Effect of fortification on the physico-chemical and sensory properties of buffalo milk yoghurt

Abstract

The buffalo milk yoghurts were prepared with the fortification of various proportion of either apple fruit pulp or honey, by using mixed starter culture containing 1:1 ratio of Streptococcus thermophilus and Lactobacillus bulgaricus. The samples of fortified yoghurt were studied to determine effects of fortification of apple fruit pulp and honey separately. The physical properties studied were setting time, syneresis, viscosity, while chemical properties were moisture content, acidity, pH and ash content. Sensory properties were evaluated by 9 point hedonic scale with the consumer taste panels to compare the properties of apple fruit pulp or honey fortified yoghurt with that of the control sample. The sensory properties evaluated were color, flavor, consistency, and overall acceptability. It is observed that yoghurts with superior sensory quality were obtained with 10 per cent apple fruit pulp and 5 per cent honey concentration.

Full text

ISSN: 1579-4377
EFFECT OF FORTIFICATION ON THE PHYSICO-CHEMICAL AND
SENSORY PROPERTIES OF BUFFALO MILK YOGHURT
P.N. Ghadge1*, K. Prasad1, P.S. Kadam2
1Department of Food Engineering & Technology,
Sant Longowal Institute of Engineering & Technology,
Longowal-148106, Punjab, India
2Department of Food Microbiology & Fermentation Technology,
College of Food Technology, M. A. U.,
Parbhani-431402, Maharashtra, India
pnghadge20@rediffmail.com
ABSTRACT
The buffalo milk yoghurts were prepared with the fortification of various proportion of
either apple fruit pulp or honey, by using mixed starter culture containing 1:1 ratio of
Streptococcus thermophilus and Lactobacillus bulgaricus. The samples of fortified yoghurt
were studied to determine effects of fortification of apple fruit pulp and honey separately.
The physical properties studied were setting time, syneresis, viscosity, while chemical
properties were moisture content, acidity, pH and ash content. Sensory properties were
evaluated by 9 point hedonic scale with the consumer taste panels to compare the properties
of apple fruit pulp or honey fortified yoghurt with that of the control sample. The sensory
properties evaluated were color, flavor, consistency, and overall acceptability. It is observed
that yoghurts with superior sensory quality were obtained with 10 per cent apple fruit pulp
and 5 per cent honey concentration.
KEYWORDS
Yoghurt, apple, honey, composition, physico-chemical characteristics, acidification

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INTRODUCTION
Yoghurt is cultured dairy product produced by fermenting milk with or without added non-
fat dry milk with Lactobacillus bulgaricus and Streptococcus thermophilus bacteria. It
usually contains 12-14 per cent total milk solids and has soft friable custard like consistency
and a clean distinct flavor. The word yoghurt is derived from Turkish word ‘jugurt’ and is
traditional food beverage in Balkan and Middle east. However, its popularity has also spread
in India. The consumption of yoghurt has increased significantly all over world in recent
years (Deeth et al., 1979).
Yoghurt is becoming more popular among fermented milk since it has nutritional and
therapeutic properties (Tamime & Robinson, 1985). In the recent times many physicians are
prescribing to consume more of this type of fermented milk for those suffering from
intestinal troubles, mostly the aged and children group (Rao et al., 1982). Yoghurt has
unique nutritional attributes as they supply high quality proteins, also excellent source of
calcium, phosphorus and potassium along with significant quantities of several vitamins.
The carbohydrate content is easily absorbed even by lactose maldigestors. Yoghurt is
valuable adjunct to any healthy diet (Symons, 1993; Lyne, 1995). Presence of b-D-
galactosidase activity in probiotic yoghurts indicates its suitability for lactose-intolerant
infants Sarkar and Mishra (1998). Yoghurt could be used for infant and adult feeding owing
to its higher Ca/Na ratio as compared to RDA value in USA (Demott, 1985).
A study at the Michigan State University showed that honey enhanced the growth,
activity and viability of bifidobacteria. Researchers also compared the prebiotic activity of
honey to that of commercial oligosaccharides. Honey is a natures original sweetener,
contains a number of fermentable carbohydrates including a variety of oligosaccharides.
Huhn et al. (1981) were developed yoghurt from buffalo milk. The milk was heated
for 30 min at about 900C then cooled to 450C. The yoghurt cultures were added (2-3 per cent
by volume) to the milk and incubated. When the coagulum formed, it was broken, passed
through a blender or liquefier and refrigerated for 12-18 hrs to improve the consistency and
viscosity.
In this study, the efforts were made to produce good quality of buffalo milk yoghurt
fortified with apple fruit pulp or honey separately. Present investigation was carried out with
objectives to determine the effect of apple fruit pulp or honey fortification on the yoghurt
formation and to study the physical-chemical and sensory properties of fortified yoghurt.
MATERIALS AND METHODS
Preparation of starter culture
Freeze dried pure culture of Streptococcus thermophilus and Lactobacillus bulgaricus were
obtained from Animal Husbandry and Dairy Department, College of Agriculture,
Marathwada Agricultural University, Parbhani, Maharashtra, India. The freeze dried cultures
were used in aseptic laminar flow chamber; 0.5 ml of sterilized skim milk was added to the
culture, mixed thoroughly and transferred quantitatively to test tubes having 10 to 20ml pre-
sterilized cooled skim milk. All test tubes were incubated at temperature of 42-430C till the
firm coagulum was obtained.

