EFFECT OF PROCESSING TECHNIQUE ON PHYSICOCHEMICAL AND FUNCTIONAL PROPERTIES OF DEFATTED CONOPHOR (Tetracarpidium conophorum) NUT FLOUR AND PROTEIN ISOLATES

Abstract

Processing techniques influence functional properties as well as potential application of proteins in food systems. The effect of processing techniques (boiling, and toasting) on conophor nut protein functional properties were determined in order to exploit its full potential as food ingredients. Conophor nuts were purchased from Owena market near Akure, sorted and divided into three portions: one portion was left as raw, the others cooked at 100oC for 30 mins and the last toasted at 120oC for 45mins. These portions were made into flours and evaluated for proximate composition and functional properties. The protein from the defatted flours was isolated by alkaline solubilization (pH 10.0) and acid precipitation (pH 4.5) and the protein obtained dialyzed against distilled water and lyophilized. The protein isolates were evaluated for proximate composition, functional properties and amino acid composition. The results showed the seed contain moisture content of 4.48%, 4.32%, and 4.68%; total ash content 5.04%, 5.55% and 5.78%; crude fat content 53.57%, 55.42%, and 55.71%; crude fibre 5.09%, 4.48% and 3.79%; crude protein 23.58%, 25.40% and 25.57%; carbohydrate content 12.72%, 9.17%, and 9.16% for raw, boiled and toasted full fat samples respectively. The defatted samples contain crude protein 58.95%, 58.86 %, and 59.02%; crude fat 3.98%, 3.87% and 3.76%, total ash 2.54%, 2.77% and 2.32%; crude fibre 3.62%, 3.68% and 2.97%; carbohydrate 30.91%, 30.82%, and 31.93% for raw, boiled and toasted samples respectively. The protein isolates contain crude protein 87.74%, 86.92 %, and 86.86%; crude fat 0.45%, 0.38% and 0.62%, total ash 3.64%, 3.86% and 3.94%; crude fibre 3.66%, 3.98% and 3.92% and carbohydrate 3.67%, 3.96%, 4.66% for raw, boiled and toasted samples respectively. The conophor nut protein isolates from defatted raw flour had the highest water absorption capacity WAC (8.96 g/g), lowest oil absorption capacity OAC (6.11 g/g) and emulsion capacity EC (4.52%). The isolates from toasted flours had the lowest WAC (7.34 g/g), highest OAC (6.24 g/g) and EC (4.86%). The foam stability of the isolates was significantly lower than those of the defatted flours while the emulsion stability was higher. Irrespective of the processing technique, hydrophobic amino acids dominated the amino acid profile but methionine (20.71, 20.71g/100g Protein) and sulphur amino acids are the limiting amino acids (35.89; 30.71g/100g Protein) for lysine and cystein respectively while threonine was the most abundant (95.5; 94.69g/100g Protein). Defatting and toasting improved foaming, emulsion, water absorption capacity and oil absorption capacity of the seed flour. Conophor seed proteins solubility is pH dependent having maximum protein solubility at pH ˂4 and pH ˃10 and minimum solubility at pH 4.The predicted biological value of the conophor nuts proteins were 61, 73 and 77 while the degree of its protein digestibility were 76.14%, 74.33% and 74.51% for raw, boiled and toasted conophor seeds respectively. The functional properties and amino acid profile showed conophor `proteins to be a good source of high quality protein and has potential for use as ingredient in food systems especially in beverages and emulsified foods.