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The size of native milk fat globules affectsphysico-chemical and sensory properties of Camembert

cheeseMarie-Caroline Michalski, Jean-Yves Gassi, Marie-Hélène Famelart, Nadine

Leconte, Bénédicte Camier, Françoise Michel, Valérie Briard

To cite this version:Marie-Caroline Michalski, Jean-Yves Gassi, Marie-Hélène Famelart, Nadine Leconte, BénédicteCamier, et al.. The size of native milk fat globules affects physico-chemical and sensory proper-ties of Camembert cheese. Le Lait, INRA Editions, 2003, 83 (2), pp.131-143. �10.1051/lait:2003003�.�hal-00895488�

131Lait 83 (2003) 131–143© INRA, EDP Sciences, 2003DOI: 10.1051/lait:2003003

Original article

The size of native milk fat globules affects physico-chemical and sensory properties

of Camembert cheese

Marie-Caroline MICHALSKI*, Jean-Yves GASSI, Marie-Hélène FAMELART, Nadine LECONTE, Bénédicte CAMIER, Françoise MICHEL, Valérie BRIARD

Laboratoire de Recherches de Technologie Laitière, INRA, 65, rue de Saint-Brieuc,35042 Rennes Cedex, France

(Received 28 February 2002; accepted 18 July 2002)

Abstract – Camembert cheeses were produced using either small (~3 �m, SFG) or large (~6 �m,LFG) native milk fat globules obtained by a patented microfiltration process. The composition ofthe cheese milk did not depend on the fat globule size. Less whey was extracted from the SFGcheeses, that subsequently contained more moisture than LFG cheeses throughout the ripeningperiod. The SFG curds were less rigid and less firm than the LFG ones and underwent greaterproteolysis during ripening. Camembert cheeses with small fat globules had a higher melting andelastic texture, a higher flowing aspect and were less yellow. The results were explained (i) by thegreater surface area of native milk fat globule membrane for SFG vs. LFG, at a given fat content,and (ii) by the thinner casein strands in SFG cheeses due to the smaller interglobular distance. Theuse of native milk fat globules with different sizes can thus lead to new products with differenttechnological and sensory properties.

Milk fat / fat globule / Camembert cheese / cheese yield / rheology / particle size /microfiltration / sensory analysis

Résumé – Des propriétés physico-chimiques et sensorielles du Camembert sont affectées parla taille des globules gras natifs du lait. Des camemberts ont été fabriqués en utilisant des globulesgras natifs du lait de petit diamètre (~3 �m) ou de grand diamètre (~6 �m), obtenus par un procédéde microfiltration breveté. La composition des laits de fromagerie ne dépend pas de la taille desglobules gras. Il s’égoutte moins de sérum des camemberts à petits globules, qui sont ensuite plushumides que les fromages à gros globules au cours de l’affinage. Les caillés à petits globules sontmoins fermes et moins rigides que ceux à gros globules et sont plus protéolysés durant l’affinage.Les camemberts à petits globules ont une texture plus fondante et plus élastique, sont plus coulantset moins jaunes. Ces résultats peuvent être expliqués (i) par la plus grande surface de membranenative pour les petits globules par rapport aux gros globules à une teneur donnée en matière grasseet (ii) par la moindre épaisseur des brins de caséine dans les camemberts à petits globules, à causede la plus faible distance moyenne entre globules. L’utilisation de globules gras natifs du lait dedifférentes tailles peut donc aboutir à de nouveaux produits présentant des propriétéstechnologiques et sensorielles différentes.