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Preparation of batch culture
Batch culture was prepared by inoculating 3 per cent of mother or starter culture into 100 ml
of pre sterilized cooled skim milk and incubated at 41-430C till firm coagulum was formed,
which was stored in refrigerator till further use in the entire investigation.
Preparation of buffalo milk yoghurt fortified with apple pulp or honey
Buffalo milk was procured from the Department of Animal Husbandry and Dairying,
College of Agriculture, M.A.U., Parbhani. Good quality red delicious apples and honey were
obtained from super market, Parbhani. Buffalo milk was collected four hours after drawing
and standardized to 6per cent fat, homogenized, sweetened (10per cent cane sugar addition),
heat treated (85-90oC for 30 min.) cooled (40-43oC) and fortified with apple fruit pulp (5,
10, and 15per cent levels) or honey were added (5, 10, and 15per cent) separately. The active
starter culture was inoculated in 1:1 ratio of Streptococcus thermophilus and Lactobacillus
bulgaricus at 3per cent of total inoculation. Then it was subjected to blender and incubated
at 37-380C temperature for overnight.
Physical properties of fortified yoghurt
The yoghurt samples prepared were studied for setting time, syneresis and viscosity. The
setting time of sample was recorded from the time of inoculation to just coagulum was
formed and time of setting for the fortified yoghurt samples were recorded in hrs. Syneresis
of sample was carried out by using 100 gm yoghurt sample. The samples were centrifuged
and 15 min whey drained. The weight of the drained whey reported as the per cent syneresis.
Viscosity was determined by using ‘Brooke Field’ syncro-electric viscometer (Model RUT)
at the speed of 12 and 30 rpm.
Chemical properties of fortified yoghurt
The yoghurt samples prepared were studied for moisture, pH, acidity, and ash. The pH of
yoghurt was measured by using digital pH meter (Global model DPH-500). The acidity was
determined as per method described by Indian Standards Institutions, “Hand Book of Food
Analysis” Part XI (1981). The moisture and ash content was determined by the method of
A.O.A.C. (1978).
Organoleptic evaluation
The final product was subjected to evaluation by selected judges. It was judged for
appearance, taste, consistency and overall acceptability. Score card provided to all
comprising 9 point hedonic scale, developed by Quarter Master, Food and Container
Institute USA (Gupta, 1976). The Dunnett test was applied to determine significant results.
RESULTS AND DISCUSSION
Experimental design: The blend of sample was coded as follows:

