Nicolas Louka

DRYING OF BAKER'S YEAST BY A NEW METHOD: DEHYDRATION BY SUCCESSIVE PRESSURE DROPS (DDS). EFFECT ON CELL SURVIVAL AND ENZYMATIC ACTIVITIES

Abstract Dehydration by Successive Pressure Drops (DDS) is a new unit operation, based on a repetition of compression/decompression cycles. In this work, we present the application of this drying process to bakers yeast. Drying rate, cycle efficiency, cell survival and the activities of four enzymes were evaluated. The effects of two parameters of DDS (PI and Dvp) on drying kinetics and product quality were studied, using the surface responses methodology. The results were also compared to those obtained with freeze-drying. PI had a positive effect on drying rate. Both PI and Dvp had an effect on cycle efficiency, particularly Dvp. Cell survival were much higher than that obtained with freeze-drying, with no significant impact of the parameters. The enzymatic activities were higher or close to the corresponding activities of freeze-dried sample, except the glucose-6-phosphate activity. The effects of PI and Dvp varied according to the enzyme.

A Study of Dehydration of Fish Using Successive Pressure Drops (DDS) and Controlled Instantaneous Pressure Drop (DIC)

Abstract Many studies have recently been carried out with a view to improve the processes used in drying foodstuffs. Optimization of the classical methods has been improved in terms of cost (mainly energy) and quality of the end product. Other work was devoted to developing new processes and a special effort was made to integrate texturing by controlled instantaneous pressure drop (DIC) into the standard drying by hot air. More recently, a new process of dehydration by successive pressure drops (DDS) has been defined. The aim of this study was to test these processes using two types of fish: the Atlantic salmon (Salmo salar) and the white tuna (Thunnus albacore), chosen mainly for the fact that they represent fatty and semi-fatty fish, respectively. A comparative analysis of the DDS and DIC processes with standard methods such as hot air convection, vacuum conduction and freeze-drying was carried out. The processes were first optimized and the comparison was made on the basis of the operation kinetics and of a physical, structural, and functional characterization of the product. Thus the analysis included measurements of the sample density, rehydration capacity, water activity, and color. Both DDS and DIC, in a similar but distinct manner, proved to be much more satisfactory than standard drying methods for improving the functional and quality aspects of the end product while limiting as much as possible the cost.

Effect of the Main Processing Parameters of the Instantaneous Controlled Pressure Drop Process on Oil Isolation from Rosemary Leaves. Kinetics Aspects

Abstract Experiments to isolate the essential oil from rosemary (Rosmarinus officinalis L.) were carried out using a new extraction process: “Détente Instantanée Contrôlée” (D.I.C) or “Controlled Instantaneous Pressure drop.” This process involves subjecting the rosemary leaves for a short period of time to a steam pressure, followed by an instantaneous pressure drop to a vacuum (about 15 mbar). This paper aims to assess the effect of processing pressure, processing time and initial moisture content of leaves before D.I.C. treatment on the extraction efficiency. The processing pressure varied from 0.5 to 5 bar, the processing time from 1 to 21 minutes and initial moisture content from 0.1 to 0.6 g H2O/g dm. It appears that a pressure of about 1 bar, and a treatment time less than 10 minutes are sufficient to extract more than 97% of the essential oil. The moisture content was not a critical parameter for the isolation efficiency. A stable yield and composition of the oil was obtained whatever the value of this parameter. The oil was also studied by quantitative and qualitative chemical analysis, the effect of modifying the operating conditions on the isolation of 10 components of the rosemary oil namely α-pinene, camphene, β-pinene, 1,8-cineole, camphor, borneol, terpinen-4-ol, α-terpineol, bornyl acetate and β-caryophyllene.

Sorption Isotherms of Granny Smith Apples Hot-Air Dried and Texturized by "Controlled Sudden Decompression to the Vacuum"

Moisture sorption isotherms of Granny Smith apples hot-air dried and texturized by Controlled Sudden Decompression (Détente Instantannée Contrôlée DIC®) were determined and compared using a gravimetric method. The DIC has been developed to confer a porous structure to partially dehydrated foods by expanding them and facilitating the drying process at lower water content. The samples were stored in a chamber; the relative humidity is controlled by an atomizing humidifier at 20, 30 and 40°C, and relative humidities ranging from 10% to 90%. The sorption capacity decreased with increasing temperature at a given water activity. The hysteresis effect was not significant for both of the dried and texturized apples. The experimental sorption data were fitted to 8 various isotherm models including two parameter relationships (BET, Halsey, Smith, Henderson, Oswin), three parameter equations (Ferro-Fontan, GAB) and four parameter equations (Peleg). A non-linear least square regression software was used to evaluate the models constants. The goodness of fit of each isotherm was quantified through the mean relative percentage deviation modulus E. The Ferro-Fontan, Peleg, GAB and Oswin equations were best for characterizing the sorption behaviour of Granny Smith apples for a whole range of temperatures and water activities studied. The surface area corresponding to the monolayer was determined for the texturized apples and compared to the dried samples. The results showed that the treatment by DIC increases the surface area of apples. For understanding the water properties and calculating the energy requirements phenomena, net isosteric heat was evaluated by the applying Clausius-Clapeyron equation.

The Impact of Long-Term Intake of Phenolic Compounds-Rich Grape Pomace on Rat Gut Microbiota

The aim of this work is to evaluate the impact on the rat microbiota of long-term feeding with phenolic compounds (PC) rich grape pomace extracts. Thirty, 2-mo-old rats, were divided into 5 groups. Four groups were treated with different concentrations of PC (2.5, 5, 10, and 20 mg/kg/d diluted in 0.1% DMSO), and 1 group received 0.1% Dimethyl Sulfoxide (DMSO) alone (control group). The daily treatment lasted 14 mo. Major phenolic compounds constituents were characterized by the high-performance liquid chromatography and free radical scavenging capacity was measured by means of the DPPH assay. Fecal samples from young rats (2-mo old), and rats daily fed with PC or DMSO were collected at 6 and 14 mo posttreatment. The gut microbiota composition was analyzed by quantitative polymerase chain reaction. Bifidobacterium was significantly higher in the groups PC 2.5 and PC 5 than in control and young rats. Lactobacillus decreased with time in all treated and untreated groups. Bacteroides, Clostridium leptum subgroup (Clostridium cluster IV), and Enterococcus were not significantly changed by PC at any concentration when compared to control; nevertheless, after 14 mo of treatment all concentrations of PC abolished the increase of Clostridium sensu stricto (cluster I) (Clostridium Cluster I) observed in the control group when compared to young rats. PC do modulate selectively rat gut microbiome to a healthier phenotype in long-term feeding rats, and could counteract the adverse outcomes of aging on gut bacterial population. PRACTICAL APPLICATION This research shows that phenolic-rich grape pomace extracts exhibiting a high antioxidant activity, selectively modulate rat gut microbiota to a healthier phenotype within age in a long-term feeding rats.