Michèle Marin

Effect of Sucrose and Maltodextrin on the Physical Properties and Survival of Air‐Dried Lactobacillus bulgaricus: An in Situ Fourier Transform Infrared Spectroscopy Study

The effect of sucrose, maltodextrin and skim milk on survival of L. bulgaricus after drying was studied. Survival could be improved from 0.01% for cells that were dried in the absence of protectants to 7.8% for cells dried in a mixture of sucrose and maltodextrin. Fourier transform infrared spectroscopy (FTIR) was used to study the effect of the protectants on the overall protein secondary structure and thermophysical properties of the dried cells. Sucrose, maltodextrin and skim milk were found to have minor effects on the membrane phase behavior and the overall protein secondary structure of the dried cells. FTIR was also used to show that the air‐dried cell/protectant solutions formed a glassy state at ambient temperature. 1‐Palmitoyl 2‐oleoyl phosphatidyl choline (POPC) was used in order to determine if sucrose and maltodextrin have the ability to interact with phospholipids during drying. In addition, the glass transition temperature and strength of hydrogen bonds in the glassy state were studied using this model system. Studies using poly‐l‐lysine were done in order to determine if sucrose and maltodextrin are able to stabilize protein structure during drying. As expected, sucrose depressed the membrane phase transition temperature (Tm) of POPC in the dried state and prevented conformational changes of poly‐l‐lysine during drying. Maltodextrin, however, did not depress the Tm of dried POPC and was less effective in preventing conformational changes of poly‐l‐lysine during drying. We suggest that when cells are dried in the presence of sucrose and maltodextrin, sucrose functions by directly interacting with biomolecules, whereas maltodextrin functions as an osmotically inactive bulking compound causing spacing of the cells and strengthening of the glassy matrix.

Collapse Temperature of Freeze‐Dried Lactobacillus bulgaricusSuspensions and Protective Media

Optimization of the freeze‐drying process needs to characterize the physical state of frozen and dried products. A protocol to measure the collapse temperature of complex biological media such as concentrated lactic acid bacteria using freeze‐drying microscopy was first elaborated. Afterward, aqueous solutions of one or several components as well as concentrated lactic acid bacterial suspensions were analyzed in order to study how the structure of these materials is degraded during freeze‐drying. A similar behavior toward collapse was observed for all aqueous solutions, which was characterized by two temperatures: the “microcollapse” temperature ( Tμc, beginning of a local loss of structure) and the “collapse” temperature ( Tc, beginning of an overall loss of structure). For aqueous solutions, these two temperatures were close, differing by less than 3 °C. Nevertheless, when lactic acid bacteria were added to aqueous solutions, the collapse temperatures increased. Moreover, the interval between microcollapse and collapse temperatures became larger. Lactic acid bacterial cells gave a kind of “robustness” to the freeze‐dried product. Finally, comparing glass transition, measured by differential scanning calorimetry (DSC) and collapse temperature for aqueous solutions with noncrystallizable solutes, showed that these values belonged to the same temperature range (differing by less than 5 °C). As suggested in the literature, the glass transition temperature can thus be used as a first approximation of the collapse temperature of these media. However, for lactic acid bacterial suspensions, because the difference between collapse and glass transition temperatures was about 10 °C, this approximation was not justified. An elegant physical appearance of the dried cakes and an acceptable acidification activity recovery were obtained, when applying operating conditions during freeze‐drying in vials that allowed the product temperature to be maintained during primary drying at a level lower than the collapse temperature of lactic acid bacterial suspensions. Consequently, the collapse temperature Tc was proposed as the maximal product temperature preserving the structure from macroscopic collapse and an acceptable biological activity of cells.

Recovery of sulfur aroma compounds using membrane-based solvent extraction

Abstract This work focuses on a non-destructive process for recovering valuable aromatic fractions from the food industry’s odorous wastewaters. Non-dispersive solvent extraction of three sulfur aroma compounds, dimethyldisulfide, dimethyltrisulfide and S -methyl thiobutanoate, was carried out from very diluted aqueous solutions representing real effluent. The mass transfer from water to n -hexane was studied using a cross-flow designed hollow fiber membrane contactor. A preliminary study showed high affinity of solutes for n -hexane, with constant partition coefficients at infinite dilution between water and hexane in a 90–560 range. The influence of tube and shell side hydrodynamics on mass transfer was studied, with the aqueous phase on the tube side, and the organic phase on the shell side. The diffusion of solutes from the bulk aqueous phase to the aqueous–organic interface controlled the separation and contributed, under the conditions tested, to more than 97% of the overall mass transfer resistance. A resistance-in-series model overestimated overall mass transfer coefficients. The main explanation is the inaccuracy of the Leveque correlation used at low Reynolds numbers. The choice of a correlation for predicting mass transfers in the solvent phase did not affect the estimation, since the corresponding mass transfer resistance was negligible. Mass transfer fluxes obtained experimentally by membrane-based solvent extraction were greater for the three aroma compounds than those obtained by pervaporation.

Membrane-based solvent extraction of sulfur aroma compounds: influence of operating conditions on mass transfer coefficients in a hollow fiber contactor

Membrane-based solvent extraction is proposed to recover sulfur aroma compounds from an industrial effluent. It consists in transferring the aroma compounds from water into an organic solvent by contacting the two phases inside the pores of a membrane. Mass transfer experiments were performed using a crossflow hollow fiber membrane module, with hexane and miglyol as stripping solvents and synthetic aqueous feed phases with three diluted sulfur compounds. Selective extraction of the aroma compounds is due to the high partition coefficients of aroma compounds between water and the selected solvents. Diffusion inside the organic-filled pores is negligible using hexane, but becomes very important using miglyol, due to its high viscosity. Both tube and shell side compartments are able to receive the feed phase. For these two configurations, mass transfer coefficients are equivalent using hexane as a stripping solvent, but a larger interfacial area is offered when the aqueous feed phase flows in the shell.

