relative buffering capacity of goat milk, cow milk, soy-based infant formulas, and commercial...

8/14/2019 Relative Buffering Capacity of Goat Milk, Cow Milk, Soy-Based Infant Formulas, and Commercial Nonprescription Antacid Drugs'92 is 0022030291785202

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BUFFERING CAPACITY OF GOAT MILK 3327MATERIALS AND METHODS

Experimental DesignTwo experiments were conducted to com-pare BC of natural goat and cow milks withsoy-based infant formulas and commerciallyavailable nonprescription antacid drugs.In Experiment 1, in a completely random-ized block design, five Alpine and five Nubiangoats and five Holstein cows in their 2nd yrlactation were selected randomly from themilking goat and cow herds of the Intema-tional Dairy Goat Research Center. Due toabsence of Jersey breed in the university herds,the milking Jersey cows were selected ran-domly from a local dairy farm located at

Waller County,TX. he milks from individualanimals of two goat breeds, two cow breeds,and two brands of soy-based infant formulaswere used for testing buffering intensities withgradual addition of .1 and .5N HCl to eachIn Experiment 2, BC of goat and cow milkswere compared with those of nonprescriptionantacid drugs. Goat and cow milks were takenfrom the bulk milk t a n k s located at two sepa-rate milking parlors once a day at 1530 h for 5d.Three brands of antacid drugs were pur-

chased from local pharmacies. The BC ofdrugs alone and drug plus goat and cow milkswere compared for the differences in bufferingintensities. Treatment groups for each drugwithin Experiment 2 were composed of goatbulk millc, cow bulk milk. drug alone (blank),drug plus goat milk, and drug plus cow milk.

milk group.

Preparatlon of Animal MilkSamplesAll animals were machine milked (BOU-MATIC, DEC International, Madison, WI),and samples were taken from a graduated mea-suring cylinder attached to individual milkingunits. Thus, a representative sample was col-

lected during each complete milking. Milksampling of goats and cows was done twicedaily at 0530 and 1530 h for 5 d Bulk milksamples were also taken at the same times.Milk samples were collected into 2-oz (59-ml)plastic bags (Whirl-Pak, NASCO. Fort Atkin-son,WI) and transported to the laboratory forimmediate examination. Initial pH conditions

were recorded prior to consecutive titrationswith .1 or .5N HC1.Preparation of Samples for Soy-BasedInfant Formulas and NonprescrlptlonAntacld Drugs

Two brands of soy-based infant formulaswere purchased from a local retail grocerystore. Both formulas were canned, ready tofeed products. After shaking, an aliquot (25ml) was transferred into a 50-ml beaker foreach testing.Three brands of commercially availablenonprescription antacid drugs were obtainedfrom the over the counter shelves of a localretail outlet or pharmacy. One tablet of eachbrand was solubilized either in 100 ml ofdeionized water or dissolved directly into thesame volume of goat or cow bulk milks con-tained within a 125-ml screwcap glass bottle.Aliquots (25 ml) of the dissolved water or milksolutions were used for testing pH.Chemical Analysis of BufferlngComponents in the Mllks

Concentrations of total N, total CP, NPN,and P205 for all m i l k samples were analyzedas the major buffering chemical constituents.Samples (10 g) were wet digested in 30-mlKjeldahl flasks, and total N, NPN, and P2O5were determined by colorimetric procedures asdescribed by Belec and Jenness (2) and AOAC(1). For NPN determination, protein fractionwas precipitated with 10% trichloroacetic acid,followed by centrifugation at 700 x g for 10min at 4'C. One milliliter of resultant superna-tant was decanted and transferred into a Kjel-dahl flask for digestion. An amount of N wasdetermined for this NPN fraction.Determlnatlon of BufferlngCapacity

Initial pH values of all milk samples ofindividual goat and cow, soy-based infant for-mulas, and antacid drug solutions were deter-mined. Two normalities of hydrochloric acid(.l and .5N) were prepared for titration of allsamples. Two aliquots (25 ml) of each samplewere placed in 50-ml beakers, whereupon 1 mlof either acid was titrated slowly with thor-ough stirring. However, only experimental datafrom .5N acid titration were reported in t i s

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3328 PARKstudy because of insufficient responses with.1N cid as titrant. The pH was measured aftercompletion of each titration, and the BC wasdetermined mathematically using the bufferingintensity formula given by Van Slyke 21):

(ml acid added) normality of acid)(volume of mi l k) (pH change .Statlstlcai Analysis

All data for the differences and changes inpH of milk and drug treatment groups wereanalyzed by analysis of variance 20).Modelincluded species, breeds, milk groups, antaciddrugs, milking time, normality of acid, andtheir interactions. Unbalanced data were ana-lyzed using the general linear models of theSAS program 19).Significance of differencesin mean BC and levels of chemical constitu-ents between milk treatment groups were ana-lyzed also by multiple mean comparison usingF values of orthogonal contrasts betweengroup means.

