Physico-chemical and sensorial variation in camel milk produced at different zones of Sindh, Pakistan

Despite camels are best milk yielders in Sindh, Pakistan; their milk is rarely consumed in significant extent probably due to unawareness of its food value, use and/or consumers’ acceptability. Present study merits, evaluating the variability in the physico-chemical properties and sensory profile of camel milk at irrigated plains (IP), sandy desert (SD) and coastal mangroves (CM) zones of Sindh, Pakistan. Experiment was randomized with complete block design, where 90 camel milk samples from each of the three studied zones were examined. Most of the characteristics were recorded significantly different. pH values and viscosity at SD and CM were found non-significant but these were significantly (P<0.05) different at IP (6.50 and 1.17cP, respectively). Titratable acidity observed considerably high at CM (0.178%) followed by SD (0.169%) and IP (0.165%). Specific gravity, conductivity (mS/cm) and refractive index (1.032, 5.04 and 1.3452, respectively) were abundant at IP compared to CM and SD. Moisture content recorded at SD (89.50%) was high followed by CM (89.21%) and IP (88.81%). Fat content was comparatively abundant at IP (3.19%) than at CM and SD. Total protein, casein, non-casein nitrogen and whey protein at IP and CM found non-significant, but significantly high from that of noted at SD (3.00, 2.07, 0.115 and 0.54%, respectively). Lactose and solids not fat contents at SD and CM noted non-significant, but appeared significantly low from that of IP (4.03 and 8.01%, respectively). Camel milk at IP perceived markedly better score for appearance/color (8.95 over 10), odor/aroma (3.36 over 5), taste/flavor (31.26 over 45), body/texture (3.64 over 5) and overall acceptability (6.32 over 9) followed by camel milk at CM and SD. Though, sensory profile of camel milk versus buffalo milk was not comparable yet score perceived for all the sensory attributes were under acceptable limits and might open the door for its utilization at Sindh, Pakistan.


Introduction
Camel (Camelus dromedarius) is a unique animal though survives and reproduces under harsh climatic conditions for longer periods without drinking, and can replenish the loss in a very short time compared to other kinds of livestock [1]. This unique adaptability makes this specie ideal for exploitation under the arid, semi-arid, mountainous and desert areas of the world, and therefore, contributes significantly to the food security of the nomadic pastoral households. Camels are generally raised under sedentary, transhumant and nomadic production systems in different camel habitats of Pakistan, and are well known and famous for milk production with an average milk yield of 4179 liters per year [2], probably the best milk yielder in the world. Despite this uniqueness, camel milk has not been utilized to significant extent probably due to unawareness of the use and the market value of camel milk or because of its saltish taste and high acidic nature [3,4]. However, it is much more nutritious than that of cow milk because it is low in fat content and rich in protein, minerals and vitamins especially in vitamin C [5]. In Pakistan, 0.862 million tons of camel milk is produced annually [6] and primarily consumed locally in raw state. Despite the fact that camel milk is produced in appreciable quantity, its composition varies greatly in several studies [7][8][9]. Very limited studies are so far reported in relation to physico-chemical and sensorial characteristics of camel milk in Pakistan; hence, present investigation was conducted in this regard at different vicinities of camel habitat zones of Sindh, Pakistan.

Fat content
Fat content of camel milk was determined by Gerber method [12]. Milk sample (11ml) was mixed with 90% sulfuric acid (10ml) and amyl alcohol (1ml) in butyrometer and closed with rubber cork. The butyrometer was placed in a Gerber centrifuge machine (Funk Gerber, Model No. 12105, Germany) and centrifuged for 5 min at 1100rpm. The fat percent was noted on the butyrometer scale. Whey protein Firstly, milk sample was treated in similar fashion as for casein [10]. Thereafter, filtrate (20ml) was analyzed for N %age. The result obtained was multiplied with 6.38 to express whey protein %.

NPN content
NPN content was determined according to the method [13]. Sample (10ml) was taken into a pre-weighed conical flask and reweighed (nearest 0.1mg). Trichloro acetic acid (TCA) solution (40ml) was added to the flask, and contents with flask weighed. Solution was swirled to mix and left to stand approximately 5min to allow the precipitate settle. Contents of the flask were filtered through filter paper and filtrate was collected in the clean, dry conical flask. Mixed filtrate (20ml) was then analyzed for N %age. The result obtained was multiplied by 6.38 to calculate protein equivalent of non-protein nitrogen content.

