The Gelatin-Coated Nanostructured Lipid Carrier (NLC) Containing Salvia officinalis Extract: Optimization by Combined D-Optimal Design and Its Application to Improve the Quality Parameters of Beef Burger

Abstract

The current study aims to synthesize the gelatin-coated nanostructured lipid carrier (NLC) to encapsulate sage extract and use this nanoparticle to increase the quality parameters of beef burger samples. NLCs were prepared by formulation of gelatin (as surfactant and coating biopolymer), tallow oil (as solid lipid), rosemary essential oil (as liquid lipid), sage extract (as active material or encapsulant), polyglycerol ester and Tween 80 (as low-molecular emulsifier) through the high-shear homogenization-sonication method. The effects of gelatin concentrations and the solid/liquid ratio on the particle size, polydispersity index (PDI), and encapsulation efficiency (EE%) of sage extract-loaded NLCs were quantitatively investigated and optimized using a combined D-optimal design. Design expert software suggested the optimum formulation with a gelatin concentration of 0.1 g/g suspension and solid/liquid lipid ratio of 60/40 with a particle size of 100.4 nm, PDI of 0.36, and EE% 80%. The morphology, interactions, thermal properties, and crystallinity of obtained NLC formulations were investigated by TEM, FTIR, DSC, and XRD techniques. The optimum sage extract-loaded/gelatin-coated NLC showed significantly higher antioxidant activity than free extract after 30 days of storage. It also indicated a higher inhibitory effect against E. coli and P. aeruginosa than free form in MIC and MBC tests. The optimum sage extract-loaded/gelatin-coated NLC, more than free extract, increased the oxidation stability of the treated beef burger samples during 90 days of storage at 4 and -18 °C (verified by thiobarbituric acid and peroxide values tests). Incorporation of the optimum NLC to beef burgers also effectively decreased total counts of mesophilic bacteria, psychotropic bacteria, S. aureus, coliform, E. coli, molds, and yeasts of treated beef burger samples during 0, 3, and 7 days of storage in comparison to the control sample. These results suggested that the obtained sage extract-loaded NLC can be an effective preservative to extend the shelf life of beef burgers.

Keywords: beef burger; combined D optimal design; gelatin; nanostructured lipid carrier; sage extract; shelf life.

Figure 1

Perturbation plots showing the effect of independent factors on the responses (a) Particle size, (b) Polydispersity index, (c) Zeta Potential, and (d) Encapsulation efficiency. Where A is the solid lipid (w/w %), B is the liquid lipid (w/w %), and C is the gelatin concentration (%).

Figure 2

The encapsulation stability (ES%) of prepared sage extract-loaded nanostructured lipid carriers (SE-NLC) for 60 days at 4 °C and 25 °C. Data are expressed as mean ± SD (n = 3). Bars in the figure without the same superscripts (a–d) represent significant differences at the 0.05 level according to the Duncan test between encapsulation stability in the different day (p < 0.05).

Figure 3

TEM image (I), particle size (II), and zeta potential (III)of the optimized NLC.

Figure 4

Fourier transform infrared (FTIR) spectra of sage extract (SE), gelatin (GL), nanocarrier structure lipid without SE, and GL (NLC without SE, and GL), GL-coated NLC, without SE, and SE-loaded GL-coated NLC (optimum NLC).

Figure 5

Differential scanning calorimetry (DSC) of free sage extract, sage extract-loaded gelatin-coated nanocarrier structure lipid (NLC OPT), NLC without SE (NLC-SE), and NLC-SE without coated gelatin (NLC-SE-GL).

Figure 6

The X-ray diffraction (XRD) pattern of free sage extract (SE), SE-loaded gelatin (GL)-coated nanocarrier structure lipid (NLC optimum), NLC without SE, NLC without SE, and GL.

Figure 7

Antioxidant activity of free sage extract (SE) on day 0, optimum-formulated nanocarrier structure lipid (NLC) on day 0, NLC without extract on day 0, free sage extract (SE) on day 30, optimum-formulated nanocarrier structure lipid (NLC) on day 30, and NLC without extract on day 30. Bars in the figure without the same superscripts (a–e) represent significant differences at the 0.05 level according to the Duncan test between antioxidant activity at different form samples (p $<$ 0.05).

Figure 8

The pH (A), peroxide value (PV) (B), thiobarbituric acid reactive substances (TBARS) (C), and sensory score (D) of beef burger samples treated with free extract, optimum-formulated nanocarrier structure lipid (NLC) with and without extract immediately after production (0), 7 (4 °C), and 90 (−18 °C) days after production. Superscripts (a–d) show significant differences between groups. Bars in the figure without the same superscripts (a and d) represent significant differences at the 0.05 level according to the Duncan test between pH, PV, TBARS, and sensory score at different forms of NLC (p $<$ 0.05).