The Effect of Microfluidization Pressure and Tocopherol Content on the Retention of Vitamin A in Oil-In-Water Emulsions

Abstract

This work investigates the oxidative stability of vitamin A encapsulated in oil-in-water emulsions, which were prepared by using a microfluidizer. All emulsions were prepared with a fixed content of vitamin A (525 µM), corn oil (10%), water (90%), and whey protein (2%), but varying two main factors: the microfluidizer pressure (10, 50, 100, 200 MPa) and the amount of α-tocopherol (0, 0.25, 0.50, 1.00 mg/g). The content of vitamin A before and after the microfluidization process, and during the subsequent five weeks of storage at 40 °C were determined by HPLC-DAD. The results of the analysis of variance performed either on the data obtained before and after the microfluidization process or during the storage showed that the highest stability of vitamin A was obtained with the highest content of α-tocopherol and with an applied pressure between 100 and 200 MPa. The highest stability was explained by the smaller particle size of the resulting oil droplets. However, high pressures (200 MPa) showed a negative effect on vitamin A retention. These results could be useful for future formulations of retinoids.

Keywords: emulsion; encapsulation; shelf-life study; stability; vitamin A.

Figure 1

Turbiscan stability index (TSI) obtained along the emulsion samples prepared with 2% (w/w) WPI for one (a); two (b); three (c) and four (d) microfluidizer cycles at a pressure of 100 MPa.

Figure 2

Turbiscan stability index (TSI) obtained for the emulsion samples prepared with 0.1% (a); 1% (b) and 2% (c) WPI (w/w) at a pressure of 100 MPa and three microfluidizer cycles.

Figure 3

Surface mean diameter D [3,2] of emulsions prepared with 2% (w/w) WPI as a function of applied pressure at day 1 (A) and after 5 weeks of storage (B).

Figure 4

Effect of the applied pressure on the percentage loss of vitamin A, measured just after the microfluidization step compared to the coarse emulsion before microfluidizer process, for samples containing increasing concentrations of α-tocopherol: (a); 0 mg/g; (b) 0.25 mg/g; (c) 0.50 mg/g; (d) 1.00 mg/g.

Figure 5

Desirability plot reporting the effects of the applied pressure and the concentration of α-tocopherol on the resulting percentage loss of vitamin A, measured after the microfluidization step of emulsion preparation.

Figure 6

Average concentration of vitamin A showing the interaction of factors on its retention during shelf-life storage: (A), pressure (from 10 to 200 MPa) and α-tocopherol (from 0 to 1 mg/g); (B), α-tocopherol (from 0 to 1 mg/g) and time (from 0 to 5 weeks); (C), pressure (from 10 to 200 MPa) and time (from 0 to 5 weeks): (a); 0 mg/g; (b) 0.25 mg/g; (c) 0.50 mg/g; (d) 1.00 mg/g. Points marked with (*) are significantly different (Tukey HSD, p < 0.05).

Figure 7

Correlation plot between percentage losses of vitamin A measured just after the microfluidizer step and after three weeks of storage.