ANALYTICAL CHEMISTRY Silicates ind., 16,338 (1951).
Slavik, K., and Michalec, C., Chem. L i s t y , 4 5 , 3 8 (1951). Smith, A. M.,Comrie, A,, and Simpson, K., A n a l y s t , 76, 58-65 (1951).
Smith, J. B., J . Assoc. O f i c . A g r . Chemists, 33, 284-7 (1950). Snedecor, G. W., J . A l a b a m a Acad. Sci., 20, 53-7 (1948). Stehlik, B., Chem. L i s t y , 38, 1-3 (1944). Storck, M. J., Ann. biol. clin. ( P a r i s ) , 7,459-60 (1949). Straaten, H. van der, and Aten, A. H. W., Jr., Rec. trav. chim., 69, 561-4 (1950).
Ssab6, Z. G., and Bartha, L., A n a l . Chim. A c t a , 5 , 33-45 (195 1).
Szab6, Z. G., and Bartha, L., Magyar K e m . Folydirat, 56, 81-3 (1950). Ibid., 5 7 , 8 4 6 (1951).
Takagi, K.. and Yamada. M., J . Electrochem. SOC.J a p a n , 18, 9-12 (1950).
Tananaev, I. V., and Koslov, A. S., Z h u r . A n a l . K h i m . , 6, 149-56 (1951).
Tarasevich, N. I., I b i d . , 4 , 108-13 (1949). Taylor, D. S.,J . Assoc. Ofic. A g r . Chemists, 33, 132-9 (1950). Templeton, D. H., and Bassett, L. G., N a t l . Nuclear Energy Ser., Div. VIII, 1 , Anal. Chem. Manhattan Project, 321-38 (1 950).
Thistlethwaite. IT. P.. Analvst. 77. 48-9 (1952). Thompson, J.’F., and Morrison’, G. R., ANAL. CHEM.,23, 1153-7 (1951).
Tinsley, J., Taylor, T. G., and Moore, J. H., A n a l y s t , 76, 300-10 (1951).
Tirouflet, J., B u l l . S O C . sci. Bretagne, 23, 129-31 (1948). Tokuoka, M., Matsuo, H., and Mori, G., J . Sci. Soil M a n u r e J a p a n , 21,90-2 (1950).
TomiEek, O., and Mandelik, J., Chem. L i s t y , 43, 169-76 (1949).
Tomoeda, M., J . P h a r m . SOC. J a p a n , 71,855-7 (1951). Triche, H.. A n a l . C h i m . A c t a , 4,12-20 (1950). Ubaldini, I., and Guerrieri, F., Ann. chim. applicata, 39, 291-7 (1949).
Urusovskaya, L. G., and Shiryaeva, T. M.,Zaaodskaya Lab., 15,16)05 (1949).
Usatenko, Y. I.,and Datsenko, 0. V., I b i d . , 16, 94-6 (1950).
