Authored by Negussie F Bussa
Yoghurt contains beneficial bacteria that
confer health benefits to the consumer. Yoghurt combined with papaya
juice may
result in a product with enhanced functional and nutritional properties,
and sensory acceptability. Papaya possesses antioxidant
properties as it is rich in β-carotene and phenolic compounds. The
objective of this research was to investigate the effect of
papaya juice supplementation and levels of gelatin addition on
physicochemical and acceptability of yoghurt. The experiment was
laid out in a 3×4 full factorial arrangement where each of three gelatin
addition levels (0.5, 0.6 and 0.7% w/v of the milk) were
combined with one of the four papaya juice addition levels (0,10,15 and
20% w/w of the base milk) to give twelve different yoghurt
formulations. Proximate composition, total phenolics, total carotenoids
and reducing power of yoghurt samples were determined
on day 1 whereas yoghurt firmness and consumer acceptance tests were
done on day 7. The addition of papaya juice to yoghurt
formula resulted in a decrease in fat and an increase in the total
solids, protein and ash values. The addition of gelatin improved
the syneresis and firmness of yoghurt. Increased amount of gelatin and
papaya juice addition significantly (P≤0.05) decreased the
syneresis of yoghurt samples and increased the firmness. The total
carotene, phenolic and reducing power of yoghurt samples were
significantly (P≤0.05) increased with the increased papaya juice level.
Panelists favored samples with 10% papaya juice and 0.5%
gelatin in terms of appearance, color and overall acceptability. The
results indicated the viability of commercially producing papaya
juice supplemented yoghurt along with gelatin to combat syneresis,
improve firmness, enhanced the total carotenoids, phenol and
reducing power, crude protein and total solid of the yoghurt samples.
Therefore, it is concluded that addition of papaya juice into
yogurt improves the nutritional and functional property of yoghurt.
Keywords: Yoghurt; Nutrition; Gelatin; Papaya juice; Syneresis
Introduction
In Ethiopia, a significant proportion of milk is consumed in
the form of Ergo were the fermentation process is usually natural
[1,2]. Yoghurt production is a well-controlled process that utilizes
pure cultures of lactic acid bacteria, which are responsible for the
fermentation process.
Yoghurt is a healthy and delicious food due to its high nutritive
and therapeutic value [3]. Generally considered as a safer product
and well known and most popular worldwide [4,5].
The associations of fruits with cultured dairy products have
created healthy perceptions in the consumers mind. Papaya fruit
provides health benefits because it is sources of vitamins, minerals,
antioxidants and dietary fibers [6].
It has nutritional, medicinal, and pharmacological and a
therapeutic effect on the human body [7]. Milk is rich in protein
and fat, but it is deficient in vitamins and fiber. Thus, blending milk
with papaya juice for yoghurt would produce a nutritionally rich
functional food.
Gelatin enhances the viscosity, influence texture, creaminess
and mouth feel as well as prevents separation of whey from yoghurt
[8]. Considering the above, the production of a functional yoghurt
with papaya juice. Is an alternative for the increasing market of
health-conscious consumers and may contribute to an increase
in the vitamins and mineral consumption? The objectives of the
present work were to develop cow’s milk yoghurt added with papaya juice and gelatin and to study the physical and nutritional
properties as a function of the levels of papaya juice and gelatine.
Materials and Methods
The experiment was conducted in the laboratory of the Food
Science, and Dairy laboratory, Haramaya University. Fresh whole
cow’s milk was collected from Haramaya University dairy farm.
Fresh papaya was purchased directly from a farmer’s field. The
milk and papaya juice were analyzed for proximate compositions.
Gelatin with 240 Blooms manufactured in Brazil by Bake Mate) was
purchased from supermarket, Addis Ababa, Ethiopia. Freeze-dried
yoghurt starter culture (YC-X11 CHR HANSEN), was purchased
from chemical supplier, Yomex- import and export, Addis Ababa,
Ethiopia.
