ORIGINALRESEARCH Manipulation of Dhaka cheese curd and effects on cheese

quality

RAIHAN HABIB,1 RODNEY ANDREW WILBEY2 and ALISTAIR STEVENGRANDISON2*1Department of Dairy Science, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh, and 2Department ofFood and Nutritional Sciences, University of Reading, Whiteknights, Reading RG6 6AP, UK

*Author forcorrespondence. E-mail:a.s.grandison@reading.ac.uk

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Dhaka cheese is a semihard artisanal variety originating from Bangladesh where manual curd kneadingis a normal stage in its manufacture. Dhaka cheeses were produced with different degrees of curd knead-ing to quantify the curd manipulation process in terms of pressure and to standardise the length of opera-tion. The effect of manipulation on the composition, rheology, texture and microstructure of fresh cheesewas also studied. Manipulation had significant effects (P < 0.05–0.001) on most of the parameters stud-ied. One minute of curd manipulation was found to be sufficient for Dhaka cheesemaking.

Keywords Dhaka cheese, Curd manipulation, Composition, Rheology, Texture, Microstructure.

INTRODUCT ION

Dhaka cheese is a small semihard cheese madefrom cow’s milk and sometimes with addition ofbuffalo milk (Van den Berg 1988). This varietywas reported to have been made mainly in the HoarTract in Mymensingh, Bangladesh, in the past(Davis 1976), though it is now widely manufac-tured all over Bangladesh. The production and mar-keting have long been carried out as a small-scalefamily business following traditional practices.Cheese quality depends more on the art of cheese-making as there is obviously no recommendedmanufacturing procedure (Miah and Quddus 1971).The cheesemaking process of Dhaka and some

other artisanal varieties involves a specialised opera-tion – kneading or working of curd by hand, alsotermed ‘manipulation’, after the first drainage ofwhey. This manipulation is performed to help breakup themass of curd, to aidwhey drainage and get thecurd to a suitable form for moulding. In some cases,it may also help to distribute salt uniformly and toknit the curd in subsequent pressing. The intensity ofpressure applied by fingers and palms plus durationof the operation affects the final condition of thecurd, which in turn may influence the composition,body and texture, and thus should be included in thestandard of identity of that cheese variety.There are very few references, for example, Le

Jaouen (2000) and Roseiro (2003), to curd manipu-lation during cheesemaking. Roseiro (2003)

reported that Serpa cheese curd is worked until itbecomes sufficiently dry to be distributed intosmall moulds. The working and hand pressing con-tinue in these moulds for a while and then the curdis left to rest. Le Jaouen (2000) suggested that suf-ficient curd kneading before final moulding cancorrect grainy texture in cheese. In contrast, thecurd of some cheese, for example, Pasta Filatatypes, is kneaded after scalding to enhance theplasticising effect, which results in an entirely dif-ferent curd structure (Robinson and Wilbey 1998).However, Dhaka cheese curd is worked soon afterenzymic coagulation and initial draining of whey.Miah and Quddus (1971) mentioned the squeezingof curd for making Dhaka cheese.Despite a wide variation in the manipulation pro-

cess by different producers of Dhaka cheese, noattempt has been made to standardise this process.The aim of this study was to quantify curd manipu-lation in terms of pressure and length of operationand to observe the effect of manipulation on thecomposition, rheology, texture and microstructureof fresh Dhaka cheese.

MATER IALS AND METHODS

Cheesemaking processDhaka cheese was manufactured in the pilot plantof the Department of Food and NutritionalSciences, University of Reading, UK. Pasteurisedunhomogenised whole milk was supplied by