(264) Vajna, S., and Gabos-Pinter, M., Magyar Kem. Folydirat, 56. 63 (1950). (265) Vanetten, C. H., and Wiele, M.B., ANAL.C H E M . , . ~1338-9 ~, (1951). (266) Vashenin, I. G., Pochvovedenie (Pedology), 1949, 359-61. (267) Veltman, G. H., Z . anal. Chem., 135, 340-9 (1952). (268) Vermast, F.A. F., Chroniea Naturae, 106, 104-10 (1950). (269) Vyakhirev, D. A., and Guglina, S.A., Zarodskaya Lab., 15, 1426-30 (1949). (270) Fadhwani, T . K., J. I n d i a n I n s t . Sci., 34, 123-33, 135-47 (1952). (271) Ibid., pp. 149-57. (272) Ibid., pp. 159-61. (273) Walter, R. N., ANAL.CHEM.,22, 1332-4 (1950). (274) Ward, F. N., Ibid., 23,788-91 (1951). (275) Watanabe, I. T., and Ichinose, Y., J . P h a r m . S O C .J a p a n , 63, 36-40 (1943). (276) Weneer. P. E.. Monnier. D.. and Jaccard. F.. H e l t . C h i m . Acta, 33,1458-63 (1950). (277) West, T. S., SchoolSci. Rev., 32, 163-4 (1951). (278) White, L. A f . , and Long, h1. h A L . CHEM., 23, 363-5 (1951). I S D . ENG.CHEM., AN.4L. ED.,9 , 136-8 (1937). (279) \vllCOX, L. IT., 1 Willard, H. H.. and Horton, C. A.. - 4 ~ 4CHEM.. ~ . 22, 119Ck4 (1950). Ibid., pp. 1194-7. Willson, A. E.,I b i d . , 23,754-7 (1951). Willson, A. E., and Wander, I. K., Ibid., 22, 195-6 (1950). Wilson, H. X., A n a l y s t , 76,65-76 (1951). Wurzschmitt, B., Chem.-Ztg., 74,356-60 (1950). Yoe, J. H., and Rush, R. hf., -4naZ. Chzm. d c f a , 6, 526-7 (1952). Yoe, J. H., and Will, F., Ibid., 6,450-1 (1952). Young, I. G., and Hiskey, C. F., ANAL. CHEY., 23, 506-8 (1951). Zaichikova, L. B., Zanodskaya Lab., 15, 1025-7 (1949). Zamyatina, V. B., Soaet. Agron., 1950, S o . 7, 58-64. Zeppelin, H. v., Angew. Chem., 63, 281-2 (1951). Zeppelin, H. v., and Fuchs, J., Ibid., 64, 223-4 (1952). Zhuravskaya, V. I., Zaaodskaya Lab., 16, 1302-4 (1950). Zimmermann, M., Angew. Chem., 62A, 291-2 (1950). Zoellner, H., Glas-Email-Keramo-Tech., 2 , 378-81 (1951).
c.,
FOOD JOHN R. MATCHETT AND HARRY W. VON LOESECKE Bureau of Agricultural & Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture, Washington, D. C.
T
HIS review covers the period of December 1951 t o October 1952. It is a sequel to the review of methods of food analyses
for the period December 1950 to November 1951 (127). MOISTURE
Rapid and simple methods of moisture determination applicable t o all types of food materials are still sought, but it seems doubtful that such a goal will ever be attained, although it has been stated that the Karl Fischer method approaches stoichiometrical accuracy for water in most foodstuffs (10). The basic causes of difficulties associated with moisture tests have been the subject of a symposium (35). An electrical apparatus has been developed for Karl Fischer titrations (66) which utilizes the dead-stop principle, automatically adds the reagent, and differentiates between “true” and “false” fleeting end points. The Karl Fischer method has also been used for estimating moisture in dehydrated vegetables by substituting formamide for dry methanol as the extraction solvent (132). A rapid, simple method for moisture in fruits and vegetables, based upon oxidation with a potassium chromate solution (193), has been applied with equal success for moisture determinations in pineapple-rice pudding, rice, prunes, and fresh frozen corn (112).
