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Comparison of buffering components in goat and cow milk
Small Ruminant Research, 8 (1992) 75-81 Elsevier Science Publishers B.V., Amsterdam
75
Comparison of buffering components in goat and cow milk Y.W. Park Cooperative Agricultural Research Center, Prairie View A&M University, The Texas A&M University System, P.O. Box U, Prairie View, Texas 77446-2886, USA (Accepted 22 July 1991 )
ABSTRACT Park, Y.W., 1992. Comparison of buffering components in goat and cow milk. Small Rumin. Res., 8: 75-81. Levels of total nitrogen (TN), crude protein (CP), nonprotein nitrogen (NPN) and phosphate (P2Os) in morning and afternoon milk of goats (Alpine vs. Nubian ) and cows (Holstein vs. Jersey) were determined. Mean concentrations (g/100 ml) of TN, NPN and P205 for Alpine, Nubian, Holstein and Jersey milk were: 0.389, 0.048, 0.166; 0.556, 0.061, 0.212; 0.392, 0.033, 0.173; 0.505, 0.038, 0.211, respectively. Results confirmed that buffering capacity (BC) of milks were directly related to contents of major buffering components. Nubian milk exhibited the highest, followed by Jersey among the milks tested for BC. The high ac value of Nubian goat milk may be of great importance in human nutrition.
INTRODUCTION
Goat milk is similar to cow milk in basic composition. On average, cow milk of all breeds combined at mid-lactation contains about 12.2% total solids, 3.2% protein, 3.6% fat, 4.7% lactose and 0.7% minerals, whereas goat milk of all European-type or European-imported breeds at mid-lactation contains about 12.1% total solids, 3.4% protein, 3.8% fat, 4.1% lactose and 0.8% mineral (Haenlein and Caccese, 1984). Cow and goat milks are slightly on the acidic side with a pH range of 6.46.7. High buffering capacity (BC) of goat milk appears to be useful for treatment of gastric ulcers (Walker, 1965; Haenlein and Caccese, 1984). Buffering intensity of milk is a function of its acid-base equilibrium, and is especially related to the casein, protein and phosphate components (Watson, 1931 ). It has been reported that cow milk has a higher BC than human milk over the pH range in digestion (Gamble et al., 1939; Parkash and Jenness, 1968 ). Buffering capacity is generally known as the ability of a solution to resist change in pH through the addition or loss of alkali or acid. The mathemati0921-4488/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
76
v.w. PARK
cally expressed buffering index (dB/dpH) by Van Slyke (1922) is the first derivative of the function expressed by the corresponding titration curve, and is the change in normality of acid or base necessary to produce a change of hydrogen ion concentration of one pH unit in a zone centered on a given pH value (Whittier, 1929). Although the high BC of goat milk has been reported, literature concerning differences in BE between goat and cow milk in relation to chemical entities, especially between species and between breeds within a species is very limited. The objectives of this study were: ( 1 ) to determine total N, crude protein (CP), nonprotein-N (NPN) and phosphate (P205) as major chemical entities affecting BE in goat and cow milk, and (2) to evaluate relationships between levels of the buffering components and strengths of BE in milk of two breeds of goats and cows. MATERIALS A N D M E T H O D S
Experimental animals Second year freshened, lactating goats, five each of Alpines, Nubians, and five Holstein cows were randomly selected from the milking goat and cow herds of the International Dairy Goat Research Center, Prairie View A&M University, TX. An additional five milking Jersey cows were randomly selected from Waller County, TX, due to their absence from the University herds.
Collection of milk samples Goat and cow milk samples were taken from separate milking parlors. All animals in the University herds were machine milked (BOU-MATIC, DEC International, Madison, WI) at 05:30 and 15:30 for 5 d. Goat and cow bulk milk were taken from separate bulk tanks located at different parlors for the same period of sampling. Milk samples were collected into 59-ml plastic bags (Whirl-PAK, Fort Atkinson, WI), transported to the laboratory at room temperature, and then pH was examined immediately. Jersey cow milk samples were collected the same way at similar milking times from five animals for 5 d at a local dairy farm of Waller County, TX, and tested for pH the same way as the other samples. Samples were refrigerated during transportation to laboratory, then warmed to room temperature before measuring pH by gradual titration.
