Showing papers in "Lait in 2000"

Biochemical pathways for the production of flavour compounds in cheeses during ripening: A review

Abstract: The principal pathways for the formation of flavour compounds in cheese (glycolysis, lipolysis and proteolysis) are reviewed. Depending on variety, microflora and ripening conditions, lac- tate may be metabolized by a number of pathways to various compounds which contribute to cheese flavour or off-flavours. Citrate metabolism by citrate-positive lactococci or Leuconostoc spp. is important in certain varieties (e.g., Dutch cheeses). Lipolysis results directly in the formation of flavour compounds by liberating free fatty acids (FFA). FFA may also be metabolized to alkan-2-ones and fatty acid lactones. Proteolysis of the caseins to a range of small- and intermediate-sized peptides and free amino acids (FAA) probably only contributes to the background flavour of most cheese varieties, but FAA are important precursors for a range of poorly-understood catabolic reactions which produce volatile compounds essential for flavour.

Current developments of microfiltration technology in the dairy industry

Abstract: This paper deals with the most recent developments of cross flow microfiltration (CFMF), some of them just patented, in the dairy industry. Combination of the use of uniform trans- membrane hydraulic pressure concept (UTP) with its different ways of carrying out microfiltrate recirculation, longitudinal porosity gradient and of new ceramic membrane materials allows nowa- days to get a differential separation of each category of milk particles. Pretreatment by CFMF of incoming milk is used for the production of low heated fluid milks having a flavor similar to that of raw milk and a shelf life 3 to 5 times longer than that of classical products. Results observed in the retention by the MF membrane of pathogenic bacterial species allow it to be said that the hygienic safety of cheeses made from raw MF milk is, at least, equal or even higher than that of cheeses made from pasteurized milk. Numerous other applications of CFMF are under development such as removal of residual fat from whey or the clarification and the removal of bacteria from cheese brine but the most promising are undoubtedly the differential separation of micellar casein and of small milk fat globules. With the products obtained on both sides of the MF membrane, dairy technology will have the possibility not only to improve yield and quality of many dairy products but also to create a diversified range of new textures. microfiltration / membrane / liquid milk / native casein / brine / whey / cheese

Transfer of monoterpenes and sesquiterpenes from forages into milk fat

Abstract: The transfer of monoterpenes and sesquiterpenes from forages into milk fat was stud- ied in a group of cows fed successively with forages containing high and low amounts of these sub- stances. In a first 24-d period the cows received 11 kg of a cocksfoot hay containing low quantities of monoterpenes and sesquiterpenes. In a second 36-d period, 3 kg of the cocksfoot were replaced by 3 kg of yarrow, a plant rich in terpenoids. In a third 24-d period the cows returned to the cocksfoot- based diet they were fed in the first period. The quantities of monoterpenes and sesquiterpenes des- orbed from the milk fat were measured by dynamic headspace - gas chromatography - mass spec- trometry. Results showed that the quantities of monoterpenes had increased by the first milking carried out 8 h after ingestion of yarrow, whereas the increase in the quantities of sesquiterpenes was observed only after the third milking, 32 h after the diet change. The maximal quantities of monoterpenes and sesquiterpenes were measured after 4 d of the yarrow-enriched diet, after which the total quantities decreased, despite the constant supply of yarrow. Four days after discontinuing yarrow the amounts of monoterpenes and sesquiterpenes desorbed from the milk fat reverted to those measured during the first period. traceability / type of feeding / terpenoid analysis / purge-and-trap / gas chromatography-mass spectrometry

Fractionation of globular milk fat by membrane microfiltration

Abstract: Separation of milk fat in small globules (SG) (diameter lower than 2 µm) and in large globules (LG) (diameter higher than 2 µm) was realized by a patented process using special ceramic microfiltration membranes. Transformations in drinking milks, yoghourts, sour cream, camembert, Swiss cheese and butters were realized from milks of which the fat content was adjusted either by ref- erence cream or by creams issued from the SG or the LG fractions. Significant differences in texture and organoleptic properties were found in the manufactured products. Except for butter, use of milks containing small fat globules led to more onctuous products and more finer textural characteristics ver- sus products made with reference creams or with mainly large fat globules. Fat globule membrane appeared to have a high ability to bind water in cheese and so, to allow a significant increase in cheese yield.

