Ultrasound-assisted microalgal docosahexaenoic acid (DHA) nanoemulsion preparation using casein, chitosan, and pectin as emulsifiers for enhanced oxidative stability and shelf life for food fortification

Abstract

The current work examines the effect of three distinct emulsifiers, such as casein, chitosan, and pectin, on the oxidative stability and physicochemical characteristics of docosahexaenoic acid (DHA) nanoemulsions. The DHA nanoemulsion formulated using chitosan (CHDN) had a greater zeta potential value of 42.2 ± 0.75 mV with a particle size of 122.5 ± 2.5 nm initially and maintained electrostatic stability (>30 mV) throughout storage (28 days). The DHA nanoemulsions were further characterized using SEM, FTIR-ATR spectroscopy, and micro-Raman spectroscopy to confirm the presence of DHA in the nanoemulsions. Rheological measurements revealed shear-thinning behavior among nanoemulsions with an increase in shear rate. From the shelf life studies (28 days), it was evident that the DHA nanoemulsion formulated using chitosan (4.94 ± 0.1 Meq O₂ per kg) had significantly (p < 0.05) higher oxidative stability compared to casein (6.4 ± 0.2 Meq O₂ per kg) and pectin (5.7 ± 0.12 Meq O₂ per kg). Furthermore, the encapsulation efficiency of CHDN was found to be 87.33%, as confirmed by GC-FID. Kalakand (a dairy confectionary) fortified with CHDN retained a higher concentration of DHA (92%) compared to neat DHA oil-incorporated kalakand (20%) after 10 days of storage. The physicochemical and textural properties of CHDN-fortified kalakand were significantly higher (p < 0.05) than plain kalakand. Moreover, CHDN-incorporated kalakand had higher sensory attributes. These results demonstrate the successful use of DHA nanoemulsions in food matrices and thereby offer a unique nanoencapsulated DHA-fortified food with increased DHA retention.