Effects of Lecithin on Reconstitutability of Dry Whole Milk S. J. Toma and S. Nakai Department of Food Science University of British Columbia Vancouver 8, B.C.
Lecithin has been used in many patents for instantization of whole milk powder (McIntire and Loo, 1%0; Nova et al., 1963; Sjollema, 1960). However no systematic study on the action mechanism has been reported to date. Some of the authors ascribed the effect of the synthetic emulsifiers either to lowering of the surface tension of water thus facilitating its penetration into the particle spaces of milk powder, or to an orientation of these substances into a layer on the powder particle surface attracting water into the powder (Gibson and Haithby, 1954). Others indicated that the lower melting point fat fraction or butterfat containing these surfactants has lower interfacial tension towards water than the higher melting point fat fraction or butterfat alone, suggesting a possible relationship between the interfacial tension of butter oil and the reconstituta hility of milk powder (Baker and Samuels, 1961). 'Ve were interested in the effect of commercially :1\'ailable lecithins from different sources on the reconstitutability of dried whole milk. Lecithins were purchased from Nutritional Biochemicals Corporation; purity: vegetable lecithin 95%, bovine lecithin 90%, soybean lecithin (oil not removcd) and refined soy lecithin (no purity indicated). One gram of lecithin dissolved in 20 ml of petroleum ether (b.p. 37 to 48.9°C), was mixed with 49 g of dried whole milk (the Borden Company, Ireland) to give a final concentration of 2% lecithin with continuous stirring for one minute. The powder was exposed to air for 3 to 4 hours in a flat container at 35°C for evaporating ether. 'fhe same solvent was used for adding Atlas Span type emulsifiers but acctone for Atlas Tween type emulsifiers because of their low solubility in petroleum ether. The dispersibility 'Of dried whole milk determined by the method of Sinnamon et al. (1957) was improved considerably after the addition of lecithin (Fig. 1). The maximum solubility was obtained in less than 1/5 the time required for the control. Lecithin, being an amphiphile, is probably capable of interacting with milk proteins thr,ough electrostatic or hydrophobic interactions. Such interactions may lead to a more hydrophilic casein micelle. The mixtures of lecithin and whole milk powder were investigated to determine the properties of interaction, if any, and also to evaluate the effect of various lecithins on the physical properties of the whole milk powder. For measuring the interaction between lecithin a nd casein, sedimentation analysis in an analytical centrifuge, gel electrophoresis and extractability of lecithin from a mixture of acid casein and lecithin were used. However, there was no difference in the sedimentation coefficient of casein and of a mixture 223
cf casein and lecithin. Their mobilities 011 the polyacrylamide gel electrophoretogram were identical. 'l'here \vas no variation in extractability of lecithin with hexane-acetone mixture 4:1 from different caseinlecithin mixtures. No chemical interaction between lecithin and casein was detected. The dispersibility test failed to show any statistically significant differences in the milk powder treated with different lecithins except for powder treated with refined soy lecithin which showed a slightly higher dispersibility compared to powder treated with other lecithins (Fig. 1). Whereas different lecithins showed different degrees of improvement in the sinkability (determined according to Bullock and Winder, 1960) of milk powder which is the ease for the powder particles to contact with water (Table 1). 'When lecithins were added to milk powder, a change in the particle size and its distribution was observed, in particular, the population of particles having a diameter 100-500(L increased (Fig. 2). Most of the published values for the average particle size is in the range of 50-110(L for spray dried whole milk (Hunziker, 1949; King, 1965). 'When the sinkability was measured for different sized particles of surfactant-treated powder, a marked effect of the particle size on the sinkability of the powder was observed. The greater the particle size, the higher was the sinkability (Fig. 3). However, particles of the size of same range, 100-500(L, of whole milk powder without surfactant prepared by moistening to 10% moisture and re-drying in a vacuum oven at 40°C did not improve the sinkability of the powder at all (Fig. 3). Greater amounts of lecithin were found in larger particles of lecithin-treated milk powder, 2.35 and 1.27% in powder particle of 400-500(L and of smaller than 100(L respectively. Higher concentrations of lecithin in the powder CQuld increase the sinkability and dispersibility (Fig. 4). Thus it is l?ossible that, besides the change in the particle SIze, there are other factors involved in improving the reo constitutability of milk powder by adding lecithin. The free flowability (static measurement determined by the method of Sjollema, 1963) of dried whole milk also changed by addition of different lecithins (Table 1). Milk powder treated with bovine lecithin improved the free flowability of the powder considerably and yielded an angle of repose very close to that of instant skimmilk powder, whereas lecithins from other sources did not improve the free flowability significantly. This may be due to the difference in degree of saturation 'of consisting fatty acid in lecithin as the iodine value of bovine lecithin was 40.9. lower than other lecithins (62 to 86). A ttempts were made to investigate the effect of lecithins and commercial emulsifiers on the surface tension of water, Can. Inst. Food ScI. Techno!. J. Vol. 5, No.4, 1972
Table. 1. Effect of different lecithins and synthetic emulsifiers on the interfacial tension of butter oil, the surface tension of water, the sinkability, the free-f1owability and the dispersibility of dried whole milk. Type of lecithin or emulsifier
Surface Interfacial tension 1 Milk powder containing tension (butter oil-water) 2% surface active agent of water Angle Sinkability Dispercontain(30 sec sibility of ing 0.05% test time) repose2 (10 sec surfactant test time) dyne/em at 25°C
dyne/em at 40°C
72.0 33.2 43.5 39.5 42.4
24.8 20.0 18.6 4.6 4.2
9.5 98 5.2 83.8 24.3
22.0 67.8 21.5 87.3 52.8
Bovine lecithin Vegetable lecithin Soybean lecithin Refined soy lecithin Without lecithin Span 20 Span 40 Tween 20 Tween 60
Concentration of surfactant in butter oil was 0.06%. Angle of repose for instant skimmilk powder was 40 ¥2 b . 3 a and b are two groups significantly different (according to analysis of variance).