Though sesame is one of the oldest cultivated oilseed crops, no systematic investigation of moisture and volatile matter methods
has been reported. A proposed method makes use of a forced draft oven at 130’ C. using a 2-gram sample (180), and a rapid dielectric method has been suggested for oilseeds and cakes (If%). However, the relation between the dielectric constant and moisture in the material cannot be expressed by a simple function and a separate calibration is necessary for each kind of seed. Problems of moisture determination in milk products (96), cereals and legumes (56), and meat and meat products (12) have been considered in the light of different methods suggested from past experiences. A modification of the Dean and Stark moisture apparatus makes possible moisture determination in materials containing large amounts of water (89). Modification consists of a graduated receiving column fitted into a small flask of known capacity. Sine such flasks are used, ranging in capacity from about 20 to 80 ml., according t o the moisture content of the sample being tested . A rapid moisture method for beet pulp is based on the release of moisture from pressed pulp by contact with molasses (36). PROTEINS AND AMINO ACIDS
Although 70 years have passed since Kjeldahl first proposed his method, i t is still being subjected t o modification and discussion. One of the more recent modifications describes a n e v digestion apparatus (206). Chromatographic separation of amino acids continues t o occupy
25
V O L U M E 25, NO. 1, J A N U A R Y 1 9 5 3 the interest of food analysts. A recent book on paper chromatography ( 1 7 ) , a review on the use of synthetic ion-exchange resins for separating amino acids (108), and a report of a continuing investigation of the nature of the phenomena that operate in paper chromatography (105) are of interest in this connection. Separation and identification of amino acids by circular paper chromatography are described in a communication from India ( 7 1 ) . Mixtures of amino acids may be separated by a series of one-dimensional buffered chromatograms and then quantitatively determined by direct photometry on the paper (124). Fading of chromatograms, especially those developed with ninhydrin, may be troublesome. Such fading can be inhibited by washing the dried paper with ethyl ether, drying, dipping in a suitable preserving varnish, and drying again (1). ,\lethods of estimating amino acids in protein hydrolyzates have been proposed in two papers (158, 177). The former, particularly suitable for studying the rate and degree of protein hydrolysis, is a rapid spectrophotometric method, based on the ultraviolet absorbency of the copper salts of the amino acids. The latter method achieves separation by one-dimensional paper chromatography with a number of alcohols, followed by photometric scanning of the developed chromatograms. METALLIC IONS
Polarographic determination of zinc (101, 130), iodine (731, and copper (130) in plants and food products has been described. Copper may also be determined by a modified dithizone method (107), particularly suitable for copper in sugar sirups and beverages because it requires only standard equipment and a single spectrophotometric reading. .4 spectrochemical method for mineral elements in beef employs a direct current arc on the ashed material, and uses standards of a “Synthetic meat ash” as a base (134). .4 simplified apparatus for Gutzeit’s arsenic test consists of a 3-ml. Ostwald-Folin pipet seated in the neck of a 100-ml. volumetric flask. A strip of lead acetate paper is placed in the bulb of the pipet, and a strip of mercuric chloride paper hung in the mouthpiece of the pipet (142). Because an arsenic deposit in the Marsh test is often not clearly visible, it has been suggested (109) that the formation of an iodide complex of arsenic with cesium, followed by treatment with pyridine, would permit distinction of arsenic from antimony. The importance of boron in plant nutrition makes desirable a simple, accurate method for its determination. A recently proposed technique (123) is a modification of the quinalizarin method to increase effective range of determination. A method has been proposed for oxalates in fresh plant material (9). It is not applicable to dry material because oxalate is lost upon drying. The old thiocyanate method for iron in molasses has been found to be unsatisfactory and the dipyridyl method of the Association of Official Agricultural Chemists has been adapted for this purpose (167). I n the determination of magnesium in plant material, magnesium is precipitated as the oxinate, which is then measured in acid solution by absorption a t 358 mp (40). Twenty to 200 micrograms of magnesium in 1 to 4 ml. can be estimated. Quantities of lead of less than 1 p.p.m. can be determined in wheat flour by dry ashing, making a preliminary separation of lead as the diethyldithiocarbamate complex, and subsequently determining it absorptiometrically by mixed color technique (80). A rapid, simple colorimetric titration procedure for estimating calcium in solutions and in fruit and vegetable tissues should be of interest to control chemists in fruit and vegetable processing plants (183). FATS AND OILS
Because peroxide values cannot always be correlated with true rancidity as detected by sensory means, considerable interest has
been shown in the use of thiobarbituric acid as a test reagent, A close correlation has been found between the thiobarbituric acid test and numerical flavor scores of milk samples having oxidized flavors of varying intensity (51). One suggested method for estimating the fat content of cheese, butter, margarine, milk, and cream involves mixing the sample with an anhydrous salt (such as sodium sulfate), allowing it to stand for an hour, and then extracting with ethyl ether in a Soxhlet for 4 to 5 hours ( 6 ) . Another proposed method for fat in milk depends upon measuring the turbidity caused by fatdroplet dispersion (21). A rapid method has also been suggested for fat determination in such products as sweetened condensed milk (170). The British have recently published their standard methods for butter analysis (22). A study has been made of odor, flavor, and peroxide values as a measure of rancidity in frozen ground pork (143). Some reagents used for the iodometric estimation of perioxides in fats give high blanks, and some react with the liberated iodine. -4 10% solution of citric acid in a mivture of tert-butyl alcohol and carbon tetrachloride appears to be free from these disadvantages (811.
