Delactosed, High Milk Protein Powder.
2. Physical and Functional Properties'
V. V. MISTRY2 and H. N. HASSAN3
Minnesota-South Dakota Dairy Foods Research Center
Dairy Science Department
South Dakota StateUniversity
Brookings m 7 G 4 7
ABSTRACT powder (HMPP) was described. Some unique
characteristics of t i powder included a low
The objective of this research was to temperature of manufacture and the presence
examine some physicochemical proper- of both casein and whey proteins. In the manu-
ties of a novel delactosed, high milk facture of HMPP, membrane filtration was
protein powder. Data indicate that the used for the separation and concentration of
solubility index of the powder was de- proteins and removal of lactose from milk.
pendent on temperature of mixing. Solu- Isoelectric precipitation or pH adjustment in
bility index decreased (solubility in- combination with high heat treatment was not
creased) as temperature increased from required. Consequently, the protein composi-
25 to WC. Foaming capacity, expressed tion of HMPP was similar to that of the skim
as percentage overrun, was low at pH 7 milk from which it was produced, and lactose
and 8 but increased at higher pH, e.g., content was less than 1%. considerably less
after 10 min of whipping, overrun in- than that of NDM.
creased from 470 to 941% as pH in- Milk protein products such as HMPP have
creased from 7 to 10. Foaming increased numerous applications as ingredients in the
with time at higher pH but not at lower food and dairy industries (4, 8, 13). Such
pH. Particles of the high milk protein products should also substitute well for NDM.
powders as examined by scanning elec- Use of these ingredients in foods would re-
tron microscopy were characterized by quire some knowledge of their physicochemi-
smooth surface and dents. Particles of cal properties. For example, HMPP may be
skim milk powder prepared in the same used in the manufacture of low fat yogurts (9).
spray dryer had a wrinkled surface. This application and others, such as protein
Commercial casein products had a struc- standardization of cheese milk or ice cream
ture similar to that of the high milk mix formulation, would require knowledge of
protein powders. solubility of the protein powder in milk or
(Key words: protein, powder, properties, water. Likewise, other applications (e.g., bak-
microstructure) ing) would require information on foaming
characteristics. Information on foaming and
Abbreviation key: HMPP = delactosed, high solubility is needed to confirm potential of
milk protein powder, SI = solubility index. HMPP for application in products requiring
these attributes. Numerous other functional
INTRODUCTION properties of protein products have been
In an earlier paper, (9) a method for the described, and procedures have been deve-
manufacture of a delactosed, high milk protein loped to measure them (7, 11). Additionally,
protein products can be specially tailored to
achieve specific functional properties in foods.
The objectives of this research were to de-
Received March 1. 1991. termine the solubility index and foaming char-
Accepted May 31, 1991. acteristics of HMPP and to examine its micro-
lPublished with the approval of director of the South structure by scanning electron microscopy.
Dakota Agricultural Expcrimcnt Station as Publication
Number 2561 of the J o d Series.
- reqacsts. MATERIALS AND METHODS
3~esent address: Department of D- science, ~ a c -
u t of Agriculture. Tanta U i e s t , Kafr-Elsheikh,
ly nvriy Delactosed, HMPP was prepared from skim
Egypt. milk using ultrafiltration, diafiltration, and
1991 J Dairy Sci 74:37163723 3716
HIGH MILK PROTEIN POWDER 3717
TABLE 1. Effect of temperature on solubility index of Milk Institute, now the American Dairy Rod-
delacrosed, high milk protein powders. ucts Institute (1). Ten grams of HMPP were
Water added to 100 ml of distilled water and blended
temperature Solubility index' SD in a mixing jar for 90 s. The mixed sample
('0 (mu was poured into conical centrifuge tubes to the
25 9.4 .9 50-ml mark and centrifuged for 5 min. The
45 6.4 1.1 the
supernatant was siphoned OF, residue was
60 3.8 1.4 dispersed in distilled water and centrifuged
75 1R II
again for 5 min. The SI was recorded as
M of three replicates. milliliters of sediment remaining after the sec-
ond centrifugation. To study the effect of tem-
perature on solubility of HMPP, water at 2' 5C
(standard temperature recommended by the
spray-drying techniques described earlier (9). American Dairy Products Institute) and at 45,
Pasteurized skim milk was ultrafiltered at 38°C 60. and 75°C was used.
