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Indian Journal of Nutrition

Research Article


Some Properties of Set Type Yoghurts Produced From Camel (Camelus Dromedarius) Milk Enriched With Native Rice Flour and Skim Milk Powder

Nazan Kavas1*, Gökhan Kavas2

1Dairy Products Program, Ege Vocational Training School, Ege University, 35100 Ä°zmir, Turkey


2Department of Dairy Technology, Faculty of Agriculture, Ege University, 35100 Ä°zmir, Turkey


Corresponding author: Nazan Kavas, Dairy Products Program, Ege Vocational Training School, Ege University, 35100Ä°zmir, Turkey; E-mail: naz.kavas@gmail.com, nazan.kavas@ege.edu.tr


Citation: Kavas N, Kavas G. Some Properties of Set Type Yoghurts Produced From Camel (Camelus Dromedarius) Milk Enriched With Native Rice Flour and Skim Milk Powder. Indian J Nutri. 2016;3(1): 120.


Copyright © 2016 Kavas N, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Indian Journal of Nutrition | ISSN: 2395-2326 | Volume: 3, Issue: 1


Submission: 08/02/2016; Accepted: 26/02/2016; Published: 04/03/2016


Abstract


Three different types of set type yoghurt were produced from camel (Camelus Dromedarius) milk (CaM). The 1st yoghurt type (YSMP) was produced by adding 9% (w/v) skim milk powder (SMP) to camel milk, the 2nd yoghurt type (YNRF) was produced by adding 9% (w/v) native rice flour (NRF) (from Oryza sativa L. ssp. japonica) to the camel milk and the 3rd yoghurt type (YSMP+NRF) was produced by adding a 4.5% (w/v) SMP+4.5% (w/v) NRF mixture to the camel milk. Samples were stored for 10 days at 4 °C±1. Physicochemical, microbiological and sensory analyses were conducted at the 12th hour and on the 1st, 5th, 7th and 10th days of storage. In the yoghurt samples, it was determined that Streptococcus thermophilus count was higher until the 5th day compared to Lactobacillus delbrueckii subsp. bulgaricus, which became the dominant flora after the 5th day. Regarding the sensory properties, in YNRF (until the 5th day) and YSMP+NRF (throughout the storage), rice flour was not felt in the mouth and also did not cause any defect related to structure and taste. In our study, the general properties of yoghurt produced from unaccompanied rice flour (YNRF) began to deteriorate after the 5th day, whereas combination with milk powder (YSMP+NRF) had a positive effect on the general properties of the samples until the 10th day of the storage.


Keywords: Camel milk; Native rice flour; Yoghurt

Introduction


Yoghurt is a fermented dairy product produced from thelactic acid fermentation of milk by Lactobacillus delbrueckii subsp.bulgaricus (Lb.bulgaricus) and Streptococcus thermophilus (Str.thermophilus) bacteria. Starter cultures used in the production growbetter in the presence of glucose and some other sugars (sucrose,maltose) [1]. Yoghurt has several industrial types including set type,stirred type, drinking type, frozen type and concentrated type [2].In order to improve consistency and viscosity in the yoghurt, dry matter should be increased in the processed milk. Skim milk powderis the most frequently used ingredient for this purpose. Camel milkhas lower viscosity (1.72 mPas) compared to cow’s milk (2.04 mPas)[3], the casein ratio in its total protein content is 52-87% [4], andit is rich in terms of sulphur-containing [5] and essential aminoacids [6,7]. There have been studies on the production of yoghurtsupplemented with skimmed milk powder [8], probiotic yoghurt[9], stabilizer-supplemented yoghurt [10,11], yoghurt supplementedwith different spices [12] and flavored yoghurt [13] from camel milk.In previous studies, it was reported that in yoghurts produced with industrial yoghurt culture, coagulum was not smooth, the structurewas heterogeneous and brittle, and viscosity did not change duringgelatinization [14,15]. Nevertheless, it was reported that it is possibleto produce hardened but low viscosity yoghurt by using twice theamount of main components of milk and yoghurt culture [13]. Theproblems that occur during fermentation have been associated withthe abundance of antimicrobial agents in camel milk (lysozyme228-500 μg.100 mL-1; lactoperoxidase 79.2%) [16,17], the poorcontent of serum proteins (20-25% of total protein) [18,19], weakinteraction between denatured serum proteins and casein, low or nocontents of different β-casein derivatives in the structure of caseinand β-lactoglobulin from the serum proteins [16], κ and low ratio ofcasein (3.47 %) compared to cow’s milk (13%) [20,21].