Spectrophotometric methods for determining polyunsaturated fatty acids in natural fats and oils have been restandardized (20) using pure, natural acids, and a further study of the tetrabromide method of estimating linoleic in fatty acid mixtures has been undertaken (198). Free fatty acids may be identified by the color of their heavy metal salts after paper chromatography (97, 98). A timesaving “sorting” procedure has been proposed for estimating water-insoluble fatty acids in cream and butter (85). Results obtained closely approximate those found by the official method. A method has also been proposed for determination of isovaleric acid in the presence of butyric and caproic acids in butter, hydrogenated fat, and margarine (156). The method is based on the principle of independent fractional distillation, and is carried out in a continuation of determination of the Reichert-Meissl number. An improved method for the determination of sesamol, aesamolin, and sesamin in sesamin concentrates and oils has been reported (186). The method not only permits accurate determination of free and bound sesamol in sesamin concentrates, but is preferred for the analysis of crude sesame oil, because interfering substances are eliminated. A rapid dielectric method for eliminating the oil content of soybeans makes use of a Stein laboratory mill for simultaneously grinding and solvent extracting the oil from the sample (88). Dielectric properties of the extract are measured by a Steinlite LOS Unit. Results on a single sample can be obtained in 15 minutes. A simple method for the extraction and identification of the coloring matter in fats consists of dropping a solution of the fat onto the center of an alumina disk and then eluting with several specified solvents (138). Disks are fixed by saturating with melted paraffin (139). ENZYMES
Identification and separation of enzymes by paper chromatography are based on the fact that most enzymes travel on paper in solvents with high water content, and by proper selection of solvents it is possible to make enzymes move on paper a t different rates. Using such solvents as aqueous solutions of acetone, ethyl alcohol, and sodium chloride, R, values have been tabulated for amylases, phosphorylases, and phosphatases (72). A simple phosphatase method, utilizing only one buffer substrate concentration and one precipitant concentration for all dairy products (104), is said to be highly accurate, sensitive, simple, and low in cost. A technique of measuring the proteolytic activity of papain
ANALYTICAL CHEMISTRY
26
makes use of a temperature of 60” C., combined with maximum activation and casein as a substrate (SO). Assay time is reduced from 3 hours to 30 minutes. Rennet, large quantities of which are used in cheese making, is standardized by measuring the clotting time in a substrate made by reconstituting skimmed milk powder in 0.01 M calcium chloride ( I S ) . Xanthene dehydrogenase is measured in chicken tissue by using methylene blue as an auto-oxidizable hydrogen acceptor (169). A microdextrinization method for alpha-amylase activity of flour has been described (186), and catechol oxidase activity in wheat bran and seeds i s based upon measurement of the reduction of o-benzoquinone to catechol by ascorbic acid (132). CARBOHYDRATES
Improved chromatographic estimation of raffinose in raw sugars has been reported (S), and a quantitative technique for raffinose in mother beets and raw beet juices involves treating the beet juice with mixed-bed ion exchangers and then determining by paper chromatography (24),usingamodification of deffhalley’s method (45). I n the pectin field, of particular interest is the publication of a review of methods of determining pectic substances and pectic enzymes in citrus and tomato products (120). The review presents the nature of the methods and types of information needed, so that the food analyst can obtain useful data with a minimum of effort. A colorimetric method for determining pectin substances will be found useful to workers in this field (121). A recently published manual has brought together selected methods of determining reducing sugars (86). Procedures are given in sufficient detail so that analyses can be made without recourse to other texts. A new titrimetric method with a sharp end point makes use of a 0.03% solution of alkaline potassium ferrocyanide, which is titrated with the sugar solution in the presence of a 1% solution of methylene blue as an indicator (171). Two improved copper reagents for sugar