Received Date: February 18, 2014; Accepted: May 27, 2014; Published Date: June 17, 2014
Citation: Barat Ali ZY, Khomeiri M (2014) Rheological Behavior of Agharan Contains Different Concentrations of Whey Powder, Starch and Gum Arabic. J Food Process Technol 5:330. doi:10.4172/2157-7110.1000330
Copyright: © 2014 Barat Ali ZY, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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The Agharan is fermented concentrated fermented camel milk which prepared in some pastoral region of Golestan Province in Iran, and among the Turkmen tribes where camels are kept and bred called Agharan. Agharan has not been introduced in any article, conferences or etc. in the world, yet. So this is the first article written about Agharan and has introduced it, and investigate the rheology of this product. Accordingly, this study can provide important information for other researchers. The aim of the this work is to study the effect of 0.05, 0.1 and 0.15% Whey Powder, Gum Arabic and Starch at 30, 40, 50, 60, 70, 80, 90, 100, 105, 120, 135, 140, 150, 160, 180, 200 rpms on rheological properties of Agharan at 24°C. Results with Mitschka Method revealed all samples were Shear Thining. All samples showed similar decrease in apparent viscosity with increasing the Shear rate. In all concentration of Agharan contain Gum arabic, viscosity decreased slightly in comparison to control. In contrast, Agharan contains 0.15% Whey powder has sharp slope. The level of decrease depended on the levels of materials added. The highest and lowest Apparent viscosity were recorded for Agharan contain 0.1, 0.05% Starch (3520.7, 2678.4) and 0.15% gum arabic (823.25) respectively. Accordingly Starch, Whey powder and Gum Arabic can alter rheological properties of Agharan.
Agharan; Fermented camel milk; Starch; Rheological behavior; Shear thinning
Rheology is the study of deformation and flow of fluids in response to stress. To make an incompressible fluid flow, a shear stress must be applied.
Camel is a useful animal which many years ago domesticated by human and used its Milk, Meat, Skin, Wool and so one. Fermented camel milk is one of the 3500 traditional fermented food exist in the world , that believed to be one of the oldest fermentation products known to humans, originating in the Middle East and Africa and is consumed by some people in pastoralis regions [2,3].
Camel milk and fermented camel milks are nutritious foods because has medicinal properties and in many region used against some diseases [4-7]. The Agharan is fermented concentrated camel milk which prepared in some pastoral region of Golestan Province in Iran, and among the Turkmen tribes where camels are kept and bred, called Agharan. It is prepared by gathering the thin layer of fermented camel milk and has a nutritious value and serve especially as a breakfast. It is similar to concentrated yoghurt.
Most of whey protein is lost in the drainage without any benefit . The environmental pollution and high cost of disposing it, also, the high nutritional value , and low cost of whey encouraged scientists to utilize it as an excellent food component in the foods . Functional properties of whey proteins, such as emulsifying, water/fat holding, extending shelf-life, foaming, thickening and gelling properties , also nutritional value , make them interesting to be used as a food ingredient in conjunction fermented milks . Several studies have used whey powder in yoghurt making which leads to provide better consistency, texture and creaminess to the product.
Plant hydrocolloids used in foods for improve texture and stability. Gums are polysaccharides that classified according to their origin . Gum Arabic, also called Acacia Gum is the natural exudate from the Acacia Senegal, which have high molecular weight consisting of branched arabinogalactan heteropolymers [15,16]. The gums have the ability to control the rheology and texture throughout the stabilization of emulsions, suspensions, foams and starch gelatinization . Gum Arabic also contains proteins (2%). Uranic acid in Gum Arabic is responsible for the polyanionic character of it with a pH around 3 [18,19].
Whey powder used in this study was a commercial product from Golestan Dairy Industries Company (PEGAH, Iran) with about composition of 11% Protein, moisture 5%, total solids 95%, 1.5% fat, and acidity (lactic acid) 0.12% as per manufacturer’s data. Starch obtained from Merck Company, (Germany). Agharan from onehumped camel (Camelus dromedarius) purchase from Bandar Torkman city in Golestan Province (Iran). Also Gum Arabic used in this study. All the examinations carry out in the laboratory of Department of Food Science and Technology of Agricultural Science and Natural Resources University, Gorgan, Iran.
Preparation method of Agharan
For preparation of Agharan allowe to camel milk to quiet in a steady place at ambient temperature after it break into two phases, the solids are remove gently from the thin layer of coagulated milk that partially fermented. In fact, it is concentrated sour camel milk which in Turkmen dialect in Iran called Agharan. Total solids, pH and acidity (Dornic) of the Agharan used in this study were 20%, 4.4 and 80, respectively.
Addition of powders and mixing
Three levels of Starch, Whey powder and Gum Arabic (0.05, 0.1 and 0.15%) were considered in this study. Powders were added to Agharan under gentle constant mixing with aid a Kitchen mixer for 1 min. Then the samples were kept at 4-5°C for 24 h before any tests were carried out. Before using Gum arabic, first its solution was prepared by hydrating in distilled water, mixed with a magnetic stirrer for 24 h at 60°C, then added to Agharan and sample kept at 4-5°C for 24 h.