Most of the rice (Oryza sativa) produced is directly as food,although some is also consumed as native rice flour (NRF)obtained via trituration. The quality of NRF varies depending onits physicochemical properties [22,23]. Starch, which is the maincomponent of NRF, consists of two glucose polymers called amyloseand amylopectin. These polymers affect the functional, adhesion,gelatinization and retrogradation properties of NRF . In this study,NRF obtained from rice (Oryza sativa L. ssp. japonica) was examinedin terms of its usability for the enrichment of camel milk used foryoghurt production. Its effects on some parameters of yogurt afterdifferent storage periods were compared with skim milk powder.


Materials and Methods


Material


Raw camel (Camelus Dromedarius) milk (CaM) used in the studywas obtained from a local camel farm in Sarayköy, Denizli (Turkey).Native rice flour (NRF) [content data according to the producer: fat0.70%; protein 6.79%; starch 85.42%; amylose 18.22%, amylopectin65.20%; moisture 6.12% and ash 0.35%] produced from Oryza sativaL. ssp. japonica was obtained from a local company in Turkey.JOINTEC VB530 freeze-dried yogurt culture was obtained from CSLlaboratories (Strade per Merlino, 3,26839, Italy). Skim milk powder[content data according to the producer: fat 0.48%; protein 35.12%;lactose 51.14%] was obtained from Pınar Sut Inc. (Kemalpaşa, Izmir,Turkey). Yoghurt samples were produced in pilot plants in EgeUniversity, Faculty of Agriculture, Department of Dairy Technology.


Set Type Yoghurt Production


Set type yoghurts were produced from camel milk enriched withskimmed milk powder (SMP), natural rice flour (NRF) and SMP+ NRF with starter cultures (Lb. bulgaricus and Str. thermophilus).Camel milk was divided into three parts. 9% (w/v) SMP (YSMP) wasadded to the 1st part, 9% (w/v) NRF (YNRF) was added to the 2nd partand 4.5% (w/v) NRF + 4.5% (w/v) SMP (YSMP+NRF) was added to the 3rdpart. The SMP ratio added to the milk was higher than the referencevalue reported by Salih and Hamid [8] (7% skim milk powder).NRF ratio was determined based on the results of preliminarytrials. In the preliminary trials, 4% (w/v), 5% (w/v), 7% (w/v) and9% (w/v) NRF were added. The best results regarding appearance,structure-consistancy, and flavor-aroma was achieved with the 9%(w/v) treatment. Milks were pasteurized considering the maximum gelatinization temperature of low amylose (18.22%) at 85 °C for 20minutes and cooled to 42-43 °C. Each treatment was inoculated with3% starter cultures and left to incubate. Incubation was stopped at pH4.60 (approximately 12 hours) and stored at 4 °C±1 for 10 days. Onthe 12th hour, 1st, 5th, 7th and 10th days, physicochemical, rheological,microbiological and sensory analyses were carried out.


Physicochemical and Proximate Analysis


In raw camel milk and yoghurt samples, dry matter (BinderED-53, Germany) and ash (Protherm PFL 110/6, Turkey) weredetermined according to gravimetric method, fat was determinedaccording to Gerber method, titratable acidity (lactic acid%), pH value(SS-3 Zeromatic pHmeter, Beckman Instruments Inc., California,USA) and protein (Kjehldahl method) were determined according toAOAC [24]. Lactose levels were measured with an Atago Polax x 2L(Japan) polarimeter [25], serum separation was measured accordingto Farooq and Haque [26], coagulum stifness was measured with apenetrometer (Model Sur PNR 6, Sommer & Runge K.G., Berlin,Germany), and viscosity levels were measured with a BrookfieldDigital Viscometer (Model DV-II+PRO, USA) [for yoghurt samples,180 rpm, 10 °C, LV4 probe, between 20-70% Torq; for raw camel milk180 rpm, 10 °C, LV1 probe and 4% Torq] [27] as cP.


