Exploring the functionality of coconut proteins
Abstract: At present, coconut proteins are discarded as a waste product by the coconut oil industry. If the range of applications of coconut proteins is to be expanded, their potential functionalities should be investigated. Emulsions and gels are of the greatest interest in food industry.
Today the dry processing of copra at elevated temperatures is used to optimize the oil recovery. The functionalities of proteins in food are mainly determined by their structure and physicochemical properties, such as amino acid composition and sequence, protein size and conformation, physical and thermal stability, solubility and surface hydrophobicity. The harsh treatment leads to denaturation and loss of protein solubility and functionality.
Wet processing is an alternative method that may yield functional proteins in addition to oil. To explore the functionalities of coconut proteins, protein fractions were obtained using the wet processing method and analysed for molecular size and isoelectric points in electrophoresis, amino acid sequencing from mass spectrometry and also for their capacity to emulsify and stabilise oil-in-water emulsions.
The results showed minimum solubility at pH 3-4, increasing in both sides of the minimum, exhibiting a V-shaped profile. Mass spectrometry and protein fingerprint did not produce conclusive results, as coconut proteomes have not been sequenced and entered in the databases. Protein mapping only matched partially to glutelin OS, tr|Q9SNZ2|Q9SNZ2_ELAGV and 7S globulin, tr|Q9AU64|Q9AU64_ELAGV from oil palm, a cultivar close to Cocos nucifera.
SDS-PAGE showed results close to those already reported, especially for the skim coconut milk proteins. The insoluble protein resolved at 32 and 21 kDa, which correlates closely to the 11S globulin or cocosin, the major coconut globulin protein.
Native coconut proteins were not able to efficiently emulsify and stabilise oil in water emulsion. The droplets were large (13 µm) and high-pressure homogenisation only reduced the droplets size down to 3-5 µm, still not sufficiently small to prevent destabilisation. Flocculation and creaming were the predominant mechanisms of destabilisation. However, under heating to protein denaturation, at 95°C and homogenisation, concentrated coconut milk (40% fat) demonstrated improved physical stability due to formation of a colloidal glass structure.
Coconut protein also demonstrated the ability to form gels with appreciable elastic modulus (G’ > 1000 Pa), but only in neutral to alkaline environments.
The study shows that colloidal glass and gelation are functional properties of coconut proteins that may lead to novel products and potentially of the greater use.
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