Évolution des connaissances sur la membrane du globule gras du lait : synthèse bibliographique

Abstract: Progress in milk fat globule membrane research: a review. The milk fat globule is essentially an oil droplet enclosed in a protective 'membrane', partially derived from the plasma membrane of the lactating cell, and which assures the dispersion of the milk fat in the milk plasma. This protective coat is generally called 'the milk fat globule membrane' (MFGM). This review examines the present state of knowledge on the MFGM. The topics dealt with are: origin and formation, isolation from milk, composition (lipids and proteins), structure (a new model is proposed), functional properties and the role that the MFGM plays in protection against lipolysis. milk fat globule membrane / isolation / composition / structure / functional property

Monitoring the identity and the structure of soft cheeses by fluorescence spectroscopy

Abstract: Les fromages a pâte molle presentent une large gamme de texture et, en consequence, de structure. L'objectif de cette etude etait d'evaluer le potentiel des fluorophores intrinseques du fromage dans la discrimination de 8 types de fromages a pâte molle. Les spectres d'emission des tryptophanes de proleines et les spectres d'excitation de la vitamine A ont ete enregistres directement sur des tromages au moyen de la fluorescence frontale. L'analyse des collections de spectres par des methodes statistiques multidimensionnelles telles l'analyse en composantes principales et l'analyse factorielle discriminante a permis de discriminer les 8 fromages. Respectivement 95 % et 92 % des echantillons principaux et de verification ont ete bien classes a partir des spectres de fluorescence des tryptophanes. Un meilleur resultat (respectivement 96 % et 93 %) a ete obtenu a partir des spectres de la vitamine A. Par ailleurs, les protils spectraux associes aux composantes principales presentent les longueurs d'onde les plus discriminantes de la collection spectrale. Ils permettent d'obtenir des informations sur la structure des proteines a l'echelle moleculaire, en relation avec la texture des fromages.

Microbiological characteristics of Parmigiano Reggiano cheese during the cheesemaking and the first months of the ripening

Abstract: The aim of this work was to gain a comprehensive view of the microbiological char- acteristics of milk, natural whey starter, and cheese during the first months of ageing of Parmigiano Reggiano. A significant presence of different microbial groups in raw milk from the initial moments of production was rapidly substituted by various lactic acid bacteria. Natural whey starter contained a large number of thermophilic lactic acid bacteria ( Lactobacillus helveticus, L. delbrueckii ssp. lac- tis, L. delbrueckii ssp. bulgaricus) and some facultatively heterofermentative lactic acid bacteria belonging to L. rhamnosus. Thermophilic lactic acid bacteria disappeared within 30 d. Rod-shaped mesophilic facultatively heterofermentative lactic acid microflora, consisting of L. casei, L. paracasei ssp. paracasei, L. paracasei ssp. tolerans, L. rhamnosus and pediococci, progressively increased up to the fifth month of ageing. Results showed that thermophilic lactobacilli were derived from natural whey starter whereas Streptococcus thermophilusoriginated from raw milk. Further, natural whey starter was the source of L. rhamnosus which was present throughout the entire period of the cheese ageing. The other components of non-starter lactic acid microflora derived from raw milk.

Interactions between $\beta$-lactoglobulin and flavour compounds of different chemical classes. Impact of the protein on the odour perception of vanillin and eugenol

Abstract: Interactions between β-lactoglobulin and flavour compounds were analysed by instru- mental and sensory studies. Affinity chromatography was used to determine binding constants of flavour substances belonging to different chemical classes. A systematic study on esters, pyrazines and phenolic compounds revealed that the increase in the hydrophobic chain length increases the affin- ity for the protein. Concerning the 4 diastereoisomers of 3-oxo- p-menthane-8-thiol, only the cis- trans isomery led to different binding constants. In general, binding constants increased with increas- ing log P values, except for the terpenic compounds studied, for which another explanation has to be found, taking into account the geometry of the molecule. Sensory analyses applying a matching test showed that the addition of β-lactoglobulin had no effect on the odour perception of vanillin, but brought about a significant decrease in the odour perception of eugenol. β-lactoglobulin / flavour / interaction / affinity chromatography / sensory analysis

Potentiality of Fourier Transform Infrared Spectroscopy (FTIR) for discrimination and identification of dairy Lactic acid bacteria

Abstract: The potentiality of FTIR spectroscopy for the identification of lactic acid bacteria (LAB) used in the dairy industry was tested. For this purpose, spectra of different strains were recorded using standardized conditions. These strains were species of Lactobacillus (12 species, 3 sub- species), Lactococcus (4 species, 3 subspecies), Leuconostoc (3 species, 3 subspecies), Weissella (1 species) and Streptococcus (2 species) involved in the soft cheese industry . Spectral libraries were then established by statistical analysis. Reference strains were then tested on these libraries, and 100% of correct identifications were obtained at the genus and species level, 86% at the subspecies level. Well-identified strains were included in libraries. Wild isolates ( n = 48) previously identified by biochemical tests and RAPD method were then tested. We obtained 100% at the genus level and 69% at the species level of correlation between FTIR and other methods. Finally, spectra of reference strains performed in other laboratories were tested with the same method, and the results tallied with official identification in 100% of the cases at the genus level and in 41% of the cases at the species level. These results concerning a few strains allow us to plan the development of a more complete database for rapid identification of LAB.

