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The acid–base buffering properties of Alxa bactrian camel milk
Accepted Manuscript Title: The acid-base buffering properties of Alxa Bactrian camel milk Author: Dian-bo Zhao Yan-hong Bai PII: DOI: Reference:
S0921-4488(14)00304-6 http://dx.doi.org/doi:10.1016/j.smallrumres.2014.10.011 RUMIN 4812
To appear in:
Small Ruminant Research
Received date: Revised date: Accepted date:
26-5-2014 17-10-2014 26-10-2014
Please cite this article as: Zhao, D.-b., Bai, Y.-h.,The acid-base buffering properties of Alxa Bactrian camel milk, Small Ruminant Research (2014), http://dx.doi.org/10.1016/j.smallrumres.2014.10.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The buffering of milk influenced many of its physico-chemical properties, by
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controlling pH during processing. There were many reports on the buffering of milk
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and of cheese, calculated from titration curves. However, the titration curves obtained
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depends on the methodology used, the forward and back titration curves of milk did
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not coincide. The buffering properties of camel milk was investigated by the forward
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and back titration. The results had shown that the forward and back titration curves
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were not identical, the camel milk had stronger buffering capacity than that of bovine
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milk.
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The acid-base buffering properties of Alxa Bactrian camel milk
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Dian-bo Zhao, Yan-hong Bai *
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College of Food and Biological Engineering, Zhengzhou University of Light Industry, Dongfeng Road # 5 Zhengzhou, Henan, P.R,China
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Abstract
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The buffering properties of Alxa bactrian camel whole milk was investigated by
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titrating with base or acid. A “loop” was observed in the pH range 6.6 to 4.3 when
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sample was firstly titrated with acid and then back titrated with base. A “loop” was not
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observed when sample was firstly titrated with base and then back titrated with acid.
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When the milk sample was titrated from initial pH to 2.0 with HCl, camel milk
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exhibited a pronounced maximum buffering at approximately pH4.4 and the value of
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dB/dpH was about 0.073. When acidified camel milk sample was back titrated from
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pH 2.0 to 11.0 with NaOH, there was low buffering index at approximately pH 4.9
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(0.024), and maximum buffering index occurred at approximately pH 6.1(0.051). The
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sample was firstly titrated from initial pH to 11.0 with NaOH, camel milk exhibited a
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weaker buffering peak at approximately pH 7.1 and the value of dB/dpH was about
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0.018, when the alkalized milk sample was back titrated from pH 11.0 to 2.0 with HCl,
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the maximum buffering index occurred at approximately pH 5.1 and the value of
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Abbreviation Key: BI=buffering index, BC=buffering capacity, TN=total
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nitrogen, NPN= non-protein nitrogen, WPN= whey protein nitrogen, CN= casein
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nitrogen
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Introduction
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dB/dpH was about 0.047.
* Corresponding author. Present address: College of Food and Biological Engineering, Zhengzhou University of Light Industry, Dongfeng Road #5 Zhengzhou, Henan,450002, P.R,China; E-mail address：[email protected] Key words: Buffering Properties, Camel Milk, Alxa Bactrian Camel
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There are 3 fine breeds of Camelus bactrianus in China, namely Xinjiang, Alxa
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bactrian and Sunite camel(Zhang et al,2005). Alxa camels can be further divided into
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Gobi and Desert camels based on their stature, physical features, and breeding
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distinctions. Alxa camels are reared mainly by natural grazing in different herd sizes
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ranging from 10 to 100 camels with a grazing radius of 40 to 50 ㎞. Alxa camel
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belong to low milk yield category, an Alxa camel can produce 0.25 to 1.5 kg of milk
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daily in addition to the amount taken by the calf.
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The chemical composition of camel milk was similar to that of cow
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milk(Yagil,1982; Farah,1993). Camel milk can be used for making various dairy
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products such as butter, shubat, cheese and milk tea. Camel milk not only supplies
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nutrition for local people, but also has therapeutic properties. Considerable
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information had been published concerning the variation of the chemical composition
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of dromedary camel milk(Yagil,1982; Farah,1993; Mehaia et al,1995; Gorban and
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Izzeldin,1997; Guliye et al, 2000; Zhang et al,2005; JiRiMuTU,2006), but little
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knowledge was available concerning the buffering properties of camel milk. The
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buffering properties of cow, goat and buffalo milks had been reported(Buchanan and
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Peterson,1927; Whittier ,1929; Watson,1931; Ismail et al,1973; Park,1991; Lucey et
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al,1993). Interest has been directed recently to the importance of the buffering value
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of milk, particularly, in regard to certain processes in the manufacture of casein, cheese, condensed milk products and nutritional studies. The buffer capacity of a solution may be expressed as its power to resist change
in pH upon the addition or loss of acid or base (Ismail et al,1973). Buffering index was defined as the number of equivalents of acid or base required to shift the pH of 1
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L of milk by one unit(Ismail et al,1973). The buffering index of a solution was not
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constant and had an exact value only at a definite pH, and therefore the value
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calculated over an observed pH range was an average one. In practise, a close
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approximation was made if the buffering index was calculated for the mean pH over a
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small pH interval(Watson,1931).
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Objectives of this study were to characterize the buffering properties, report the
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BC, demonstrate that the forward and back titration curves are not identical in Alxa
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bactrian camel milk.
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Materials and methods
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Preparation of animal milk samples
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Ten 5-year old Alxa bactrian female camels cloose to giving birth for the first time
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were randomly selected from different herds that depended on natural grazing. The
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camels, which all belonged to the Alxa nomads in Inner Mongolia, were kept under
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muster management before giving birth and fed with hay supplemented with corn
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after parturition. Sampling collection started following parturition at 90d post partum
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（PP）. Representative sample was collected 500ml each camel, and the sample was
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cooled in ice-water and stored at 4℃, for a period not exceeding 72 hours, ten
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samples were warmed to 20℃ and mixed thoroughly until analyzed. The control cow
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The bovine milks (Holstein, breed) as a control which were obtained from the Inner
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Mongolia Agricultural University farm.
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Physical parameters analysis
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Milk sample physical parameters were measured as follows: titratable
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acidity(TA)and specific gravity were determined according to the method of
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nitrogen (NPN) fraction was calculated as follows: NPN = TN – CN – WPN. Milk
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The casein nitrogen (CN) was determined according to the method of Rowland (1938)
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with some modifications. Trichloroacetic acid (36%) was added into the whey to a
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final concentration of 12% (v/v) to precipitate the whey proteins for determination of
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whey protein nitrogen (WPN). Dry matter (DM) of the samples was determined
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Association of Official Analytical Chemists (AOAC, 1990a). Chemical analysis
The mixed sample was analyzed and the data was determined by triplicates.
Nitrogen was determined by the Kjeldahl method. A nitrogen conversion factor of 6.38 was used for calculation of protein contents of milk samples. Non-protein
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gravimetrically after drying in a forced-draft oven at 105°C until a steady weight was
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achieved. Fat percentage was determined according to the method of Rose-Gottlieb
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and ash content was measured gravimetrically (Aggarawala and Sharma, 1961).
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Lactose content was determined by the difference of DM minus other solid
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components. Levels of Ca in the milk samples was determined with an atomic
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absorption spectrophotometer (Hitachi U-2000, Japan) according to standard methods
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in the AOAC (1980). Phosphorus content was determined spectrophotometrically
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using the procedure of Watanabe and Olsen (1965).
