Syrup Ingredient and Thermoplastic Resin Contact

Materiaru Raifu Gakkaishi, Vol.28, No.3 51

マテリアルライフ学会誌（Materiaru Raifu Gakkaishi），28［3］51～61（Oct. 2016）

Syrup Ingredient and Thermoplastic Resin Contact : Influence on Resin Physical Properties and Syrup Taste

Tetsuya YAMAMOTO*1, Takuya HAMAZAKI*2, Yasuo KAZUMA*3, Minoru INAGAKI※*2

(Received June 27, 2014, Revised August 1, 2016, Accepted October 13, 2016)

Abstract　To evaluate functional component durability of valves and nozzles in cup-dispensing vending machines and drink dispensers, three thermoplastic resin types (linear low density polyethylene (LLDPE), polyoxymethylene (POM) and polyamide 612 (PA612)) used as such components were soaked in various syrups differing in ingredient composition (citric acid, ascorbic acid, ethanol, sucrose, and limonene) and the influence on resin physical properties and syrup taste were investigated. We found that syrups have the ability to alter the physical properties of the resin, such as tensile strength, elongation, and elasticity, while simultaneously, resins have a negative effect on syrup taste. In relation to LLDPE, swelling of the resin and a remarkable drop in tensile strength were observed in case of soaking in the syrup containing limonene. In the case of PA612, the physical properties of the resin underwent significant changes with respect to swelling, tensile strength, elongation and elastic modulus. POM soaked in ethanol showed swelling and lower elastic modulus. Furthermore, syrup taste changed considerably when in contact with POM for syrups containing both ethanol and citric acid. This study revealed the importance of choosing suitable resins for syrup ingredients to improve the durability of parts and quality of drinks.

Keywords : Thermoplastic resin, Molded resin, LLDPE, PA612, POM, Concentrated beverage syrup, Cup-dispensing vending machine, Drink dispenser, Unpleasant taste

Abbreviations : LLDPE, Linear low density polyethylene ; PA612, Polyamide 612 ; POM, Polyoxymethylene ; AsA, Ascorbic acid ; GC/MS, Gas chromatography/mass spectrometry.

Original Paper

1. Introduction

Industrial cup-dispensing beverage vending machines and

beverage dispensers store refreshing and alcoholic beverages

as a concentrated syrup. The concentrated syrup is diluted

with hot or cold water before being dispensed to the customer

as a final product. Thus, the syrup directly comes into contact

with the functional components of the machine, to include the

storage tank, tubing, valves and nozzles1). The components of

the machine are commonly prepared by several crystalline

thermoplastic resin types, because of their advantages in

chemical resistance and workability during the injection and

extrusion molding process. Syrups contain various ingredient

types : acidulants, alcohols, sweeteners, dispersants, fra-

grances and preservatives, often possessing acid, hydroxyl,

olefin and hydrocarbon functional groups. Accordingly, syr-

ups may interact with the resins, altering their physical prop-

erties, such as dimension, weight, strength, elongation, rigid-

ity, hardness and color stability. Concomitantly, the resin

leaches various substances into the syrup, impacting the bev-

erage taste. Low usage rates of the machines result in ex-

tended contact time between the resin and syrup, further in-

※

*1

*2

*3

Corresponding authorDevelopment Division, Food & Beverage Distribution Busi-ness Group, Fuji Electric Co., Ltd.(Fuji 1-27, Yokkaichi, Mie 510-0013, Japan)Department of Life Science, Faculty of Bioresources, Mie University(Kurima-Machiya 1577, Tsu, Mie 514-8507, Japan)Department of Technical Development, Sanpho Chemical Co., Ltd.(Yamanokami 297-10, Ota, Gunma 379-2302, Japan)

マテリアルライフ学会誌 2016 年 10 月52


creasing the risk. The resin and the syrup undergo mutual

interactions ; therefore, studying the resin–syrup interaction

is crucial to improving the functional components of beverage

vending machines and beverage taste. Herein, we investigat-

ed the influence of resin soaking in water and/or concentrated

syrups of varying compositions2)-4) to determine how the

physical properties of the resin change and impact beverage

taste.