Matière grasse du lait / globule gras / Camembert / rendement fromager / granulométrie /rhéologie / analyse sensorielle / microfiltration

* Correspondence and reprintsTel.: +33 2 23 48 53 22; fax: +33 2 23 48 53 50; e-mail: mcmichal@labtechno.roazhon.inra.fr

132 M.-C. Michalski et al.

1. INTRODUCTION

Milk fat is recognized to contributegreatly to the texture, flavor and physico-chemical properties of many dairy prod-ucts, especially cheese. Particularly,depending on its solid fat content, it actsmore or less as a plasticizer [12]. Morethan 95% of the mass of lipids in cow’smilk is present in the form of sphericalmilk fat globules (MFG) [13]. The diame-ter of MFG ranges from 0.1 �m to 15 �m,with a volumetric average around 4 �m,depending e.g. on cow breed, feed and sea-son [28]. They are surrounded by a nativestabilizing membrane, allowing them to becompatible with the aqueous environment:the milk fat globule membrane (MFGM).This complex MFGM, around 15 nm thick,originates from a primary membrane in thesecretory cell, additioned with the mem-brane of the apical cell after secretion. TheMFGM is composed mainly of phospholi-pids, glycolipids, proteins (25�60% ofMFGM mass), lipoproteins and enzymessuch as butyrophilin and xanthine oxidase[3, 13]. This composition results in anaverage �-potential of �13.5 mV [21] andin uncommon surface active properties,with the MFG interfacial tension being aslow as 1�1.5 mN·m–1 [22]. Moreover, atleast 25 different enzyme activities havebeen found to be associated with theMFGM, which also presents a high water-binding ability [8, 13]. Considering theaverage milk fat globule size distribution,the MFGM surface area is ~1.85 m2·g–1

fat, i.e., ~75 m2·kg–1 milk [20]. The small-est globules (<1 �m) represent more than80% of the total number of globules,although a few percent of the fat volume,and have a much higher specific surfacearea. A few large globules (>10 �m) alsoexist, comprising about 2% of the fat, witha lower specific surface area [28]. It hasbeen suggested that small and large fatglobules would differ slightly in composi-tion [24], but this is still not fully eluci-dated [28].

The structure and texture of dairy gelsand cheeses are affected by the interactionsbetween the surface of milk fat globulesand the casein matrix. In this respect,native milk fat globules do not interactwith the protein network in dairy gels andact mainly as inert fillers or structurebreakers, depending on their size andnumber [19, 25]. For a given fat content, ifnative MFG were smaller, they wouldrepresent a greater number of weak pointsin the matrix and a larger surface area ofMFGM, with a higher water-bindingability and enzymatic content. Conversely,large fat globules can be expected toprovide larger weak points, although lessnumerous. The use of small or large nativeMFG can be expected to result in differentcheese texture and aroma, as alreadyobserved for various dairy products in apreliminary study [8] and in low-fatCheddar cheese [23]. We should point outthat the use of small globules produced byhomogenization, where the native MFGMhas been disrupted and replaced by caseinmicelle fragments, results in structureenforcement by creating links with thecasein network [2]. Therefore, this type ofglobule does not possess the genuinecharacteristics of native globules and couldnot be compared with products made withsmall native MFG.

Until recently, it was not possible toselect milk fat globules efficiently accord-ing to their size, since centrifugationtechniques were not selective enough.However, it is now possible to obtainnative milk fat globules of varioussizes from whole milk by using a newmicrofiltration process developed in ourlaboratory [7], that can lead to new manu-facture processes. Using this technology,milk is filtered on tubular microporousceramic membranes with a uniform trans-membrane pressure, which allows the col-lection of the smallest fat globules in thepermeate or the largest ones in the reten-tate. The small globules obtained in thisway are native, conversely to globules

Camembert with small and large fat globules 133

formerly obtained by homogenization, thatare disrupted and covered by caseins.

The aim of this work was to investigatethe influence of the size of the native milkfat globules on the physico-chemicaland sensory characteristics of Camembertcheese, using milk fractions with small(~3 �m) or large (~6 �m) fat globulesobtained by microfiltration.

2. MATERIALS AND METHODS

2.1. Camembert cheese production

Three series of Camembert cheesemanufactures were performed accordingto the following process. The resultspresented are the average of the threemanufactures for each type of Camembertcheese (small or large fat globules).

