preparation characteristics of water-in-oil emulsion using

© 2017 Japan Society for Food Engineering

Japan Journal of Food Engineering, Vol. 18, No. 2, pp. 103 - 111, Jun. 2017

◇◇◇ Original Paper ◇◇◇

(Received 6 Mar. 2017: accepted 16 May. 2017)

† Fax: +81-3-5707-1171 Ext. 5800; E-mail address: [email protected]

DOI : 10.11301/jsfe.17489

Preparation Characteristics of Water-in-oil Emulsion Using Olive Oil as a Continuous Phase in Microchannel Emulsification

Miki ITO1, Midori UEHARA1, Ryota WAKUI2, Makoto SHIOTA2, Takashi KUROIWA1,†

1Department of Chemistry and Energy Engineering, Faculty of Engineering, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya-ku, Tokyo 158-8557, Japan

2Milk Science Research Institute, Megmilk Snow Brand, Co., Ltd., 1-1-2 Minamidai, Kawagoe, Saitama 350-1165, Japan

We investigated the factors affecting preparation of water-in-oil (W/O) emulsions using olive oil as the continuous phase, based on direct observation of microchannel (MC) emulsification. Monodisperse droplets were produced using polyglycerin polycondensed ricinoleic acid ester (PGPR) as an emulsifier. The mean droplet diameter and the time required for droplet formation (droplet detachment time) increased with increased viscosity of the continuous phase. Emulsifier concentration af fects droplet formation, and stable emulsification was obser ved at PGPR concentrations exceeding 1wt％. Adsorption of PGPR was analyzed based on inter facial tension measurement with dif ferent measurement time scales. Monodisperse droplets with mean droplet diameters of 24 µm to 90 µm and coefficients of variation below 7％ could be produced using MC plates having dif ferent MC geometries. Furthermore, we demonstrated that droplet formation behavior differed with the addition of milk components (skimmed milk powder and whey powder) to the dispersed phase, based on high-speed observation of individual droplet formation.

Keywords: Microchannel emulsification, Water-in-oil emulsion, Olive oil, Food emulsion, Viscosity, Direct observation

1. Introduction

Emulsion is a quasi-stable dispersion system consist-

ing of two or more immiscible liquids, one dispersed as

small spherical droplets (dispersed phase) in the other

(continuous phase). Water-in-oil (W/O) emulsions

obtained by emulsification using oils as a continuous

phase have been utilized in various industries including

foods, cosmetics, and printing industries; for example,

butter and margarine are well-known W/O emulsified

foods [1-3]. Droplet diameters in W/O emulsified foods

usually lie between 100 nm and 100 µm depending on the

intended application.

W/O emulsions for food applications are generally pre-

pared by emulsification involving mechanical processes,

such as those using simple pipe flow, static mixers

(blenders), general stirrers, rotor-stator high-speed

mixers, colloid mills, high-pressure homogenizers, and

ultrasonic homogenizers, as well as preparation of oil-in-

water (O/W) emulsions with water as the continuous

phase [1-3]. Using these emulsification instruments,

direct observation of the emulsified mixture is not possi-

ble during the emulsification process. Thus, the effects

of type of continuous and dispersed phases, type of emul-

sifiers, and various operational parameters have been

evaluated based on empirical rules. However, there is lit-

tle information on emulsification characteristics of W/O

emulsions compared with those of O/W emulsions. In

fact, there are still many unclear points about operational

factors affecting physicochemical properties and product

quality during W/O emulsification. Therefore, optimum

conditions for practical W/O emulsification have been

determined using the trial-and-error approach.

In the last two decades, a microchannel (MC) emulsifi-

cation technique for preparing very uniform emulsion

droplets has been developed and investigated to extend

its application field [4-8]. In MC emulsification, droplets

are produced by pressing a dispersed phase into a con-

tinuous phase through MCs fabricated on single crystal

silicon, polymer, and stainless-steel plates. Unique emul-

sification mechanisms with an interfacial tension-driven

process have been characterized from both experimental

and theoretical approaches [9-12]. To date, various

examples of characteristics of MC emulsification have

Miki ITO, Midori UEHARA, Ryota WAKUI, Makoto SHIOTA, Takashi KUROIWA104


been demonstrated mainly for O/W emulsification [13-

19]. Since droplet formation can be observed directly

and individually using MC emulsification, it is advanta-

geous to characterize the behavior of the liquid and liq-

uid inter face during droplet formation in detail.

