Microbial Astaxanthin Production from Agro-Industrial Wastes—Raw Materials, Processes, and Quality

Abstract

The antioxidant and food pigment astaxanthin (AX) can be produced by several microorganisms, in auto- or heterotrophic conditions. Regardless of the organism, AX concentrations in culture media are low, typically about 10–40 mg/L. Therefore, large amounts of nutrients and water are necessary to prepare culture media. Using low-cost substrates such as agro-industrial solid and liquid wastes is desirable for cost reduction. This opens up the opportunity of coupling AX production to other existing processes, taking advantage of available residues or co-products in a biorefinery approach. Indeed, the scientific literature shows that many attempts are being made to produce AX from residues. However, this brings challenges regarding raw material variability, process conditions, product titers, and downstream processing. This text overviews nutritional requirements and suitable culture media for producing AX-rich biomass: production and productivity ranges, residue pretreatment, and how the selected microorganism and culture media combinations affect further biomass production and quality. State-of-the-art technology indicates that, while H. pluvialis will remain an important source of AX, X. dendrorhous may be used in novel processes using residues.

Microalgae, Seaweeds and Aquatic Bacteria, Archaea, and Yeasts: Sources of Carotenoids with Potential Antioxidant and Anti-Inflammatory Health-Promoting Actions in the Sustainability Era

“…Many studies on carotenoid synthesis in yeast cultures have been conducted in synthetic media with pure carbon sources, such as glucose, sucrose, xylose, cellobiose, glycerol, or a combination of some of them [ 253 ]. To lower production costs and in the search for circular economy strategies, many by-products, wastes, and raw materials from agro-industries, such as raw glycerol, brewery effluents, molasses, grape must, and milk whey, have been proposed as alternative carbon sources for carotenoid production [ 226 , 254 , 255 , 256 ].…”

Agro-Industrial Wastewaters for Algal Biomass Production, Bio-Based Products, and Biofuels in a Circular Bioeconomy

“…Some studies demonstrate higher productions of chlorophyll a and b as well as proteins and carbohydrates associated with the presence of determined percentages of vinasse in the media [78,79]. Inoculating a microalgae culture typically cultivated in synthetic media into the agro-industrial residue can lead to a culture crash [3]. This is due to the high concentrations of certain compounds in effluents, which can damage the microalgae osmoregulation and metabolic processes [80].…”

“…The use of agro-industrial residues, produced in huge volumes in agro-industrial and agroenergy processing, could be a way of enabling biofuel production. The idea is to couple a need with an opportunity: the need to carry out biological treatments of agro-industrial liquid effluents and returning clean water to the environment and the opportunity of reclaiming nutrients and water by cultivating microalgae culture in these residues, in raw or minimally treated form [3][4][5].…”