2. Methods and materials

2. 1 Beverage syrup and molded resin sample compositions

As ingredients of beverage syrups, citric acid, L-(+)-ascor-

bic acid (AsA), ethanol, sucrose, and (R)-(+)-limonene were

purchased from Wako Pure Chemical Industries (Osaka, Ja-

pan). The formulations and abbreviated syrup names are sum-

marized in Table 1.

Resin plates (88×49 mm, 2.5 mm t) and dumbbell speci-

mens (No. 1A, JIS K 7162)5) were prepared by injection mold-

ing using the following base resins : linear low density poly-

ethylene (LLDPE, Evolue SP2540, cast film grade, Prime

Polymer, Tokyo, Japan), polyamide 612 (PA612, Zytel 151L,

standard grade, Du Pont, Tokyo, Japan), and polyoxymeth-

ylene (POM, Duracon M90S, standard grade, Polyplastics,

Tokyo, Japan) without a parting agent. Maximum molding

operating temperatures to manufacture the resin plates were

240℃ (LLDPE), 245℃ (PA612), and 200℃ (POM), respec-

tively.

2. 2 Taste evaluation of soaked syrup molded resin samples

Twenty molded resin plates (88×49 mm, 2.5 mm t) were

soaked in syrups (300 mL, Table 1) at 37℃ for 336 h (14

days) in a sealed glass container. The ratio of the plate surface

area to the syrup volume was 6.25 cm2/mL. The soaked syrup

was cooled to room temperature, diluted six times with puri-

fied Milli-Q water (Millipore Japan, Tokyo, Japan), and sub-

mitted to a sensory test. In this study, both oral and odor sen-

sory receptors define taste when a sample solution was orally

consumed. A series of diluted samples was presented to

trained panelists who were instructed to taste three samples.

Each set of experiments consisted of one sample cup and two

control specimens at room temperature6). For tests comprising

10 panelists, the impact of taste is evaluated as significant

(significance level 5%), when the average rating exceeds

70%. The taste rating scale is a function of the degree of un-

pleasantness observed and is defined over six levels : 0, no

observable unpleasantness ; 1, slightly unpleasant ; 2, mildly

unpleasant ; 3, moderately unpleasant ; 4, unpleasant ; and

5, very unpleasant7). The taste rating was calculated by aver-

aging the reported values from the panelists. If panelists could

not differentiate the sample cup from the control cups, the rat-

ing value reported by the panelist was counted as zero. Ten

panelists were randomly selected from the top 50 candidates

who had been trained and selected from 215 employees based

on sensory test scores from a previous test8) using compounds

that contribute to the five fundamental specific tastes : su-

crose (sweet), sodium chloride (salty), tartaric acid (sour),

Table 1　Testing syrup used in this study

a C: Citric acid, A : L-(+)-Ascorbic acid, E : Ethanol, L : (R)-(+)-Limonene, S : Sucrose.b Purified water prepared by the Milli-Q system (Millipore Japan, Tokyo, Japan) was used as control and dilution of solutes.


Tetsuya YAMAMOTO, Takuya HAMAZAKI, Yasuo KAZUMA, Minoru INAGAKI

quinine sulfate (bitter), and sodium glutamate (umami). The

age of the participants ranged from 19 to 45 years old (mean,

28 years old).

2. 3 Physical property measurement of syrup soaked resin

samples

No. 1A dumbbell specimens (JIS K 7162) were soaked in

concentrated syrups at 37℃ for up to 1344 h (56 days) in a

sealed glass container. Tensile strength at break (MPa), ten-

sile yield stress (MPa), ultimate elongation at break (%), and

elastic modulus (MPa) were measured according to the Japa-

nese Standards Association JIS K 71625) using an RTF-1350

auto graph (A&D, Tokyo, Japan) with an elongation rate of

100 mm/min (LLDPE), 20 mm/min (PA612), and 10 mm/min

(POM). Hardness (Hs Duro A) was measured according to

JIS K 72159). Color difference (CIE L*a*b, reflection) was

measured according to JIS Z 872210) and JIS Z 872911). All

parameters were obtained from five independent measure-

ments (n＝5) with standard deviations.

