Compositional, Rheological and Organoleptic Qualities of Camel Milk Labneh as Affected by Some Milk Heat Treatments

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1 World Journl of Diry & Food Sciences 8 (2): , 2013 ISSN X IDOSI Publictions, 2013 DOI: /idosi.wjdfs Compositionl, Rheologicl nd Orgnoleptic Qulities of Cmel Milk Lbneh s Affected by Some Milk Het Tretments Mrw M. Desouky, Smh M. Shlby nd K.A. Soryl 1 Deprtment of Breeding, Animl Production Division, Desert Reserch Center, Mtriy, Ciro, Egypt 2 Deprtment of Food Science, Fculty of Agriculture, Ain Shms University, Shoubr El Kheim, Ciro, Egypt strct: The present study ws crried out to investigte the chemicl, rheologicl nd microstructure properties of cmel milk Lbneh. Lbneh smples were mnufctured from cmel milk thermlly treted t 63 (T1), 85 (T2) nd 95 C (T3) for 30 min, wheres the control smple ws mnufctured from cmel milk psteurized on 72 C for 15 sec. Chemicl composition of resultnt Lbneh smples showed tht totl solids, protein nd ft contents were only significntly incresed in Lbneh smples which mnufctured from cmel milks thermlly treted t 85 nd 95 C for 30 min., while the lctose content ws decresed by incresing the therml tretment of cmel milk. The ph rnged from 4.90 to 4.78 during 1 to 9 dys of the study nd titrtble cidity rnged from 0.82 to 1.02% s percentge of lctic cid. The differences in cidity nd ph vlues in response to the pplied therml tretments were only significnt in highest tretment (95 C/30 min). The chnges in the pprent viscosity were incresed liner with the increse in the therml tretment of cmel milk nd lso incresed with storge time. The control smple hs presented higher index of syneresis thn the other tretments nd this index ws decresed s storge time progressed (9 dys) in ll smples. Scnning electron microscopy (SEM) reveled tht the protein mtrices of the high thermlly treted Lbneh smples (T2 nd T3) ppered to be reltively more intensive thn the control. In these tretments, the csein micelles were predominntly linked by prticle to prticle ttchment in chins with comprtively smll interspced voids (T2), rther thn by prticle fusion into big ggregtes (T3). However, the control exhibited more open, loose nd less dense protein network thn experimentl tretments. The overll cceptbility scores of the sensory evlution reveled tht T3, fresh s well s, stored ws the significntly most ccepted, while the control smple ws the lest. As storge progressed the orgnoleptic scores insignificntly decresed in ll tretments. The obtined results showed tht the therml tretment of cmel milk t 95 C for 30 min hd good significnt impct on the physiochemicl, texture nd sensory properties of resultnt Lbneh. Key words: Cmel milk Lbneh Chemicl composition Microstructure Milk het tretments Rheologicl properties Sensory evlution INTRODUCTION one of the technology options for mnufcturing diry functionl products. Cmel milk nd its products re The interest of both food producers nd consumers good nutritionl source for humn diet in severl prts of for functionl foods hs been exponentilly incresing the world s they contin ll essentil nutrients [1]. It hs during the lst decde. The use of milk with prticulr been reported tht cmel milk hs potentil therpeutic nutritionl properties such s cmel milk, in combintion properties, such s nticrcinogenic [2], ntidibetic [3] with bcteril strins hving probiotic properties nd/or nd ntihypertensive [4] nd hs been recommended to producing physiologiclly ctive metbolites, represents be consumed by children who re llergic to bovine milk Corresponding Author: Smh M. Shlby, Food Science Deprtment, Fculty of Agriculture, Ain Shms University, Shoubr El Kheim, Ciro, Egypt. 118

