent sources of minerals and vitamins. 

The most commonly used juices are: 

carrots, tomatoes and beetroot, alone or in 

combination with each other and with other 

vegetable juices: parsley, spinach, celery 

[4]. 

The researches presented in this 

paper followed the variation of density, 

electrical conductivity, pH, refractive 

index, and the parameters specific for the 

color of orange (Citrus sinensis), lemon 

(Citrus limon), kiwi (Actinidia chinensis), 

carrot (Daucus carota) and beet (Beta 

vulgaris) juices stored at +4ºC and normal 

atmospheric pressure in two types of 

container (a brown bottle and polyethylene 

terephthalate, respectively) at 2 days and 5 

days of storage respectively. 

The main objective of this survey is 

to investigate the change in density, 

electrical conductivity, pH, refractive 

index, dry soluble solids, as well as the 

parameters specific for the color of natural 

juices stored at +4°C and normal 

atmospheric pressure in two types of 

container. 

 

2. Matherials and methods 

 

2.1. Samples and equipment 

 

Juices were prepared from fruits and 

vegetables purchased from the local market 

in Suceava, Romania, using a Vital juicer 

and they were divided into 25 samples, from 

which 5 were analyzed immediately and the 

remaining 20 samples were stored 

individual in brown glass containers 

respectively polyethylene terephthalate 

(PET) opaque in the cooler at +4ºC and 

normal atmospheric pressure. Samples of 

fruit and vegetables are coded according to 

Table 1.  

Equipment used was from the Food 

Safety Research Center of the Faculty of 

Food Engineering, Stefan cel Mare 

University of Suceava, Romania. 

 

Table 1.  

Coding the juice samples studied 

Type of juice 

Coding 

Fresh 

juice 

Juice stored 2 days Juice stored 5 days 

Brown glass bottle PET container Brown glass bottle PET container 

Orange 

(Citrus sinensis) 
1 2 3 4 5 

Lemon 

(Citrus limon) 
1 2 3 4 5 

Kiwi 

(Actinidia chinensis) 
1 2 3 4 5 

Carrot 

(Daucus carota) 
1 2 3 4 5 

Beet 

(Beta vulgaris) 
1 2 3 4 5 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
261 

2.2. Determination of density 

 

Density of juices was calculated by 

using density determination kit (XA, 

RADWAG) of analytical balance (Partner 

XA 160).  

 

2.3. Determination of conductivity and pH 

Conductivity of juices were 

determined by using a conductivity meter 

(Accumet XL30, Fisher Scientific) and the 

pH of samples was measured with a 

calibrated digital pH meter (HQ11d pH by 

HACH), by the glass electrode being 

immersed in samples. 

 

2.4. Refractive index and % solids 

measurement  

Refractive index (nD) and % solids 

in juices were measurement by using Abbe 

Refractometer (Leica MARK II PLUS). 

The dry soluble solids content (% solids) of 

a sample is estimated from its refractive 

index, with reference to the refractive index 

of a pure sugar solution. The refractive 

index is proportional to the solution 

concentration (following the theory of 

Lorentz and Lorenz). In fruit juices the 

refractive index is therefore dependent upon 

sugar concentration and also upon the 

concentration of other soluble materials 

(organic acids, minerals, amino acids etc.).  

 

2.5. Color measurement 

The color measurement involves the 

determining of the reflection spectrum of a 

sample and applying it to a standard 

illuminant. The amount of light energy the 

sample reflects is manipulated and reduced 

to tristimulus values X, Y and Z. These 

values correspond to the physiological 

response of the three types of color 

receptors in the human eye. X, Y and Z 

values are combined into the uniform color 

space values such as L*, a* and b* [5-6]. The 

Chroma, considered a quantitative attribute 

of coloring, is used to determine the 

difference degree of a hue in comparison 

with a grey color of the same luminosity. 

The description of a color using the hue (h*) 

attribute refers to how humans perceive an 

object’s color - red, orange, green, blue, etc. 

A 0º or 360 º angles represent the red hue, 

while angles of 90º, 180º and 270º represent 

yellow, green and blue hues [7-8]. ΔE* – 

represents the color difference magnitude 

between the value of the initial color and the 

value of the final color and gives the 

distance between the points representing the 

color, being calculated according to the 

equation: 
2*2*2**

LbaE   (1) 

Within the study, the HR 4000 CG-

UV-NIR spectrometer (Ocean Optics Inc., 

Dunedin, FL) which is based on the 

reflection property of samples was used. In 

this respect, a scanning with 0.025nm 

resolution has been carried out for the entire 

wavelength spectrum ranging from 200 up 

to 1100 nm. A tungsten halogen light source 

(UV-VIS-NIR Light Source DH-2000, 

Mikropack) was used in this study. The 

experimental data was displayed and stored 

using the operating software OOI Base32 

including OOIColor from Ocean Optics. 

The light from Light Source DH-2000 was 

focused to the sample through an array of 

optical fibres (QR400-7-UV/BX, Ocean 

Optics Inc., Dunedin, FL). Reflectivity was 

measured as against a reference standard – 

WS- Diffuse Reflectance Standard [5-6]. 