Rennet coagulation of skim milk and curd drainage: effect of pH, casein concentration, ionic strength and heat treatment

Abstract: The effect of the pH of skim milk (6.4 to 6.0), the casein concentration (27 to 36 g .kg -1 ), a reduction in the ionic strength to 0.6 compared to that of unmodified milk and the effect of heat treat- ment on rennet coagulation, gel syneresis and drainage were tested. Coagulation was measured using a formagraph and by viscoelasticimetry, while syneresis was studied using a centrifugation test. Drainage was followed under conditions similar to those of cheesemaking, using either a mesophilic or thermophilic process. The effects of pH and casein concentration on rennet coagulation, gel syneresis and drainage were in accordance with those reported in the literature. Reduction in ionic strength led to shorter coagulation time and firming time. It also led to an increase in gel firmness, gel syneresis, drainage rate, final amount of expelled whey, solids content and hardness of drained curd. Ionic strength appeared to have an interactive effect with pH on coagulation and with the concentration of casein on syneresis and drainage. This effect of the reduction in ionic strength is discussed. rennet coagulation / pH / casein concentration / ionic strength / drainage

Hydrodynamic factors affecting flux and fouling during ultrafiltration of skimmed milk

Abstract: The effects of independently varying both wall shear stress ( τ w ) and transmembrane pres- sure (TMP) on permeate flux and fouling during ultrafiltration of reconstituted skimmed milk in total recycle mode have been investigated. Irreversible fouling resistance ( R if ) increased as TMP increased. Increasing τ w at constant TMP led to an increase in both the initial flux, and subsequent flux decline, and to a decrease in R if . At the highest τ w , increasing TMP resulted in greater initial flux accom- panied by increasing rates of flux decline and more irreversible fouling. Increasing and then decreas- ing TMP in a controlled, stepwise manner at constant τ w suggested that flux is governed by both a reversible, and an irreversible fouling layer which forms at higher TMP; this also controlled the transmission of protein. Critical operating conditions producing the least fouling were evaluated during this procedure.

Acid stress susceptibility and acid adaptation of Propionibacterium freudenreichii subsp. shermanii

Abstract: The probiotic application of dairy propionibacteria as well as their use in cheese tech- nology implies exposure to various environmental stresses, including acidic pH. The acid tolerance response (ATR) of Propionibacterium freudenreichiiwas investigated. One strain present in Swiss- type cheese proved to be acid-tolerant, since no lethal effect was observed during exposure at pH 3. Moreover, survival at pH 2 (acid challenge) was conferred by pre-exposure to a moderate acid stress (acid adaptation). This adaptative response was triggered quickly, and showed a maximal efficiency upon exposure to pHs between 4 and 5. Stationary phase ATR and acid habituation were also demon- strated, and conferred increased survival at pH 2 without pre-exposure. Exponentially-growing bac- teria were partially protected towards acidity by pre-exposure to other stresses (heat, starvation, but not hyperosmolarity). A comparative study of different strains revealed that acid stress susceptibil- ity is strain-dependent within this species. Adaptation and survival at low pH is likely to determine the efficacy of a P. freudenreichii strain both as a cheese starter and as a probiotic. Swiss-type cheese / Propionibacterium / acid tolerance response / stress / probiotic

Cheesemaking properties of a new dairy-based powder made by a combination of microfiltration and ultrafiltration.

Abstract: Partial removal of whey protein before heat-treatment, by a combination of membrane microfiltration and ultrafiltration according to an Inra patented process, was expected to avoid the for- mation of the β-lactoglobulin-κ-casein complex during thermal processing and thus to allow the production of a milk powder with cheesemaking abilities similar to those of raw milk. The prin- ciples of the process, the characteristics of the resulting new milk powder, and the manufacture of Moz- zarella cheese from milk prepared by recombination of this powder were studied with special empha- sis on rennet coagulability, melting properties and improvements observed on cheese yielding capacity. Mozarella produced by recombination had same composition and properties as control Mozarella (produced with raw fresh milk), but when the powder was used, the cheesemaking yields were 7.3 ∠ 1.8% higher in comparison with the control cheese. The recovery in total solids, fat and total nitrogen contents showed similar trends. Therefore, such a process may give rise to a new gene- ration of milk powders, especially suitable for cheesemaking in countries suffering a shortage in milk supply.

