Background: Rhizopus arrhizus is a potential microorganism for lipase production. Solid-state fermentation is used for microbial biosynthesis of enzymes, due to advantages, such as high productivity, utilization of abundant and low-cost raw materials, and production of enzymes with different catalytic properties. Objective: The objective of the research is optimization of the conditions for lipase production in solid-state fermentation by Rhizopus arrhizus in a nutrient medium, containing agroindustrial wastes. Method: Biosynthesis of lipase in solid-state fermentation by Rhizopus arrhizus was investigated. The effect of different solid substrates, additional carbon and nitrogen source, particles size and moisture content of the medium on enzyme production was studied. Response surface methodology was applied for determination of the optimal values of moisture content and tryptone concentration. A procedure for efficient lipase extraction from the fermented solids was developed. Results: Highest lipase activity was achieved when wheat bran was used as a solid substrate. The addition of 1% (w/w) glucose and 5% (w/w) tryptone to the solid medium significantly increased lipase activity. The structure of the solid medium including particles size and moisture content significantly influenced lipase production. A mathematical model for the effect of moisture content and tryptone concentration on lipase activity was developed. Highest enzyme activity was achieved at 66% moisture and 5% (w/w) tryptone. The addition of the non-ionic surfactant Disponyl NP 3070 in the eluent for enzyme extraction from the fermented solids increased lipase activity about three folds. Conclusion: After optimization of the solid-state fermentation the achieved 1021.80 U/g lipase activity from Rhizopus arrhizus was higher and comparable with the activity of lipases, produced by other fungal strains. The optimization of the conditions and the use of low cost components in solid-state fermentation makes the process economicaly effective for production of lipase from the investigated strain Rhizopus arrhizus.
The possibilities of using low-esterified amidated pectin isolated from Bulgarian plant cultures have been studied. The comparison between pectin extracted from celery and commercial low-esterified amidated pectin showed that celery pectin can be used successfully for preparation of functional fermented dairy products enriched with soluble dietary fibers. It was found that the addition of amidated pectin extracted from celery in an amount exceeding 1 g.kg-1 deteriorates the organoleptic characteristics of the product, but viscosity of the produced experimental dairy product remained unchanged in comparison with that of the control sample. Therefore, it is recommended that the concentration of low-esterified amidated pectin used in preparation of dairy products do not exceed the limits established in this study.
Background: Purification of enzymes by conventional methods such as precipitation and chromatographic techniques is a costly and time-consuming procedure and may lead to low yields of enzyme activity. Alternative liquid-liquid extraction methods such as Aqueous Two-Phase Systems (ATPS) and Three Phase Partitioning (TPP) are characterized by the high enzyme yields and purification degree. Objective: The objective of this study was the application of partitioning systems ATPS and TPP for purification of lipase produced in solid-state fermentation by Rhizopus arrhizus. Methods: ATPS and TPP were used for purification of lipase, obtained by solid state cultivation of Rhizopus arrhizus. Results: Lipase was isolated with PEG4000/potassium sodium tartrate ATPS and the effect of the system composition, including PEG 4000 and potassium sodium tartrate concentrations on lipase partitioning was studied. When using 30% PEG4000/21% potassium sodium tartrate, lipase was distributed in the top phase, and the highest recovery yield of 217% and purification fold of 6.1 were achieved. It was found that at PEG4000 concentration of or higher than 15%, the enzyme was present in the top polymer-rich phase with a partitioning yield of over 90%. Upon application of TPP for lipase isolation, the effect of t-butanol concentration, ammonium sulfate concentration and pH on enzyme partitioning was investigated. The highest lipase recovery yield of 71% and 19.1-fold purification were achieved in the interfacial phase in the presence of 30% ammonium sulfate saturation with 1.0:0.5 crude extract/t-butanol ratio at pH 7 in a single step. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis and zymographic analysis showed significant purification of lipase by TPP and the presence of two multiple forms of the enzyme. Conclusion: ATPS (PEG4000/ Potassium sodium tartrate) and TPP (1.0:0.5 crude extract/t-butanol ratio, 30% ammonium sulfate saturation, pH 7) proved to be rapid methods for the isolation and purification of lipase and they can be used in downstream processing for industrial preparation of the enzyme.
In the present work, ice cream mixtures with 5%, 10% and 15% lingonberry extract were studied. The lingonberry (Vaccinium vitis-idaea L.) is a source of anthocyanins and flavonoids, which are the bioactive components with good antioxidant properties. There was a significant increase in antioxidant activity (p<0.05) from 133.3 ± 5.6 mM TE/100 g to 249.8 ± 8.3 mM TE/100 g (ABTS method) with increasing the concentration of the extract from 5% to 15%, respectively. Significant changes (p<0.05) in the acidity and dry matter of the samples with lingonberry extract were recorded. After 30 days of storage, a decrease in the antioxidant properties (p<0.05) of the ice cream samples was observed but higher values (mM TE/100 g) were maintained compared to the sample without extract. The color characteristics of the samples were also influenced by the concentration of the extract used. During storage, the highest stability of the colorimetric index a* (red component) was established, which indicates relative color stability during storage.
Spirulina platensis is a cyanobacterium (blue-green algae) that grows in alkaline waters. In food industry, Spirulina’s phycocyanin is used as a natural colorant and stabilizer. The influence of three different concentrations of Spirulina platensis (0.5%, 1% and 1.5%) on physicochemical, textural, antioxidant and sensory parameters of ice cream was studied. It was found that with increasing spirulina concentration, the overrun increases from 30.6% (IC–0) to 48.3% (IC–3). The analysis of texture profile (hardness, adhesiveness, cohesiveness, gumminess) of samples showed a statistically significant difference (p<0.05) between reported values for control sample (IC–0) and the samples with spirulina. Ice cream samples supplemented with spirulina differed with significant increase (p<0.05) in antioxidant activity from 2.8±2.2 mM TE/100 g DW (control sample) to 112.9±4.1 mM TE/100 g DW (IC–3). The addition of Spirulina platensis in ice cream mixture improves its quality and antioxidant properties.
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