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Waitrose Ltd., Bracknell, UK. Each batch of curd was pro-duced from 51 kg of milk. Milk was preheated to 30 �C beforebeing inoculated with a mesophilic homofermentative starterculture (CHN 12; Chr. Hansen’s Laboratories Ltd., Hungerford,UK) at 0.3 g ⁄kg cheese milk. Commercial standard coagulant(CHY-MAX Plus; Chr. Hansen’s Laboratories Ltd) at 0.3 g ⁄kgof cheese milk was added 30 min after the starter addition, tocoagulate the cheese milk within 1 h. The coagulum was cutinto 20 · 20 · 50 mm pieces with a knife and allowed to standfor 15 min before being stirred for 20 s. Pitching took placewithin 20 min from the end of stirring. The curd and whey mixwas scooped into 1.5 m2 muslin cloths, each of them beingspread over 15 L buckets, and then folded over to encompass12 L of the mix to drain the whey. Initially, the curd was gentlypressed by hand several times to aid drainage and then hung for2 h. After drainage, approximately 2 kg of moist curd wasrecovered from each bag.The mass of curd was placed in a tray and weighed. Approxi-

mately 2 kg of curd was kneaded by hand for up to 3 min,while 0.8 kg of portions of curd were transferred in polypropyl-ene moulds (110 mm in diameter, 90 mm in depth; Ascott Ltd,Four Crosses, UK) at the start of manipulation and then at 30 sintervals during the operation for up to 180 s to gradually breakthe curd into smaller portions. Finally, the seven unsalted curdswere pressed at 15.6 kPa gauge pressure for 12 h at 24 �C and70% RH.

Quantification of manipulationThe pressure of manipulation was measured by a manometer(Figure 1) made in the laboratory. The manometer consistedof a rubber balloon (65 mm in length, 50 mm in diameter,and 0.27 mm wall thickness) connected by nylon tubing(1.4 m in length, 4 mm outer diameter, and 2 mm inner dia-meter) to an acrylic capillary tube (1.1 m in length, 6 mmouter diameter, and 4 mm inner diameter) through a T-shapedconnector, the side arm being connected via a valve to a res-ervoir (140 mL). As water from the reservoir was allowed toflow, it filled the balloon and part of the capillary tube. Thevalve was then closed. A metre scale was placed adjacent tothe capillary tube to aid measuring the height of the water col-umn. The entire assembly was fixed to a stand. The balloonwas placed inside the curd mass before manipulation wasstarted. Pressure applied on the curd during kneading wastransmitted through the balloon, and the fluctuation of waterlevel in the capillary tube was recorded by the video optionof a camera (Canon IXUS 95IS Digital Camera, Canon (UK)Ltd, Surrey, UK). The pressure data were recovered from theimages. A number of practice trials were run to make theprocedure perfect, and then, three trials were recorded.

Compositional analysesMilk and cheese were sampled according to standard methods(AOAC 2005) and analysed in duplicate. The cheese sampleswere coarsely cut into small pieces to make a homogeneous

mass for analysis. Fat, protein and lactose in whole milk andwhey were determined by a DairyLab II infra-red analyser(Foss UK Ltd., Warrington, UK). Cheese samples were analy-sed for total nitrogen by the Kjeldahl method (AOAC Interna-tional 2005), fat by a gravimetric method (IDF, 2004), andmoisture by an atmospheric oven method (Kosikowski andMistry 1997). Cheese slurries were prepared by blendingcheese with deionised water at 1:1 ratio prior to measuring thepH. A digital pH metre (Fisher Scientific, Leicester, UK) wasused to determine the pH of milk, whey and slurry.

Texture analysisTexture profile analysis (TPA) was carried out for freshly pre-pared cheeses. The two-bite test as specified by Bourne (2002)was adopted, to monitor the physical characteristics includinghardness, cohesiveness and springiness. Cylindrical cheesesamples, 20 mm high and 20 mm in diameter, were carefullycut from the cheese with a knife and a cork borer. Each cheesesample was put on the sample retaining plate where the auto-trigger detected the surface of the sample. All the samples wereanalysed in duplicate by a TA-XT2i Texture Analyser with a50 N load cell (Stable Micro Systems Ltd., Godalming, UK)

Metre scale

Stand

Reservoir

Acryliccapillary tube

Valve

Nylon tubing

T-shapedconnector

Rubber balloon

Figure 1 Manometer used to measure the pressure during manipulation.

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and with built-in software (TEXTURE EXPERT EXCEED,version 2.03, Stable Microsystems Ltd, Surrey, UK) to get acomplete three-dimensional analysis of force, distance andtime. The maximum force (N) was derived from the force –time curve. A cylindrical probe of 10 mm diameter was used,with a probe velocity of 1 mm ⁄ s. The samples were com-pressed to 50% of their original height. All the measurementswere carried out at 22 ± 1 �C.

