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Delactosed_ High Milk Protein Powder 2 Physical and


									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)
                                                                                            x   loo.


   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
                                                                     03                             4082
SD                                    48
                                     2.                                49
                                                                      1.                             38.4
 9                                  595.7                           708.5                           754.7
SD                                   1.
                                    128                             1135                             43.0
10                                  9205                            941.1                           9802
SD                                   46.4                             93
                                                                     2.                               72
     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.
                                                                                 792                    39
                                                            '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
                         f                                                 ec,
                                                         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

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