and Its Practical Application to Panna-Cotta

[Article]

Properties of a Thermostable Emulsion Prepared from

Process Whey Protein and Olive Oil; Use as a Cream-Substitute

and Its Practical Application to Panna-Cotta

Yuko Koga, Takako Koga, Yoh-ichi Kinekawa, and Naofumi Kitabatake

Rheological and sensory properties of a thermostable emulsion prepared from Process whey protein

(whey protein isolate preheated under desalted conditions at 9% protein concentration and 90℃ for

30 min) and edible oil(soybean oil or olive oil) were investigated, comparing with those of commer-cial cream. The emulsion prepared by 1 part of process whey protein and 0.35 parts olive oil gave

equivalent properties to those of the control commercial cream. The emulsion prepared from Process

whey protein and edible oil was thermostable. This suggests that the emulsion prepared from Process

whey protein can be used as a new type of cream-substitute. A panna-cotta was made using the

emulsion prepared with process whey protein and oil instead of milk and commercial cream. Similar

properties of panna-cotta to those of the panna-cotta made with milk and cream could be obtained

when milk and cream were substituted with the emulsion prepared from Process whey protein and

olive oil.

Keywords : milk whey protein, process whey protein, emulsification, heating, cream, panna-cotta

Introduction

Fresh cream and commercial cream are both used

to improve taste and flavor of foods, to invest the

food with a creamy feeling, and to produce a whitish

appearance of foods". Addition of a small amount

of cream to foods at the final stage of cooking and

food processing is effective to modify and improve

their texture".

FIowever, the heat-stability of fresh cream and

commercial cream is not satisfactory, for instance,

33% of oil was separated from fresh cream and 14%

of oil was separated from the commercial cream

when heated2). That is, oil exudes from the fresh

cream by warming above 10°C and oil is apparently

separated from the cream between 30°C and 60°C).

It is known that oil is separated from cream in a

panna-cotta during heating and cooking. Oil separa-

tion from cream is inconvenient for cooking and

processing of foods by heating.

Many sorts of fat- or cream-substitutes based on

starch-dextrin, polysaccharides, cellulose, protein,

and non-calorie fat have been developed and used

for dairy products, sauces, dressings, ice cream, and

mayonnaise°. These cream-substitutes were devel-

oped with a view of low-calorie foodstuffs. How-

ever, the improvement of the functional properties

was not well considered. That is, they are not as

stable as the fresh cream on heating. Therefore, it is

important and required for cooking, food process-

ing, and the food industry to develop a new type of

heat-stable cream-substitute.

The emulsion-SO, that is, the emulsion prepared

from soybean oil and process whey protein did not

show any separation of oil on heating, which was

evaluated by the standard force - separation

*1 Faculty of Home Economics , Nakamura Gakuen University :

Johnan-ku, Fukuoka 810-0198, Japan

Daiichi-Kasei Co., Ltd., Research and Development Center *3 Research Institute for Food Science , Kyoto University

32 (154

Properties of a Therrnostable Emulsion Prepared from Process Whey Protein and Olive Oil

method'', when 10 to 20% of sucrose was added. Process whey Protein (PWP) is a novel food mate-

rial prepared from whey protein isolate under a

specific condition°. The emulsion-SO showed a

similar rheological behavior and whiteness to that

of commercial cream°. However, the emulsion-SO elicited a rather heavier mouth-feeling than that of

commercial cream, and the soybean flavor was

detected in the emulsion-SO. Both heavy mouth-

feeling and soybean flavor are disadvantages for the

emulsion-SO to be used commercially as a cream-substitute.

In the present study the rheological behavior of an

emulsion (emulsion-OL) prepared with PWP and

olive oil instead of soybean oil was examined and compared with that of commercial cream. The

objective of the present study was to evaluate the

availability of the emulsion-OL as a cream-substi-

tute. Another objective was to clarify the quality of

a panna-cotta prepared using the emulsion-OL instead of the fresh cream and the commercial

cream.