Day D-1. Raw whole milk purchasedfrom a local dairy plant (Entremont,Montauban-de-Bretagne, France) wascollected and stored at 4 °C the day beforeCamembert production (D-1). Milk wasmicrofiltered with a uniform transmem-brane pressure according to a process pat-ented in the laboratory [7]. Appropriatemembrane pore sizes and hydrodynamicconditions were used, so as to obtain twomilk fractions differing in the diameter offat globules, namely, around 3 and 6 �m,respectively. The corresponding fractionswill be called small fat globule (SFG) andlarge fat globule (LFG) fractions. The SFGfraction was concentrated using a creamseparator (Elecrem, Vanves, France). Itwas checked that the milk fat globulesremained native and were not disrupted bythe microfiltration process by measuringthe globule ��potential, with the procedureand apparatus described by Michalskiet al. [21]. Milk samples were adjusted to afat content of 28 g·kg–1 using skimmedmilk, before being pasteurized at 72 °Cfor 20 s (Actini, France). Cooling wasperformed in a milk vat at 11 °C. The milkwas inoculated (2 � 1011 per 100 kg)with mesophilic starters MM100 (Rhodia,

Tours, France) – Lactococcus lactis subsp.lactis, cremoris, and lactis biovardiacetylactis – and ripening flora (Rhodia):Geotrichum candidum GEO 17 (2 dosesper 1000 kg), Penicillium camemberti LV2(5 doses per 1000 kg), and Kluyveromyceslactis 71 (2 doses per 1000 kg). 14 mL of asolution of CaCl2 at 510 g·L–1 was addedper 100 kg of milk. The milk was thenmatured at 11 °C for 18 h.

Day D. The milk was heated at 34 °C inthe milk vat and left to ripen until itreached a pH of 6.35. After transfer into acheese vat, renneting was carried out at33 °C using 0.22 mL·L–1 of rennet (at520 mg·L–1 of chymosin, Gand Gassiot,purchased from Chris Hansen, Arpajon,France). Setting time was in the range8–10 min in a room at 28 °C. The curd wascut after four setting times into 1.5 � 1.7 �1.7 cm cubes. Two stirrings were operated,at 10 and 25 min after cutting, beforemoulding into 20 cm diameter moulds at26 °C. The cheeses were turned at thefollowing times after moulding andtemperature: 45 min (23 °C), 2 h (21 °C)and 5 h (18 °C). Whey was extractedcontinuously from stirring at day D totaking the cheeses out of the moulds at dayD+1.

Day D+1. The cheeses were taken outof the moulds and salted in brine (350 gNaCl per L water, no calcium added) at12 °C for 25 min.

Ripening was performed at 12 °C, 98%relative humidity for 10 d, with one turningafter 6 d. After 10 d, the cheeses werecooled to 4 °C and packed in laminatedpaper and poplar boxes for Camembert.

2.2. Biochemical and physico-chemical analyses

Cheese samples were analyzed after 1,10, 20, 30 and 40 d (D+1, ... D+40). ThepH was measured at D+1. Total solids (TS)were estimated by drying 2 g of cheesemixed with sand at 102 °C (�� 2 °C) for7 h [4]. Fat content was determined using

134 M.-C. Michalski et al.

the acid butyrometric method of vanGulick [6]. Total nitrogen (TN) in cheeseswas obtained from nitrogen analysis usingthe Kjeldahl method [5]. For all samples,the protein breakdown during ripening wasmeasured by the evolution of solublenitrogen at pH 4.6 (NCN, non-caseinnitrogen), and 12% TCA-soluble nitrogen(NPN, non-protein nitrogen), according tothe method described by Gripon et al. [9].To quantify the evolution of proteolysis,the following ratios were calculated: NPN/TN and (NCN-NPN)/TN, expressed as apercentage of the cheese TN content.Analyses were performed in triplicate.