determinations have also been described (176). The anthrone method for carbohydrates has been improved by eliminating the dissolving of anthrone in sulfuric acid ( l f 3 ) . This does away with colqr variations arising from the source, and allows a single standardization curve to suffice. Paper chromatographic techniques for sugar have been described in several papers (14, 16, 46, 140, 195). Sucaryl (sodium cyclohexylsulfamate) has recently become an article of commerce as an artificial sweetener. Its determination in sugar-free beverages as cyclohexylsulfamic acid has been suggested (203). The technique is subject to check by precipitation of barium sulfate. Sucrose in chocolate is determined by a polarographic method ( I & ) , and lactose in milk is estimated (63) by a modification of Hassid’s method (82), which is well adapted to routine use. hlethods of analysis used in the starch and dextrose industry have been greatly extended and improved during the past 20 years. One recent paper is of interest in this respect, as it deals with methods used in the sales of starch and dextrose (60). White malt sirup, more common in England than in the United States, and obtained by enzymatic conversion is indistinguishable from glucose sirup, an acid conversion product, when ordinary methods of copper reduction and polarimetry are used. Three special methods have been described for comparing the composition of white malt sirup and liquid glucose (28). Methods for determining molecular weights of amylodextrins, amylose8, and amylopectins based on osmotic pressure or ultracentrifuging measurements are laborious and require large samples. Colorimetric methods involving determination of aldehyde end groups give only relative molecular weights. Of interest, however, is a method (144) based on the old Folin and RIalmros (69) colorimetric technique for glucose. This new method shows fair agreement with molecular weights obtained by osmotic pressure, is rapid, and requires little material.
Glycogen has been determined with anthrone (149) and by measuring the turbidity of aqueous alcoholic suspensions of the material (77). I n the range of 0.1 to 0.5 mg. of glycogen, it is necessary to measure turbidity with a nephelometer, but for larger amounts a spectrophotometer is adequate. A colorimetric method for methycellulose involves the use of anthrone (165) and is of interest because it permits estimation of Methocel (Dow methylcellulose) incorporated with other material that would interfere with the methoxyl determination. VITAMINS
A series of papers dealing with the determination of vitamin A in margarine encompasses studies by both American (116-118, 129) and Norwegian (19) research workers. Recent assessments of the precision of geometric correction procedures for the spectrometric estimation of vitamin A are discussed in a recent paper from England ( 7 ) . Application of the Morton-Stubbs correction geometrically shows that the precision of corrected values depends on the precision differences between the readings a t 328 mp and the two fixation points (154). The usual MortonStubbs formula can be written in terms of these differences. Perhaps it would be well to call attention to a caution given by Morton (SI), that the Morton-Stubbs correction should be used only where it is applicable. Unexplained variations in adsorpton chromatography used for vitamin A are described in a method for evaluating or standardizing one of the more important factors -namely, the strength or adsorptive capacity of the adsorbent (199). In the case of low-potency fish oils, a chromatographic technique is used for removal of irrelevant absorption, rather than saponification (48). A critical review of vitamin A procedures and correction factors in spectrophotometric determinations (8) and recent books on chemical and physical methods for vitamin determinations (5, 75) should be of interest to those engaged in vitamin assays. Antimony trichloride has been much used in vitamin A determinations, and the desired effect is alleged to be caused by the presence of antimony pentachloride in small amounts. Thus, a more effective reagent is a solution containing more antimony pentachlaride and prepared in a specific manner (26). A simplified method for thiamine in rice is based on the fact that about 85% of the thiamine in rice is in the free form and it is not necessary to free thiamine from cocarboxylase by enzymatic digestion (119). The method depends upon the color developed with diazotized p-aminoacetophenone, first