Physico-chemical and antimicrobial properties of d-limonene oil nanoemulsion stabilized by whey protein-maltodextrin conjugates.

In the present investigation d-limonene oil (4-isopropenyl-1-methylcyclohexene) was encapsulated by ultra-sonication method using whey protein (WP)-maltodextrin (MD) conjugates as coating material and their characterization was done with respect to physico-chemical and antimicrobial properties. Antimicrobial activity of limonene oil (LO) nanoemulsion and bulk LO dissolved in dimethyl sulphoxide (DMSO) were assessed by agar well diffusion method. Stable formulation of d-limonene oil nanoemulsion [5.0% LO + 9.0% WP-MD (1:2 w/w) conjugate] had shown mean particle size, zeta potential and poly dispersity index of 116.60 ± 5.30 nm, - 19.64 ± 0.23 mV and 0.205 ± 0.02 respectively. LO nanoemulsion were stable to different food processing conditions like heat treatments, ionic strength (0.1-1.0 M) and pH (3.0-7.0). LO nanoemulsion was stable for 15 days at 25 °C and it had shown particle size of 332.20 ± 5.40 nm at 15th day. It was observed that minimum inhibitory concentration (MIC) of both LO nanoemulsion and bulk LO dissolved in DMSO were at 12.50 µl/ml against Bacillus cereus (ATCC 14459), Escherichia coli (ATCC 25922), Enterococcus faecalis (NCDC 115) and Salmonella typhi (NCDC 6017). Since d-limonene has been considered to be a safer alternative compared to synthetic antimicrobial food additives, the present investigation will be helpful in developing a more effective antimicrobial system for the production and preservation of foods.