Trace Minerals in Cottage Cheese N. P. WONG, D. E. LaCROIX, and J. H. VESTAL Nutrition Institute Agricultural Research Service United States Department of Agriculture Beltsville, MD 20705
ABSTRACT The trace minerals, iron, zinc, copper, and manganese were determined in cottage cheese curd by flameless atomic absorption. Larger curd size, added calcium chloride, and fewer washes increased the iron and zinc content in the curd. We recently reported on the major mineral constituents of cottage cheese and the manufacturing variables that affect the retention of minerals in curd (8). We now report the trace mineral content of cottage cheese and the effects of those same variables. Cottage cheese was prepared as in (8), and made from nonfortified skim milk pasteurized at 71.5 C for 15 s. Five percent starter and rennet at 1 ml per 453.6 kg of milk were added, and the milk was set at 32.2 C. When the pH reached 4.8, the curd was cut with .64 cm cheese knives. The curd was cooked to 60.0 C in 2 h, allowed to stand for 15 min, and then drained of approximately 80% of the whey. The curd then was washed three times with 4 C water. This procedure was altered as follows to produce experimental lots: (a) calcium chloride was added at .01 and .1% to the skim milk prior to pasteurization, (b) the curd was cut with 1.28 cm knives instead of .64 cm knives, (c) the whey was drained completely, and the curd was washed once or twice with a volume of water equal to the amount of whey drained. During the cheese making operation samples were taken of (a) the milk after addition of the starter, (b) drained whey, (c) each wash water, and (d) the drained curd. Representative samples were analyzed for total solids and pH. The same samples were analyzed for minerals in the following manner: weighed samples were dried overnight at 125 C, charred on a burner, and then ashed in a muffle at 460 C. This temperature was necessary to avoid losses of low-boiling
Received March 7, 1977. 1977 J Dairy Sci 60:1650-1652
elements, specifically zinc. The sample was heated in a mixture of HC1-HNO3 to insure complete ashing and solubilization and was taken up in distilled demineralized water. The trace minerals, iron, zinc, copper, and manganese, were determined by flameless atomic absorption with a Heath Model 703 Spectrophotometer which had been modified with a collimating lens system so that it would be compatible with the Varian Model 63 Carbon Rod Atomizer. Details of the modification and experimental parameters for trace mineral analysis were in (6). Special precautions were taken in the analyses for trace minerals. In addition to ashing at a temperature below the volatilizations point of the minerals, i.e., zinc below 500 C, steps were taken to avoid contamination. Common sources of zinc contamination which were avoided were black plastic caps and liners and rubber stoppers. Eppendorf pipette tips from some sources also were contaminated and were rinsed with dilute HCI. iron contamination from two sources, filter papers and graphite tubes, was eliminated by rinsing the papers several times with HCI and demineralized water and by heating the tubes several times to the atomization temperature or until they showed no peaks for iron.