Chemical analysis of milk constituents Chemical constituents of milk samples were assayed for total N, NPN, total CP and P205. Milk samples were wet digested in 30-ml Kjeldahl flasks, and concentration of total N and P205 were determined by colorimetric method as described by Belec and Jenness ( 1962 ).
BUFFERING COMPONENTS IN GOAT AND COW MILK
77
NPN was determined after precipitation of the protein fraction from the milk samples by 10% trichloroacetic acid. After centrifugation, an aliquot ( 1 ml of supernatant) was decanted into the Kjeldahl flask, digested and the amount of NPN was determined by the same procedure as performed for the total N.
Evaluation of buffering capacity The initial pHs of all samples were determined before any titration as reference controls. Two normalities of hydrochloric acid (0.1 and 0.5 ) were prepared for titration of all treatment samples. An aliquot of milk (25 ml) was placed in a 50-ml beaker, and 1 ml of the acid was titrated with thorough stirring. Only data from 0.5 N acid titrations were reported in this study due to insufficient responses with 0.1 N acid as titrant. The pH was recorded after completion of each titration and buffering capacity was mathematically determined with the buffering intensity formula of Van Slyke ( 1922 ): dB/dpH =
(ml acid added) (normality of acid) (volume of milk) (pH change)
Statistical analysis All data for changes in milk pH were analyzed by analysis of variance, mean difference among species, breeds, milking time, normality of acid, and interactions between the parameters as described by Steel and Torrie (1960). Differences in concentration of components and their relations with ac were evaluated by the same procedure. Statistics of unbalanced data were analyzed by the General Linear Model of the SAS ( 1982 ) Program. RESULTS AND DISCUSSION
Mean contents of the major buffering constituents of the four milk types are in Table 1. Nubian goat milk contained the highest and significantly ( P < 0.01 ) greater levels of total N and CP among all four breeds tested. Nubian milk also had significantly ( P < 0.01 ) higher NPN than Alpine, Holstein and Jersey milks. However, there were no differences in the levels of phosphate among the four milks. Nubian milk had higher N and phosphate contents than Alpine, while similar relationships were observed between the two cow milks with Jersey milk being higher in N and P205 than Holstein milk. The difference in total N contents between breeds was significant ( P < 0.01 ), while those between pooled data of species was non-significant (Table 2). Effects of breed within species in total N contents were significant ( P < 0.01 ) for both goat and cow milks (Table 2). There was no significant difference in the levels of phosphates among milks of the four breeds. However, it was observed that some Jersey milk samples, depending upon individual cow, sam-
78
Y.W. PARK
TABLE 1 Concentrations (g/100 ml) of mean total N, total crude protein (CP), nonprotein N ( N P N ) , and phosphate (P205) of goat and cow milk Milk
Goat milk ~ Alpine Nubian Cow milk 2 Holstein Jersey
Total N
Total CP
P205
NPN
Mean
SE
Mean
SE
Mean
SE
Mean
SE
0.389 c 0.556 a
0.014 0.006
2.49 ¢ 3.55 a
0.081 0.070
0.048 b 0.061 a
0.003 0.006
0.166 a 0.212 ~
0.010 0.007
0.392 ¢ 0.505 b
0.026 0.019
2.50 ¢ 3.22 b
0.166 0.113
0.033 ¢ 0.038 ¢
0.009 0.002
0.173 a 0.211 a
0.011 0.059
~'2Numbers of observations for each breed were 25. CP=6.38×N SE: Standard error of the mean a.b,C,dMean with different superscript within the same column are significantly different ( P < 0.01 ). TABLE 2 Analysis of variance (F values) for the effects of species, breed and breed/species on the levels of total N, NPN and P205 Source
Species Breed Breed/species (Goat) Breed/species
df
F Values Total N
NPN
P20~
1 3 1
2.74 6.60** 7.80**
39.84** 22.54** 9.26**
0.11 1.07 3,95
1
7.35**
1.24
0.98
(Cow) *Significant at 5% level. **Significant at 1% level.