Liquid-liquid extraction and air stripping in membrane contactor: application to aroma compounds recovery

This work focuses on a non-destructive process for recovering valuable aromatic fractions from odorous industry aqueous effluent. Non-dispersive extraction often selected aroma compound was carried out on very diluted model aqueous solutions, using membrane contactors, in two configurations: liquid-liquid and liquid-gas. Mass transfers from water to n-hexane, from water to miglyol (two solvents widely used in aromatic industry) and from water to air were studied using a cross-flow designed hollow fibre membrane contactor. The influence of physico-chemical properties of the aroma compounds and the influence of the solvent viscosity on mass transfer are discussed. Moreover, a resistance-in-series model has been applied and allowed to predict the mass transfer intensity in agreement with experimental values whatever the separation principle, liquid-liquid or liquid-gas.

Eating patterns and food systems: critical knowledge requirements for policy design and implementation

Eating patterns are important for building sustainable food and agricultural systems. This paper begins by presenting the main features of eating patterns worldwide. These eating patterns include the relative convergence of diets, more rapid food transition in emerging and developing countries, development of a more complex food chain, and substantial food losses and waste at distribution and final consumption stages. These patterns have negative consequences on health and the environment. The drivers of these patterns are examined to identify knowledge gaps, the filling of which should facilitate the design and implementation of actions and policies aimed at making food systems more sustainable.

Improvement of cryopreservation of Lactobacillus delbrueckii subsp. bulgaricus CFL1 with additives displaying different protective effects

In order to improve the acidification activity of frozen suspensions of Lactobacillus delbrueckii subsp. bulgaricus CFL1, the protective effect of nine additives, in binary and multicomponent solutions, was quantified during freezing and storage at –20°C. The best protective media were those containing sodium ascorbate and betaine or sodium glutamate, greatly improving the acidification activity recovery after freezing (+70%) and frozen storage (+90%) when compared to a control medium. However, the effect of each additive was different before than after freezing or during frozen storage. The presence of an antioxidant in the protective media appeared essential to maintain the acidification activity of L. bulgaricus during the cryoprotection stage and frozen storage. Betaine and sodium glutamate provided the highest resistance to freezing, while leading to the greatest reduction of the cryoscopic point of the medium. Their cryoprotective effect was explained by a decrease in the number of ice crystals formed during freezing and frozen storage.

State diagrams and sorption isotherms of bacterial suspensions and fermented medium

Abstract Physical properties of lactic acid bacteria suspensions were determined by means of state diagrams and sorption isotherms. Differential scanning calorimetry (DSC) was used to establish the thermal transitions of concentrated “fresh” (before freeze-drying) and freeze-dried bacterial suspension equilibrated at different relative humidities. The bacterial cells and the re-suspending medium (fermented culture medium) were studied separately in order to determine each individual effect. No glass transition ( T g ) was detected in thermal profiles of washed bacterial cells. Correspondingly, T g curves were similar for fermented medium and bacterial suspension. Simple glass transitions (one heat capacity step) were observed at T g in the case of low moisture samples. For samples containing more than 60.7% water, two steps remained in the glass transition region ( T g1 ′ and T g2 ′), even after annealing treatments. Water plasticising effect was well predicted by Gordon–Taylor equation. The invariant point ( C g ′, T g ′), characteristic of maximally freeze-concentrated samples, was estimated from the intersection of the T g curve and the melting curve T m . A linear relationship was proposed to rapidly predict the T g ′ region of complex aqueous solutions, from T g ′ values of single solute aqueous solutions. Water sorption properties of fermented medium and bacterial suspension were determined at 25°C and described by the Guggenheim–Anderson–de Boer equation.

Pervaporation as a deodorization process applied to food industry effluents: recovery and valorisation of aroma compounds from cauliflower blanching water

Abstract In the food industry, unit operations of stabilisation (such as blanching) produce aqueous effluents generally non-polluting but often odorous. The objective of this study was to apply the pervaporation process to the deodorization of a cauliflower blanching effluent in order to reduce its volatile organic compounds content and to try to recover a valuable food flavouring fraction. A systematic study of pervaporation has been performed on three sulfur compounds identified as typical compounds of the cauliflower odour. Then, the separation performances obtained on an industrial effluent were evaluated through physico-chemical and sensorial analysis. They showed that pervaporation was an efficient process for deodorization and offers a real potential for valorisation of the permeate.

Recovery of aroma compounds from tomato industry effluent using membrane-based solvent extraction☆

This work focuses on a non-destructive process for recovering valuable aromatic fractions from an odorous tomato industry aqueous effluent. Non-dispersive solvent extraction of four selected aroma compounds, chosen as key aroma, was, at first, carried out on very diluted model aqueous solutions. Mass transfers from water to n-hexane and from water to Miglyol (two solvents widely used in aromatic industry) were studied using a cross-flow designed hollow fibre membrane contactor. The influence of physico-chemical properties of the aroma compounds studied and the influence of the solvent viscosity on mass transfer are discussed. The results obtained with model solutions have been validated on the industrial process effluent.