606
T H E JOCR-VAL OF I S D C S T R I d L . i S D E S G I S E E R I S G C H E M I S T R Y
i t permits of much greater accuracy. T h e corresponding percentage Of “lids in the and the percentage Of “lids in the Pulp f r o m which it is prepared may be ascertained f r o m the index Of refraction b y Table 11’. T h e per cent of solids in t h e filt r a t e m a y also be calculated f r o m t h e scale reading of t h e immersion refractometer a t 17.j o C . , b y t h e following f o r m u l a , which is derived from Table IT‘: Per cent SOLIDS I N FILTRATE = 0.258 (scale reading -15)
DETERMIKATIOS O F SCGAR
T h e sugar of tomatoes
probably always pre,ent
as invert sugar, If cane sugar is ever present I n l h e r a w product i t is doubtless inverted during t h e concentration of pulp, The per cent of sugar giT.en i n Tables I and 11 T~.asdetermined b y the method of nlunson and ffalker.l D E T E R MI S A T I O 5 0 F A C I D I T Y
- 0.0165 (scale reading - 26.4).
If t h e index of refraction has been determined b y means of a n AbbC refractometer, t h e per cent of solids i n t h e filtrate m a y be calculated b y t h e following formula : P e r cent SOLIDS I N FILTRATE = 666 ( ~ Z D-1,3332) - 20.7 ( Z D -1.3376). T h e per cent of total solids in t o m a t o pulp m a y also be ascertained from t h e index of refraction of t h e liquor prepared b y filtering t h e pulp as shown in Table IT‘; or, it m a y be calculated from t h e immersion refractometer reading b y t h e following formula, which is derived from Table IV: P e r cent S O L I D S I N P U L P = 0.289 (scale reading of filtrate -15)
T‘ol. 7 . S o . 7
- 0.0185 (scale reading -26.4).
If t h e index of refraction of t h e filtrate has been determined b y means of a n AbbC refractometer, t h e per cent of solids in t h e pulp m a y be calculated b y t h e following formula: Per cent SOLIDSI X PULP = i 4 8 ( W D -1.3332) - 25.5 ( n -1.3376). ~ It is of interest t o n o t e t h a t t h e relation between t h e index of refraction of t h e liquor obtained b y filtering t o m a t o pulp a n d t h e per cent of solids in t h a t liquid is very similar t o t h e relation between t h e index of refraction a n d dis;olved solids i n beer a n d wine ext r a c t , as shown in t h e table prepared b y 1Vagner.l In t h e formula given above. as well as in Table I V , i t is assumed t h a t salt is absent. If i t b e desired t o calculate t h e percentage of solids in a sample containing salt from t h e index of refraction of t h e filtrate, i t is necessary first t o determine t h e a m o u n t of salt present a n d make correction therefor. For t h i s purpose t h e table of Wagner2 m a y be employed. T h i s correction is necessary, however. if t h e percentage of solids be determined b y drying, or calculated f r o m specific gravity. DETERMIKATIOK O F IKSOLUBLE SOLIDS
Transfer 20 grams of the pulp t o an eight-ounce nursing bottle, nearly filled with hot water, mix by shaking, and centrifuge until the insoluble matter is collected in a cake in the bottom of the bottle. Transfer the supernatant liquor onto a double, tared filter paper covering the bottom of a Buchner funnel, using suction t o facilitate filtration. Again fill the nursing bottle with hot water, stir the cake of insoluble solids so that it is thoroughly mixed with the water, centrifuge, and decant the supernatant liquor on the filter. Repeat the centrifuging and the filtration of the supernatant liquor once more, and then finally transfer the insoluble solids to the filter paper and thoroughly wash with hot water. Dry the paper and insoluble solids, and weigh. The insoluble solids are quite hydroscopic and the weight must he taken quickly. 1 “ U e b e r q u a n t i t a t i v e Bestimmungen misseriger Lbsungen mit d e m Zeiss-schen Eintauchrefraktometer,” T a b l e X V I I . Ibid.. Table I.
