Natural astaxanthin encapsulation: Use of response surface methodology for the design of alginate beads.

Nowadays, consumers are more conscious about healthier products consumption benefits. Astaxanthin obtained from the microalgae Haematococcus pluvialis represents a natural ingredient for the nutraceutical and functional food industries. It is claimed that astaxanthin has much stronger antioxidant activity than vitamin E and ß-carotene, providing different health benefits. However, the unstable structure of the molecule limits its application in functional foods development. Therefore, the present study evaluates the effect of five independent formulation and process variables for natural astaxanthin oleoresin encapsulation using an external ionic gelation technique. Response surface methodology can be used for studying the effect of several factors at different levels and their influences on each other, which overcomes the shortcoming of the traditional orthogonal method. The results showed that alginate and CaCl2 concentrations have a significant effect on particles size obtained, while alginate/oleoresin ratio and surfactant concentration greatly influence the astaxanthin oleoresin release rate. In vitro studies under simulated intestinal conditions showed that astaxanthin oleoresin release process can be described by Hopfenberg model. Three mathematical models were obtained for predicting particle size, astaxanthin release rate and encapsulation yield under different process conditions, providing a platform for microencapsulation technology optimization for healthy food design.

Enhancement of astaxanthin production from Haematococcus pluvialis under autotrophic growth conditions by a sequential stress strategy.

The study of microalgal culture has been growing in recent decades, because the cellular structure of microalgae has diverse highly valuable metabolites that have attract attention of numerous companies and research groups. The pigment astaxanthin is considered one of the most powerful antioxidants in nature. The microalga Haematococcus pluvialis was proposed as one of the best natural astaxanthin sources, because it can accumulate high amount of the pigment. In this work, we studied different stress treatments on H. pluvialis growth cultures as well as astaxanthin production under autotrophic growth conditions. The results showed that extending nitrogen starvation before increasing radiation intensity up to 110 µmol photons m-2 s-1 during late the palmella cell phase incremented the astaxanthin concentration up to 2.7% of dry biomass with an efficient light energy utilization during the stress stage.

Stratification of the radiation field inside a photobioreactor during microalgae growth.

Light availability is a main issue in autotrophic growth of photosynthetic microorganisms. The change of the suspended cells concentration and that of their chlorophylls content during microalgal growth alters the optical properties of the aqueous suspension. This brings about changes in the properties of the radiation field inside the reactor. In this work, we have computed the evolution in time of the local volumetric rate of absorption of photons inside a photobioreactor by means of a Monte Carlo simulation algorithm previously developed. From this study, we have computed two operational variables that are useful tools for the analysis, performance comparison, optimization and scaling up of photobioreactors: the average rate of photon absorption and the volumetric distribution function of photons absorption rates. Based on these two variables, it is possible to systematically quantify the degree of stratification of the culture medium, which is a decisive aspect that hampers the reactor efficiency regarding the energy usage for biomass production.

Analysis and design of photobioreactors for microalgae production I: method and parameters for radiation field simulation.

Having capabilities for the simulation of the radiation field in suspensions of microalgae constitutes a great asset for the analysis, optimization and scaling-up of photobioreactors. In this study, a combined experimental and computational procedure is presented, specifically devised for the assessment of the coefficients of absorption and scattering, needed for the simulation of such fields. The experimental procedure consists in measuring the radiant energy transmitted through samples of suspensions of microalgae of different biomass concentrations, as well as the forward and backward scattered light. At a microscopic level, suspensions of microalgae are complex heterogeneous media and due to this complexity, in this study they are modeled as a pseudocontinuum, with centers of absorption and scattering randomly distributed throughout its volume. This model was tested on suspensions of two algal species of dissimilar cell shapes: Chlorella sp. and Scenedesmus quadricauda. The Monte Carlo simulation algorithm developed in this study, when used as a supporting subroutine of a main optimization program based on a genetic algorithm, permits the assessment of the physical parameters of the radiation field model. The Monte Carlo algorithm simulates the experiments, reproducing the events that photons can undergo while they propagate through culture samples or at its physical boundaries.

Analysis and design of photobioreactors for microalgae production II: experimental validation of a radiation field simulator based on a Monte Carlo algorithm.

In a previous study, we developed a methodology to assess the intrinsic optical properties governing the radiation field in algae suspensions. With these properties at our disposal, a Monte Carlo simulation program is developed and used in this study as a predictive autonomous program applied to the simulation of experiments that reproduce the common illumination conditions that are found in processes of large scale production of microalgae, especially when using open ponds such as raceway ponds. The simulation module is validated by comparing the results of experimental measurements made on artificially illuminated algal suspension with those predicted by the Monte Carlo program. This experiment deals with a situation that resembles that of an open pond or that of a raceway pond, except for the fact that for convenience, the experimental arrangement appears as if those reactors were turned upside down. It serves the purpose of assessing to what extent the scattering phenomena are important for the prediction of the spatial distribution of the radiant energy density. The simulation module developed can be applied to compute the local energy density inside photobioreactors with the goal to optimize its design and their operating conditions.