Lactose and solids not fat contents (SNF)
Both variables were computed by difference methods. In case of lactose content, the sum of percent of protein, fat and ash contents were subtracted from the percent of total solids content, while SNF content was calculated by deducting the percent of fat content from the percent of total solids content [10]. Evaluation of sensory variables Sensory characteristics of camel milk were evaluated according to the method reported by [14]. A panel of six judges was selected, and they were first familiarized with sensory profile of milk. Thereafter, camel milk from each block variable was offered one by one for evaluation using sensory protocol. The score was rated on hedonic scale of 10 for appearance/color, 5 each for odor/aroma and body/texture, and 45 for taste/flavor. Overall acceptability score was rated on nine-point hedonic scale where one for "disliked extremely" and nine for "liked extremely" [15].

Statistical analysis
The data so obtained were processed using computerized statistical package i.e. Student Edition of Statistix (SXW), Version 8.1 (Copyright 2005, Analytical Software, USA). Statistical procedure of analysis of variance (AOV) under Linear Models was applied, and in case of significant differences appeared, the treatment variables were further differentiated using least significant difference (LSD) test [16]. Results and discussion Physical characteristics of camel milk The physical characteristics like pH, acidity, conductivity, refractive index, specific gravity and viscosity of camel milk varied zone to zone ( Table 1). The H + intensity in milk of camel raised at coastal mangroves (6.48pH) recorded slightly high from camel milk produced at sandy desert (6.49pH) zone, but found statistically non-significant (P>0.05). However, camel milk at irrigated zone (6.50pH) noted significantly high (P<0.05) in H + from milk of camel reared at both former zones. These results were further confirmed through titratable acidity test, whereby acidity percent in camel milk appeared significantly high (P<0.05) at coastal mangroves (0.178%) compared to milk of camel habitat at sandy desert (0.169%) and irrigated plains (0.165%). The percent of acidity in milk of camel at both of later zones noted non-significant (P>0.05). It is noteworthy that intensity of H + in camel examined under current study found high than that of reported studies [17,18], who examined the pH values 6.63 and 6.64±0.02 (0.15±0.01% acidity), respectively. However, in another study camel milk recorded more intense in H + (5.97±0.03pH) [19] contrast to that of present study. Specific gravity of camel milk varied significantly (P<0.05) at camel habitat zones of Sindh province. It was comparatively high at irrigated plains (1.032) followed by coastal mangroves (1.030) and sandy desert (1.029). It is intended to say that specific gravity of milk had positive correlation with solids not fat content [20]. This correlation was apparently confirmed in the present investigation as trend in variation is specific gravity (  (Table 1) recorded significantly (P<0.05) high in milk of camel reared at irrigated plains (1.07767cP) contrast to that of at coastal mangroves (1.68569cP) and sandy deserts (1.6500cP). It is noteworthy that viscosity of milk of camel reared at irrigated plains found relatively similar, and habitat at coastal mangroves or sandy desert the low from that of reported by [24]. Moreover, it is expressed that incorporation of viscosity in milk might be due to friction of fat and dispersed protein, and increase in these components might increase the viscosity [25] and this probably happened in the present study, where viscosity of camel milk appeared with similar trend of fat and total protein in camel milk ( Table 2).
Conductivity of camel milk varied area to area (Table 1). It recorded high at irrigated plains (5.0389 mS/cm) and low at sandy desert (4.6971 mS/cm); while at coastal mangroves, it was at intermediate level (4.8622 mS/cm). It has been reported that the conductivity is directly correlated with level of mineral + (ions) [25]. This probably happened in the present investigation where trend of conductivity appeared with similar fashion as for mineral contents recorded in all three zones of Sindh, Pakistan ( and other camel browse vegetation though might be rich in carbohydrates at irrigated plains other than former two zones, and resulted the above said trend in lactose content in camel milk. Nevertheless, the concentration of lactose content in camel milk observed in the current study found in a range of reported percent of [21,37,38]. Regardless, the ash content of camel milk ( Table 2) recorded high in milk of camel reared at irrigated plains (0.79%) from that of at coastal mangroves (0.76%) and sandy deserts (0.74%), the differences existed statistically non-significant (P>0.05) among them. Nevertheless, significant fluctuation in ash content in camel milk was reported [21, 37, 39, 40], and reasons had been attributed with differences in type and availability of water and camel browse vegetation. No significant (P>0.05) variation was recorded in solids not fat content in camel milk (Table 2) at sandy desert (7.65%) and coastal mangroves (7.78%). However, in both of the above camel habitat zones, the concentration of SNF contents in camel milk varied significantly (P<0.05) from milk of camel raised at irrigated plains (8.01%). In fact, the variation in SNF content (range 5.56 to 8.29%) in camel milk was also reported in a study conducted by [21] and though supports the current study.