2 [5]. Cmel milk is somehow different from cow milk in its to hve greter resistnce to bcteril growth leding to chemicl composition but it contins ll essentil less ctive cultures nd thus cusing qulity problems in nutrients s cow milk, lso its high whey proteins such s its fermented products. The proteolysis rte in fermented lctoferrin nd immunoglobulin confer to it the high cmel milk hs been reported to be greter compred with ntimicrobil properties. The quntity of whey proteins is cow s milk [15]. Mohmed et l. [16], observed tht cmel higher in cmel milk thn cow's milk, t 0.9 to 1.0 percent milk filed to form gel like structure fter 18 h incubtion nd 0.7 to 0.8 percent, respectively. This is primrily due with lctic cid culture, this ws ttributed to the presence to the higher content of lbumin nd lctoferrin [6, 7]. of ntibcteril fctors such s lysozymes, lctoferrin Compred to cow, bufflo nd ewe milk ft, cmel milk ft immunoglobulin in cmel milk. These ntimicrobil fctors contins less short-chined ftty cids [8]. Some were present t significntly greter concentrtions in reserchers clim tht the vlue of cmel milk is to be cmel milk nd were more het stble compred with those found in the high concentrtions of linoleic cid nd the in cow nd bufflo milks [17]. Frh et l. [18] studied the polyunsturted cids, which re essentil for humn preprtion nd consumer cceptbility tests of fermented nutrition; cholesterol in cmel milk is lower thn cow or cmel milk. They found tht the consistency of fermented got milk [9]. The het stbility of cmel milk whey milk (under lb conditions) ws thin nd precipitte in proteins ws found to be considerbly higher thn in the form of flcks ws formed rther thn cogulum fter cow's milk. The verge lctose content of cmel milk is fermenttion. These reports clerly show the difficulty of slightly lower (4.62%) thn cow's milk (4.80%). Close producing fermented cmel milk products with high nlysis of cmel milk does show some medicinl consistency due to the problem ssocited with milk potentil. The milk protein lctoferrin, which present in cogultion. Concentrted yogurt is populrly known s lrge quntities in cmel milk (ten times higher thn in cow Lbneh in the Middle Est or s strined yogurt in milk), does hve some nti-virl nd nti-bcteril Greece nd rest of Europe. Lbneh is semisolid properties. Furthermore, cmel milk hs greter contents fermented diry food produced by removing prt of the of vitmin C, sh nd sodium, potssium, phosphorus, whey from yogurt to rech totl solid levels between 23 zinc, iron (10 times s rich in iron s cow's milk) nd nd 25 g/100 g, of which 8 11 g/100 g is ft [19]. Lbneh mngnese thn cow s milk [10]. In Russi, Kzkhstn mde from cmel milk hs not been given such ttention nd Indi s much s Liter dy being prescribed to in reserches compred with tht mde from cow milk. hospitl ptients to id recovery from tuberculosis nd Therefore, the objectives of this study were to dibetes. Cmel milk hs positive effects in controlling develop Lbneh from cmel milk, in ddition to study the high blood pressure nd helps in the mngement of effect of vrious therml tretments of cmel milk on the rteriosclerosis nd osteoporosis. Also, cmel milk physiochemicl properties nd the microstructure of contins high insulin nd insulin-like protein, which cn resultnt Lbneh. help in regulting the blood glucose levels in the dibetic ptients [11, 12]. Moreover, cmel milk lcks MATERIALS AND METHODS -lctoglobulin nd contins -lctlbumin, similr sitution to tht in humn milk. Previous reserch hs Mterils: Cmel milk btches were collected from the recommended the potentil use of cmel milk in the herd of Desert Reserch Center, Mrriott Sttion, Egypt. mnufcture of infnt formul [13]. All nimls were kept under the sme conditions. Every Products mde from cmel milk include the bulk milk btch ws nlyzed for chemicl composition trditionlly fermented products grris nd koumiss, nd divided into 4 lots for mnufcturing subsequent Domiti cheese, fresh soft white cheese, hrd cheese nd Lbneh tretments. The pproximte composition of used ice-crem [10]. The consumption of cmel s milk, cmel milk is shown in Tble 1. Commercil yogurt strter especilly in fermented form, is very old trdition in culture (YC-087) ws from Chr. Hnsen, Inc., Milwukee, different regions of the world such s Afric nd Middle WI nd consisting of Streptococcus thermophilus nd Estern countries [14]. Fermented cmel milk is high in Lctobcillus delbrueckii ssp. bulgricus. Commercil lctic bcteri, which hve been shown to be effective stbilizer (Grindstred ES 255) ws from Emulsifier nd ginst pthogens including Bcillus, Stphylococcus, Stbilizer System, Dnisco Ingredients, Brbrnd, Slmonell nd Escherichi [12]. Cmel milk ws shown Denmrk. 119