Materials and Methods

Materials

Process whey protein (PWP, Genesis°) was from

Daiichi-Kasei Co., Ltd., Kyoto, Japan. Soybean oil

and sucrose were of specially prepared reagent

grade and purchased from Wako Pure Chemical Industries, Ltd., Osaka and Katayama Chemical

Industries, Co., Ltd., Osaka, respectively. Olive oil

was purchased from Nissin Oil Mills Ltd., Tokyo.

Cow's milk (hereafter milk) and the commercial cream prepared from vegetable oil were purchased

from Snow Brand Milk Products Co., Ltd. Tokyo.

Gelatin powder and milk flavoring agent (Dry Coat

Milk 8093) were obtained from Miyagi Chemical Industrial Co., Ltd., Tokyo and Takata Koryo Co.,

Ltd., Hyogo, Japan, respectively.

Preparation of the emulsion from PWP and

soybean oil or olive oil

Soybean oil was added to PWP a sample (9.0%-

protein, pH 7.0) and homogenized using a homogen-izer (DX-11, Nihonseiki Kaisha Ltd., Tokyo) at

10,000 rpm at room temperature for 5 min. The

weight ratios of PWP and soybean oil were 1 .0 : 0.5, 1.0 : 0.4, and 1.0 : 0.35. The emulsions

obtained were heated at 80°C for 30 min and kept at

5°C for 20 hr. The emulsion-OL was prepared simi-lar to that for the emulsion-SO. The weight ratios

of PWP and olive oil were fixed at 1.0 : 0.35 (w/

w). Determination of oil droplet size and

rheological properties of the emulsion

The size and dispersion of oil droplets in the

emulsion were determined and observed by video-

optical microscopy (Olympus BX 40, C-35 AD-4, objective lens, x 40) equipped with a microscopy

image analyzer (Olympus XL-10, camera lens X5, monitor 29 inches). Measurements were repeated 10

times and the mean size of the oil droplets was

calculated. For one measurement, the diameters of 20 oil droplets in a microscopic field were counted . Flow behavior of the emulsion-SO and emulsion-

OL was measured by a cone-plate type rotational

viscometer (E type, EMD, Tokyo-Keiki Co., Ltd., Tokyo, Japan). The diameter of the cone-plate used

for this experiment was 28 mm and the cone angle

was 3°. The sample volume was 1.0 ml and mea-

surements were carried out at 20°C. Viscosity was measured at 0.277s' (1rpm), 0.6925s' (2.5 rpm),

1.385s" (5rpm), (lOrpm), 5.54s" (20

rpm), 13.85s" (50rpm), and 27.7s" (100 rpm).

Commercial cream was used as the control.

Sensory evaluation of the emulsion and the commercial cream

Sensory evaluation of flavor, smoothness, and

whiteness of the emulsion (PWP/soybean oil or

PWP/olive oil ; 1.0/0.35 w/w) and the commercial cream were performed with the one-way layout

method'''. Rating was done against the control.

Rating "+2" means better than the control, " +1" ;

slightly better than the control,"0" ; similar to the

control, " —1" ; slightly worse than the control, " —2" ; worse than the control . Taste for the sam-

ples was evaluated with a ranking method, and was analyzed using the table by Newell and Mac-Farlane', and with the pair test (paired preference

test). Panels were 12 females aged between 21 and

30 years, and belonged to the Department of Food

(155) 33

J. Cookoy Sci. Jpn. Vol. 34 No. 2 (2001)

and Nutrition of Nakamura Gakuen University. Preparation of panna-cotta

The emulsion prepared with PWP and soybean oil

or olive oil (PWP/oil 1.0/0.35 (w/w) ) were

added to the mixture of ingredients for panna-cotta at 40.1% or 45.1%. Milk and commercial cream

were used for the control panna-cotte'9). Panna-

cotta was prepared as follows. The powdered gela-

tin was swollen with water at 20°C for 10 min and dissolved at 60°C. Then, the gelatin was mixed with

the emulsion at room temperature and sucrose and

flavoring agents were added. The final emulsion

mixture (250g) was poured into a stainless steel vat

(120 x 77 x 45mm) and kept at 5°C for 16 hr. Measurement of texture and creep parameters