Corrected cheese yield (Y, kg per100 kg milk) on a 440 g·kg–1 TS basis wascalculated as follows [16]: Y = (TSmilk–TSwhey)/(440–TSwhey) � 100. Moisture ona fat-free basis (MFFB, %) was calculatedas follows: MFFB = (1000–TS)/(1000–Fat content) � 100. Fat in dry matter(FDM, %) was calculated as follows:FDM = Fat/TS � 100.

2.3. Size distribution measurements

The particle size distribution of cali-brated milk was measured by laser lightscattering (LLS) using a Mastersizer 2000(Malvern Instruments, Malvern, UK) withtwo laser sources. The refractive index ofmilk fat was taken to be 1.460 at 466 nmand 1.458 at 633 nm [18]. The milk samplewas diluted (1:1) in EDTA (99%, Merck,Darmstadt, Germany) 35 mmol·L–1 pH 7,before a few drops were introduced intothe apparatus circulating cell containing100 mL of distilled water with 0.05% SDS(sodium dodecyl sulfate, Merck). EDTA isused to dissociate casein micelles in orderto detect the fat globules only, and theslight quantity of SDS dissociates clusters.The refractive index of the aqueous phasewas 1.33. From the size distribution, theaverage diameter d43 = ��vi � di)/�vi wascalculated by the software (where vi is thevolume of globules in a size class of dia-meter di) as well as the specific surfacearea. In order to estimate the fat globule

size distribution within the cheese curd,the casein matrix was dissociated with6 mol·L–1 urea, 100 mmol·L–1 EDTA,20 mmol·L–1 imidazole buffer pH 7 andshaken gently for 30 min, prior to measure-ment as described above.

2.4. Rheological measurementson Camembert curds

Rheological properties of Camembertcurd at the end of drainage were measuredwith a universal testing machine (Instron,model 4501) using the series IX software,equipped with a 100 N load cell and a plateof 60 mm. Sampling was performed on thedrained curds at 18 °C and involved thecutting of � 10 plugs (20 mm in diameterand 20 mm height). Plugs were stored at20 °C for at least 1 h in an aluminium foilprior to compression. The crosshead speedwas 30 mm·min–1. The rheologicalparameters were the fracture stress (Pa),the fracture Hencky’s strain and theYoung’s modulus (Pa) [26]. Stress datawere corrected for the increase in the plugsurface during compression, assuming aconstant sample volume.

2.5. Scanning electron microscopy (SEM)

Slices (1 � 1 � 3 mm) of SFG and LFGCamembert cheeses at day D+10 were leftovernight at 4 °C in 0.1 mol·L–1 cacodylatebuffer, pH 7.0, with 2.5% glutaraldehyde(Sigma, Saint-Louis, USA). They wererinsed thoroughly with osmosed water anddehydrated in successive 20 min-baths ofethanol (10, 25, 50, 75, 95) at 4 °C,followed by two baths in absolute ethanol(Merck, Darmstadt, Germany). Sampleswere dried by the critical point techniquein liquid CO2. After fracture and glueingonto sample holders, they were stainedwith gold by sputtering. Observationswere performed with a SEM microscopePhilips XL 20 (acceleration tension: 8 or10 kV).