Microbiological Analysis


The enumeration of starter cultures in yoghurt samples wereperformed according to International Dairy Federation standardmethods [28, 29]. Lb. bulgaricus enumeration was carried out byincubating the petri dishes in microaerophilic conditions (5% CO2) at37 °C for 72 hours by using De Mann Rogosa Sharpe (MRS) Agar (pH5.4) (Merck Darmstadt, Germany). Str. thermophilus enumerationwas conducted by incubating the petri dishes in aerobic conditions at37 °C at 48 hours on Ml7 Agar (Merc Darmstadt, Germany). At theend of the incubation, colonies formed in petri dishes were countedas cfu/mL on the 12th hour, 1st, 5th, 7th and the 10th days of the storage.


Sensory Evaluation


The sensory evaluation of yoghurts was performed by a consumeracceptance test [30] based on the appearance, texture, flavor, aroma,and overall impression of the product using a 9-point hedonic scale(1- disliked extremely; 9- liked extremely). The sensory evaluation ofthe yoghurt samples was performed after the 1st and the 10th days ofrefrigerated storage.


Statististical Analysis


Samples were examined with 3 parallels and 2 repetitions. SPPSversion 15 (IBM SPSS Statistics) statistical analysis package softwarewas used for the statistical analyses. The significant differences basedon analysis of variance (ANOVA) were tested according to theDuncan multiple comparison test at P<0.05 level.


Results


The composition of the raw camel milk (CaM) used in the studywas dry matter 12.63%, fat was 3.70%, protein was 2.90%, lactose was4.70%, ash was 2.721%, and lactic acid was 0.125%. The pH value was6.60, density was 1.0286 g/l.


Proximate Composition


Proximate Composition of set type yoghurts which wereproduced with the fortification of CaM with 9% (w/v) SMP(YSMP), 9%(w/v) NRF(YNRF) and SMP (4.5% w/v)+NRF (4.5% w/v) (YSMP+NRF) aregiven in Table 1.


Table 1: Proximate Composition of YSMP, YNRF and YSMP+NRF samples (n=3).


Fat values were stable in all samples until the 5th day, afterwhich they decreased. These changes in fat values were found to becompatible with Eissa et al. [31]. In the study, the relationship betweencolloid type/ratios and fat values of the yoghurt samples up until the5th day were not significant (P>0.05). However, after the 5th day, therelationship between the decrease in the dry matter due to syneresisand the decrease in fat values of YNRF was found to be significant(P< 0.05). The highest decrease in protein value was determined inYSMP, followed by YSMP+NRF and finally by YNRF, which showed thesmallest decrease. The high level decrease in protein in YNRF wasassociated with the low protein content in the composition of NRF(6.79%). The high-level protein decreases in YSMP and YSMP+NRF wereassociated with the low protein content in the composition of SMP(35.12%). Lactose levels decreased in all samples on all days of storage.The relationship between the colloid type/ratio and the decrease inlactose was found to be significant (P< 0.05). The relationship betweenthe ash value and the colloid type/ratio was found to be not significant(P>0.05).


Physicochemical properties


Physicochemical properties of set type yoghurts produced with the fortification of CaM with 9% (w/v) SMP(YSMP), 9% (w/v) NRF(YNRF)and SMP (4.5% w/v)+NRF (4.5% w/v) (YSMP+NRF) are given in Table 2. In yoghurt samples, pH decreased throughout the storage whiletitration acidity (lactic acid %) increased. This was associated with theglucose levels found in the NRF used in yoghurt production. In thisstudy, dry matter decreased in YSMP+NRF and YSMP during storage. Drymatter value of YSMP+NRF was higher than that of YSMP. The relationshipbetween colloid type/ratio and dry matter was found to be significant(P< 0.05). The effect of storage period on the changes in dry mattervalues was found to be not significant (P>0.05).


Table 2: Physicochemical properties of YSMP, YNRF and YSMP+NRF samples (n=3).