Characterization of the dromedary milk casein micelle and study of its changes during acidification

Abstract: Biochemical and physical properties of dromedary milk were studied at initial pH and during an acidification with glucono-δ-lactone. In comparison with bovine milk salt, citrate and nitrogen partition between soluble and micellar phases revealed several characteristics. Dromedary milk micelle presented a more important mineral plus citrate charge (~ 98 mg .g -1 casein). Micellar Mg, P and citrate proportions were higher, about 2/3, 2/3 and 1/3, respectively. During acidification, micellar mineral and citrate release started tardily (~ pH 5.8) and the maximum of casein and Pi solubilization took place at lower pH values, 4.9 and 4.8, respectively. Dromedary milk micelle see- med to maintain its integrity until about pH 5.5, below, it underwent extensive biochemical and structural modifications mainly at pH 5.0. At this point, dromedary milk was characterized by a loose microstructure, by a maximum of loss modulus and of micelle hydration and by a minimum of apparent viscosity. The pH 5.0 would be a transition pH between micellar structure and coagulum struc- ture.

Characterization of mare caseins. Identification of $\alpha_{{\bf S1}}$- and $\alpha_{{\bf S2}}$- caseins

Abstract: Whole mare (Mongolian and French breeds) casein was obtained from skim milk by iso- electric precipitation (pH 4.6) at 22 °C. In another series of experiments, equine caseins were frac- tionated after isoelectric precipitation at 4 °C, according to their sensitivity to temperature, on one hand, the pH of the resulting pellet was adjusted to 6.5 before centrifugation (45 000 g for 30 min) at 4 °C; on the resulting casein fraction which precipitated was named the cold precipitated (CP) fraction. On the other hand, the supernatant obtained from the centrifugation of skim milk at pH 4.6 and 4 °C was warmed to 30 °C before being centrifuged at 30 °C, 45 000 g, for 30 min. The resulting casein frac- tion which precipitated was named the thermally precipitated (TP) fraction. Equine caseins were then purified by high resolution gel chromatography on an anion-exchange column followed by reversed phase-high performance liquid chromatography. The casein fractions were analyzed by urea- and SDS-polyacrylamide gel electrophoresis, their amino acid compositions were determined and their first 15 N-terminal amino acids were sequenced. This analysis showed the presence of α s - like caseins isolated from the CP fraction. α s1 -Like-casein showed 4 major double bands by elec- trofocusing with a pI range of 4.3-4.8. In the same conditions, α s2 -like casein showed 2 major bands with a pI range of 4.3-5.1. The TP fraction revealed the existence in equine milk of 6 subfractions of β-like caseins, occurring in the following ratios: 1:5:18:20:15:10, differing at least in their degree of phosphorylation (as shown also by the action of acid phosphatase). Since no evidence of the presence of κ-casein was found in equine milk, it is proposed that part of its functions in the milk of the Equidae could be assumed by the population of less phosphorylated β-caseins. mare milk / α s1 -casein / α s2 -casein / β-casein

Implementation of integrated membrane processes for pilot scale development of fractionated milk components.

Abstract: Numerous opportunities for the separation and fractionation of milk and whey compo- nents are presented as a result of continuing developments in filtration membranes modules and processes. The preparation of sufficient quantities of selected protein groups for functionality stud- ies and food application tests requires considerable amounts of starting material, particularly in the case of whey-based constituents. Adequate amounts of membrane filtration surface area are, there- fore, needed in order to expedite processing time, limit conditions for microbial growth and increase productivity from a product development point of view. With this objective in mind, a series of large pilot plant membrane separation systems based on microfiltration, ultrafiltration and electrodialysis were recently installed and commissioned. Rapid ultrafiltration of whey for the generation of high pro- tein concentrates under a wide variety of conditions, including 'cold' filtration, is facilitated by a Memtech™ spiral wound membrane plant with a maximum surface area of 144 m 2 that is accom- modated within 3 modules mounted in parallel. Designed to operate on a continuous feed-and-bleed principle, product is heated while pumping via a plate-heater to the plant's balance tank in order to raise temperature to the desired operating condition. Magnetic flow meters mounted on the feed, permeate and diafiltration water lines enable the volume concentration ratio to be controlled through- out a run. Defatting of rennet whey by microfiltration using a Tetra Pak Alcross ™ M, Type 2 〈 19 Spe- cial, crossflow microfiltration (MF) plant fitted with a 0.1 μm pore size ceramic membrane with a fil- tration area of 13.3 m 2 trebled flux rate during ultrafiltration at 12 °C under steady state conditions. High protein whey protein concentrates (ca. 80% total protein) were processed in the defatted and non- defatted state at either 50 °C or 12°C for functional characterisation. Preliminary analyses indicate that all 4 WPC's produced weak gels. Native phosphocasein was prepared from skim milk using the above MF plant. Partial demineralisation of skim milk prior to MF was facilitated using an Ionics (Ion- ics Inc.) Electromat™ ED, featuring a 100-cell pair Mark III electrodialysis membrane stack. Elec- trodialysis resulted in improvements in the heat stability profile of phosphocasein, at the expense of rennet coagulation properties which were totally eliminated even in the presence of added calcium.