Camembert with small and large fat globules 135

2.6. Confocal laser scanning microscopy (CLSM)

The CLSM (LSM 410 Axiovert, LePecq, France) was performed in fluores-cence mode [10]. Cheese pieces cut fromthe Camembert center were frozen at–150 °C by plunging into isopentanemaintained into liquid nitrogen. Sampleswere transferred in a cryotome chamber at–20 °C. Slices (20 �m thick) were cut fromthe cheese pieces and left to dry. The pro-tein matrix of SFG and LFG Camembertcheeses was stained by the fluorescentdye FITC (Sigma, St-Quentin-Fallavier,France) and the fat globules were stainedby Nile red (Aldrich, St-Quentin-Fallavier,France) [1]. The dyes were dissolved in anethylene glycol/water mixture and onedrop was left in contact with the cheeseslice for 15 min, before rinsing with dis-tilled water. Labeled cryotomed sliceswere transferred to microscope slides withconcave cavities, covered with a sealedcover slip. Observations of the cheeseswith the CSLM were performed onthe same field with a �63 oil immersionobjective at wavelengths of 543 and488 nm, which are close to the excitationmaximum of Nile red and FITC, respec-tively. Nile red fluorescence emission wasrecorded between 575 and 640 nm,whereas that of FITC was recordedbetween 510 and 525 nm, which allows agood spectral discrimination between thetwo components. This procedure allows acolocalization of fat and proteins in thesame field of observation. Observationswere performed for each sample at zooms2 and 4, and typical pictures were chosen.

2.7. Sensory analysis

Sensory analyses were performed by aspecialized company (Les Maisons duGoût, Rennes, France). The sensorialprofile of the Camembert cheeses (3rdmanufacture) at D+25 was described induplicate by a panel of 12 individuals. Thepanel was specially trained to test soft

ripened cheeses. The descriptive approachallowed the identification of organolepticdifferences between the two types ofCamembert cheese (SFG vs. LFG). Mark-ing for each descriptor was performed onan intensity scale ranging from 0 to 10.Sensory descriptors were: homogeneousaspect of the curd, flowing aspect of thecurd, color of the curd, odor intensity, elas-tic texture, firm texture, crust perception,chalky texture of the curd, sticky texture,melting texture, flavor intensity, richnessof aromas, salt savor, acid savor, bittersavor, picking taste, ammoniac flavor.Samples were kept at 15 °C for 2 h beforebeing served at 13 °C. Sensory analyseswere performed with ¼ of SFG and LFGcheeses for each consumer, in air-condi-tioned individual boxes, with natural light.Samples were encoded to remain anony-mous to the panel, and the consumers wereasked to consume them in a specifiedorder, so that half of the panel tasted theSFG cheese first, and vice versa.

2.8. Statistical analysis

The StatGraphics Plus software (Manu-gistics, Rockville, USA) was used to per-form analysis of variance. A Fisher testwas followed by a least square differenceprocedure by size, to test the significanceof result differences. Below, a significantlydifferent result means P < 0.05 and avery significantly different result meansP < 0.01. Concerning sensory analysis,analysis of variance with two factors(product and consumer, Newman-Keulstest) identified significantly differentcharacteristics between both cheeses (SFGand LFG).

3. RESULTS AND DISCUSSION

The �-potential of SFG was –13.5 �0.6 mV and that of LFG –13.4 � 0.4 mV,which is the same value as that of the ori-ginal globules from whole milk and showsthat the fat globules remained nativethroughout the microfiltration process [21].

136 M.-C. Michalski et al.

As shown in Table I, the composition ofSFG and LFG milks used to preparecheeses was not significantly different.Figure 1 shows that less whey (0.93%)was collected from the SFG fraction,with similar composition (Tab. I). Thisdifference was significant even at the firstturn. Consequently, the corrected yieldwas thus 3.7% higher for SFG cheeses(Fig. 1). Moreover, fat recovery was verysignificantly different between both typesof cheeses: 93.4 � 1.8% for LFG vs. 99.9 �0.1% for SFG. However, the fat globulesize did not affect other technologicalparameters such as manufacture timeand pH decrease. Throughout the entire

ripening period, the FDM and totalnitrogen were not different according tothe fat globule size of the cheeses. How-ever, Table II shows that the MFFB was

Table I. Physico-chemical properties and composition of the milk and fat globule used to produceCamembert, and of the whey extracted from the corresponding Camembert curd (average of thethree different cheese productions).

d43(�m)

Fat(g·kg–1)

TN(g·kg–1)

NCN(g·kg–1)

NPN(g·kg–1)

TS(g·kg–1)

