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Volatile Flavor Compounds of Sweetened Condensed Milk

Volatile Flavor Compounds of Sweetened Condensed Milk
Volatile Flavor Compounds of Sweetened Condensed Milk

Food Chemistry and Toxicology JFS:Food Chemistry and Toxicology

Volatile Flavor Compounds of

Sweetened Condensed Milk

M. S HIMODA,Y. Y OSHIMURA, T. Y OSHIMURA, K. N ODA, AND Y. O SAJIMA

ABSTRACT: The volatile compounds of sweetened condensed milk (SCM) were investigated to explain their contri-bution to SCM flavor. Commercially processed SCM was diluted with water and the volatiles were isolated by simultaneous steam distillation-extraction under reduced pressure. Commercial liquid milk was used for compari-son. The odor concentrate was analyzed by GC and GC-MS, and then fractionated by silica gel TLC and preparative GC to determine the contributors to SCM flavor. Major volatile compounds were 10 fatty acids, 14 lactones, 10 ketones, 13 hydrocarbons, 8 alcohols, 4 aldehydes, and 8 miscellaneous compounds. ?-Decalactone and ?-dodecalactone were the principal contributors to SCM flavor although the other lactones may contribute as well.

Key Words: volatiles, flavor, aroma, sweetened condensed milk, milk products

Introduction

S WEETENED CONDENSED MILK (SCM)

I s essentially concentrated liquid milk

preserved by the addition of a high con-

centration of sugar. The high osmotic

pressure of SCM inhibits the growth of

most spoilage organisms and provides

long shelf life without refrigeration. Now-

adays, SCM is used not only as a spread

or sweetening but also as a material for

various food products to improve their

flavor, taste, and mouthfeel. It is interest-

ing to note that the characteristic sweet

and milky flavor of SCM develops during

manufacturing.

To date, no information is available on

the flavor of SCM, the most important as-

pect of its quality, although much work

has been carried out on the flavor of liq-

uid milk and dairy products (Badings and

Neeter 1980; Rerkrai and others 1987;

Badings 1991; Gaafar 1991; Shiratsuchi

and others 1994a, 1994b, 1995; Stevenson

and others 1996). We have carried out,

therefore, a study on the isolation and

identification of volatiles in SCM to deter-

mine the contributors to SCM flavor.

Materials and Methods

Materials Used

Commercially processed SCM was

obtained from Meiji Milk Products Co.,

Ltd. (Tokyo, Japan), with a composition

as shown in Table 1. In addition, SCM

samples were prepared in our laborato-

ry. To carry out this evaluation for SCM

flavor, recombined sweetened con-

densed milk with reduced characteristic

flavor of SCM was made from skim milk

powder, sucrose, and water (Newstead

1982). Liquid milk was purchased locally.

Silica gel 60 F254 plates for thin-layer

chromatography (TLC) of the odor con-

centrates were obtained from Merck

(Darmstadt, Germany). Diethyl ether

and anhydrous sodium sulfate were ob-

tained from Nakarai Tesque Inc. (Kyoto,

Japan), and 2-ethylhexyl acetate was ob-

tained from Tokyo Kasei Kogyo Co. Ltd.

(Tokyo, Japan). ?-decalactone and ?-

dodecalactone were received from Oga-

wa Perfumery Co. Ltd. (Tokyo, Japan).

Isolation of volatile flavor

compounds

Canned SCM (379 g) and 800 mL

deionized water were placed in a 2000-

mL round-bottom flask. Volatiles were

separated with 80 mL diethyl ether

from the diluted SCM solution by si-

multaneous distillation-extraction un-

der reduced pressure (approximately

80 mmHg) for 1 h, using a modified Lik-

ens-Nickerson apparatus. After addi-

tion of 20 ?L of 1% diethyl ether solu-

tion of 2-ethylhexyl acetate, the extract

was dried over anhydrous sodium sul-

fate for 6 h and concentrated to about

100 ?L. Twenty-five samples of the SCM

were successively treated. The concen-

trates were combined and further con-

centrated to about 500 ?L. The odor

concentrate from liquid milk (10 L) was

prepared in the same way as the isola-

tion of flavor volatiles from the SCM.

The odor concentrate from 10 kg of

SCM, which had a typical SCM odor

(sweet and milky), was fractionated by

silica gel TLC (the solvent was diethyl

ether/n-pentane, 20:80). The 2 polar

fractions with sweet and milky odor,

which seemed to contribute directly to

the characteristic flavor of SCM, were

eluted with diethyl ether (30 mL) from

the silica gel support scraped from the

TLC plate and then concentrated to

about 100 ?L.