Rheological Analysis (Consistency, serum separation,viscosity)


Coagulum stability is an important quality criterion. Manyfactors affect the consistency (coagulum stability=hardness), whichis known as the rheological property of the coagulum, serumseparation and viscosity. Among these factors, pH value, dry matterand protein content [32], denatured serum protein content, andinteractions between β-lactoglobulin and k-casein are especiallyimportant [33]. In this study, the interactions between consistencyvalues, hydrocolloid types and storage period of the samples weresignificant (p< 0.05). Consistency (penetrometer value) values of YSMPand YSMP+NRF decreased; in other words, coagulum stability (hardness)increased. The effect of storage on the consistency values was foundto be significant (P< 0.05). In our study, hardness increased in YSMP+NRFand YSMP during storage. Hardness increased until the 5th day in YNRF(19.46%) then decreased. Hardness value of YNRF on the 10th day (271.61 1/10mm) was close to the value on the 12th hour (275.061/10mm). In YNRF, the decrease in hardness value after the 5th daywas verified by the increase in serum separation after the 5th day (thehighest serum separation value among all samples) and the decreasein viscosity (the lowest viscosity value among all the samples).Additionally, it was found that an increase in acidity and storage timehad a significant effect on the serum separation. The relationshipbetween the viscosity and the colloid type/ratio was found to besignificant (P< 0.05). In YSMP+NRF and YSMP, viscosity values increasedduring storage and fat loss values were the lowest. In our study, 9%(w/v) rice flour fortification (YNRF) increased the viscosity until the 5thday of the storage, while 4.5% (w/v) rice flour fortification (YSMP+NRF)increased the viscosity throughout the entire storage period.


Microbiological Analysis


Lb. bulgaricus and Str. thermophilus development are given inFigure 1. Lb. bulgaricus increased until 5th day of the storage anddecreased on the 7th and the 10th days in all samples. Lb. bulgaricuscounts in YNRF and YSMP+NRF increased by 2 log between the 1st andthe 5th day of the storage, after which they decreased by a total of 1log in YSMP+NRF, 2 log in YNRF, with a decrease of 1 log in YNRF andmaintenance 106 cfu/ml levels in YSMP+NRF between the 7th and the10th days. Lb. bulgaricus counts in YSMP increased 1 log between the12th hour (5.98x106 cfu/ml) and the 7th day (7.38x107 cfu/ml) anddecreased by 1 log on the 10th day (5.1x106 cfu/ml), a decrease which was higher than that of YSMP+NRF (6.63x106 cfu/ml). The increase in Lb.bulgaricus counts was higher in YNRF and YSMP+NRF (until the 5th day)than that of YSMP, and the decrease (especially 2 log between the 5thand the 7th days and 1 log on the 10th day) was higher in YNRF. Lb.bulgaricus levels in YSMP+NRF were high throughout the storage period.


Figure 1: Lb. bulgaricus and Str. thermophilus development in YSMP (a); YNRF (b) and YSMP+NRF (c)samples (cfu/ml).


The lowest Str. thermophilus counts were found at the 12th hour(6.54x107 cfu/ml) and the 1st day (6.32x107 cfu/ml) in YSMP. The highestStr. thermophilus levels on the 12th hour and the 1st day were detectedin YNRF and YSMP+NRF, respectively. The decrease in samples on the 5th,7th and the 10th days were 1 log for each storage day. Str. thermophiluslevels in YNRF decreased to the lowest levels in the following days. Onthe 5th day, Str. thermophilus decreased to 2.33x106 cfu/ml in YSMP+NRF,a decrease that reached to 1.31x106 cfu/ml on the 7th day followed bya 1 log decrease to 6.52x105 cfu/ml on the 10th day. On the 7th and the10th days, the highest count was in YSMP+NRF, and the lowest was inYNRF. Between the 5th and the 7th days, the decrease in Str. thermophiluscounts was the lowest in YSMP+NRF and highest in YNRF.