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Titration methods
Titrations were performed on 30ml mixed sample at 20℃ by a automatic titrator
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（Model ZDJ-5, Lei-Ci Instruments, Shanghai, China）using 0.5N HCl or 0.5N
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NaOH, added in 0.1ml increment at 30 sec intervals to allow for equilibrium while the
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sample was stirred with an electrically driven agitator. Two different titration methods
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were used in this experiment (Lucey et al,1993). In the first method involved the
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sample was titrated from the initial pH6.6 to 2.0 with 0.5N HCl(was termed
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acidification) and then back titrated to pH 11.0 with 0.5N NaOH(was termed
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alkalinization).The second method involved
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6.6 to 11.0 with NaOH (was termed alkalinization)and then back titrated to pH 2.0
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Slyke,1922). Van Slyke revealed that the volume change due to the added acid or
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alkali may be ordinarily neglected, if the maximum increase was below 50 per cent of
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the original volume. Inasmuch as the volume changes which occurred in the present
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work were below these limits, no correction for
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in the formula. The buffering index for each 0.2 pH interval was calculated by the
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sample titration from the initial pH
with HCl(was termed acidification). Titration curve
From these data a titration curve was drawn by plotting the amount of alkali or
acid used, against the change in pH produced. Buffering curve
In this work Van Slyke's method of measuring buffering values was used(Van
them was
considered necessary
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dB (ml acid added) (normality factor) ＝ . dpH (volume of milk ) (pH change) A plot of buffering index against pH produced a buffer intensity (dB⁄dpH-pH)
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formula.
curve, the "peak" in the graph, was a characteristic of the kind of buffer. Results and discussion
Chemical composition
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The gross composition of camel milk and cow milk was showed in Table 1. The
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titratable acidity was denoted in terms of lactic acid content (g/100g). The contents of
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fat, protein, lactose, total solids, TN, NPN, P, Ca and ash in camel milk were higher
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than that of in bovine milk. However, the values of acidity (%) and density were
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similar with that of in bovine milk.
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Titration curves for samples
The titration curves for camel and bovine raw milk samples had a similar shape
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and were essentially superimposable. The typical curves had been shown in Fig.1 and
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Fig.2. A “loop” was observed in the pH range 6.6 to 4.3 and 6.6 to 5.0 for camel and
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bovine milk, when the titration were performed according to the first method (Fig.1).
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Both milks exhibited a similar shape of the titration curves,
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were similar with that of
bovine milk had been published( Lucey et al, 1993). That means the titration curves samples did not coincide in the pH range 6.6 to 4.3 and 6.6 to 5.0 for camel and bovine milk samples, respectively. The “loop”
observed
was likelycontributed by
diversified buffering constituents in milk exerted buffering action, such as carbon dioxide, proteins, phosphate, citrate and a number of minor constituents, especially, the colloidal calcium phosphate(CCP) in different pH conditions was
solubilized or
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precipitated. A “loop” was not observed in either or bovine milk when the titration were performed according to the second method (Fig.2), although they did not coincide, the curves had a similar shape. Buffering curves for samples titrated by using the first method
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Milk was acidified from original pH 6.6 to 2.0, the typical buffering curves
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were shown in Fig.3 and Fig.4. Both milks exhibited a pronounced maximum
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buffering index at approximately pH 4.4 and 5.1 for camel and bovine milk, and the
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values of dB/dpH were about 0.073 and 0.042, respectively. Comparing with the
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bovine milk, the buffering curve indicated that there was the other one buffering peak
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at approximately pH 4.9 and the value of dB/dpH was about 0.052 in camel milk
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(Fig.3 and Fig.4). The difference in buffering curves between the camel and the
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bovine milk may be related to the casein and the structure of CCP in milk.
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Park(1991) and Whittier(1929) indicated that the buffer action of milk casein
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was exerted principally between pH 4.5 to 5.7 with a maximum at approximately pH
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5.2, in this range the casein was evidently one of the chief factors in the buffer action
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of milk. The present study of bovine milk was similar with that had been published by
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Park(1991) and Whittier(1929). Buchanan and Peterson(1927) illustrated that the
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casein was precipitated in the range pH 4.5 to 5.0, usually at about pH 4.7. The camel
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milk exhibited a pronounced maximum buffering at approximately pH 4.4, which it
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was may be concluded that the casein of camel milk exerted very little influence
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compared with that of bovine milk in the buffering action in this pH range. The
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present study of camel milk was similar with that published by Buchanan and
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Peterson(1927). The casein in camel milk was not one of the chief factors in the
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buffering action of milk, possibly due to the difference of the size and the fractions of
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casein in camel milk compared with that of in cow milk. The casein micelle was the backbone of the colloidal milk system, and
determined milk stability. Zhao (2006) revealed that the size of casein micellares in Alxa bactrian camel milk was larger than that of cow milk. From a few available literatures on camel casein micelles it can be concluded that camel milk casein
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significantly broader than that of bovine milk in terms of micellar size distribution,
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and showed a great number of large particles and the average diameter of casein was
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320 nm, and the average diameter of camel casein micelles was more two times than
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that of bovine milk (Zhao, 2006; Sawaya et al, 1984; Larsson-Raznikiewicz and
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Mohamed, 1986; Farah and Ruegg, 1989; Farah, 1993).
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Zhang et al (2005) revealed that there
were no protein bands homologous to
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bovine κ-casein
clearly detected in Alxa bactrian camel milk. Farah and
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Farah-Riesen (1985) demonstrated that there were no protein bands homologous to
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bovine κ-casein
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reported that there was
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milk(Larbaa breed), whereas there was very low
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Targui breed. Authors reported that there was a low amount of κ-casein( only about 5
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percent in camel casein), compared with about 13.6 percent in bovine casein (Jardali
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and Ramet, 1991 and Farah, 1993). Therefore, it
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absence or very low content of κ-casein in Alxa bactrian camel milk compared with
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that of bovine milk.
clearly detected in dromedary camel milk. Naima Alim et al（2005）
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absence of κ-casein in Algerian dromedary camel milk of
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content of κ-casein in
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might be concluded that there was
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The structure of CCP may be solubilized on acidification, especialy below pH
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5.6, the solubilization of CCP resulted in the formation of phosphate ions which
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combined with H+,
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structure of CCP in bovine milk may be completely solubilized at pH 5.1 and
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resulting in the maximum buffering, while the structure of CCP in camel milk may be
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completely solubilized at pH 4.4 and resulting in the maximum buffering. It would be
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concluded that the structure of CCP in camel milk was different from the bovine milk.
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about buffering action (Dalgleish & Law,1989). The
The buffering curves of either camel or bovine milks indicated the same
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brought
tendency for the change in the milk buffering index at different pH. Below the initial pH in both milk the buffering index increased very sharply till the maximum index at approximately pH4.4 in camel and 5.1 in bovine, thereafter the buffering index dropped very sharply from the maximum buffering index. The buffering index gradually increased from the initial pH to 4.9, and then the buffering index decreased from pH 4.9 to 4.7, thereafter the index increased to the maximum in camel milk at
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approximately pH4.4. Comparing with the camel milk, the buffering index in bovine
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milk gradually increased from the initial pH to 5.1 in bovine milk.