Milk: SFG 3.30 � 0.03 28.6 � 0.6 33.5 � 0.3 7.7 � 0.1 1.7 � 0.0 115.9 � 0.8

LFG 6.03 � 0.04 28.8 � 0.9 33.4 � 0.1 7.9 � 0.2 1.7 � 0.0 114.8 � 1.3

Whey: SFG 1 � 0 9.6 � 0.2 65.3 � 0.5

LFG 1 � 0 9.7 � 0.0 65.3 � 0.6

TN: total nitrogen; NCN: non casein nitrogen; NPN: non protein nitrogen; TS: total solids (dry matter).SFG: small fat globule milk; LFG: large fat globule milk.

Figure 1. Weight ofdrained whey (�) andcorrected yield accoun-ting for a dry matter of440 g·kg–1 (�) fromCamembert cheeseswith different diameterof native fat globules(d43). Bars representthe standard deviation.

Table II. Composition of Camembert cheeses,with different sizes of fat globules, after 40days of ripening.

SFG LFG

FDM (% w/w) 51.1 � 0.6 51.2 � 0.6

MFFB (% w/w) 71.5 � 0.6 69.3 � 0.2

FDM: fat on dry matter; MFFB: moisture on afat-free basis. SFG: small fat globule milk;LFG: large fat globule milk.

Camembert with small and large fat globules 137

significantly different between SFG andLFG cheeses, SFG cheeses having 2.2%more moisture (MFFB) than LFG 40 dafter manufacture. As presented inFigure 2, peptide and amino acid content(NPN/TN) was significantly higher inSFG cheeses, as well as soluble proteins

([NCN-NPN]/TN), throughout the entireripening period.

In Figure 3, we can see that largerparticles than the original fat globulesremained in the Camembert cheese whenthe casein matrix had been dissociated. Asobserved by optical microscopy (result not

Figure 2. Evolution of soluble nitrogen of cheeses during ripening, as a function of native fatglobule size. Peptides and amino-acids (NPN/TN): (�) SFG, (�) LFG. Soluble proteins ([NCN-NPN]/TN): (�) SFG, (�) LFG. Bars represent the standard deviation.

Figure 3. Particle size distri-bution of small (�) and large(�) fat globules in cheesemilk (thin line) and in cheesecurd (thick line) the day aftermanufacture, after dissocia-tion of the casein matrix byEDTA, urea and SDS (typicalexample).

138 M.-C. Michalski et al.

shown), these particles corresponded to fatglobule aggregates. The latter represent theway fat globules were arranged within thecheese structure. Figure 4 shows confocalmicrographs of SFG and LFG cheesecentres. The difference in fat globule sizecan be readily observed, as well as thepresence of globule aggregates, especiallyfor LFG. It is clear that milk fat globulesare embedded within the casein matrix.Scanning electron micrographs, taken inthe cheese center or in the crust (below

Penicillium), are shown in Figure 5. Voidscorrespond to the fat globules, only thecasein matrix structure is observed. It canbe seen from the highest magnification(Fig. 5 �� bottom) that some fat globulesmay be interconnected, which is consistentwith the aggregates observed by CLSMand particle size measurements. Thedistribution of fat globules throughout thematrix seems to be rather homogeneous. Itwas observed that bacteria colonies werelocalized around milk fat globules (results

Figure 4. Confocal laser scanning micrographs of small (SFG) and large (LFG) native fat globulesat the center of Camembert cheeses, at two different magnifications. Fat is coded in red and proteinsin blue. Scale bar represents 10 �m.

Camembert with small and large fat globules 139

Figure 5. Scanning electron micrographs of the center and the crust of Camembert cheeses withsmall (SFG) and large (LFG) native fat globules, at different magnifications. Scale bar represents10 �m.

140 M.-C. Michalski et al.

not shown); however, it is not knownwhether this is significant, considering thenumber of micrographs.

