Characterisation of Cowpea Protein Isolate and Its Application in Rice Bran Oil-in-Water Emulsion

Tan, Pang Yu (2025) Characterisation of Cowpea Protein Isolate and Its Application in Rice Bran Oil-in-Water Emulsion. Masters thesis, Tunku Abdul Rahman University of Management and Technology.

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Abstract

Cowpea is a valuable plant-based protein source with high nutritional content, and its protein isolate (CPI) shows potential as an emulsifier due to its amphiphilic properties. Rice bran oil (RBO), being rich in bioactive components like γ-oryzanol and tocopherols, offers various health benefits as well. This highlights the potential of CPIemulsified RBO emulsions in food applications. This study aimed to evaluate emulsifying potential of CPI in producing RBO emulsion, using whole cowpea powder (WCP) and soy protein isolate (SPI) as controls. Stage one focused on the nutritional and physical characterisation of CPI, including proximate composition and antinutritional factors. Stage two examined how pH, temperature, and ionic strength affect the physicochemical and emulsifying properties of CPI. Stage three focused on the development and characterisation of CPI-emulsified emulsions developed under factors such as sample concentration, RBO concentration, homogenisation speed, and time. The CPI produced via isoelectric precipitation showed a crude protein content of 87.32 ± 0.71%, higher than WCP (23.27 ± 0.53%) but lower than SPI (91.22 ± 0.37%), with a percentage yield of 19.51 ± 0.84%. The highest emulsifying stability index for CPI (74.31 ± 2.26 min) was achieved at pH 7, 25 °C of temperature, and 200 mM NaCl of ionic strength, which is lower than SPI (105.26 ± 1.97 min). The lowest creaming index of CPI-emulsified emulsion (5.61 ± 0.43%) was achieved with a 5% CPI concentration, 5% RBO, and 10000 rpm of homogenisation speed for 9 minutes, which is higher than SPI (4.51 ± 0.30%). For oxidative stability, CPI-emulsified emulsion exhibited the lowest peroxide value with a 5% CPI concentration, 20% RBO, and homogenisation for 3 minutes at 5000 rpm. These findings indicate that CPI exhibits promising emulsifying properties for RBO emulsions. Keywords: Cowpea protein isolate; Isoelectric precipitation; Rice bran oil; Homogenisation; Emulsification