Accurate results cannot be obtained b y t h e titration of t o m a t o products in t h e presence of t h e insoluble solids. If i t be desired t o determine t h e acidity in t h e entire sample of tomatoes or t o m a t o pulp rather t h a n in t h e expressed juice, t h e insoluble solids should first be removed b y t h e method given in t h e determinntion of insoluble solids. T h e per cent of acid given in Tables I a n d I1 was obtained b y titrating t h e liquor obtained b y filtering t h e pulp. I n products of this nature, t h e addition of a n alkali causes a brownish color which has a tendency t o obscure t h e end point shown b y t h e indicator. T o obviate this, t h e sample should be diluted t o a t least zoo cc. a n d a larger a m o u n t of indicator employed t h a n is necessary with a clear solution. T h e following details are suggested: Dilute 20 grams of the filtrate under examination with over zoo cc. of water. Add a t least I, 2 cc. of phenolphthalein solution (prepared by dissolving I gram of phenolphthalein in IOO cc. of 95 per cent alcohol) and titrate with sodium hydroxide until the end point is obtained. Add I cc. of tenthnormal hydrochloric acid, heat the solution quickly to boiling and boil one minute to expel carbon dioxide. Cool the solution quickly t o about room temperature, and then add tenth-normal sodium hydroxide until the end point is obtained. The volume of hydrochloric acid added must, of course, be taken into consideration in the final result. h7ATIONAL C A N N E R S ’ ASSOCIATION,
WASHINGTON, D. C
A CONCISE GROUP METHOD FOR THE DETECTION O F GELATINIZING AGENTS, PASTY MATERIAL AND THICKENERS, USED IN FOOD PRODUCTS B y LEON -4. CONGDON Received J a n u a r y 12, 1915
T h e extreme difficulty of detecting various gelatinizing agents, pasty material a n d thickeners used in food products, has led t h e writer t o work o u t a group method, b y which these substances can be identified even if t h e unknown contains one or all of t h e common substances used for gelatinizing agents, e t c . , such as starch, dextrin, gelatine, acacia, agar-agar, tragacanth, albumen a n d pectin bodies of t h e fruit juices. T h e use of these substances has been quite general in recent years. Hence a s t u d y of these materials a n d their detection in food products is imp o r t a n t t o t h e chemist. Thickeners. pasty materials, a n d gelatinizing agents frequently are used t o cheapen t h e genuine articles of food. I n t h i s class m a y be mentioned agar-agar, which has been found in imitation lemon slices; starch, agar-agar, a n d gelatine in imitation jelly; dextrin in imitation cocoa cubes. These materials are also used t o cover u p inferiority. I n this class might b e mentioned albumen, or n-hite 1
Bureau of Chemistry, U . S. Dept. Xgr., Bull. 107, revised.
T H E J O I ' R S . 4 L O F Ia\TDL-STRIdL d S D ESGI.\*EERISG
July. 191j
CHEMISTRY
607
T ~ B LIE REACTIONS WITH Gnorrps Group I . .
. . ......
G R O U P REAGENTS
Iodine solution
(;roup 11.. , . , , , .
IIillon's or Stokes' reagent (acid nitrate of mercury)
(:roup 1 1 1 . . , . , , , . . ,
Concentrated solution of sodium borate
(;roup I V ,
, , ,
(:roup I'. .
,
, ,
,
,
.,
(;roup 1.1,. . , , . . . .
