Development of drinking yoghurt by incorporating corn (Zea mays) milk and corn seeds
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Date
2015
Journal Title
Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Cereal grains are considered as important sources of dietary proteins, carbohydrates, vitamins,
minerals and fiber for people all over the world (Chavan and Kadam, 1989). Corn (Zea mays)
is locally grown cereal that can be purchased at low price from several areas in Sri Lanka.
Corn milk is considered as a new innovation, especially in making yoghurt based products.
Vegetable based corn milk yoghurt is an alternative to substitute the cow milk based yoghurt.
Drinking yogurt is the fastest growing food and beverage category in worldwide (Yasni and
Maulidya, 2013). However, still value added drinking yoghurts are rare in Sri Lankan market.
Adding cereal grains is a perfect way to upgrade a drink to a nutritious breakfast. Therefore,
this study was conducted to develop yoghurt by incorporating corn (Zea mays) milk and corn
seed to cow milk.
Methodology
The study was carried out at Lucky Lanka Milk Processing Com. Ltd (LLMP), Matara and
Uva Wellassa University. Six experimental trials with different treatments were conducted. In
trial I, mature fresh corn seeds, mature boiled corn seeds and germinated corn seeds were
separately used to extract corn milk and the best extract of corn milk was evaluated by sensory
properties (odor, taste, color and mouth feel) using untrained panelist. In trial II the most
compatible sugar (8%, 9% and 10% w/v) and gelatin (0%, 0.2% and 0.4% w/v) levels for
different corn milk percentages (5%, 10%, 15% and 20% w/v) were identified. After selection
of appropriate combinations of sugar and gelatin levels, trial III was done to select the best
corn milk incorporation level by narrow downing the corn milk percentages (6%, 8%, 10%,
12% and 14%). Preserved in sugar syrup and boiled corn seeds were crushed into two sizes
(> 3.15 mm and 2 mm –3. 15 mm) to prepare different types of corn seeds. Trial IV was
carried out to select best corn seeds particles on the textural basis and trial V was done to
assess the consumer acceptability for the presence of corn seeds in the corn milk incorporated
drinking yoghurt. Finally three treatments (trial VI) were prepared and evaluated on sensory,
chemical and microbiological properties. The sensory evaluation was done using 35 untrained
panelists. In chemical analysis, proximate analysis (moisture content, crude fat, total solid,
crude protein, ash and crude fiber content) was conducted. pH value and titratable acidity were
evaluated and microbiological analysis was done for Yeast and Moulds, and Escherichia coli
for three weeks in one day interval. The sensory data were analyzed using Friedman
nonparametric test. Complete Randomized Design was conducted and data obtained from
chemical and microbiological tests were analyzed by Analysis of Variance using the General
Linear Model procedure of SAS. Significant means of treatments were separated using the
Least Significant Difference test (P< 0.05).
Result and Discussion
In trial I, boiled corn seeds (mature) based method was selected to extract corn milk. Other
two methods were rejected due to the unpleasant odour and taste which may be due to the
activation of various food enzymes and breaking down the higher molecular components to
simple molecules during germination.
Eight per cent sugar (w/v) for 5% corn milk (w/v) and 10% sugar (w/v) for other 10%, 15%
and 20% corn milk (w/v) incorporation levels were selected due to desirable sweetness. The
gelatin level (w/v) was selected as 0% due to the presence of appropriate drinking yoghurt
properties including texture, mouth feel, appearance and viscosity. The whey separation has
been prevented by stabilizing effect of corn starch in corn milk.
In sensory evaluation, 8% corn milk incorporation level was significantly highly preferred by
panelist with respect to mouth feel, taste and overall acceptability (P<0.05). However, there
is no significant difference in color and aroma of the three treatments (P>0.05) (Figure 01).
Addition of corn milk had no influence to change colour and aroma of the product.
Overall
acceptabilty
6
4
2
0
Aroma
7% corn milk
incorporation level
8% corn milk
incorporation level
Taste
Mouth feel
9% corn milk
incorporation level
Figure 01. Web diagram for level of corn milk incorporation in sensory evaluation
In trial IV, sugar syrup based method was rejected due to hardness of the seeds and crushed
boiled corn seeds were selected. Further, the sensory results revealed that the preference (taste,
aroma, mouth feel, color and overall acceptability) for corn seeds >3.15 mm or 2 mm to 3.15
mm particles incorporated drinking yoghurt is less whereas preference for corn milk
incorporated drinking yoghurt without corn seeds was high. The observed difference is due to
the disturbance for the drinkable property of product by presence of corn seed particles. The
composition of the selected corn milk incorporated drinking yogurt is given in Table 01.
There was a significant difference between treatments for change in pH with the storage period
(P<0.05). pH values of the T8 (with preservative) and control were not changed dramatically.
Control of pH by potassium sorbate could be due to inhibition of the activity of starter culture
by inhibiting various enzymes in microbial cell (Rajapaksha et al., 2013).
There was a significant difference between treatments with respect to acidity (P<0.05) and
titratable acidity increased significantly with storage period and in treatments without
preservatives. According to Rajapaksha et al. (2013), titratable acidity of yogurts increased
over the time and acidity of yoghurt without potassium sorbate increases drastically than other
treatments reflecting the inhibitory activity of potassium sorbate on post fermentation.
Table 01. Composition of select corn milk incorporated drinking yoghurt
Raw material
Percentage
Quantity (g)
Milk
79.54%
867.03
Dairy cream
1.03%
11.33
SMP
1.42%
15.49
Corn milk
8.00%
87.20
Sugar
10.00%
109.00
Total
100.00%
1090.00
There were no contaminations with Coliform and Escherichia coli and thus safe for human
consumption. There were no yeast colonies in T8 and control sample. At day 11, yeast
colonies were exceed the SLS standards of <1000 only in T7 (without preservative).
Proximate analysis revealed all the physiochemical characteristics of corn incorporated
drinking yogurt (protein, fat, ash, fiber and total solid), except moisture significantly higher
compared to plain drinking yoghurt (P<0.05). Usually drinking yoghurt does not contain fiber.
However, due to addition of corn, milk fiber was increased up to 0.5%.
Conclusion
Eight per cent corn milk incorporation level with selected sugar (10%) and gelatin (0%) level
has best consumer preference with respect to the taste, mouth feel and overall acceptability
(P<0.05). Moreover, drinking yoghurt without corn seed particles is preferred by the panelists.
Shelf life of product without potassium sorbate is around 11 days at 4 ºC with respect to
microbiological analysis and physiochemical analysis.
Description
Keywords
Food Science, Food Technology, Animal Sciences, Animal Production Technology