Sensory Evaluation


In the sensory evaluation of yoghurt samples, YSMP+NRF sample wasmore appreciated than YSMP by the end of the storage period and moreappreciated than YNRF by the 5th day in terms of physicochemical,rheological and sensory properties. By the 1st day of the storage,YSMP+NRF received 6.52 aroma, 6.48 flavor and 5.94 texture points and YSMP received 7.12, 6.80 and 6.20. By the 10th day of storage, YSMP+NRFreceived 7.87 aroma, 7.38 flavor and 7.00 texture points and YSMPreceived 7.39, 7.15 and 6.84. By the end of the storage, YSMP+NRF wasfound more sour than YSMP, however this sour taste was not describedas a fault. This was associated with the fact that Turkish people haveconsumed sour yoghurt for many years.


Discussion


In some studies, it was reported that the type and ratio ofcolloid used in order to increase the dry matter had an effect onthe development of acidity, while in other studies (alginate andgelatin), this relationship was reported to be not significant [31,32].It has been reported that lactic acid bacteria developed better in thepresence of glucose and some other sugars (sucrose, maltose) andthat the increase in acidity was higher [1]. The results obtained in ourstudy were found to be consistent with those found in the literatureregarding the increase in acidity as the glucose ratio increased.


The improvements in rheological properties up until the 5th dayof the storage along with the increases in dry matter and acidity,the decelerating acidity increase after the 5th day, the increasein dry matter content, the sudden increase in serum separation,and the decreases in hardness and viscosity were all considered tobe related to the starch content of the rice flour. During storage at+4 °C, syneresis also occurred due to starch content [22,23]. Thiscaused the decrease in stability of YNRF after the 5th day of the storage.Throughout the storage, acidity development, hardness and viscosityvalues were lower and the serum separation value was higher in YSMPthan in YSMP+NRF. This was associated with higher levels of SMP addedto the milk [2,34].


In studies on yoghurt production from cow’s milk, SMPsupplementation at optimum levels (3-4%) and incubation todesired pH values (for 2.5-3 hours) led to an earlier improvementof the rheological properties [2]. In this study, in YSMP, which wasproduced with 2-3 fold SMP supplementation, and YSMP+NRF, whichwas produced with 4.5% SMP supplementation, the desired pH levelswere achieved on the 7th and the 10th days of the storage. This resultis consistent with previous studies describing problems that occurdue to the milk composition in the production of fermented dairyproducts from camel milk [16,17,19,21]. It was determined that thelower speed of pH value decrease of dairy products produced fromskimmed camel milk was higher than the decreased speed observed incow’s milk by [35]. In fact, milk buffering capacity varies dependingon the levels of various milk components including casein, solubleminerals, whey proteins and colloidal calcium phosphate, also onlactation, nutrition/feeding and animal health [36]. Besides, despitethe delayed acidity increase, an increase was detected in viscosity. Inyoghurts produced from camel milk, it was reported that the viscosityincreased with longer cold storage [37]. Additionally, the increasesin acidity, viscosity and hardness in all samples (until the 5th day inYNRF) were found to be related with the decrease in serum separation.The increase in viscosity in YSMP+NRF was considered to be relatedwith the interaction between SMP ratio (4.5% w/v), amylose in thestarch composition (at low levels), starch (NRF) and casein (SMPand CaM). This interaction reveals the relationhip between positivelycharged casein (pH< 4.6) and negatively charged starch molecules.Takeuchi [38] explains that this starch-protein interaction causesan electrostatic change. Additionally, it was explained that calcium[the concentration of calcium in the casein micelles of camel milkvaries between 109 mg/100ml and 114 mg/100ml, levels which make it regarded as a good source of calcium [15,39] became more solubleand interacted with the negatively charged starch molecules as the pHdecreased, which strengthened the gel structure [40]. In our study,syneresis was observed after the 5th day in YNRF after cold storage. Asa result, serum separation increased, hardness dropped and viscositydecreased. However, the opposite situation was observed in YSMP+NRF,in which the rheological properties were found to be better those ofthe other samples throughout the storage period. This was associatedwith some factors related to the decrease in pH (interactions betweenstarch-casein, starch-calcium, and casein-amylose). SMP (4.5% w/v)and NRF (4.5% w/v) ratios used in YSMP+NRF were found to be moresuitable for yoghurt production from camel milk. According to Salihand Hamid [8], a 7% SMP ratio used for yoghurt production fromcamel milk, compared to 5% SMP, improved the sensory propertiesrelated to viscosity and caused an increase in total bacterial count.The SMP ratio used in YSMP in our study (9% w/v) had an effect on drymatter, viscosity and rheological properties. However, the SMP ratioused in YSMP+NRF (4.5% w/v), which also contained with starch, had astronger effect on these properties.