3 Tble 1: Chemicl composition (%) nd ph of cmel milk used in the mnufcture of Lbneh Chemicl composition (%) nd ph Smple Ft % ** Protein % Ash % *** Crbohydrtes % Totl solids % ph * Cmel milk 3.5± ± ± ± ± ±0.028 ** *** *: Bulk cmel milk smples Protein%=N 6.38 Clculted by the difference Mnufcture of the Experimentl Cmel Milk Lbneh Djurdjevic et l. [24] using Brookfield DV-E viscometer (Concentrted Yogurt): The mnufcture of Lbneh from (Brookfield Engineering Lbortory Inc., Stoughton, MA) cmel milk ws done bsed on the results of the with spindle size 0.15cm tht rotted t different rpm preliminry trils in n ttempt to increse firmness of rnged from (20-200) t sher rtes rnging from 4.2 to Lbneh. Three percentges of commercil stbilizers 42.1/s. Dt were collected Using Wingther soft wre (0.5, 0.75 or 1%) [10] nd strter culture (2, 3 or 4%) hs (Brookfield Engineering Lbortory Inc., Stoughton, MA). been dded to the cmel milk to prepre Lbneh. Bsing Viscosity ws monitored during storge t 5 C during on the sensory results of Lbneh (i.e., with the highest storge fter 1, 3, 6 nd 9 dys. intensities), the best results were 1.0% commercil stbilizer nd 4 % yogurt strter culture. Lbneh ws Scnning Electron Microscopy (SEM) Exmintion: mnufctured by procedure similr to tht reported by Lbneh smples were prepred for SEM ccording to the Al-Otibi nd El-Demerdsh [20]. Cmel milk smples were method of Brooker nd Wells [25]. The specimens were divided into 4 equl portions. One of them ws thermlly viewed in scnning electron microscope (JXA-840A treted t 72 C/15 sec nd served s control, while 3 Electron Probe Micronlyzer-JEOL-Jpn) fter other prts were thermlly treted t 63 (T1), 85 (T2) nd dehydrted using Criticl Point Dried instrument nd 95 C (T3) for 30 min in thermostticlly-controlled wter coting with gold using S150A Sputter Coter-Edwrdsbth nd were gently stirred during heting, then cooled Englnd. immeditely to 43 C using running tp wter nd then 1.0% commercil stbilizer ws dded. All tretments were Sensory Evlution: Cmel milk Lbneh smples were inoculted with 4% yogurt strter culture, then gitted subjected to orgnoleptic evlution by 10 pnelists of nd dispensed in plstic cups nd incubted t 43 C for the Stuff member of Animl Production Division, Desert 14 h ± 0.5 until it ws completely cogulted. The Reserch Center, Ciro, Egypt. Orgnoleptic evlution resultnt Lbneh smples were then put into cheese cloth ws crried out ccording to scheme of Slem et l. [26]. bgs nd mixed thoroughly with 0.5% NCl, which were Smples were orgnolepticlly scored for flvor hung in the refrigertor t 5 ± 1 C for 18 h, to llow (60 points), consistency (30 points) nd ppernce dringe of the whey. Lbneh tretments were stored t (10 points) when fresh nd fter storge for 9 dys 5 C over night nd then tested t different periods of cold t 5±1 C. storge (fresh, 3, 6 nd 9 dys). Sttisticl Anlysis: All dt were expressed s men Methods of Anlyses: Lbneh tretments were tested for vlues. Sttisticl nlysis ws performed using one wy protein, ft, sh, totl solids (TS) nd cidity (expressed nlysis of vrince (ANOVA) followed by Duncn s s grms of lctic cid/100 g of Lbneh) s given in the Multiple Rnge Test with P 0.05 being considered AOAC [21]. The ph vlues were determined sttisticlly significnt using SAS progrm (SAS) [27]. electrometriclly with ph meter (model Cole-Armer Instrument Co., USA). Synersis ws mesured s RESULTS AND DISCUSSION mentioned by Frooq nd Hque [22] s the mount of spontneous whey (ml/100g) drined off fter 2 h t 7 C Chemicl Composition of Cmel Milk Lbneh: The when fresh nd during storge of ll Lbneh tretments. chemicl composition of Lbneh smples mnufctured Firmness ws mesured in fresh nd stored Lbneh s from cmel milk subjected to different therml tretments described by Amtykul et l. [23] using penetrometer is shown in Tble 2. The vlues of Lbneh totl solids (Kochler Co. Inc., USA). The speed of penetrtion ws set content reflect clerly the effect of the milk therml t 2 mm/s nd the depth of penetrtion ws set t 10 mm. tretments. The significntly (P 0.05) highest vlues of Viscosity ws mesured s formerly described by totl solids were found in Lbneh smples mnufctured 120

