PLANNING NUTRITION STUDIES Involving Canned Foods T
HE first comprehensive study of the nutritive values of commercially canned foods was initiated by Kohman and Eddy and their associates about twenty years ago (9). These pioneer studies soon attracted other investigators t o the field, and a considerable amount of work has since been carried out on foods preserved by canning procedures. Despite this fact, a relatively meager amount of information on canned foods appears in recent critical rev i e w s o r s u m m a r y tables covering the nutritive values of common foods ( 3 , 5 ,7). This paucity of data on canned foods considered suitable for inclusion in critical tabulations may be attributed to a number of factors. Important among these are the relatively long times required for execution of the early bioassay methods for vitamins in foods, the nonspecificity of the older bioassay techniques, and the nonavailability of standards of reference which would have permitted quantitative expression of the results obtained. During the past ten years the development of physical, chemical, and microbiological methods for estimating vitamins has progressed rapidly. Stable reference standards for the better known factors have also been made available. Accordingly, during the past decade a number of investigators have undertaken studies on canned foods with these new tools, and the volume of information regarding their nutritive values is rapidly expanding. However, it is evident that the value of some of the reports could have been enhanced by more careful planning and execution. The primary purpose of this paper is t o outline some of the considerations which must receive attention if the results of the experiments are to be translated to commercial canning practices.
J. F. Feaster a n d 0. R. Alexander AMERICAN CAN COMPANY, MAYWOOD, ILL.
preserving operations (canning included) on specific nutrients in raw materials. A number of factors must be considered in planning and executing experiments of the above types, and a few of the most important are briefly reviewed here. SELECTION OF NUTRIENTS
Of all the nutrients i n common foods, certain of the vitamins are most a p t to be affected by the chemical and physical changes which raw foods may undergo during canning. Therefore, it has become well-nigh standard procedure t o measure the effect on such factors of the over-all or specific operations in canning procedures. With the exception of vitamin A, the provitamins A, riboflavin, thiamine, and ascorbic acid, the procedures commonly employed in canning have little effect on vitamins in raw food materials. The chief factors affecting vitamin A activity appear to be associated with the mechanical separations incident to preparing the food for canning; there is some evidence that oxidative effects on this vitamin may also be present in some procedures. Other than removal by solution, which is also characteristic of thiamine and ascorbic acid, the chief interest in studying riboflavin i n packaged foods is t o determine the possible effects of light when foods are packed in transparent and translucent containers. The sensitivity of thiamine to heat and of ascorbic acid to oxidation, together with the water-soluble nature of these two vitamins, have been largely responsible for selection of either or both of these factors as yardsticks in investigating the effects of canning procedures on raw foods, Further, with a few wellknown exceptions, the standard chemical methods for estimation of these vitamins give reliable and reproducible results with most fruits and vegetables. A study of the retention of thiamine or ascorbic acid or both in food materials during canning has become universal procedure. Sometimes the scope of a n experiment on acid fruits or vegetables must be limited; the estimation of thiamine may then be eliminated, and the effects of canning judged by the retention of ascorbic acid alone. The reasons are t h a t not only are the ma-
PRINCIPAL TYPES O F N U T R I T I O N STUDIES
Apart from highly specialized studies, there are four common types of investigations on the nutritive values of foods subjected to canning procedures. Frequently experiments are conducted to determine the relation between the contents of nutrients in raw foods and in the same food after canning. I n addition to the effect of the over-all canning procedure, it is sometimes desired to establish the specific effects of individual steps or operations within the canning procedure on the nutrients in raw canning stock. Information of this type is valuable in establishing canning procedures designed t o retain maximum amounts of the nutrients in raw foods. A third type of study is the statistical establishment of the nutritive values of canned foods through the examination of a large number of canned samples of known history. Studies of this kind help fix the ranges of nutritive values within which the canned products included can reasonably be expected t o fall. As a fourth less frequent type of study, comparisons involving canned foods are sometimes undertaken. These studies seek to determine the relative effects of food-preparing and/or food-
112
INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1944
TABLE I. EFFECT OF ACID MEDIUMON ASCORBIC ACID TITER VALUESOF IDENTICAL CANNEDPBABRINES Storage Conditions Months Temp. 8 Room 8 Room 12 Room 12 Room 8
8 12 12
98O
F.
