FLAVORING EXTRACTS
LEMON EXTRACT
The important ingredients of lemon extract are lemon oil and citral, its
aromatic constituent. Oil of citronella and oil of lemon grass are
sometimes substituted for lemon oil. Methyl alcohol is sometimes used in
place of the more expensive spirit alcohol as a solvent for the lemon
oil.
LEMON OIL
The presence of lemon oil may be detected by adding a large excess of
water to a small amount of the extract in a test tube. If the mixture
does not show some cloudiness, it is a strong indication that no lemon
oil is present. The degree of cloudiness gives an idea of the amount of
oil present.
CITRAL
This is present in the oil of lemon grass, which is sometimes used as a
substitute for lemon oil. Citral may be detected by the following test
by Burgess:
Add 20 cc. of sulfuric acid to 85 cc. of water. Dissolve in this mixture
10 grams of mercuric sulfate. Shake 2 cc. of the sample with 5 cc. of
this reagent in a test tube. If citral is present, the liquid will be
bright red, and will quickly disappear and give place to a whitish
compound, which floats on top.
OIL OF CITRONELLA
This is often substituted for lemon oil. It may be detected by the same
test which was used for citral. Instead of the red color and the white
compound, citronella gives a bright yellow color, which does not
disappear for some time.
TARTARIC OR CITRIC ACID
Precipitate the oil by the addition of an equal volume of water. Filter
and add a very little of the filtrate to a test tube nearly full of cold
lime water. A precipitate will form if tartaric acid is present and it
will dissolve in an excess of ammonium chlorid or acetic acid. Filter,
or, in case no precipitate forms, heat the liquid. Citric acid is
precipitated in the presence of a large excess of hot lime water.
METHYL ALCOHOL
_Mullikin and Scudder._--Take 2 ft. of No. 12-15 copper wire and bend at
right angles about 8 or 10 inches from one end. Grasp this bent end and
an ordinary lead pencil side by side in such a way that the bend will be
about the middle of the pencil. Wind the wire around the pencil and
toward the free end of the short part of the wire until you have a coil
3 or 4 cm. long. Remove the pencil and twist the unwound parts together
for a handle for the coil.
Dilute a portion of the sample 3 or 4 times, and oxidize 10 cc. of the
diluted liquid (preferably in a test tube) by heating to a red heat the
above copper coil in the oxidizing flame of a Bunsen lamp. Thrust the
heated coil quickly into the liquid contained in the test tube. In a
second withdraw and immerse in water. Continue this operation till the
oxid of copper fails to be reduced (usually 4 or 5 times is sufficient).
Cool the liquid by immersing the tube in water. Separate into two parts
and test each for formaldehyde by the following methods:
_Mullikin, S. P._--Place one of these parts in an evaporating dish, and
add to it 1 cc. of strong ammonia, boil gently over the free flame till
the vapors cease to smell of ammonia. Add 2 or 3 drops of strong
hydrochloric acid and heat just to boiling, and cool quickly by dipping
the dish in cold water. Make the test for formaldehyde: Add a drop of a
solution of resorcin (1 : 200) and pour this mixture slowly down the
side of an inclined test tube which contains 3 cc. of strong sulfuric
acid, taking care to keep the liquids separate. After 3 minutes give the
tube a rotary motion by rolling between the hands for a minute or more
but only gradually mixing the water and acid, but mixing only about half
of the acid.
Flecks of a rose-red color form if methyl alcohol is present. Bands of
color or flecks of other colors, even though they be tinged with red or
a rose-red solution without the precipitate, should never be taken as
proof that methyl alcohol is present. These conditions, however, are
good grounds for repeating the test; 10 per cent or even less may be
detected by this test.
_Hydrochloric Acid and Ferric Chlorid Test._--Add a few drops of the
other part of the above oxidized liquid to about 10 cc. of milk, known
to be free from formaldehyde, in a porcelain casserole, and add 10 cc.
of commercial hydrochloric acid (sp. gr. 1.2) which contains 1 cc. of 10
per cent ferric chlorid per 500 cc. Heat slowly over the open flame
nearly to boiling. Give the liquid a rotary motion to break up the
curd. If formaldehyde is present, the liquid will be colored violet. If
not, it slowly turns brown. The presence of formaldehyde proves that
methyl alcohol was in the original extract.
