Potential of White Jack Bean (Canavalia ensiformis L. DC) Kefir as a Microencapsulated Antioxidant.

Oxidative stress plays a major role in the pathogenesis and progression of noncommunicable diseases. Kefir is a fermented food that has been reported to repress oxidative stress. This study aimed to assess the antioxidant activity, bioactive composition, and encapsulation efficiency of white jack bean (WJB) kefir. The following procedures were conducted: WJB was prepared and converted into juice using water solvent. The sterilized WJB juice was then fermented with kefir grain (10%) for 24∼72 h. Every 24 h, the kefir was evaluated for antioxidant activity, and the dominant bioactive component suspected to be the source of the antioxidant activity was identified. The final stage was the encapsulation process. WJB kefir showed high antioxidant activity, inhibiting DPPH radicals by 90.51±4.73% and ABTS radicals by 86.63±2.34% after 72 h of fermentation. WJB kefir contained 0.35±0.01 mg GAE/g total phenolics and 0.08 mg/g total flavonoids. The LC/MS identification suggested that the bioactive antioxidant components of the WJB kefir were from the alkaloid, saponin, phenolic, and flavonoid groups. The encapsulation with maltodextrin using freeze drying resulted in microencapsulation of WJB kefir with a particle size of 6.42±0.13 µm. The encapsulation efficiency was 79.61%, and the IC50 value was 32.62 ppm. The encapsulation method was able to maintain the antioxidant stability of the kefir and extend its shelf life. WJB kefir, a nondairy, lactose-free kefir, can be used as an antioxidant functional food.

Highly efficient production of 2,3-butanediol from xylose and glucose by newly isolated thermotolerant Cronobacter sakazakii.

BACKGROUND: 2,3-Butanediol (2,3-BD), a valuable compound used for chemicals, cosmetics, pesticides and pharmaceuticals, has been produced by various microbes. However, no high-temperature fermentation of the compound at high productivity has been reported. METHODS: Thermotolerant xylose-utilizing microbes were isolated from 6 different districts in Laos and screened for a low accumulation of xylitol in a xylose medium at 37 ˚C. One isolate was found to produce 2,3-BD and identified by 16S rDNA sequencing. The 2,3-BD fermentation capacity was investigated at different temperatures using xylose and glucose as carbon sources, and the fermentation parameters were determined by a high-performance liquid chromatography system. RESULTS: By screening for a low accumulation of xylitol in a xylose medium, one isolate that accumulated almost no xylitol was obtained. Further analyses revealed that the isolate is Cronobacter sakazakii and that it has the ability to produce 2,3-BD at high temperatures. When xylose and glucose were used, this strain, named C. sakazakii OX-25, accumulated 2,3-BD in a short period before the complete consumption of these sugars and then appeared to convert 2,3-BD to acetoin. The optimum temperature of the 2,3-BD fermentation was 42 ˚C to 45 ˚C, and the maximum yield of 2,3-BD was 0.3 g/g at 12 h in 20 g/l xylose medium and 0.4 g/g at 6 h in 20 g/l glucose medium at 42 ˚C. The 2,3-BD productivity of the strain was higher than the 2,3-BD productivities of other non-genetically engineered microorganisms reported previously, and the highest productivity was 0.6 g/l·h and 1.2 g/l·h for xylose and glucose, respectively. CONCLUSIONS: Among thermotolerant microbes isolated in Laos, we discovered a strain, C. sakazakii OX-25, that can convert xylose and glucose to 2,3-BD with high efficiency and high productivity at high temperatures, suggesting that C. sakazakii OX-25 has the potential for industrial application to produce 2,3-BD as an important platform chemical.

Author Correction: MIG1 as a positive regulator for the histidine biosynthesis pathway and as a global regulator in thermotolerant yeast Kluyveromyces marxianus.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Integration of comprehensive data and biotechnological tools for industrial applications of Kluyveromyces marxianus.

Among the so-called non-conventional yeasts, Kluyveromyces marxianus has extremely potent traits that are suitable for industrial applications. Indeed, it has been used for the production of various enzymes, chemicals, and macromolecules in addition to utilization of cell biomass as nutritional materials, feed and probiotics. The yeast is expected to be an efficient ethanol producer with advantages over Saccharomyces cerevisiae in terms of high growth rate, thermotolerance and a wide sugar assimilation spectrum. Results of comprehensive analyses of its genome and transcriptome may accelerate studies for applications of the yeast and may further increase its potential by combination with recent biotechnological tools including the CRISPR/Cas9 system. We thus review published studies by merging with information obtained from comprehensive data including genomic and transcriptomic data, which would be useful for future applications of K. marxianus.

MIG1 as a positive regulator for the histidine biosynthesis pathway and as a global regulator in thermotolerant yeast Kluyveromyces marxianus.

Kmmig1 as a disrupted mutant of MIG1 encoding a regulator for glucose repression in Kluyveromyces marxianus exhibits a histidine-auxotrophic phenotype. Genome-wide expression analysis revealed that only HIS4 in seven HIS genes for histidine biosynthesis was down-regulated in Kmmig1. Consistently, introduction of HIS4 into Kmmig1 suppressed the requirement of histidine. Considering the fact that His4 catalyzes four of ten steps in histidine biosynthesis, K. marxianus has evolved a novel and effective regulation mechanism via Mig1 for the control of histidine biosynthesis. Moreover, RNA-Seq analysis revealed that there were more than 1,000 differentially expressed genes in Kmmig1, suggesting that Mig1 is directly or indirectly involved in the regulation of their expression as a global regulator.

Functional analysis of Mig1 and Rag5 as expressional regulators in thermotolerant yeast Kluyveromyces marxianus.

To analyze the glucose repression mechanism in the thermotolerant yeast Kluyveromyces marxianus, disrupted mutants of genes for Mig1 and Rag5 as orthologs of Mig1 and Hxk2, respectively, in Saccharomyces cerevisiae were constructed, and their characteristics were compared with those of the corresponding mutants of S. cerevisiae. MIG1 mutants of both yeasts exhibited more resistance than the corresponding parental strains to 2-deoxyglucose (2-DOG). Histidine was found to be essential for the growth of Kmmig1, but not that of Kmrag5, suggesting that MIG1 is required for histidine biosynthesis in K. marxianus. Moreover, Kmrag5 and Schxk2 were more resistant than the corresponding MIG1 mutant to 2-DOG, and only the latter increased the utilization speed of sucrose in the presence of glucose. Kmrag5 exhibited very low activities for gluco-hexokinase and hexokinase and, unlike Schxk2, showed very slow growth and a low level of ethanol production in a glucose medium. Furthermore, Kmrag5, but not Kmmig1, exhibited high inulinase activity in a glucose medium and exhibited greatly delayed utilization of accumulated fructose in the medium containing both glucose and sucrose. Transcription analysis revealed that the expression levels of INU1 for inulinase and GLK1 for glucokinase in Kmrag5 were higher than those in the parental strain; the expression level of INU1 in Kmmig1 was higher, but the expression levels of RAG1 for a low-affinity glucose transporter in Kmmig1 and Kmrag5 were lower. These findings suggest that except for regulation of histidine biosynthesis, Mig1 and Rag5 of K. marxianus play similar roles in the regulation of gene expression and share some functions with Mig1 and Hxk2, respectively, in S. cerevisiae.