piing time and stage of lactation, had closer levels of total N and P 2 0 5 to Nubian goat milk. Haenlein and Caccese (1984) noted percentage of protein in goat and cow milk averages 3.0, but there are differences due to breeds, lactation, diet, milking time and stage of lactation. Levels of N P N in goat and cow milks in this study agreed with those of Haenlein and Caccese (1984), Parkash and Jenness ( 1968 ) and Jenness (1980), where goat milk contained more N P N than cow milk. Buffering capacities of the goat and cow milks are shown as buffering index values (Table 3) and patterns of pH changes (Fig. 1 ). Initial pH of Jersey milk was slightly higher than of the other milks. At the addition of I ml 0.5 N
79
BUFFERING COMPONENTS IN GOAT AND COW MILK 7 [] Alpine o Nubien o Holstein
~ ' ~
6
5
-r
tn 4
3
0
1
2
3
4
5
Volume Acid Added in ml (0.5 NHCI) Fig. 1. C o m p a r i s o n o f p H changes a n d buffering capacities o f goat milk with those o f cow milk for the gradual a d d i t i o n o f 0.5 N HCI. D a t a represent m e a n values o f 5 a n i m a l s per b r e e d for 5 d. Differences in p H between milks at each t i t r a t i o n especially b e y o n d 2 ml were significant ( P < 0.05 or 0.01 ). TABLE 3 Effect of gradual addition of 0.5 N HCI on buffering index values ( d B / d p H ) of goat and cow milk Milk group
Goat milk Alpine Nubian COW milk Holstein Jersey
d B / d p H value after addition of 0.5 N HC1
1 ml
2 ml
3 ml
4 ml
5 ml
0.02439 b 0.03030 a
0.02899 c 0.03704 a
0.02666 c 0.04072 a
0.02247c 0 -03226a
0.02469c 0"02500b
0.02944 ab 0.02128 c
0.02666 d 0.03333 b
0-02469 d 0.02857 b
0-02222~ 0.02817 b
0-02597b 0.02857 a
a,b,C,dmeans with different superscript within a column are significantly different ( P < 0.01 ).
HCI, pH of all milks dropped significantly, but differences in pH between milks for the initial titration were not as great as the subsequent titrations. The pH of Alpine milk was lowest and significantly ( P < 0.01 ) lower than in the other milks for all titrations (Fig. 1 ), which is supported by the concentrations of chemical components (Table 1 ). Alpine milk contained the lowest levels of total N and phosphate. In contrast, Nubian milk maintained the greatest and significantly ( P < 0.01 ) higher pH than the other three milks for the entire titration treatments (Fig. 1 ). This higher buffering capacity of Nubian milk is undoubtedly
80
Y.W. PARK
related to the highest levels of total N, nonprotein N and phosphate (Table 1 ). The higher Bc of Nubian goat milk in this study agrees with previous reports (Walker, 1965; Haenlein and Caccese, 1984), and the greater Bc of Nubian goat milk may be important and significant in h u m a n nutrition. This result may support the idea that goat milk can be utilized in treatment of gastric ulcers (Walker, 1965 ). Moreover, the value of goat milk as an alternative food for children and sick people due to its higher digestibility extends also to feeding animals, young dogs, calves and foals (Haenlein and Caccese, 1984). Jersey milk showed the 2nd highest pH, which was significantly ( P < 0.01 ) greater than in Alpine and Holstein milks, which is also supported by the differences in levels of its buffering components (Table 1 ). However, the buffering intensity value ( d B / d p H ) for Jersey milk at the 5 ml titration was greater than the Nubian milk (Table 3), which may be associated with the high phosphate content of the Jersey milk. Data in Table 3 and Fig. 1 also suggest that not all breeds of goat are superior to their cow counterparts in milk Bc. Jersey and Holstein milk had significantly ( P < 0.01 ) greater a c than Alpine. These data indicate that breed differences play an important role in the ac of a specific milk in question. The order of strength of a c for up to 4 ml of 0.5 N HC1 addition was maintained in Nubian, Jersey, Holstein and Alpine milk, indicating that the acs were influenced by breeds and species of milk. ACKNOWLEDGEMENTS The author appreciates H.I. Chukwu, T.L. Gilchrist and R. Attaie for their laboratory assistance, and Sherlynn Perrow for typing the manuscript.
