Encapsulation by Nanostructured Lipid Carriers

Nanostructured lipid carriers (NLCs) are considered as developed SLNs to overcome the problems of SLNs such as low-loading capacity and possibility of expulsion during storage (Fathi et al., 2012). It was first developed by Radtke and Muller (2001). NLCs are produced by similar methods as SLNs but use a mixture of different types of lipids (solid lipids and liquid lipids). The obtained NLCs have higher loading capacity and low expulsion risk.

Similar to the SLNs, NLCs can also be prepared by cold or hot high- pressure homogenization. In recent years, several researches have successfully prepared NLCs loaded with fish oils as core materials. In one of these studies, Zhu, Zhuang, Luan, Sun, and Cao (2015) produced NLCs with high load of krill oil using palm stearin and lecithin by hot homogenization method. They optimized the content of the krill oil and lecithin by central composite design using mean diameter and polydispersity index. According to the results of optimization, usage of 65% krill oil and 1.1% lecithin resulted in the lowest mean diameter and polydispersity index. The obtained NLCs were found to be stable under high-speed centrifugation. Also NLCs were found to be more stable in low-temperature longtime treatment than high-temperature short time application. Chemical stability during storage was also tested and EPA, DHA and astaxanthin content of the NLCs were determined. The NLCs protected the krill oil especially at 4°C and room temperature.

Effectiveness of low-melting lecithin and high-melting lecithin on physical and chemical stability of fish oil-loaded NLCs were evaluated by Salminen, Helgason, Kristinsson, Kristbergsson, and Weiss (2013). NLCs produced with both lecithins were stable during 50 days of storage in terms of their mean diameter. However, high-melting lecithin was found to be more protective against lipid oxidation.

Salminen, Aulbach, Leuenberger, Tedeschi, and Weiss (2014) compared the fish oil-loaded NLCs and nanoemulsions in terms of physical and chemical stability. The content of the fish oil and surfactant was similar in two systems but tristearin was also used in the production of NLCs. Using same surfactant concentration, NLCs yielded in the smaller particles than nanoemulsions. Additionally, NLCs maintained their size throughout the storage. On the other hand, aggregation was observed for the nanoemulsions during storage. NLCs were also more protective against lipid oxidation and had 72%, 53%, and 57% lower content of lipid hydroperoxides, propanal, and hexanal than nanoemulsions, respectively.

Averina, Muller, Popov, and Radnaeva (2011) produced PUFA-loaded NLCs from fish oil and pine seed oil using Tween 80 and Poloxamer 188 as surfactant. According to the results of the study, Poloxamer 188 was a suitable surfactant for both oils in terms of physical stability. Fatty acid compositions of the NLCs slightly changed even at 40°C after storage for 90 days.

Wang et al. (2014) prepared NLCs from microalgal oils using stearic acid and Poloxamer 188 by microfluidization method. The mean size of the carriers was determined as 300—350 nm. High encapsulation efficiency (> 88.8%) was obtained even in high oil concentrations. Higher pH values than 8.0 and high storage temperatures caused increase in both particle size and polydispersity index of the NLCs.

Zhu et al. (2015) studied the effectiveness of the fish oil-loaded NLCs as carrier of the water insoluble ingredients. They first produced stable fish oil- loaded NLCs using glyceryl monostearate and Tween 80 by ultrasonication. Then fluorescein isothiocyanate-loaded NLCs were produced using obtained conditions. Finally, loaded NLCs were tested using cytometric assays. The results showed that NLCs are not only effective to deliver fish oil but also have potential to increase cellular uptake of water insoluble bioactives.

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