COLORING MATTER
_Preliminary Test._--Treat the sample with strong hydrochloric acid, and
if tropæolin or methyl orange be present the solution will turn pink;
Martius yellow partially decolorizes the solution; dinitrocresols
decolorizes the solution. Turmeric or naphthol yellow produces no color
change.
TURMERIC
Turmeric may be detected by soaking a piece of filter paper in the
sample, drying and dipping it in a dilute solution of boric acid or
borax which has been slightly acidulated with hydrochlorid acid. Dry
again and a cherry-red color forms if turmeric is present. Add a drop of
dilute alkali and if turmeric be present the paper will be colored dark
olive.
COAL-TAR COLORS
Evaporate some of the extract to dryness; take up the residue with water
and extract the coal-tar colors if present, and test for them by the
method given under canned vegetables.
VANILLA EXTRACTS
The best grades of vanilla extract are made by treating vanilla beans
with 50 per cent alcohol. Coumarin, an extract from tonka beans, may be
used in making the extract. This of course would make a cheaper product.
If less than 50 per cent alcohol is used in making the extract, some
alkali must be added to dissolve the resins which will not dissolve in
a weaker alcohol. In artificial extracts some such coloring matter as
caramel or tannin is used.
_Preliminary Test._--To a portion of the extract add a few drops of lead
acetate solution. The absence of a bulky flocculent precipitate shows
the extract not to be of high quality. Leach recommends that normal
acetate of lead be added to the sample, and if a precipitate does not
form it is conclusive evidence that it is not a pure extract.
When a precipitate forms with the above reagent, it should settle
immediately and leave a clear and almost colorless liquid. When there is
a mere cloudiness only, it may be due to caramel, in which case the
extract is to be suspected.
ALKALI
Shake a portion of the sample with twice its volume of water. If no
precipitate forms, an alkali is present. A flocculent reddish-brown
precipitate shows no alkali is present. If the solution is milky it
indicates the presence of a foreign resin.
Add hydrochloric acid drop by drop to the diluted extract. Nothing more
than a mere turbidity should result. Should it be quite turbid and the
color fading after a time, it shows that an alkali has been used.
FOREIGN RESINS
Mix a portion of the extract slowly with twice its volume of water,
frequently shaking the mixture. When this solution is milky, it
indicates a foreign resin.
_Hess’ Test._--Dealcoholize 25 cc. of the sample by concentrating on the
water-bath, adding water from time to time to retain the original
volume. When no alkali is present in the extract, pure vanilla resin
will be thrown down as a reddish-brown flocculent precipitate. Collect
the resin, whatever its color, on a filter, and wash. Save the filtrate
to test for caramel. Place a piece of the paper and resin in a dilute
solution of potassium hydroxid. If the resin is that of pure vanilla it
will dissolve, giving a deep-red color, and is reprecipitated when the
alkali is neutralized with hydrochloric acid. Dissolve another part of
the precipitate in alcohol, and to a part of this solution add a few
drops of ferric chlorid; and to the other part, hydrochloric acid. There
should be no marked coloration in either case if the resin is that of
pure vanilla. Foreign resins nearly always produce a coloration.
CARAMEL
Shake the bottle of vanilla, and if the bubbles, which form, are a
bright caramel color, keeping the color till all are gone, the presence
of caramel is indicated.
Concentrate a portion of the filtrate, which was saved in making the
test for foreign resins, at a rather low temperature until it has about
the same color as the original extract. Add a few drops of strong
hydrochloric acid and heat very gently. If caramel is present, a
yellowish-red flocculent precipitate will form. After the liquid cools,
filter and wash with water. Should this precipitate contain caramel, it
will not dissolve in water, ether, and alcohol, but will dissolve in
sodium hydroxid, dilute alcohol, and glacial acetic acid.
TANNIN
Test another portion of the filtrate made in testing for foreign resins,
with a few drops of a solution of gelatin. A slight precipitate only
should form due to the presence of a small amount of tannin normally
present in this filtrate. A large excess shows that it has been added to
the extract.
COUMARIN
_Leach’s Test._--Dealcoholize a portion of the sample as above and treat
with ammonia, add 3 or 4 volumes of chloroform in a separatory funnel.
Evaporate the chloroform extract in an oven, not permitting the
temperature to rise above 60° C. To the residue add a few drops of
water; warm gently, and add a little of a solution of 1 gram of
crystallized potassium iodid in 50 cc. of water, and the solution
saturated with iodin. If coumarin is present, a brown, precipitate will
form, and if stirred with a rod it will collect in dark green flecks.