Rheological studyRheological tests were performed on cheese samples usinga Bohlin C-VOR Rheometer (Malvern Instruments Ltd.,Malvern, UK). The method was adapted from Solorza and Bell(1995) with some modifications. Cheeses were sliced into1-mm-thick portions by a food slicing machine (Graef MasterM188; EPE International Ltd, Huddersfield, UK), and then, sam-ples were carefully collected as 20 mm discs, using a cork borer.Samples were packed in airtight plastic bags and kept at 2 �C, toavoid drying or structural disturbances, until the tests were car-ried out. Dynamic oscillatory measurements were performedusing a 20 mm diameter parallel plate system with 1 mm gapsetting for 90 s at 25 �C. Cheese samples were ‘rested’ for15 min to allow any stresses induced during loading to disperse.To ensure essentially linear viscoelastic behaviour, measure-ments were made by first making stress amplitude sweeps (stressrange 10–100 Pa; torque range 90–100 · 10)6 Nm) at afrequency of 1 Hz. All the samples were studied in triplicate.

Study of microstructureConfocal scanning laser microscopy was used to study thedistribution of fat and protein in cheese (Auty et al. 2001).Sections of samples, 20 mm in diameter and �5 mm thickfrom cheeses kept at 4 �C overnight, were collected with a corkborer and then sliced with a razor blade. One drop of stain,which was a mixture of Nile Red (Sigma-Aldrich Co., UK) andNile Blue (Sigma-Aldrich Co.), was put in the centre of a smallPetri dish and a sample was placed on it so that the finely cutstained surface faced the bottom. Nile Red was used to labellipid, while Nile Blue was used to label protein. Images fromthree different locations in each sample were captured by aLeica TCS-SP2-AOBS confocal laser scanning microscopeattached to a Leica DM IRE2 inverted epifluorescence laserwith bright field (Leica Microsystems, Mannheim, Germany).Images were processed with overlays of the two channels usingthe Leica DM IRE2 software.

Statistical analysis and data treatmentThe results were analysed for descriptive statistics includingmean and standard deviation (SD) followed by analysis of vari-ance (ANOVA) and Pearson’s linear regression analysis using theSPSS version 17.0 (IBM – SPSS, IBM UK Ltd, Portsmouth,UK). The effect of curd manipulation was evaluated for chemi-cal composition and physical parameters of freshly preparedDhaka cheese in a complete randomised design (Steel and

Torrie 1996). Duncan’s new multiple range test was performedto find the differences between means. The whole experimentwas carried out in duplicate.

RESULTS AND DISCUSS ION

Pressure during manipulationThe pressure of manipulation in all three observations showed asimilar pattern, gradually rising to the peak during the 2ndminuteand then dropping during the 3rd minute. The average pressurescalculated during the 1st, 2nd and 3rd minutes were 0.88 ± 0.09,1.06 ± 0.06 and 0.63 ± 0.08 kPa, respectively. The mean pres-sure during the 2nd minute was significantly higher (P < 0.001)than the 1st minute. This might in part be due to the largemass ofcurd which restrictedmovement of fingers during the initial min-ute, resulting in a lower pressure being applied. The ease of oper-ation during the second minute because of smaller and moremanageable curd pieces permitted an increase in both the fre-quency and force of kneading. Thereafter, the significant(P < 0.001) drop in pressure during the 3rd minute was becauseof the breakdown of the curd, giving less resistance.

Effects on compositionThe gross composition of cheese was changed slightly by curdmanipulation (Table 1). Dhaka cheese made from unmanipulat-ed curd showed higher dry matter (hence less moisture)(P < 0.001), fat (P < 0.01) and protein (P < 0.01) contents.The data indicated greater moisture retention in cheese aftercurd manipulation – no significant difference between 30 and180 s for DM, while protein content decreased with manipula-tion, although remained stable in cheeses made from 90 to150 s manipulation. The DM content was similar to that incommercial Dhaka cheese, on an average 60.7%, as observedby Miah and Quddus (1970). However, the fat content ofcheese in the current experiment was found to be slightly less

