Influence of stinging nettle (Urtica dioica L.) extract-loaded nano-emulsion on the storage stability and antioxidant attributes of Doogh (Traditional Iranian yoghurt beverage)

Abstract

In the present study, stinging nettle extract (SNE)-loaded nano-emulsion was produced utilizing tween 20 and cress seed gum as the wall materials. The developed nanoparticles were evaluated based on their particle size, zeta potential and encapsulation efficiency. Then, fabricated extract-loaded nano-emulsion was added to Doogh as a functionalizing agent (at 5 and 10% w/w concentrations) and consequently the properties of the samples including total phenolic content (TPC), DPPH radical scavenging activity, reducing power (FRAP), pH, acidity, phase stability and sensorial characteristics were assessed during 21 days of storage. The untreated Doogh as well as fortified Doogh with free extract (at 5 and 10% w/w concentrations) were used as the control samples. The average droplet size of the fabricated nano-emulsion was 404.6 nm, the overall formulation possessed a negative charge and the encapsulation efficiency was 58.04%. After 3 weeks of analysis, Doogh sample enriched with 10% SNE-bearing nano-emulsion displayed the highest TPC (30.3 mg GAE/100 mL), DPPH (50%), FRAP (0.76), pH (3.45), and phase stability (64%) as well as the lowest acidity (2.1%) (p < 0.05). SNE possesses astringent and bitter flavors which could limit its application in food products. However, compared to the free extract-enriched Doogh, fortified samples with nano-emulsion had closer sensory characteristics scores to untreated Doogh which clarified the minimization of these undesired flavors following encapsulation. In conclusion, SNE can be successfully entrapped within tween 20 and cress seed gum nano-emulsions with an excellent encapsulation efficiency and be utilized in the functionalization of dairy fermented beverages.