Some Chemical Properties of Alum Used in Foods

MARDIRes. J.20(1) 1992: 105-108

ShortConun.

Somechemical properties of alum usedin foods (Beberapasifat kimia tawas yang digunakan dalam makanan)

B. T. Lim*

Key words: chemicalproperties, alum

Abstrak Dua puluh con[oh tawas yang digunakan dalam makanan telah diperoleh dan dianalisis secarakualitatif dan kuantitatif. Semua contoh tawas didapati mudah larut di dalam air dan asid hidroklorik (l7o), sederhanalarut di dalam natrium hidroksida (lVo), dan tidak larut di dalam etznol (957o\. Larutan tawas (57o b/i) bersifat asid (pH 3.0-3.2). Apabila dibandingkan dengan tawas potash yang tulen, semua contoh tawas tidak menunjukkan perbezaan yang ketara (p > 0.05) dalam kandungan aluminium, kalium dan sulfat serta kekurangan berat selepas dikeringkan. Keputusan ini menunjukkan bahawa semua contoh tawas ialah aluminium kalium sulfat dodekahidrat atau tawas potash dan mempunyai ketulenan sekurang-kurangnya 97Vo.

Abstract Twenty samples of alum used in food were collected and analysed qualitatively and quantitatively. All the alum sampleswere readily soluble in both water and l7o hydrochloric acid, sparingly soluble in 19osodium hydroxide and insoluble in 957o ethanol. The aqueoussolution (5V") of alum was acidic (pH 3.0-3.2). All the alum samples, when compared with pure potash alum, showed no significant difference (p > 0.05) in the contents of aluminium, potassium and sulphate, and weight loss on drying. Results showed that all the alum samples were aluminium potassium sulphate dodecahydrateor potash alum, and that their prrity was at least9T%.

Introduction Aluminium compoundsare usedin food Alum is the commonname given to the as buffering, neutralizingor firming agents. doublesulphate salt of aluminiumand The acidicsalts iue commonlyused as ammoniumor potassiumor sodium. Alum leaveningacids while the alkaline saltsare is popularin rural regionsas a water usedin cheesemanufactue. Certain clarifyingagent. In water,aluminium aluminiumcompounds are used in the compoundsform an insoluble hydroxide preparationof self-raisingflours, prepared floc that readily absorbssediments of cloudy food mixesand frozenbread doughs (Anon. waterand precipitatesfrom the solution. 1972a;Ellinger 1972). Aluminium

*Food Technology ResearchCentrc, MARDI, P.O. Box 1230L,50774 Kuala llmprr, Malaysia Author's full name: Lim Bon Tang OMalaysian Agricultural Researchand Development Institute 1992