4 Tble 2: Gross chemicl composition (%) of fresh cmel milk Lbneh s ffected by milk het tretments Chemicl composition (%) Lbneh tretments Totl solids Protein Ft Ash Lctose * Control c b 9.15 b 8.21 b T1 bc b 9.32 b 8.91 b T2 b b b 1.14 b 3.42 T b 3.35,b,c Mens not followed by the sme lower cse letter in ech row re significntly different (p 0.05). * Clculted by the difference Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. from milk treted to 85 C or 95 C for 30 min compred with ph nd Acidity (%) Vlues of Cmel Milk Lbneh: The control (mnufctured from psteurized milk t 72 C for chnge in ph nd cidity in Lbneh during storge t 5 C 15 sec.). The protein content ws only significntly for 9 dys s ffected by therml tretments of cmel milk ffected by the pplied tretment t 95 C for 30 min, while prior to the mnufcture re illustrted in Tble 3. The ph it ws not significntly between the control nd other nd cidity vlues for the entire Lbneh smples were tretments. The ft content ws not ffected by the similr. The ph rnged from 4.90 to 4.78 during 1 to 9 dys pplied therml tretments of cmel milk with the of the study nd titrtble cidity rnged from 0.82 to exception in Lbneh smples from thermlly treted cmel 1.02% s percentge of lctic cid. Previous study, milk more thn 85 C for 30 min (Tble 2); the differences Hshim et l. [10] indicted tht lctose content ws in this respect were significnt. The highest sh content responsible for the cogulum formtion nd the reduction (1.22%) ws significntly chieved in the Lbneh from in ph s result of the production of orgnic cids thermlly treted milk t 95 C for 30 min, followed by the (e.g. lctic cid). As the storge period dvnced the verge vlue of 1.14% in milk treted by heting t 85 C cidity in ll Lbneh tretments incresed grdully with for 30 min. The control showed the lowest verge vlue very slow rte. The differences in cidity in response to (1.03%) for sh content. The hydrolysis of lctose ws the pplied therml tretments were only significnt in significntly highest in the cmel milk thermlly treted for highest tretment nd could be due to the phse chnge 85 C for 30 min thn the other tretments. This my be of clcium phosphte from the soluble phse to the due to the effect of therml tretment on cmel milk colloidl one. The phse chnge is thought to result from proteins by ntimicrobil fctors [17, 28]. Also, the libertion of hydrogen ion [29] nd this in greement Djurdjevic et l. [24] reported tht during het tretment with the findings of Hssn et l. [31] for cmel milk. of milk, ph decresed, while titrtble cidity incresed These results re in greement with those obtined by nd lctose content decreses during het tretment. Oliveir et l. [32] nd Lucs et l. [33] who reported tht The obtined results showed tht the therml L. delbrueckii subsp. bulgricus produces lctic cid tretment of cmel milk for 85 C or 95 C for 30 min before during refrigerted storge, known s postcidifiction. the mnufcture Lbneh led to products with different Also, these results re in greement with those obtined chemicl composition. This confirms tht het-tretments by Suliemn et l. [34] in Grris (Sudnese trditionlly ffected the chemicl composition of the milk. Similr fermented cmel milk). results were obtined by El-Agmy [17] nd Httem et l. An opposite trend ws recorded concerning ph [29], who reported tht for therml tretment of cmel milk vlues which decresed grdully s the storge period 80 C/30 min, hd significnt impct on milk composition, dvnced reching minimum vlues t the end of storge in terms of the content of totl solids, protein nd sh. period. However, the slow development of cidity, despite On the other hnd, the therml tretment t 63 C for ddition of sufficient mounts of ctive yoghurt strter 30 