Selective diffusion of glucose, maltose, and raffinose through calcium alginate membranes characterized by a mass fraction of guluronate

Characterization of Alginate-Crystalline Nanocellulose Composite Hydrogel as Polyphenol Encapsulation Agent

Alginate hydrogel is broadly known for its potential as an encapsulation agent due to its compatibility and versatility. Despite its predominance, alginate hydrogel naturally has macropores and a less rigid structure, which leads to syneresis and uncontrolled diffusion of bioactive compounds from the gel network. Combining alginate with other biopolymers has been considered to improve its properties as an encapsulation agent. This research aimed to evaluate the effect of Crystalline Nanocellulose (CNC) to the physical properties and the diffusion of gallic acid (GA), as a water-soluble polyphenol model, through the alginate-CNC composite hydrogels performed as an encapsulation agent. The hydrogel mixtures were made from 1:0, 1:1, 2:0, 2:1, 2:2, and 2:3 solid-basis ratio of sodium alginate:crystalline nanocellulose and evaluated for syneresis, gel strength and stiffness, rehydration properties and gel porosity. Alginate-CNC and GA interaction was observed through zeta-potential analysis and Fourier Transform Infrared (FTIR) spectroscopy. Results showed that composite hydrogel with the highest proportion of CNC increased the gel rehydration capacity (87.33 %), gel strength and stiffness as well as reduced the gel syneresis (14.72 %) and dried gel porosity (0.62). GA pre-loaded gel with 2:2 and 2:3 S-C ratios reduced the diffusion of gallic acid by 92.07-92.27 %. FTIR showed hydrogen bonding between GA and the alginate-CNC hydrogel. Alginate-CNC hydrogel had a fibrous and compact structure as shown in the cryo-SEM and confocal microscope images.

A modular microfluidic bioreactor to investigate plant cell-cell interactions

Plants produce a wide variety of secondary metabolites, which often are of interest to pharmaceutical and nutraceutical industry. Plant-cell cultures allow producing these metabolites in a standardised manner, independently from various biotic and abiotic factors difficult to control during conventional cultivation. However, plant-cell fermentation proves to be very difficult, since these chemically complex compounds often result from the interaction of different biosynthetic pathways operating in different cell types. To simulate such interactions in cultured cells is a challenge. Here, we present a microfluidic bioreactor for plant-cell cultivation to mimic the cell-cell interactions occurring in real plant tissues. In a modular set-up of several microfluidic bioreactors, different cell types can connect through a flow that transports signals or metabolites from module to module. The fabrication of the chip includes hot embossing of a polycarbonate housing and subsequent integration of a porous membrane and in-plane tube fittings in a two-step ultrasonic welding process. The resulting microfluidic chip is biocompatible and transparent. Simulation of mass transfer for the nutrient sucrose predicts a sufficient nutrient supply through the membrane. We demonstrate the potential of this chip for plant cell biology in three proof-of-concept applications. First, we use the chip to show that tobacco BY-2 cells in suspension divide depending on a "quorum-sensing factor" secreted by proliferating cells. Second, we show that a combination of two Catharanthus roseus cell strains with complementary metabolic potency allows obtaining vindoline, a precursor of the anti-tumour compound vincristine. Third, we extend the approach to operationalise secretion of phytotoxins by the fungus Neofusicoccum parvum as a step towards systems to screen for interorganismal chemical signalling.

Pre-purification of Plantago lanceolata extracts with biologically active compounds using yeast cells

Leaves of the plant Plantago lanceolata contain many economically interesting bioactive compounds, among them aucubin and catalpol are the most attractive. However, soluble saccharides passing to water extracts during isolation complicate chromatographic purification of these compounds. Their degradation by microbial cells transforming, for example, glucose, fructose, or sucrose to ethanol could bring important production costs savings and improved final product quality. It has been shown that the best saccharide degradation in extracts is achieved with the Saccharomyces cerevisiae cells. The cells were very active also in their immobilized form and they were able to completely remove glucose from the extract within four hours in a packed bed reactor combined with a stirring system with infinite medium recirculation.

A simple mathematical model involving reaction kinetics and mass transfer limitations in the cell particles was proposed for the evaluation of cell effectiveness in their immobilized form in term of effectiveness factor. Values of the effectiveness factor calculated from the model were far below 1, indicating strong mass transfer limitations of the reaction. The model is suitable for optimization of preparation of immobilized cell particles, mainly from the point of view of cell charge in particles.

Chlorine toxicity to Navicula pelliculosa and Achnanthes spp. in a flow-through system: The use of immobilised microalgae and variable chlorophyll fluorescence

Chlorination is a widely used antifouling method for freshwater and marine applications. Chlorine added to seawater reacts to form oxidants that are toxic to biofouling organisms. Further, the oxidants that result are short-lived, but may nevertheless affect non-target species in waterbodies receiving the antifouling effluent. This study evaluated the toxicity of chlorinated seawater (e.g. following sodium hypochlorite addition) on two different species of marine benthic diatoms (Achnanthes spp., and Navicula pelliculosa), which are representative of microphytobenthos communities - an important component in coastal habitats that may be exposed to chlorinated seawater. To evaluate the growth inhibition over a 72 h period, algae were immobilised in alginate beads and exposed to different levels of chlorination in a flow through system. Growth rates and physiological condition of the microalgae were evaluated using a Fast Repetition Rate fluorometer (FRRf). To determine whether alginate influenced the sensitivity of algal response, studies were also conducted in a static test system (without renewal of test solutions) using both free cells and immobilised cells with initial chlorine added to achieve a similar range of concentrations as those used in the flow-through study. Within the first hour of the exposure period there was an indication that, for both species, the free algal cells in the static system were more sensitive to exposure to chlorinated seawater than were alginate-immobilised cells in the flow through system. Immobilised cells in a static system with a single addition of chlorine were also less sensitive to chlorination than free algal cells. However, for periods of 24 h or more due to decay of TRO in the static system the exposure of immobilised algae in the flow through system had a greater impact and hence lower effect concentrations. For the flow-through studies Achnanthes spp. was the most sensitive after 72 h exposure with a potential no effect concentration EC₁₀ value of 0.02 mg l^-1 as Cl₂ equivalents expressed as total residual oxidants (TRO) compared 0.04 mg l^-1 TRO for N. pelliculosa. Immobilisation of algal cells in alginate was found to be an effective means of determining the impact of chlorination and is likely to be effective for other non-persistent substances. Based on the data produced, the extent and significance of ecological effects of chlorination upon algal species typical of microphytobenthos are likely to be limited providing discharges comply with a maximum allowable concentration of 0.01 mg l^-1 TRO at the edge of an agreed mixing zone.