Fat is known to be important in allowingmoisture to be retained in cheese [17],which is linked to the ability of the nativemilk fat globule membrane to bind water.This water-binding ability can explain thelower whey to milk ratio of SFG cheesescompared with LFG. Indeed, for a givenfat content, SFG have a greater total sur-face area of MFGM: ~2.2 m2·g–1 for SFLvs. ~1.2 m2·g–1 for LFG in this study, i.e.,the surface is two-fold when the diameteris halved. Consequently, the 0.4 kg differ-ence in the drained whey ratio betweenboth fractions (Fig. 1) corresponded toabout 250 mg of water per m2 of MFGM.Moreover, considering Figure 3 andFigure 4, it seems that SFG formed lessaggregates than LFG, which would alsocontribute to their greater water-bindingability. Finally, the cavities formed by thefat globules in the casein matrix aresmaller for SFG (Fig. 5), and these smallerpores are more likely to retain the serumthan large pores. The better fat recovery forSFG suggests that small globules are betterentrapped in the casein matrix, eventhough they do not interact positively withcaseins. These results are consistent withthe higher MFFB observed for SFG.This increase in available water is alsolikely to explain the greater proteolysis ofSFG compared with LFG, as enzymaticactivities are enhanced.

The rheological properties of the curdare presented Table III. The compression

curves of the Camembert cheese showedquite a linear part until a Hencky’s strain of0.5, followed by a marked fracture. Therigidity (Young’s modulus) and the firm-ness (fracture stress) of SFG cheese curd atD+1 were significantly lower than those ofLFG cheese. No difference was observedregarding flexibility (fracture strain) theday after manufacture. The lower rigidityand firmness of SFG curds can be relatedto the finer dispersion of small fat globuleswithin the matrix, corresponding to morenumerous weak points in the casein net-work. Roughly, the SFG average diameterbeing about half the LFG diameter, thiswould correspond to eight times moreglobules in the SFG curd. The interglobu-lar distance (or mean free distance betweenfat globules) can be estimated from the fatglobule diameter and fat volume fractionaccording to Walstra [27]: ~1.8 �m forSFG cheese vs. ~3.3 �m for LFG cheese.Thinner casein strands are thus formedbetween the globule pores in SFG (Figs. 4and 5), resulting in a more fragile structure.

Sensorial profiles of SFG and LFGcheeses are presented Figure 6. Significantdifferences concerned the greater flowingaspect of SFG, together with its more elas-tic and melting texture, and the yellowercolor of LFG, together with its firmer andchalkier texture. Overall, the SFG cheesescan be defined as smoother, which is con-sistent with their higher MFFB (Tab. II),the more advanced proteolysis (Fig. 2) andrheological properties of curds (lowerrigidity and firmness, Tab. III). The cheesemeltability is known to be due to the

SFG LFG

Number of repetitions 50 47

Young’s modulus (Pa) 42581a � 8108 53639b � 8338

Fracture strain 0.45a � 0.04 0.46a � 0.04

Fracture stress (Pa) 16343a � 2491 20613b � 2958

Significant differences exist between values followed by differentsuperscripts.

Table III. Rheological characteristics of Camembert curd made with small (SFG) or large (LFG)fat globules.

Camembert with small and large fat globules 141

melting of milk fat, followed by collapsingof the cheese matrix due to reduced sup-port by the fat [14]. This collapse can occurfaster in SFG cheeses, because the inter-globular distance is smaller and thus caseinstrands are thinner. The overall smooth-ness can also be due to the in-mouthperception of milk fat globules. The SFGsurface area being larger than that of LFG,it provides a greater fat interface in contactwith the mouth. Moreover, SFG are closerto each other, which we suppose may leadto a better fat perception. The firmer tex-ture of LFG cheeses is also consistent withrheological measurements on curds (frac-ture stress, Tab. III). Their chalkier texturecan be related to their lower MFFB and totheir thicker (almost twice) inter-globulecasein strands. The yellower color of LFGcan be related to the light diffraction phe-nomenon, that is lower in LFG and resultsin a more intense color perception. Com-positional differences between globulesthat would lead to color differences wouldhave to be investigated.