--:~-----:"!"::_----....,...----~-20 30 40 50
STIRRING TIME (SEC. ) Figure 1. Dispersibility
( 0---0 ), whole milk powder containing 2% refined . soy-lecithin ( Ls---6. ), bovine lecithin ( 0---0 ), soy lecithin ( ..-.--..... ), vegetable lecithin ( 0-0 ) and the control (
lnst. Can. Sci. Techno!. Ailment. Vol.
Figure 2. Distribution of particle size of dried whole milk before and after treating with 2% vegetable lecithin. ( ), dried whole milk with 2% vegetable lecithin ( 'Y.----.. ), control dried whole milk.
PARTICLE SIZE (-At) Figure 3. Effect of particle size on the sinkability (15 sec test time) of whole milk powder containing 2% Span 20 ( 0--0 ), Tween 20 ( bovine lecithin ( D----O ), Tween 60 ( 0-0 ), refined soy lecithin (_______ ), Span 40 ( . . - . . ), and the control ( ).
the interfacial tension of butter oil, measured accord· ing to Baker and Samuels (1961), and the possible relationship with the sinkability ,or dispersibility of milk powder. It was found that lecithins which reveal· ed a greater ability to improve the sinkability of milk powder altered considerably the interfacial tension of butter oil and the surface tension of water (Table 1). However, the same relationship was not observed for synthetic emulsifiers. In conclusion it was found that powder particles were partially agglomerated by adding lecithins. However, the particle size itself showed no effect on the sinkability of the milk powder without lecithin. For lecithins the more improved the sinkability of the milk powder the more decreased the interfacial tension of butter oil and the surface tension of water. Interactions between casein and lecithin were not detected.
Acknowledgements The authors gratefully acknowledge the financial support of the Canada Department of Agriculture (OG 0012).
Figue 4. Effect of concentration of vegetable lecithin on the sinkabiJity (30 sec test time) and the dispersibility (10 sec test time) of whole milk powder.
References Baker, B. E.• Samuels, E. R.. 1961. Milk powders. V. Effect of interfacial tension of butter 011 In powder on the wettabllity of the powder. J. Dairy ScI., 44: 407. Bullock, D. H., and Winder, W. C. 1960. ReconstltutabllIty of dried whole milk. I. The effect on sinkability of the manner of handling freshly dried milk. J. Dairy ScI., 43: 301. Gibson, D. L., and Ralthby, T. W., 1954. Studies on improving the ease of reconstitution of skim milk powder Canad. J. Techno!. 32: 60. Hunziker, O. F., 1949. Condensed milk and milk powder. 7th Edn. La Grange, Ill. King, N., 1965. The physical structure of dried milk. Dairy ScI. Abst., 27: 91. McIntire, J., and Loo, C., 1960. Fat containing dried dairy product and method of manufacturing. U.S. Patent 2,914,886. Nova, L. J., Hotton, J., Shields, J. A.. and Kempf, G. A., 1963. Fat containing Instant milk. Belg. Patent 645,418. Sinnamon, H. I., Aceto, N. C., Eskew, R. K., and Schoppet, E.F., 1957. Dry whole milk. I. A new physical form. J. Dairy Bel., 40: 1036. Sjollema, A., 1960. Process for modifying powdered milk products. U.S. Patent 2,953,458. Sjollema, A., 1963. Some Investigations on the free-flowing properties and porosity of milk powders. Neth. Milk Dairy J., 17: 245. ReceIved July 22, 1971
Can. Inst. Food ScI. Techno!. J. Vol. 5, No.4, 1972