Selective isolation of cationic amino acids and peptides by electro-membrane filtration

Abstract: In the food industry there is a clear trend towards the production of speciality products with a high added value. Electro-membrane filtration (EMF) can be used to separate and concentrate these products from complex solutions. With EMF, lysine was separated from a model solution and a protein hydrolysate both containing leucine. The lysine fraction in the permeate ranged from 0.86 to 0.96. The lysine transport rate and purity were improved by increasing the potential difference from 20 V to 40 V. Reduction of the transmembrane pressure from 2 to 0.5 bar improved the purity at a practically unchanged lysine transport rate. An enriched fraction of antibacterial cationic peptides (e.g. lactoferricin-B) could be produced from a lactoferrin hydrolysate using EMF. Isolation of these bioactive peptides is normally expensive due to the complex nature of the hydrolysate feed. EMF has the potential to become an attractive (partial) isolation technology.

Effect of peptide distribution on the fractionation of whey protein hydrolysates by nanofiltration membranes

Abstract: The fractionation of tryptic and chymotryptic hydrolysates of whey proteins by nanofil- tration (NF) membranes has been investigated Enzymatic hydrolysates were prepared by tryptic (TH) or chymotryptic (CH) hydrolysis of a commercial whey protein isolate followed by UF-treat- ment using a 10 000 gmol -1 MWCO in order to remove the enzyme and non-hydrolyzed material from the reaction mixture Both hydrolysates were further fractionated using a SG13 (Osmonics) cellulose acetate NF membrane with a molecular weight cut-off (MWCO) of 2 500 gmol -1 A detailed exam- ination of the peptide separation revealed that, for both TH and CH, the negatively charged pep- tides were in lower proportion in the permeates whereas the opposite trend was observed for neutral and positively charged peptides However, the fractionation of TH lead to a better separation between charged fragments than that of CH This can be explained by the broader range of peptide characteristics (mass, charge) in CH as a result of the broader specificity of chymotrypsin

Effect of the botanical composition of hay and casein genetic variants on the chemical and sensory characteristics of ripened Saint-Nectaire type cheeses.

Abstract: Forty-two multiparous dairy cows of 3 different breeds (Holstein, Montbeliarde and Taren- taise) were divided into 2 groups (A and B) according to β- and κ-casein genetic variants, and were fed 3 floristically different types of hay (cocksfoot, rye-grass-rich and native mountain grassland hay) according to a 3 〈 3 Latin-square design. The milk produced by these cows was used to make Saint-Nectaire-type cheese, using identical and controlled cheesemaking techniques. The cheeses made from cocksfoot diet milk had higher pH (P < 0.01), lower fat in dry matter ( P < 0.05), more elas- tic texture and a strong cellar odour ( P < 0.1). The cheeses produced from the milk of cows fed native mountain grassland hay exhibited a slightly gritty and yellower body, and had a pronounced vinegar and cabbage odour. Rheological analysis confirmed the beneficial effect of the B variant of β- and κ-caseins on milk rennet clotting ability. This effect did not seem to affect the cheeses because they could not be distinguished by any of their sensory characteristics. milk / cheese / genetic variant / diet

Evolution of Lactococcus strains during ripening in Brie cheese using Fourier transform infrared spectroscopy

Abstract: The diversity of the Lactococcus flora during maturation of soft cheese, produced using one of 2 different starter cultures (S A and S B ), was determined using Fourier transform infrared spectroscopy (FTIR). Identification of Lactococcus sp. was achieved using a model composed of the 6 strains of Lc. lactis ssp. lactis and the 2 strains of Lc. lactis ssp. cremoris, present in the starter cultures S A and S B , as well as a reference strain for each of the subspecies considered. For the cheeses made with the starter culture S A , the proportion of strains within the cheeses was relatively homo- geneous throughout maturation, while in the cheeses made with the starter culture S B , one strain predominated. However, with both starters the strains of Lc. lactis ssp. cremoris failed to develop in the milk culture and in the cheeses. Results demonstrated that FTIR spectroscopy is a rapid and robust method for the qualitative analysis of cheese flora.