of panna-cotta

The hardness, cohesiveness, springiness, and ad-hesiveness of panna-cotta (20 x 20 x 20 mm, 20°C)

were measured by a texturometer (GTX-2 IN, Zen-

ken Ltd., Tokyo) . A plunger, with a diameter of 50

mm, compressed the sample on a flat plate with a

diameter of 100 mm ; the compression was 62% ; the sample was successively compressed twice ; and

the recording chart speed was 750 mm/min. The

mechanical model and viscoelasticity constant were

determined by a creep meter (Yamaden Co., Ltd., Tokyo, RE-3305) . Rheological parameters and a

compliance curve were calculated and depicted

using an equipped software for analysis (Yamaden

Co., Ltd., Tokyo, CA-3305-16) . The cylindrical

plunger with a diameter of 40 mm was used and the loading time was fixed to 600 s. The rate of compres-

sion of the sample was 1 mm/s and the linear range

of the proportional deformation by a constant stress was 17.7%.

Sensory evaluation of panna-cotta

Sensory evaluation of panna-cotta (40 x 40 x 20

mm, 20°C) was carried out using the one-way layout method') for smoothness, firmness, whiteness, flavor,

gloss, and overall acceptance. Panels were 15 females aged between 22 and 40 years. Rating was

similar to that described in the section of "Sensory

evaluation of the emulsion and the commercial cream."

Results and Discussion

Characteristics of the emulsion-SO

The emulsion prepared from PWP and soybean

oil with the mixing ratio of 1.0 1.0 (w/w) as shown in a previous study') was slightly more vis-

cous and slimy than the commercial cream. There-

fore, to reduce the viscosity of the emulsion the

proportion of oil in the emulsion was reduced to 0.5

parts (A) , 0.4 parts (B) , and 0.35 parts (C) against one part of PWP. The protein concentration and pH

of the PWP used was 9.0% (w/w) and 7.0, respec-

tively. The flow behavior of the emulsion prepared with

the PWP and soybean oil (the emulsion-SO) was

investigated using a rotational viscometer with

different shear rates. The emulsion-SO showed

time-dependent thixotropic and non-Newtonian flow. The thixotropy value of the emulsion-SO was

calculated from the following equation':

Th = A 102/U, where Th is the thixotropy value

[Pa • s-1], A is the area of the closed part of the flow curve, and U is the area of the closed rectangular

part of the flow curve at 10 Pa of stress and 10 s-1 of strain. In Table 1 the Th values of emulsion-SO

with different ratios of PWP/soybean oil (A, B, and

C in Table 1) and the commercial cream as the control (Cream) are shown.

All samples including the control showed time-

dependent thixotropic flow behavior. Sample A

showed significantly higher Th values than that of the commercial cream control. As the ratio of the

PWP/soybean oil decreased, the Th value was

reduced. Samples B and C showed similar Th values

to that of the commercial cream, and sample C showed a slightly lower Th value than that of the

control. These finding suggested that the destruction

of the emulsion structure in sample A occurred

under the stress during measurements, and samples B and C were resistant against the stress under the

rotational condition used.

Apparent viscosity values at 50 s-1 are shown in

Table 1. Comparing with commercial cream, emul-sions-SO (A, B, and C in Table 1) gave much higher

values of apparent viscosity. In the present study the

34 (156)

Properties of a Thermostable Emulsion Prepared from Process Whey Protein and Olive Oil

Table 1. Flow behavior and oil droplet size of the emulsions

° The emulsion prepared from process whey protein (PWP) and soybean oil.

2) The emulsion prepared from PWP and olive oil . 3) Measurements were in triplicate

.

Apparent viscosity was measured at shear rate of 50 s-1. 4) Details are described in the text .

shear rate to measure viscosity was fixed at 50 s-1.

Concerning the shear rate of the liquid food in the

mouth, various arguments have been reported.