105 Chemical p,ropenies of alum

out accordingo the standardprocedures ammoniumsulphate, aluminium potassium describedby Svehla(1979). sulphateand aluminiumsodium sulphate are The solubility of the samplesin water, listedas multiple-purposeGRAS (generally l7o sodiumhydroxide, l% hydrochloricacid regardedas safe) food substancesunder the and95voethanol were determined by U.S. Codeof FederalRegulations (Anon. dissolvingknown weightsat room 1985a).In Malaysiaat the time of writing, temperature. thesethree aluminium compounds are not The pH of 5Vo(wlv) aqueoussolutions permitted for food use. of alum weredetermined with an Orion The type of alum availablelocally is ResearchpH meter(Model 501). Standard calledtawas.It is easilyavailable in the buffer solutionsof pH 7.0 and4.0 wereused sundryshops, especially the traditional for calibration. Chinesemedicine shops. It is colourless, The weightloss on drying was odourlesswith a sweetish,astringent taste determinedby drying the sampleat 240 f and is availablein large,hard ransparent for 6 h in a muffle furnance. cystals. t-ocally availablealum is a popular Aluminium wasdetermined by direct firming agentfor the pickling of fruits precipiradonas the aluminium8- (Yeoh et al. 1990)and vegetables.It is also hydroxyquinolate,using 8-hydroxyquinoline a popularleavening acid for makingChinese and ammoniumacetate (Furman 1975). The you-tiao(deep-fried twisted dough sticks). determinationof potassiumwas done using The amountof alum usedin you-tiaomay a Varisn Techtronatomic absorption be as high as 2-37oof the formulation, spectrophotometerModel 175at wavelength basedon 1007oflour (He et al. 1987). 769.9nm. Potassiumchloride was usedas Accordingto a comprehensivesurvey of the standard(Williams 1979). Sulphatewas the U.S. food industry(Anon. 1972b), determinedby usinga gravimetricmethod aluminiumammonium sulphate is usedin basedon the insolubilityof bariumsulphate meatproducts, condiments, relishes and salt (Williams1979). substitutes;aluminium potassium sulphate in The assayfor potashalum reconstitutedvegetable proteins, dairy laluminium potassiumsulphate dodecahydrate, productanalogues, condiments, relishes and AIK(SOr2.l2lIr0 wascarried out by salt substitutes;whereas aluminium sodium I mixing a solutionof the samplewith 0.05 M sulphateis usedin bakedgoods, baking disodiumEDTA, followedby tination with mixesand reconstituted vegetable proteins. 0.05M zinc sulphate(Anon. 1978). Theaim of this studyis to determine The experimentwas a completely the chemicalidentity of the locally available randomdesign with unequalreplications alum usedin food, so that a better (Steeland Tonie 1980). The testused to understandingof its usesand functionin comparethe meanswas a t-testwith unequal food canbe obtained. numbersof observationsand pooled variance,with ttreformula given a^s: Materialsand methods Samplesof alum (20) usedfor food were t = (Xr-\) *{1 + (s2+4)l collectedrandomly from the shops in the 1s2*20) northern,ffNtern, central and southernstates wheres2 is ttrepooled variance, and i, and of PeninsularMalaysia. The sampleswere Xrare the samplemeans of alum samples groundinto powderusing an /r(A micromill usedfor food and that of pure laboratory and storedin air-tight containersuntil potashalum. analysis. detectionof cationsand Qualitative Resultsand discussion anions(K, Na, NH4.Al, SOo werecanied ) Aluminium,potassium and sulphateions

106 B. T. Lim weredetected in all the alum samples, quality, with a purity of at least97Vo pcttash whereasboth sodiumand ammoniumions alum(Table 2). Theoretically,by calculation werenot detected.The alum samples usingthe atomicweights, pure aluminium collectedfrom different shopswere potassiumsulphate dodecahydrate has a thereforeof the similar type. The samples molecularweight of 474.38,and contains werefound to be readilysoluble (10 g/100 5.687oaluminium,8.24% potassium, mL) in both waterud lVo hydrochloric 40.47Vosulphate and 45.53Vo water. It can acid, sparinglysoluble (2 gl{U|.^mL) in l%o be concludedthat the locally availablealum sodiumhydroxide, and insolublein95Vo samplesused in food arealuminium etlranol. The pH of 5Vo(wlv) aqueous potassiumsulphate dodecahydrate, solutionsof alum rangedfrom 3.0 to 3.2. commonlycalled potash alum. Thesecharacteristics of alum samplesare Studieson humanshave shown that similar to that of aluminiumpotassium aluminiumwhen absorbed is readily sulphate(Anon. 1978). excretedby the normalkidney. However, Therewas no significantdifference personswith kidney diseasemay be at risk (p > 0.05) in the contentof aluminium, if they consumeexcessive amounts of potassium,sulphate, and weight loss on aluminiumsalts, as an elevatedserum drying of alum sampleswhen compared aluminiumlevel canbe oxic owing to the with tlroseof purepotash alum (Table I and interferencein phosphorusmetabolism Table2). The alumsamples were of high (Anon.1975). Even though alum is used

Table l. Aluminium, potassium and sulphate contents of alum used in foods and that ofpure potash alum

Sample Content(7o)