Use of cold microfiltration to produce unique β-casein enriched milk gels

Abstract: Bovine milk was modified using cold microfiltration to produce β-casein enriched fractions with unique gelation properties. Skim milk at 4 °C was microfiltered using membranes with pore diameter of 0.2 μm, 0.1 μm, or 100 000 g.mol -1 MWCO. Resulting permeates were filtered again using membranes with 10 000 g.mol -1 MWCO to create retentates with 9% solids that were used in the gelation study. Ash, calcium, lactose, solids, and protein contents of all fractions were monitored to determine separation trends. Cold microfiltration significantly reduced the casein:whey protein ratio and increased the β-casein:α s -casein ratio in the retentates from the second filtration; the smaller the pore size of the initial separation membrane, the greater the change in the ratios. When treated with glucono-δ-lactone and rennet, the β-casein enriched fractions produced using the 0.2 and 0.1 μm membranes formed softer gels that had greater syneresis and hydration, and lower water holding capacities than skim milk gels.

Biochemical characteristics of fermented milk produced by mixed-cultures of lactic starters and bifidobacteria

Abstract: Strains of bifidobacteria of human origin ( Bifidobacterium bifidum, B breve, B infan- tis and B longum) were inoculated simultaneously with mixed cultures of lactococci, citrate- fermenting lactococci and leuconostocs to determine their impact on biochemical characteristics of fermented dairy products Fermentations were carried out under different conditions of tempera- ture, milk protein concentration and ratio of acidifying/aromatic lactic acid bacteria The survival or growth of bifidobacteria during production of fermented milk was not affected by the presence of lac- tic starters On the other hand, the presence of bifidobacteria during the production of fermented milk did not influence the growth of total lactococci, citrate-fermenting lactococci and leuconos- tocs The variation of the milk protein content did not modify the growth of bifidobacteria and mixed-cultures of lactic starters However, the presence of bifidobacteria changed the final charac- teristic of the fermented milk Residual lactose in fermented milks containing B breve, B bifidum and B infantis was lower than that found in fermented milks without bifidobacteria and those containing B longum The fermented milks without bifidobacteria contained less acetaldehyde than those con- taining bifidobacteria whereas the concentration of diacetyl was less important in the presence of bifi- dobacteria However, the ethanol concentration increased when bifidobacteria were used with mixed cultures of lactococci, citrate-fermenting lactococci and leuconostocs A temperature of 35 °C seems to be desirable because it allows the growth of bifidobacteria without affecting in a drastic way the growth and activity of leuconostocs and other lactic starters bifidobacteria / starter / leuconostoc / fermented milk / volatile compound

Critical stability conditions in skimmed milk crossflow microfiltration: impact on operating modes

Abstract: There exists a critical ratio (convection towards the membrane/erosion) in crossflow micro- filtration, MF, below which there is no marked fouling by colloidal particles and above which per- formance are altered: sharp increase of fouling, reduced operating time, large decrease in perme- ability and solute transmission. This paper outlines the impact of the critical ratio on skimmed milk MF processing (separation of casein micelles from the soluble proteins) and gives objective ele- ments (taking into account the critical ratio) for the selection of start-up procedures and stationary modes of operation: controlled transmembrane pressure or permeation flux; "static" or "dynamic" counter- pressure, the latter achieved by circulating the permeate co-current to the retentate to maintain an equal transmembrane pressure profile along the filtering path. Results showed that the controlled trans- membrane pressure mode of operation was appropriate for conducting skimmed milk filtration, since it prevented from sharp increase of the hydraulic resistance of fouling and maintained nearly constant performances (permeability, selectivity) over the course of the time. In order to determine the more appropriate counter pressure mode and to predict skimmed milk performances, a four step method was proposed : i) assessment of the critical ratio; ii) selection of the critical flux at the required wall shear stress; iii) determination of the corresponding critical transmembrane pressure in "dynamic" counter-pressure; iv) calculation of the MF performance in "static" mode taking into account the gradient of transmembrane pressure induced by the retentate pressure drop. hydrodynamics / crossflow microfiltration / operating mode / critical permeation flux / milk