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The present study revealed when samples were titrated from initial pH to 2.0 the
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volume of acid added were 8.8 and 6.8ml for camel and cow milk, respectively, which
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indicated that the camel milk had stronger buffering capacity than that of bovine milk.
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Figure 3 and 4 shown that the maximum buffering index of camel milk(0.073) was
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higher than that of bovine milk(0.042), and higher than that of buffalo and cow milk
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reported by Ismail et al (1973). Ismail et al(1973)reported that the height of the peak
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is proportional to the concentration of the buffer constituents. Park(1991) revealed
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that the greater resistance to pH change was related to the higher content of total N,
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NPN and P2O5. Salaün et al (2005) indicated that the buffering capacity was
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increased by increasing the level of Ca in milk. The level of TN, NPN, Ca and P in
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camel milk were found to be higher than that in bovine milk (Table 1). It was thought,
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therefore, that the higher level of TN, NPN, Ca and P in camel milk resulting in the
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stronger buffering capacity than that of bovine milk, and the concentration of the
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buffering constituents within camel milk was higher than that of bovine milk.
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could be significant in human nutrition because the camel milk
having the strong buffering properties can be utilized therapeutically in treatment of
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gastric stomach ulcers. In fact, the camel milk was successfully used in the treatment
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of peptic ulcers in Russia(Sukhov et al,1986) because of the higher buffering capacity
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than that of bovine milk.
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Camel milk was acidified from initial pH to 2.0, the the maximum buffering
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index at approximately pH 4.4(0.073), and the other one buffering peak at
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approximately pH 4.9(0.052). The acidfied camel milk was back titrated with NaOH from pH 2.0 to 6.6, the value of the buffering index was about 0.034 at approximately pH 4.4, the minimum buffering index at approximately pH 4.9(0.024), and the maximum buffering index occurred at approximately pH 6.1(0.051)( Fig.3). Bovine milk was acidified from initial pH to 2.0, the the maximum buffering index at
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approximately pH 5.1(0.042), the acidfied milk was back titrated from pH 2.0 to 6.6
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the minimum buffering index occurred at approximately pH 5.1(0.019) and the
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maximum buffering index occurred at approximately pH 6.3(0.031) ( Fig.4). Which
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was different from the camel milk Fig.3 and Fig.4). This may be due to buffering by
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higher content of glutamic acid residues(pK4.6) and citrate(pK4.1) in camel milk. In
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addition to, it might be related to the difference in physicochemical specificity and
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stereochemical configuration of buffering protein molecules in the two milks. The
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reason that resulting in the buffering index was not low at approximately pH 4.4 in
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camel milk would be need of further study. The maximum buffering index occurred at
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approximately pH 6.1 and pH 6.3 in camel and bovine milk, which can be explained
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by
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can combine with OH-, and increased the buffering capacity as suggested by lucey et
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al(1993). The buffering curves of either camel or bovine milks indicated the same
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tendency for the change in the milk buffering index at different pH, the buffering
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index was low at pH 8.1～9.3, but gradually increased thereafter.
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the formation of Ca3(PO4)2 with the release of H+ from HPO42- and H2PO4- which
It was concluded, therefore, that the proportion to buffering constituents, and the
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buffering system, stereochemical configuration of buffering protein molecules in
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camel milk was different from the bovine milk, which resulted in the difference in the
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titration curves between the camel and the bovine milk.
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Buffering curves for samples titrated by using the second method
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It was shown that camel milk exhibited a weaker buffering peak at
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approximately pH 7.1 and the value of dB/dpH was about 0.018, when the milk
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sample was titrated from original pH to 11.0 with NaOH (Fig.5), however, the
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buffering peak was not observed in cow milk(Fig.6). In addition to, when alkalized
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samples
were back titrated, the buffering curves of either camel or bovine milks
indicated the same tendency for the change in the milk buffering index at different pH, the buffering index were observed gradually decreasing from the value of pH 11.0 to 9.0,
and at pH values below 9.0 the buffering index were observed increasing
gradually thereafter (Fig.5 and Fig.6).
Maxima were observed
occurring at
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approximately pH 5.1(0.047) and pH 5.4(0.032) for camel and bovine milk, when
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alkalized milk samples were back titrated from pH 11.0 to 2.0 with HCl.
269 270 271 272
Conclusions The results of
this study indicated that the Alxa bactrian camel milk had
stronger buffering capacity than that of bovine milk. It was observed that there were
Page 10 of 18
two buffering peaks at approximately pH 4.4 and 4.9, and the value of dB/dpH was
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about 0.073 and 0.052, respectively, when the camel milk was acidified from original
275
pH 6.6 to 2.0. When the camel milk was acidified from initial pH to 2.0 and then back
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titrated from pH 2.0 to initial, the maximum and the minimum buffering index did not
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occurred at the same pH. There was one buffering peak was obviously observed at
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approximately pH 7.1, and the value of dB/dpH was about 0.018, when the camel
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milk was alkalized from original pH 6.6 to 11.0. The results of the present study
280
demonstrated that any investigation of the buffering properties of camel milk should
281
include a back titration step as the buffering curve during acidification was very
282
different to that during the back titration with base.
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Refference
285
Aggarawala, A. C., and R. M. Sharma. (1961). A Laboratory Manual of Milk
Analytical Chemists, Washington, DC.
289
AOAC, (1990a). Acidity of milk (Titrimetric method). In: Official Methods of
290
Ac ce p
288
AOAC.(1980). Official Methods of Analysis. 13th ed. Association of Official
d
287
Inspection. 4th ed. Asia Publishing House, Bombay, India.
te
286
M
284
291 292 293 294 295 296 297 298 299 300
Analysis, No. 947.05. Association of Official Analytical Chemists Inc. Virginia, USA.
Buchanan, J.H., & Peterson, E.E. (1927). Buffer of milk and buffer value. Journal of Dairy Science, 10, 224-231
Dalgleish, D.G., Law, A.J.R.(1989). pH-induced dissociation of bovine casein micelles. Ⅱ. Mineral solubilization and its relation to casein release. Journal of Dairy Research, 56, 727-735 Farah, Z. and Farah-Riesen, M.(1985). Separation and characterization of major components of camel milk casein. Milchwissenschaft, 40, 669-671 Farah, Z. & Ruegg, M.W.(1989). The size distribution of casein micelles in camel milk. Food Microstructure, 8, 211-212.