98' F. 98' F. 9 8 O F.
Ascorbic Acid, Mg./Ml. 0.130 0.145 0.134 0.149 0,102 0.143 0.117 0.144,
Diluting Acid,
%
8 acetic 8 acetic 8 acetic 8 acetic 8 acetic 8 acetic 8 acetic 8 acetic
+ 2 HPOs + 2 HPOs + 2 HPOs
173
terial as i t enters the canning line is suitable for sampling as the raw product control. Certain products, however, receive considerable mechanical handling whereby both edible and nonedible tissues are removed, such as skins, cores, butts, stems, and &ones or pits. I n certain of these operations vitamin-bearing portions of the food may be removed either by loss of tissues or by bleeding of plant juices or saps. The extent of weight loss incident t o canning is indicated by the following yields per ton of raw material:
4- 2 HPOs Product
jority of such products low in thiamine, but also the heat treatments given them are not very severe; such foods are processed at the temperature of boiling water or lower. However, where t h e scope of the experiment need not be limited and where the initial thiamine content of the acid food is relatively high (tomatoes and tomato juice), i t is preferable from the standpoint of complete information to follow the retention of both ascorbic~acid a n d thiamine through the procedure. ASCORBIC ACID METHOD
The original titration technique for ascorbic acid described by Bessey and King (8) called for acetic or trichloroacetic acid in preparing the food extract for titration with 2,6-dichlorophenolindophenol. Later i t was demonstrated t h a t a solution containing acetic and metaphosphoric acids was preferable for extracting raw food materials because of the increased stability of ascorbic acid in such a medium (IS). This modification of the original technique has since been widely used in estimating ascorbic acid i n canned foods. Hauck (8) verified an observation previously made by several laboratories associated with the canning industry-namely, t h a t metaphosphoric acid in the extracting medium permits interference by ferrous iron present in canned foods through reaction of these foods with the metal containers. As a result, titer values on a canned food extracted with acetic-metaphosphoric acid mixture are consistently higher than on the same food extracted with acetic acid alone. Since the food had been processed this difference could not be due t o enzyme activity. Differences obtained by the two types of extracting media are shown in Table I. Work in this laboratory has indicated that ferrous iron up t o 100 p.p.m. does not interfere with the indicator titration if acetic acid alone is present (IO). It is therefore suggested t h a t the original Bessey and King technique be used for estimating ascorbic acid in canned foods unless there is definite evidence t h a t the ferrous iron content of the sample is insignificant. Work during the current year has suggested that, when the standard practice of comminuting raw foods i n 3% metaphosphoric acid is followed, difficulty may be experienced from enzyme activity, specifically with foods such as green peas which are likely t o be covered with plant juices as a result of the vining (podding) operation. After comminution, there is apparently a rapid decline of ascorbic acid on standing, due t o enzyme action, which is not impeded by 3% metaphosphoric acid. This action may be inhibited by 6% metaphosphoric acid (14). This recent experience suggests caution in the handling of raw product samples used as controls in canned food nutrition studies. OVER-ALL EFFECTS OF CANNING
RAWMATERIAL. In studies of this type, the prime consideration is the proper control of the raw material, since the over-all effect of the canning procedure is t o be judged by the relative vitamin contents of the raw and final canned product. Obviously it is important t h a t the raw stock selected as the control be closely comparable if not absolutely identical with that which appears in the final product. For many products the ma-
Beets Carrots, diced or sliced Corn, whole grain (based on husk corn as raw stock) Peas Spinach Tomatoes
Total Weight of Solids in Can, Lb. 1250-1500 140&1500 590-630 1800-2000
1500-1700 906-1431
Although the figures reflect the loss of weight due t o a variety of causes, they suggest t h a t judgment should be exercised as to the tissue or tissues which are allowed to remain in the r a t product control sample. I n field work in canneries, our practice is to begin with a large well-mixed raw stock sample weighing between 50 and 300 pounds, depending upon the food under test. Then a 1- or 2-kg, sample can be selected as the raw product control; from this small portion the edible and nonedible portions of the food which will be removed during the canning procedure can be removed by hand. B y slight interruption of production, the remainder of the sample can readily be traced through the canning procedure and the comparable final product obtained. SIZE AND QUALITYGRADINQ. Not only may the validity of over-all comparisons be influenced by removal from the raw stock of portions of the food which do not appear in the final product, but the reliability of the results may also be influenced by differences in raw or unprocessed stock resulting from quality or size separations