Sensory characteristics of camel milk
In contrast to buffalo milk, sensory profile (appearance/color, odor/aroma, taste/flavor and body/texture) of camel milk rated comparatively (P<0.05) low, and found less acceptable (Table 3). It is noteworthy that sensory attributes of camel milk vary with ruminant species because of their physicochemical properties [40] and buffalo milk reported dominant in these properties compared to camel milk [41,42]. Color/appearance score rated for milk of camel at irrigated plains (8.95) recorded significantly high (P<0.05) followed by coastal mangroves (8.64) and sandy desert (8.40) over total score of 10. However, the score for color/appearance of camel milk at above three areas did not reach at the score rated for similar attributes of buffalo milk (9.28) and found significantly (P<0.05) low (Table 3). Although, camel milk perceived low score for color/appearance from that of buffalo milk, it was ranked at highly acceptable limit. In fact the color/appearance of milk correlates with concentration of fat and casein contents present in such milk [30] and this correlation has been confirmed in the present study. The score for color/appearance of camel milk rated in sandy area (Table 3) noted in similar trend as for fat and/or casein content observed in the current study (Table  2), and buffalo milk reported high in fat content than that of camel milk [42] where score was in similar manner. Odor/aroma score rated for camel milk at three camel habitat zones of Sindh province (irrigated plains, sandy deserts and coastal mangroves) found under acceptable limit. However, it varied considerably area to area in the present study. Camel milk at irrigated plains perceived better (P<0.05) score (3.36) for odor/aroma over total score of 5 (Table 3) compared to coastal mangroves (3.24) and sandy desert (3.15). Nevertheless, score for odor/aroma perceived by camel milk at sandy desert area did not compete with that of received by buffalo milk as control (4.47). It could be argued that odor/aroma in milk might be enhanced from feed eaten, type of water intake and surrounding environment, and these conditions vary at camel habitat zones of Sindh province. These conditions reflected the dominancy on odor/aroma attributes of camel milk accordingly. Taste/flavor is of course assumed to be important attribute of sensory space map of milk. The score perceived for this attribute found in similar trend as for color/appearance and/or odor/aroma whereby control milk (buffalo) rated significantly (P<0.05) better score compared to camel milk at three zones of Sindh province (Table 3). Nevertheless, among camel milk taste/flavor score rated comparatively (P<0.05) high at irrigated plains (31.26) followed by coastal mangroves (30.17) and sandy desert (29.34) over total score of 45. These scores probably ranked under acceptable limit. This trend of score for taste/flavor rated for camel milk might correlate with trend of fat content of camel milk observed in the current study (Table 2). In fact, the fraction of fat and protein in milk might enhance the taste/flavor of milk [20]. Moreover, type of fodder and availability of drinking water were reported to cause changes in taste /flavor in camel milk [30]. In the current study, the influence of above two factors on taste/flavor attributes of camel milk found dominant whereby camel browse vegetation and availability of type of water vary area to area. Variation in milk flavor might also occur due to animal metabolism and interaction between animal, environmental conditions and feed [43]. Body/texture score of camel milk (Table 3) at irrigated plains rates significantly (P<0.05) better (3.64) than that of coastal mangroves (3.51) and sandy desert (3.41) area of Sindh province. These scores for body/texture for camel milk in these areas although found not comparable with that of received for buffalo milk, but are at acceptable limit. However, the variation in score for body/texture might correlate with availability of camel browse vegetation and drinking water [30]. Overall acceptability score also rated in similar manner as for other sensory attributes for camel milk in the current study (Table 3). Moreover, buffalo milk found more acceptable compared to that of camel milk, though ruminant species had significant influence on accepted profile because of its chemical properties [40].

Conclusion
Prominent variation appeared in most of the physico-chemical and sensorial characteristics of camel milk produced at different camel habitat zones of Sindh, Pakistan, whereby irrigated plains found dominant followed by coastal mangroves and sandy desert. Regardless, score for sensory attributes of camel milk did not reach at the score rated for buffalo milk; its level was in fact under acceptable limit.