to 15% protein and then batch diafiltered three
times at 32°C to 18.9% protein and .OS% Foaming Capacity
lactose. It was then spray-dried at inlet and
outlet ar temperatures of 120 to 125'C and 75
i Foaming capacity of HMPP was determined
to 8WC, respectively. The powder was stored by the method of Phillips et al. (14). Powders
at room temperature and analyzed for solubil- (3.75 g) were weighed into a beaker, and dis-
ity index (SI), foaming, and microstructure. tilled water was added to form a paste. Volume
was brought up to 60 ml with water, and the
Solubility Index dispersion was stirred for 30 min, after which
pH was adjusted to 7.00 with .1N NaOH solu-
Solubility index of HMPP was determined tion. Volume was adjusted to 75 ml after an
according to methods of the American Dry additional 30 min of stirring. The dispersion
was poured into a mixer bowl and whipped in
a double beater Sunbeam Mixmaster (Sunbeam
Appliance Co., Milwaukee, WI) with the tum-
table rotation speed set for egg white foam. At
5-min intervals, the mixer was stopped, and
samples of foam were scooped out with a
rubber spatula and gently placed into pre-
weighed aluminum dishes of known volume.
The top of the foam was leveled with a metal
spatula, and the dish was immediately
weighed. Foam was returned to the mixing
bowl and mixing resumed. Measurements were
made at 5-, 10- and 15-min intervals. Foaming
capacity was expressed as percentage overrun,
which was calculated as follows:
% overrun =
(wt of protein solution) -
(wt of equal volume of foam)
(wt of equal volume of foam)
Figure 1 . Effect of pH of mixture and time of whip Protein powders were prepared for scanning
ping on foaming capacity of high milk protein powders. electron miscroscopy according to published
Journal of Dairy Science Vol. 74, No. 11. 1991
3718 MISTRY AND H A S S A N
TABLE 2 Influence of whipping
. the and pH on foaming pmperticS* of dclaaosed, high milk protein powdas.
PH 5min 10 min 1 min
7 469.7 470.9 441.7
SD 56.7 3.36 292
8 430.2 46
9 595.7 708.5 754.7
128 1135 43.0
10 9205 941.1 9802
SD 46.4 93
1MCan of three rqltilxtes.
methods (5, 6). A double sticky tape was S
ples were examined in an I 1 Super IIIA scan-
attached to a scanning electron miscroscopy ning electron microscope (International Scien-
aluminum stub using a silver-based paint. A tific Instruments Inc., Korea) operated at 90
thin layer o powder was spread on the tape
f pA. Photomicrographs were taken on a Type
and sputter-coated with gold in a Hummer VI 55 Polaroid@ 50 ASA f l (Polaroid Corp.,
sputter coater (Tezhnics Electron Microscopy Cambridge, MA). To examine the interior o f
Systems Inc., Munich, Germany). Coated sam- powder particles, particles were cracked open
FigurC 2. Scanning ckctmn minograph of high milk protein powder showing a wide range of parlick sizcs.
Journal of Dairy Science Vol. 74, No. 11, 1991
HIGH MlLK PRO'I" POWDER 3719
by running a razor blade continuously for 5 TABLE 3. mmt of PH treatment' on foaming capacity of
min through a small sample of the powder delactosed, high milk protein powders.
placed on a glass microscopic slide (2). The Whipping time Ov-2 SD
powder was then prepared and examined as
described earlier. (W
5 511.9 88
10 622.2 95
RESULTS AND DISCUSSION 15 3.
'pH of powder mixture raised to 10 and then lowered
Solublllty Index back to 7.
