Degradation of 2-sec-butylphenol:3-sec-butylcatechol, 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid, and 2-methylbutyric acid as intermediates

Pseudomonas sp. strain HBP1 Prp, a mutant of strain HBP1 that was originally isolated on 2-hydroxybiphenyl, was able to grow on 2-sec-butylphenol as the sole carbon and energy source. During growth on 2-sec-butylphenol, 2-methylbutyric acid transiently accumulated in the culture medium. Its concentration reached a maximum after 20 hours and was below detection limit at the end of the growth experiment. The first three enzymes of the degradation pathway - a NADH-dependent monooxygenase, a metapyrocatechase, and a meta-fission product hydrolase - were partially purified. The product of the the monooxygenase reaction was identified as 3-sec-butylcatechol by mass spectrometry. This compound was a substrate for the metapyrocatechase and was converted to 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid which was identified by gas chromatography-mass spectrometry of its trimethylsilyl-derivative. The cofactor independent meta-cleavage product hydrolase used 2-hydroxy-6-oxo-7-methylnona-2,4-dienoic acid as a substrate. All three enzymes showed highest activities for 2-hydroxybiphenyl and its metabolites, respectively, indicating that 2-sec-butylphenol is metabolized via the same pathway as 2-hydroxybiphenyl

Synthesis of highly branched alpha-glucans with different structures using GH13 and GH57 glycogen branching enzymes

Glycogen branching enzymes (GBEs) convert starch into branched alpha-glucan polymers. To explore if the amylose content of substrates effects the structure of the branched alpha-glucans, mixtures of amylose and amylopectin were converted by four thermophilic GBEs. The degree of branching and molecular weight of the products increased with an increasing percentage of amylose with the GH57 GBEs of Thermus thermophilus and Thermococcus kodakarensis, and the GH13 GBEs of Rhodothermus marinas and Petrotoga mobilis. The only exception is that the degree of branching of the Petrotoga mobilis GBE products is not influenced by the amylose content. A second difference is the relatively high hydrolytic activity of two GH57 GBEs, while the two GH13 GBEs have almost no hydrolytic activity. Moreover, the two GH13 GBEs synthesize branched alpha-glucans with a narrow molecular weight distribution, while the two GH57 GBEs products consist of two or three molecular weight fractions

Effect of light and preservatives on the stability of the phycocyanin from the extremophilic red microalgae Cyanidioschyzon merolae

Synthetic dyes are replaced more and more in food products by natural pigments. A growing number of consumers are concerned with the potential health risk and behavior problems related to synthetic dyes. The phycocyanin of the cyanobacterium Arthospira platensis is the only natural blue pigment commercially available. The thermoacidophilic red microalgae Cuanidioschyzon merolae could provide an alternative phycocyanin source. As C. merolae grows at relatively high temperatures (45 to 56°C), the phycocyanin has a high thermostability even at relatively low pH. The stability of the C. merolae phycocyanin was determined for several products of relevant parameters. Average daylight (300-500 Lux) did not significantly affect the stability, while intense light (20,000 Lux) reduced the half-life to 35 hours. The preservatives such as glucose, sucrose, fructose, and sorbitol improved the stability of C. merolae phycocyanin considerably, with 20% glucose resulting in no loss of color at all. The results show that C. merolae phycocyanin can be used in various food products as a natural blue colorant

The influence of amylose content on the modification of starches by glycogen branching enzymes

Glycogen branching enzymes (GBEs) have been used to generate new branches in starches for producing slowly digestible starches. The aim of this study was to expand the knowledge about the mode of action of these enzymes by identifying structural aspects of starchy substrates affecting the products generated by different GBEs. The structures obtained from incubating five GBEs (three from glycoside hydrolase family (GH) 13 and two from GH57) on five different substrates exhibited minor but statistically significant correlations between the amount of longer chains (degree of polymerization (DP) 9-24) of the product and both the amylose content and the degree of branching of the substrate (Pearson correlation coefficient of ≤-0.773 and ≥0.786, respectively). GH57 GBEs mainly generated large products with long branches (100-700 kDa and DP 11-16) whereas GH13 GBEs produced smaller products with shorter branches (6-150 kDa and DP 3-10)