min of cmel milk did not differ significntly in gross my be scribed to the presence of ntibcteril composition of Lbneh thn control one. This mens tht substnces in cmel milk which inhibited the ctivity of the norml psteuriztion method do not ffect the yoghurt culture nd the effect of therml tretment on chemicl composition of cmel milk Lbneh nd these cmel milk proteins by ntimicrobil fctors [17, 28]. results re in greement with tht result given by Frh Generlly, the decrese in ph ws greter in cmel milk [30] who indicted tht the therml tretment t 63 C for thn in bovine milk, which could hve been due to the low 30 min did not ffect the chemicl composition of cmel buffering cpcity of cmel milk [35]. The difference in milk. buffering cpcity between bovine nd cmel milks is 121

5 Tble 3: Chnges in ph vlues nd cidity (%) of cmel milk Lbneh during storge t 5 C s ffected by milk het tretments. ph vlues Acidity (% lctic cid) Storge period (dys) Control T1 T2 T3 Control T1 T2 T3 A Bb Bb Bb B Fresh ABb Bb Bb ABb ABb Bb B ABb ABb ABb AB ,b,c Mens not followed by the sme lower cse letter in ech column re significntly different (p 0.05). A,B,C Mens not followed by the sme lower cse letter in ech row re significntly different (p 0.05). Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. relted to the differences in the proportion of proteins nd mount of whey protein present in skim milk ffect the certin slts in both milks [36]. The obtined results for quntity of formed complex; s well s tht csein micelle ph nd cidity re consistent with tht of u-trboush possess only certin number of sites which re vilble et l. [37] who reported tht ph reched 4.6 to 4.8 in cmel for the interction with -lctoglobulin. Therefore the milk incubted with Bifidobcteri nd the cidy reched smple T3 with the highest therml tretment lso hd the 0.95 %. By the sme wy, Nnd et l. [38] found tht the highest protein content nd consequently T3 hd the cidity reched 1.1% lctic cid in cmel cheese. highest pprent viscosity, s shown in Fig. 1. The obtined results in ccordnce with tht of Sömer nd Rheologicl Properties of Cmel Milk Lbneh Kýlýç [44], who reported tht het tretment promotes Viscosity: The effect of the different therml tretments of protein denturtion, which increses wter binding nd cmel milk on the pprent viscosity of Lbneh is viscosity. Moreover, Ozer et l. [45] indicted tht depicted in Fig. 1. The pprent viscosity decresed s different mnufcturing techniques led to differences in the sher rte incresed in ll smples, so Lbneh the rheology of concentrted yogurts nd tht rheologicl exhibited sher thinning behvior. This sher thinning behvior of Lbneh depended on the protein behvior is due to the progressive brekdown of concentrtion, smples with high protein contents hd ggregtes formed between milk cseins by the ction greter gel strengths. In this sense, Cyot et l. [46] of the decrese in ph [39]. It cn be seen tht the chnge reported tht the consistency index of stirred cid gels, in the pprent viscosity ws liner with the increse in clculted from the Ostwld model, incresed s milk the therml tretment of cmel milk, where the highest heting temperture incresed from 70 to 100 C. An tretment (95 C/30 min) increse in the solids increse in milk heting temperture resulted in n concentrtion led to highest pprent viscosity. The fll increse in pprent viscosity of stirred yogurts [47]. in viscosity with sher rte might be due to the Furthermore, s the storge period dvnced the viscosity destruction of the interctions within the Lbneh network in ll Lbneh smples incresed grdully with slow rte structure. These interctions re electrosttic nd s shown in Fig. 1. These results re comptible with hydrophobic ones, which re considered s wek physicl Nsbimn et l. [48], who found tht t constnt sher bonds [40]. As shown experimentlly by Ozer et l. [41], rte, the pprent viscosity of Lbneh incresed with the preprtion of Lbneh using cloth bg hd the storge time nd storge time hd negligible effect on highest protein nd ft content, since the cloth bgs flow properties of destructured Lbneh. Similr