Page 11 of 18
302 303 304 305 306
Farah,Z.(1993).Composition and characteristics of camel milk. J. Dairy Res, 60, 603-626 Gorban, A.M.S., and Izzeldin,O.M.(1997). Mineral content of camel milk and colostrum. J. Dairy Res, 64, 471-474
ip t
301
Guliye,A.Y.,Yagil,R. and Hovell,F.D.D.(2000). Milk composition of Bedouin camels under semi-nomadic production system. J. Camel Pract. Res, 7, 209-212
Ismail, A.A., Eldeeb,S.A., & Eldifrawi, E.A. (1973). The buffering properties of cow
308
and buffalo milks. Zeit-schr. Lebensm.-Unters. Und-Forschung , 152, 25-31
309
Jardali, Z. & Ramet, J. P. (1991). Composition et taille des micelles du lait de
us
dromedaire. Le lait
an
310
cr
307
JiRiMuTU.(2006). Studies on Molecular Evolution of Domestic and Wild Bactrian
312
and the Physical-chemical Properties of Camel Milk. Diss.ETH No 219208,China
313
Larsson-Raznikiewicz, M. & Mohamed, M.A.(1986). Analysis of the casein content
316
Lucey,J.A., Hauth,B., Gorry,C., & Fox, P. F.(1993). The acid-base buffering properties
d
315
in camel (Camelus dromedarius milk. Swedish J. Agric. Res, 16,13-18.
of milk . Milchwissenschaft, 48(5), 268-272
te
314
M
311
Mehaia, M.A., Hablas, M.A., Abdel-Rahman, K.M. and El-Mougy, S.A.(1995). Milk
318
composition of Majaheim, Wadah and Hamra camels in Saudi-Arabia. Food
319 320 321 322 323
Ac ce p
317
Chemistry, 52, 115-122
Naima Alim, Fabio Fondrini, Ivan Bonizzi, Maria Feligini and Giuseppe Enne.(2005). Characterization of Casein Fractions from Algerian Dromedary(Camelus dromedarius) Milk. Pakistan Journal of Nutrition, 4(2), 112-116
Park,Y.W.(1991). Relative buffering capacity of goat milk, cow milk, soy-based infant
324
formula and commercial nonprescription antacid drugs. Journal of Dairy Science,
325
74, 3326-3333
326 327 328 329
Rowland, S. J. (1938). The determination of the nitrogen distribution in milk. J. Dairy Res. 9:42-46. Sawaya, W.N., Kalil, J.K., Al-Shalhat, A. & Al-Mohamed, H. (1984). Chemical composition and nutritional quality of camel milk. J. Food Sci, 49, 744-747
Page 12 of 18
330
Sukhov,S.V.,kalamkarova,L.I.,Il’chenko,L.A.&Zhangabylov,A.K.(1986). Changes in
331
the microflora of the small and large intestine in patients with chronic enteritis
332
after dietary treatment with cultured milk products. Voprosy Pitaniya, 4, 14-17
334 335
Salaün,F., Mietton, B., Gaucheron,F. (2005). Buffering capacity of dairy products. International Dairy Journal,15, 95-109
ip t
333
Van Slyke,D.D. (1922). On the measurement of buffer values and on
the
relationship of buffer value to the dissociation constant of the
buffer and the
337
concentration and reaction of the buffer. Journal of Biological Chemistry, 52,
338
525-571
us
cr
336
Watanabe, F. S., and Olson，S. R. (1965). Test of an ascorbic acid method for
340
determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc.
341
Am. Proc. 29:677–678.
343
Watson, P.D.(1931). Variations in the buffer value of herd milk. Journal of Dairy
M
342
an
339
Science, 14, 50-58
Whittier, E.O.(1929). Buffer intensities of milk and milk constituents.
345
action of casein in milk. Journal of Biological Chemistry, 83, 79-88
348 349 350 351 352 353 354 355 356 357 358 359
te
347
.The buffer
Yagil, R.(1982). Camels and camel milk. Animal Production and Health Paper FAO. Rome, No.26
Ac ce p
346
d
344
Zhang,H.,Yao,J.,Zhao,D(Zhao Dianbo)., Liu, H.,Li,J.and Guo,M. (2005).Changes in chemical composition of Alxa Bactrian camel milk during lactation. J. Dairy Sci, 88, 3402-3410
ZhaoDianBo.(2006). Studies on the Chemical Composition and Chemical-physical Properties of Alxa Bactrian Camels Milk in Inner Mongolia. Master’s Thesis. ETH No 101153, China
Table 1. Comparison of chemical composition and physiochemical properties between Alxa bactrian camel and bovine milk (mean values ±sd, ten camel milk mixed) Camel milk
Bovine milk
Page 13 of 18
Fat (%)
3.90±1.03
5.65 ± 0.12
Lactose (%)
4.17±0.24
4.24 ± 0.12
Total Solid (%)
11.09±0.42
14.31 ± 0.19
Ash (%)
0.79±0.04
0.87 ± 0.03
Acidity (%)
0.16±0.016
0.17±0.013 1.028±0.001 0.56±0.02 0.04±0.01 155±4.90 116±3.57
cr
Ca (㎎/100ml) P (㎎/100ml)
1.028±0.001 0.49±0.01
0.03±0.01 122±3.72 93±3.12
us
Density TN (g/100ml) NPN (g/100ml)
an
Data are means of triplicate determinations
M
360 361 362 363 364
3.15±0.08
3.55 ± 0.04
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Protein (%)
10
te
8
d
pH
12
Ac ce p
6 4 2
camel milk bovine milk
0
365 366 367 368 369
ml of titrant
Fig.1 Titration curves of camel and cow milk samples acidified from the initial pH to 2.0 with HCl and back titrated to pH 11.0 with NaOH(arrows indicate the direction of titration)
Page 14 of 18
pH
12 10
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8 6 camel milk
2
bovine milk
us
0
an
ml of titrant
370 371 372
Fig.2 Titration curves of camel and cow milk samples alkalized from the initial pH to 11.0 with NaOH and back titrated to pH 2.0 with HCl (arrows indicate the direction of titration)
M
373
Ac ce p
te
d
374 375
cr
4
Page 15 of 18
0.08 0.07
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acid titration
base titration
cr
0.05 0.04 0.03
us
dB/dpH(BI)
0.06
0.02
an
0.01 0 4
6
8
10
12
M
2
pH
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Fig.3 Buffering curves of camel milk samples acidified from the initial pH (6.6) to 2.0 with HCl and back titrated to pH 11.0 with NaOH
Ac ce p
377 378
d
376
0.05
acid titration base titration
dB/dpH(BI)
0.04
0.03
0.02
0.01 pH
0
379 380
2
4
6
8
10
12
Fig.4 Buffering curves of cow milk samples acidified from the initial pH (6.6) to 2.0
Page 16 of 18
381 382 383
with HCl and back titrated to pH 11.0 with NaOH
0.05
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0.04 0.03
cr
acid titration
0.02 0.01
us
dB/dpH(BI)
base titration
pH
0 4
6
12
Fig.5 Buffering curves of camel milk samples alkalized from the initial pH (6.6) to 11.0 with NaOH and back titrated to pH 2.0 with HCl
te
d
385 386
10
M
384
8
an
2
base titration acid titration
Ac ce p
0.05
dB/dpH(BI)
0.04 0.03 0.02 0.01
pH
0
387 388 389 390 391
2
4
6
8
10
12
Fig.6 Buffering curves of cow milk samples alkalized from the initial pH (6.6) to 11.0 with NaOH and back titrated to pH 2.0 with HCl (arrows indicate the direction of titration)
392
Page 17 of 18
Conflict of interest statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “The acid-base buffering properties of Alxa Bactrian camel milk”
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392 393 394 395 396 397
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S0921-4488(14)00304-6 http://dx.doi.org/doi:10.1016/j.smallrumres.2014.10.011 RUMIN 4812
To appear in:
Small Ruminant Research
Received date: Revised date: Accepted date:
26-5-2014 17-10-2014 26-10-2014
Please cite this article as: Zhao, D.-b., Bai, Y.-h.,The acid-base buffering properties of Alxa Bactrian camel milk, Small Ruminant Research (2014), http://dx.doi.org/10.1016/j.smallrumres.2014.10.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The buffering of milk influenced many of its physico-chemical properties, by
2
controlling pH during processing. There were many reports on the buffering of milk
3
and of cheese, calculated from titration curves. However, the titration curves obtained
4
depends on the methodology used, the forward and back titration curves of milk did
5
not coincide. The buffering properties of camel milk was investigated by the forward
6
and back titration. The results had shown that the forward and back titration curves
7
were not identical, the camel milk had stronger buffering capacity than that of bovine
8
milk.