Uniformity in droplet size is also advantageous from the

viewpoint of emulsion stability [2, 20].

Several studies on the preparation of W/O emulsions

using various types of MC devices have been reported

[4, 21-27], although more studies have focused on O/W

emulsions. Applications for formulating uniformly sized

hydrogel microspheres [28-33] and giant lipid vesicles

[34-37] from monodisperse water droplets prepared

using MC emulsification have also been demonstrated.

However, in these studies, low-viscosity, non-food-grade

organic solvents such as hydrocarbons were often used

as the continuous phase solvent, and reports on W/O

emulsification using edible oils as a continuous phase are

still limited to a few cases [22-24]. Furthermore, few

reports address the influence of food ingredients added

to the aqueous phase on droplet formation with the inten-

tion of application for emulsion-based foods.

In this study, we evaluated the effect of process param-

eters in MC emulsification for preparing monodisperse

W/O emulsions on droplet formation in olive oil as the

continuous phase. The experimental results reveal the

effect of emulsifier type, viscosity of the continuous oil

phase, emulsifier concentration, type of MC plate, and

addition of food-grade ingredients to the dispersed water

phase. We believe that the results obtained here are use-

ful for understanding W/O emulsification characteristics

not only in MC emulsification but also in practical emul-

sification techniques, because we present information on

the relationship between the microscopic behavior of liq-

uids or liquid-liquid interfaces and physicochemical

properties of each component, providing the basis of

interfacial and microfluidic phenomena in W/O emulsifi-

cation in actual food systems. Although emulsification

mechanisms are dif ferent between MC emulsification

and other general emulsification methods, they include

two common processes: (1) creation of new oil-water

interfaces in very short time during droplet formation

and (2) stabilization of them by emulsifier adsorption

after the interface creation. Direct, high-speed observa-

tion and analysis of MC emulsification should bring new

findings about the behavior of the interface during vari-

ous emulsification operations.

2. Materials and methods

2.1 Chemicals

Olive oil, oleic acid, tetradecane, sodium chloride,

sodium caseinate (SC), sorbitan trioleate (Span 85), and

1,1,1,3,3,3-hexamethyldisilazane (HMDS) were pur-

chased from Wako Pure Chemical Industries, Co., Ltd.

(Osaka, Japan). Ethyl oleate and monoolein were pur-

chased from Tokyo Chemical Industry, Co., Ltd. (Tokyo,

Japan). Decaglycer yl penta oleic acid (PODG) was

donated by Nikko Chemicals Co., Ltd. (Tokyo, Japan).

Skimmed milk powder (SKM) and whey powder (WHP)

were obtained from Megmilk Snow Brand, Co., Ltd.

(Tokyo, Japan). Polyglycerin polycondensed ricinoleic

acid ester (PGPR) was obtained from Taiyo Kagaku Co.,

Ltd. (Yokkaichi, Japan). The water used in all experi-

ments was prepared using a Direct-Q water purified sys-

tem (Merck Millipore Corporation, Billerica, USA) and

had 18.2 MΩcm resistivity. All other chemicals were pur-

chased from Wako Pure Chemical Industries, Co., Ltd.,

and were of extra pure grade.

2.2 Preparation of W/O Emulsions using MC

Emulsification

W/O emulsions were prepared by MC emulsification

using a laboratory-scale MC emulsification setup at

room temperature. Three grooved silicon MC plates (two

cross-flow types (MC-A and MC-B) and one dead-end

type (MC-C)), glass plates, and stainless-steel modules

were purchased from EP-Tech (Hitachi, Japan). Figure 1

indicates the dimensions [13, 38] (MC depth (DMC), MC

width (WMC), and terrace length (LT)) of the MCs fabri-

Fig. 1 Schematic illustrations and digital microscope images of MC plates used in this study.