where such operations are involved in the canning procedure. I n any canning procedure in which one or more operations result in the segregation of certain portions of the raw product, i t is essential t h a t the material selected t o represent the raw control sample should contain only the portions or fractions which would appear i n the final product. I n canning procedures which do employ quality grading or size grading operations, the problem of relating the raw material to the final product may be somewhat difficult. Peas, for example, are commonly separated according t o sieve size, and each fraction is canned separately. It is apparent t h a t a composite sample containing a number of sieve sizes cannot be oompared directly with the final canned product which may represent only one sieve size of peas. Peas may also be quality graded, or separated into groups according to maturity by virtue of their ability to float or sink in salt solutions of specific concentrations. As in size grading, a physical separation of the peas is effected; whether the various types of quality graders may also influence the nutritive values of peas as a result of their exposure to turbulent salt brines is still undetermined.
TABLE11. EFFECTOF SIEVE SIZE, VARIETY,AND YEAR OF GROWTHON THIAMINE AND ASCORBIC ACID IN RAWPEAS Variety Alaska
sieve Sine 1 2 3 4
Thiamine, Mmg./G. 1941 1942 2.4 2.8 (2'7] 3.1 3.4
3.5 3.6
Ascorbio Acid, Mg./G. 1941 1942 0.39 0.32 0.27 0.27
0.50 0 46
INDUSTRIAL AND ENGINEERING CHEMISTRY
174
TABLE 111. Type of Container Plain Enameled
E F F E C T O F STORAGE ON T I X AND I R O N C O N T E N T O F
Months Stored a t 98' F. 0 6 12 0 6 12
KO.Cans Sampled 8 8
Vacuum, In. Hg. Max. Min. Av;
8
13.5 10 11
8 8 8
13 11 10
9 7 6 9 8 0
TOMATO JUICE
Head Space (32 In.) Max. Min. Av;
11 9 8 11 9 7
Both size and quality grading may influence the results of studies on the over-all canning effect. It is known that degree of maturity may have a marked effect on the level of certain nutrients in raw foods; there is apparently a similar influence with size differences. Table I1 illustrates the variation in ascorbic acid and thiamine contents of raw peas with sieve size. These data indicate the need for close control of the raw material sample where size grading is a n integral part of the canning procedure. Where size grading is practiced, a proper raw product control sample may be obtained by size grading before the material enters the initial step of the canning procedure. To control the quality grading operation, it is necessary to determine the percentage of sinkers and floaters present in a large well-mixed batch of the raw material for the particular quality grader used, since the mechanical operation varies for different types of graders. Further, it is not advisable t o depend on current factory experience as t o the average percentage separation into sinkers and floaters because such a figure represents a n over-all average, and the actual percentage separation may vary considerably with each lot of peas. Knowing this distribution and the content of each fraction with respect t o the nutrients under study, the relations between the nutrient contents of the initial raw material, the resulting separated fractions, and the final product prepared from these fractions can more readily be established. SPECIFIC CANNING OPERATIONS
Although specific operations may vary considerably in detail from product $0 product in commercial canning, the operations in general consist of combinations of cleaning (dry cleaning and/ or washing), grading (either size and/or quality), blanching or preliminary heat treatment to wilt the product and inhibit enzyme action, filling into cans, exhausting, and thermal sterilization. During recent years, with development of rapid methods for vitamin determination, certain of these operations have become the subject of special studies. Again, there are certain precautions which should be observed in a properly controlled experiment. I n any determination of the effect SELECTION OF EQUIPMENT. of a particular step in the canning procedure, it is highly desirable t h a t commercial canning equipment be used in the study, and that such equipment be operated in accordance with accepted canning practice. This is particularly true if the investigator desires t h a t his results be accepted as indicative of the changes incident to commercial practice, which is usually his intention. While it is possible in certain instances t o make laboratory experimental packs which duplicate commercial packs within reasonable limits, it is preferable in most cases that such work be carried out under actual cannery conditions. Many reports in the literature purport to show the effects of canning operations, presumably commercial, which actually represent work on a limited scale with laboratory equipment. Likewise, the effects of home canning techniques (carried out manually and necessarily on a small scale) have also been freely suggested as representing the effects of commercial canning operations. The desirability of using the type of equipment employed commercially instead of laboratory equipment should be obvious. One major advantage is that commercial equipment
..
