Improving astaxanthin production of Haematococcus pluvialis by an efficient fed-batch strategy in a photobioreactor

A comprehensive review on the heterotrophic production of bioactive compounds by microalgae

Bioactive compounds derived from microalgae have garnered considerable attention as valuable resources for drugs, functional foods, and cosmetics. Among these compounds, photosynthetic pigments and polyunsaturated fatty acids (PUFAs) have gained increasing interest due to their numerous beneficial properties, including anti-oxidant, anti-viral, anti-bacterial, anti-fungal, anti-inflammatory, and anti-tumor effects. Several microalgae species have been identified as rich sources of bioactive compounds, including the Chlorophyceae Dunaliella and Haematococcus, the Bacillariophyta Phaeodactylum and Nitzschia, and the dinoflagellate Crypthecodinium cohnii. However, most of the reported microalgae species primarily grow through autotrophic mechanisms, resulting in low yields and high production costs of bioactive compounds. Consequently, the utilization of heterotrophic microalgae, such as Chromochloris zofingiensis and Nitzschia laevis, has shown significant advantages in the production of astaxanthin and eicosapentaenoic acid (EPA), respectively. These heterotrophic microalgae exhibit superior capabilities in synthesizing target compounds. This comprehensive review provides a thorough examination of the heterotrophic production of bioactive compounds by microalgae. It covers key aspects, including the metabolic pathways involved, the impact of cultivation conditions, and the practical applications of these compounds. The review discusses how heterotrophic cultivation strategies can be optimized to enhance bioactive compound yields, shedding light on the potential of microalgae as a valuable resource for high-value product development.

Enhancing astaxanthin biosynthesis and pathway expansion towards glycosylated C40 carotenoids by Corynebacterium glutamicum

Astaxanthin, a versatile C40 carotenoid prized for its applications in food, cosmetics, and health, is a bright red pigment with powerful antioxidant properties. To enhance astaxanthin production in Corynebacterium glutamicum, we employed rational pathway engineering strategies, focused on improving precursor availability and optimizing terminal oxy-functionalized C40 carotenoid biosynthesis. Our efforts resulted in an increased astaxanthin precursor supply with 1.5-fold higher β-carotene production with strain BETA6 (18 mg g-1 CDW). Further advancements in astaxanthin production were made by fine-tuning the expression of the β-carotene hydroxylase gene crtZ and β-carotene ketolase gene crtW, yielding a nearly fivefold increase in astaxanthin (strain ASTA**), with astaxanthin constituting 72% of total carotenoids. ASTA** was successfully transferred to a 2 L fed-batch fermentation with an enhanced titer of 103 mg L-1 astaxanthin with a volumetric productivity of 1.5 mg L-1 h-1. Based on this strain a pathway expansion was achieved towards glycosylated C40 carotenoids under heterologous expression of the glycosyltransferase gene crtX. To the best of our knowledge, this is the first time astaxanthin-β-D-diglucoside was produced with C. glutamicum achieving high titers of microbial C40 glucosides of 39 mg L-1. This study showcases the potential of pathway engineering to unlock novel C40 carotenoid variants for diverse industrial applications.

Advancement of Carotenogenesis of Astaxanthin from Haematococcus pluvialis: Recent Insight and Way Forward

The demand for astaxanthin has been increasing for many health applications ranging from pharmaceuticals, food, cosmetics, and aquaculture due to its bioactive properties. Haematococcus pluvialis is widely recognized as the microalgae species with the highest natural accumulation of astaxanthin, which has made it a valuable source for industrial production. Astaxanthin produced by other sources such as chemical synthesis or fermentation are often produced in the cis configuration, which has been shown to have lower bioactivity. Additionally, some sources of astaxanthin, such as shrimp, may denature or degrade when exposed to high temperatures, which can result in a loss of bioactivity. Producing natural astaxanthin through the cultivation of H. pluvialis is presently a demanding and time-consuming task, which incurs high expenses and restricts the cost-effective industrial production of this valuable substance. The production of astaxanthin occurs through two distinct pathways, namely the cytosolic mevalonate pathway and the chloroplast methylerythritol phosphate (MEP) pathway. The latest advancements in enhancing product quality and extracting techniques at a reasonable cost are emphasized in this review. The comparative of specific extraction processes of H. pluvialis biological astaxanthin production that may be applied to large-scale industries were assessed. The article covers a contemporary approach to optimizing microalgae culture for increased astaxanthin content, as well as obtaining preliminary data on the sustainability of astaxanthin production and astaxanthin marketing information.

Abiotic stress as a dynamic strategy for enhancing high value phytochemicals in microalgae: Critical insights, challenges and future prospects

Microalgae showcase an extraordinary capacity for synthesizing high-value phytochemicals (HVPCs), offering substantial potential for diverse applications across various industries. Emerging research suggests that subjecting microalgae to abiotic stress during cultivation and the harvesting stages can further enhance the accumulation of valuable metabolites within their cells, including carotenoids, antioxidants, and vitamins. This study delves into the pivotal impacts of manipulating abiotic stress on microalgae yields, with a particular focus on biomass and selected HVPCs that have received limited attention in the existing literature. Moreover, approaches to utilising abiotic stress to increase HVPCs production while minimising adverse effects on biomass productivity were discussed. The present study also encompasses a techno-economic assessment (TEA) aimed at pinpointing significant bottlenecks in the conversion of microalgae biomass into high-value products and evaluating the desirability of various conversion pathways. The TEA methodology serves as a valuable tool for both researchers and practitioners in the quest to identify sustainable strategies for transforming microalgae biomass into high-value products and goods. Overall, this comprehensive review sheds light on the pivotal role of abiotic stress in microalgae cultivation, promising insights that could lead to more efficient and sustainable approaches for HVPCs production.

