Extraction and characterisation of protein fraction from date palm (Phoenix dactylifera L.) seeds
Akasha, Ibrahim Abdurrhman Mohamed
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To meet the challenges of protein price increases from animal sources, the development of new, sustainable and inexpensive proteins sources (nonanimal sources) is of great importance. Date palm (Phoenix dactylifera L.) seeds could be one of these sources. These seeds are considered a waste and a major problem to the food industry. In this thesis we report a physicochemical characterisation of date palm seed protein. Date palm seed was found to be composed of a number of components including protein and amino acids, fat, ash and fibre. The first objective of the project was to extract protein from date palm seed to produce a powder of sufficient protein content to test functional properties. This was achieved using several laboratory scale methods. Protein powders of varying protein content were produced depending on the method used. Most methods were based on solubilisation of the proteins in 0.1M NaOH. Using this method combined with enzymatic hydrolysis of seed polysaccharides (particularly mannans) it was possible to achieve a protein powder of about 40% protein (w/w) compared to a seed protein content of about 6% (w/w). Phenol/TCA extraction gave the protein powder with the highest protein percentage of 68.24% (w/w) and this powder was used for subsequent functional testing. Several factors were found to influence seed protein extraction such as pH, temperature, the extraction time, the solvent to sample ratio and the solvent concentration. Optimum conditions for extraction were found to be pH 10, 45˚C and extraction time of 60 min. The results showed that use of enzymes to hydrolyse and remove seed polysaccharides improved the extraction of date seed protein. Optimal improvement was obtained using Mannaway, which hydrolyses mannans and galactomannans, which gave a powder with 34.82% (w/w) protein compared to the control of 11.15% (w/w) protein. The proteins in the extracted date seed protein were profiled using LC/MSMS. Three-hundred and seventeen proteins were identified. The proteins belonged to all major functional categories. The most abundant proteins were glycinin and β-conglycinin, the two major seed storage proteins of plants. The functional properties of extracted date seed protein were investigated using a range of tests. The thermal properties of date seed proteins were consistent with a powder containing high levels of conglycinin and β-glycinin. The solubility had a similar pH profile to soy protein, but differed in absolute solubility due to differences in non-protein composition. Similarly, water holding and oil holding capacity of date seed protein was lower than for soy protein, probably because of compositional differences. Date seed proteins were able to emulsify oils and had a comparable emulsifying ability and emulsion stability to soy protein isolate. The date seed protein was not a good foaming agent compared to soy protein or whey protein concentrate.