llow, minly, the seprtion of lctose nd minerls into observtion ws reported lso by u-jdyil et l. [49]. the whey nd thereby decrese in the porosity. Also, The sme trend ws founded in the stirred yogurt by during het tretment whey protein ssocited with csein Bel et l. [50], who found tht, the longer the storge micelles lters properties of micelles, so they become more time ws, the higher the viscosity ws, especilly between hydrted thn nturl csein micelles [42]. d 1 nd 7 dys of cold storge. Whey proteins prticipte in gel structure due to formed coggregtes nd in this wy contribute to the Firmness: An importnt criterion for qulity ssessment flow behvior of gels. Corredig nd Dlgleish [43] found of set-style cultured milk products is the texture of the gel, tht not only time nd temperture of heting, but lso the so the texture of Lbneh is n importnt chrcteristic tht 122

6 Fig. 1: Apprent viscosity of cmel milk Lbneh during storge t 5 C s ffected by milk het tretments. Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. 123

7 Fig. 2: Chnges in the penetrtion vlues (mm) of cmel milk Lbneh during storge t 5 C s ffected by milk het tretments. Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde rom heted milk t 63 C/30min. determines the cceptbility of the product. Idelly, it tht during storge, the firmness of ech yoghurt should hve smooth nd psty texture with semisolid incresed until dy 8, but remined reltively constnt mss. Penetrometer vlues of ll Lbneh smples re therefter until dy 20. In the sme line, Frooq nd Hque given in Fig. 2. Higher penetrometer vlues indicted [22] reported tht the penetrtion significntly incresed higher firmness. High thermlly tretment resulted in n in ll smples between d 0 nd 7, but not (P >.05) during increse in gel strength of Lbneh smples. In terms of 7 to 14 d of storge. penetrometer vlues, significnt increses (P < 0.05) in penetrometer vlues were observed only in the Whey Seprtion: Whey seprtion (wheying-off) is smples with highest thermlly treted cmel milk Lbneh defined s the expulsion of whey from the network which (T2 nd T3). Theses obtined results re in ccordnce then becomes visible s surfce whey. Yogurt with Lee nd Lucey [51], who reported tht ntive whey mnufcturers use stbilizers, such s, pectin, geltin nd proteins from unheted milk re inert fillers in yogurt. strch, to try to prevent wheying-off. Another pproch When milk is heted t >70 C, the mjor whey proteins, is to increse the totl solids content of yogurt milk, such s, -lctoglobulin, re dentured. During especilly the protein content, to reduce wheying-off. denturtion -lctoglobulin intercts with the -csein Spontneous syneresis, which is contrction of gel on the csein micelle surfce (nd ny soluble -csein without the ppliction of ny externl force, is the usul molecules, i.e. -csein tht dissocites from the micelle cuse of whey seprtion [55]. The dringe method is t high tempertures) by disulfide bridging, which results useful in products tht hve serum seprtion step in incresed gel firmness nd viscosity of yogurt. through screen, such s, trditionlly mnufctured Lucey et l. [52] mentioned tht dentured whey proteins concentrted yogurt (Lbneh). In this test, surfce whey tht hve become ttched to the surfce of csein tht is expelled from cid milk gels is gently poured off micelles re criticl fctor involved in the incresed nd quntified. This test hs been used to evlute whey stiffness of yogurt gels mde from heted milk. Soluble seprtion in set-type yogurt gels [47]. Chnges in complexes of dentured whey proteins with -csein lso syneresis rte of cmel milk Lbneh during the cold ssocite with the micelles during the cidifiction storge of control nd different therml tretments re process. Het tretment of milk for 15 min t 80 C results shown in Fig. 3. It cn be seen tht the control Lbneh in significntly incresed denturtion of -lctoglobulin hs presented higher index of syneresis thn the other compred with milk heted t 75 C for similr time. tretments. However, significnt rte ws only recorded The extent of denturtion of whey proteins during the in the highest thermlly treted Lbneh (T2 nd T3). het tretment of milk ffects the firmness nd viscosity This might be relted to the greter protein concentrtion of cid milk gels [53]. On the other hnd, during cold in these smples, becuse of intensified wter retention storge, the firmness of ech smple incresed until dy by the protein mtrix. Also, it cn be observed tht the 9. This incresed in the penetrtion vlues re in whey seprtion in ech smple decresed s storge time greement with tht of Brrntes et l. [54], who found progressed (9 dys) in ll smples nd this is comptible 124