REFERENCES Belec, J. and Jenness, R., 1962. Dephosphorization of casein by heat treatment in caseinate solutions. J. Dairy Sci., 45: 12-19. Gamble, J.A., Ellis, N.R. and Besley,A.K., 1939. Composition and properties of goat's milk as compared with cow's milk. U.S. Dept. Agric.Tech. Bull. 671. pp. 1-72. Haenlein, G.F.W., and Caccese,R., 1984. Goat milk versus cow milk. In: G.F.W. Haenlein and D.L. Ace (Editors), Extension Goat Handbook. Washington,D.C., pp. 1-3. Jenness, R., 1980. Composition and characteristics of goat milk: Review 1968-1979. J. Dairy Sci., 63: 1605-1630. Parkash, S. and Jenness, R., 1968. The composition and characteristics of goat's milk. A Review. Dairy Sci. Abst., 30: 67. SAS, 1982. SAS User's Guide. Statistics, 1982 edn. SAS Institute Inc., Cary, N.C. Steel, R.B.P. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill Co. Inc., New York, N.Y., pp. 99-128. Van Slyke,D.D., 1922. On the measurement of buffer values and on the relationship of buffer
BUFFERING COMPONENTS IN GOAT AND COW MILK
81
value to the dissociation constant of the buffer and the concentration and reaction of the buffer solution. J. Biol. Chem., 52: 525-570. Walker, V.B., 1965. Therapeutic uses of goat's milk in modern medicine. Brit. Goat Soc. Yearbook, 24-26. Watson, P.D., 1931. Variations in the buffer value of herd milk. J. Dairy Sci., 14: 50-58. Whittier, E.O., 1929. Buffer intensities of milk and milk constituents. I. The buffer action of casein in milk. J. Biol. Chem., 83: 79-88.
75
Comparison of buffering components in goat and cow milk Y.W. Park Cooperative Agricultural Research Center, Prairie View A&M University, The Texas A&M University System, P.O. Box U, Prairie View, Texas 77446-2886, USA (Accepted 22 July 1991 )
ABSTRACT Park, Y.W., 1992. Comparison of buffering components in goat and cow milk. Small Rumin. Res., 8: 75-81. Levels of total nitrogen (TN), crude protein (CP), nonprotein nitrogen (NPN) and phosphate (P2Os) in morning and afternoon milk of goats (Alpine vs. Nubian ) and cows (Holstein vs. Jersey) were determined. Mean concentrations (g/100 ml) of TN, NPN and P205 for Alpine, Nubian, Holstein and Jersey milk were: 0.389, 0.048, 0.166; 0.556, 0.061, 0.212; 0.392, 0.033, 0.173; 0.505, 0.038, 0.211, respectively. Results confirmed that buffering capacity (BC) of milks were directly related to contents of major buffering components. Nubian milk exhibited the highest, followed by Jersey among the milks tested for BC. The high ac value of Nubian goat milk may be of great importance in human nutrition.