Solution of sodium hydrate Solution of mercuric chloride Schweitzer's reagent (solution of cupra-ammonia]
of egg, which is sometimes used t o glaze coffee beans t o make t h e m appear better t h a n t h e y really are. .Again t h e thickeners, etc., are used in such products as ice cream and custards, primarily t o add bulk t o the product. and t o gire the material in which they are used a frothy appearance. T h e y are also used in this connection t o make t h e ice cream and custards " s t a n d up." A great many ice cream manufacturers use a so-called "ice cream powder." These "ice cream powders" vary in composition, but generally contain one or more of t h e following: dext r i n , acacia. tragacanth, gelatine, albumen. a n d st:ir ch . This paper deals more specifically with t h e detection of these gelatinizing agents, pasty materials. and thickeners in food products b y a group method. T h e above table, prepared and worked out b y the writer o n actual experiments in the laboratory, places t h e above-mentioned materials in six groups : I---the iodine solution group; 11-the acid nitrate of mercury group: 111-the concentrated solution of sodium borate group; IT-the solution of sodium hydrate group ; \---the solution of mercuric chloride group; TI-the solution of cupra-ammonia group. -4 careful s t u d y of this group method shows t h a t a new means for testing agar-agar has been discovered. This test is based on Groups 11. 111 a n d IT7. The characteristic reactions for agar-agar depend on a new test for acacia in Group 11, t h a t is, one drop of acid nitrate of mercury plus t h e unknonm water solution. which test yields a stringy gelatinous precipit a t e . solzbble i i t c x r c s s of the reageut. Since the reagent in Group 111 precipitates only agar-agar and acacia, it is simply a test t o pr0T-e whether one or both are present in t h e unknown water-soluble mixture. The reagent in Group IT' does not precipitate agar-agar. and hence if no precipitate is obtained here, agaragar is present in Group 111; if a white, cloudy precipit a t e occurs, t h e unknown is acacia, and if a brownish yellow color occurs on heating, t h e unknown is tragacanth. -Acacia may be further tested for with a solution of so1ut)le basic lead acetate, which gives a whitish gelatinous precipitate a n d again tested for b y t h e acid nitrate of mercury test in Group I 1 as already indica-
W A T E R - S O L ~ B L Es O L U T I O N S O F T H E G E L A T I N I Z I N G hCIEHTS
PASTY hf A T E R I A L S A N D T H I C K E N E R S Blue coloration indicates slarrh. (Sometimes green apples made into jelly will give traces of starch.) Purple coloration iridicates A mylo-dextrin. Red coloration indicates Erylhro-dextrin. iXo coloration may indicate neither starch nor dextrin. b u t may he Achtodextrin. Mixture. after shaking substance in solution with reagent is cloudy. Yellow precipitate with picric acid solution indicates Gelatine. Drop of this reagent. Gelatinous precipitate, soluble in excess of this reagent, indicates Acacia. X slight white cloudy precipitate may indicate either Agar-agar or Traga'aiilh o r both (test for tragacanth as in Group IV). A white gelatinous precipitate indicates either Agav-ago? or Acacia or both. C . T. Acacia will give a gelatinous, opaque white precipitate with solution basic lead acetate. Acacia may he further tested for as in Group I1 or Group IT' or by adding a solution of tannin which gives a bluish black coloration. A brownish yellow color on heating indicates Tvagacanlh. A white cloudy precipitate indicates Acuria. A slight turbidity may indicate Dexlvin. A white precipitate may indicate Albumen and Geluline. If a concentrated water solution of the unknown is treated with this reagent and placed on glass slide under microscope, a delicate framework of cupric pectate is evident. showing a Pectin of fruit or vegetable origin present.
t e d . The remaining tests in t h e other groups gi\-en in the table are rather well known, b u t t h e writer thinks t h a t this group method mill be helpful t o those interested in food chemistry. DIVISIOSOB FOOD A K D Dnnr,s BOARD OF IIEALTII, TOPEK.%
KAXSAS STATE
TAMARIND SYRUP By \V.
c.T a a E n '
Received March 2 5 , 1915
syrup prepared from the pulp of tamarinds with added sugar has come into use in the United States as a summer beverage t h a t is highly esteemed by Italians. Xfter dilution with water this syrup forms a refreshing drink. The making of this syrup apparently originated in Italy some years ago. The districts of Lombardy and Piedmont are the Italian sections most prominently identified v i t h the making of this product. The tamarinds used in this country are practically all imported. T h e y are t h e fruit of a leguminous tree, T a m a v i i i d u s i n d i r a , which grows in tropical and semi-tropical countries. A native probably of Africa, i t was early introduced into the East Indies. West Indies, Brazil, hiexico and most of the tropical countries. The fruit is a large, flat pod from 4 t o 8 in. long, filled with a n acid pulp, seeds and a stringy, fibrous matter. In t h e samples examined in this laboratory t h e pulp constituted about sixty per cent of t h e whole fresh fruit as removed from t h e pod. T h e reported analyses of tamarinds are not uniform. The statements in regard t o the presence of citric and malic acids are quite conflicting. Yauquelin,? who published one of the earliest analyses of tamarind, reported a large amount of citric acid as one of the constituents. This report can have little xeight as the method of identification was faulty. Xfter concentration, the addition of calcium carbonate produced a precipitate. which. on decsomposition, gave an acid precipitate with lime water. This n ~ o u l dnot be sufficient t o distinguish between tartaric acid and citric acid. 1
Assistant Chemist, Bureau of Chemistry. A n n . d e C h i m . . [ I ] 5 ( l i 9 0 ) , 92.