Barostability of milk plasmin activity

Abstract: The influence of high pressure (HP) on the stability and activity of the milk alkaline pro- teinase plasmin was examined. Assays of enzyme activity following HP treatment of plasmin in phosphate buffer (pH 6.7) indicated that the enzyme was extremely pressure stable, retaining almost all activity even after treatment at 600 MPa for 20 min at 20 °C. Plasmin was also extremely stable when HP treated in buffer containing 25 mg.mL -1 sodium caseinate, and in cheese. However, HP treat- ment in buffer containing 5 mg.mL -1 β-lactoglobulin resulted in enzyme inactivation at pressures > 400 MPa, indicating that the presence of β-lactoglobulin greatly destabilises the enzyme under high pressure, which is analogous to the effect of this protein on the heat stability of plasmin. In separate experiments, hydrolysis of β-casein by plasmin at 20 °C for 30 min at various pressures (300-800 MPa) was studied. Parallel control incubations were performed at atmospheric pressure. Urea-PAGE analysis of digests showed that primary proteolysis of β-casein was decreased at P > 400 MPa. As judged from RP-HPLC analysis, production of 2%-TCA soluble peptides by plas- min appeared unaffected at P < 700 MPa, above which pressure the rates of peptide production decreased. Overall, plasmin is relatively pressure stable in most systems and can hydrolyse its pre- ferred substrate (β-casein) at pressures up to 700 MPa, but is sensitive to destabilisation by denatured β-lactoglobulin. plasmin / high pressure / specificity / stability

Effect of homogenization of cream on composition, yield, and functionality of Cheddar cheese made from milk supplemented with ultrafiltered milk

Abstract: Cheddar cheeses were made from milks supplemented with ultrafiltered skim milk to 4.57 and 5.93% protein and from milks without supplementation to serve as controls (3.18% protein). Milks were standardized (casein-to-fat ratio of 0.7) with unhomogenized cream or homogenized (6.9/3.45 MPa) cream. The six treatments were replicated five times. Rennet clotting time decreased with protein concentration and homogenization of cream increased it. k 20 , the time to reach an ampli- tude of 20 mm on formagraph after rennet clotting time, decreased with homogenization and concen- tration. a 40 , the amplitude on formagraph after 40 min of rennet addition, increased with protein and homogenization. Cheese moisture ranged from 37.29 to 39.37% and the proportion of fat in dry matter ranged from 52.9 to 53.7%. Cheese yield adjusted to 37% moisture and 1.5% salt and adjus- ted yield per kg protein increased significantly in treatments with both protein concentration and homogenization. Fat recovered in cheese decreased with concentration in unhomogenized treat- ments while it increased in homogenized treatments. Protein recovery increased with protein concen- tration. A sensory panel did not detect any significant difference in flavor, flavor intensity, and body and texture with protein supplementation, but there was a significant increase in the body and texture scores in treatments with homogenization. Hardness of cheeses increased in treatments with concen- tration. Meltability of cheese increased with age in homogenized treatments. Free oil and free oil on fat basis decreased in treatments with homogenization and concentration. These two parameters also decreased with cheese age with a larger decrease for the homogenized treatments.

Nanofiltration of sweet whey by spiral wound organic membranes: impact of hydrodynamics.

Abstract: The influence of permeation flux J and wall shear stress τ w , on performances of the nanofiltration of concentrated sweet whey at volume reduction ratio 2, 18 °C and using organic membranes was studied. It was concluded that sweet whey nanofiltration could be optimised through the parameter J/τ w , since J and τ w act together in a competing mechanism of convection/erosion at the membrane surface, that governs membrane fouling and selectivity. Hence, the overall fouling was strongly dependent on the ratio J/τ w , with a critical J/τ w value of approximately 6.0. When J/τ w < 6.0, the total membrane fouling was relatively low and almost independent on operating conditions. For higher ratios of J/τ w , there was a spectacular increase in fouling and a very strong dependence between the fouling index and J/τ w . Simultaneously, selectivity was altered under these conditions, with higher retention of monovalent ions and lower retention of lactose. Finally, optimal hydrodynamic conditions were defined in the range 3-6. Under these conditions, longer operating times, lower chemical oxygen demand in permeate and higher demineralization could be expected at lower pro- cessing costs.

Purification and characterization of an extracellular esterase from Arthrobacter nicotianae 9458.