INTRODUCTION
Goat milk is similar to cow milk in basic composition. On average, cow milk of all breeds combined at mid-lactation contains about 12.2% total solids, 3.2% protein, 3.6% fat, 4.7% lactose and 0.7% minerals, whereas goat milk of all European-type or European-imported breeds at mid-lactation contains about 12.1% total solids, 3.4% protein, 3.8% fat, 4.1% lactose and 0.8% mineral (Haenlein and Caccese, 1984). Cow and goat milks are slightly on the acidic side with a pH range of 6.46.7. High buffering capacity (BC) of goat milk appears to be useful for treatment of gastric ulcers (Walker, 1965; Haenlein and Caccese, 1984). Buffering intensity of milk is a function of its acid-base equilibrium, and is especially related to the casein, protein and phosphate components (Watson, 1931 ). It has been reported that cow milk has a higher BC than human milk over the pH range in digestion (Gamble et al., 1939; Parkash and Jenness, 1968 ). Buffering capacity is generally known as the ability of a solution to resist change in pH through the addition or loss of alkali or acid. The mathemati0921-4488/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
76
v.w. PARK
cally expressed buffering index (dB/dpH) by Van Slyke (1922) is the first derivative of the function expressed by the corresponding titration curve, and is the change in normality of acid or base necessary to produce a change of hydrogen ion concentration of one pH unit in a zone centered on a given pH value (Whittier, 1929). Although the high BC of goat milk has been reported, literature concerning differences in BE between goat and cow milk in relation to chemical entities, especially between species and between breeds within a species is very limited. The objectives of this study were: ( 1 ) to determine total N, crude protein (CP), nonprotein-N (NPN) and phosphate (P205) as major chemical entities affecting BE in goat and cow milk, and (2) to evaluate relationships between levels of the buffering components and strengths of BE in milk of two breeds of goats and cows. MATERIALS A N D M E T H O D S
Experimental animals Second year freshened, lactating goats, five each of Alpines, Nubians, and five Holstein cows were randomly selected from the milking goat and cow herds of the International Dairy Goat Research Center, Prairie View A&M University, TX. An additional five milking Jersey cows were randomly selected from Waller County, TX, due to their absence from the University herds.
Collection of milk samples Goat and cow milk samples were taken from separate milking parlors. All animals in the University herds were machine milked (BOU-MATIC, DEC International, Madison, WI) at 05:30 and 15:30 for 5 d. Goat and cow bulk milk were taken from separate bulk tanks located at different parlors for the same period of sampling. Milk samples were collected into 59-ml plastic bags (Whirl-PAK, Fort Atkinson, WI), transported to the laboratory at room temperature, and then pH was examined immediately. Jersey cow milk samples were collected the same way at similar milking times from five animals for 5 d at a local dairy farm of Waller County, TX, and tested for pH the same way as the other samples. Samples were refrigerated during transportation to laboratory, then warmed to room temperature before measuring pH by gradual titration.
Chemical analysis of milk constituents Chemical constituents of milk samples were assayed for total N, NPN, total CP and P205. Milk samples were wet digested in 30-ml Kjeldahl flasks, and concentration of total N and P205 were determined by colorimetric method as described by Belec and Jenness ( 1962 ).
BUFFERING COMPONENTS IN GOAT AND COW MILK
77
NPN was determined after precipitation of the protein fraction from the milk samples by 10% trichloroacetic acid. After centrifugation, an aliquot ( 1 ml of supernatant) was decanted into the Kjeldahl flask, digested and the amount of NPN was determined by the same procedure as performed for the total N.
Evaluation of buffering capacity The initial pHs of all samples were determined before any titration as reference controls. Two normalities of hydrochloric acid (0.1 and 0.5 ) were prepared for titration of all treatment samples. An aliquot of milk (25 ml) was placed in a 50-ml beaker, and 1 ml of the acid was titrated with thorough stirring. Only data from 0.5 N acid titrations were reported in this study due to insufficient responses with 0.1 N acid as titrant. The pH was recorded after completion of each titration and buffering capacity was mathematically determined with the buffering intensity formula of Van Slyke ( 1922 ): dB/dpH =