pointed out by Prebluda and McCollum (163). A paper chromatographic method for thiamine comes from Japan (135), and the microbiologic assay for niacin has been further studied from the standpoint of effect of total volume per tube on accuracy of results (83). Thiamine and riboflavin may be separated from niacin and pyridoxine by paper chromatograms developed with watersaturated butyl alcohol (166). The separated groups are eluted from the paper and the solutions read in a spectrophotometer. It has also been suggested that pyridoxine can be separated from niacin by adsorption on Decalso, followed by elution with ammonium hydroxide (189). If pyridoxine is present, it is converted and oxidized with sulfuric acid and selenium, and the color reaction of the pyridine ring with cyanogen bromide and sulfanilic acid is measured photometrically. A manometric adaptation for rapid microbiological assay of certain vitamins of the B complex is based on a determination of growth of the organism used as measured by carbon dioxide pressure (178). This pressure is generated in a medium containing carbonate, as a result of formation of lactic acid by the bacteria used in the assay. In the case of assays utilizing fungi, determination of growth is measured by oxygen consumption. Ascorbic acid is generally estimated by titration with dichloroindophenol, but the titration is not specific because other substances, such as sulfite, iron, and tin, also reduce the reagent. Effect of iron can be overcome by oxidation with hydrogen per-
V O L U M E 25, NO. 1, J A N U A R Y 1 9 5 3 oxide and complexing the resulting ferric iron m-ith tartaric acid (204), or by removing the iron with a n ion exchange resin such as Zeo Karb 215 (147). Free and bound ascorbic acid in vegetables have been determined chromatographically in a hydrogen atmosphere (174). It has been reported that solutions of ascorbic acid can be stabilized by keeping under carbon dioxide a t 0” C. and adding Trilon B alone or with formic acid (55). A rough test for vitamin DZ involves spotting the vitamin on filter paper and then irradiating photographic paper through the spotted filter paper a i t h ultraviolet light (61). Two papers on the estimation of tocopherols make use of a chromatographic method (23) and a chemical technique (190). Results of laboratory investigations of certain basal medium constituents in the microbiological assay of vitamin BIZ have been reported (115); a statistical analysis of the 1950 collaborative study of the U.S.P. method for Blz gave 95% confidence limits ranging from 24 to 68% (25). Use of a mutant of Escherichia coli for B I assays ~ is described (18, 79, 200), but high concentrations of methionine are said to interfere when the agar cup method is used (18). Vitamin BIZassays by means of Euglena gracilis have also been mentioned (194). A colorimetric method for BIZ involves hydrolysis of the vitamins in dilute hydrochloric acid, liberating the so-called “red acid,” which has greater color intensity than any other known compound (84). The color of an ester of this acid is measured a t 552 mp. A chemical method for Bi2 is based on the difference between the visible spectrum of this vitamin and the spectrum of the dicyanide complex formed in solutions containing excess cyanide ions (161). ACIDS
One method of determining organic acids involves initial separation on a silica gel column, followed, when necessary, by additional separation by both chromatographic and chemical techniques (29). It has been reported, however, that silica gel column separation is limited in sensitivity, particularly in the case of the more water-soluble acids (47). Paper chroinatographic methods for organic acids have been reported in two papers (27, 42), and small amounts of tartaric acid can he determined polarographically in the presence of fairly large amounts of other fruit acids (128). Determination of citric acid in milk as the pentabromoacetone has been suggested (166). Results in normal inilk are said to be accurate to the third decimal place. COLOR AND TASTE
