Development and characterisation of functional walnut oil blends enriched with marine omega-3 fatty acids : A dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Abstract

Walnut oil is rich in PUFAs, particularly linoleic acid (50-63%) and alpha-linolenic acid (11-19%). However, it lacks long-chain omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), essential for brain health and development. It also has a high n-6/n-3 ratio (4:1) which is not ideal for a balanced fatty acid profile. This study aimed to enhance walnut oil’s DHA and EPA content by blending it with four marine-based oils: krill, algal, mussel, Hoki fish oils, at varying concentrations (10%, 20% and 30%, w/w) and to develop functional walnut oil blends. To achieve the goal, this study assessed their fatty acid composition, the effect of blending on the positional distribution of omega-3 fatty acids and the oxidative stability (PV, AV) at room temperature (22℃) over storage periods (0, 3, 6, 9, 30 days). Results showed that walnut oil blended with 30% algal oil (walnut+30% algal) had the highest n-3 content (31.21 g/100 g fatty acids) and DHA concentration (12.8 g/100 g). In contrast, the walnut+30% mussel and walnut+30% Hoki oil blends had lower DHA levels (3.5 and 2.8 g/100 g, respectively). EPA content was similar across walnut+30%-marine based oil (krill, algal and mussel) blends (5.5 - 4.9 g/100 g). ALA was highest (15 g/100g each) in the walnut+10% krill and walnut+10% mussel oil blends, slightly lower in walnut+10% Hoki (14.9 g/100 g) and walnut+10% algal (14.6 g/100 g) oil blends. Positional distribution of fatty acids in triglycerides (TAG) revealed that DHA was mainly retained at sn-2 position in the 30% algal oil blends. EPA was consistently positioned at sn-2 position in all 30% blends. Oxidative stability tests showed that walnut+30% krill oil blend had the best stability (PV, 5.75 meq O2/kg oil after 30 days) while walnut+30% algal oil blend was more prone to oxidation (PV, 14.45 meq O2/kg). However, walnut+30%krill oil blend were more susceptible to hydrolysis (AV, 3.91 mm KOH/g) whereas walnut+30%algal oil blend was more resistant (AV, 3.44 mm KOH/g). This study concluded that walnut+30% krill oil blend offered the best balance of oxidative stability and omega-3 enrichment. The walnut+30% algal oil blend had the highest omega-3 content with DHA predominantly retained at the sn-2 position. These findings suggest that blending walnut oil with marine oils can enhance the nutritional value, making it a potential functional food ingredient. Future studies should investigate storage stability under acceleratetd conditions to better understand shelf life.