(ml acid added) (normality of acid) (volume of milk) (pH change)
Statistical analysis All data for changes in milk pH were analyzed by analysis of variance, mean difference among species, breeds, milking time, normality of acid, and interactions between the parameters as described by Steel and Torrie (1960). Differences in concentration of components and their relations with ac were evaluated by the same procedure. Statistics of unbalanced data were analyzed by the General Linear Model of the SAS ( 1982 ) Program. RESULTS AND DISCUSSION
Mean contents of the major buffering constituents of the four milk types are in Table 1. Nubian goat milk contained the highest and significantly ( P < 0.01 ) greater levels of total N and CP among all four breeds tested. Nubian milk also had significantly ( P < 0.01 ) higher NPN than Alpine, Holstein and Jersey milks. However, there were no differences in the levels of phosphate among the four milks. Nubian milk had higher N and phosphate contents than Alpine, while similar relationships were observed between the two cow milks with Jersey milk being higher in N and P205 than Holstein milk. The difference in total N contents between breeds was significant ( P < 0.01 ), while those between pooled data of species was non-significant (Table 2). Effects of breed within species in total N contents were significant ( P < 0.01 ) for both goat and cow milks (Table 2). There was no significant difference in the levels of phosphates among milks of the four breeds. However, it was observed that some Jersey milk samples, depending upon individual cow, sam-
78
Y.W. PARK
TABLE 1 Concentrations (g/100 ml) of mean total N, total crude protein (CP), nonprotein N ( N P N ) , and phosphate (P205) of goat and cow milk Milk
Goat milk ~ Alpine Nubian Cow milk 2 Holstein Jersey
Total N
Total CP
P205
NPN
Mean
SE
Mean
SE
Mean
SE
Mean
SE
0.389 c 0.556 a
0.014 0.006
2.49 ¢ 3.55 a
0.081 0.070
0.048 b 0.061 a
0.003 0.006
0.166 a 0.212 ~
0.010 0.007
0.392 ¢ 0.505 b
0.026 0.019
2.50 ¢ 3.22 b
0.166 0.113
0.033 ¢ 0.038 ¢
0.009 0.002
0.173 a 0.211 a
0.011 0.059
~'2Numbers of observations for each breed were 25. CP=6.38×N SE: Standard error of the mean a.b,C,dMean with different superscript within the same column are significantly different ( P < 0.01 ). TABLE 2 Analysis of variance (F values) for the effects of species, breed and breed/species on the levels of total N, NPN and P205 Source
Species Breed Breed/species (Goat) Breed/species
df
F Values Total N
NPN
P20~
1 3 1
2.74 6.60** 7.80**
39.84** 22.54** 9.26**
0.11 1.07 3,95
1
7.35**
1.24
0.98
(Cow) *Significant at 5% level. **Significant at 1% level.
piing time and stage of lactation, had closer levels of total N and P 2 0 5 to Nubian goat milk. Haenlein and Caccese (1984) noted percentage of protein in goat and cow milk averages 3.0, but there are differences due to breeds, lactation, diet, milking time and stage of lactation. Levels of N P N in goat and cow milks in this study agreed with those of Haenlein and Caccese (1984), Parkash and Jenness ( 1968 ) and Jenness (1980), where goat milk contained more N P N than cow milk. Buffering capacities of the goat and cow milks are shown as buffering index values (Table 3) and patterns of pH changes (Fig. 1 ). Initial pH of Jersey milk was slightly higher than of the other milks. At the addition of I ml 0.5 N
79
BUFFERING COMPONENTS IN GOAT AND COW MILK 7 [] Alpine o Nubien o Holstein
~ ' ~
6
5
-r
tn 4
3
0
1
2
3
4
5
Volume Acid Added in ml (0.5 NHCI) Fig. 1. C o m p a r i s o n o f p H changes a n d buffering capacities o f goat milk with those o f cow milk for the gradual a d d i t i o n o f 0.5 N HCI. D a t a represent m e a n values o f 5 a n i m a l s per b r e e d for 5 d. Differences in p H between milks at each t i t r a t i o n especially b e y o n d 2 ml were significant ( P < 0.05 or 0.01 ). TABLE 3 Effect of gradual addition of 0.5 N HCI on buffering index values ( d B / d p H ) of goat and cow milk Milk group
Goat milk Alpine Nubian COW milk Holstein Jersey
d B / d p H value after addition of 0.5 N HC1
1 ml
2 ml
3 ml
4 ml
5 ml
0.02439 b 0.03030 a
0.02899 c 0.03704 a
0.02666 c 0.04072 a
0.02247c 0 -03226a
0.02469c 0"02500b
0.02944 ab 0.02128 c
0.02666 d 0.03333 b
0-02469 d 0.02857 b
0-02222~ 0.02817 b
0-02597b 0.02857 a
a,b,C,dmeans with different superscript within a column are significantly different ( P < 0.01 ).