RESULTS AND DISCUSSIONConcentrations of total N, N,and P2O5

in goat milk, cow milk, and commercial soy-based infant formulas are shown in Table 1.Among the six milks, Nubian goat milk con-tained the highest concentration of each of thethree major buffering chemical entities. Soy-based infant formulas had lower total N andNPN compared with natural goat and cowmilks. No differences in phosphate contentswere found among the six milks.Significance of F values for orthogonalcon-trast between differentmilk groups in terms ofthe levels of chemical constituents (Table 2)revealed highly significant (P e .01)differ-ences in total N and NPN between naturalmilks and formula milks. Orthogonal contrastof goat and cow milk revealed no differencesin total N and PzO5. but a significant(P .01)difference was observed in NFW content. Noneof the contrasts between milks for PzO5 con-tent was significant, but ll combinations be-tween species and breeds in total N and NPNlevels were significant (P< .05 or P < .01)except in the case of Alpine versus Holsteinfor total N and Holstein versus Jersey for NPN

content. The differences in total N and NFcontents between the two brands of infant for-mula were not significant (Table 2).

Comparisons of BC and pH changes amongthe six milks upon titration with .5NHC1 arepresented in Tables 2 and 3 and Figure 1. Thegreater resistance to pH change for Nubian andJersey m i l k (Table 3) was related to the highercontents of total N, NPN, and P2O5 in thesemilks (Table 1). Others 9, 21,24 25) havereported that BC is correlated highly with thecontent of these buffering components.Nubian milk showed consistently greaterpH values (P e .01)han the other five milksfor ll titration volumes (Table 3). This higherBC of Nubian milk undoubtedly is attributableto ts higher total N, NPN, and phosphateconcentrations. The stronger BC of Nubiangoat milk is in agreement with previous reports(8, 22). This fact may be significant in humannutrition because foods having higher BC canbe utilized therapeutically in treatment of gas-tric stomach ulcers (8).Depending upon milking time, stage of lac-tation, and individual animals tested data notpresented), no differences in total N and phos-phate contents existed between Nubian andJersey milks. However, levels of NPN in Nu-bian milk were consistently greater than thosein Jersey m i l k (Table 1).Jersey milk in a few cases showed strongerresistance to pH changes than Nubian milk.Differences in physicochemical specificity andstereochemical configuration of buffering pro-tein molecules within the two milks mightresult in their differential exposure to H+ ion inthe titration medium. In addition to molecularspecificity of protein, processing factors suchas pasteurization and homogenization mightinfluence BC of the milks. For example, ap-proximately one-half of a major buffering enti-ty, C02, contained in commercial unpasteu-rized milk is lost by heating, agitation, orvacuum treatment (1). All m i l k s evaluated inthis study were not pasteurized or homoge-nized.

Acid secretion of stomach depends largelyon the amounts of food protein or amino acidpresent 13,16)as well as the specific proteinsource 12) because proteins differ in theirability to stimulate gastric secretion. This ef-fect is related directly to the BC of the specific

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3330 PARK

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Figure 1. Buffering capacities of natural goat and cow miIks compared with those of soy-based infant formulas.Number of observations for Alpine, Nubian, Holstein, Jersey, and brand A and B formula milks were 2 5 , 2 5 , 2 5 , 2 5 . 5 ,and 5.

values (dB/dpH) among the six milks (Figure1). The difference among the natural goat andcow milks then became minimal at the timationof 5 ml of the HCl. The buffering index valuesof Nubian m lk were consistently superior tothose of Alpine. The similar relationship ob-served between Jersey and Holstein milk indi-cated that breed differences in BC existedwithin both species (Tables 2 and 3; Figure 1).

The buffering index values of the infantformulas were lower (P 01) than the naturalmilks up to pH near 2.4 (Figure 1). Althoughthe BC indices of the formula m i l k s weresubstantially higher than those for goat andcow milks beyond 4-ml volume of titrant, theformula m i l k s did not have higher BC thannatural milks. Rather, the high buffering indexvalues less than pH 2.4 were due to excessivedissociated free acid. Van Slyke 21) demon-Journal of Dairy Science Vol. 74. No. 10, 1991

strated that, at the more acid and alkalineranges, the partial buffering index values be-come highly significant solely because of dis-sociated i5ee acid and alkali, respectively.This, in turn suggests that the high bufferingindices may not represent strong BC of thetesting solution if it has excess dissociated freeacid or alkali. On addition of 23 ml of HC1,brand A formula had a significantly (P < .01)lower pH than the brand B formula and thenatural milks (Table 3).