 

2.6. Statistical Analysis 

All the assays were conducted at 

least in duplicate, and the results were 

expressed as the mean ± standard deviation. 

Statistical significance was accepted at p < 

0.05. 

 

3. Results and discussion 

According to Figure 1 a), from the 

analysis of experimental results, there is an 

increase in density over time, for all 

samples. The highest increase was observed 

for beet, while the lowest variation was 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
262 

observed in carrot. Also, analyzing the 

behavior depending upon the nature of juice 

container, it can be seen an increase in 

density for kiwi and lemon juice stored in a 

brown glass bottle compared to the PET 

container. For the beet juice there is a 

greater variation in sample density 

packaged in PET.

 

 
a) b) 

c) d) 

e) 

Figure 1. Variation a) density, b) pH, c) conductivity, d) refractive index, e) dry soluble solids  
for the analyzed juice samples 

 

From the analysis of experimental 

results, according to Figure 1 b), there is an 

increase in pH only for orange juice, while 

neither for the other juices is nor observed 

its variation neither is observed the pH 

dependence upon the nature of the 

container. 

There is a decrease in conductivity 

at the samples analyzed in time, from the 

analysis of experimental results, according 

to Figure 1c). We can observe the biggest 

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5

D
e
n

s
it

y
 [

g
/m

l]

Sample

orange

lemon

kiwi

carrot

beet

0

1

2

3

4

5

6

7

8

1 2 3 4 5

p
H

Sample

orange

lemon

kiwi

carrot

beet

0

2

4

6

8

10

12

14

16

1 2 3 4 5

C
o

n
d

u
c
ti

v
it

y
 [

u
S

/c
m

2
]

Sample

orange

lemon

kiwi

carrot

beet

1.33

1.335

1.34

1.345

1.35

1.355

1.36

1 2 3 4 5

R
e
fr

a
c
ti

v
e
 i

n
d

e
x

Sample

orange

lemon

kiwi

carrot

beet

0

2

4

6

8

10

12

14

16

18

1 2 3 4 5

%
 s

o
li

d
s

Sample

orange

lemon

kiwi

carrot

beet



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
263 

variation in the carrot juice and beet juice 

and the least for kiwi. There are no changes 

in conductivity for samples 2 (juice stored 2 

days in brown glass bottle) and 3 (juice 

stored 2 days in PET container) or samples 

4 (juice stored 5 days in brown glass bottle) 

and 5 (juice stored 5 days in PET container) 

where we conclude that conductivity is not 

influenced by the container material. For 

orange and kiwi is irrelevant. 

Many people consume fruit juices 

on a daily basis. Fruit juices are a 

convenient way for people to receive the 

benefits of various fruits. However, they 

may also have high sugar content. Although 

the sugar is natural, it may not be healthy in 

high quantities. It was suggested that too 

much sugar could pose harmful health 

effects, as people could develop diabetes, 

obesity, heart disease, and other 

complications from excess consumption 

[9]. A significant variation is found from the 

analysis of experimental results for beet, 

carrot and lemon juices and irrelevant for 

orange and kiwi juices, according to Figure 

1 d) and e), for the refractive index and dry 

soluble solids.  

In the food industry, colour is a 

quality attribute that affects consumers in 

terms of choice and food preferences. From 

the physical point of view, the colour is a 

numerical expression which is evaluated as 

the difference in colour against a known 

standard. Instead, from the consumer's point 

of view, the colour is the first quality 

parameter and is even more important as it 

influences the acceptability or the 

unacceptability of the product. The 

appearance of the food, which is one of the 

most important sensory attribute of the food 

products, both fresh and processed is in 

close correlation with the visual appearance 

and hence the colour of the food. The 

consumer uses colour as a measure of food 

quality and associates it with other sensory 

attributes such as flavor and pigment 

content [7], [10]. Food visual aspect has a 

strong influence on consumer’s opinion on 

food quality. Color can be correlated with 

other quality attributes such as: sensory, 

nutritional and visual or non-visual defects 

and helps control the products’ quality. 

Color is a perceptual phenomenon which 

depends on the observer and on the color 

observing conditions. L*, a*, b*, hue angle 

(h*) and Chroma parameters for the samples 

subjected to the assay analysis were 

measured [6]. 

As it can be seen from Figure 2 a), 

there is an increase for L* for the stored 

juices comparing to the fresh ones. A 

significant increase is found after 2-day 

storage of samples (2 and 3). 

Considering that the a* parameter 

has positive values for red colors and 

negative values for green colors and the b* 

parameter has positive values for yellowish 

colors and negative values for bluish colors 

[8-9], it can be observed from Figure 2 b) 

and Figure 2 c) that all samples tend to 

modify their color (to become brownish). 

Significant variations are observed in all the 

studied juices. Analyzing the Chroma 

parameters, Figure 2 d) it can be observed a 

growth for juices stored for 2 days in both 

the glass bottle (samples 2), and the PET 

container (samples 3), and then a decrease 

after a storage for 5 days (samples 4 and 5). 