..
..
34 35
16 16
22 24
30 30
19 21
24 25
..
..
..
Vol. 36, No. 2
P A C K E D IS P L A I N AND E N a M E L E D C A N S
Max,
Iron, P.P.M. Min. Av.
4.60 4.16 6.0 13.50 12 30 21.9
3.53 3.51 4.4 3.78 3.04 6.7
4.08 3.82 5.3 6.34 6.83 10.6
Xax.
Tin, P.P.M. Min. Av.
139 213 286 ,55 70 126
60
150 232 7 26 38
99 180 267 18 44 63
permits use of a larger amount of raw material than is possible in the laboratory and thus helps t o even out the natural variations in nutrient content inherent in raw materials. Further, actual work in canneries is less subject to the waits and delays usually attendant upon small scale laboratory operations. Commercial canneries are widely distributed, and the majority of canners are glad t o cooperate in any studies which will throw light on the efficiency of their operations. OBSERVATION OF COMMERCIALPRACTICES. Of particular importance in studies on specific canning operations is the maintenance of commercial operating conditions such as the proper relation between fill-in weight, brine volume, head space, etc. Commercial canning practice should also be followed in the preparation of all brines and sirups. It is of major importance that the time schedules involved should conform closely with those in commercial operations; this is particularly true in sny survey involving estimation of ascorbic acid where the possibility of rapid oxidation of the vitamin in food held warm or hot for long periods is greatly favored. A typical example of deviation from commercial canning practice in experimental work is the recent report of Farrell and Fellers (6). SAMPLING STATIONS.I n the study of any specific canning operation on vitamins in foods, an acquaintence with the physical or chemical changes which may be involved usually permits proper selection of the correct sampling stations. Sometimes, however, the operations under study have companion operations which may influence the results. As a typical example, the matter of station selection after water blanching may be cited. The decision must be made as t o whether the blanched sample should be taken a t the discharge end of the blancher or after the spray wash usually applied to check the effect of the blanch. There is a significant difference between the ascorbic acid and thiamine contents of blanched peas sampled before and after the rinse, as indicated by the following data on Pride variety peas: Treatment of Peas Blanched Blanched & washed
Thiamine, Mmg./G. Fancy No. 4 Std. KO.6 2.4 2.1
3.4 2.7
Ascorbic Acid, Mg./G. Fancy No. 4 Std. No. 6 0.15 0.12
0.13 0.12
This difference may be due to adhering blanch liquor containing these soluble vitamins which is removed by the spray, to removal of these soluble vitamins from the blanched peas by the spray, or t o both. With steam blanching, or under special conditions of water blanching which may be applied t o peas or other products, this effect of the companion operation to blanching may be negligible. It is desirable t o establish, however, whether the influence of these companion operations is insignificant or incapable of measurement. Otherwise the entire effect of the operations may be incorrectly attributed to the specific operation under study. Even simple washing must be presumed guilty of affecting nutritive values of raw foods unless proved innocent, particularly where such operations are applied to raw cut plant tissues with distinct tendencies t o bleed. THERMAL PROCESS EFFECT. Because of the known lability of thiamine to heat, the thermal process accorded canned foods, particularly those of the semi- or nonacid types, has received
February, 1944
INDUSTRIAL AND ENGINEERING CHEMISTRY
considerable study. The validity of many of the results are open t o serious question because the experiments were not properly controlled. This has been especially true in those cases where the results of laboratory or home canning operations have been held up as indicative of the effects of commercial thermal processing operations. It was therefore considered advisable to discuss separately the factors which may condition this type of investigation. If the investigator desires to establish the effects of commercial processing operations, i t is imperative t h a t commercial conditions with respect t o fill-in weights, head spaces, and the composition, volume, and temperatures of added brines or sirups be closely observed. Further, the cans should be closed only after comparable conditions of partial deaeration (whether accomplished by hot filling or brining, exhausting, steam flow closure, or other means) t o those used commercially have been imposed. As Ijreviously emphasized, the simple selected to represent t h e material a t the beginning of the process must be comparable t o that actually present. Therefore