Probiotic and starter bacteria are generally dried to produce easy-to-use ingredients that are stable and flexible for applications in the food, feed and pharmaceutical industry. The overall demand ...for dried probiotic bacteria has increased in the context of a rapidly growing market, evidencing the need for their larger scale production.
The spray-drying of bacteria enables a larger production scale than the freeze-drying currently used; energy costs are lower and the process is sustainable. This is also a promising way to microencapsulate bacteria within various protective matrices to ensure their improved resistance during storage, technological processes and digestive stresses.
This review highlights some key strategies to improve the viability and efficacy of probiotics spray-drying, such as the enhancement of bacterial resistance, improved protection of the drying medium and optimization of the drying process. It also focuses on factors during the pre- and post-drying stages which may influence the quality and efficacy of spray-dried probiotic powders.
•The factors influencing growth, spray drying, storage and application.•Selection of robust strain and application of cellular stress response.•Employment of protective agent coupled with optimization of drying process.•Stability and functionality of spray-dried probiotics.•Current key message, future trends and challenges for spray drying of probiotics.
The swelling of polyelectrolyte hydrogels usually depends on the pH, and if the pH is high enough degradation can occur. A microindentation device was developed to dynamically test these processes in ...whey protein isolate hydrogels at alkaline pH 7⁻14. At low alkaline pH the shear modulus decreases during swelling, consistent with rubber elasticity theory, yet when chemical degradation occurs at pH ≥ 11.5 the modulus decreases quickly and extensively. The apparent modulus was constant with the indentation depth when swelling predominates, but gradients were observed when fast chemical degradation occurs at 0.05⁻0.1 M NaOH. In addition, these profiles were constant with time when dissolution rates are also constant, the first evidence that a swollen layer with steady state mechanical properties is achieved despite extensive dissolution. At >0.5 M NaOH, we provide mechanical evidence showing that most interactions inside the gels are destroyed, gels were very weak and hardly swell, yet they still dissolve very slowly. Microindentation can provide complementary valuable information to study the degradation of hydrogels.
Few investigations have attempted to connect the mechanism of dairy fouling to the chemical reaction of denaturation (unfolding and aggregation) occurring in the bulk. The objective of this study is ...to contribute to this aspect in order to propose innovative controls to limit fouling deposit formation. Experimental investigations have been carried out to observe the relationship between the deposit mass distribution generated in plate heat exchangers (PHE) by a whey protein isolate (WPI) mainly composed of β-lactoglobulin (β-Lg) and the ratio between the unfolding and aggregation rate constants. Experiments using a PHE were carried out at a pilot scale to identify the deposit distribution of a model fouling solution with different calcium contents. In parallel, laboratory experiments were performed to determine the unfolding/aggregation rate constants. Data analysis showed that (i) β-Lg denaturation is highly dependent on the calcium content, (ii) for each fouling solution, irrespective of the imposed temperature profile, the deposit mass in each channel and the ratio between the unfolding and aggregation rate constants seem to be well correlated. This study demonstrates that both the knowledge of the thermal profile and the β-Lg denaturation rate constants are required in order to predict accurately the deposit distribution along the PHE.
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•A CFD model for duodenum that explicitly takes the villi structure into account.•Enhancement of mass transfer and absorption quantified by an enhancement factor.•Ambient bulk flow ...reduces the enhancement effect from the pendular activity.•Top part of villi plays a significant role in nutrient absorption.
Given the complex motility of the intestinal wall featuring villous structure, the mechanisms by which the motility can enhance mass transfer and absorption in the small intestine have been a mystery. In this work, the challenging task to couple the intestinal lumen flow and the contraction movement of the villi is tackled by a multi-physics model. The effects of motility of an entire duodenum on the mass transfer and absorption under the influence of ambient flow can be systematically explored. It is revealed that the top of the villi plays a major role in mass absorption. For a rat duodenum, the pendular movement can enhance mass transfer and absorption by up to about 72%. With the introduction of ambient flow, although the absorption amount increases, the enhancement of mass transfer by pendular activity is inhibited. Specifically, the average enhancement factor decreases sharply from ~1.35 to ~1.05.
Understanding how shear affects whey protein stability is crucial to deal with typical industrial issues occurring at the bulk solution/surface interface, such as fouling during heat treatments. ...However, at the state of the art, this effect remains unclear, contrary to that of temperature. This article presents a novel strategy to study the impact of shear rate and concentration on the accumulation of whey protein surficial deposits. It consists in applying a range of shear rates (0–200 s−1) at controlled temperature (65 °C) on whey protein solutions (5–10 wt%) by a parallel plate rheometer equipped with a glass disc, thus allowing the off-line characterization of the deposits by microscopy. Our results highlight an unequivocal effect of increasing shear stress. At 5 wt%, it fosters the formation of primary deposits (≈ 10 μm), whereas at 10 wt% it results in the development of complex branched structures (≈ 50 μm) especially for shear rates ranging from 140 s−1 to 200 s−1. Based on the classification by size of the observed populations, we discuss possible hypotheses for the deposit growth kinetics, involving the interplay of different physico-chemical protein-surface interactions and paving the way to future further investigations.
•A novel methodology to study how shear rate influences protein surface deposition.•Increasing shear rates lead to enhanced surficial deposits.•Number and morphology of surficial deposits depend on protein concentration.•Thicker branched structures results from the connection of primary deposits.