Table 1 Composition (mean % w ⁄w) of cheese made from curd afterdifferent levels of manipulation1

Duration ofmanipulation(s)

Drymatter*** Fat** Protein** pH#

0 61.2a ± 2.4 33.0a ± 0.5 25.0a ± 0.3 5.10a ± 0.0530 56.8b ± 1.5 30.7b ± 1.3 22.9bc ± 1.3 5.09a ± 0.0560 57.7b ± 0.8 31.3b ± 0.7 23.5ab ± 0.6 5.12a ± 0.0690 56.8b ± 1.2 30.3b ± 1.5 22.3bc ± 1.5 5.08a ± 0.04120 57.0b ± 1.0 30.7b ± 1.0 22.7bc ± 1.2 5.07a ± 0.03150 56.6b ± 0.7 30.0b ± 0.7 21.9bc ± 0.9 5.06a ± 0.04180 55.7b ± 1.6 29.7b ± 1.1 21.4c ± 1.2 5.07a ± 0.011Mean values ± SD for two replicates of each type of cheese analysed

in duplicate (N = 4). a,b,cMeans within the same column without a

common superscript are significantly different: ***P < 0.001;

**P < 0.01; #not significant, P > 0.05.

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(29.67–32.97% w ⁄w) than that observed by Miah and Quddus(1970) for commercial cheese (35.5–36.0% w ⁄w). This wasprobably due to the composition of the milk used for cheese-making because commercial Dhaka cheese is made mainlyfrom milk of the Zebu-cattle (Bos indicus) which has a higherfat content than that from most of the European breeds such asHolstein-Friesian (typically �4% w ⁄w in the UK). Moreover,the curd was manipulated at �30 �C while a portion of fat wasin liquid form. Thus, some of the fat could have been churnedout of the curd matrix and lost in the whey as the curd wasbroken and manipulated.

Effects on textureResults of TPA parameters of cheese are shown in Table 2.Hardness decreased significantly (P < 0.001) with the progressof manipulation showing less solid-like behaviour as describedby Ramkumar et al. (1997). The highest firmness was observedin cheese made with curd without manipulation, while at theend of the third minute, the curd was very soft and the resultingcheese also showed the lowest hardness. There was a stronginverse correlation between hardness of curd and manipulationtime (R2 = 0.83). Rayan et al. (1980) observed that increasedstructural uniformity of the matrix improved firmness of pro-cessed cheese. They suggested that decreased structural unifor-mity resulted in an uneven distribution of stress, which wouldthen result in cheese having decreased firmness. Thus, becauseof increased curd manipulation, the strands of casein in the mat-ted curd were extensively destroyed and that probably facili-tated structural rearrangements in the protein matrix while thecurd was under press. The more manipulation the curdreceived, the greater was the breakdown; hence, the cheeseswith highly manipulated curd showed the lowest hardness pro-files. Progressive damage to fat globules during manipulationresulted in observable free fat at the later stage of manipulation(after 60 s) which acted as a barrier between curd grains.

Therefore, decreased protein-to-protein interactions wouldresult in a weakening of the protein matrix that led to decreasedhardness of the cheese. Johnson and Law (1999) mentionedthat excess amounts of free fat, if present between contact areasof curd particles, might prevent the curds from knitting prop-erly. Therefore, manipulation up to 60 s could be considered asthe maximum acceptable limit.The springiness in cheese made from unmanipulated curd

was slightly higher (P < 0.001) than manipulated samples butthere was little relationship between time of manipulation andspringiness. The figures decreased until 60 s manipulation, butslightly increased from 90 s. During manipulation, the caseinnetwork was disrupted, leading to more deformable curd grains.This and the slight reduction in DM may explain the decreasedvalues for springiness observed for manipulated curd cheeses.Curd manipulation made a significant difference (P < 0.001)