Yoghurt production
Prior to yoghurt preparation all equipment used for yoghurt
manufacturing were sterilized in autoclave after thoroughly
washing them. A freeze-dried yoghurt starter culture was used to
inoculate fresh milk 1lt, which had been heated at 90 °C for 30 min.
and immediately cold to 45 °C. The inoculated milk was incubated
at 43 0C until pH 4.6 was attained, then stored overnight at 4 °C
and then used in the yoghurt preparation. Three different blends
of gelatin at a level of 0.5, 0.6 and 0.7% with sugar at 4% milk base
were prepared. The fresh milk 3x4L was preheated to 50 0C to
facilitate melting of gelatin and uniform mixing of ingredients.
The mixes were pasteurized at 90 °C for 30 minutes and the
three premixes each was further divided into four equal portions
and in each portion papaya juice (at a level of 0, 10, 15 and 20%
(w/v) was added and then rapidly cooled to 45 °C. The inoculated
milk was added at the rate of 0.03% served as starter culture into
each mix. The resulting 12 different yoghurt formulations were
further divided into three each coded screw capped glass jars and
a temperature of 43 °C was maintained throughout the incubation
period until the pH of the control yoghurt reached 4.7.
The yoghurt samples were transferring to a refrigerator at
4 °C and then taken out and left at room temperature prior to
analyses. The samples were then homogenized to obtain a uniform
mixture for further analysis. Physico-chemical, total phenolics and
carotenoids of yoghurt samples were determined on day1 whereas
yoghurt firmness and consumer acceptance tests were done on day
7.
Physicochemical analysis
The papaya juice, fresh milk and yoghurt samples were
analysed for moisture by oven- drying method crude fat using the
Mojonnier method, crude protein using Kjeldahl method and ash by
furnace-drying [9]. The total soluble solid content was determined
with a refractometer (Hanna H1 96801, USA). The carbohydrate
and calorie values were obtained by calculation.
A firmness analysis was performed with a texture analyser, TAXT2
model using an Expert Software version 1.05 (Stable Micro
Systems, Surrey, UK). The analytical method was modified from
[10]. An aluminium cylinder probe P36R with a diameter of 35mm
was used. A compression strain of 60% was used with a 5 kg load
cell at a speed of 5mms
-1. The firmness of the yoghurt samples was
measured in triplicates.
Syneresis of the homogenised yoghurt was determined by
placing the no. 1 Whatman filter paper in a Buchner funnel. The
funnel was then placed in an Erlenmeyer flask and attached to a
vacuum pump (Fisher Scientific, FB 70155). A total of 20g of each
yoghurt samples was then spread evenly on the filter paper and
vacuum-filtered for 10 min. The collected residue was weighed
and percent syneresis was calculated by dividing the weight of the
residue by the initial sample weight multiplied by 100 [11].
Total phenolic, carotenoids and reducing power
The total phenolic content of the papaya juice and yoghurt
samples was determined using the DCPIP titrimetric method [9].
The standard used was a solution of 100 mg gallic acid diluted with
3% HPO3: HOAC to 100 ml in a volumetric flask. The dye solution
was prepared by dissolving 50 mg 2, 6-dichloroindophenol in hot
water containing 42 mg sodium carbonate. A total of 10 g each of
the sample was then added to 3% HPO3: HOAC and filtered with no.
42 Whatman filter paper. The sample extract was titrated against
the dye solution to a pink colour endpoint lasting for 15 sec. The
extract obtained was used for Spectrophotometric analysis of total
phenolics and reducing power. All of the analyses were run in
triplicate.
Total carotenoids content of papaya juice and yoghurt samples
was determined according [12-15]. Papaya juice sample (1g)
and yoghurt samples (5g) were mixed with 37.5ml methanol
and 12.5ml of 50% Potassium hydroxide solution in a flask for
saponification. Then unsaponifiable materials were extracted
twice with Diethyl ether (20 ml each time) and the ether extract
was washed twice with distilled water (40 ml each time). Next, the
extract was dried over anhydrous sodium sulfate. The diethyl ether
was evaporated on steam bath and the dried residue was then redissolved
in petroleum ether (20 ml). The yellow to orange color of
the petroleum ether was measured at wavelength of 450 nm with
a Spectrophotometer. The Total Carotenoids content of samples
were computed using the formula shown below and the result was
reported in mg equivalent of β- carotene per kg of papaya juice.