8 Fig. 3: Chnges in whey seprtion of cmel milk Lbneh during storge t 5 C s ffected by milk het tretments. Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. with the results of Al-Kdmny et l. [56], who ttributed corresponding microgrphs re shown in Fig. 4. In tht to the whey seprtion in cid milk gels hs been generl, the microstructures of the Lbneh therml linked to rerrngements of prticles mking up the csein tretments were similr in protein mtrices composed of gel network. These results re in greement with those csein micelle chins nd clusters. However, SEM obtined by Djurdjevic et l. [24], who reported tht het reveled tht the protein mtrices of the high thermlly tretment plys very importnt role in yogurt mnufcture treted Lbneh smples (T2 nd T3) ppered to be nd qulity. During het tretments, complex between reltively more intensive thn the control (Fig. 4c & d). csein nd whey protein is formed, which directly In these tretments, the csein micelles were influences hydrtion of csein micelles. It is generlly predominntly linked by prticle to prticle ttchment ccepted tht set-style yogurt produced from unheted in chins with comprtively smll interspced voids milk hs wek gel, with worse rheologicl nd sensory (Fig. 4c), rther thn by prticle fusion into big ggregtes chrcteristics nd pronounced syneresis. Also, s (Fig. 4d). However, for control protein structure result of insufficient het tretments wek gel is formed. chrcterized by short csein micelles chins nd no By the sme wy, Trchoo [57] mentioned tht yogurt pprecible csein micelle fusion were observed. The mde from UHT-treted milk (138 C/3-6 sec) hd lower control exhibited more open, loose nd less dense viscosity nd firmness but less syneresis thn tht mde protein network thn therml tretments. These SEM from vt-treted milk (82 C/20 min). Whey protein observtions reinforce conclusion lredy drwn denturtion ws believed to be responsible for this concerning firmness difference between control nd high phenomenon. Also, Sömer nd Kýlýç [44] reported tht thermlly treted cmel milk Lbneh gels. Similr het tretment promotes protein denturtion, which observtions were reported by Tmime et l. [60] increses wter binding nd viscosity. Hshim et l. [10] during the mnufcture of Lbneh. This structure nd Mehi [58] found tht the cogulum obtined develops in milk which hd been heted to minimum of from cmel milk is softer thn tht from cow 85 C, t this temperture; -lctoglobulin forms complex milk. Therefore, the drining of cid curd mde with -csein t the csein micelle surfce. This complex from cmel milk is chrcterized by rpid syneresis gives the csein micelles the form of minute globulr compred with cow s milk. Moreover, the low wter prticles in replics of cryofixed micelles [54]. Also, retention cpcity of the gel mde from cmel milk my be Lee nd Lucey [61] reported tht yogurt gels mde from ttributed to the low kpp frction, which is very milk heted t high temperture (>80 C) hd more hydrophilic [59]. cross-linked nd brnched protein structure with smll pores compred with milk heted t low temperture. Microstructure of Cmel Milk Lbneh: Microstructure On the other hnd, Tmime et l. [62] demonstrted tht hs mjor impct on the texture nd other physicl concentrted yogurt (Lbneh) from cmel milk exhibited properties of cid milk gels. Thus, scnning electron more homogeneous nd compct microstructure in microscopy (SEM) ws performed for control nd high comprison to the microstructure of products from got thermlly treted cmel milk Lbneh tretments nd nd sheep milk. 125

