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The composition and oxidative stability of vegetarian omega-3 algal oil nanoemulsions suitable for functional food enrichmentAbstract Background: Long chain omega-3 polyunsaturated fatty acid (LCn3PUFA) nanoemulsion enriched foods offer potential to address habitually low oily fish intakes. Nanoemulsions increase LCn3PUFA bioavailability, but may cause lipid oxidation. This study examined oxidative stability of LCn3PUFA algal oil-in-water nanoemulsions created by ultrasound using natural and synthetic emulsifiers during 5-weeks of storage at 4, 20 and 40°C. Fatty acid composition, droplet size ranges and volatile compounds were analysed. Results: No significant differences were found for fatty acid composition at various temperatures and storage times. Lecithin nanoemulsions had significantly larger droplet size ranges at baseline and during storage regardless of temperatures. While combined Tween 40 and lecithin nanoemulsions had low initial droplet size ranges, there were significant increases at 40°C after 5-weeks storage. Gas chromatograms identified hexanal and propanal as predominant volatile compounds, along with 2-ethylfuran; propan-3-ol; valeraldehyde. The Tween 40 only nanoemulsion sample showed formation of lower concentrations of volatiles compared to lecithin samples. Formation of hexanal and propanal remained stable at lower temperatures although higher concentrations were found in nanoemulsions than bulk oil. The lecithin only sample had formation of higher concentrations of volatiles at increased temperatures despite having significantly larger droplet size ranges than the other samples. Conclusions: Propanal and hexanal were the most prevalent of five volatile compounds detected in bulk oil and lecithin and/or Tween 40 nanoemulsions. Oxidation compounds remained more stable at lower temperatures indicating suitability for enrichment of refrigerated foods. Further research to evaluate the oxidation stability of these systems 35 within food matrices is warranted.
Development, Digestibility and Oxidation Properties of LC3PUFA Nanoemulsion and Its Effects on Sensory Profile of FoodThe long chain omega-3 polyunsaturated fatty acids (LC3PUFA) in human diets are mainly derived from oily fish and fish oil based supplements. Currently, the consumption of oily fish in the UK is far below the recommended level. LC3PUFA's non-fish sources such as algal oil with DHA (docosahexaenoic acid) are particularly important for vegetarians, non-fish eaters, and pregnant women. In previous work, high DHA vegetative algal oil load 50% w/w was successfully used to develop an oil-in-water nanoemulsion system suitable for functional food enrichment. The aims of this study included to investigate the effect of selected emulsifiers on oil-in-water nanoemulsions of algal oil prepared using ultrasonic technology. To improve the stability and digestibility of nanoemulsions within an In vitro digestion model. To examine the oxidation stability of nanoemulsions of algal oil and bulk algal oil with composition and droplet size changes during a 5 weeks storage trial at a temperature of 4 °C, 20 °C and 40 °C respectively. To evaluate sensory properties and consumer acceptability of food products with the incorporation of resulted nanoemulsion and find out possible relationship between the sensory profile of foods and the characteristics of added nanoemulsion. Nanoemulsion of LC3PUFA algal oil was developed with selected 6% w/w emulsifiers, including Lecithin (LN), Tween 40 (TN), Tween 60, equal ratio of Tween 40 and lecithin (LTN), 50% w/w Algal oil and 44%w/w water using a homogenizer and ultrasound processor. The results show that the nanoemulsion has been stabilised with selected emulsifiers (LN, TN & LTN) and the smallest droplet size of nanoemulsion was obtained using the combination of lecithin and Tween 40 at ratio 50:50. The In vitro digestion experiments were conducted with a model of fed state gastric and duodenal digestion using method of Lin et al (2014). The results show that the omega-3 oil nanoemulsion (LE/TW 50:50) were stable over 60 min in the gastric phase, in contrast omega-3 nanoemulsion (LE 100%) was destabilised at the gastric phase in 60 min, in which the droplet size diameter was significantly larger than at the beginning of gastric phase (P ≤ 0.05). The droplet size, fatty composition and oxidised compounds were measured to compare bulk algal oil and nanoemulsions stabilised with lecithin (LN) and Tween 40 (TN) solely and in combination (LTN) over a storage period of 5 weeks at temperatures of 4, 20 and 40°C. The results show the droplet size of nanoemulsions had no significant changes for samples stored at tested temperatures over 5 weeks storage. There were no significant differences in DHA composition within the weeks and temperatures used. For the GCHS analysed results, the increase in temperature to 40 ºC and storage time had a significant effect on the development of propanal for all samples (P≤0.05). Nanoemulsions prepared with lecithin alone had significantly higher development of propanal in week 1 at both 40 ºC and 20 ºC (P≤0.05). Lecithin (sole and combination with Tween 40) had more significant increases in oxidised volatiles at 40°C, which may be due to the instability of linoleic acid found in lecithin molecules which located in the outer layer of the oil droplets. There were no significant increase in oxidised compounds from the beginning to the end of storage for all tested samples stored at 4 °C. The sensory testing was also conducted on white sauce incorporated with omega-3 nanoemulsions with selected emulsifiers and bulk algal oil. The results show that the sensory attributes and overall acceptability of foods enriched with omega-3 nanoemulsion were statistically significantly lower than that of control sample (P≤ 0.05). Overall, the smallest droplet size of nanoemulsion was achieved with combination of lecithin and Tween 40 at a ratio of 50:50 by using ultrasonic processor. The stability and digestibility of nanoemulsion with the combination of lecithin and Tween 40 was improved in an In vitro digestion approach. A storage period of 5 weeks and temperature have no significant effect on the droplet size of tested nanoemulsion samples. However, there is a significant increase of the oxidised volatiles at 40 °C for all samples. Sensory testing show the white sauce with nanoemulsion has a stronger fishy taste and less overall liking than with bulk oil, indicating the smaller drop size is more ready to spread and reach the sensors of the mouth.