Effect of bacterial cellulose addition on physical properties of WPI emulsions. Comparison with common thickeners

In this work, we investigated the role of bacterial cellulose (BC) as a cheaper alternative thickener in o/w emulsions properties compared to xanthan gum (XG) and locust bean gum (LBG) which are highly priced. Emulsions were prepared at pH 3.8 using whey protein isolate (WPI) (2–5% wt) and BC in various concentrations (0–1% wt). Size distribution of the emulsions showed two distinct peaks: the first one (D50 = 600 nm) reflected the oil droplets diameter, as it remained constant for all the emulsions prepared and the second peak reflected aggregated flocs of BC fibrils that remained in the aqueous phase and their size increased as the concentration of BC increased. At lower BC concentrations (0.5–0.7% wt), extensive aggregation between the oil droplets led to unstable emulsions due to bridging interactions. Higher BC concentration (1% wt), resulted in stable emulsions, possibly due to the formation of a BC network between the oil droplets, which prohibited coalescence. The rheological behavior of BC emulsions showed two shear thinning regions, in between which, the viscosity remained constant. The shear rates, at which the plateau was present, increased with increasing BC concentration. Rheological properties of emulsions with XG, LBG or BC were assessed; lower BC concentration (0.1%) was required than XG (0.7%) or LBG (1%) to obtain the same yield stress. BC showed a greater shear thinning behavior than XG and LBG. BC is more efficient to increase the zero-shear viscosity and the rheological profiles of BC-stabilized emulsions with potential interest in the food industry

Ethanol production by Zymomonas mobilis entrapped in alumina pellets

Zymomonas mobilis cells were immobilized on pellets of alumina (Al2O3) by entrapment based on electrostatic forces. Entrapped cells produced 52 g/l-1 ethanol every 24 h for many successive fermentation batches, when inoculated in batch synthetic media containing 12% glucose. It was shown that the rate of growth, ethanol production and glucose utilization increased when Al2O3 was added in the growth medium. This increase was dependent upon the concentration of Al2O3. The optimum conditions for immobilization of Z. mobilis on Al2O3 were established. Reduction in productivity and yield was not observed for up to 15 successive fermentation batches using the same entrapped cells. © 1988 Springer-Verlag

Grape skins as a natural support for yeast immobilization

Grape skins were used to immobilize Saccharomyces cerevisiae. In repeated batch fermentations of grape by immobilized and free cells, the maximum specific rate of alcohol production on glucose decreased from 7.98 h-1 at 25°C to 0.7 h-1 at 5°C. The rate was approximately twice as high as that on fructose. The rates for free cells were very low. The maximum alcohol yield (0.45 g g-1) was obtained at 5°C when the immobilized biocatalyst was used

Vinegar production from corinthian currants finishing side-stream: Development and comparison of methods based on immobilized acetic acid bacteria

Fruit wastes and side-streams can be used for vinegar production to create added value for the agri-food sector and enhance farmer incomes and local economies. In this study, methods for vinegar production by wild and selected acetic acid bacteria (the quick starter Acetobacter aceti and the acid-resistant Komagataeibacter europaeus), free (FC) and immobilized (IC) on a natural cellulosic carrier, are proposed using sweet wine made from the industrial finishing side-stream (FSS) of Corinthian currants as raw material. The results showed all cultures can produce vinegar with 46.65 ± 5.43 g/L acidity, from sweet FSS wine containing 5.08 ± 1.19% alcohol. The effect of immobilization was more obvious in the case of the selected culture, presenting better acetification efficiency, both fresh and after cold storage for 2 months. The vinegars had an antioxidant capacity of 263.5 ± 8.4 and 277.1 ± 6.7 mg/L (as ascorbic acid) and phenolic content 333.1 ± 12.0 and 222.2 ± 2.9 mg/L (as gallic acid) (for FC and IC, respectively). They also had a rich volatilome (140 compounds identified by SPME GC-MS), with higher percentages of esters identified in vinegars made by IC. The results are encouraging for vinegar production with IC of a mixed A. aceti and K. europaeus culture. © 2021 by the authors. Licensee MDPI, Basel, Switzerland