Abstract: A 32 kg·mol -1 extracellular esterase from Arthrobacter nicotianae9458 was purified to homogeneity by 4 chromatographic steps. The optimum pH and temperature for enzyme activity for β-naphthyl butyrate were 7.0 and 30 °C, respectively. The esterase retained between 50-55% of the maximum activity at pH 5.5 and 15 °C and was completely inactivated by heating for 1 min at 65 °C. Among the β-naphthyl derivatives of various chain length (C2-C18:1), the highest activity was on β-naphthyl butyrate. The enzyme was moderately active on tributyrin and was less active on tri- caproin. The esterase was markedly inhibited by phenylmethylsulfonyl fluoride and to a lesser extent by EDTA. Divalent cations such as Fe 2+ , Sn 2+ , Ca 2+ and Hg 2+ also inhibited the enzyme. This char- acterization showed that the extracellular esterase of Arthrobacter nicotianae9458 may contribute to the ripening of smear surface-ripened cheeses.

Effect of bile on the β-galactosidase activity of dairy propionibacteria.

Abstract: In the present study, the effect of bile on the growth, cell permeabilization and β-galac- tosidase activity of dairy propionibacteria was determined. Two groups of strains with different behavior in media with oxgall (dehydrated fresh bile) could be observed, and were named bile-tol- erant and non bile-tolerant groups. The β-galactosidase activity of bile-tolerant strains increased during the growth in media containing 0.15 and 0.30% oxgall. The incubation of cell suspensions in phosphate buffer with oxgall increased the β-galactosidase activity of all the studied strains. They were permeabilized by bile, permitting more substrate to enter the cells to be hydrolyzed by β-galactosi- dase. A higher specific activity was observed in cell-free extracts obtained from cultures in media with oxgall, indicating increased enzyme synthesis in the presence of bile. The enzyme activity was also increased by sodium taurocholate and sodium chloride. These results suggest that bile-tolerant strains of propionibacteria can provide meaningful β-galactosidase activity by permeabilization of the cells and increased enzyme synthesis during growth in the gut. The non bile-tolerant strains did not grow in media with bile. They were permeabilized, but their β-galactosidase was inactivated when they were exposed for a long time to bile in the growth media. Thus, their contribution to the β-galactosidase activity in the gut does not appear to be significant. Propionibacteria / bile tolerance / β-galactosidase

Selective extraction of lysozyme from a mixture with lactoferrin by ultrafiltration. Role of the physico-chemical environment

Abstract: Variation of the physico-chemical environment was used to optimize the selective extrac- tion of lysozyme (14 300 g.mol -1 ) from a model protein mixture with lactoferrin (77 000 g .mol -1 , in monomer form) by ultrafiltration (UF). The system protein-membrane-electrolyte was studied using electrokinetic measurements, in order to determine the charge of both free proteins and fouled mem- brane, depending on the physico-chemical environment (pH, ionic strength, chemical nature of added salts). This paper shows that, in order to achieve the extraction of a protein from a mixture, the fol- lowing strategy can be used: the target protein recovered in the permeate has to be uncharged, whereas the retained protein has to be charged in order to exploit the electrostatic repulsion of the mem- brane partly fouled by the charged protein. This approach was successfully used to achieve the lysozyme/lactoferrin separation with a high selectivity (lysozyme transmission/lactoferrin trans- mission) using an anionic membrane of pore diameter close to 28 nm. The selectivity of the separa- tion was studied according to the variation of the ionic strength, in the range 1 to 150 mmol . L -1 , with either sodium chloride or potassium phosphate. Whereas selectivities were close to 20 in sodium chloride, they were always greater in potassium phosphate and increased up to 120. ultrafiltration / protein / selectivity / electrophoretic mobility / specific adsorption

UHT processed milk concentrates

Abstract: Ultrafiltration and reverse osmosis concentrates made from milk with differing fat and protein contents were sheared in defined flow conditions to establish the critical concentration of the constituents beyond which flow properties and heat stability change. The viscosity of the concentrates at 20 °C was calculated for volume concentrations below 0.5. Non-Newtonian flow occurred above this concentration, and heat coagulation tests at 140 °C revealed a dramatic drop in heat stability. The dense packing of the constituents above a volume concentration of 0.5 led to altered flow properties and decreased heat stability. The heat stability at 140 °C and storage stability correlated with the ash content and these increase as the ash contents decrease. Milk may be treated by applying ultra- filtration and nanofiltration to reduce ash content and enable high quality milk concentrates with a long- life stability to be produced by means of ultra-high temperature heating. milk / ultrafiltration / nanofiltration / rheology / ultra-high temperature