A control batch (without whey protein, starch and Gum Arabic) was also mixed under similar conditions.
The Apparent viscosity of the Agharan determined at 24°C at various Shear rates (from 9.51 to 100 s−1) with the aid of a Brookfield RDVD-II, viscometer (Brookfield Engineering Laboratories, USA) using spindle No 3 at different rpms (30, 40, 50, 60, 70, 80, 90, 100, 105, 120, 135, 140, 150, 160, 180, 200). For each sample three readings were taken and their means were reported.
The sample was placed in a 600 mL low form Griffin beaker and a disc was inserted into the sample. To eliminate any time-dependent behavior, sample was subjected to pre-shearing until a constant torque was observed. Formal data collection of torque at various rotational speeds followed immediately. All data were collected at room temperature, approximately 24°C.
τi = katai
Pairs of τi - Ni (rotational speed in rpm) valid for spindle are plotted in the log – log form.
When this dependence is sufficiently close to a linear one, the fluid under test is of the power –law type. The slope of the log τi - log N dependence in this case is equal to the flow index of the fluid or n.
Using values of kny (n) for this flow index and spindle number, the corresponding values of the Shear rates yi (in s-1) are then calculated as
yi = kny (n) Ni
The relevant pairs τi - yi are assumed to be the points of the viscosity function of the fluid sample tested. Conversion factor for the method described by mitschka show in Table 1.
Table 1: Conversion factor for the spindles of the Brookfield R.V.T. viscometer (under standard measuring conditions).
The effects of concentration, N, and Shear rate on the Apparent viscosity were studied. Related graphs and curves drown by Excel. A significance level of 0.05 was utilized for all analyses.
After calculating the Shear rate, Shear stress and Apparent viscosity (Tables 2-5), established the related curves. The Apparent viscosity of Agharan samples decreased with increase shear rate, indicating a non- Newtonian fluid and showed shear-thinning behavior (Figures 1-3) that characterized by flow behavior index values of less than 1.
|Agharan without additives|
|Shear stress (pa)||Shear rate (s−1)||Apparent viscosity( pa. s)|
Pa=pascal, pa.s=pascal second
Table 2: Agharan without additives.
|Agharancontains 0.05% Starch||Agharan contains 0.1% Starch||Agharan contains 0.15% Starch|
|Ss (pa)||Sr (s−1)||A.vis(pa.s)||Ss (pa)||Sr(s−1)||A.vis (pa.s)||Ss (pa)||Sr(s−1)||A.vis (pa.s)|
Ss=shear stress, Sr=shear rate, A. vis=Apparent viscosity, Pa=pascal, pa.s=pascal. second
Table 3: Agharan with different concentration of Starch.
|Agharancontains 0.05% Gum arabic||Agharancontains 0.1% Gum arabic||Agharancontains 0.15% Gum arabic|
|Ss (pa)||Sr(s−1)||A.vis(pa.s)||Ss (pa)||Sr(s−1)||A.vis (pa.s)||Ss (pa)||Sr (s−1)||A.vis (pa.s)|
Ss=shear stress, Sr=shear rate, A. vis=Apparent viscosity, Pa=pascal, pa.s=pascal. Second
Table 4: Agharan with different concentration of Gum Arabic.
|Agharancontains 0.05% whey powder||Agharancontains 0.1% whey powder||Agharancontains 0.15% whey powder|
|Ss (pa)||Sr (s−1)||A.vis (pa.s)||Ss (pa)||Sr (s−1)||A.vis (pa.s)||Ss (pa)||Sr (s−1)||A. vis (pa.s)|
Ss=shear stress, Sr=shear rate, A. vis=Apparent viscosity, Pa=pascal, pa.s=pascal. Second
Table 5: Agharan with different concentration of Whey powder.
The consistency index (K) was greatest for Agharan contains starch 0.1%, Gum arabic 0.05% and whey 0.1% and calculated 4.0548, 3.83 and 3.6845 respectively, and for Agharan without additives was 3.0633. The flow behavior index was highest for Agharan contains 0.15% whey, 0.1% Gum Arabic and 0.15% starch and calculated 0.812, 0.4851 and 0.7952 respectively in comparison to Agharan without additives (0.7961). All samples showed rather similar flow curves except Agharan contains 0.15% whey powder that had sharp slope. In general, all samples showed the decrease in apparent viscosity with increasing the shear rate and in all of Agharan contain Gum Arabiconcentrationc, apparent viscosity decreased slightly in comparison to control and has mild slope (Figures 1-3).
Effect of concentration on viscosity
Figures 4, 5 and 6 show the influence of concentration on Shear stress versus Shear rate at constant temperature. The Apparent viscosity analysis of the samples revealed a significant decrease in apparent viscosity values for samples containing 0.05% Whey powder, but a higher value seen in higher concentration of Whey powder. The results suggested that rheological parameter values in the Agharan contains whey powder depended on whey concentration when present at low concentration because the whey proteins were not able to gel .