Capillary gas chromatography (GC)

Capillary GC analysis was carried out

on a Hewlett-Packard Model 5890A gas

chromatograph equipped with a flame

ionization detector (FID) and connected

to a Shimadzu Chromatopak C-R5A in-

tegrator. Separation was achieved on a

60 m ? 0.25 mm i.d. fused silica capillary

column, coated with cross-linked poly-

ethylene glycol 20M, film thickness 0.25

?m (DB-Wax; J&W Scientific, Folsom,

Calif., U.S.A.). The oven temperature was

programmed from 50 to 230 ?C at 2 ?C /

min (60-min hold). The injector and de-

tector temperatures were 230 and

250?C, respectively. The helium carrier

gas flow rate was 25 cm/s with an injec-

tion splitter at a split ratio of 25:1. Reten-

tion indices were estimated in accor-

dance with a modified Kovats method

(Van den Dool and Kratz 1963).

Capillary gas chromatography-

mass spectrometry (GC-MS)

Electron impact mass spectrometric

data were collected on a JEOL Auto-

Table 1—Comp osition of the sweet-

ened condensed milk (%)

Sucrose44.2

Water25.5

Lactose12.2

Fat8.3

Protein7.9

Ash 1.9

804JOURNAL OF FOOD SCIENCE—Vol. 66, No. 6, 2001? 2001 Institute of Food Technologists

Vol. 66, No. 6, 2001—JOURNAL OF FOOD SCIENCE

805

F o o d C h e m i s t r y a n d T o x i c o l o g y

mass 50 mass spectrometer interfaced to a Hewlett-Packard 5890 Series II gas chromatograph. The column and chro-matographic conditions were the same as described for the GC analysis. The mass spectrometer was operated at an ionization voltage of 70 V and an ion source temperature of 200 ?C. The mass spectra of the unknown compounds were compared with those in the Wiley/NBS Registry of Mass Spectral Data (1989).

Preparative GC and sniffing

The odor extracts from 2 polar frac-tions with sweet and milky odor were further fractionated by preparative GC (Shimoda and others 1993) to detect contributors to the odor attributes.

Results and Discussion

T

HE COMPOUNDS IDENTIFIED INCLUD -

ed 10 fatty acids, 14 lactones, 10 ke-tones, 13 hydrocarbons, 8 alcohols, 4aldehydes, and 8 miscellaneous com-pounds (Table 2). Total area of 67 peaks which were identified definitely by re-tention indices and mass spectra or ten-tatively by only mass spectra represent-ed about 94% of the chromatogram peak surface area (excluding solvent and internal standard peak). Among fat-ty acids, even-carbon-numbered satu-rated fatty acids, which have buttery,milky, creamy or waxy odors, were pre-dominant. These compounds were also found to be important in the silica gel TLC fraction of skim milk flavor com-pounds (Shiratsuchi and others 1995). It was shown that a pronounced amount of lactones was included. Major com-ponents were ?-decalactone, ?- and ?-dodecalactone, and ?-tetradecalactone.These compounds have milky, buttery,or creamy odors, and hence, are added to some margarines to simulate butter flavor (Kinsella and others 1967). It was reported that ?-lactones were pro-duced from 4-hydroxy fatty acids by heating and ?-lactones were produced from 5-hydroxy fatty acids (Forss 1979).Methyl ketones are a notable feature in the flavor of milk and milk products.Among the ketones, odd-carbon-num-bered ones, that is, 2-heptanone, 2-nonanone, 2-undecanone and 2-tride-canone were principal https://www.wendangku.net/doc/a610939526.html,ngler and Day (1965) found that fla-vor potency varied with carbon-chain length and 2-heptanone had the lowest flavor threshold value (700 ppb). The content of methyl ketones in the SCM was quite low, far below the flavor thresholds in milk. Volatile compounds of other chemical classes were present

Table 2–Volatile flavor compounds identified in sweetened condensed milk Peak

Kovats index a

ppb

(A) Fatty acids

17acetic acid 1452 2.832hexanoic acid 1852 1.043octanoic acid 206910.049decanoic acid

228879.55110-undecenoic acid b 2358 1.357dodecanoic acid 2503182.063tetradecanoic acid 271662.765tetradecenoic acid 276314.167pentadecanoic acid 28198.269hexadecanoic acid

