Fermentative intensity of L-lactic acid production using self-immobilized pelletized Rhizopus oryzae

L-Lactic acid is a promising three-carbon building-block chemical, widely used in the food, pharmaceutical, leather and textile industries and Rhizopus oryzae is an important filamentous fungus for the production of L-lactic acid with high optical purity. This study investigated the medium compositions for the maximum biomass cultivation of R. oryzae L-lactic acid fermentation, and optimized the operation parameters for semi-continuous repeated fermentation in a stirred tank fermentor using response surface method (RSM) analysis. The results indicated that a higher biomass cultivation of 3.750±0.05 g/L was achieved when the medium was composed of 12% (w/v) glucose, 0.4% (w/v) ammonium sulfate and 0.045% (w/v) monopotassium phosphate. The optimal fermentation conditions for the initial batch were as follows: the aeration was 0.75 L/(L·min), inoculation of germs was 11% and agitation speed was 560 rpm. The fermentative intensity of the initial batch and the sequentially repeated batches with self-immobilized pelletized R. oryzae were 2.162 g/(L·h) and 3.704 g/(L·h), respectively. Key words: Self-immobilized, Rhizopus oryzae, pellet, lactic acid, response surface method (RSM)

Effect of Infrared Pretreatment on Quality and Storage Stability of Cold-Pressed Pecan Oil

After infrared (IR) pretreatment for 22, 41, 68, 104 and 148 s, the internal temperature of pecan kernels reached 70, 90, 110, 130 and 150 ℃, respectively. To investigate the effect of IR pretreatment on the quality and storage stability of cold-pressed pecan oil, oil yield, fatty acid composition, lipid concomitants, physicochemical indicators, microstructure, and antioxidant capacity and storage stability were analyzed. The results showed that IR pretreatment increased the oil yield of pecan kernels by 11.10%–58.42% compared with the control group, but had no significant effect on the fatty acid composition of cold-pressed pecan oil. Moreover, IR pretreatment significantly the activities of lipase and polyphenol oxidase in pecan oil (P 0.05), and a 23.52% and 13.16% increase in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and ferric reducing antioxidant power (FRAP), respectively, thereby significantly enhancing the storage stability. To summarize, IR pretreatment for 148 s is the best pretreatment method to obtain cold-pressed pecan oil. The results of this study provide a theoretical basis for the application of IR pretreatment in the preparation of cold-pressed pecan oil

Effect of prodigiosin on the alleviation of the intestinal inflammation of weaned rats based on 1H-NMR spectroscopy study and biochemistry indexes

Weaning results in intestinal dysfunction, mucosal atrophy, transient anorexia, and intestinal barrier defects. In this study, the effect of prodigiosin (PG) on the intestinal inflammation of weaned rats was investigated by using 1 H-NMR spectroscopy and biochemistry indexes to regulate the intestinal metabolism. After administration for 14 days, the body mass of the PG group was increased by 1.29‑ and 1.26-fold compared with those of the control and alcohol groups, respectively, using a dose of 200 μg PG·kg-1 body weight per day. PG increased organic acid content and decreased moisture, pH values, and free ammonia in feces. In addition, PG alleviated the intestinal inflammation of weaned rats. The analysis of 1 H-NMR signal peak attribution and the model validation of metabolic data of feces contents showed that PG significantly affected the metabolism of small molecular compounds in the intestinal tract of weaned rats. This study presents the promising alternative of using PG to alleviate intestinal inflammation effectively in the intestinal tract of weaned rats

Heterologous signal peptides-directing secretion of Streptomyces mobaraensis transglutaminase by Bacillus subtilis

Microbial transglutaminase (MTG) from Streptomyces mobaraensis has been widely used for crosslinking proteins in order to acquire products with improved properties. To improve the yield and enable a facile and efficient purification process, recombinant vectors, harboring various heterologous signal peptide-encoding fragments fused to the mtg gene, were constructed in Escherichia coli and then expressed in Bacillus subtilis. Signal peptides of both WapA and AmyQ (SP wapA and SP amyQ ) were able to direct the secretion of pre-pro-MTG into the medium. A constitutive promoter (P hpaII ) was used for the expression of SP wapA -mtg, while an inducible promoter (P lac ) was used for SP amyQ -mtg. After purification from the supernatant of the culture by immobilized metal affinity chromatography and proteolysis by trypsin, 63.0 ± 0.6 mg/L mature MTG was released, demonstrated to have 29.6 ± 0.9 U/mg enzymatic activity and shown to crosslink soy protein properly. This is the first report on secretion of S. mobaraensis MTG from B. subtilis, with similar enzymatic activities and yields to that produced from Escherichia coli, but enabling a much easier purification process