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Sample
Honey or Fruit pulp
G (Control)
Nil
A
5 per cent Honey
B
10 per cent Honey
C
15 per cent Honey
D
5 per cent Apple pulp
E
10 per cent Apple pulp
F
15 per cent Apple pulp
Chemical Composition of Ingredients
The data for chemical composition of buffalo milk, honey and apple are presented in Table-
1. A perusal data from Table-1 revealed that honey contained maximum carbohydrate i.e.
82.0 per cent; however it was lower in fat and protein content. The results were in close
agreement with White and Rudyj (1962). Also from Table-1 revealed that buffalo milk
contains high fat and protein content. The high protein content of buffalo milk and total
solids helped in developing high viscosity curd. Regarding the ash content of ingredients
buffalo milk contains high ash content (0.8 per cent) than apple pulp (0.3 per cent) and
honey (0.17 per cent).
Table 1: Means & Standard deviations of Chemical Composition of Ingredients*
Sr.
no.
Ingredient
M C
(per cent)
TSS
(per cent)
Fat
(per cent)
Protein (per
cent)
CH2O
(per cent)
Ash
(per cent)
1.
Buffalo milk
84.20±0.95
15.80±0.36
6.06±0.17
3.90±0.30
5.20±0.22
0.80±0.10
2.
Honey
17.20±0.35
82.80±0.98
0.30±0.03
0.20±0.02
82.0±0.36
0.17±0.01
3.
Apple pulp
84.60±0.62
16.40±0.61
0.50±0.02
0.20±0.03
14.4±0.26
0.30±0.02
* each value given in table as a result of t riplicate analysis
Physical properties of yoghurt
The result pertaining to physical properties of buffalo milk yoghurt fortified with honey and
fruit pulp are reported in Table-2.

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Table 2: Setting time and syneresis of fortified yoghurt**
Samples
Setting time (min)
Syneresis (per cent)
G (Control)
480
20.00±0.46a
A
450
21.07±0.15a
B
360
23.23±0.45 b
C
300
27.80±0.36 b
D
420
21.20±0.26 a
E
330
22.43±0.08 b
F
270
24.60±0.30 b
** samples with same superscripts in same column are not significantly different
Setting time
It is observed from Table-2 that setting time of yoghurt reduced with increase in the
concentration of the fortification. The minimum setting time was required for sample ‘F’
(270 min) in case of yoghurt fortified with 15 per cent apple pulp. The setting time recorded
minimum (300 min) in case of buffalo milk yoghurt fortified with 15 per cent honey sample
‘C’. Londsted (1974) reported the coagulation time of 300-360 min. The present results are
in close confirmation with this. Reduction in setting time of fortified yoghurt of present
investigation is due to the increase in concentration of honey and apple pulp. The higher
setting time required for the control sample ‘G’ (480 min) as compared with the other
samples prepared with buffalo milk and fortified with honey or apple pulp separately at
different concentration. The reduction in setting time should be considered for industrial use.
Syneresis
The yield of syneresis was influenced by increase in concentration of honey and apple pulp.
All the fortified samples had significant yield of syneresis compared to controlled sample.
The yoghurt containing 5 per cent honey sample ‘A’ had lower syneresis. The minimum
syneresis was found in control sample ‘G’ (20 per cent). In case of apple pulp yoghurt the
maximum syneresis is found in sample ‘F’ (24.60 per cent). The maximum syneresis was
found in 15 per cent honey yoghurt i.e. sample ‘C’ (27.80 per cent). This is because of
higher acidity developed may results in separation of whey and total solids.
Viscosity
Table 3: Viscosity of fortified yoghurt*
Viscosity (Centipoises)
Samples
12 rpm
30 rpm
G (control)
1240
690
A
1040
670
B
990
645
C
940
620
D
1060
680
E
1010
650
F
970
630

