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University of Namibia (2018)

Profiling studies of five Namibian indigenous seed oils obtained using three different extraction methods

Cheikhyoussef, Natascha

Titre : Profiling studies of five Namibian indigenous seed oils obtained using three different extraction methods

Auteur : Cheikhyoussef, Natascha

Université de soutenance  : University of Namibia

Grade : Doctor of Philosophy of Science (Biochemistry) 2018

Résumé
Namibia has a rich biodiversity of plant species of which a great variety is used for food, cosmetics and medicinal applications. Seed oil production from indigenous sources has economic importance for Namibia and is an asset for improving the livelihoods of local communities. Knowledge of the quality and composition of these oils can be used towards value-added product development strategies and improved marketing of indigenous resources. A comprehensive profile of indigenous seed oils currently produced in Namibia at traditional and commercial level was developed. This profile included a presentation of the physico-chemical properties of the oils and their quality characteristics among three different extraction techniques, namely the traditional extraction method, machine-operated cold pressing and Soxhlet extraction. The oils studied were Citrullus lanatus (Kalahari melon) oil, Schinziophyton rautanenii (Schinz) Radcl.-Sm. (Manketti) nut oil, Sclerocarya birrea (A. Rich) Hochst. (Marula) nut oil, Ximenia americana (Blue sour plum) nut oil and Acanthosicyos horridus Welw. ex Hook.f. (!Nara) oil. Significant differences (p<0.05) among the three extraction methods for Manketti nut oil were found for the characteristics of AV, p-AV, IV and RI. Cold pressed Manketti nut oil was significantly different (p<0.05) in terms of its PV from the traditionally and the Soxhlet extracted Manketti nut oil, with a higher PV. Significant differences (p<0.05) were found for the characteristics of AV, PV and IV for Marula nut oil. No significant differences (p≥0.05) were found for the p-AV among the three extraction techniques. Significant differences (p<0.05) were found for the characteristic of the RI for Ximenia nut oil. The traditionally extracted Ximenia nut oil was significantly different (p<0.05) from the cold pressed and the Soxhlet extracted Ximenia nut oil for the characteristics of PV and p-AV, with higher values. Significant differences (p<0.05) among the two extraction techniques for the !Nara seed oil were found for the characteristics of SV, AMW, EV, IV, SG and RI and non-significiant differences (p≥0.05) for the characteristics of AV, PV and p-AV. Major fatty acids found were linoleic (31.2-32.2%) acid, α-eleostearic (24.2-35.7%) acid (Manketti), oleic (66-6-67.6%) acid (Marula), oleic (46.3-44.1%) acid, ximenynic (6.5-12.0%) acid (Ximenia), linoleic (52.6-57.0%) acid, oleic (10.5-17.7%) acid (Melon) and linoleic (53.1-54.5%) acid, oleic (12.8-13.9%) acid (!Nara). Highest total tocopherol content found was 205.64 mg/100g (Manketti ; Soxhlet extracted), 29.72 mg/100g (Marula ; traditionally extracted), 10.75 mg/100g (Ximenia ; traditionally extracted), 46.10 mg/100g (!Nara, Soxhlet extracted) and 74.39 mg/100g (Melon ; cold pressed). The highest stigmasterol (53.11 mg/100g) was found in traditionally extracted Marula nut oil and the highest β-sitosterol content (682.43 mg/100g) was found in Soxhlet extracted Manketti nut oil. The hydrolysis of Marula and Manketti nut oils for fatty acid production with Candida rugosa lipase was studied using a 23 full factorial design was applied to study the interactions of experimental factors such as pH, temperature, oil concentration and C. rugosa lipase concentration. The degree of hydrolysis ranged from 49.5% to 77.0% and 56.3% to 75.7% for Manketti oil and Marula oil, respectively. The effect of initial pH, temperature, oil and enzyme concentration and their interaction had significant effect on the degree of hydrolysis of Manketti oil. For the Marula oil hydrolysis, oil concentration, enzyme conentration and the interaction between temperature and oil concentration were observed to be significant. The optimal conditions for achieving a %H of 76.5% for Manketti oil was initial pH of 6.0, a temperature of 30 °C, an oil concentration of 30% and an enzyme concentration of 10 mg/g of oil. The optimal condition for achieving %H of 62.5% for Marula oil hydrolysis, was temperature of 36.8 °C, oil concentration of 11.3% and enzyme concentration of 23.6 mg/g of oil. The present study revealed that the indigenous seed and nut oils obtained from three different extraction techniques have the potential for promotion in the food, in particular as functional foods, cosmetics and the pharmaceutical industry.

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