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Page 1 of 18
The acid-base buffering properties of Alxa Bactrian camel milk
11
Dian-bo Zhao, Yan-hong Bai *
12 13
College of Food and Biological Engineering, Zhengzhou University of Light Industry, Dongfeng Road # 5 Zhengzhou, Henan, P.R,China
14
Abstract
ip t
10
The buffering properties of Alxa bactrian camel whole milk was investigated by
16
titrating with base or acid. A “loop” was observed in the pH range 6.6 to 4.3 when
17
sample was firstly titrated with acid and then back titrated with base. A “loop” was not
18
observed when sample was firstly titrated with base and then back titrated with acid.
19
When the milk sample was titrated from initial pH to 2.0 with HCl, camel milk
20
exhibited a pronounced maximum buffering at approximately pH4.4 and the value of
21
dB/dpH was about 0.073. When acidified camel milk sample was back titrated from
22
pH 2.0 to 11.0 with NaOH, there was low buffering index at approximately pH 4.9
23
(0.024), and maximum buffering index occurred at approximately pH 6.1(0.051). The
24
sample was firstly titrated from initial pH to 11.0 with NaOH, camel milk exhibited a
25
weaker buffering peak at approximately pH 7.1 and the value of dB/dpH was about
26
0.018, when the alkalized milk sample was back titrated from pH 11.0 to 2.0 with HCl,
27
the maximum buffering index occurred at approximately pH 5.1 and the value of
33
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15
34
Abbreviation Key: BI=buffering index, BC=buffering capacity, TN=total
35
nitrogen, NPN= non-protein nitrogen, WPN= whey protein nitrogen, CN= casein
36
nitrogen
37 38 39
Introduction
28 29 30 31 32
dB/dpH was about 0.047.
* Corresponding author. Present address: College of Food and Biological Engineering, Zhengzhou University of Light Industry, Dongfeng Road #5 Zhengzhou, Henan,450002, P.R,China; E-mail address：[email protected] Key words: Buffering Properties, Camel Milk, Alxa Bactrian Camel
Page 2 of 18
There are 3 fine breeds of Camelus bactrianus in China, namely Xinjiang, Alxa
41
bactrian and Sunite camel(Zhang et al,2005). Alxa camels can be further divided into
42
Gobi and Desert camels based on their stature, physical features, and breeding
43
distinctions. Alxa camels are reared mainly by natural grazing in different herd sizes
44
ranging from 10 to 100 camels with a grazing radius of 40 to 50 ㎞. Alxa camel
45
belong to low milk yield category, an Alxa camel can produce 0.25 to 1.5 kg of milk
46
daily in addition to the amount taken by the calf.
cr
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40
The chemical composition of camel milk was similar to that of cow
48
milk(Yagil,1982; Farah,1993). Camel milk can be used for making various dairy
49
products such as butter, shubat, cheese and milk tea. Camel milk not only supplies
50
nutrition for local people, but also has therapeutic properties. Considerable
51
information had been published concerning the variation of the chemical composition
52
of dromedary camel milk(Yagil,1982; Farah,1993; Mehaia et al,1995; Gorban and
53
Izzeldin,1997; Guliye et al, 2000; Zhang et al,2005; JiRiMuTU,2006), but little
54
knowledge was available concerning the buffering properties of camel milk. The
55
buffering properties of cow, goat and buffalo milks had been reported(Buchanan and
56
Peterson,1927; Whittier ,1929; Watson,1931; Ismail et al,1973; Park,1991; Lucey et
57
al,1993). Interest has been directed recently to the importance of the buffering value
59 60 61 62
an
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us
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of milk, particularly, in regard to certain processes in the manufacture of casein, cheese, condensed milk products and nutritional studies. The buffer capacity of a solution may be expressed as its power to resist change
in pH upon the addition or loss of acid or base (Ismail et al,1973). Buffering index was defined as the number of equivalents of acid or base required to shift the pH of 1
63
L of milk by one unit(Ismail et al,1973). The buffering index of a solution was not
64
constant and had an exact value only at a definite pH, and therefore the value
65
calculated over an observed pH range was an average one. In practise, a close
66
approximation was made if the buffering index was calculated for the mean pH over a
67
small pH interval(Watson,1931).
68
Objectives of this study were to characterize the buffering properties, report the
Page 3 of 18
69
BC, demonstrate that the forward and back titration curves are not identical in Alxa
70
bactrian camel milk.
72
Materials and methods
73
Preparation of animal milk samples
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71
Ten 5-year old Alxa bactrian female camels cloose to giving birth for the first time
75
were randomly selected from different herds that depended on natural grazing. The
76
camels, which all belonged to the Alxa nomads in Inner Mongolia, were kept under
77
muster management before giving birth and fed with hay supplemented with corn
78
after parturition. Sampling collection started following parturition at 90d post partum
79
（PP）. Representative sample was collected 500ml each camel, and the sample was
80
cooled in ice-water and stored at 4℃, for a period not exceeding 72 hours, ten
81
samples were warmed to 20℃ and mixed thoroughly until analyzed. The control cow
82
The bovine milks (Holstein, breed) as a control which were obtained from the Inner
83
Mongolia Agricultural University farm.
84
Physical parameters analysis
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Milk sample physical parameters were measured as follows: titratable
86
acidity(TA)and specific gravity were determined according to the method of
91
Ac ce p
85
92
nitrogen (NPN) fraction was calculated as follows: NPN = TN – CN – WPN. Milk
93
The casein nitrogen (CN) was determined according to the method of Rowland (1938)
94
with some modifications. Trichloroacetic acid (36%) was added into the whey to a
95
final concentration of 12% (v/v) to precipitate the whey proteins for determination of
96
whey protein nitrogen (WPN). Dry matter (DM) of the samples was determined
87 88 89 90
Association of Official Analytical Chemists (AOAC, 1990a). Chemical analysis
The mixed sample was analyzed and the data was determined by triplicates.
Nitrogen was determined by the Kjeldahl method. A nitrogen conversion factor of 6.38 was used for calculation of protein contents of milk samples. Non-protein
Page 4 of 18
gravimetrically after drying in a forced-draft oven at 105°C until a steady weight was
98
achieved. Fat percentage was determined according to the method of Rose-Gottlieb
99
and ash content was measured gravimetrically (Aggarawala and Sharma, 1961).
100
Lactose content was determined by the difference of DM minus other solid
101
components. Levels of Ca in the milk samples was determined with an atomic
102
absorption spectrophotometer (Hitachi U-2000, Japan) according to standard methods
103
in the AOAC (1980). Phosphorus content was determined spectrophotometrically
104
using the procedure of Watanabe and Olsen (1965).