to TPA cohesiveness values among the cheeses. All the manipu-lated samples had higher values than the control, but there wasno clear relationship with time of manipulation. The lower valuefor the unmanipulated curd cheese could be linked to themoisturecontent. It has been suggested (Tunick 2000; Pastorino et al.2003a,b) that moisture content may affect cheese cohesiveness.In the unmanipulated curd cheese, the water trapped in thecheese matrix is accumulated principally in pockets embedded inthe curd matrix (Figure 2a). Manipulation of curd disrupted thewhey drainage channels, leading to more thoroughly dispersedmoisture, which induces water retention in the cheese matrix.The cohesiveness value was found to be highest in 60 s manipu-lated cheese, which could be attributed to the optimum curddeformation followed by better curd matting during pressing.Although the moisture contents of the manipulated curd cheeseswere similar, the differences in fat and protein contents, changesin protein interaction, and distribution of moisture might alsohave affected cohesiveness. Pastorino et al. (2003a) proposedthat decreased long-range protein interactions may cause thecheese to become less cohesive and elastic, andmore crumbly.

Effects on small amplitude oscillatory shear rheologyparametersValues of G¢, G¢¢ and G* followed a similar pattern with manipu-lation time (Table 3). In each case, the maximum value was seenafter 60 s manipulation, but other differences were less clear.Values for tan d showed no clear relationship. It is difficult toexplain these changes in terms of compositional changes.Curd manipulation may alter the arrangement of protein and

the dispersion of fat. Thus, rheological measurements were car-ried out to investigate cheese homogeneity as a function of curdmanipulation. Lucey et al. (2003) stated that the rheologicalproperties of cheese are influenced by a number of factorsincludingmanufacturing procedures. The complex interaction ofthe constituents of cheese gives it its characteristic viscoelasticity(Solorza and Bell 1995). All of the three major constituents ofcheese – casein, fat and water – contribute to the structure, hencethe rheology of the product (Lee et al. 1992). The viscoelastic

Table 2 Results of texture profile analysis parameters of fresh unsaltedDhaka cheese made from different levels of curd manipulation1

Duration ofmanipulation(s) Hardness*** (N) Cohesiveness*** Springiness***

0 7.20a ± 0.3 0.46c ± 0.02 0.74a ± 0.0130 5.33b ± 0.2 0.51b ± 0.02 0.73ab ± 0.0260 5.18b ± 0.2 0.55a ± 0.03 0.65d ± 0.0290 4.06c ± 0.1 0.53ab ± 0.02 0.70c ± 0.01120 4.07c ± 0.2 0.54ab ± 0.03 0.71bc ± 0.02150 3.84c ± 0.3 0.54ab ± 0.01 0.69c ± 0.01180 3.37d ± 0.3 0.53ab ± 0.02 0.71bc ± 0.02R2 0.83 0.34 0.061Mean values ± SD for two replicates of each type of cheese analysed

in duplicate (N = 4). a,b,cMeans within the same column without a

common superscript are significantly different: ***P < 0.001.

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Table 3 Results of small amplitude oscillatory shear rheometry parameters of fresh unsalted Dhaka cheese made from different levels of curdmanipulation1

Duration ofmanipulation (s)

Elasticmodulus*** (kPa)

Viscousmodulus*** (kPa)

Complexmodulus*** (kPa) Tan d#

0 111c ± 7 36b ± 2 127c ± 6 0.33a ± 0.0630 101d ± 4 32cd ± 2 110e ± 6 0.32a ± 0.0360 143a ± 3 45a ± 3 153a ± 4 0.32a ± 0.0290 133b ± 3 42a ± 3 141b ± 6 0.32a ± 0.01120 87e ± 6 29d ± 2 93f ± 3 0.33a ± 0.03150 113c ± 5 35bc ± 3 119d ± 5 0.31a ± 0.01180 111c ± 7 36b ± 4 118d ± 4 0.32a ± 0.011Mean values ± SD for two replicates of each type of cheese analysed in triplicate (N = 6). a,b,cMeans within the same column without a common

superscript are significantly different: ***P < 0.001; #not significant, P > 0.05.

(a) (b) (c)

(d) (e) (f)

(g)

Figure 2 Confocal laser scanning microscopy micrographs showing protein matrix (blue background) and fat globules (red patches) in fresh unsalted Dhakacheeses made from different levels of curd manipulation: (a) cheese made from unmanipulated curd; (b) cheese made from 30 s manipulated curd; (c) cheesemade from 60 s manipulated curd; (d) cheese made from 90 s manipulated curd; (e) cheese made from 120 s manipulated curd; (f) cheese made from 150 smanipulated curd; (g) cheese made from 180 s manipulated curd.