Glycated Soy β-Conglycinin Nanoparticle for Efficient Nanocarrier of Curcumin: Formation Mechanism, Thermal Stability, and Storage Stability

In this study, soy β-conglycinin (7S) was glycated with dextran of different molecular masses (40, 70, 150, 500 kDa) by the dry-heating method to synthesize soy β-conglycinin-dextran (7S-DEX) conjugates. The curcumin (Cur) loaded nanocomplexes were prepared based on 7S-DEX conjugates by a pH-driven self-assemble strategy to enhance the solubility and thermal stability of curcumin. Results showed that the 7S-150 conjugates (glycated from 7S with dextran (150 kDa)) could remain stable in the pH 3.0–pH 8.0 range and during the heat treatment. The results of fluorescence quenching and FT-IR indicated that glycated 7S were combined with curcumin mainly by hydrogen bonding and hydrophobic interaction, and 7S-150 conjugates had higher binding affinity than natural 7S for curcumin. The loading capacity (μg/mg) and encapsulation efficiency (EE%) of 7S-150-Cur were 16.06 μg/mg and 87.51%, respectively, significantly higher than that of 7S-Cur (12.41 μg/mg, 51.15%). The XRD spectrum showed that curcumin was exhibited in an amorphous state within the 7S-150-Cur nanocomplexes. After heating at 65 °C for 30 min, the curcumin retention of the 7S-150-Cur nanocomplexes was about 1.4 times higher than that of free curcumin. The particle size of 7S-150-Cur nanocomplexes was stable (in the range of 10–100 nm) during the long storage time (21 days)

Improvement of the activity and thermostability of microbial transglutaminase by multiple-site mutagenesis

<p>Microbial transglutaminase (MTG) is an enzyme widely used in the food industry. Mutiple-site mutagenesis of <i>Streptomyces mobaraensis</i> transglutaminase was performed in <i>Escherichia coli</i>. According to enzymatic assay and thermostability study, among three penta-site MTG mutants (DM01-03), DM01 exhibited the highest enzymatic activity of 55.7 ± 1.4 U/mg and longest half-life at 50 °C (418.2 min) and 60 °C (24.8 min).</p

Fermentation Process and Metabolic Flux of Ethanol Production from the Detoxified Hydrolyzate of Cassava Residue

With the growth of the world population, energy problems are becoming increasingly severe; therefore, sustainable energy sources have gained enormous importance. With respect to ethanol fuel production, biomass is gradually replacing grain as the main raw material. In this study, we explored the fermentation of five- and six-carbon sugars, the main biomass degradation products, into alcohol. We conducted mutagenic screening specifically for Candida tropicalis CICC1779 to obtain a strain that effectively used xylose (Candida tropicalis CICC1779-Dyd). By subsequently studying fermentation conditions under different initial liquid volume oxygen transfer coefficients (kLα), and coupling control of the aeration rate and agitation speed under optimal conditions, the optimal dissolved oxygen change curve was obtained. In addition, we constructed metabolic flow charts and equations to obtain a better understanding of the fermentation mechanism and to improve the ethanol yield. In our experiment, the ethanol production of the wild type stain was 17.58 g·L−1 at a kLα of 120. The highest ethanol yield of the mutagenic strains was 24.85 g·L−1. The ethanol yield increased to 26.56 g·L−1 when the dissolved oxygen content was optimized, and the conversion of sugar into alcohol reached 0.447 g·g−1 glucose (the theoretical titer of yeast-metabolized xylose was 0.46 g ethanol/g xylose and the glucose ethanol fermentation titer was 0.51 g ethanol/g glucose). Finally, the detected activity of xylose reductase and xylose dehydrogenase was higher in the mutant strain than in the original, which indicated that the mutant strain (CICC1779-Dyd) could effectively utilize xylose for metabolism