the material in the filled, brined, closed, but unprocessed can as i t enters the retort is properly the initial control sample, not the material as i t leaves the blancher or any other item of equipment? Another important consideration is that the duration and temperatures of the total heat treatments applied should be closely similar if not identical t o those employed for the same cans i n commercial practice. It is necessary not only t o duplicate the temperature and duration of the process, but also t o approximate closely the initial temperatures, heating rates, and cooling schedules observed in commercial practice. For this reason data taken in small retorts may not be strictly comparable t o those in large commercial retorts because of the difference in the rates a t which the product attains retort temperature. The factor which will largely account for this difference is the come-up times of the retorts used. Commercial come-up times are comparatively rapid (2-5 minutes), whereas the average small apparatus in which steam is generated within the retort are notoriously slow in this respect. For this reason processing equipment other than the commercial type is likely to impose more severe heat treatments, other factors remaining equal. Unless commercial cooling schedules are observed] the product may be more rigorously handled from the standpoint of heat treatment than in commercial practice. I n some past comparisons between the same product packed in metal and in glass containers, the results may be open t o question because of the differences in the necessary processes as well as the heating rates for the product in the two types of containers. H e a t penetration in a glass container is usually slower than in a metal container of comparable size for the same product. Likewise, glass containers cool more slowly, It is suggested t h a t comparisons between these two types of containers be made on the basis of equal sterilizing or F values for the processes applied ( I ) . I n any determination of the effect of heat sterilization alone, i t is also important t h a t the product be examined soon after cooling in order to avoid any effects of storage where they may be of significance This is particularly important in the case of glasspacked products where the decline of ascorbic acid during storage may be particularly rapid (10). CHANGESIN MOISTUREC O N T ~ N TAnother . important factor i n studies on both over-all effects and specific operations is the possibility of increases in the moisture content of the raw food. Examples are the canning of spinach, peas, lima beans, and other blanched or brine-packed products where the moisture content of the canned material may differ materially from t h a t of the original raw stock. It is seldom possible to relate the analysis of raw material exactly to that of the canned product through a consideration of moisture changes alone. In many cases sufficient soluble material may be extracted from the food during processing t o introduce errors in any conclusion which may be based
175
on the use of the moisture content as the sole index in relating the raw stock t o the processed product. As unsatisfactory as the relation between the moisture contents of the initial and final products may be, there is often no other practical basis of comparison. Where a comparison involving an extractable or soluble nutrient is involved, expressing the result on a dry or equimoisture basis is sometimes the most conservative procedure. It should, however, be emphasized t h a t the entire contents of the can of the final product should be analyzed both for nutrient and moisture so that the comparison on the dry basis will reflect the actual effect of canning procedure. Frequently i t is desirable to determine weight changes during specific operations as well as t o have knowledge of moisture changes so as to relate processed or heated samples t o the original raw material. Samples of raw or unprocessed materials for moisture determinations may be conveniently taken by filling known weights of the material and distilled water into cans, and then sealing, processing, and cooling the container. By this procedure the samples may be held indefinitely for laboratory analysis. RELATIVE EFFECTS OF FOOD-PRESERVING METHODS. This type of study seeks t o establish the relative effect of various methods of food preservation on the nutrients in raw foods. While such cofnparisons are frequently of great interest, practically the results may permit incorrect implications as far as the nutritive values of canned foods are concerned. Of the common methods of food preservation-dehydration, freezing, and canning-the latter provides a product for which a minimum of operations are required to render the food ready for consumption. It is suggested that, in making comparisons of this type, the food be prepared for consumption before examination for vitamin content is made. PROBLEM