When three commercial antacid drugs weresolubilized in the double deionized water, theinitial pH of each drug was significantly (P


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BUFFERING CAPACITY OF GOAT MILK 3331TABLE 3. Comparison of pH changes in diffmnt group milks by gradual addition of .5N HCl to 25-ml samples.

pH after addition of .5N HClMilk p u p n1 Initial l m l 2 m l 3 m l 4 m l 5 m lGoat milkAlpine 25 6.53 5.71b 5.02b 4.27 3.38' 2.57Nubm 25 6.48 5.82b 5.28' 4.79' 4.17' 3.37'cow milkHolstein 25 6.58 5 w 5Mab 4.34' 3.44= 2. 67Jersey 25 6.80 5.86b 5.26' 4.56b 3.85b 3.UbBrand A 5 6.62 4 . w 3 .4 9 2.2v 1.76' 134'Brand B 5 6.68 4.85' 3.87 3.14d 2.28d 186d

~*C*~MXULS with different superscripts wth n the same column are significantly different (P < .01).'Numbex of samples tested for milk pH changes using .5N HCI as titrant.

soy infant formula

justed for the outlying data points. Drug Acontained dihydroxyaluminum sodium carbon-ate, but drugs B and C were made of calciumcarbonate and aluminum magnesium hydrox-ide. Drug A had significantly higher initial pHthan drugs B and C.The alkaline pH of theinitial drug solutions were reduced drasticallyat the first titration with 1 ml .5NHCI (Table4; Figure 2). The abruptly changing patternsfor dBIdpH values, which characterized thethree drug-alone groups, were due to the dras-

tic changes in pH that occurred upon subse-quent titrations (Figure 2). Drug B showed thegreatest pH and buffering intensity values asthe sample solutions were titrated gradually(Table 4). The initial pH of the drugs plus milksamples of drugs A and B were close to the pHvalues of initial goat or cow m i l k alone. ThepH was neutral when drug C and the milkswere combined. This phenomenon indicatedthat goat and cow m i l k had sufficient BC toneutralize the excessive alkaline buffering

TABLE 4. Rofiies of pH changes after addition of HCl to 25-ml antacid drug solutions, drugs plus milks, and goat andcow bulk milk p p s .pH after addition of .5N HClTreatmentm u u l n Confro1 1 ml 2 m l 3 m l 4 m l 5 m l

5 9.22' 4 . d 4.04d 2.4p 2.04' 1.87fM H2QA+Goat m i l k 5 6.61' 5.84b 5.30b 4.7LlbC 4 .W 3. 27DrugA

A Cow milk 5 6.8gd 6.22' 5.39b 4.54' 3.65d 3 . wd

B +Goa t m i l k 5 6.52f 5.81b 5.34b 4.95b 4.67' 4.45'

B M H20) 5 8 . d 2.45= 2 .0s 1 85f 1.73f 1.66fC Goat milk 5 7. e 6.12 5.61' 5.04' 4.21b 3.53'c + c o w m i l k 5 7.09' 6.27 5.63' 4 S b C 4.08' 3 . e

BB M H2Q 5 8.49b 5.61' 5.14' 4.94b 4.5Ea 2.35'B Cow milk 5 6.7@ 6.14' 5.52' 4.80bC 4.3gb 4.ab

Drug c

Goat bulk milk 5 6.4 18 5.84b 5.l@ 4.49c 3.61d 2.82dcow bulk milk 5 6.Sf s.93b 5 . 2 9 4.39d 3.5od 2.86d.05).hydroxide.

qbic7qe*fpyIeans wth different superscript wthin the same column are significantly different (P < .01 or P eb u g A, ~ihydroxyalumirmm od ium carbonate; drug B, calcium cartmate; drug C, l umnummagnesium

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BUFFERING CAPACITY OF GOAT MILK 3333a c e to indicate that the buffer action of caseinis exerted primarily between pH 4.5 and 5.7with a maximum at approximately pH 5.2.Casein is evidently one of the primary factorsin the buffer action of milk in this range.Comparison of goat and cow bulk milkswith the respective milks plus d r u g s indicatedthat the latter had significantly (P< .05 or P

relative buffering capacity of goat milk, cow milk, soy-based infant formulas, and commercial...

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