Exploring the functionality of coconut proteins

• 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.

• Popular Abstract in English The potential of coconut proteins as food ingredients was studied with the aim of evaluating how plant proteins, in particular those from coconut, could find industrial applications and compete with proteins of animal origin based on meat, fish, milk or eggs. Three research directions were chosen for investigation, to evaluate how coconut proteins would perform in each of the following situations: Would coconut proteins be able to keep stable oil in water dispersions (emulsions), as in cows’ milk? Do coconut proteins stiffen when heated, like when an egg is boiled? Does full-fat coconut milk, heat-treated and homogenised, behave like mayonnaise, showing some initial resistance to flow under stress? These questions address important issues, as they can provide a general picture regarding the potential of coconut proteins for further investigation. There is a growing segment of vegetarians demanding nutritious protein products, comparable to those of animal origin. Products comparable to cows’ milk, yoghurt, butter, cheese, but based on plant ingredients, are desirable. However, the results were only satisfactory for the final two issues. In particular we were able to manufacture an additive free stable coconut milk despite the challenging properties of the coconut protein. This achievement was possible by using heat treatments and by concentrating the emulsion to obtain a loose gel like system. To understand the role of proteins in food systems, it is first necessary to determine the protein structure and intrinsic properties, such as amino acid composition, physical and thermal stability, and solubility. This then allows evaluation of the behaviour of protein in a particular food product. These properties are very important in food processing, as they determine characteristics such as texture, hardness, viscosity, and water and fat absorption. Plant oilseeds, including coconut, store reserve proteins for embryo growth during germination, and these proteins also have great potential for human consumption. They provide well-balanced nutrients, are cheap, widely available, and renewable. World oilseed production was 380 million tons in 2005 and protein meal 207 million, 69% derived from soya bean. Coconut protein has been overlooked for decades, unlike coconut oil, which is still the most important product in the sector. Despite the moderate protein content in the fresh coconut kernel (3-4%), the annual global output of 60 million tons of coconut provides a potential source of approximately 5000 tons of protein, which today is not utilized at all. The technology used in oil extraction is detrimental to the quality of coconut protein, because of negative effects arising from high processing temperatures, traces of solvents, and insect contamination during copra desiccation. This makes the protein unfit for human consumption. Our experiments were carried out using mild wet processing conditions, on fresh materials to meet food quality standards.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Annan teknik -- Livsmedelsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Other Engineering and Technologies -- Food Engineering (hsv//eng)

Nyckelord

Coconut

coconut milk

extraction

proteins

emulsions

functional properties

denaturation

gels

yield stress

glass structure

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