Hue (h*) attribute, Figure 2 e) presents 

negative values, which is consistent with 

the parameters a* and b* which indicate that 

the changes are perceptible by the human 

eye, and thus accepts the consumer to 

consume the product or not.  

In Figure 2 f) it can be seen ΔE* for 

all the juice samples that represent the color 

difference magnitude between the value of 

the initial color and the value of the final 

color. 



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
264 

 
a) b) 

c) d) 

e) f) 

Figure 2. The variation in color parameters for the analyzed samples: a) L*,  

b) a*, c) b*, d) chroma, e) hue angle, f) ΔE* 

 

Due to storage without 

preservatives biochemical changes occur 

that causes changes in the color and in the 

other physical parameters, regardless of the 

storage containers. 

 

4. Conclusion 

 

This paper presents an experimental 

study on the change of density, electrical 

conductivity, pH, refractive index, and on 

the parameters specific to the color of 

natural juices stored at a temperature of 

+40C and normal atmospheric pressure in 

two types of containers. From the analysis 

of experimental results, it results that there 

is an increase in density, in all samples, 

while the pH changes only slightly in 

orange juice. Storage temperatures of +4ºC 

reduce the risk of contamination and 

40

50

60

70

80

90

100

1 2 3 4 5

L
*

Sample

orange

lemon

kiwi

carrot

beet

-50

-40

-30

-20

-10

0

10

20

1 2 3 4 5

a
*

Sample

orange

lemon

kiwi

carrot

beet

-35

-30

-25

-20

-15

-10

-5

0

5

1 2 3 4 5

b
*

Sample

orange

lemon

kiwi

carrot

beet
0

10

20

30

40

50

60

1 2 3 4 5

C
h

ro
m

a

Sample

orange

lemon

kiwi

carrot

beet

-200

-150

-100

-50

0

50

1 2 3 4 5

h
*

Sample

orange

lemon

kiwi

carrot

beet 0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5

Δ
E

*

Sample

orange

lemon

kiwi

carrot

beet



Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava 

Volume XV, Issue 3  – 2016 

 
Mihaela JARCĂU, Maria POROCH-SERIŢAN, Analysis of physical parameters of natural juices, Food and Environment 

Safety, Volume XV, Issue 3 – 2016, pag. 259 - 265 

 

 
265 

decrease the speed of biochemical changes, 

but this fcat is not sufficient to guarantee the 

nutritive and organoleptic qualities of the 

juice and its acceptability by the consumer. 

 
5. References 
 

[1]. TOFAN I., TOFAN C., Utilizarea frigului 
artificial la procesarea, depozitarea și 

comercializarea produselor alimentare perisabile, 

Editura AGIR: București, România, (2002). 

[2]. GLEVITZKY M., BOGDAN I., 
BRUSTUREAN G. A., PERJU D., SILAGHI-

PERJU D., Studiul procesului de inhibare a 

degradării sucurilor naturale supuse la tratament 

termic prin pasteurizare, Revista de Chimie, 

București, 59, 5, 595 – 60, (2008).  

[3]. BANU C., NOUR V., STOICA A., 
BĂRASCU E., Alimentație pentru sănătate, Editura 

Asab, București, România, (2009). 

[4]. COSTIN G.M., Alimente pentru nutriție 
specială, Editura Academica, Galați, România, 

(2001). 

[5]. *** 2007, Ocean Optics, Inc 2007 Product 
Catalog

 

[6]. POROCH – SERIȚAN M., POPESCU N. G., 
The relationship between nitrite concentration and 

colour parameters during storage of meat product - 

summer sausages, Food and Environment Safety, 

XV, 146 – 154, (2016). 

[7]. PATHARE P.B., OPARA U.L., AL-SAID F. 
AL-J., Colour Measurement and Analysis in Fresh 

and Processed Food, Food Bioprocess Technol., 6, 

36 – 60, (2013). 

[8]. *** 2007, A guide to Understanding Color 
Communication, accesed in May 2014: 

[http://www.x_rite.com] © X-Rite, Incorporated 

[9]. SERPEN J. Y., Comparison of Sugar Content 
in Bottled 100% Fruit Juice versus Extracted Juice 

of Fresh Fruit, Food and Nutrition Sciences, 3, 1509 

– 1513, (2012). 

[10]. MUREȘAN A., Curs 14, Evaluarea culorii, 
Information on: 

http://www.tex.tuiasi.ro/biblioteca/carti/CURSURI/

Prof.%20Dr.%20Ing.%20Augustin%20Muresan/, 

(2013) 01-Aug-2013. 

http://www.tex.tuiasi.ro/biblioteca/carti/CURSURI/Prof.%20Dr.%20Ing.%20Augustin%20Muresan/
http://www.tex.tuiasi.ro/biblioteca/carti/CURSURI/Prof.%20Dr.%20Ing.%20Augustin%20Muresan/