Center for Algal Innovations: ASTA Project

The Problem

Haematococcus pluvialis. cells — *Figure 1. Haematococcus pluvialis.*cells

Astaxanthin is a blood-red pigment that is experiencing heightened attention because of its budding role in several consumer products such as in cosmetics, pharmaceuticals, and as a food additive in agriculture and aquaculture. At the moment the majority (95%) of astaxanthin is being manufactured synthetically by way of petrochemicals, however, there has been considerable interest in developing a market for naturally acquired astaxanthin. Several microorganisms are known to produce astaxanthin biologically and they in turn are responsible for the characteristic reddish color found in shrimp, salmonid fish, and other aquatic organisms. Haematococcus pluvialis (Figure 1.), a green freshwater microalga found around the world, is considered to be the most promising natural producer of astaxanthin due to its high yield and purity. However, the current production cost for astaxanthin derived from H. pluvialis is hampering its progress as it is nearly three times as expensive to produce when compared to its synthetic counterpart.

The Challenge

*Figure 2. Aerial view of net pen aquaculture (Melissa D. Smith)*

The reddish-pink color characteristic of wild salmon has its roots in the pigment astaxanthin which is acquired naturally by the fish as a result of their diet. On the other hand, salmonid fish produced via aquaculture will not develop this reddish-pink coloration and therefore color additives are incorporated into their food to help develop a suitable flesh color critical for the marketplace. Astaxanthin is the pigment frequently used by fish farmers to help bring about the pink color to their cultured product.

Among the many decisions faced by fish farms today is whether to cultivate a healthier and safer product by moving away from lower-priced synthetic chemicals and start incorporating more natural ingredients throughout production. Astaxanthin, for instance, in the form of dried algal meal has been approved by the FDA for specific use in animal food and could feasibly be used to replace the dyes currently used in the industry. Haematococcus pluvialis cells produce astaxanthin as a response to environmental stress (light, salinity, low nutrients) at which time they undergo a life-cycle change from a green vegetative swimming phase to a resting cyst phase, a process thought to be for self-preservation. Astaxanthin production is associated with the formation of these resting cysts, which will also develop complex cell walls. The complex cell walls make it difficult to break down the encysted cells chemically and physically therefore creating challenges for commercial astaxanthin extraction.

The Solution

*Figure 3. Culturing H. pluvialis in a photobioreactor (PBR)*

Currently, worldwide commercial culture of H. pluvialis takes place in open ponds or in continuous culture photobioreactors (PBR) with the cultures allowed to fully encyst. Extracting astaxanthin from the encysted cells remains a costly challenge and the Center for Algal Innovations (CAI) is exploring process improvements that could help shift production away from the complex steps currently used. For example, understanding and manipulating the levels of light and/or nutrients capable of initiating cell stress to increase peak cellular astaxanthin concentrations and/or modifying PBR designs to produce cleaner and/or denser cultures and improving the overall quality of the end product

Current Progress in Astaxanthin

The Center for Algal innovations (CAI) has several ongoing H. pluvialis projects that are investigating the timing of harvest, nutrient enrichment, and improved photobioreactor (PBR) design. Furthermore, we are currently accumulating freeze-dried H. pluvialis intended for use in upcoming salmonid feeding trials with our research partners.