High-intensity electric fields have been successfully applied to the destruction of Salmonella Enteritidis in diaultrafiltered egg white. The effects of electric field strength (from 20 to 35 kV x ...cm(-1)), pulse frequency (from 100 to 900 Hz), pulse number (from 2 to 8), temperature (from 4 to 30 degrees C), pH (from 7 to 9), and inoculum size (from 10(3) to 10(7) CFU x ml(-1)) were tested through a multifactorial experimental design. Experimental results indicate that, for Salmonella inactivation, the electric field intensity is the dominant factor with a strongly positive effect, strengthened by its positive interaction with pulse number. Pulse number, temperature, and pH have also significant positive effects but to a lesser extent. In the most efficient conditions, the pulsed electric field (PEF) treatment is capable of 3.5 log10 reduction in viable salmonellae. Simultaneously, the measure of surface hydrophobicity does not indicate any increase after PEF treatment. These results suggest that no protein denaturation occurs, unlike what is observed after comparable heat treatment in terms of Salmonella inactivation (55 degrees C for 15 min).
Four lactic acid bacteria (LAB) strains were cultured in reconstituted skim milk with different solids contents to compare the thermotolerance of resulting cultures. As milk concentration was ...increased from 5 to 30 wt%, the population of non-lactose-fermenting strains increased by around 1 log at stationary growth phase. High solids milk maintained relative stable pH (ΔpH<0.5) when fermented with a lactose-fermenting strain, compared to a drastic pH drop by 1.35 in low solids milk. All four strains cultured in 20 or 30 wt% milk demonstrated significant improvements in cell survival (remaining viability > 108 CFU/mL) and growth capability after heat treatment at 65 °C for 10 min, indicating a general thermoprotective effect irrespective of metabolic pathways. Besides cellular response to high osmolality during bacterial growth, we proposed that the increased concentration of protective dairy components and the increased viscosity and thermal resistance of culture medium also contributed to the excellent thermotolerance.
•LAB grown in 20%–30% skim milk showed better thermotolerance than that in 5% milk.•The improved thermotolerance was general for four strains with different metabolism.•After 10-min heating at 65 °C, residual viability of each strain was > 108 cfu/mL.•Cellular stress response may be activated when grown in high solids milk.•The rich protective agents and high viscosity of milk medium may protect cells.
Particle size distribution (PSD) is known to influence product properties such as flowability and compressibility. When producing crystalline lactose, different steps can affect the PSD of the final ...powder. The aim of this study was to investigate the influence of PSD on caking and the mechanisms involved. Smaller particles showed higher moisture sorption and a greater caking tendency, measured by dynamic vapor sorption and ring shear testing, respectively. Therefore, moisture sorption isotherms appeared as a valuable tool to predict the effect of PSD on humidity caking, as confirmed by the results of ring shear testing. Controlling the amount of fines, characterized by a higher content of impurities, a larger specific surface area and a broader span of the PSD, was found critical to limit caking. More precisely, both the total surface area and the span of the PSD require close attention as they can significantly influence humidity and mechanical caking.
•Smaller particles showed enhanced moisture sorption and higher caking tendency.•Fine particles had a larger surface area, more impurities and a broader span.•Moisture sorption isotherms help predicting the effect of PSD on humidity caking.•Both the span of the PSD and the specific surface area influence caking.
Lactococcus lactis ssp. cremoris and Lactobacillus acidophilus NCFM were cultured in growth media supplemented with CaCl2 to induce intracellular accumulation of Ca2+. Both strains grown with 10 mM ...Ca2+ demonstrated enhanced thermal stability, with increased survival after spray drying from 49.9% to 64.9% for the coccus and from 35.5% to 43.3% for the rod. The increased intracellular Ca2+ level was confirmed with murexide assay. Adding Ca2+ in the reconstitution solution could not improve the viability of spray dried cells at extended storage stages. We hypothesized that the over-presence of intracellular Ca2+ might stimulate the activity of heat shock proteins, increasing cell survival towards heat stress. The positive effect of calcium partly explained the protective mechanism of some calcium-containing protectants. The reported approach, which improves the stress tolerance of cells, can be combined with the optimization of spray drying conditions and protectant formulation for developing a consolidated powder production scheme.
•10 mM CaCl2 was added to growth medium to induce accumulation of intracellular Ca2+.•The resulting L.cremoris and L. acidophilus cells showed enhanced heat stability.•By culturing with Ca2+, both strains showed increased survival after spray drying.•Reconstitution with Ca2+ did not improve LAB viability for powders at storage stage.•The effect of Ca2+ was ascribed to stimulating the activity of heat shock proteins.
Energy savings in industrial processes have become one of the main goals of the current society. This paper aims to propose a systematic approach for the assessment of mixing equipment energy ...performance for highly viscous fluids. The framework is illustrated and applied by performing a rational comparison of the homogenization efficiency of classical mixing systems (involving an agitator revolving around a vertical axis centred in the tank) with that of planetary mixers when mixing highly viscous fluids. For that purpose, the pioneering framework of Zlokarnik is first reminded and its limitations with regard to non-traditional mixing equipment are discussed. Then, the theoretical background to extend this approach to these latter is presented. Experimental data on power consumption and mixing time are provided to demonstrate the applicability of the present frame. The results illustrated that a planetary mixer can be an economic solution for performing highly viscous fluids homogenization.
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•Framework to rank different mixing equipment in terms of power and mixing time.•Generic determination of operation conditions minimizing the work of a mixing equipment.•Complementary experimental characterization of two homogenization equipment.•One-plot performance comparison of a helical ribbon impeller and a planetary mixer.
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