PubMed Health⌕ Search

Biomedical subjects

Eric Johansen

Publications and source records attributed to Eric Johansen.

6 recordsLinked to original sources
PubMed2006

Characterization of recombinant camel chymosin reveals superior properties for the coagulation of bovine and camel milk.

Enzymatic milk coagulation for cheese manufacturing involves the cleavage of the scissile bond in kappa-casein by an aspartic acid protease. Bovine chymosin is the preferred enzyme, combining a strong clotting activity with a low general proteolytic activity. In the present study, we report expression and enzymatic properties of recombinant camel chymosin expressed in Aspergillus niger. Camel chymosin was shown to have different characteristics than bovine chymosin. Camel chymosin exhibits a 70% higher clotting activity for bovine milk and has only 20% of the unspecific protease activity for bovine chymosin. This results in a sevenfold higher ratio of clotting to general proteolytic activity. The enzyme is more thermostable than bovine chymosin. Kinetic analysis showed that half-saturation is achieved with less than 50% of the substrate required for bovine chymosin and turnover rates are lower. While raw camel milk cannot be clotted with bovine chymosin, a high clotting activity was found with camel chymosin.

Amino Acid Sequence↗
PubMed2005

The long and winding road from the research laboratory to industrial applications of lactic acid bacteria.

Research innovations are constantly occurring in universities, research institutions and industrial research laboratories. These are reported in the scientific literature and presented to the scientific community in various congresses and symposia as well as through direct contacts and collaborations. Conversion of these research results to industrially useful innovations is, however, considerably more complex than generally appreciated. The long and winding road from the research laboratory to industrial applications will be illustrated with two recent examples from Chr. Hansen A/S: the implementation in industrial scale of a new production technology based on respiration by Lactococcus lactis and the introduction to the market of L. lactis strains constructed using recombinant DNA technology.

Biotechnology↗
PubMed2003

Identification of the host determinant of two prolate-headed phages infecting Lactococcus lactis.

A gene responsible for host determination was identified in two prolate-headed bacteriophages of the c2 species infecting strains of Lactococcus lactis. The identification of the host determinant gene was based on low DNA sequence homology in a specific open reading frame (ORF) between prolate-headed phages with different host ranges. When a host carrying this ORF from one phage on a plasmid was infected with another phage, we obtained phages with an altered host range at a frequency of 10(-6) to 10(-7). Sequencing of phage DNA originating from 10 independent single plaques confirmed that a genetic recombination had taken place at different positions between the ORF on the plasmid and the infecting phage. The adsorption of the recombinant phages to their bacterial hosts had also changed to match the phage origin of the ORF. Consequently, it is concluded that this ORF codes for the host range determinant.

Amino Acid Sequence↗
PubMed2003

Challenges when transferring technology from Lactococcus laboratory strains to industrial strains.

Many genetically modified Lactococcus strains have been constructed in research laboratories around the world. Most of these have originated from laboratory strains and therefore there are several barriers to using them in an industrial setting. Laboratory strains are often plasmid-free and consequently Lac- and Prt-, rendering them unable to grow in milk. Many of the commonly used techniques have been optimised for laboratory strains and their application to industrial strains may require a great deal of effort. Often genetically modified organisms produced in the laboratory do not fit the published definition of 'food-grade' (Johansen, 1999, Encyclopedia of Food Microbiology, Academic Press, London, pp. 917-921) and a great deal of effort is required to eliminate undesirable DNA sequences. As a consequence, it is often necessary to recreate the strains in industrial backgrounds before the innovations described in the scientific literature can be applied to the real-world dairy industry.

Biotechnology↗
PubMed2002

Product development strategies for foods in the era of molecular biotechnology.

Breakthroughs in science and technology are accelerating development of new products that are impacting our regulatory systems. Genetically modified or bioengineering plant varieties have entered the food supply on a global basis, especially in the U.S. The U.S. Food and Drug Administration regulates on the premise of 'substantial equivalence' and has developed premarket notification procedures and voluntary labeling guidelines. Japan's Ministry of Health, Labor and Welfare regulates biotechnology products and has imposed biotechnology labeling regulations. However, the EU continues to be in a regulatory gridlock between member states and has proposed strict traceability and labeling guidelines. These requirements are currently restricting imports of bioengineered foods and are creating an international debate. In contrast to bioengineered plant varieties, to our knowledge, there are no strains of lactic acid bacterial starter cultures on the market that contain rDNA. The majority of strains have been improved via selection and mutagenesis. However, conjugation and electroporation have been used to transfer native lactococcal phage resistance plasmids to industrial strains. In addition, plasmids have been introduced to allow for selection of certain characteristics and then been eliminated by curing. The potential benefits of bioengineered foods are far reaching and are one of the most important opportunities of this century. However, bioengineered foods remain an emotional debate that is affecting world trade.

Biotechnology↗