Woodwmentioned that the shear rate for perceiv-

ing the viscosity of liquid food in the mouth was

about 50 s-1. Shama et al.1213) reported that the shear

rate of liquid food was below 100 s-1. Akabane

also measured the viscosity of liquid at 58.5 s-I to

represent the inner mouth conditions. Although the

shear rate of liquid in the mouth is still controver-

sial and requires much more information, in the

present study we tentatively used 50 s-1 for shear rate as a present general value for the shear rate in

the mouth.

The mean size of the oil droplets from emulsion-

SO was much higher than that prepared using the

commercial cream, while the mean value decreased

as the ratio of oil decreased. The size range of oil

droplets was also larger for emulsion-SO than that

of the commercial cream. These findings suggest

that the characteristics of emulsion-SO are distinct

from those of commercial cream. However, these

characteristics approached those of the commercial

cream by decreasing the ratio of soybean oil. Hence,

sample C had the most similar characteristics to

commercial cream among the samples tested.

Characteristics of the emulsion prepared with

olive oil

The characteristics of emulsion-SO were not

satisfactory as a cream - substitute from the

rheological point of view. The physical properties of

olive oil are distinct from those of soybean oil due to

the differences in the fatty acid composition. There-

fore, olive oil was used instead of soybean oil to

prepare the emulsion.

In Table 1, emulsion-OL corresponds to sample C

as the proportion of oil in the emulsion was similar,

e.g. 0.35 to that used for soybean oil. The thix-

otropy value of the emulsion-OL was similar to that

of commercial cream, which was slightly higher

than that of the emulsion-SO. The apparent viscos-

ity of emulsion-OL was lower than that of sample C,

and both the mean size value and the size range of

oil droplets were lower than those of sample C, and

these values were similar to those of commercial

cream. Figure 1 shows the particle size distributions

Fig. 1. The size frequency of the oil droplets in the

emulsions prepared using process whey protein

and soybean oil or olive oil

Emulsion-SO means the emulsion prepared using pro-

cess whey protein and soybean oil and Emulsion-OL

means the emulsion prepared using process whey protein

and olive oil.

The ratio of protein solution and oil was 1.0 : 0.35 (w/

w).

Details are shown in the footnote of Table 1.

(157) 35

J. Cookery Sci. Jpn. Vol. 34 No. 2 (2001)

of oil droplets in the emulsion-SO, the emulsion-OL, and the commercial cream. The particle size distri-

bution pattern of emulsion-OL was similar to that

of commercial cream, while that of emulsion SO

differed from the others. These findings indicate that emulsion-OL was composed of small oil dro-

plets that were similar to those of commercial cream. The physical and rheological behavior of the

emulsion appeared to depend on the oil droplet size and distribution that were influenced by the prop-

erties of the oil and PWP. The properties of the oil

depend on the fatty acid composition. Kimura et

al.") reported that oils and fats consisting of fatty acids with the longer carbon chains and/or the more

double bonds in the molecules gave the higher

specific emulsification capacity. The number of

double bonds greatly affected the emulsion capacity,

when the emulsion was prepared with bovine serum albumin and edible oils. The main fatty acids of

soybean oil are linoleic acid (18: 2, 55 . 6%) and

oleic acid (18 : 1, 22 . 7%) , and those of olive oil are linoleic acid (11.2%) and oleic acid (74 .4%)15). The

apparent viscosity of soybean oil is lower than that

of olive oil at 20°C"). These findings suggest that

emulsion-SO gives higher emulsification stability

than emulsion-OL. In the present study, however,

the mean size of oil droplets in emulsion-OL was smaller than that of emulsion - SO, and the

emulsification stability in emulsion-OL was higher

than that in emulsion-SO. In the commercial cream

the major oil was milk fat that is rich in palmitic acid (16 : 0) , oleic acid (18 : 1) , and stearic acid

(18 : 0) , while soybean oil is rich in linoleic acid

(18 : 2) and oleic acid (18 : 1) as shown above, and olive oil is primarily rich in oleic acid (18 : 1) . The difference in physical and rheological properties of

panna-cotta might be due to the differences in the fatty acid composition of these oils and fats. To

clarify this effect, an additional systematic study will be required. Another possible reason that

produced the different properties in the oil source is PWP. PWP has a distinct characteristic, including

interface activity5). The distinct adsorption charac-

teristics of PWP to the oil droplet may influence the stability of its emulsion. Although PWP is a soluble

protein, it was denatured completely by preheating and easily interacted with oil droplets to adsorb on

the oil droplet, which subsequently stabilizes the

emulsion. The difference in fatty acid composition

should make some difference to the adsorption characteristics. Another possibility is the contami-

nation of impurities in olive oil as a commercial

edible oil. If certain kinds of monoglycerides or

surface-active compounds were contained in the olive oil, these may have influenced the emulsion

properties. Further investigations are required to clarify the differences noted between SO and OL.