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behaviour of cheese largely depends on the protein and fat con-centrations and on the physical state of the fat (Visser 1991).However, their specific roles vary depending on their individualcharacteristics and orientation. Cheese gets its solid appearancefrom casein, which provides a continuous elastic framework forthe individual granules (Lee et al. 1992; Solorza and Bell 1995).Fat is embedded in this casein framework, often called ‘matrix’.Casein chains of neighbouring granules may be bonded togethereither by physical or by chemical bonds to give some rigidity tothe agglomeration of granules, resulting in an overall continuouselastic framework (Lee et al. 1992). A high level of interactionbetween casein micelles is indicated by a high value for G¢, theelastic modulus, (Karlsson et al. 2005).Moisture fills the spaces in between casein and the fat glob-

ule surface and therefore, acts as a low viscosity lubricant andplasticiser in the casein matrix. Even slight differences in mois-ture in Cheddar cheese have been shown to cause major differ-ences in rheological properties (De Jong 1978). The ratio ofsolid to liquid fat affects the rheological properties of cheese.Higher moisture content would result in wider gaps between fatsurfaces and the casein matrix, which would eventually allowgreater movement of water. Therefore, cheese would show lessoverall resistance to any deformation and greater ease withwhich it may recover after being deformed (Lee et al. 1992).Higher moisture content will make the casein plastic and viceversa (Prentice et al. 1993). Increase in water causes a swellingof the para-casein matrix and decrease in the molecular interac-tions. Lowering the moisture content increases the intermolecu-lar links by concentrating the proteins (Millet 2000: quoted byKaroui and Dufour 2003). Karoui and Dufour (2003) men-tioned that the firmness of cheese depends on the amount ofwater bound to the casein and on the presence of fat and freewater. Decreasing water content decreases the viscous modulus(G¢¢), while proteolysis increases this value.The cheese made from unmanipulated curd showed higher

G¢, G¢¢ and G* values than for 30 s manipulated curd cheese.This breakdown of the protein network was because of the curdmanipulation. The presence of curd junctions in the 30 smanipulated cheese was responsible for its structural weakness.Curd manipulation for 60 s, however, led to an increase in thetype of network interactions probably because of better curdknitting which improved the elasticity of cheese. Beyond 60 s,then perhaps the greater free fat, observable in the micrographs(Figure 2), resulted in less effective bridges between curd parti-cles and weaker structure. Although the cheese made fromunmanipulated curd had the highest percentage of DM, thepresence of small whey pockets (Figure 2a) might have hin-dered its solid structure and was responsible for its weakness ascompared to the 60 s manipulated cheese. This result was con-sistent with the comment by Gunasekaran and Ak (2003), whostated that the rheology of cheese could be affected by the het-erogeneities such as curd granule junctions, cracks and fissures.Curd without manipulation or slightly manipulated, for

example, 30 s, probably resulted in cheeses with coarse and

strong bonds between casein particles, but lacked the spatialdistribution. This distribution was enhanced by a proper degreeof manipulation, as after 60 or 90 s, and then reinforced bypressing. Further manipulation softened the curd excessively,releasing free fat and preventing drainage of whey to someextent as the ducts for whey passage were also disrupted. Allthese factors could be responsible for the decrease in G¢ and G*in cheeses that were made with longer curd manipulation.Lucey et al. (2003) reported that changes in the bonding withinthe elastic network could be responsible for a general decreasein G¢ and G*. The G¢ was greater than G¢¢ for all treatments,indicating a dominant contribution of the elastic component tothe viscoelasticity as mentioned by Kahyaoglu and Kaya(2003). Ustunol et al. (1995) reported this to be the typicalbehaviour for a solid viscoelastic material. Values for tan dwere constant, suggesting no fundamental change in the natureof the visco-elastic properties as a result of manipulation. Therheological parameters suggest that the manipulation of Dhakacheese curd should be limited to 60 s.