During the production of fermented dairy products, especiallyduring the incubation period, lactose is metabolized to itscomponents glucose and galactose by the culture bacteria and theglucose is metabolized to lactic acid. The increase in bacterial countsin YNRF and YSMP+NRF were likely due to the high levels of starch inthe NRF. Str. thermophilus first metabolizes starch to maltose andglucose using α-amylase, then metabolizes maltose to glucosemonomers via α-glucosidase [41]. As a result, sugar concentration inthe medium increases. High levels of Str. thermophilus in YNRF andYSMP+NRF until the 5th day of the storage is associated with the effect ofStr. thermophilus on the hydrolysis of starch. The higher levels of Str.thermophilus in YSMP+NRF on the 7th and the 10th days of the storage wereassociated with combined use of NRF and SMP. The lowest levels ofLb. bulgaricus and Str. thermophiles and slower acidification on the7th and the 10th days of the storage of YNRF is associated with the serumseparation observed in YNRF after the 5th day. With the increase inserum separation in yoghurts, the symbiotic relationship between themicroorganisms is disrupted and thus pH progress decelerates or halts[2]. Consequently, the increase in sugar concentration within the milkdue to the hydrolysis of starch promotes the development of yogurtbacteria on the one hand and increases the acidity on the other hand.In our study, there were relationships of glucose levels with bacterialgrowth and bacterial growth with an increase in acidity. Moreover,there were relationships between increase in acidity and hardness andbetween viscosity and serum separation. These results are consistentwith other studies [1]. In previous studies, it was demonstrated thatcombined use of microorganisms in yoghurt production is important[42,43]. Microorganism levels (except YNRF sample after the 5th day)were also compatible with the literature [33,34]. Until the 5th day,Str. thermophilus levels were found to be higher than Lb. bulgaricuslevels. This result was compatible with some studies [44], but notcompatible with some others [45]. Lb. bulgaricus became dominant inthe flora on the 5th day and on the following days. This case verifies thedominance of Lactobacillus ssp. in the flora of traditional fermenteddairy products produced from camel milk [22,46,47]. In our study, considering the incubation period (12 hours), the lag phases of themicroorganisms were determined to be long [9].


In YNRF and YSMP+NRF set type yoghurts, the rice flour additionwas not perceived and that the yoghurt aromas of the samples weresatisfactory. In YNRF and YSMP+NRF set type yoghurts, it was determinedthat rice flour addition had no significant effect on color. Also,colloids which were added to high levels to the milk did not cause anydefects of the texture properties of the yoghurt; on the contrary, thetexture was homogeneous and smooth. In the sensory analysis, YNRFand YSMP+NRF set type yoghurts created a better feeling of fullness in themouth, compared to YSMP.


Rheological properties of yoghurt coagulum vary depending onsome factors. Interactions of one or more of these factors duringfermentation affect the acidity. Increases in acidity led to an increasein the interaction between serum proteins and casein micelles andbetween casein micelles and starch molecules, and a decrease inhardness; as a result, viscosity increases. It has been reported that some problems are observed during the production of fermented dairyproducts from camel milk (especially depending on the composition)due to increases in acidity, which leads to unsuitable rheologicalproperties [9,25,29,30]. However, it was reported that with a certainratio of thickener and gelling agent concentration, the formationof a gel with appropriate rhelogical properties can be encouraged[21]. In this study, despite the long incubation period (12 hours),physicochemical (especially the increase in acidity), rheological,microbiological and sensory properties were suitable in YNRF until the5th day and YSMP+NRF and YSMP until the 10th day of the storage. In thisstudy, unaccompanied use of rice flour in yoghurt production wasnot possible. However, it was concluded that it is possible to produceyoghurt from camel milk with the addition of 4.5% SMP and 4.5%NRF containing low levels of amylose (18.22%).


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