Chemical, Functional and Processing Characteristics of Varieties of Melonseeds: Asushie (Cucumerdpsis Epulis Hook.F) and Neri (Citrullus Lanatus Var.Neri. Thunb)

Abstract

Melonseeds namely Agushie variety 1 and variety 2 (Cucumeropsi.s edulis) and Neri (Citrullus lanatus) were studied. These were distinguished from each other by the colour of their seedcoat and1 their size. Neri was found to have the lowest protein content (19.62%) compared to approximately 28% for the agushie. All three melonseeds contained approximately 4-7'/. oil. There was very little carbohydrate in all the varieties and starch was absent. The oils extracted from the three varieties of melonseeds were pale yellow in colour. They had similar physicochemical characteristics. Their high iodine and saponification values suggest the presence of polyunsaturated fatty acids'. Distilled water, 5% sodium chloride and 0.4% sodium hydroxide solutions were used as protein extracting solvents. All three varieties showed very low protein solubility in water. Solubility in 5% sodium chloride was high and nearly al-1 the protein was extracted by 0.<+% sodium chloride in all the varieties. On the basis of pH, agushie variety 1 and neri had their lowest solubility at pH 3.0, and variety 2 had its lowest protein solubility at pH A-.O. The maximum protein solubility in sodium chloride solutions occured at ionic strength 0.6 for all the varieties. Roasting at 140"C did not reduce protein solubility significantly but roasting at 160°C reduced protein solubility considerably. In water, solubility did not decrease when roasting temperature was increased from 160°C to 180°C. In sodium chloride solution however, solubility was further decreased when roasting temperature increased to 180°C. Water absorption capacities of the melonseed flours were low. Agushie variety ￡ had the highest water absorption capacity (WAC) at all ionic strengths. Increasing the incubation temperature above 50°C increased the WAC for all the agushie varieties ConsfcFerably. The increase for neri was not great. Roasting at 14-0°C decreased WAC of the agushie but this increased on roasting “ at 160°C. It remained the same when roasting was at 180°C. The fat absorption capacities of the three varieties were higher than their water absorption capacities. Roasting caused a decrease in fat absorption capacity. This was for all three varieties. The melonseed flours showed good foaming properties. Foams of good structure and stability were obtained at pH 3.0. Foaming in sodium chloride solutions was better than in distilled water - Roasted samples showed very poor foaming properties in water though foams formed at pH 11.0 were very good. The temperature of whipping did not have a marked effect on the initial foam volumes of neri and agushie variety 2. Whipping temperatures above 50°C however increased the foam volume of agushie variety 1 considerably. Stability at 5°C and 80°C was poor for all samples. Emulsifying capacities of the three varieties were also good. When pH was varied the lowest emulsifying capacities were obtained at pH 4.0 for agushie varieties 1 and H and at pH 10.0 for neri. Emulsifying capacities of the three varieties were not markedly different from each other- Roasting above 140°C, and boiling drastically reduced emulsifying capacities of all the varieties. All the varieties showed good emulsifying stabilities. Coagulation studies indicated that all varieties showed lowest coagulation temperature in sodium chloride solutions of ionic strength O.H. On the basis of pH, the best coagulation temperature and biggest clots were obtained in slurries at the natural pH <6.2 to 6.8). No coagulation occured at very acid and alkaline pH's. Slurries of roasted samples <160&C and 180°C) prepared with distilled water did not coagulate when heated. Coagulation however occured on addition of sodium chloride. An emulsion product was formulated, using agushie as emulsifier. The product did not have good shelf stability. Addition of cooked rice flour helped to reduce the separation of water from the emulsion. Stability was better when stored in the cold. A baby food product was also formulated. Agushie and rice flour on the proportion 3:1 was found to to give the best product.Storage under cold temperature improved shelf stability. Freezing and thawing gave the product an undesirable change of consostency and texture. More work needs to be done to improve both products to make them more acceptable and shelf-stable. Examination of the microstructure of the cotyledons of the agushie varieties and neri, showed that their microstructure was very similar Oil and protein bodies occurred in all the cells except the inner and outer epidermal cells.