Microencapsulation of Hibiscus sabdariffa L. Calyx Anthocyanins with Yeast Hulls.

Yeast hulls, due to their specific thin mannoprotein layer and high content of ß-glucan, constitute a promising material to stabilise the colour of anthocyanins. This study evaluates the potential of yeast hulls on the freeze-drying encapsulation of anthocyanins-rich extract from Hibiscus sabdariffa L. calyx with comparison to maltodextrin microcapsules. The moisture content (5.28-16.38%), water activity (< 0.039-0.307) and hygroscopicity (17.50-25.99 g/100 g) of obtained powders were evaluated. The stability of encapsulated anthocyanins, monitored through the total anthocyanin content, was evaluated with the pH differential method immediately after production and after a 10-week storage under different conditions of temperature (5 or 37 °C), humidity (45 or 85% RH), in presence or absence of light. The colour parameters (a, b*, L*, C*, H°, ΔE*) of powders were measured. The results indicated that yeast-hulls showed a good ability to protect anthocyanin against the influence of temperature, light, moisture compared to freeze-dried anthocyanins-rich extracts (p < 0.05). Yeast hulls protected anthocyanin better than maltodextrin under high humidity conditions (p < 0.05).

Encapsulation of Hibiscus sabdariffa L. anthocyanins as natural colours in yeast.

Hibiscus sabdariffa extracts, a rich source of anthocyanin, were subjected to encapsulation in yeast cells. An encapsulation yield (EY) of 208 µg/100 mg of cells and an encapsulation efficiency (EE) of 27%, were reached after optimisation of the ratios (0.5 g wet yeast cells for 5 ml of anthocyanin extracts at 1 g·L-1) and with 10% of ethanol. The storage stability of encapsulated pigments was investigated in water and buffer pH 1.5 at 5 & 37 °C for 10 days and 90 °C for 30 min. The percentage of loss of colour was determined by colourimetry assays. The microparticles made of yeast with or without heat treatment exhibited different protecting effects (P < 0.01). At 37 °C, the percentage of loss of colour in water was of 2.5% for heat-treated and 36.5% for non-treated yeast microparticles, suggesting that yeast enzymes would be responsible for the loss of anthocyanin during storage. These results are confirmed by the percentage of loss of colour which was far lower in conditions of low enzymatic activity: 3.1% at 5 °C for non-heat-treated cells in water. The pH of solvent had also an important effect on the degradation of encapsulated anthocyanin; in buffer at pH 1.5 and 37 °C with the non-heat-treated cells, the degradation decreased strongly to 9.4% compared with 36.5% in water. These results show that yeast cells are a good mean of encapsulation of pigments for a colouring purpose and that they provide anthocyanins a good protection as long as their enzymes are inactivated.