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Viscosity of yoghurt sample measured at 12 rpm and 30 rpm using spindle number
three was found to be decreased due to addition of honey and apple pulp. Results in Table-3
shown that yoghurt sample fortified with apple pulp was having more viscosity than honey
fortified yoghurt sample. It is observed that the viscosity of control sample ‘G’ (plain
yoghurt) was more as compared to other fortified yoghurt sample. This may happen because
of lower acidity gave lesser protein coagulation and formation of soft curd this offered
reduced resistance to flow i.e. viscosity.
Fig. 1: Viscosity of Yoghurt samples
Chemical properties of fortified yoghurt
The result pertaining to chemical properties of buffalo milk yoghurt fortified with honey and
apple fruit pulp are reported in Table-4.
Table 4: Chemical properties of fortified yoghurt*
Chemical Properties
Samples
Moisture (per cent)
pH
Acidity (per cent)
Ash (per cent)
G (Control)
78.2±0.23a
4.39±0.10 a
1.40±0.02 a
1.40±0.02 a
A
76.8±0.83b
4.27±0.10 b
1.44±0.01 a
1.42±0.01 a
B
75.4±0.17 c
4.22±0.10 b
1.51±0.02 b
1.47±0.04 b
C
74.6±0.05 c
4.10±0.17c
1.53±0.02 b
1.50±0.02 c
D
77.8±0.80 a
4.21±0.10 b
1.49±0.03 b
1.44±0.01 a
E
76.0±0.46 b
4.14±0.10 c
1.54±0.02 b
1.49±0.02 b
F
75.9±0.26 c
4.11±0.10 c
1.59±0.03c
1.52±0.02 c
** samples with same superscripts in same column are not significantly different
Moisture
The control sample ‘G’ (78.2 per cent) has maximum moisture. While in fortified yoghurts,
sample ‘D’ (77.8 per cent) was recorded higher moisture content. Sample ‘C’ (74.6 per cent)
was with minimum moisture content. From Table-4 it was also observed that moisture
content was decreased as rate of concentration of honey or apple pulp increased. The results
are found similar to the results obtained by Deeth and Tamime (1979).
Viscosity of Apple pulp fortified yoghurt
400
550
700
850
1000
1150
1300
G (Control) D (5 %) E (10 %) F (15 %)
Apple pulp concentration (%)
Viscosity (cp)
12 rpm
30 rpm
Viscosity of honey fortified yoghurt
400
550
700
850
1000
1150
1300
G (Control) A (5% ) B (10%) C (15%)
Honey concentration (%)
Viscosity (cp)
12 rpm
30 rpm

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pH
Table-4 shows the pH content of control sample ‘G’ (4.32) was maximum as compared to
fortified yoghurt samples, while minimum pH was recorded in sample ‘C’ (4.10) with 15 per
cent honey. The pH values of samples varied from 4.10 to 4.32. It is observed that values
were decreased as the concentration of honey or apple pulp was increased. From this it can
be reported that variation in pH content of fortified yoghurt samples may be due to addition
of honey and apple pulp, which have different pH values. Laye et al., (1962) reported pH
values of yoghurt in the same range obtained in present study.
pH of Yoghurt Samples
3.9
4
4.1
4.2
4.3
4.4
4.5
G A B C D E F
Samples
pH
Series1
Fig. 2: pH of Yoghurt samples
Acidity
The acidity is increased from 1.40 per cent to 1.59 per cent. The values of acidity were in
close agreement with O’Neil et al., (1979) who observed an increase in acidity with increase
in concentration. From Table-4 it is also shown that control sample ‘G’ had acidity 1.40 per
cent, while sample ‘C’ had maximum acidity 1.53 per cent and in sample ‘F’ had maximum
acidity 1.59 per cent. The acidity of fortified yoghurt increases as the concentration of
fortification increases. That means, acidity of ingredients affects acidity of yoghurt.
Fig. 3: Acidity& Ash content of Yoghurt samples
Acidity & Ash content of Yoghurt samples
1.3
1.35
1.4
1.45
1.5
1.55
1.6
1.65
G A B C D E F
Samples
units (per cent)
Acidity
Ash