Triglyceride is intrinsically tasteless and odor-less, whereas autoxidative products of lipids induce

unfavorable odors even in edible oils and fats").

Autoxidation easily occurs in highly unsaturated

fatty acids including linoleic acid, which is the major fatty acid in soybean oil"), while less amounts

of unsaturated fatty acids are contained in olive oil

as show above. Olive oil is superior to soybean oil in

flavor due to this characteristic.

Sensory evaluation of the emulsion Sensory evaluation for the quality characteristics

of emulsion-SO, emulsion-OL, and the commercial

cream were carried out using the one-way layout

method (Table 2) . No difference between the emul-

sion-OL and the commercial cream was found in smoothness, and the emulsion-OL was whiter than

the commercial cream. Further more, differences in

the flavor and the overall acceptance were observed

between the emulsion-OL and the commercial cream. This may be due to the finding that the

emulsion-OL had a lower disagreeable flavor than

the emulsion-SO. By the Newell and MacFaleneis

test, some differences among emulsion-OL, emul-sion-SO, and the commercial cream were observed

(Table 2 (b)). However, as shown in Table 2 (c) , emulsion-SO was significantly less preferred to

emulsion-OL and the commercial cream. From

these findings, it has become clear that emulsion-OL would be acceptable as a cream-substitute with

heat-resistant properties.

Physical properties of panna-cotta Five types of panna-cotta were prepared accord-

ing to the recipes shown in Table 3. The control

36 (158)


Table 2. Sensory evaluations of cream, emulsion-SO , and emulsion-OL by the scoring method, the ranking

test, and the preference pair test

(a) Average scores by scoring method

(b) Ranking scores by ranking test

(c) Acceptable points by preference pair test

PWP and emulsion-SO, -OL : see footnote in 'Fable 1.

n=12.

(a) *p<0.05, F test.

(b) *p<0.05, **p<0.01, Newell & MacFarlane's table.

(c) ***p<0.001, pair test table.

panna-cotta contained both milk and cream. PWP was used in the other four types of panna - cotta

(SO-40, SO-45, OL-40, and OL-45) in which emul-sion-SO or emulsion-OL was used instead of milk

and cream. That is, SO-40 and SO-45 contained

10.4% and 11.7% soybean oil, respectively, and

OL-40 and OL-45 contained 10.4% and 11.7% olive oil, respectively. The panna-cotta samples prepared

with emulsion-SO or emulsion-OL (SO-40, SO-45,

OL-40, OL-45) retained a stable appearance, and

exuded no oil droplets after heating. The textural

parameters ; hardness, springiness, cohesiveness, and adhesiveness of the prepared panna-cotta sam-

ples are shown in Table 4. SO-40 (p<0.01) and SO-

45 (p <0.05) gave significantly high springiness

values compared with that of the control, and SO-40

showed a significantly (p <0.05) lower adhesiveness value than that of the control. However, all parame-

ters of OL-40 and OL-45 showed no significant

differences from those of the control.