2. 4 GC/MS analysis of resin soaked syrups

Twenty molded plates (88×49 mm, 2.5 mm t) were soaked

in concentrated syrups (300 mL, Table 1) at 37℃ for 336 h

(14 days) in a sealed glass container. After cooling to room

temperature, the soaked syrups were extracted three times

with dichloromethane (40, 30, and 20 mL). Sodium chloride

was added to a separating funnel for syrup extraction contain-

ing ethanol. The combined extract was dried by sodium sul-

fate, and concentrated under reduced pressure at 30℃ to ca.

1 mL. The concentrated residue was re-diluted to a fixed vol-

ume with dichloromethane and analyzed by GC/MS [Shimad-

zu GC-17 ; column, DB-1 (0.32 mm I.D., 30 m length, 0.25-

µm thickness), GL Science Co. Tokyo]. The GC analysis

method is as follows : injection oven, 250℃ ; column oven,

40℃ (maintained for 3 min) elevated to 250℃ (10℃/min) ;

carrier gas, He (10 mL/min) ; splitting ratio, 6.0 ; GC inter-

face, 250 ℃, (Shimadzu QP-5050A) ; acceleration voltage,

1.6 kV ; detected by scan mode at mass range 45-500 m/z.

3. Results and discussion

3. 1 Syrup composition influence on LLDPE resin physi-

cal properties and resulting syrup taste

LLDPE samples were soaked for 14 days in syrups of vary-

ing concentration. The soaked syrups were diluted six times

with purified water, and evaluated to the sensory test (Table

2). All taste ratings of soaked syrups containing ethanol (syrup

E, CE, AE, and LSE) have values above 1.0. This taste range

indicates differences between the soaked syrup and the con-

trolled syrup, as the panelists identified significant differences

during the sensory test. The majority of panelists indicated

the taste of “Resin” in syrups soaked in LLDPE. Conversely,

the taste ratings of soaked syrups A and C had values below

1.0, which contained only individual single ingredients of cit-

Table 2　Taste of syrup after soaking with LLDPEa

a LLDPE was soaked with testing syrup at 32℃ for 14 days.Then the syrup was diluted 6 times with purified water and submitted to the sensory test.b ( ) : Number of indicated counts by panelists in the sensory test.



ric acid or ascorbic acid. Soaked syrups were extracted with

dichloromethane, and the extracts analyzed by GC/MS. Di-

tert-butylated hydroxytoluene (BHT), fatty acids, and hin-

dered phenols were detected in soaked syrups containing

ethanol (E, CE, AE, and LSE), and are considered to be at-

tributable to the unpleasant taste (Table 3).

The physical properties of LLDPE dumbbells soaked in

syrups for up to 56 days are shown in Fig. 1. In contrast to the

taste rating, the physical properties of LLDPE were not sig-

nificantly affected by syrups containing ethanol (E, CE, AE,

and LSE). However, with respect to syrups containing limo-

nene (LSE), dimensions and weight evidently increased (Fig.

1A and 1B), while tensile strength, elastic modulus, and hard-

ness decreased (Fig. 1C, 1E and 1F).

The above experimental results indicate ethanol as a key

factor impacting syrup taste, and the physical properties of the

LLDPE resin were affected by the presence of limonene.

Swelling of LLDPE by syrups containing ethanol resulted in

low molecular weight additive elution and spoiling of the syr-

up taste. Extreme swelling of LLDPE by syrups in the pres-

ence of limonene affected various physical properties.

3. 2 Syrup composition influence on PA612 resin physical

properties and resulting syrup taste

The sensory test results for soaked syrups in the presence of

the PA612 resin are shown in Table 4. Taste ratings of soaked

Table 3　Substances detected in the soaked syrup with resin by GC/MSa

a The resin was soaked with the syrup for 14 days at 37℃.b (s) : The compounds which were detected as strong TIC peak in the soaked syrup.

Table 4　Taste of the syrup after soaking with PA612a

a PA612 was soaked with syrup at 32℃ for 14 days. Then the syrup was diluted 6 times with purified water and submitted to the sensory test. b ( ) : Number of indicated counts by panelists in the sensory test.