292859.5(B) Lactones

36?-heptalactone 19760.638?-octalactone 1999 1.945?-decalactone 2185 1.147?-decalactone 222962.650?-undecalactone 2345 2.252?-dodecalactone 239714.054?-dodecenolactone b 2427 5.855?-dodecalactone 246654.756?-tridecalactone b 2488 3.959?-tridecalactone b 2565 2.061?-tetradecalactone b 2628 4.362?-tetradecalactone b 270124.166?-pentadecalactone b 2802 6.268?-hexadecalactone b

2912 4.0(C) Ketones

12-pentanone 996 1.842-heptanone 118325.1162-nonanone 13897.1192-decanone 1496 2.2222-undecanone b 159815.3252-dodecanone 1692 1.2312-tridecanone b

181611.7332,3,4-trimethylacetophenone b 1859 1.1342-tetradecanone 19410.5422-pentadecanone b

2041 1.5(D) Hydrocarbons

3toluene

10390.75propylbenzene

1203 1.861-ethyl-4-methylbenzene 1216 3.271-ethyl-3-methylbenzene 12198.581,3,5-trimethylbenzene 1237 4.191-ethyl-2-methylbenzene 1254 3.2101,2,4-trimethylbenzene 127518.6111,3-diethylbenzene 1296 1.712tridecane

1300 1.1131,2,3-trimethylbenzene 1329 3.7141,1-dimethylethylbenzene b 1359 1.526heptadecane 1700 5.228octadecane

1800 2.5(E) Alcohol

22-methyl-3-buten-2-ol b 10350.8182-ethyl-1-hexanol b 1492 1.8232-furanmethanol 16550.6292-methyl-1-decanol b 180316.046tetradecanol 2205 1.258heptadecanol 2524 1.260octadecanol

2626 1.1(F) Aldehydes

15nonanal

138911.720benzaldehyde 1531 6.921(E )-2-nonenal 1557 1.0402-tetradecenal b

2012 1.0(G) Miscellaneous Compounds

24cyclohexyl isothiocyanate b 1667 3.927N,N-dibutyl acetamide 1805 5.835benzothiazole 1968 2.139phenol

2006 1.341methyl tetradecanoate 20289.5441-methoxynaphthalene b 2135 2.648methyl hexanoate 2251 1.364

dibutyl phthalate

2726

26.4

a Modified Kovats indices calculated for DB-Wax capillary column on the GC system.

b Tentative identification by mass spectrum alone.

Food Chemistry and Toxicology

806JOURNAL OF FOOD SCIENCE —Vol. 66, No. 6, 2001

in extremely low concentrations. There-fore, they could play only a secondary role in SCM flavor.The absolute contents of classes of the volatile compounds from the SCM and commercial liquid milk are shown in Figure 1. A comparison of the levels

of each class showed that all of the lev-els in the SCM were much higher than

in the liquid milk, that is, the class of fatty acids was 8.4 times, lactone 35.3times, ketones 2.2 times, hydrocarbons 5.4 times, alcohols 20.7 times, and al-dehydes 12.1 times higher in SCM than in liquid milk. There were large differ-ences in the concentration of flavor compounds between SCM and liquid milk. The difference in the lactones was most noteworthy. Such a striking difference in the concentrations might result from decomposition of their precursors or the release of bound volatiles during the manufacturing processes of SCM.

To specify the compounds that di-rectly contribute to the flavor of SCM, a fractionation of odor concentrate was carried out by thin-layer chromatogra-phy. Among 9 fractions separated, frac-tions 8 and 9 had sweet and milky odors, reminiscent of the flavor of SCM. It is possible that contributors to SCM flavor are included in these frac-tions. Therefore, fractions 8 and 9 were each separated into several portions by

preparative GC (Figure 2). As shown in Figure 2, fractions 8B, 8C, and 8D had sweetened condensed milk-like odors.Each peak of 8B, 8C, and 8D was fur-ther separated and their odors were sniffed during elution. Peak 1, nonanoic acid, had a sweet, fatty, and milky odor;peak 2, ?-decalactone, a sweet, fatty,milky odor; peak 3, ?-undecalactone, a sweet and milky odor; peak 4, ?-dode-calactone, a sweet and milky odor; and peak 5, ?-dodecalactone, a condensed milk-like odor. Fractions 9D and 9E had sweet, fatty and milky odor as shown in Figure 2. Judging from the sniffing and their quantitative values, the most im-portant contributors seemed to be ?-decalactone and ?-dodecalactone.Therefore, after addition of authentic compounds of ?-decalactone and ?-dodecalactone to a laboratory-made SCM sample the flavor was evaluated organoleptically by a triangle test with a 10-member panel. Both the lactones were added in the same and double concentrations as in the commercial SCM product (Table 3). It was con-firmed that the sweet and milky flavor of sample A was more intense than that of the control (p ? 0.01), and p ? 0.001for sample B. These results indicated that ?-decalactone and ?-dodecalac-tone were the principal compounds contributing to the flavor of SCM, al-though the other lactones are probably

also contributors.