O F SAMPLING
The sampling technique may have a n important bearing on the validity of the results. Commercially canned foods are known t o exhibit differences in cans of the same product packed a t the same time on the same canning line. These differences are reflected by variations in head space, net weight, and can vacuum. The can-to-can variations, while usually slight, exist even in liquid or semiliquid products capable of being intimately mixed before canning. McHenry (19) pointed out t h a t $he ascorbic acid contents of canned tomato juice may vary as much from can to can in the same pack as from one canner’s pack to another. This fact suggests t h a t selection of only one can t o represent the final processed product or failure to specify the number of cans sampled, as was done in certain studies in the past (4, 1 1 ) , is a highly questionable procedure. To even out these can-tocan variations, more than one can should be included in the final product sampling, and the investigator should report the number of cans so included. However, i t has been the exception rather than the rule for the number of cans considered individually or as a composite t o be stated in literature reports. Occasionally the results of the study clearly suggest t h a t inadequate sampling of the canned product had been involved. On this basis the results of Theriault and Fellers (16) can readilbe explained. They noted a difference between the iron contents of canned fish in cans from the same laboratory pack; the higher value was found iq the sample of lesser storage age. The authors imply t h a t this difference was due t o a “plating” out of the iron; however, the result is more easily explained on the basis of can-to-can variation. They give no indication as t o the number of cans sampled at each examination. Such differences have often been observed between cans in carefully controlled packs during studies on tin plate corrosion. I n one experimental pack of tomato juice every effort was made to minimize can-to-can variation by carefully controlling the tin plate used in fabricating the containers; but the data of Table
COPPER SOAPS
I11 still reveal a wide variation in iron and tin pickup. For this reason it is customary to include six to twelve cans as one sample for examination at any one date. The problem of adequate sampling received considerable attention in the planning of experiments in the current nutrition program on commercially canned foods ( 1 5 ) . The decisions reached as to the methods of procedure and sampling t o be used were made after full consideration of the problem by the collaborating laboratories at universities and in the industry. I n the belief that these sampling methods may prove of service to other investigators, the salient points of procedure are listed:
As Rot-Proofing Agents on Fabrics
1. STATISTICAL DETERMINATIOKS OF RANGESIN NUTRITIYE
VALUESOF COMMERCIALLY CANNED FOODS.Only commercial samples of known history are t o be examined. A sample is to be composed of six retail size cans packed in the same cannery on the same day. These six are to be composited and assays made on the composite. I n most instances samples are to be taken from each cannery on three days during different times in the season. 2. OVER-ALL CANNING EFFECTS a. As a raw stock control a 2-kg. sample from a well-mixed 300-pound batch comparable t o the material appearing in the processd product is collected. b. The final product sample consists of twelve retail size cans; six are composited and sampled for assay immediately after cooling, and six are returned to the laboratory for food inspection measurements. c. Ascorbic acid determinations are made in the field on both raw and processed samples. d. Samples for B vitamin assays are pureed (in the field) with sulfuric acid t o give a pII of 3 or below, chloroform and toluene added, and the samples held under refrigeration until assayed. e . Samples for carotene assay are pureed with alcoholic potassium hydroxide and held under refrigeration in the dark until assayed. f. Samples for moisture determination are weighed into cans, known amounts of distilled water added, the cans closed and heat-sterilized. 3. SPECIFICCANNERY OPERATIONS a. As in section 2a, the initial control is composed of a 2-kg. sample taken from the well-mixed material as it enters the operation. b. As in section 2b, the sample emerging from the specific operation is 2 kg., collected from various portions of the batch. c. Samples for ascorbic acid, B vitamins, carotene, and moisture aye treated as under 2c, d, e, and f.