The SI measures the ability of a milk pow- 2Mcau of t r e replicates.
der to go into dispersion in water and reflects
the extent of denaturation o whey proteins in
the powder (7). This method does not directly
measure the solubility o milk proteins, but it
centrifuge tube. H n e the smaller the quan-
is used by the American Diy Ruducts Insti-
ar t t of sediment, the greater the solubility; e.g.,
tute in establishing standards for the different extra grade NDM produced by the spray pro-
grades o dried milk products. It is also used as
f cess is highly soluble and has an SI of S1.25
a quality criterion by commercial manufactur- ml at room temperaom, whereas extra grade
ers of dried milk products. According t o drumdried NDM, which is not as soluble as
prescribed procedures (l), the test was con- spraydried NDM, has an SI of S15 ml (1).
ducted at mom temperature, and r e d s were Results of the SI test of HMPP are shown
expressed as millimeters of sediment in the in Table 1. At room temperature, the powders
smface and data on particles.
figure 3. Scanning electron micrograph of high milk protein powder showing smotL~
Joumd of Dairy Scicoce Vol. 74. No. 11, 1991
3720 MISTRY AND H A S S A N
P i 4. Intcmal stnrctare o high milk proteinpowder. Particle wall thickness is approximately 2 p. Small particles
trapped imide the cavity of a large particle can be seen. Particle wall is marked by an mow.
had a mean SI of 9.4 ml. As temperature of tions, many food protein preparations are spe-
mixing increased, SI decreased (solubility in- cially designed to produce large amounts of
creased) to 1.8 ml at 7572. The mixture was foam, e.g., total milk protein isolates, casein-
stable, and no precipitation occurred during ates, whey protein concentrates, and egg
storage. U e of this powder for reconstitutim
s whites (12, 14).
in water or for fortification o fluid milk in
f Results of foaming capacity of the HMPP
manufacture of products should therefore be are shown in Table 2 and Figure 1. Data reveal
feasible. It is conceivable that, with the instan-that pH and time of w i p n both have an
tization process or with use of two-stage to effect on foaming capacity of the powders.
three-stage spray dryers for the manufacture of iia
S m l r effects have been observed for other
HMPP, solubility can be tinther i n d at high protein powder products (14). Foaming
low mixing temperatures. capacity at pH 7 and 8 ranged f o 406 to
47096 at 5- to 15-min whipping times but
Foaming Capaclty n
i- considerably as pH w s increased to
9 and 10, reaching a maximum o 980% at pH
The foaming property of a protein is depen- 10 after 15 min of whipping. Also, foam be-
dent on its surface activity and is a measure of came visually drier and did not drain as pH
the ability of a protein to entrap and retain air was increased. In contrast, commercial milk
(7, 14, 15). This property of proteins is useful protein powders (caseinates) designed to gen-
in many food applications such as in whipped erate foam consistently produced an overrun of
toppings, breads, etc. (7). For these applica- 110096 and above at all pH.
Journal of Diy Science Vol. 74, No. 11, 1991
HIGH MILK PROTEIN POWDER 3721
figure 5. Scanning electron micrograph of praydried skim m & powda. Powda particles an characterized by a
wrinkled surface with dents.
Fat interferes with foam formation and may proteins, thereby improving foaming. Increase
even cause the foam lamellae to break (15). in pH will decrease calcium ion activity (15),
This may explain in part why the new protein which may also help increase foaming capaci-
powders have a lower foaming capacity than ty. The manufacturing procedure for HMPP
some commercial powders. The HMF'P con- may, therefore, be modified to include pH
tained approximately 2.3% fat, whereas com- treatment to skim milk prior to or after
mercial casein powders and isolates contain ultrafiltration and diafiltration to improve
approximately 1%fat (9). With more efficient foaming characteristics of the resulting pow-
centrifugal separation or with microfiltration, der.
fat content of the powders may be lowered if a
high foaming capacity is requird Microstructure
In a separate foaming capacity experiment,
pH of the HMPP solution was raised to 10 and Figures 2 and 3 illustrate the microstructure
then lowered back to 7, and foaming capacity of HMPP, The powder consisted of particles of
was measured as described. Results show that varying size ranging f o 2 to 33 p in di-
with this treatment the foaming capacity of the ameter. The surface of protein powder particles
protein powders could be increased consider- w s always smooth with large dents. Occasion-
ably at 10 and 15 min of whipping (Table 3). a , small particles were trapped in larger
Proteins must be solubilized, disaggregated, dents of large particles. The interior o the f
and unfolded to promote foaming (10); hence, particles was usually hollow; the wall of large
this pH treatment may have solubilized whey particles w s approximately 2-p thick (Figure
Journal of Dairy Science Vol. 74. No. 11, 1991
3722 MISTRY AND HASSAN
Figm 6 Suonisg eleclron miaograph ofconrmcrcialmilkpmt&~ powder!$. Powder pattides have smooth surface
and possess dents. A w d muge of p&le sizes am evident.