W/O emulsification using olive oil 105


cated on each silicon plate. The surfaces of the silicon

microchannel plates and the glass plate were originally

hydrophilic due to silanol groups on the surface of these

materials. To prepare W/O emulsions, the silicon MC

plates and the glass plates must be hydrophobic to avoid

wetting by the to-be-dispersed water phase [21].

Therefore, these plates were treated with HMDS to

obtain hydrophobic MCs, as described previously [31].

Olive oil, oleic acid, ethyl oleate, and tetradecane con-

taining emulsifiers were used as the continuous oil

phase. An aqueous solution of 0.2 M NaCl was used as

the dispersed phase unless otherwise specified. Both oil

and aqueous solutions were fed to the emulsification

module with an installed silicon MC plate and glass plate

using two syringe pumps. Figure 2 depicts droplet forma-

tion at the end of an MC [9,14]. The to-be-dispersed

aqueous solution that passed through the MC inflates in

a disk-like shape on a terrace filled with continuous oil

phase (inflation). When the dispersed phase reaches the

end of the terrace, it flows into the deep well and trans-

forms into a spherical shape (detachment). This transfor-

mation-detachment process was driven by interfacial

tension [9]. The emulsification behavior in the MC mod-

ule was observed from the bottom of the glass plate

using a microscope video system equipped with a digital

camera (Nikon 1 J1, Nikon, Tokyo, Japan) with a high-

speed recording mode.

Number-weighted mean droplet diameter (dm) was

determined from the measurement data obtained by

measuring the diameters in the captured images of at

least 100 droplets using Microsoft PowerPoint software.

The coefficient of variation (CV) was calculated based on

the following equation:

CV ＝ σ/dm × 100 (1)

where σ is the standard deviation of droplet diameter.

2.3 Physical Property Measurements

2.3.1 Viscosity measurement

Viscosities of both the continuous phase and the dis-

persed phase were measured using a vibrational viscom-

eter (SV-10, A&D, Tokyo, Japan). The temperature of

the sample was adjusted to 25℃ using a sample chamber

with a water-circulating constant-temperature bath.

2.3.2 Interfacial tension measurement

Interfacial tension was measured at ambient tempera-

ture by the pendant drop method using an automatic

inter facial tensiometer (DM-301, Kyowa Inter face

Science Co., Ltd., Niiza, Japan). The time required to

form the pendant just before detaching from the bottom

edge of the needle was set to 5 s (short-time measure-

ment (STM)) or 90 s (long-time measurement (LTM)).

After the pendant drop formed, its image was captured,

and interfacial tension was obtained using image analysis

software FAMAS (Kyowa Interface Science Co., Ltd.,

Niiza, Japan). Each measurement was repeated at least

10 times, and the calculated mean values and standard

deviation were used. Prior to measurement of interfacial

tension, the density of each sample solution was deter-

mined using pycnometers.

3. Results and discussion

3.1 Effect of Emulsifier Type

First, the effect of the type of emulsifier added to the

continuous olive oil phase was investigated. Here, a

dead-end plate with MC-C was used. This plate had long

terraces (57 µm) and a simple flow-path structure, thus

it should be suitable for analyzing emulsification charac-

teristics. Olive oils containing monoolein, PODG, Span

85, or PGPR at a concentration of 3wt％ were used as the

to-be-continuous phase. Aqueous solution containing 0.2 Fig. 2 Schematic illustrations of droplet formation at the end of

an MC.