9 Fig. 4: Scnning electron microscopy (SEM) microgrphs of cmel milk Lbneh s ffected by milk het tretments Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. Orgnoleptic Properties of Cmel milk Lbneh: Cmel milk Lbneh of different therml tretments were evluted for flvor, consistency nd ppernce. Dt pertining to the overll evlution nd preference of Lbneh when fresh nd t the end of storge t 5 C re depicted in Tble 4. The overll cceptbility scores of the sensory evlution reveled tht T3 fresh s well s stored were the significntly most ccepted nd gined higher scores, while the control smple ws the lest. As storge progressed the orgnoleptic scores insignificntly decresed in ll tretments nd these results re in greement with Slem et l. [26]. The obtined results 126

10 Tble 4: Orgnoleptic properties of cmel milk Lbneh during storge t 5 C s ffected by milk het tretments Lbneh tretments Orgnoleptic properties Storge period (dys) Control T1 T2 T3 Flvor (60) Fresh Consistency (30) Fresh Appernce (10) Fresh Totl (100) Fresh ,b,c Mens not followed by the sme lower cse letter in ech row re significntly different (p 0.05). A,B,C Mens not followed by the sme lower cse letter in ech column for ech score re significntly different (p 0.05). Control: Lbneh mde from heted milk t 72 C / 15 sec. T1: Lbneh mde from heted milk t 63 C/30min. reveled tht there ws resonble greement between the 2. Mgjeed, N.A., Corrective effect of cmel milk rheology results of the tested smples s previously on some cncer biomrkers in blood of rts shown nd its sensory scores. Wheres, the increse in intoxicted with fltoxin B1. Journl of the Sudi penetrtion nd pprent viscosity seem to be the Chemicl Society, 9: resons for improved texture in this smple tht ws 3. Agrwl, R.P., S. Budni, P. Shrm, R. Gupt nd evidenced by smooth body nd mouthfeel in the D.K. Kochr, Zero prevlence of dibetes in sensory evlution. These results re in greement with cmel milk consuming Ric community of northwest Cyot et l. [46], who reported tht the consistency Rjsthn, Indi. Dibetes Reserch nd Clinicl index of stirred cid gels, incresed s milk heting Prctice, 76: temperture incresed from 70 to 100 C. An increse in 4. Qun, S., H. Tsud nd T. Miymoto, het tretment r esulted in n increse in orl viscosity Angiotensin I-converting enzyme inhibitory peptides nd perceived mouth coting ttributes, s well s, in skim milk fermented with Lctobcillus helveticus decrese in the chlkiness ttribute of stirred yogurt 130B4 from cmel milk in Inner Mongoli, Chin. [47, 63]. Journl of the Science of Food nd Agriculture, CONCLUSION 5. 88: El-Agmy, E.I., M. Nwr, S.M. Shmsi, S. Awd nd G.F.W. Henlein, Are cmel milk proteins Lbneh from cmel milk with good texture nd convenient to the nutrition of cow milk llergic cceptble sensory qulity could be obtined. The min children. Smll Ruminnt Reserch, 82: 1-6. fctors tht govern the success of the mnufcture of the 6. Frh, Z., Composition nd chrcteristics of cmel milk Lbneh is the therml tretment of the milk t cmel milk. J. Diry Res., 60: C for 30 min with the use of 1.0% commercil stbilizer 7. Wlstr, P., T.J. Geurts, A. Noomen, A. Lellem nd nd 4 % yogurt strter culture. This therml tretment M.A.J.S. vn Boekel, Diry Technology: ppers to ply n importnt role in the enhncement of Principles of Milk Properties nd Processes, curd firmness nd subsequently whey seprtion rte. (pp: ). Mrcel Dekker, New York, NY, USA. Moreover, the obtined Lbneh hd good viscosity, more 8. Khn, B.B. nd A. Iqbl, Production nd dense nd closed protein network. composition of cmel milk. Pkistn J. Agric. Sci., REFERENCES 9. 38: Gorbn, A.M.S. nd O.M. Izzeldin, Study on cholesterols ester ftty cids in cmel nd cow milk 1. dulrhmn, A. Al-Selh, A.M. Metwlli nd lipid. Int. J. Sci. Technol., 34: A.E. Ismil, Physicochemicl properties of 10. Hshim, B., A.H. Khlil nd H. Hbib, Qulity probiotic frozen yoghurt mde from cmel milk. Int. nd cceptbility of set-type yogurt mde from J. Diry Techn., 64: cmel milk. J. Diry Sci., 92:

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