Astaxanthin production from the microalga Haematococcus lacustris with a dual substrate mixotrophy strategy

This study investigates the development of dual-substrate mixotrophy strategy to cultivate the microalga Haematococcus lacustris for astaxanthin production. The influence of different concentrations of acetate and pyruvate on biomass productivity was first assessed individually, and then both substrates were used together to improve biomass growth in the green phase and astaxanthin accumulation in red the phase. The results showed that dual-substrates mixotrophy significantly increased the biomass productivity during green growth phase up to 2-fold compared to phototrophic controls. Furthermore, supplementation of dual-substrate to the red phase increased astaxanthin accumulation by 10% in the dual-substrate group compared to single-substrate acetate and no substrate. This dual-substrate mixotrophy approach shows promise for cultivating Haematococcus for commercial production of biological astaxanthin in indoor closed systems.

Microbial astaxanthin: from bioprocessing to the market recognition

The attractive biological properties and health benefits of natural astaxanthin (AXT), including its antioxidant and anti-carcinogenic properties, have garnered significant attention from academia and industry seeking natural alternatives to synthetic products. AXT, a red ketocarotenoid, is mainly produced by yeast, microalgae, wild or genetically engineered bacteria. Unfortunately, the large fraction of AXT available in the global market is still obtained using non-environmentally friendly petrochemical-based products. Due to the consumers concerns about synthetic AXT, the market of microbial-AXT is expected to grow exponentially in succeeding years. This review provides a detailed discussion of AXT's bioprocessing technologies and applications as a natural alternative to synthetic counterparts. Additionally, we present, for the first time, a very comprehensive segmentation of the global AXT market and suggest research directions to improve microbial production using sustainable and environmentally friendly practices. KEY POINTS: • Unlock the power of microorganisms for high value AXT production. • Discover the secrets to cost-effective microbial AXT processing. • Uncover the future opportunities in the AXT market.

Natural Pigments Production and Their Application in Food, Health and Other Industries

In addition to fulfilling their function of giving color, many natural pigments are known as interesting bioactive compounds with potential health benefits. These compounds have various applications. In recent times, in the food industry, there has been a spread of natural pigment application in many fields, such as pharmacology and toxicology, in the textile and printing industry and in the dairy and fish industry, with almost all major natural pigment classes being used in at least one sector of the food industry. In this scenario, the cost-effective benefits for the industry will be welcome, but they will be obscured by the benefits for people. Obtaining easily usable, non-toxic, eco-sustainable, cheap and biodegradable pigments represents the future in which researchers should invest.

A review of natural astaxanthin production in a circular bioeconomy context using Paracoccus carotinifaciens

Astaxanthin (AXT) is a ketocarotenoid with several properties, including antioxidant, antidiabetic and anticancer with a wide range of applications in cosmeceutical, feed, food and pharmaceuticals sectors. The large fraction of AXT available in the market is obtained by chemical route, but the consumers preference for natural products are changing the global market of AXT, and due to that several companies are looking for potential alternative sources such as Gram-negative bacteria Paracoccus carotinifaciens (P. carotinifaciens) to obtain natural AXT. The aim of this critical review is to provide a comprehensive overview of the latest AXT research findings and characteristics of the hyperproducer-AXT P. carotinifaciens. Moreover, a brief description of the potential application of P. carotinifaciens for the production of natural AXT at industrial scale for commercial purposes and the latest advancements in the upstream and downstream procedures following the biorefinery and circular economy percepts are considered.

Optimization of culture medium and scale-up production of astaxanthin using corn steep liquor as substrate by response surface methodology

Astaxanthin is a natural carotenoid with strong antioxidant activity. In this paper, the effects of carbon source, corn steep liquor, distiller grains, and initial pH on the growth and astaxanthin production of Phaffia rhodozyma D3 were evaluated. The optimal medium composition was 32 g/L glucose, 12 g/L corn steep liquor as nitrogen source, and the initial pH was 6.7. Phaffia rhodozyma D3 was cultured in a shake flask under these optimized conditions, the biomass was 6.47 g/L, the astaxanthin/OD₄₇₅ was 15.16, and the astaxanthin content was 1.41 mg/g. The astaxanthin content was further increased to 4.70 mg/g by the combination of TiO₂ stimulation and the expanding cultivation of P. rhodozyma D3 in a 5 L fermenter, which was 2.81 times that of the control group. Expanding fermentation implies the possibility of large-scale production in the astaxanthin industry. Corn steep liquor was used as an alternative nitrogen source to culture P. rhodozyma D3, which could both reduce the production cost of astaxanthin and increased the by-products utilization rate.