Where: Abs= absorbance reading, 259.2=extraction coefficient
of β-carotene in petroleum ether
20ml= volume of petroleum ether used to dissolve carotenoids
extract.
Sensory evaluation
Twenty-five panellists (13 males and 12 females from Haramaya
University) were purposely selected for sensory evaluation. A
hedonic form with a 9-point scale was given to each panel. The yoghurt samples were served in randomised order in small cups
coded with three random digits. The hedonic form scales ranged
from 1, representing ‘dislike very much’, to 9, representing ‘like very
much’. The sensory parameters used were color, appearance, body
and texture, flavor and over all acceptability.
Statistical analysis
All data were analysed using SPSS version 17.0 for Windows
(SPSS Inc., Chicago, IL, USA) with a one-way analysis of variance
(ANOVA). A Duncan’s multiple range tests was used to analyse the
differences between the individual means at a 5% significance level.
Results and Discussions
Chemical analysis of milk and papaya juice
Quality of Milk and papaya used for yoghurt production was
analysed before use. Moisture, total solid, fat, protein, ash, acidity,
pH, and solid-non-fat (SNF) were determined. Results of chemical
analysis of milk and papaya are shown in (Table 1 & 2). The results
were more or less similar to earlier studies, [16-18], respectively.
Physical and nutritional properties of papaya yoghurt
The results of the proximate composition, Total phenolics, Total
carotenoids, reducing power, Texture analysis (yoghurt firmness)
and syneresis of the yoghurt samples are presented and discussed
in the subsequent sections.
Proximate composition of yoghurt
Total solids content, moisture content, crude protein, fat, ash
and solids-not-fat of yoghurt samples were ranged from 16.29±0.06
to 16.85±0.19%, 83.04±0.05 to 83.79±0.09, 3.02±0.01 to
3.24±0.08, 2.86±0.09 to 3.16±0.09%, and 0.71±0.01 to 0.74±0.01%
and 13.04±0.29 to 13.96±0.09%, respectively (Table 3). The total
solids, protein, solid-not-fat, and ash contents of papaya added
yoghurt were higher than in control (without papaya) yoghurt. The
fat content of papaya added yoghurts decreased compared with
control yoghurts. The maximum protein content was recorded in
the yoghurt samples with papaya juice and gelatine. Papaya was
rich in protein and these papaya fibres increased protein contents
in yogurt in high ratio (Table 2).
The ash content of the control (yoghurt without papaya juice)
was lower than that of the papaya supplemented yoghurt (Table 3).
The ash content is the amount of non-combustible matter and total
minerals present in a food. Therefore, addition of the papaya juice
to the milk had increased the ash and thus the mineral contents of
the papaya - yoghurt than in the control (Table 3).
The variation in the proximate composition of yoghurt samples
was due to the compositional difference between papaya juice
and the base milk used (Table 1 and 2). Generally, the addition
of papaya juice had a concentration effect on the composition
of yoghurt, and this was due to higher total solid (TS) content of
papaya juice as compared to milk. According to the draft COMESA/
East African standard, yoghurt should have a minimum total solidnot-
fat content of 8.2% (w/w). Codex stated yoghurt should have
a minimum of 2.7% protein and a fat content of less than 15%.
Similarly, in this study, all yoghurt samples satisfied the above
requirements (Table 3).
Total carotenoids, total phenolics and reducing power
The TC, TP and RP content of plain yoghurt samples observed
in this study were almost similar with findings of [17], and little
higher than the findings of [4] who reported TP content of 2.025 mg GAE/100 g in the plain yoghurt samples. This could probably
be due to differences in phenol content of milk samples used in the
experiments. The occurrence of TC, TP and consequently RP in milk
and dairy products may be consequence of several factors, e.g., the
consumption of particular fodder crops by cattle, the catabolism
of proteins by bacteria, contamination with sanitizing agents,
process- induced incorporation or their deliberate addition as
specific flavouring or functional ingredients [19].
The TC and TP content of papaya in the literature is quite
variable, which could be due to differences in cultivar [20] preharvest
management [21], post-harvest handling and storage [22],
processing method and the methods of analysis [19,23]. The TP
content of the papaya juice used in this study was higher than the
value (28mg GAE/100g) reported [29-32] and lower than the result
reported [33] which was 54mg GAE/100g of juice. The content of
carotene was within the range from 8.66mg/Kg to 78.07mg /Kg
reported [34].
