Stabilisation of a DHA-rich oil with green tea extract as antioxidant and its further incorporation into a new hypernutritious product

DHA is an essential long-chain polyunsaturated omega-3 fatty acid (omega-3 LC-PUFA) with multiple health benefits. Due to its essential nature, it is recommended to consume at least 250 mg/day. However, in Western diet, this daily recommendation is generally not met. This has led to numerous attempts to enrich the diet with omega-3 LC-PUFA, but this enrichment is often difficult to implement due to the high sensitivity of these PUFA to oxidation, which can lead to a permanent deterioration in product quality. In this respect, the objectives of this thesis were to promote its consumption by offering a stabilized DHA-rich oil and by incorporating this oil in an easy-to-eat and nutritionally balanced product, while promoting its shelf life for future commercialisation. The work of this master’s thesis was divided into two main parts, one part aimed at stabilising the DHA-rich oil with natural antioxidants, and the second part aimed at incorporating this stabilised DHA-rich oil into a hypernutritious product, referred to as “crackers”. For these purposes, oven storage tests at 30°C or 60°C were carried out to accelerate oxidation, and measurements of peroxide value (PV) and p-anisidine value (p-AV), representing the primary and secondary oxidation compounds, respectively, were carried out during storage. In the first part, aimed at stabilising the DHA-rich oil, the two natural antioxidants tested at different concentrations showed opposite reactions to oxidation. Green tea extract (GTE) showed an antioxidant effect while tocopherol showed a more pro-oxidant effect in the oil. Among the three concentrations of GTE, GTE at 1000 ppm, i.e. the highest concentration, showed the most powerful antioxidant effect. The resulting oil presented significantly lower oxidation values (p < 0.05) than all other samples, during up to 42 days of storage at 30°C for the PV and up to 63 days for the p-AV. In the second part, where the objective was to incorporate this DHA-rich oil into the crackers, several experiments were performed. In the first experiment, carried out at 60°C for 6 days, it was shown that the mode of incorporation of GTE into the carrot-based crackers did not have a significant influence on its antioxidant efficiency. In the second experiment, the two sub-experiments performed at 30°C for 63 days and at 60°C for 3 days, showed similar oxidation patterns. In both experiments, none of the concentrations of GTE, at 1000 ppm or 10,000 ppm (relative to the oil fraction) showed antioxidant power in the carrot-based crackers, and provoked even a more pro-oxidant tendency compared to the control, which was significantly demonstrated for GTE at 1000 ppm at the beginning of storage. While comparing two control crackers (without GTE) during storage, the beetroot crackers showed quite similar oxidation patterns to the carrot crackers. Cooking process (10-12h at 85°C) had a significant effect on the oxidation of the crackers, increasing the formation of primary and secondary oxidation compounds in each sample, particularly in those GTE-supplemented. In conclusion, GTE showed a strong antioxidant effect in the pure DHA-rich oil, but had a neutral or even pro-oxidant effect in crackers, demonstrating that the efficacy of an antioxidant in a food system is strongly influenced by the complexity of a food matrix and many other factors. The inclusion of a DHA-rich oil in these hypernutritious crackers adds nutritional value to the product, helping the consumer to meet the daily recommendation, but its practical implementation is more complicated from an oxidative and organoleptic point of view and deserves further optimization.