4). However, particles of NDM produced un- and dents (16). This similarity in microstruc-
der drying temperatures identical to those of ture of HMPP suggests that composition will
HMPP were considerably different (Figure 5). influence the structural properties of protein
There was less variation in size of particles, powders, but microstructure may not directly
and. unlike the HMPP. these particles had a affect functional properties.
wrinkly surface. These particles, too, were
characterized by dents on the surface. These CONCLUSIONS
characteristics o NDM have been observed by
other researchers as well (2, 3). The difference As indicated in an earlier publication (9),
in surface structure between NDM and HMPP HMPP is a milk protein powder manufactured
is likely due to difference in composition of at low temperahues without pH adjustment.
the two powders; NDM contains approxi- This powder was soluble in water at room
mately 35% protein, whereas HMPP contained temperature and exhibited improved solubility
84% (9). The microstructure of commercial with modera& increases in temperature. Addi-
casein powders was similar t that of HMPP
o tionally, this powder was lactose free. Its use
(Figure 6). Particles of these powders also as an ingredient or for fortification of milk for
were characterized by a smooth surface and the yogurt, cheese, and ice cream m a n u f w
presence of dents. Other dried protein powders, should, therefore, be feasible. Foaming charac-
based on SOY milk and with functional pr~per- teristics o HMPP were pH dependent and
ties different from those of HMPP and casein- improved with an increase in pH. Foaming
ates, also exhibit particles with smooth surface capacity of HMPP may be increased by reduc-
Journal of Dairy Science Vol. 74, No. 11, 1991
HIGH MILK PROTEIN POWDER 3723
ing fat content of powder and by pH treating 5 KaJAb, M. 1981. E e t o microscopy of milk prod-
s i milk prior to concentrating and drying or
km ucts: a review of techniques. Scarming Electron
Microsc. Part m:453.
pH treating the diafiltered concentrate prior to 6KaLlb, M ,M. CariC, M. zaba, agd V. R.HarwalLar.
drying. The microstructure of HMPP was char- 1989.Composition and some Propaties of spy-dried
acterized by smooth surfaced particles of vary- retcntates obtained by ultrafiltration of milk. Food
ing size and with dents. Commercial dahy and Microstract. 8925.
7KinCellp.J. E. 1984. Milk proteins: physicochemical
nondairy powders of similar gross composition and functional pr'opatia. CRC Crit Rev. Food Sci.
had similar microstructure, suggesting that the Nutr. 21:197.
microstructure is dependent on the gross com- 8 Khkp&~k, K.J., and R. M.Fenwick. 1987. Manu-
position of the powder. Applications in foods facture and general properties of dairy ingredients.
and structural properties of HMPP are being Food Techwl. 4 ( 0 : 8
9 Mishy, V. V.,and H.N. W a n . 1991. Delactosed,
investigated. high m l protein powder. 1. Manufacture and com-
position. J. Diy Sci. 741163.
ACKNOWLEDGMENTS 10 Mom, C V. 1985.Composition, physicochemical and
functional properties of reference whey protein con-
The authors are grateful to the Minnesota- centrates. J. Food Sci. 50:1406.
llMorr, C. V. 1985. Manufacture, functionality and
South Dakota Dairy Research Center for fund- utilization of milk-protein products. Page 171 in Ruc.
ing this project and to D. Robison of the Int. Diy C o w . Milk Proteins. T. E.Galeshoot and
Veterinary Diagnostic Laboratory of South Da- B. L. Taegn ed. Pudoc, Wagenhgen, Neth.
kota State University for help with the scan- 1 Morr, C. V. 1987. Effect of HTST pastearkation of
ning electron microscopy. m l , cheese wbey and cheese whey Up retentate
upon the composition, physicoclmnicd and functional
proper(ics of wbey protein COIICCntcateS. J. Food Sci.
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Journal of Dairy Science Vol. 74, No. 11, 1991