Jens Schrader

Bio: Jens Schrader is an academic researcher from DECHEMA. The author has contributed to research in topics: Bioprocess & Methylobacterium extorquens. The author has an hindex of 38, co-authored 129 publications receiving 4239 citations.

Biotechnological production of 2-phenylethanol

Abstract: 2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.

Biotechnological production of astaxanthin with Phaffia rhodozyma / Xanthophyllomyces dendrorhous

Abstract: The oxygenated β-carotene derivative astaxanthin exhibits outstanding colouring, antioxidative and health-promoting properties and is mainly found in the marine environment. To satisfy the growing demand for this ketocarotenoid in the feed, food and cosmetics industries, there are strong efforts to develop economically viable bioprocesses alternative to the current chemical synthesis. However, up to now, natural astaxanthin from Haematococcus pluvialis, Phaffia rhodozyma or Paracoccus carotinifaciens has not been cost competitive with chemically synthesized astaxanthin, thus only serving niche applications. This review illuminates recent advances made in elucidating astaxanthin biosynthesis in P. rhodozyma. It intensely focuses on strategies to increase astaxanthin titers in the heterobasidiomycetous yeast by genetic engineering of the astaxanthin pathway, random mutagenesis and optimization of fermentation processes. This review emphasizes the potential of P. rhodozyma for the biotechnological production of astaxanthin in comparison to other natural sources such as the microalga H. pluvialis, other fungi and transgenic plants and to chemical synthesis.

Applied biocatalysis for the synthesis of natural flavour compounds--current industrial processes and future prospects.

Abstract: The industrial application of biocatalysis for the production of natural flavour compounds is illustrated by a discussion of the production of vanillin, γ-decalactone, carboxylic acids, C6 aldehydes and alcohols (`green notes'), esters, and 2-phenylethanol Modern techniques of molecular biology and process engineering, such as heterologous expression of genes, site-directed mutagenesis, whole-cell biocatalysis in biphasic systems, and cofactor regeneration for in vitro oxygenation, may result in more biocatalytic processes for the production of flavour compounds in the future

Electroactive bacteria—molecular mechanisms and genetic tools

Abstract: In nature, different bacteria have evolved strategies to transfer electrons far beyond the cell surface. This electron transfer enables the use of these bacteria in bioelectrochemical systems (BES), such as microbial fuel cells (MFCs) and microbial electrosynthesis (MES). The main feature of electroactive bacteria (EAB) in these applications is the ability to transfer electrons from the microbial cell to an electrode or vice versa instead of the natural redox partner. In general, the application of electroactive organisms in BES offers the opportunity to develop efficient and sustainable processes for the production of energy as well as bulk and fine chemicals, respectively. This review describes and compares key microbiological features of different EAB. Furthermore, it focuses on achievements and future prospects of genetic manipulation for efficient strain development.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

High-value products from microalgae—their development and commercialisation

Abstract: Microalgae (including the cyanobacteria) are established commercial sources of high-value chemicals such as β-carotene, astaxanthin, docosahexaenoic acid, eicosahexaenoic acid, phycobilin pigments and algal extracts for use in cosmetics. Microalgae are also increasingly playing a role in cosmaceuticals, nutraceuticals and functional foods. In the last few years, there has been renewed interest in microalgae as commercial sources of these and other high-value compounds, driven in part by the attempts to develop commercially viable biofuels from microalgae. This paper briefly reviews the main existing and potential high-value products which can be derived from microalgae and considers their commercial development with a particular focus on the various aspects which need to be considered on the path to commercialisation, using the experience gained in the commercialisation of existing algae products. These considerations include the existing and potential market size and market characteristics of the product, competition by chemically synthesised products or by ‘natural’ compounds from other organisms such as fungi, bacteria, higher plants, etc., product quality requirements and assurance, and the legal and regulatory environment.

The Ehrlich Pathway for Fusel Alcohol Production : a Century of Research on Saccharomyces cerevisiae Metabolism

Abstract: Saccharomyces cerevisiae has been used for at least eight millennia in the production of alcoholic beverages (41). Along with ethanol and carbon dioxide, fermenting cultures of this yeast produce many low-molecular-weight flavor compounds. These alcohols, aldehydes, organic acids, esters, organic sulfides, and carbonyl compounds have a strong impact on product quality. Indeed, the subtle aroma balance of these compounds in fermented foods and beverages is often used as an organoleptic fingerprint for specific products and brands (42). Food fermentation by yeast and lactic acid bacteria is accompanied by the formation of the aliphatic and aromatic alcohols known as fusel alcohols. Fusel oil, which derives its name from the German word fusel (bad liquor), is obtained during the distillation of spirits and is enriched with these higher alcohols. While fusel alcohols at high concentrations impart off-flavors, low concentrations of these compounds and their esters make an essential contribution to the flavors and aromas of fermented foods and beverages. Fusel alcohols are derived from amino acid catabolism via a pathway that was first proposed a century ago by Ehrlich (13). Amino acids represent the major source of the assimilable nitrogen in wort and grape must, and these amino acids are taken up by yeast in a sequential manner (23, 32). Amino acids that are assimilated by the Ehrlich pathway (valine, leucine, isoleucine, methionine, and phenylalanine) are taken up slowly throughout the fermentation time (32). After the initial transamination reaction (Fig. ​(Fig.1),1), the resulting α-keto acid cannot be redirected into central carbon metabolism. Before α-keto acids are excreted into the growth medium, yeast cells convert them into fusel alcohols or acids via the Ehrlich pathway. FIG. 1. The Ehrlich pathway. Catabolism of branched-chain amino acids (leucine, valine, and isoleucine), aromatic amino acids (phenylalanine, tyrosine, and trytophan), and the sulfur-containing amino acid (methionine) leads to the formation of fusel acids and ... Current scientific interest in the Ehrlich pathway is supported by increased demands for natural flavor compounds such as isoamyl alcohol and 2-phenylethanol, which can be produced from amino acids in yeast-based bioconversion processes (14), as well as by the need to control flavor profiles of fermented food products. The goal of this paper is to present a concise centenary overview of the biochemistry, molecular biology, and physiology of this important pathway in S. cerevisiae.