Other sensory parameters of impor-tance, even though not significantly

different, were the richer and more intenseflavor of SFG, and the higher acidity ofLFG. This difference in flavor is consistentwith the higher proteolysis of SFG, espe-cially concerning the presence of free pep-tides and amino acids (NPN/TN, Fig. 2).Moreover, for a given fat content, SFG aremore numerous than LFG, which results ina larger surface area of MFGM. This inter-face being the specific site for lipolyticactivity, flavor-producing reactions arethus likely to be enhanced in the SFGcheese. Moreover, the MFGM containsmore than 25 enzymes, half of which beingmembers of the hydrolase class (includinglipases), that are involved in the develop-ment of cheese flavor [13]. Consequently,the richer and more intense flavor of SFGcheese may be due to its greater MFGMcontent, too. This larger MFGM surfacearea also provides a greater contact surfaceof fat in the mouth, that is likely to enhancearoma perception. Wijesundera [30] indi-cates that the sphericity and composition ofmodel fat globules affect Cheddar cheeseflavor. However, the process for this typeof cheese induces fat globule distortion and

Figure 6. Sensorial profile of Camembert cheeses with small (�) and large (�) native milk fatglobules. Arrows show significantly different characteristics (P < 0.05, Newman-Keuls test).

142 M.-C. Michalski et al.

coalescence, which cannot be comparedwith Camembert cheese. Saint-Gelaiset al. [23] found that low-fat Cheddarcheeses with native globules of 2.4 �mdiameter had improved sensory character-istics compared with globules of 1.6 �mdiameter. However, we can hardly com-pare these results with ours since both theprocess and the fat globule diameter aredifferent.

We should discuss that part of theresults can be due to physico-chemical andbiochemical differences between milk fatglobules according to their size. Indeed,when artificial recombined fat globules arecreated by emulsifying milk fat in skimmilk, whatever their size, they have thesame composition and their membrane iscomposed of caseins. Conversely, nativemilk fat globules are likely to differ accord-ing to their size, even though this has stillto be fully elucidated [28]. It has beenfound, using recombined fat globules ofvarious sizes with milk fat or model fat,that a deeper supercooling is needed tocrystallize smaller fat globules, that alsohave a lower crystallization rate [15, 29].We can suppose that these results wouldalso hold for native milk fat globule of var-ious sizes, since they are explained by thelesser number of catalytic impurities perglobule for smaller ones [29]. Moreover,the composition of the interface, using var-ious proteins, has been found to affect thecrystallization properties of model fatglobules [15]. Therefore, the solid fatcontent in cheese fat globules at a giventemperature is likely to be lower for SFG.This could contribute to the greater flowingaspect and melting texture of SFG cheeses[11, 12]. Finally, possible compositionaldifferences according to fat globulesize [24] could contribute to the differencesin cheese flavor, as different aroma precur-sors would exist in the two fractions.

4. CONCLUSION

The size of native milk fat globules wasfound to affect the physico-chemical and

sensory properties of Camembert cheese.The use of smaller milk fat globulesresulted in cheese with more moisture anda more melting texture, which suggests thepossibility of developing products withnew technological and sensory properties.These results can be explained by thelarger surface area of the milk fat globulemembrane and thinner casein strands ofsmall fat globule cheese. Experiments arebeing carried out in our laboratory to fur-ther characterize the possible differencesof composition, crystallization and fusionproperties of native milk fat globulesaccording to their size. This current workwould provide a better knowledge con-cerning the role of these fat globules incheese. Moreover, the influence of the sizeof native milk fat globules on the proper-ties of other dairy products should beinvestigated.

ACKNOWLEDGEMENTS

J. Berrier and C. Garnier are acknowledgedfor performing SEM and CLSM observations,respectively. We thank E. Le Put, M.N. Madecand H. Goudédranche for technical assistance.

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