M NaCl was used as the to-be-dispersed phase since

typical W/O emulsion foods such as butters, margarines

or fat spreads contains NaCl. In addition, osmotic pres-

sure of the dispersed phase is an important factor and at

least 0.42 MPa is necessary for stable production of W/O

emulsions [23]. Osmotic pressure of 0.2 M NaCl solution

was calculated as 1.1 MPa using the van’t Hoff equation

[32], thus the osmotic pressure was sufficient to achieve

stable emulsification. Photomicrographs of emulsifica-

tion in each case are depicted in Fig. 3. The water phase

continuously flowed out from the end of the MC or water

droplets coalesced immediately after formation when

monoolein (HLB＝3.8 [39]), PODG (HLB＝3.5, informa-

tion from supplier), or Span 85 (HLB＝1.8 [31]) were

used, while uniform 90-µm-diameter water droplets

were generated when PGPR (HLB<1 [23]) was used as

an emulsifier. Similar results were obtained using MC-B

(data not shown) although the produced droplets were

3.2 Effect of Continuous Phase Solvent

The viscosity of the continuous phase generally affects

d r o p l e t f o r m a t i o n d u r i n g M C e m u l s i f i c a t i o n

[16,17,21,23,24]. For W/O emulsification using vegetable

oil as the continuous phase, the viscosity of the continu-

ous phase (ηc ) is several ten times higher than that of

the dispersed water phase (ηd). Indeed, the viscosity of

olive oil used in this study exceeds 60 mPa s, which is

much higher than the viscosity of water. Thus, water

droplet formation in continuous olive oil phase differs

from that of oil droplet formation in the continuous water

phase in O/W emulsification, in which the viscosity of

the dispersed oil phase is higher than that of the continu-

ous water phase. In previous studies on preparation of

W/O emulsion using MC emulsification, various organic

solvents with low viscosity (e.g., low molecular weight

hydrocarbon) were used as the continuous phase, while

reports of W/O emulsification using a highly viscous oil

phase such as vegetable oils are limited. Thus, we stud-

ied the effect of the type of oil phase with various viscosi-

ties on the formation of water droplets during MC emul-

sification. Here, we used tetradecane, ethyl oleate, oleic

Fig. 4 Emulsif ication using dif ferent continuous phases containing 3wt% PGPR. (a) tetradecane. (b) ethyl oleate. (c) oleic acid. (d) olive oil. (e) Effect of viscosity ratio (ηd /ηc ) on mean droplet diameter (dm) and detachment time (td).

Fig. 3 Emulsi f icat ion using dif ferent emulsi f iers in the continuous phase (olive oil). (a) monoolein. (b) PODG. (c) Span 85. (d) PGPR. Concentration of emulsifiers was 3wt％.

smaller than those obtained using MC-C. In previous

studies [22,23,25], good ability to stabilize W/O emul-

sion droplets was also reported for PGPR. Since PGPRs

are polymeric (M.W. ～2,000) and extremely lipophilic

emulsifiers (HLB<1 [23]), their emulsifying ability might

be attributed to their unique molecular structure. As

mentioned in a previous report [40], polymeric hydro-

phobic surfactants can form a viscoelastic adsorbed layer

at an oil-in-water interface, which is preferable to stabi-

lize W/O emulsions. Thus, we used PGPR as the emulsi-

fier in the following experiments.



acid, and olive oil with 3wt％ PGPR as the continuous

phase. As illustrated in Figs. 4a through d, uniform water

droplets could be produced in all cases tested, while the

formed droplet diameter depended on the oil phase.

Figure 4e depicts the effect of the viscosity ratio of the

phases (ηd /ηc ) on droplet formation. Mean droplet

diameter, dm, increased with decreased viscosity ratio,

and dm in the olive oil system with the lowest viscosity

ratio reached 1.8 times that in the tetradecane system

with the highest viscosity ratio. This tendency agreed

with the results reported previously [21,23,24], although

the obtained droplet diameters were larger than those

expected from the correlation between viscosity ratio

and normalized channel diameter [23,33]. In addition,

droplet detachment time (td: time needed for detach-

ment) decreased with increased viscosity ratio (Fig. 4e).

When the viscosity of the continuous phase is higher, the

flow of the continuous phase from the well into the ter-

race to divide the to-be-dispersed phase becomes

slower, resulting in longer droplet detachment time and

larger droplet diameter [14]. Direct observation of the

MC part during emulsification with a high time resolu-

tion facilitated determination of the unique characteris-

tics of emulsification using olive oil as the continuous

phase, as described above.

3.3 Effect of Emulsifier Concentration

Figure 5 depicts emulsification at different emulsifier

(PGPR) concentrations in the continuous olive oil phase.