Figure 2 and Table 5 show the creep parameters and strain ratios of the panna-cotta samples. The

creep behavior of the samples were analyzed using

a Voigt-body viscoelastic six-element mechanical

model consisting of Hookean instantaneous elastic-ity (E 0), two pairs of Voigt's retardation elasticity

(E 1, E 2), and retardation viscosity and instantaneous viscosity (77 1, 2, N). r 1 and r 2 are relaxa-

(159) 37


tion time. Table 4 shows that E 0, r 1, r 2, and 7/ N

in SO-40 and OL-40 were not different from those of

the control. However, E 1 and 2? 1 values of SO-40, SO-45, OL-40, and OL-45 were less than those of the

control by 24 to 52%. E 2 of SO-40 was a value as

low as 83% that of the control (r 2=131%) , while

OL-40 had a higher value than the control by 30%

(r 2 = 80%) . SO-40 and OL-40 gave similar physical

properties to those of the control except slight differences in the retardation elasticity (E 1, E 2)

and the retardation viscosity (77 1, 2? 2) . Further more, in both SO-45 and OL-45, the relaxation time

(r 1, r 2) and retardation viscosity value (2? 2) showed higher values than those of SO-40 and OL-

40. The contribution of Hookean instantaneous

elasticity, Voigt's viscoelasticity body, and the

Newtonian viscous body to the whole strain was

calculated in each sample (Fig. 2). In the case of the

control, 65%, 19%, and 16% of the strain are from

the Hookean body, Voigt body, and Newtonian body, respectively. The patterns of SO-40 and SO-

45 were different from those of the control, while

those of OL-40 and OL-45 were similar to those of

the control. In particular, the pattern of OL-40 was most similar to that of the control. This suggests

that the emulsion-OL had similar physical prop-

erties to those of the commercial cream. Similar

creep compliance curves (data not shown) to that of

the control were obtained except that the initial

Table 3. Recipes for panna-cotta

PWP : see footnote in Table 1.

Control : control panna-cotta.

SO-40, SO-45, OL-40, OL-45 : the panna-cotta prepared

using the emulsion from PWP and edible oil (soybean

oil ; SO, olive oil ; OL) for 40 or 45% of total weight.

Strain ratios (%)

0: hookean body, voigt body, [7: newtonian body.

Fig. 2. Strain ratios of panna-cotta Details of the samples are shown in the footnote

of Table 3. Measurement conditions are in the footnote of

Table 5.

Table 4. Textural parameters of panna-cotta

Textural parameters were measured with a texturometer (GTX-2 IN, Zenken Ltd.).

Details are described in the text.

1) See footnote in Table 3.

Each value represent "the mean±SD" calculated from 5 determinations (n=5). *p<0 .05, **p<0.01.

38 (160)


Table 5. Viscoelasticity of panna-cotta

Mechanical model and the viscoelasticity constant were determined using a

creep meter.

1) See footnote in Table 3.

Eo : instantaneous elasticity, El, F2: retardation elasticity, r, r 2: relaxation

time, 7)2 : retardation viscosity, 7)N: instantaneous viscosity.

Measurements were in triplicate.

Fig. 3. Confidence interval rating of sensory

attributes of panna-cotta

Details of the samples are shown in the footnote

to Table 3.

n=15.

F test, *p<0.05, **p<0.01.

slope of SO-45 was rather steeper than those of the

other samples including the control, meaning that SO-45 was softer than the others.

Sensory evaluation of panna-cotta

Figure 3 and Table 6 show the sensory evaluation

of five types of panna-cotta (SO-40, SO-45, OL-40, and OL-45, control) . Using the one-way layout

method (Table 6), significant differences (p <0.01)

were found between five samples in smoothness,

whiteness, flavor, gloss, and overall acceptance

except firmness. When compared with the control

(Fig. 3), significant differences (p <0.01) were ob-served in all attributes of SO-40 and SO-45. As for

OL-45, no significant difference (p<0.05) was ob-

served in any attributes except whiteness and gloss, while for OL-40, significant differences (p<0.05,

p<0.01) were shown except for flavor and overall acceptance. Judging from the physical properties,

OL-40 and OL-45 were quite similar to the control, while the sensory evaluation showed that OL-45

was the most similar to the control.

Effects of PWP

PWP is a denatured protein prepared by heating

whey protein isolate (WPI) at pH 7.0 at low ionic strength. PWP has a high surface hydropho-

bicity''''') and high emulsion stability. The physical

properties of the emulsion depend on the amount of PWP dissolved during the non-oil phase of the

emulsion8). The emulsion prepared with PWP and soybean oil or olive oil at the ratio of 1: 0.35 (w/

w) and heating (80°C, 30 min) without salt does not

form gels but gives a viscous liquid, which may give

(161) 39


Table 6. Analysis of variance in sensory attributes

of panna-cotta

n=15. **p<0 .01.