RESULTS The trace mineral contents of various fractions during the manufacture of cottage cheese are in Table 1. A dearth of published information about trace minerals in cottage cheese limits comparison. From analyses of milk (1, 2, 5, 7) ranges were: for zinc, from .2 to .5 mg/100g; for iron, from .02 to .1 mg/100g; for copper, from 2 to 15 /ag/100g; and for manganese, from 2 to 10 /lg/100g. Gormican (4) reported that creamed cottage cheese contained .4 mg zinc/100g. Freeland (3) reported .46 mg/100g for farmer's cheese, a similar product. Published values for trace elements in cottage cheese whey were not
TECHNICAL NOTE TABLE 1. Distribution of trace minerals during cottage cheese manufacture. Trace minerals (#g/100 g) Fraction
Milk and starter Whey Wash 1 Wash 2 Wash 3 Curd
401.0 381.3 221.8 121.0 93.6 482.6
67.0 60.8 12.5 8.0 1.5 174.1
8.2 8.5 4.5 2.4
2.5 2.6 1.1 .8 ... 3.7
TABLE 2. Recovery of minerals during cottage cheese manufacture. Trace minerals (°,6 of total in milk) Fraction
Whey Wash 1 Wash 2 Wash 3 Curd
64.6 28.1 15.4 11.7 18.0
61.7 3.8 5.8 1.1 38.9
70.1 27.8 14.8 . . 4.7
70.7 20.4 16.3
found. Data f o r recovery o f trace minerals, as a p e r c e n t a g e o f t h o s e in the original milk, are in Table 2. A f t e r a d j u s t m e n t for the mineral c o n t e n t o f tap w a t e r which was used to wash the curd, total recoveries ranged f r o m 111% to 138%. The r e t e n t i o n o f the trace minerals in the curd ranged f r o m 5% o f c o p p e r to 39% o f iron. A m o u n t s recovered f r o m w h e y ranged f r o m 62% f o r iron to 71% f o r m a g n e s i u m . Table 3 s h o w s the e f f e c t o f size o f curd,
TABLE 3. Effect of size of curd, added calcium chloride and washing procedure on iron and zinc in cottage cheese curd. % Increasea Product
Large curd Small curd Small curd Small curd Small curd
12 34 22 18 26
18 25 32 46 66
+ .01% CaCI2 + .1°6 CaCI2 after 2 washes after 1 wash
apercent of increase over small curd cottage cheese, washed three times.
. 21.0 128.4
a d d e d calcium chloride, and washing p r o c e d u r e on r e t e n t i o n o f iron and zinc in the curd. Each t r e a t m e n t increased r e t e n t i o n o f b o t h iron and zinc. T h e s e t r e a t m e n t s generally had the same e f f e c t on trace minerals as t h e y did on the m a j o r minerals (8) e x c e p t t h a t t h e a d d i t i o n o f calcium chloride did n o t a f f e c t the m a j o r minerals. A l t h o u g h c o t t a g e cheese is a n u t r i t i o u s f o o d , little is k n o w n regarding its trace mineral c o m p o s i t i o n . We have p r e s e n t e d c o m p o s i t i o n data o f iron, zinc, c o p p e r , and m a n g a n e s e in c o t t a g e cheese curd, w h e y , and wash w a t e r and have d e m o n s t r a t e d t h a t the c o n t e n t o f iron and zinc is a f f e c t e d by certain m a n u f a c t u r i n g variables. REFERENCES
1 Capella, P., G. Losi, R. Rastelli, and C. R. Lerichi. 1974. Su Alcuni Componenti minerale del ratte in caldaia e die sieri relativi variazioni stagionali. Scienza e tech. degli alimenti 4: 295. 2 Dequidt, J., F. Erb, A. Brice, and J. GromezPotencier. 1974. Determination a'elements minerauz traces darts le lair. Ann. Fals. Exp. Chim. 67:567. 3 Freeland, J. H., and R. J. Cousins. 1976. Zinc content of selected foods. J. Amer. Dieter. A. Journal of Dairy Science Vol. 60, No. 10
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68: 562. Gormican, A. 1970. Inorganic elements in foods used in hospital menus. J. Amer. Dietet. A. 56: 367. J o n n s o n , Hans. 1976. Determination of copper, iron and manganese in milk with flameless AAS a n d a survey o f the c o n t e n t s o f these metals in Swedish m a r k e t milk. Milchwissenschaft 31:210. LaCroix, D. E., and N. P. Wong. 1972. A simple
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collimating lens s y s t e m for flameless atomic absorption. Spect. Ltrs. 9: 31. Murthy, G. K., U. S. Rhea, and J. T. Peeler. 1972. Copper, iron, manganese, s t r o n t i u m and zinc content of market milk. J. Dairy Sci. 55:1666. Wong, N. P., D. E. LaCroix, W. A. Mattingfy, J. H. Vestal, and J. A. Alford. 1976. The effect of m a n u f a c t u r i n g variables on the mineral c o n t e n t of cottage cheese. J. Dairy Sci. 59:41.