PAUL B. MARSH, GLENN A. GREATHQUSE, KATHARINA BOLLEKBACHER, AKD MIPRY L. BUTLER U. S. Department of Agriculture, Beltsville, Md. a
Copper naphthenate prevents rotting of cotton fabric in soil at lower concentrations on the fabric than do coppep oleate, copper “talla te”, or copper hydrogenated resinate. Several methods have demonstrated that the high preservative capacity of copper naphthenate in contact with soils is related to the fact that naphthenic acid itself is a potent fungicide. Various factors affecting the behavior of copper preservatives in contact with soils are studied. They include solubilization by acid hydrolysis and b y complex formation, and deactivation by chemical combination. Data from pure culture test procedures are contrasted with the results obtained by exposure to soils.
T
HE present emergency has intensified interest in methods for the prevention of rotting and mildewing of fabrics. Sandbags, tents, jungle hammocks, insect netting, and other articles of military importance are commonly subject to severe deterioration by microorganisms. This is particularly true in moist, warm climates. This report deals with the fabric-preservative values of four copper soaps and with the utility of certain laboratory procedures for the estimation of mildew-proofness or rot-proofness of fabric. The term “mildew” i s here used in a broad sense to refer to either fungal or bacterial mirroorganisms, regardless of whether they produce actual tendering of fabric, An organism which may grow on fabric without causing tendering is here termed a “superficial” organism. “Rot” refers to t h e tendering of fabric by microorganisms. Many chemical compounds have been used as mildew and rot preventives for fabrics. Jarrell, Stuart, and Holman (15) report the effectiveness of copper compounds. Furry, Robinson, and Humfeld (10) find preservative value in various commercial preparations, including copper, mercury, and phenolic materials; they propose also the use of a cadmium treatment. Bertolet (4) discusses a large number of fabric preservatives, including several of recent development. Several attempts have been made by various workers to develop rapid, accurate, and reproducible methods for estimating the value of mildew-proofing treatments. Important advances have been made along this line. However, laboratory test methods have not yet developed to such a stage t h a t their results alone may be used as accurate predictions of the resistance t u mildewing or rotting of a treated fabric under all of the varied service conditions to which i t may be subjected. The field performance of any particular protective agent depends not only on its initial germicidal value, but also on i t s reaction to those environmental agencies which tend to cause it t o be deactivated, dissipated, or destroyed. Use of different test methods has resulted in apparently conflicting data and much confusion as t o the actual value of each preservative. I t was thought that some clarification of this perplexing situation might result from a closer examination of the causal factors operating in
LITERATURE CITED
(1) American Can Co., Canned Food Reference Manual, 2nd ed., 1943. (2) Bessey, 0. A . , and King, C. G., J . Biol. Chem., 103, 687-98 (1933). (3) Booher, L. E., Hartzler, E. R., and Hewston, E. M., U. S. Dept. Agr., Circ. 638 (1942). (4) Clifcorn, L. E., and Heberlein, D. G., IND.ENG.CHEM.,36, 171 (1944). (5) Clouse, R. C., J . Am. Dietet. Assoc., 19, 496-504 (1943). (6) Farrell, K. T., and Fellers, C. R., Food Research, 7 , 171-7 (1942). (7) Fixsen, M. A. B., Nutrition Abstracts & Revs., 8 , 281-307 (1938). ( 8 ) Hauck, H. M., J. Home Econ., 35, 295-300 (1943). (9) Kohman, E. F., Natl. Canners Assoc., Bull. 19-L (1937). (10) Lueck, R. H., and Pilcher, R. W., IND. ENC.CHmr., 33, 292-300 (1941). (11) Maclinn, W. A., and Fellers, C. R . , Mass. Agr. Expt. Sta., Bull. 354 (1938). (12) McHenry, E. W., Can. Pub. Health J . , 26, 124-7 (1935). (13) Musulin, R. R., and King, C. G., J . Biol. Chem., 116, 409-13 (1936). (14) Stern, R. M., and Vavich, M.P., private communication. (15) Stewart, J. A., and Pilcher, R. W., Chem. Eng. News, “Can
Makers Wartime Problems”.
(16) Theriault, F. R., and Feilers, C. R., Food Research, 7 , 503-8 (1942). PRESEN~E before D the Division of Agricultural and Food Chemistry at the AN SOCI~TY, Pittsburgh, Pa. 106th Meeting of the A M ~ R X CCHEMICAL
176
