STUDIES ON PREPARATION OF SOY PROTEIN ISOLATE WITH IMPROVED FUNCTIONAL PROPERTIES USING ULTRAFILTRATION TECHNIQUE
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Date
2020
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CIAE BHOPAL ICAR- INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Soy protein isolate (SPI) is the purest form of soy protein having many industrial and food
applications because of its high protein content. Ultrafiltration (UF) is eco-friendly, energy
saving and water conserving process to produce SPI with enhanced functional properties.
Along with its high protein content, good amount of bio active components also promotes
the use of SPI in food applications. Use of UF membrane modules with low molecular
weight cut off (MWCO) may be the solution to prepare SPI with improved functional
properties and to maintain its nutritional value.
The present study attempts to prepare SPI using UF involved optimization of process
parameters of UF, optimization of different drying methods to get maximum protein
powder yield and comparison of physicochemical and functional properties of protein
isolate obtained via UF with commercially available counterpart.
UF process parameters were optimized using Response surface methodology (RSM) -Box
Behnken design. The optimum process parameters of ultrafiltration were obtained from
the desirability function approach, having a desirability of 0.767. Optimised parameters
were membrane module of 13.38 kDa, trans membrane pressure of 117.21 kPa, volume
concentration ratio of 3.6, diafiltration of 1 time and flow rate of 63.04% of pump capacity.
With these optimised conditions, predicted permeate flux was 11.13 LPH, protein content
in retentate was 85.52 % and protein rejection was 98.99 %. Resistance in series model
approach was used to model flux decline in ultrafiltration membrane module and cake
layer resistance was found to be having significant effect on fouling. RSM- 3 level factorial
design was used to optimize spray drying and oven drying conditions. Spray drying
conditions were optimised (inlet air temperature 180°C and air flow rate 0.02 m3
/min) to
get maximum protein yield (97.59%) and minimum moisture content (5.4%) with
desirability 0.838. Oven drying conditions were optimised (drying temperature 47°C and
drying time 48 hours) to get maximum protein yield (98.27%) and minimum moisture
content (4.42%) with desirability 0.722. The physico-chemical and functional properties
of spray dried and oven dried SPIs were compared with freeze dried and commercial SPIs.
Overall protein yield from spray drying, oven drying and freeze drying were 33%, 43%
and 54% respectively. Protein content of ultra-filtered SPI and commercial SPI were
comparable (Approx. 83%). UF-spray dried SPI showed smallest particle size (76μm) with
lighter colour (∆E 12.62). Ultra-filtered SPI exhibited highest values of water solubility
ii
index (8.3% for UF-spray dried SPI), oil absorption capacity (3.2 mL/g of protein for UFspray dried SPI), emulsion properties (51% emulsion stability for UF-spray dried and 62%
emulsion capacity for UF-oven dried SPI), nitrogen solubility index (94%) and protein
dispersibility index (95%). Viscosity in UF- spray dried and freeze dried SPIs showed
shear thickening behaviour. SDS-PAGE showed that the storage proteins in SPI (11S and
7S) were also superior in ultra-filtered SPI spray dried and freeze dried SPIs (73% and
76% respectively). Hence UF along with spray drying or freeze drying can be
recommended as a potential alternative to conventional methods to make high quality
SPIs
Description
T-10422