105
Titration methods
Titrations were performed on 30ml mixed sample at 20℃ by a automatic titrator
107
（Model ZDJ-5, Lei-Ci Instruments, Shanghai, China）using 0.5N HCl or 0.5N
108
NaOH, added in 0.1ml increment at 30 sec intervals to allow for equilibrium while the
109
sample was stirred with an electrically driven agitator. Two different titration methods
110
were used in this experiment (Lucey et al,1993). In the first method involved the
111
sample was titrated from the initial pH6.6 to 2.0 with 0.5N HCl(was termed
112
acidification) and then back titrated to pH 11.0 with 0.5N NaOH(was termed
113
alkalinization).The second method involved
114
6.6 to 11.0 with NaOH (was termed alkalinization)and then back titrated to pH 2.0
115
120 121
Slyke,1922). Van Slyke revealed that the volume change due to the added acid or
122
alkali may be ordinarily neglected, if the maximum increase was below 50 per cent of
123
the original volume. Inasmuch as the volume changes which occurred in the present
124
work were below these limits, no correction for
125
in the formula. The buffering index for each 0.2 pH interval was calculated by the
116 117 118 119
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sample titration from the initial pH
with HCl(was termed acidification). Titration curve
From these data a titration curve was drawn by plotting the amount of alkali or
acid used, against the change in pH produced. Buffering curve
In this work Van Slyke's method of measuring buffering values was used(Van
them was
considered necessary
Page 5 of 18
128 129 130 131 132
dB (ml acid added) (normality factor) ＝ . dpH (volume of milk ) (pH change) A plot of buffering index against pH produced a buffer intensity (dB⁄dpH-pH)
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formula.
curve, the "peak" in the graph, was a characteristic of the kind of buffer. Results and discussion
Chemical composition
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126
The gross composition of camel milk and cow milk was showed in Table 1. The
134
titratable acidity was denoted in terms of lactic acid content (g/100g). The contents of
135
fat, protein, lactose, total solids, TN, NPN, P, Ca and ash in camel milk were higher
136
than that of in bovine milk. However, the values of acidity (%) and density were
137
similar with that of in bovine milk.
138
Titration curves for samples
The titration curves for camel and bovine raw milk samples had a similar shape
140
and were essentially superimposable. The typical curves had been shown in Fig.1 and
141
Fig.2. A “loop” was observed in the pH range 6.6 to 4.3 and 6.6 to 5.0 for camel and
142
bovine milk, when the titration were performed according to the first method (Fig.1).
143
Both milks exhibited a similar shape of the titration curves,
144 145 146 147 148 149
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133
were similar with that of
bovine milk had been published( Lucey et al, 1993). That means the titration curves samples did not coincide in the pH range 6.6 to 4.3 and 6.6 to 5.0 for camel and bovine milk samples, respectively. The “loop”
observed
was likelycontributed by
diversified buffering constituents in milk exerted buffering action, such as carbon dioxide, proteins, phosphate, citrate and a number of minor constituents, especially, the colloidal calcium phosphate(CCP) in different pH conditions was
solubilized or
154
precipitated. A “loop” was not observed in either or bovine milk when the titration were performed according to the second method (Fig.2), although they did not coincide, the curves had a similar shape. Buffering curves for samples titrated by using the first method
155
Milk was acidified from original pH 6.6 to 2.0, the typical buffering curves
156
were shown in Fig.3 and Fig.4. Both milks exhibited a pronounced maximum
150 151 152 153
Page 6 of 18
buffering index at approximately pH 4.4 and 5.1 for camel and bovine milk, and the
158
values of dB/dpH were about 0.073 and 0.042, respectively. Comparing with the
159
bovine milk, the buffering curve indicated that there was the other one buffering peak
160
at approximately pH 4.9 and the value of dB/dpH was about 0.052 in camel milk
161
(Fig.3 and Fig.4). The difference in buffering curves between the camel and the
162
bovine milk may be related to the casein and the structure of CCP in milk.
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Park(1991) and Whittier(1929) indicated that the buffer action of milk casein
164
was exerted principally between pH 4.5 to 5.7 with a maximum at approximately pH
165
5.2, in this range the casein was evidently one of the chief factors in the buffer action
166
of milk. The present study of bovine milk was similar with that had been published by
167
Park(1991) and Whittier(1929). Buchanan and Peterson(1927) illustrated that the
168
casein was precipitated in the range pH 4.5 to 5.0, usually at about pH 4.7. The camel
169
milk exhibited a pronounced maximum buffering at approximately pH 4.4, which it
170
was may be concluded that the casein of camel milk exerted very little influence
171
compared with that of bovine milk in the buffering action in this pH range. The
172
present study of camel milk was similar with that published by Buchanan and
173
Peterson(1927). The casein in camel milk was not one of the chief factors in the
174
buffering action of milk, possibly due to the difference of the size and the fractions of
176 177 178 179
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casein in camel milk compared with that of in cow milk. The casein micelle was the backbone of the colloidal milk system, and
determined milk stability. Zhao (2006) revealed that the size of casein micellares in Alxa bactrian camel milk was larger than that of cow milk. From a few available literatures on camel casein micelles it can be concluded that camel milk casein
180
significantly broader than that of bovine milk in terms of micellar size distribution,
181
and showed a great number of large particles and the average diameter of casein was
182
320 nm, and the average diameter of camel casein micelles was more two times than
183
that of bovine milk (Zhao, 2006; Sawaya et al, 1984; Larsson-Raznikiewicz and
184
Mohamed, 1986; Farah and Ruegg, 1989; Farah, 1993).
185
Zhang et al (2005) revealed that there
were no protein bands homologous to
Page 7 of 18
186
bovine κ-casein
clearly detected in Alxa bactrian camel milk. Farah and
187
Farah-Riesen (1985) demonstrated that there were no protein bands homologous to
188
bovine κ-casein
189
reported that there was
190
milk(Larbaa breed), whereas there was very low
191
Targui breed. Authors reported that there was a low amount of κ-casein( only about 5
192
percent in camel casein), compared with about 13.6 percent in bovine casein (Jardali
193
and Ramet, 1991 and Farah, 1993). Therefore, it
194
absence or very low content of κ-casein in Alxa bactrian camel milk compared with
195
that of bovine milk.
clearly detected in dromedary camel milk. Naima Alim et al（2005）
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absence of κ-casein in Algerian dromedary camel milk of
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content of κ-casein in
an
us
might be concluded that there was
196
The structure of CCP may be solubilized on acidification, especialy below pH
197
5.6, the solubilization of CCP resulted in the formation of phosphate ions which
198
combined with H+,
199
structure of CCP in bovine milk may be completely solubilized at pH 5.1 and
200
resulting in the maximum buffering, while the structure of CCP in camel milk may be
201
completely solubilized at pH 4.4 and resulting in the maximum buffering. It would be
202
concluded that the structure of CCP in camel milk was different from the bovine milk.
204 205 206 207 208 209
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about buffering action (Dalgleish & Law,1989). The
The buffering curves of either camel or bovine milks indicated the same
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brought
tendency for the change in the milk buffering index at different pH. Below the initial pH in both milk the buffering index increased very sharply till the maximum index at approximately pH4.4 in camel and 5.1 in bovine, thereafter the buffering index dropped very sharply from the maximum buffering index. The buffering index gradually increased from the initial pH to 4.9, and then the buffering index decreased from pH 4.9 to 4.7, thereafter the index increased to the maximum in camel milk at
210
approximately pH4.4. Comparing with the camel milk, the buffering index in bovine
211
milk gradually increased from the initial pH to 5.1 in bovine milk.