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Ash
Ash content of control sample ‘G’ was 1.40 per cent, where it was reported maximum in 15
per cent apple pulp fortified yoghurt sample ‘F’ (1.52 per cent). From Table-4 it was
observed that apple pulp fortified samples had more ash content than honey fortified
samples. The difference in ash content may be due to insoluble solids and fiber content
which may contribute in increasing the ash content. Rajasekaran and Rajor (1989) reported
similar results.
Sensory or Organoleptic evaluation of Fortified Yoghurt
The result pertaining to sensory properties of buffalo milk yoghurt fortified with honey and
fruit pulp are reported in Table-5 and Fig. 4:
Color
The apple fortified yoghurt sample ‘D’ with 5 per cent scored maximum score with 8.2. In
case of honey fortified yoghurt sample ‘A’ with 5 per cent had scored maximum score with
8.1. In all the cases, control sample ‘G’ was superior to other fortified yoghurts. It was
observed at higher concentration due to increase in total solids and acidity, firm curd was not
obtained which had spoiled the color of product.
Table 5: Sensory qualities of Fortified Yoghurt*
Samples
Color
Flavor
Consistency
Overall
acceptability
G (Control)
8.4±0.52a
8.2±0.63 a
8.3±.0.67 a
8.4±0.52 a
A
8.1±0.63a
8.4±0.53 a
8.0±0.67 a
8.4±0.52 a
B
8.0±0.67a
8.0±0.67 a
7.7±0.52 b
7.8±0.53 b
C
7.6±0.52b
7.8±0.63 b
7.5±0.53 b
7.6±0.52 b
D
8.2±0.74a
8.3±0.63 a
8.2±0.63 a
8.2±0.57 a
E
8.1±0.74b
8.2±0.74 a
8.2±0.63 a
8.3±0.67 a
F
7.8±0.63b
7.6±0.52 b
7.7±0.48 b
7.6±0.52 b
Scores within same column with same superscripts are non-significan t at p=0.05
Fig. 4: Sensory evaluation of Yoghurt samples
Sensory evaluation of fortified yoghurt samples
7
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
Color Flavor Consistency Overall
acceptability
Sensory para me ters
Sensory scores
G-control
A
B
C
D
E
F

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Flavor
It was observed the sample ‘A’ with 5 per cent honey and sample ‘D’ with 5 per cent apple
pulp scored maximum 8.4 and 8.3 respectively. Also, it was shown that increasing the
concentration decreased the flavor score. Because, increase in concentration resulted in
increasing the alcoholic aroma and acidic taste of yoghurt. So, the minimum concentration
should be preferred for the maximum flavor score.
Consistency
It is revealed that, higher level of concentration of honey or fruit pulp reduced the score for
consistency. Consistency was generally affected due to separation of whey at high level of
honey and apple pulp concentration due to production of acids, to give the reduced
coagulation and formation of soft and loose textured curd. With respect to consistency the
highest score of 8.3 per cent was obtained in control sample ‘G’ followed by 8.2 per cent
and 8.0 per cent, in sample ‘D’ and ‘A’ respectively.
Overall acceptability
The overall acceptability of fortified yoghurt was found varying at different concentrations
of honey or apple fruit pulp. Sample ‘A’ fortified with 5 per cent honey found superior in all
aspect over other samples followed by sample ‘E’ with 10 per cent apple fruit pulp. The
results are in good comparison to Kumar and Mishra (2004).
CONCLUSION
1. The lower concentration levels were superior over higher concentration levels of
apple pulp and honey fortification.
2. It was found that setting time, viscosity, pH, moisture content were reduced with
increase concentration level of apple pulp or honey, where as syneresis, acidity, ash
content were found to be increased with increase in concentration.
3. The maximum syneresis was found in 15 per cent honey yoghurt i.e. sample ‘C’
(27.80 per cent). This is because of higher acidity results in separation of whey and
total solids.
4. Amongst all the samples, sample ‘A’ prepared from 5 per cent honey followed with
sample ‘E’ prepared from 10 per cent apple pulp was rated as the best on the sensory
quality evaluation
ACKNOWLEDGEMENT
The authors wish to thank the Dean, Prof. D.B. Wankhede, College of Food Technology,
Marathwada Agricultural University, Parbhani, Maharashtra State, India for his cooperation
and technical assistance to accomplish this research endeavor.
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