At 0.1wt％ PGPR concentration (Fig. 5a), continuous flow

out of the to-be-dispersed water phase and immediate

coalescence of generated droplets were observed. Thus,

it was impossible to produce W/O emulsions stably. At

0.5wt％ (Fig. 5b), water droplets were obtained at the

downstream of MCs, but the CV value of droplet diame-

ter was higher (12.1％) than those obtained at higher

PGPR concentrations. At 1.0 and 3.0wt％ PGPR concen-

trations (Figs. 5c and d), uniform water droplets

(CV<6％) with dm of 90 µm were obtained. These results

were attributed to the interfacial activity of PGPR at dif-

ferent concentrations. Therefore, we investigated the

interfacial tension between the water phase and the oil

phase containing different concentrations of PGPR.

Figure 6 plots interfacial tension measured using the

pendant drop method via two dif ferent procedures:

quasi-equilibrated pendant drops formed quickly (within

5 s (STM)) and slowly (within 90 s (LTM) just before fall-

ing from the bottom edge of the needle. The interfacial

tensions obtained using both procedures decreased with

increased PGPR concentration, although the values in

STM were significantly higher than those in LTM at all

PGPR concentrations tested. This result indicates that

adsorption takes at least several tens of seconds to reach

equilibrium, which is much slower than droplet detach-

ment (100 ms (Fig. 4e)). In fact, based on the Wilke-

Chang correlation [41], estimated diffusivity of PGPR in

olive oil is less than 1/10 that of sodium dodecyl sulfate

in water. Therefore, unstable emulsification at low PGPR

concentration is due to insufficient adsorption of PGPR

molecules at the newly created (expanding) oil-water

interface during droplet formation at the end of the MC

[15]. Detailed analysis on the relationship between the

rates of interface expansion and emulsifier adsorption is

a subject of future investigation.Fig. 5 Effect of PGPR concentration in olive oil on emulsification.

PGPR concentration: (a) 0.1wt％, (b) 0.5wt％, (c) 1wt％, (d) 3wt％.

Fig. 6 Effect of PGPR concentration on the interfacial tension obtained in STM and LTM.



3.4 Effect of MC Structure

Figure 7 presents the results of MC emulsification

using three different MCs (MC-A, B, and C). These

MCs had different geometries (e.g., channel width, chan-

nel depth, and terrace length (Fig. 1)), which affected

droplet diameter in MC emulsification [13,42]. Olive oil

containing 3wt％ PGPR was used as the continuous

phase, and water containing 0.2 M NaCl was used as the

dispersed phase. Successful emulsification producing

uniform water droplets was observed using all types of

MC. The mean diameters were 24 µm for MC-A, 45 µm

for MC-B, and 90 µm for MC-C; and the CV values were

below 7％ in all cases. These results suggest that the

droplet diameter in W/O emulsions can be controlled

using appropriate MCs.

3.5 Effect of Component Added to the

Dispersed Phase

Actual emulsion foods contain various hydrophilic

materials in their aqueous phases, such as milk compo-

nents consisting of proteins and carbohydrates. Thus,

the effect of adding milk components to the to-be-dis-

persed water phase on emulsification was investigated to

evaluate emulsification characteristics in a food-simulat-

ing system. Here, we used food-grade SKM and WHP as

milk components. Figure 8 presents photomicrographs

Fig. 7 Photomicrographs (a, c, e) and number-weighted droplet diameter distributions (b, d, f) of W/O emulsion prepared by MC emulsification using (a, b) MC-A, (c, d) MC-B, and (e, f) MC-C. PGPR concentration in olive oil was 3wt％.

Table 1 Effect of the composition of to-be-dispersed water phase on MC emulsificationa.

System To-be-dispersed water phase ηd [mPa s]b γ[mN/m]bEmulsification results

Behavior dm [µm] CV [％] td [ms]

A 0.2 M NaCl aq. 0.91 11.1±1.5c Sd 98.7 3.3 101±16.1c

B 1wt% SKM/0.2 M NaCl aq. 1.01 7.3±0.58c Sd 85.3 6.6 119±13.0c

C 1wt% WHP/0.2 M NaCl aq. 0.94 6.8±0.54c FOe －－－

D 0.3wt% SC/0.2 M NaCl aq. 0.93 7.1±0.15c Sd 89.7 5.8 129±23.0c

a Olive oil containing 1wt％ of PGPR was used as the to-be-continuous phase.b Data obtained at 25℃c Mean value ± standard deviation.d “S”: Successful emulsification for generating monodisperse water dropletse “FO”: Water phase was flowed out continuously from MC.