212
The present study revealed when samples were titrated from initial pH to 2.0 the
213
volume of acid added were 8.8 and 6.8ml for camel and cow milk, respectively, which
214
indicated that the camel milk had stronger buffering capacity than that of bovine milk.
Page 8 of 18
Figure 3 and 4 shown that the maximum buffering index of camel milk(0.073) was
216
higher than that of bovine milk(0.042), and higher than that of buffalo and cow milk
217
reported by Ismail et al (1973). Ismail et al(1973)reported that the height of the peak
218
is proportional to the concentration of the buffer constituents. Park(1991) revealed
219
that the greater resistance to pH change was related to the higher content of total N,
220
NPN and P2O5. Salaün et al (2005) indicated that the buffering capacity was
221
increased by increasing the level of Ca in milk. The level of TN, NPN, Ca and P in
222
camel milk were found to be higher than that in bovine milk (Table 1). It was thought,
223
therefore, that the higher level of TN, NPN, Ca and P in camel milk resulting in the
224
stronger buffering capacity than that of bovine milk, and the concentration of the
225
buffering constituents within camel milk was higher than that of bovine milk.
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This fact
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could be significant in human nutrition because the camel milk
having the strong buffering properties can be utilized therapeutically in treatment of
228
gastric stomach ulcers. In fact, the camel milk was successfully used in the treatment
229
of peptic ulcers in Russia(Sukhov et al,1986) because of the higher buffering capacity
230
than that of bovine milk.
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Camel milk was acidified from initial pH to 2.0, the the maximum buffering
232
index at approximately pH 4.4(0.073), and the other one buffering peak at
233 234 235 236 237
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231
approximately pH 4.9(0.052). The acidfied camel milk was back titrated with NaOH from pH 2.0 to 6.6, the value of the buffering index was about 0.034 at approximately pH 4.4, the minimum buffering index at approximately pH 4.9(0.024), and the maximum buffering index occurred at approximately pH 6.1(0.051)( Fig.3). Bovine milk was acidified from initial pH to 2.0, the the maximum buffering index at
238
approximately pH 5.1(0.042), the acidfied milk was back titrated from pH 2.0 to 6.6
239
the minimum buffering index occurred at approximately pH 5.1(0.019) and the
240
maximum buffering index occurred at approximately pH 6.3(0.031) ( Fig.4). Which
241
was different from the camel milk Fig.3 and Fig.4). This may be due to buffering by
242
higher content of glutamic acid residues(pK4.6) and citrate(pK4.1) in camel milk. In
243
addition to, it might be related to the difference in physicochemical specificity and
Page 9 of 18
244
stereochemical configuration of buffering protein molecules in the two milks. The
245
reason that resulting in the buffering index was not low at approximately pH 4.4 in
246
camel milk would be need of further study. The maximum buffering index occurred at
247
approximately pH 6.1 and pH 6.3 in camel and bovine milk, which can be explained
248
by
249
can combine with OH-, and increased the buffering capacity as suggested by lucey et
250
al(1993). The buffering curves of either camel or bovine milks indicated the same
251
tendency for the change in the milk buffering index at different pH, the buffering
252
index was low at pH 8.1～9.3, but gradually increased thereafter.
us
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the formation of Ca3(PO4)2 with the release of H+ from HPO42- and H2PO4- which
It was concluded, therefore, that the proportion to buffering constituents, and the
254
buffering system, stereochemical configuration of buffering protein molecules in
255
camel milk was different from the bovine milk, which resulted in the difference in the
256
titration curves between the camel and the bovine milk.
257
Buffering curves for samples titrated by using the second method
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an
253
It was shown that camel milk exhibited a weaker buffering peak at
259
approximately pH 7.1 and the value of dB/dpH was about 0.018, when the milk
260
sample was titrated from original pH to 11.0 with NaOH (Fig.5), however, the
261
buffering peak was not observed in cow milk(Fig.6). In addition to, when alkalized
263 264 265 266
te
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262
d
258
samples
were back titrated, the buffering curves of either camel or bovine milks
indicated the same tendency for the change in the milk buffering index at different pH, the buffering index were observed gradually decreasing from the value of pH 11.0 to 9.0,
and at pH values below 9.0 the buffering index were observed increasing
gradually thereafter (Fig.5 and Fig.6).
Maxima were observed
occurring at
267
approximately pH 5.1(0.047) and pH 5.4(0.032) for camel and bovine milk, when
268
alkalized milk samples were back titrated from pH 11.0 to 2.0 with HCl.
269 270 271 272
Conclusions The results of
this study indicated that the Alxa bactrian camel milk had
stronger buffering capacity than that of bovine milk. It was observed that there were
Page 10 of 18
two buffering peaks at approximately pH 4.4 and 4.9, and the value of dB/dpH was
274
about 0.073 and 0.052, respectively, when the camel milk was acidified from original
275
pH 6.6 to 2.0. When the camel milk was acidified from initial pH to 2.0 and then back
276
titrated from pH 2.0 to initial, the maximum and the minimum buffering index did not
277
occurred at the same pH. There was one buffering peak was obviously observed at
278
approximately pH 7.1, and the value of dB/dpH was about 0.018, when the camel
279
milk was alkalized from original pH 6.6 to 11.0. The results of the present study
280
demonstrated that any investigation of the buffering properties of camel milk should
281
include a back titration step as the buffering curve during acidification was very
282
different to that during the back titration with base.
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283
Refference
285
Aggarawala, A. C., and R. M. Sharma. (1961). A Laboratory Manual of Milk
Analytical Chemists, Washington, DC.
289
AOAC, (1990a). Acidity of milk (Titrimetric method). In: Official Methods of
290
Ac ce p
288
AOAC.(1980). Official Methods of Analysis. 13th ed. Association of Official
d
287
Inspection. 4th ed. Asia Publishing House, Bombay, India.
te
286
M
284
291 292 293 294 295 296 297 298 299 300
Analysis, No. 947.05. Association of Official Analytical Chemists Inc. Virginia, USA.
Buchanan, J.H., & Peterson, E.E. (1927). Buffer of milk and buffer value. Journal of Dairy Science, 10, 224-231
Dalgleish, D.G., Law, A.J.R.(1989). pH-induced dissociation of bovine casein micelles. Ⅱ. Mineral solubilization and its relation to casein release. Journal of Dairy Research, 56, 727-735 Farah, Z. and Farah-Riesen, M.(1985). Separation and characterization of major components of camel milk casein. Milchwissenschaft, 40, 669-671 Farah, Z. & Ruegg, M.W.(1989). The size distribution of casein micelles in camel milk. Food Microstructure, 8, 211-212.