Fig. 1　Change of physical properties of LLDPE during the soaking with syrup containing various ingredients.(A) Stability of dimension, (B) Weight, (C) Tensile strength, (D) Ultimate elongation, (E) Elastic modulus, (F) Hardness, × : Water (Control), ○ : Citric acid (C), △ : Ascorbic acid (AsA), □ : Ethanol (E), ● : Citric acid and ethanol (CE), ▲ : Ascorbic acid and ethanol (AE), ◆ : Limonene, sucrose, and ethanol (LSE).



Fig. 2　Change of physical properties of PA612 during the soaking with syrup containing various ingredients.(A) Stability of dimension, (B) Weight, (C) Tensile strength, (D) Ultimate elongation, (E) Elastic modulus, (F) Hardness, (G) Color difference, × : Water (Control), ○ : Citric acid (C), □ : Ethanol (E), ● : Citric acid and ethanol (CE), ▲ : Ascorbic acid and ethanol (AE), ◆ : Limonene, sucrose, and ethanol (LSE).



syrups containing ethanol (E, CE, AE, LSE) ranged above

1.0, while syrups containing only the individual single ingre-

dients, ascorbic acid or citric acid (A and C), ranged below

1.0. The results are similar to the case of LLDPE. The major-

ity of panelists indicated the taste of “Resin”, “Bitter”, and

“Sour” in syrups soaked in PA612 ; however, the tastes were

different from those of LLDPE.

The physical properties of PA612 dumbbells soaked in syr-

ups up to 56 days are shown in Fig. 2. The parameters were

significantly affected in the cases of syrups containing ethanol

(E, CE, AE, and LSE). Dimensions and weight increased

(Fig. 2A and 2B), and hardness decreased (Fig. 2F) in the

presence of ethanol (E, CE, AE, LSE). The degree of change

in the parameters were much more intense in PA612 com-

pared with those in LLDPE. However, ultimate elongation

increased Fig. 2D), and tensile strength and elastic modulus

degreased (Fig. 2C and 2E) across all concentrated syrups.

Furthermore, a similar influence was also observed for PA612

resin samples even when soaking in purified water (Control).

Accordingly, water absorption within hydrophilic amidogen

affects the physical properties of PA612. The degree of pa-

rameter change of syrups containing limonene (LSE) was in-

significant in PA612. The color of the molded plate turned

brown from initial white after contacting the AsA syrup for 56

days (Fig. 2G). The above experimental results indicate etha-

nol as a key factor impacting syrup taste in the case of PA612.

3. 3 Syrup composition influence on POM resin physical

properties and resulting syrup taste

The results of the sensory test of POM soaked syrups are

shown in Table 5. Although the taste ratings of syrups con-

taining only one single ingredient of citric acid or ethanol (C,

E) ranged below 1.0, the corresponding syrups containing

both citric acid and ethanol (CE) ranged over 1.0. This phe-

nomenon strongly indicates the effect of the citric acid–etha-

nol interaction towards POM. The acidic compounds, AsA

and citric acid, did not show such phenomenon even in the

cases of the syrup containing AsA and ethanol (AE). Addi-

tionally, the citric acid–ethanol interaction was not observed

in other syrup and resin (LLDPE, PA612) samples. The ma-

jority of panelists indicated the taste of “Resin” and “Sour” in

syrups soaked with POM, and further indicated a clear distinc-

tion in taste compared with formaldehyde generated by the

deterioration of the POM polymer. Furthermore, GC/MS

analysis of the soaked syrups revealed significant concentra-

tions of fatty acids and hindered phenols in the CE syrup

(Table 3). Fatty acids and hindered phenols are considered to

attribute to the unpleasant taste.

Physical properties of the soaked POM dumbbells are

shown in Fig. 3. Dimensions and weight increased slightly

(Fig. 3A and 3B) in the syrup containing ethanol (E, CE, AE,

and LSE). Elastic modulus (Fig. 3E) decreased across all

syrups (C, E, CE, AE, and LSE) except for the control water

sample. Combination of acid type, in addition to the presence

Table 5　Taste of syrup after soaking with POMa

a The molded POM sample was soaked with the syrup at 32℃ for 14 days. The syrup was diluted to 6 times and submitted to the sensory test. b ( ) : Number of indicated counts by panelists in the sensory test.