Aluminium Potassium Sulphate Alum 5.66at 0.01 7.80bt 0.02 40.33ct 0.12 (n = 20) Potashalum 5.64af 0.01 7.83b t 0.04 40.32ct 0.17 (n=4) t-value 1.24 0.80 0.07 df 22 22 22 n = number of samples Values in each column with the same letters are not signihcantly different (p > 0.05)

Table 2. l,oss of weight on drying and the purity assayof alum used in foods and that of potash alum

Sample Weight loss (%) Potash alum (7o) Alum 44.68at 0.06 97.87i 0.04 (n = 20) Potashalum M.50at 0.12 (n=4) t-value 1.39 df 22 Values in each column with the same letters are not significantly different (p > 0.05)

107 Chemical propenies of alum widely as an ingredientin variousfood additives (FAO Food and Nutrition Paper No. products,at the time of writing it hasnot 7). Rome: FAO - beenlisted as a permittedfood conditioner (1985a). Mulriple purposeGRAS food substances.lnCodes of Fedcral Reguluions. in the MalaysianFood Regulations 1985 Title 21 CFR. Ch. I (4-l-85 ed.), sections (Anon. 1985b)or Food(Amendment) 182.11n, n2.1129 and l82l13l, p. 384. Regulations1988 (Anon. 1988). However, WashingtonD.C: FDA the Minisry of Healthis currentlyin the - (1985b). Permined food conditioner processof reviewingthe statusof potash (Regulation25). In Food Regulations 1985 alum for food use. Kuala Lumpur: Ministry of Health, Malaysia - (1988). Fd 161rnn7r*nr) Regulations 1988. Kuala Lumpur: Ministry of Health, Malaysia Acknowledgements Ellinger, R. H. (1972). Phosphatein food The authorwishes to thankMs Patimah processing. ln Handbook of fod additives Hasimand Mr ChanSwe Thong for 2nd ed. (Furia" T. E. ed.). Cleveland : CRC cirrying out the chemicalanalysis. The Press authoris alsograteful to Ms Chia Joo Suan Furman,N. H. (1975). Standardmethods of chemical analysis. Vol. 1, 6th d., p. 52. in for assistance carryingout the New York : Robert E. Krieger Publishing Co. experiment. Inc. He, H., Shen,X. and Ponte,Jr. J. G. (1987). Study References of Chineseyou tiao. 1. Relationshipof Anon. (1972a). Aluminium ammonium sulfate; leaveningagents to frying temperature, aluminium potassiumsulfat; aluminium resting time, and qualiry of the producr sodium sulfate; aluminium sulfate; sodium Cereal Foods World. 32(5): 379-83 aluminium phosphate,acidic; sodium Steel,R. G. D. and Torrie, J. H. (1980). Principles aluminium phosphate,basic. In Foad and proceduresof statistics- a biometrical chemical codet2nd ed., p. 34--40 and-122-5. approach. 2nd ed., p. 13147. New York: WashingtonD.C.: NationalAcademy of McGraw-Hill Sciences Svehla,G. (1919). Vogel's texlbookof macro and -(1912b). A comprehensivesumey of industry semimicro qual itative inor gonic analysis. 5th on thc use offood chemicals generally ed. New York: Longman Inc. recognisedas safe. WashingtonD.C: Williams, W. J. (1979). Handbook of anion National Academy of Sciences determination, p.531. l,ondon: Butterworth - (1975). Evaluation of the health aspectsof & Co Ltd. aluminiwn conpounds asfood ingredients Yeoh, Q. L., Osman,N. and AMul Rahman,A. O. WashingtonD.C.: FDA Departmentof (7990). Industrial processing offruit picHes Health, Educationand Welfare. (in BahasaMalaysia). Scrial guide No. ll. - (1978).Aluminium potassiumsulphate. In 2nd ed. Serdang:MARDI Specificationsfor identity and purity : food colours, enzytncpreparations and other food

Accepedfor publication on 12 Septemberl99l

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