Page 11 of 18
302 303 304 305 306
Farah,Z.(1993).Composition and characteristics of camel milk. J. Dairy Res, 60, 603-626 Gorban, A.M.S., and Izzeldin,O.M.(1997). Mineral content of camel milk and colostrum. J. Dairy Res, 64, 471-474
ip t
301
Guliye,A.Y.,Yagil,R. and Hovell,F.D.D.(2000). Milk composition of Bedouin camels under semi-nomadic production system. J. Camel Pract. Res, 7, 209-212
Ismail, A.A., Eldeeb,S.A., & Eldifrawi, E.A. (1973). The buffering properties of cow
308
and buffalo milks. Zeit-schr. Lebensm.-Unters. Und-Forschung , 152, 25-31
309
Jardali, Z. & Ramet, J. P. (1991). Composition et taille des micelles du lait de
us
dromedaire. Le lait
an
310
cr
307
JiRiMuTU.(2006). Studies on Molecular Evolution of Domestic and Wild Bactrian
312
and the Physical-chemical Properties of Camel Milk. Diss.ETH No 219208,China
313
Larsson-Raznikiewicz, M. & Mohamed, M.A.(1986). Analysis of the casein content
316
Lucey,J.A., Hauth,B., Gorry,C., & Fox, P. F.(1993). The acid-base buffering properties
d
315
in camel (Camelus dromedarius milk. Swedish J. Agric. Res, 16,13-18.
of milk . Milchwissenschaft, 48(5), 268-272
te
314
M
311
Mehaia, M.A., Hablas, M.A., Abdel-Rahman, K.M. and El-Mougy, S.A.(1995). Milk
318
composition of Majaheim, Wadah and Hamra camels in Saudi-Arabia. Food
319 320 321 322 323
Ac ce p
317
Chemistry, 52, 115-122
Naima Alim, Fabio Fondrini, Ivan Bonizzi, Maria Feligini and Giuseppe Enne.(2005). Characterization of Casein Fractions from Algerian Dromedary(Camelus dromedarius) Milk. Pakistan Journal of Nutrition, 4(2), 112-116
Park,Y.W.(1991). Relative buffering capacity of goat milk, cow milk, soy-based infant
324
formula and commercial nonprescription antacid drugs. Journal of Dairy Science,
325
74, 3326-3333
326 327 328 329
Rowland, S. J. (1938). The determination of the nitrogen distribution in milk. J. Dairy Res. 9:42-46. Sawaya, W.N., Kalil, J.K., Al-Shalhat, A. & Al-Mohamed, H. (1984). Chemical composition and nutritional quality of camel milk. J. Food Sci, 49, 744-747
Page 12 of 18
330
Sukhov,S.V.,kalamkarova,L.I.,Il’chenko,L.A.&Zhangabylov,A.K.(1986). Changes in
331
the microflora of the small and large intestine in patients with chronic enteritis
332
after dietary treatment with cultured milk products. Voprosy Pitaniya, 4, 14-17
334 335
Salaün,F., Mietton, B., Gaucheron,F. (2005). Buffering capacity of dairy products. International Dairy Journal,15, 95-109
ip t
333
Van Slyke,D.D. (1922). On the measurement of buffer values and on
the
relationship of buffer value to the dissociation constant of the
buffer and the
337
concentration and reaction of the buffer. Journal of Biological Chemistry, 52,
338
525-571
us
cr
336
Watanabe, F. S., and Olson，S. R. (1965). Test of an ascorbic acid method for
340
determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc.
341
Am. Proc. 29:677–678.
343
Watson, P.D.(1931). Variations in the buffer value of herd milk. Journal of Dairy
M
342
an
339
Science, 14, 50-58
Whittier, E.O.(1929). Buffer intensities of milk and milk constituents.
345
action of casein in milk. Journal of Biological Chemistry, 83, 79-88
348 349 350 351 352 353 354 355 356 357 358 359
te
347
.The buffer
Yagil, R.(1982). Camels and camel milk. Animal Production and Health Paper FAO. Rome, No.26
Ac ce p
346
d
344
Zhang,H.,Yao,J.,Zhao,D(Zhao Dianbo)., Liu, H.,Li,J.and Guo,M. (2005).Changes in chemical composition of Alxa Bactrian camel milk during lactation. J. Dairy Sci, 88, 3402-3410
ZhaoDianBo.(2006). Studies on the Chemical Composition and Chemical-physical Properties of Alxa Bactrian Camels Milk in Inner Mongolia. Master’s Thesis. ETH No 101153, China
Table 1. Comparison of chemical composition and physiochemical properties between Alxa bactrian camel and bovine milk (mean values ±sd, ten camel milk mixed) Camel milk
Bovine milk
Page 13 of 18
Fat (%)
3.90±1.03
5.65 ± 0.12
Lactose (%)
4.17±0.24
4.24 ± 0.12
Total Solid (%)
11.09±0.42
14.31 ± 0.19
Ash (%)
0.79±0.04
0.87 ± 0.03
Acidity (%)
0.16±0.016
0.17±0.013 1.028±0.001 0.56±0.02 0.04±0.01 155±4.90 116±3.57
cr
Ca (㎎/100ml) P (㎎/100ml)
1.028±0.001 0.49±0.01
0.03±0.01 122±3.72 93±3.12
us
Density TN (g/100ml) NPN (g/100ml)
an
Data are means of triplicate determinations
M
360 361 362 363 364
3.15±0.08
3.55 ± 0.04
ip t
Protein (%)
10
te
8
d
pH
12
Ac ce p
6 4 2
camel milk bovine milk
0
365 366 367 368 369
ml of titrant
Fig.1 Titration curves of camel and cow milk samples acidified from the initial pH to 2.0 with HCl and back titrated to pH 11.0 with NaOH(arrows indicate the direction of titration)
Page 14 of 18
pH
12 10
ip t
8 6 camel milk
2
bovine milk
us
0
an
ml of titrant
370 371 372
Fig.2 Titration curves of camel and cow milk samples alkalized from the initial pH to 11.0 with NaOH and back titrated to pH 2.0 with HCl (arrows indicate the direction of titration)
M
373
Ac ce p
te
d
374 375
cr
4
Page 15 of 18
0.08 0.07
ip t
acid titration
base titration
cr
0.05 0.04 0.03
us
dB/dpH(BI)
0.06
0.02
an
0.01 0 4
6
8
10
12
M
2
pH
te
Fig.3 Buffering curves of camel milk samples acidified from the initial pH (6.6) to 2.0 with HCl and back titrated to pH 11.0 with NaOH
Ac ce p
377 378
d
376
0.05
acid titration base titration
dB/dpH(BI)
0.04
0.03
0.02
0.01 pH
0
379 380
2
4
6
8
10
12
Fig.4 Buffering curves of cow milk samples acidified from the initial pH (6.6) to 2.0
Page 16 of 18
381 382 383
with HCl and back titrated to pH 11.0 with NaOH
0.05
ip t
0.04 0.03
cr
acid titration
0.02 0.01
us
dB/dpH(BI)
base titration
pH
0 4
6
12
Fig.5 Buffering curves of camel milk samples alkalized from the initial pH (6.6) to 11.0 with NaOH and back titrated to pH 2.0 with HCl
te
d
385 386
10
M
384
8
an
2
base titration acid titration
Ac ce p
0.05
dB/dpH(BI)
0.04 0.03 0.02 0.01
pH
0
387 388 389 390 391
2
4
6
8
10
12
Fig.6 Buffering curves of cow milk samples alkalized from the initial pH (6.6) to 11.0 with NaOH and back titrated to pH 2.0 with HCl (arrows indicate the direction of titration)
392
Page 17 of 18
Conflict of interest statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “The acid-base buffering properties of Alxa Bactrian camel milk”
ip t
392 393 394 395 396 397
Ac ce p
te
d
M
an
us
cr
398
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