Fig. 8 Emulsification using 0.2 M NaCl aq. (a) with no milk components (system A in Table 1), (b) with 1wt％ SKM (system B), or (c1, c2) with 1wt％ WHP (system C) as the to-be-dispersed phase.



of emulsification with MC-C using olive oil containing

1wt％ PGPR as the continuous phase. As described in

section 3.3, successful emulsification was carried out

using 0.2 M NaCl solution without any milk components

as the to-be-dispersed phase (Fig. 8a). When 1wt％

SKM was added to the water phase, uniform droplet for-

mation could be achieved (Fig. 8b), although it became

unstable at several MCs after a few hours. When 1wt％

WHP was added, the water phase continuously flowed

out at the end of all but a few MCs (Figs. 8c1 and c2).

SKM contains 30wt％ casein proteins and 5wt％ of whey

proteins, whereas WHP contains 12.5wt％ of whey pro-

teins and no casein proteins. Instability of SKM-added

system after a few hours might be due to partial adhe-

sion of the water phase on MC walls caused by non-

casein components such as whey proteins as described

in the following high-speed analysis of emulsification.

We also examined the addition of SC as a model milk

component to the water phase. The results are summa-

rized in Table 1. Emulsification in the SC-added system

was similar to that in the SKM-added system. When

SKM or SC was added to the water phase, the mean

droplet diameter decreased slightly, and the detachment

time increased 20 to 30％ over that of the system without

any milk components.

Figure 9 depicts successive photomicrographs of to-

be-dispersed phases on the terrace during droplet for-

mation taken using the high-speed mode (1250 frames/

s) of a digital camera attached to the microscope system

in the MC experiment setup. The to-be-dispersed aque-

ous solution passed through an MC inflated on the ter-

race in a disc-like shape during inflation. The aqueous

solution reached the end of the terrace, then flowed into

the deep well, and transformed into a spherical droplet

via detachment. The images in Fig. 9 depict differences

in the shape of the aqueous phase just detaching: the

positions of the “neck” at which the to-be-dispersed

phase was divided to generate a droplet [11,12] shifted to

the well-side end of the terrace, compared with the case

without milk components (dashed line). Since adding

milk components affected both the viscosity of the water

phase and interfacial tension (Table 1), physical proper-

ties of the system might be attributed to the change in

droplet formation at the end of the MC. Above results

could be explained qualitatively by the decreased mobil-

ity of the to-be-dispersed phase, which caused changes

in droplet diameter, detachment time, and detachment

length [14,16]. Furthermore, for the WHP-added sys-

tem, the interfacial shape of the detaching water phase

was asymmetric to the center line of the MC, due to par-

tial adhesion and wetting by the to-be-dispersed water

phase [15]. This result also supports the instability of the

WHP-added system with a high risk of flowing out due

to wetting of the MCs. To clarify the mechanisms of

instability in the presence of milk components, further

investigation, including precise evaluation of interfacial

properties, must be carried out.

4. Conclusions

We investigated factors affecting the preparation of W/

O emulsions based on direct observation of emulsifica-

tion by MC emulsification using olive oil as the continu-

ous phase. The findings in this paper are summarized as

follows.

(1) PGPR was a good emulsifier for producing monodis-

perse W/O emulsions using olive oil as the continu-

ous phase solvent.

(2) Increased viscosity of the continuous phase increased

droplet diameter and droplet detachment time.

(3) Adsorption of the emulsifier to the interface takes a

long time compared to the time scale for droplet for-

mation.

(4) Monodisperse droplets (CV<7％) with 24 µm to 90

µm mean diameter could be produced selectively by

choosing MC plates having different geometries.