Fig. 3　Change of physical properties of POM during the soaking with syrup containing various ingredients.(A) Stability of dimension, (B) Weight, (C) Tensile strength, (D) Ultimate elongation, (E) Elastic modulus, (F) Hardness, (G) Color difference, × : Water (Control), ○ : Citric acid (C), □ : Ethanol (E), ● : Citric acid and ethanol (CE), ▲ : Ascorbic acid and ethanol (AE), ◆ : Limonene, sucrose, and ethanol (LSE).



of ethanol accelerates the decrease of elastic modulus because

of POM polymer hydrolysis. A significant change in the phys-

ical properties was not observed in the syrup containing limo-

nene (LSE) for this case. The results are similar to PA612,

and contrary to LLDPE. The citric acid-ethanol interaction

was not observed to affect the physical properties. The color

of the soaked plate turned yellow from initial white after con-

tacting the syrup containing AsA for 56 days (Fig. 3G). Syr-

ups containing both citric acid and ethanol (CE) in the pres-

ence of the POM resin significantly influenced the syrup taste,

although the physical properties were not affected.

3. 4 Overview : syrup composition characteristic influence

on resin physical properties and resulting syrup taste

To review the characteristic influence of syrup composition

to the three molded resin types, changes in stability of dimen-

sion, weight and tensile properties were normalized over a

relative scale and are outlined in Table 6. Additionally, hard-

ness and color difference of the molded resins were compared

relatively. The soaked syrup taste was the most stable in POM

Table 6　Summary of change of taste of the syrup and physical properties of the resina

a Soaking conditions: The resin samaple was soaked for 14 days (for sonsory test) and 56 days (for mechanical test) at 32℃.

Rates (%) of stability of dimension, weight, tensile strength and ultimate elongation at break were cal-culated based on the data of non-soaked sample.Taste rating, hardness and color difference were evaluated in amount of changes compared with the data of non-soaked sample.

b △△△ : 2.0≦taste, △△ : 1.5≦taste＜2.0, △ : 1≦taste＜1.5, Blank : 0≦taste＜1c ＋＋＋ : 3×α≦y, ＋＋ : 2×α≦y＜3×α, ＋ : α≦y＜2×α, Blank : －α＜y＜α,

－ : －2×α＜y≦－α, －－ : －3×α＜y≦－2×α, －－－ : y≦3×α, α : Stability of dimension, 1% ; Weight, 2% ; Tensile strength, 15% ; Ultimate elongation at break, 50% ; Elastic modulus, 20% ; Hardness, 5° ; Colour difference, 5

d Tensile strength was evaluated at break point for LLDPE, and at yield point for PA612 and POM. e Fatty acid and hinderd phenol (BHT, etc.) were intensively detected by GC/MS of the soaked syrup containing ethanol.f Fatty acid and hindered phenol (proposed compound) were intensively detected by GC/MS of the soaked syrup CE.



resin samples compared with other resins. However, syrups

containing both citric acid and ethanol (CE) significantly

changed in taste. The influence of syrup on the resin physical

properties observed the following order : LLDPE＜POM＜ PA612. The physical properties of LLDPE are indeed sta-

ble ; however, the coverage of use of this resin is limited, be-

cause the principal properties of LLDPE are not superior to

those of other resins. Furthermore, LLDPE shows a distinc-

tive decrease in the physical properties when soaking in syr-

ups containing limonene (LSE). The soaked POM and PA612

resins in syrups containing ethanol (E, CE, AE, and LSE)

also showed this characteristic tendency. Therefore, POM

was observed to have the best balance between syrup taste and

physical properties among the tested resins. A key advantage

of the POM resin in cup-dispensing vending machines is that

the resin is in continuous contact with syrups containing mul-

tiple ingredient types. However, special attention should be

paid when the POM resin is in direct contact with syrups con-

taining both citric acid and ethanol (CE) over extended peri-

ods of time to prevent the formation of unpleasant taste. Fur-

ther detailed investigations studying the citric acid–ethanol

interaction in the presence of POM resins is necessary to im-

prove beverage quality.

