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The Patterson-Kelley Co., Inc. 1002 Hanson St., E. Stroudsburg, Pa.

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2 4 A · ANALYTICAL CHEMISTRY

ence of spurious or materials of lower quality.

Through such studies much progress has been made in determining constit­uents of citrus flavors.

In the past, analysis of citrus oils has been confined to measurement of such physical properties as refractive index, optical rotation, density, and distillation characteristics and such chemical properties as free acidity, total carbonyl, and total ester count.

Chromatographic and chromatostrip separations have aided greatly in de­termining constituents of citrus flavors. Ultraviolet spectra of whole oils are also used to characterize or identify genuine oils, mixture of oils, and oils of doubtful origin.

Strawberry Flavor Classical methods alone are inade­

quate in research work on flavors, said Winter. These methods may lead to isolation of a characteristic flavor sub­stance but generally they isolate only the chief and most stable components. Volatile, unstable compounds found in very small quantities do not yield to classical methods.

Analysis of the volatile odorous sub­stances in the strawberry is a good ex­ample. Research to date has led to isolation of about 35 odorous sub­stances. It still is not possible, how­ever, to reconstitute a really fresh strawberry flavor, probably because of failure to identify trace substances and alteration of unstable constituents. The existence of unstable materials is evi­dent when strawberries are crushed. The finest flavor is developed in one minute. In 5 minutes, there is a notice­able change and in 10 minutes, the change is very marked.

Improvements in microchemical tech­niques and development of efficient physical instruments give promise.

Gas chromatography, while consid­ered useful as a complementary method, has limitations in strawberry flavor analysis. The need first to obtain a concentrated strawberry oil results in flavor alteration and losses. Secondly, the temperature and column activity and other physical-chemical conditions encountered in gas chromatography may alter unstable substances.

In this research chromatography is used mainly for chemical separation processing. Volatile substances are transformed to nonvolatile ones by processes and reagents which require the fewest possible chemical or physical operations. This procedure, called the "direct method," yields crystallized de­rivatives and at the same time separates functional groups.

Advantages of these procedures are

that volatile or unstable substances are fixed rapidly and thus protected from change. In using column and paper chromatographic methods only small quantities of the crystallized derivatives are required for separation and identifi­cation.

A major problem is the selection of reagents which will give the desired derivative. The reagents, for example, should react quickly and quantitatively,, yielding stable, easily crystallized prod­ucts with characteristic melting points. The derivatives should be splittable-into their original components, intensely colored to facilitate chromatographic analysis, and appropriate for paper chromatography.

Typical reagents used include aroma­tic azo acid chlorides for alcohols and phenols, p-phenylazophenacyl bromide for acids, and 2,4-dinitrophenylhydra-zine and some substituted phenylsemi-carbazides for carbonyls.

Techniques involve crushing the fruit, followed by low-temperature vac­uum steam distillation. The small quantities of very volatile substances which pass through the cold condenser are fixed with different reagents.

The distillate, which is unstable, amounts to 12 to 16% of the weight of the fruit. Dilution to fruit weight yields a fresh natural strawberry flavor.

The essential odorous substances in­cluding carbonyl compounds, esters, free organic acids, alcohols, and phenols may be converted to derivatives. Acids, and alcohols, corresponding to esters as λνβΐΐ as lactones, can also be captured after saponification.

Chromatographic separation and identification of the mixtures of deriva­tives requires much experimental skill and experience. In the first steps, chromatography on pure silicic acid columns is used. The fractions are ex­amined by qualitative paper chroma­tography in different systems. Where only partial separations are effected, the fractions are reseparated on new columns or by paper chromatography.

In this work, it is important that solvents, chromatographic supports and reagents be very pure.

USDA Flavor Research. Role of the U .S . Department of Agriculture in the field of strawberry flavor is part of an extensive fundamental research pro­gram on fruit flavors designed to find out what chemical compounds are pres­ent, in what quantities, which are es­sential, and how they are to be assayed. This work, Corse said, will help in de­veloping new strains, in processing, and in problems met between processing and consumption.

The initial problem in USDA work on fruit flavors is to separate the small

P-K Customer Service Lab w i l l test-blend any desired formulations, give samples of results — without obligation !

The economical way to determine what blender is most suitable for your blending needs is to see tangible results of your own for­mulation — before you buy! That is why P-K cordially invites you to come to our laboratory and witness your own material for­mulations blended to your exact specifications. Or, if you prefer, send us materials for your formu­lation and a test blend will be returned to you for your analysis together with a complete report on the kind of blender that will best serve your needs. Just fill in the coupon or write to Mr. J. J. Fisher at P-K — There is no obli­gation whatsoever.