HCI, pH of all milks dropped significantly, but differences in pH between milks for the initial titration were not as great as the subsequent titrations. The pH of Alpine milk was lowest and significantly ( P < 0.01 ) lower than in the other milks for all titrations (Fig. 1 ), which is supported by the concentrations of chemical components (Table 1 ). Alpine milk contained the lowest levels of total N and phosphate. In contrast, Nubian milk maintained the greatest and significantly ( P < 0.01 ) higher pH than the other three milks for the entire titration treatments (Fig. 1 ). This higher buffering capacity of Nubian milk is undoubtedly
80
Y.W. PARK
related to the highest levels of total N, nonprotein N and phosphate (Table 1 ). The higher Bc of Nubian goat milk in this study agrees with previous reports (Walker, 1965; Haenlein and Caccese, 1984), and the greater Bc of Nubian goat milk may be important and significant in h u m a n nutrition. This result may support the idea that goat milk can be utilized in treatment of gastric ulcers (Walker, 1965 ). Moreover, the value of goat milk as an alternative food for children and sick people due to its higher digestibility extends also to feeding animals, young dogs, calves and foals (Haenlein and Caccese, 1984). Jersey milk showed the 2nd highest pH, which was significantly ( P < 0.01 ) greater than in Alpine and Holstein milks, which is also supported by the differences in levels of its buffering components (Table 1 ). However, the buffering intensity value ( d B / d p H ) for Jersey milk at the 5 ml titration was greater than the Nubian milk (Table 3), which may be associated with the high phosphate content of the Jersey milk. Data in Table 3 and Fig. 1 also suggest that not all breeds of goat are superior to their cow counterparts in milk Bc. Jersey and Holstein milk had significantly ( P < 0.01 ) greater a c than Alpine. These data indicate that breed differences play an important role in the ac of a specific milk in question. The order of strength of a c for up to 4 ml of 0.5 N HC1 addition was maintained in Nubian, Jersey, Holstein and Alpine milk, indicating that the acs were influenced by breeds and species of milk. ACKNOWLEDGEMENTS The author appreciates H.I. Chukwu, T.L. Gilchrist and R. Attaie for their laboratory assistance, and Sherlynn Perrow for typing the manuscript.
REFERENCES Belec, J. and Jenness, R., 1962. Dephosphorization of casein by heat treatment in caseinate solutions. J. Dairy Sci., 45: 12-19. Gamble, J.A., Ellis, N.R. and Besley,A.K., 1939. Composition and properties of goat's milk as compared with cow's milk. U.S. Dept. Agric.Tech. Bull. 671. pp. 1-72. Haenlein, G.F.W., and Caccese,R., 1984. Goat milk versus cow milk. In: G.F.W. Haenlein and D.L. Ace (Editors), Extension Goat Handbook. Washington,D.C., pp. 1-3. Jenness, R., 1980. Composition and characteristics of goat milk: Review 1968-1979. J. Dairy Sci., 63: 1605-1630. Parkash, S. and Jenness, R., 1968. The composition and characteristics of goat's milk. A Review. Dairy Sci. Abst., 30: 67. SAS, 1982. SAS User's Guide. Statistics, 1982 edn. SAS Institute Inc., Cary, N.C. Steel, R.B.P. and Torrie, J.H., 1960. Principles and Procedures of Statistics. McGraw-Hill Co. Inc., New York, N.Y., pp. 99-128. Van Slyke,D.D., 1922. On the measurement of buffer values and on the relationship of buffer
BUFFERING COMPONENTS IN GOAT AND COW MILK
81
value to the dissociation constant of the buffer and the concentration and reaction of the buffer solution. J. Biol. Chem., 52: 525-570. Walker, V.B., 1965. Therapeutic uses of goat's milk in modern medicine. Brit. Goat Soc. Yearbook, 24-26. Watson, P.D., 1931. Variations in the buffer value of herd milk. J. Dairy Sci., 14: 50-58. Whittier, E.O., 1929. Buffer intensities of milk and milk constituents. I. The buffer action of casein in milk. J. Biol. Chem., 83: 79-88.