S: sum of squares, f: degrees of freedom, V: variance,

Fo : variance ratio.

the emulsion a creamy feeling in the mouth.

As ionic strength was sufficiently low in the emul-

sion-SO and the emulsion-OL to prevent the aggre-

gation of PWP, the formation of a gel network was

repressed even on heating. When gelatin and su-

crose were added to this emulsion of PWP heated

and than cooled, this emulsion was homogeneously

gelified by the effect of gelatin. The product

obtained had the property requisite for panna-cotta.

As a result, it was suggested that the physical

properties and feeling in the mouth of panna-cotta

appeared to be reflected by the characteristics of the

viscous solution of PWP. The interaction of PWP

with the network of gelatin may play an important

role for the properties of panna-cotta. This interac-

tion may influence the phase separation or forma-

tion of mixed gels of gelatin and PWP. Further

studies are required to clarify this effect.

From the above findings, the emulsion prepared

with PWP and olive oil will be used to make panna-

cotta in place of milk and commercial cream.

Summary

The possibility of a heat-stable substitute for

commercial cream using emulsions prepared at

different mixing ratios of process whey protein and

soybean oil or olive oil was investigated, and

panna-cotta was prepared using these emulsions. 1. The emulsion-OL prepared from process

whey protein and olive oil at a mixing ratio of 1.0:

0.35 (w/w) had the most similar properties to those of the commercial cream. The rheological prop-

erties of the emulsion-OL including the thixotropy

values and the particle size of oil droplets were

similar to those of the commercial cream, but the apparent viscosity and the size distribution pattern

of oil droplets of the emulsion were different from

those of the commercial cream.

2. The emulsion-OL prepared from process

whey protein and olive oil could be used as a substi-tute for commercial cream.

3. In panna-cotta using the emulsion prepared

from process whey protein and olive oil substituting

the milk and cream, no significant difference in the textural parameters (hardness, cohesiveness, sprin-

giness and adhesiveness) were found in comparison with the control in which milk and commercial

cream were used. In addition, the creep parameters were also similar to those of the control.

4. In the sensory evaluation using the one-way

layout method no differences were observed

between the panna-cotta made with the emulsion

prepared from process whey protein and olive oil and the control panna-cotta with regard to firmness,

smoothness, flavor, and overall acceptance.

Part of this study was published in the 1996 meeting of Japan Society of Cookery Science.

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(Received Jan. 27, 2000)

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改質乳清タンパク質とオリーブ油で調製した熱安定乳化物の特性

-クリームの代替およびパンナコッタへの利用-

古賀菱子　古賀貴子　杵川洋一　北畠直文

キーワード:乳清タンパク質,改質乳清タンパク質,乳化,加熱,クリーム,パンナコッタ

改質乳清タンパク質(乳清タンパク質を脱塩した状

態において,タンパク質濃度9%および90℃,30分間

予熱したもの)で調製した熱安定乳化物の流動特性お

よび官能特性を市販クリームと比較検討した。改質乳

清タンパク質および食用油で調製した乳化物は熱安定

性が高かった。改質乳清タンパク質およびオリーブ油

の割合が1.0:0.35で調製した乳化物は対照の市販ク

リームと近い特性を示した。これは改質乳清タンパク

質で調製した乳化物を新しいタイプのクリーム代替品

として用いることができるということを示唆してい

る。牛乳と市販クリームを改質乳清タンパク質とオリ

ーブ油で調製した乳化物を置き換えた場合 , 牛乳およ

び市販クリームで普通に調製したパンナコッタと同様

の特性のパンナコッタが得られた。

(2000年1月27日受理)

*i中村学園大学(〒814-Ol98福岡市城南区別府)

*2(株)第一化成R&Dセンター

*3京都大学食糧科学研究所

42(164)

Documents

and Its Practical Application to Panna-Cotta