Color measurements as a quality control tool have been discussed in relation to different methods used (188)) and a recent book in this field should be of interest for all concerned m-ith color measurements (95). h new and rather novel objective method for color comparison is by means of black and white photographs (54). Paper chromatography, combined with chromatography on aluminum oxide, has been reported as a reliakile method for estimating coloring matter in food (173), and foreign coloring matter in wine is detected by chromatographic methods (162). Using the Kent-Jones and Martin flour color grader and a photoelectric procedure, the color of flour as affected by grade has been reported ( 9 9 ) ; a simple, accurate, and rapid method for flour brightness consists of reflectance measurements (by attachment to a spectrophotometer) on hard pellets of flour (91). It has been reported that tomato juice color by the Hunter color difference meter was the most accurate of the methods tried and correlated best with grades given by Production and Marketing Administration inspectors (160). The so-called Purdue color meter, which measures color by photoelectronic means, is believed to hold promise for color measurements on
21 tomatoes (32, 44). -4 study of tomato color has also been reported (67). A photoelectric reflectance method for color of granulated sugar has been developed for plant control purposes (69). The importance and application of organoleptic panel testing as a research tool have been reviewed (33). A popular article on smell and taste (76) will be of interest to those who do not care to go too deeply into the subject, but the more serious will find a recent discussion of the critical frequency of taste (94), perhaps, more to their liking. A4new technique for taste panel rating, called the “hedonic scale method,” has been offered (148), although the basic approach is not claimed to be new. Other papers of interest to those engaged in this field of study deal with selection of sensory testing panels (70) and methods of reducing the number of observations (191). .4 new concept of onion pungency has been described, along with a method for measuring pungency and flavor (103). INSECTICIDE RESIDUES
Increased use of the newer insecticides and fungicides ash necessitated the development of sensitive and specific methods for their detection on foods. A discussion of proper solvent to use to separate insecticides from plant and animal tissues (93) is of value in this respect. .4n infrared spectrophotometric method has been proposed for aldrin and dieldrin (68), a colorimetric procedure for piperonyl butoxide (92), an improved technique for dithiocarbamate residues permitting detection of less than 1 p.p.m. of the insecticide (114), and detection of pyrethrum in flour picked up in bags with pyrethrum-treated warp (169), and in pyrethrum-coated paper bags (53). Detection of residues of chlorinated insecticides has been reported in several papers (34, 49, 68, 145. 150. 168). The infrared absorption spectrum of toxaphene has been published (100) and should he of considerable use in insecticide residue determinations. Bioassays of insecticide residues, using houseflies or mosquito larvae, are being increasinglv used ( 6 4 ) . I n some instances this technique obviates the meticulous purification of sample extracts frequently necessary for other bioassay procedures. Bioassays of lindane residues make use of houseflies (87); in another method for toxic spray residues, mosquito larvae are utilized (39). CONTAMINATION AND SPOILAGE
Increased use of surface active agents in cleaning and preparation of foods makes desirable methods of detecting their presence in products for human consumption. TKOmethods have recently been presented for detecting dodecylbenzene sodium sulfonate (an anionic surfactant) (78); and identification of quaternary ammonium compounds as reineckates has been proposed (202). Benzoic acid has been detected by the colors formed by nitration and subsequent neutralization n-ith sodium hydroxide (1577, and by chromatographic methods (146). The latter method deals with concentrations of from 20 to 220 p.p.m. Insect fragments in flour and other granular foods, long a problem in the grain and seeds processing industries, have been detected by means of low-energy radiation from a cobalt-target beryllium-window x-ray tube (IS,??), and by using a spectrophotometric technique (161). Detection of horse fat in the presence of pork and beef fats is based on a spectrophotometric analysis for trienoic fatty acids (50). A recent critical review deals with the detection of starting decomposition of meat and meat products (172) while a number of chemical methods have been evaluated as indicators of various stages of spoilage of tuna, mackerel, and sardines (59). hdded water in canned tomatoes is detected by the ratio of lycopene of the canned fruit to lycopene content of the drained liquor (106). When water has been added, this ratio increases.