In general addition of papaya juice results in increased TC, TP,
and RP of yoghurt and consequently the functional food property of
yoghurt was improved due to increased carotenoids and phenolic
contents which in turn could act as antioxidant and provitamin
A. Vitamin A malnutrition is one of the three most important
nutritional problems (i.e., iron, iodine and vitamin A) in the
developing countries [35] (Table 4).
Firmness and syneresis analysis
Significant differences (p<0.05) were found in firmness (Table
5) and syneresis (Table 6). The values for firmness were highest
for the highest level of papaya juice and gelatine and lowest for
the control yoghurt samples. The papaya yoghurt was significantly
lower syneresis and more firmness than the control. The papaya
juice had the most influence on the textural quality of the yoghurt.
This result could be due to the pectin component of the papaya juice
reinforcing gelatine, which tended to produce resistance to the
structural deformation of the yoghurt. It was speculated that the
addition of the fruit juices to the yoghurt might increase syneresis
and affect the strength of the internal bonds formed in the food. The
ability of a gel to exhibit syneresis, viscosity, rigidity and elasticity
will be affected by the types of protein, the temperature and
time of heating, the protein concentration, and the ionic strength
[36]. Several studies of milk gel interaction and its rheological
properties have previously been reported and noted that various
polysaccharides such as xanthan gum, wheat starch, gelatine
and locust bean gum can be used in yoghurt for higher shear
consistency and viscosity [37-40]. The combination of pectin and
sugar in the presence of acid contributed to the gelling properties
of milk and subsequently affected its texture [41]. An appropriate
thermal process was applied during the sample preparation to
denature the enzymes papain found in papaya juice to avoid the
hydrolytic digestion of milk protein. Proteolytic enzymes would
have interfered with the interaction between milk casein and whey
protein to form the milk-clotting structure [42].
Sensory analysis
Table 5 shows the sensory analysis of the yoghurt samples.
Addition of papaya juice significantly (p<0.5) affected the score of
yoghurt samples by the consumer panelists for appearance, color,
body and texture and overall acceptability (Table 5). Panelists’
rating for appearance and color was similar for all yoghurt samples
but yoghurt with 10% papaya juice was rated significantly (p<0.5)
higher than the (control) without papaya juice (Table 6). Addition
of up to 15% papaya juice received significantly higher mean score
for overall acceptability, which was in the range of 6.20 to 7.55 (i.e.,
in the range between like and like very much). However, addition of
20% papaya juice decreased the ratings to 4.45 to 5.30, which was
between dislike slightly and like slightly.
Yoghurt samples with 10% papaya juice received higher mean
scores for overall acceptance than yoghurt samples with other
all papaya juice levels but the difference in mean scores between
yoghurt sample without papaya juice (control) was not significant
(Table 7). For all sensory attributes, yoghurt samples with 10%
papaya juice had significantly higher mean hedonic scores than the
control (without papaya juice), except for appearance in which case
both samples received similar scores (Table 7).
Most of the scores given by consumers for appearance,
texture, flavor and overall acceptability for each treatment, were
concentrated between 5.50 (like slightly) and 7.50 (like very much),
on the liked part of the scale for all the treatments.
However, despite the unfamiliarity of the consumers to papaya
supplemented yoghurt, participants found the sensory attributes
of yoghurt supplemented with papaya juice to be very acceptable.
This could be explained by the familiarity of consumers for the
individual ingredients, i.e., papaya and milk [43]. In this study,
yoghurt containing 10% papaya juice at all gelatin level had overall
acceptability compared to all the other treatments (Table 7).
Conclusion
Functional and nutritional values of yogurt and fermented dairy
products can be enhanced by adding papaya fruit. In this study, the
physicochemical and the majority of the characteristics of yogurts
remained unaffected. This value-added functional yogurt appeals
to a wide variety of consumers; therefore, it may have the potential
to increase sales in the yogurt market. Generally, the results of the
current study indicated the possibility of producing papaya juice
supplemented yoghurt commercially under small or large-scale
condition.
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