Effects on microstructureThe weakening of curd by excess manipulation can beexplained by inspection of the confocal micrographs. The spa-tial distribution of protein (blue) and fat (red) in the cheeses wasclearly observed in the different micrographs in Figure 2a–g.Horizontal sections of unmanipulated and manipulated curdcheeses showed that protein formed the continuous phase. Thefat occurred as discrete globules or irregular pools trapped inthe protein matrix. The porous network in the microstructure ofthe cheese made with unmanipulated curd is because of a largenumber of voids (black rings) in the matted curd (Figure 2a),remaining after pressing. However, these voids were reducedon manipulation of the curd as a result of breakdown of the curdinto finer granules. There were still a number of pores present inthe 30 s manipulated curd (Figure 2b). The trapped whey wasproperly dispersed during more extended manipulation, whichwas important for the quality of cheese.Breakdown of the curd particles was accompanied by the

release of free fat and the agglomeration of the fat into largerpools. By 120 s of manipulation, a number of these pools were‡100 lm in size (Figure 2f), with larger pools of fat observedat 180 s (Figure 2g). The micrograph of the cheese made fromcurd manipulated for 30 s showed a continuous casein networkwith dispersion of fat in tiny droplets. In the following twostages (60 and 90 s), these droplets had coalesced together toform larger droplets in the matrix (Figure 2c,d). The final stagesof manipulation (beyond 90 s) showed a partial separation offat to form very large droplets. Pools of free fat appeared by180 s manipulation. The presence of fat pools in the later stagesof manipulation (120–180 s; Figure 2e–g) indicated the dam-age to the fat globule membrane during curd manipulation,while the curd was still warm. These microstructural observa-tions were fairly consistent with those found previously formozzarella cheese (Guinee et al. 2002). It was clear from the

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micrographs that a compact protein matrix with finely dispersedfat globules was the result of 30–60 s of curd manipulation,and this could be considered as the baseline to determine theextent of manipulation needed for the commercial productionof Dhaka cheese.

CONCLUS ION

There were considerable variations in the compositional, tex-tural, rheological and microstructural properties of Dhakacheese samples. These differences probably reflect the variationin a single processing condition – the manipulation of curdbefore pressing. Deformability, enhanced by manipulation,affected the overall consistency of the cheese. The results ofthis study indicated that the cheese made from 60 s manipu-lated curd could be regarded as the most balanced one, with30 s manipulation as the next best option. Extended manipula-tion was counter-productive, with the release of free fat. How-ever, more extensive research is needed to determine the effectsof pH change, temperature and coagulant on the pressure ofmanipulation, with their subsequent effects on cheese quality.Greater understanding of pressure during manipulation ofcheese curd may help the cheese maker to learn how to regulatethe quality of Dhaka cheese and similar varieties.

R E F E R E N C E S

AOAC International (2005) Dairy products. In Official Methods of Analysisof AOAC International, pp 1–73. Horwitz W, ed. Gaithersburg, MD:AOAC International.

Auty M A E, Twomey M, Guinee T P and Mulvihill D M (2001) Develop-ment and applications of confocal scanning laser microscopy methodsfor studying the distribution of fat and protein in selected dairy products.Journal of Dairy Research 68 417–427.

Bourne M C (2002) Food Texture and Viscosity: Concept and Measurement,pp. 107–340. London: Academic Press.

Davis J G (1976) Cheese. Volume III Manufacturing Methods, pp. 906–907.Edinburgh: Churchill Livingstone.

De Jong L (1978) Protein breakdown in soft cheese and its relation to consis-tency. 3. The micellar structure of Meshanger cheese. Netherlands Milkand Dairy Journal 32 15–25.

Guinee T P, Feeney E P, Auty M A E and Fox P F (2002) Effect of pH oncalcium concentration on some textural and functional properties ofMozzarella cheese. Journal of Dairy Science 85 1655–1669.

Gunasekaran S and Ak M M (2003) Cheese Rheology and Texture, pp.1–27. Boca Raton, FL: CRC Press LLC.

IDF (2004) IDF 005:2004 Cheese and Processed Cheese Products – Deter-mination of Fat Content– Gravimetric Method (Reference Method).Brussels: International Dairy Federation.