Figure 1—Levels of volatile compounds grouped according to chemical class

in sweetened condensed milk and liquid milk.Figure 2—Sniffing of the fractions obtained by p rep arative gas chromatogra-p hy on fractions 8 and 9 from the thin-layer chromatogram.

Vol. 66, No. 6, 2001—JOURNAL OF FOOD SCIENCE

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F o o d C h e m i s t r y a n d T o x i c o l o g y

References

Badings HT. 1991. Milk. In: Maarse H, editor. Volatile compounds in foods and beverages. New York:Marcel Dekker. P 91-106.

Badings HT, Neeter R. 1980. Recent advances in the study of aroma compounds of milk and dairy prod-ucts. Neth Milk Dairy J 34(1):9-30.

Forss DA. 1979. Reviews of the progress of dairy sci-ence. Mechanisms of formation of milk and milk products. J Dairy Res 46(3):691-706.

Gaafar AM. 1991. Chemical changes in ultra-high-treated milk during storage. 2. Production of vola-tile flavor compounds. Milchwissenschaft 46(4):233-235.

Kinsella JE, Patton S, Dimick PS. 1967. The flavor potential of milk fat. A review of its chemical na-ture and biological origin. J Am Oil Chem Soc 44(7):449-454.

Table 3–Comp osition of the sweetened condensed milk for addition evalua-tion.Ingredient

Control Sample A Sample B Skim milk powder (%)24.024.024.0Sucrose (%)48.048.048.0Water (%)

28.028.028.0?-decalactone(ppb)0.062.6125.2?-dodecalactone (ppb)

0.0

54.7

109.4

Langler JE, Day EA. 1965. Development and flavor properties of methyl ketones in milk fat. J Dairy Sci 47(12):1291-1296.

Newstead DF . 1982. Recombined sweetened con-densed milk. Int Dairy Federation Bull 142. P 59-62.

Rerkrai S, Jeon IJ, Bassette R. 1987. Effect of various direct ultra-high temperature heat treatments on flavor of commercially prepared milks. J Dairy Sci 70(10):2046-2054.

Shimoda M, Shiratsuchi H, Minegishi Y, Osajima Y.1993. Flavor deterioration of nonfermented coarse-cut sausage during storage. 2. Flavor as a factor of quality for nonfermented sausage. J Agric Food Chem 41(6):946-950.

Shiratsuchi H, Shimoda M, Imayoshi K, Noda K, Osa-jima Y. 1994a Volatile flavor compounds in spray-dried skim milk powder. J Agric Food Chem

42(4):984-988.

Shiratsuchi H, Shimoda M, Imayoshi K, Noda K, Osa-jima Y. 1994b Off-flavor compounds in spray-dried skim milk powder. J Agric Food Chem 42(6):1323-1327.

Shiratsuchi H, Yoshimura Y, Shimoda M, Noda K, Osa-jima Y. 1995 Contributors to sweet and milky odor attributes of spray-dried skim milk powder. J Agric Food Chem 43(9):2453-2457.

Stevenson RJ, Chen XD, Mills OE. 1996. Modern anal-yses and binding studies of flavour volatiles with particular reference to dairy protein products. Food Research Int 29(3):265-290.

Van den Dool H, Kratz PD. 1963. A generalization of the retention index system included linear tem-perature programmed gas-liquid chromatography.J Chromatogr 11(3):463-471.

Wiley/NBS Registry of Mass Spectral Data. 1989.Wiley-Interscience.MS 20000510

Authors Shimoda, Y oshimura, and Y oshimura are with the Dept. of Food Science and Technology,Faculty of Agriculture, Kyushu Univ., 6-10-1Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.Author Noda is with the Central Research Insti-tute, Meiji Milk Products Co., Ltd., Tokyo, Japan.Author Osajima is with the School of Bioresources,Hiroshima Prefectural Univ., Hiroshima, Japan.Direct inquiries to author Shimoda (E-mail:mshimoda@agr.kyushu-u.ac.jp).

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