Sodium caseinate particles with co-encapsulated resveratrol and epigallocatechin-3-gallate for inhibiting the oxidation of fish oil emulsions

Food is prone to oxidation and the reproduction of harmful microorganisms during the preparation and storage process, which is not conducive to maintaining its quality and nutritional value. Bioactive components such as polyphenols and vitamins are used to fortify food owing to their antioxidant properties. Besides enhancing the quality and nutritional functions of food, they also provide associated physiological benefits. Recent research findings have established that the administration of multiple bioactive components simultaneously could yield excellent bioactivity and stability properties than the single one. This has been observed in different scenarios, including the co-encapsulation of α-tocotrienol and astaxanthin in liposomes. However, most of the related research has focused on bioactive components with the same solubility.

Previous observations have indicated the potential to co-encapsulate various components in homogenous particles based on proteins. In particular, casein has drawn significant research attention owing to its relatively flexible and open conformation. It also exhibits remarkable binding capacity to low-molecular-weight molecules like hydrophilic epigallocatechin-3-gallate (EGCG) and hydrophobic resveratrol as well as to metal ions. Casein and sodium caseinate (prepared via a substitution reaction of casein acid and sodium hydroxide) micelles are natural nano-delivery vehicles for encapsulating and protecting different polyphenols. However, despite the possibility of co-encapsulating various polyphenols in sodium caseinate, there is little understanding of their co-existence and competition. This is of great importance to improve the applications and performance.

Oil-in-water (O/W) emulsions are considered effective vehicles for delivering vitamins and poly-unsaturated fatty acids (PUFAs). Unfortunately, emulsions with higher interfacial area are easily altered than bulk oils. Interfacial antioxidants have been extensively studied to address such limitations. Generally, the addition of antioxidants prevents oxidation by suppressing free radical chain reactions. However, most studies on interfacial antioxidants concentrate on using single polyphenolic compounds for enhancing the oxidative stability of the oil/water emulsions. Notably, co-encapsulated polyphenols could produce enhanced bioactivity or stability properties.

Herein in a new study, Xin Yin, Huanhuan Dong, Hao Cheng, Chuye Ji and Li Liang from Jiangnan University investigated the feasibility of sodium caseinate particles with co-encapsulated EGCG and resveratrol with different solubility in preventing the oxidation and stabilizing of fish oil emulsions. The resulting co-encapsulation was analyzed based on polyphenolic microenvironment, loading efficiency, particle characterization, antioxidant activity and retention properties. The authors purposed to provide a thorough understating of the co-encapsulated antioxidants in homogenous protein particles and their potential application in enhancing food quality and nutritional value. The work is published in the journal, Food Hydrocolloids.

Results showed that at polyphenol concentration of 0.4 mM, the loading efficiencies of resveratrol and EGCG in sodium caseinate particles were about 68% and 98%, respectively. Despite partially masking their cumulative antioxidant activities, co-encapsulation exhibited a higher activity than individual polyphenol encapsulation. The sodium caseinate particles having dual polyphenols successfully stabilized 10% fish oil emulsions with 87% EGCG at the interface between oil and water and 77% resveratrol in the emulsified oil droplets. In addition to improving the resveratrol stability in sodium caseinate particles, co-encapsulated EGCG also protected the fish oil emulsions from oxidation before resveratrol.

In summary, the study demonstrated the stabilization of fish oil emulsions using resveratrol/EGCG-co-encapsulated sodium caseinate particles. The co-encapsulated EGCG significantly enhanced the resveratrol stability in the sodium caseinate particles. It also played a great role in suppressing the oxidation of fish oil emulsions. Overall, the results showcased the effectiveness of using protein particles containing dual antioxidants to protect oil against oxidation. In a statement to Advances in Engineering, Professor Li Liang pointed out that the study insights would promote the application of multiple bioactive compounds in food and pharmaceutical preservation.