(5) Adding milk components SKM and WHP to the dis-

persed phase affected droplet formation, including

microscopic flow at the end of the MC, indicating

Fig. 9 Photomicrographs of droplet generation taken using high-

speed mode (1250 frames/s). Photo (A) corresponds to System A; (B) corresponds to system B; (C) corresponds to system C, and (D) corresponds to system D in Table 1. The dashed line represents the position of the “neck” in system A.



changes in interfacial properties with the addition of

milk components.

As mentioned in the Introduction section, few studies

have focused on the detailed process of droplet forma-

tion in W/O emulsions. In particular, information on

experiments using food-grade materials is limited. We

believe that our findings provide the scientific basis for

clarification of W/O emulsification, as well as various

empirical factors to control product quality at actual man-

ufacturing sites.

Nomenclature

CV : coefficient of variation, ％

DMC : channel depth, µm

dm : mean droplet diameter, µm

LT : terrace length, µm

td : droplet detachment time, s

WMC : channel width, µm

γ : interfacial tension, mN s-1

ηc : viscosity of the continuous phase, mPa s

ηd : viscosity of the dispersed phase, mPa s

σ : standard deviation of droplet diameter, µm

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オリーブ油を連続相とするマイクロチャネル乳化における油中水滴エマルションの作製特性

伊藤美希 1，上原緑 1，泉井亮太 2，塩田誠 2，黒岩崇 1,†

1 東京都市大学工学部エネルギー化学科 , 2 雪印メグミルク株式会社ミルクサイエンス研究所

エマルションとは，水と油のような互いに混ざり合わない 2つの液体の一方が他方の液体中に準安定的に分散している状態を指し，食品，化粧品，塗料など幅広い分野で利用されている．油を連続相とした乳化によって得られる油中水滴型（W/O）エマルションからなる乳化食品としてはバターやマーガリンに代表されるように広く利用されているものの，水を連続相とする水中油滴型（O/W）エマルションに比べ詳細な研究データに乏しく，W/Oエマルションの製造工程における乳化挙動や製品品質に影響する乳化特性については不明な点が多い．本研究では，オリーブ油を連続相としたマイクロチャネル (MC)乳化によるW/Oエマルションに作製に対する影響因子について，乳化挙動の直接観察に基づき実験的に検討した．種々の乳化剤を用いて乳化剤実験を行った結果，ポリグリセリン縮合リシノレートを用いた場合に均一性の高い液滴を作製できた．オリーブ油および種々の溶媒を連続相とした乳化実験から，連続相の粘度が高いほど液滴径が大きくなり，粘度の上昇に伴い 1つの液滴形成に要する時間（液滴離脱時間）が長くなるこ

とを明らかにした．さらに，界面張力の時間変化に関する検討の結果，乳化剤が界面に吸着する過程は液滴形成過程に比べてはるかに長い時間を要するプロセスであることを示し，合わせて乳化剤濃度が液滴形成に及ぼす影響についても考察した．また，形状の異なる 3種類のMC基板を用いてMC乳化を行ったところ，平均液滴径が約 24 µmから 90 µmにわたる均一な液滴を生成することができた．続いて，実際の乳化食品を模擬した検討として，分散相に乳由来成分を添加しMC乳化を行い，脱脂粉乳やホエイパウダーなどの添加により液滴形成挙動が変化することを示した．これまでに，W/O乳化物における液滴形成過程を詳

細に検討した例は少なく，とくに食品グレードの材料を用いた研究は情報が不足していた．本研究は，オリーブ油を連続相とする W/O界面の挙動について MC乳化を通じて詳しく検討することで，食用 W/Oエマルションの形成に及ぼす諸因子の影響について報告したものである．示された検討結果は実際の食品製造現場における様々な経験的制御因子を理解する上で有用な情報を提供すると期待される．

（受付 2017年 3月 6日 , 受理 2017年 5月 16日）

1 〒 158-8557　東京都世田谷区玉堤 1-28-1

2 〒 350-1165　埼玉県川越市南台 1-1-2

† FAX: 03-5707-1171, E-mail: [email protected]

◇◇◇ 和文要約 ◇◇◇

「日本食品工学会誌」, Vol. 18, No. 2, p. 113, Jun. 2017

preparation characteristics of water-in-oil emulsion using

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