Johnson M and Law B A (1999) The origins, development and basic opera-tions of cheesemaking technology. In Technology of Cheesemaking, pp1–32. Law B A, ed. Sheffield: Sheffield Academic Press.

Kahyaoglu T and Kaya S (2003) Effects of heat treatment and fat reductionon the rheological and functional properties of Gaziantep cheese. Interna-tional Dairy Journal 13 867–875.

Karlsson A O, Ipsen R, Schrader K and Ardo Y (2005) Relationship betweenphysical properties of casein micelles and rheology of skim milk concen-trate. Journal of Dairy Science 88 3784–3797.

Karoui R and Dufour E (2003) Dynamic testing rheology and fluorescencespectroscopy investigations of surface to centre differences in ripenedsoft cheeses. International Dairy Journal 13 973–985.

Kosikowski F V and Mistry V V (1997). Cheese and Fermented Milk Foods,3rd edn. Westport: FV Kosikowski LLC.

Le Jaouen J C (2000) Curd carry over. In Cheesemaking from Science toQuality Assurance, pp 341–352. Eck A, Gillis J-C, eds. Paris: LavoisierPublishing.

Lee H O, Luan H and Daut G D (1992) Use of an ultrasonic technique toevaluate the rheological properties of cheese and dough. Journal of FoodEngineering 16 127–150.

Lucey J A, Johnson M E and Horne D S (2003) Invited review: perspectiveson the basis of the rheology and texture properties of cheese. Journal ofDairy Science 86 2725–2743.

Miah A H and Quddus A (1970) Standards and standardization in the manu-facture of Dacca cheese – I. A. Standards of commercial Dacca cheese.Bangladesh Journal of Animal Science 3 33–38.

Miah A H and Quddus A (1971) Standards and standardization in the manu-facture of Dacca cheese – II. B. Effect of manufacturing. BangladeshJournal of Animal Science 4 23–31.

Pastorino A J, Hansen C L and McMahon D J (2003a) Effect of salt on struc-ture-function relationships of cheese. Journal of Dairy Science 86 60–69.

Pastorino A J, Ricks N P, Hansen C L and McMahon D J (2003b) Effect ofcalcium and water injection on structure-function relationships of cheese.Journal of Dairy Science 86 105–113.

Prentice J H, Langley K R and Marshall R J (1993) Cheese rheology. InCheese: Chemistry, Physics and Microbiology, Vol. 1, General Aspects,pp 303–340. Fox P F, ed. London: Chapman & Hall.

Ramkumar C, Creamer L K, Johnston K A and Bennett R J (1997) Effect ofpH and time on the quantity of readily available water within freshcheese curd. Journal of Dairy Research 64 123–134.

Rayan A A, Kalab M and Ernstrom C A (1980) Microstructure and rheologyof process cheese. Scanning Electron Microscopy 3 635–643.

Robinson R K and Wilbey R A (1998) Cheesemaking Practice. Gaithers-burg, MD: Aspen Publishers Inc.

Roseiro L B (2003) Characterisation and Authentication of Serpa Cheese,pp. 70. PhD thesis, Reading: University of Reading.

Solorza F J and Bell A E (1995) Effect of calcium, fat and total solids on therheology of a model soft cheese system. Journal of the Society of DairyTechnology 48 133–139.

Steel R G D and Torrie J H (1996). The Oneway Classification; MultipleComparisons; Multiway Classifications; Linear Regression; Linear Cor-relation. In Principles and Procedures of Statistics: A BiometricApproach, pp 139–299. Dickey D A, ed. New York: McGraw-Hill Inc.

Tunick M H (2000) Rheology of dairy foods that gel, stretch, and fracture.Journal of Dairy Science 83 1892–1898.

Ustunol Z, Kawachi K and Steffe J (1995) Rheological properties of Cheddarcheese as influenced by fat reduction and ripening time. Journal of FoodScience 60 1208–1210.

Van den Berg J C T (1988) Dairy Technology in the Tropics and Subtropics,pp. 194–222. Wageningen: Pudoc.

Visser J (1991) Factors affecting the rheological and fracture properties ofhard and semi-hard cheese. In Rheological and Fracture Properties ofCheese, Bulletin 268. pp 49–61. Brussels: International Dairy ederation.

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