4. Conclusion

Three crystalline thermoplastic resin types, LLDPE, PA612

and POM were soaked in beverage syrups containing either

single or combined ingredients, such as citric acid, ascorbic

acid, ethanol, sucrose, and limonene. The soaked syrups were

diluted and evaluated by a sensory test, and the soaked dumb-

bells were submitted to physical measurements. Specific

combinations of resins and syrup ingredients were observed to

be key factors to best balance syrup taste and the physical

properties of resin. Specifically, the citric acid–ethanol inter-

action in the presence of the POM resin negatively impacts

such properties, which was reported for the first time. These

results strongly reveal the requirement of detailed studies on

syrup ingredient–resin type properties to hinder the formation

of compounds attributable to the unpleasant taste in beverag-

es. This study is valuable to help avoid selected syrup–resin

combinations that lead to poor quality control of beverages

dispensed from cup vending machines and beverage dispens-

ers.

References

1）Ishii, H. and Fukushima, T. : “Fuji Automatic Cold Drink

Cup Vender”, Fuji Jihou, 47 [6], 473-477 (1972). (in

Japanese)

2）Kazuma, Y., Inagaki, M. : Materiaru Raifu Gakkaishi,

22 [2], 77-85 (2010). (in Japanese)

3）Yamamoto, T., Inagaki, M., Kazuma, Y. : Food Sci. Tech-

nol. Res., 15 [5], 491-498 (2009)

4）Yamamoto, T., Inagaki, M., Kazuma, Y. : Materiaru

Raifu Gakkaishi, 23 [1], 41-47 (2011)

5）JIS K 7162-1994.

6）ISO 13301 : 2002, Sensory Analysis-Methodology-Gen-

eral Guidance for Measuring Odor, Flavor and Taste De-

tection Thresholds by a Three Alternative Forced Choice

(3-AFC) Procedure.

7）Likert, R. : “A Technique for the Measurement of Atti-

tudes”, Archives of Psychology No. 140, Columbia Uni-

versity Press, (1932), p. 44-55

8）D. L. Gallagher : Water Sci. Technol., 49 [9], 107-114

(2004)

9）JIS K 7215-1986.

10）JIS K 8722-2009.

11）JIS K 8729-2004.



シロップ成分と熱可塑性樹脂との接触 : 樹脂の力学的特性とシロップの異臭味への影響

山本哲也 *1，浜崎卓也 *2，数馬安男 *3，稲垣　穣 *2 ※

＊1 富士電機株式会社　食品流通事業本部　開発統括部（〒510-0013 三重県四日市市富士町 1-27）＊2 三重大学大学院　生物資源学研究科（〒514-8507 三重県津市栗真町屋町 1577）＊3 三豊化成株式会社　技術開発部（〒379-2302 群馬県太田市山之神町 297-10）

※連絡先要　旨　カップ式自動販売機やディスペンサーで使用されているバルブやノズルなど機能部品の耐久性評価として，それらの部品に使用されている 3種類の熱可塑性樹脂（LLDPE，POMおよび PA612）を成分組成（クエン酸，アスコルビン酸，エタノール，ショ糖，リモネン）が異なる種々のシロップに浸漬し，樹脂の物理的特性やシロップの異臭味の変化を調べた．シロップが，樹脂の物理特性（引張強度，伸び，弾性率など）に影響し，同時に，樹脂がシロップの味に影響することがわかった．LLDPEでは，リモネンを含むシロップに浸けると樹脂の膨潤と引張強度の低下が顕著に見られた．PA612では，膨潤および，引張強度，伸び，弾性率などの物理的特性に大きな変化が見られた．POMでは，エタノールによる膨潤と弾性率の低下が見られ，さらに，エタノールとクエン酸両方を含むシロップに浸漬した場合にシロップの味がかなり変化した．本研究により，部品の耐久性や飲料の品質を確保するためには，シロップの成分に応じた樹脂を選択することが重要であることが示された．

キーワード : 熱可塑性樹脂，成形樹脂，直鎖状低密度ポリエチレン，ナイロン 612，ポリアセタール，濃縮飲料シロップ，カップ式販売機，ディスペンサー，異臭味（不快な味）

［マテリアルライフ学会誌，28［3］，51-61（Oct. 2016）］

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Syrup Ingredient and Thermoplastic Resin Contact