ANALYTICAL CHEMISTRY
28
Water addition to human milk is detected by measuring the refractive index of the ultrafiltered milk (163). Kormal readings are between 44’ and 46” and deviations below this level show water addition. -4 hemocytometer is suggested as a tool for determining potato starch in flour (41), while detection of potassium bromate in flour consists of extracting the flour with zinc sulfate solution and estimating bromate iodometrically in the clarified filtrate (4). A method has been proposed for estimation of isomers of butylated hydroxyanisole in lard (125), and a simple, rapid technique for detecting trichloroethylene in vegetable oils makes use of a modified Beilstein test, a-hich consists of applying the oil sample to a 40-mesh copper gauze in a specified manner and then holding the gauze in the colorless flame of a burner (264). Practical limit of the test is about 0.01% trichloroethylene. The method for monochloroacetic acid in beverages has been modified to be applicable to beverage bases containing halogenated weighting oils (201). An interesting technique for detecting glass fragments in food products consists of removing large pieces by sieving and then suspending the sample in chloroform (66). The glass will sink, and is drawn o f f ,washed with dilute hydrochloric acid and water, dried, treated with phenolphthalein in alcohol, and gently ground. The grinding noise and development of red spots indicate glass. Of interest, too, are methods for detecting tetrachloronitrobenzene residues on potatoes (196) and bromoacetic acid in milk (110). The latter method is based on inhibition of yeast fermentation of glucose by bromoacetic acid. A rapid method for detecting substitution and adulteration in certain fatty food products makes use of ultraviolet spectrophotometric measurements (136). Rigid bacteriological control during the processing of frozen concentrated orange juice is being recognized as being of increasing importance for a quality product. Requirements of suitable bacteriological plating media have been discussed in a recent paper (141), and some results obtained with various media are reported and evaluated. An improved method for the bacteriological examination of shell eggs using thioglycollate broth has been presented (205), and an apparatus, working somewhat on the principle of an eudiometer, has been suggested for the collection and analysis of gases in swelled cans (11). Differentiation between fruit and grape wine can be accomplished by chromatographic methods (175, 187). MISCELLANEOUS
Application of chromatography to the separation of flavonoid compounds has been reported (go), as well as to the separation of terpenes from citrus oils (231). A uniform drying oven for quantitative chromatography should be of interest in this connection (2). Research on the application of high-speed electrons in the preservation of biological materials makes necessary reliable means of measuring depth of penetration and areas covered by the electroxs. A recent method makes use of dyes (methylene blue and resazurin) that undergo color changes nThen exposed to ionizing radiations (74). Bran and germ particles in wheat flour are detected by differential staining with crvstal violet (111); and a method for estimating the skin conteut of peanuts is based on the fact that the pigments in the skin consist chiefly of a catechol tannin and related compounds that give a red color when heated with alcoholic hydrochloric acid ( 179). A simplified method for filtering roller process dried milk powder is based on using a hot 10% sodium citrate solution in place of the pepsin-hydrochloric acid method (185), and a technique and apparatus for extraneous matter in roller-dried milk powder has been suggested (15). An apparatus for measuring the efficiency of defoamers con-
sists of a device for passing clean, measured air through a standard mixture of yeast, molasses, and the test defoamer a t a controlled temperature (157). A consistometer made from medium book weight paper for measuring the consistency of cream style corn should be of interest to plant control chemists, as it eliminates time and expense of washing necessary when the Adams consistometer is used (193). Results are, however, less than those obtained with the Adams consistometer. continuous electronic device for measuring rapid temperature changes within a system should be of interest to food bacteriologists concerned with heat penetration studies (181). Because ethylene gas in minute quantities plays an important part in plant metabolism, especially in ripening fruits, a sensitive quantitative method would be of value. A recent method makes use of formation of an ethylene-mercury complex from which ethylene is later removed and measured manometrically (152). The method is best suited for ethylene concentrations of 0.5 p.p.m. and higher. Extensive use of a variety of polysaccharides as stabiliaing or thickening agents in foods creates need for methods of detection and estimation. A recent paper (57) sets forth a scheme of identification for such stabilizing agents as pectin, de-esterified pectin, algin, Irish moss, gum tragacanth, karaya, locust bean, bean, ghatti, and arabic, and agar, starch, carboxymethylcellulose, methylcellulose, and gelatin. Other methods of interest to the food chemist deal a i t h size distribution of suspended particles in tomato products (102), cooling curves as a means of determining the temper of molten chocolate (52), and quantitative means of differentiating cinnamon powder from cassia by measuring the fiber length of the former (43). Some variations from standard analytical procedures in food analysis are worthy of note. A simple rapid method for crude fiber consists of gelatinizing starch in the sample by autoclaving, cooling, digesting with proteolytic and amyolytic enzymes, filtering, drying, weighing, ashing, and reweighing (197). Loss in weight represents crude fiber. Pre-ashing, using a special apparatus (37) has been found to be a dependable and time-saving procedure where large amounts of samples of highly foaming and sugar-containing products must be ashed (38). LITERATURE CITED
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