In all samples with increasing Shear rate, decreased the Shear stress. The slope of decrease in Agharan contains 0.15% Whey powder is slight greater and in Agharan without additives is near to newtonian fluids. Agharan contains 0.15% Starch is slight same to Agharan without additives. Sample contains 0.1% Starch in comparison to 0.05% had milder slope. In between all samples, Agharan with 0.05% Whey powder in compared to others had lower Shear stress with increase the Shear rate.
The highest viscosity values were recorded for Agharan contains 0.1, 0.05% Starch, were 3520.7, 2678.4, and lowest for Agharan contains 0.15% Gum Arabic (823.25). Representative plots for Shear stress versus Shear rate is shown in Figures 4, 5 and 6.
Whey proteins at low concentration do not influence significantly on rheological properties and at high Starch concentrations, it was possible to produce a hard firm structure. The presence of Gum Arabic, Starch especially Whey powder at low concentrations led to weaker structure. Similar effects of Starch addition on the properties of stirred yoghurts have been reported by Williams . Also In the previous study noticed a similar tendency .
Effect of non-viscosity values
Agharan had Shear thining behavior and as expected in all samples apparent viscosity decreased gradually with increase in RPM, probably due to the disruption of the Agharan structure. Figures 7, 8 and 9 show the influence of RPM on Apparent viscosity of Agharan. As showed in figures, addition of whey powder, starch and Gum arabic to the Agharan resulted in a depression of apparent viscosity. All samples showed Shear thining behavior, as apparent viscosity decreased gradually when samples were subjected to shear rate. The Apparent viscosity showed a decrease with increasing Shear rate at all concentration ranges. The effect of the gelation process on the rheological properties of yogurt prepared from sheep, goat, cow and camel milks was investigated by Jumah et al. . They found that the highest value for viscosity was earned by sheep milk, followed by goat, cow and camel milks. Three different transient viscosity stages were identified for cow, sheep and goat milk, whereas camel milk showed no significant variation in viscosity during gelation. The ratio of casein and whey protein in cow, sheep and goat milks are almost 80: 20, and for camel milk is about 70: 30, this ratio seems have effect on viscosity and rheology properties of products made from cow, sheep, goat and camel milks. And differences in viscosity and rheology properties of these products can be attributed to the different nature of these milks.
After the aggregation/gelation of the whey proteins, rearrangements of the gel network are observed [25,26], and may be due to aggregation of casein particles at iso-electric pH (pH 4.6). Such rearrangements lead to a transition from an initial denatured whey protein (associated with casein micelles) induced gel formed at a high pH (pH 5.2) to a network dominated by casein–casein interaction at a lower pH (pH 4.6) .
Adding 6% whey protein is sufficient to form stable three dimensional structures and reveals higher rheological parameters values. It can be due to change in the flow characteristic in the samples that arose from structural formation, while in lower whey protein concentrations, the addition of whey powder produced a marginal decrease in viscosity of system typical for shear thining behavior, without contributing to the formation of intermolecular bonds .
The concentration dependence of the Apparent viscosity on Shear rate, described by other researchers for Whey protein, Starch and Gum Arabic systems, was confirmed by this study also for undenatured Whey proteins [23,22,28].
Near neutral pH, whey proteins gels can be formed either by heatinduced gelation in which it is necessary to heat whey proteins in the presence of ions, or by cold- or ion-induced gelation in which the whey proteins form a three-dimensional network by aggregation. In the latter case, it is prerequisite to unfold the whey protein monomers by prior heating to expose sulfhydryl and hydrophobic amino acid residues that are buried in the interior of the globules. The unfolded proteins form polymers mainly via sulfhydryl/disulfide interactions and also via hydrophobic interactions . Same reasons exist for formation of firm structure by starch and Gum arabic but with slight different in regard with they are hydrocolloids. Same results approached in this study and these hydrocolloids and whey powder decreased the apparent viscosity.
A rapid breakdown of the structure occurs on initial shearing followed by much slower changes at higher shear rates. This behavior can be attributed to combined effects of breakdown of weak linkages between the proteins and/or between the proteins and stabilizer, and of reformation of such linkages as a result of Brownian motion and molecular collisions .
The Mitschka method produces very useful information for quality control a variety of shear-thinning fluid foods. The present work has shown that addition Starch, Whey powder and Gum Arabic decrease the Apparent viscosity. The level of decrease was dependent on the level of adding.
The amount of Whey powder, Starch and Gtexturalum arabic affected the rheological and attributes of the Agharan. All Agharan samples in this study were Shear Thinning. Accordingly, we concluded that use of Whey powder, Starch and Gum arabic in the manufacture of Agharan can improve its physical properties.
The authors wish to thank engineer Rahil Rezaei and dr Seid Mahdi Jafari for his critical helps and valuable suggestions.