Process optimisation and quality evaluation of fruit pulp based yoghurts
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Date
2019
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Department of Community Science, College of Horticulture,Vellanikkara
Abstract
Yoghurt is a coagulated milk product that results from the fermentation of
lactose in milk by Lactobacillus bulgaricus and Streptococcus thermophilus.
Yoghurt is known for its nutritional, therapeutic and functional properties. The
present study was undertaken to standardise fruit pulp based yoghurts and to
enrich the standardised products with functional ingredients like garden cress
seed and flax seed. The study also envisaged to evaluate the organoleptic, physico
chemical, nutritional and keeping qualities of the standardised products.
Fruit pulp based yoghurts (FPBY) were prepared using locally available
fruits such as sapota, guava, jackfruit (Koozha type), banana (Palayamkodan) and
papaya. Twenty six treatments were evaluated for various organoleptic qualities
and was compared with 100 per cent milk yoghurt (control). In different
treatments tried for the preparation of FPBY, the mean scores for different quality
attributes showed a decreasing trend with increase in the quantity of fruit pulps.
Yoghurts prepared by incorporating 10 per cent fruit pulp was selected as the
most acceptable treatment from all FPBY.
Physicochemical properties like moisture and pH decreased during storage
and a gradual increase in acidity, syneresis, curd tension and viscosity was
observed in FPBY. In the selected products TSS, reducing sugar, total sugar,
energy, carbohydrate, lactose, fat, vitamin C and iron content decreased during
storage. Protein content of freshly prepared control yoghurt was 4.59 per cent and
on 15th day of storage it decreased to 3.35 per cent. The protein content varied
from 3.76 to 2.71 per cent in SPBY (Sapota pulp based yoghurt), 3.23 to 2.61 per
cent in GPBY (Guava pulp based yoghurt), 3.91 to 3.08 per cent in BPBY
(Banana pulp based yoghurt), 4.42 to 3.22 per cent in JPBY (Jackfruit pulp based
yoghurt) and 3.23 to 3.24 per cent in PPBY (Papaya pulp based yoghurt) in initial
and at the end of storage respectively.
Vitamin A and vitamin C content was found to be increased with
incorporation of fruit pulp. The highest calcium content was found to be in
control (78mg/100g) and a slight decrease in calcium content was observed
among FPBY. A slight increase in iron and potassium content was observed in
FPBY compared to control. The highest potassium content was observed in
BPBY with an initial content of 83.25 to 83.05 mg/100g at the end of storage.
The selected FPBY was incorporated with garden cress seeds (GCS) and
flax seeds (FS) at 0.5 per cent and 2 per cent level, respectively. The highest total
organoleptic scores were attained for control (51.67) which was incorporated with
garden cress seeds. This was followed by GPBY (48.45), SPBY (48.33), JFPBY
(47.81), BPBY (46.73) and PPBY (43.72). In flax seeds incorporated yoghurts
the highest organoleptic score was attained for control (40.78) which was
followed by GPBY (40.15), SPBY (40.14), BPBY (39.94), PPBY (39.82) and
JFPBY (39.78). Incorporation of 0.5 per cent garden cress seeds and 2 per cent
flax seeds increased the protein content from 4.59 per cent to 4.78 and 4.93 per
cent respectively. Incorporation of functional ingredients increased the fat, iron,
calcium and potassium content in all yoghurts.
During storage, E coli and coliform bacteria were not detected in all
yoghurt samples. Yeast and fungi was not detected up to 10th day of storage and
at 15th day of storage the presence of yeast and fungi were observed among all the
selected yoghurt samples, indicating a shelf life of ten days.
The cost of production of plain yoghurt was Rs. 13.50/100 ml and for
FPBY it varied from Rs. 17.00 to 20.00/100 ml. Incorporation of functional
ingredients increased the cost of production from Rs. 17.16 to 21.00/100 ml.
The standardised products are suitable for commercialisation and
diversification. Milk based functional food products will be a boon to the dairy
food industry.
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174796