T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
432 Run No. 2a 2b 4a 4b 12a 12b 11 10 6a 8 7
Run No.
Feed Lbs. per Hr. 0.38 0.38 0.38 0.38 0.38 0.38 0.78 0.78 0.38 0.38 0.38
Temp. OC. 650 650 750 750 875 875 650 750 800 800 800 7 -
coz
2.7 2.2 1.9 1.7 1.1 0.9 1.8 1.6 1.6 1.1 1.7
-__
co
15.2 12.1 12.3 12.0 15.7 16.5 12.0 12.4 11.9 12.3 12.4
Size of Coal Mesh 20-60 20-60 20-60 20-60 20-60 20-60 20-60 20-60 40-50 30-40 20-30
Cu. Ft. Gas Per Lb. Coal 2.82 2.79 3.92 3.96 6.14 6.26
....
3.40 4.90 4.60 4.30
Ill. 6.7 5.6 2.7 2.8 2.0 1.3 4.5 2.5 1.6 1.5 1.7
Vol.
IO,
No. 6
spores, and molds is very effectual; when this is followed by a single period of sterilization, we contend that the success of canning is just as sure as though three periods on three successive days were used.
Bitting and Bitting,’ in discussing the influence of cooling, make the following statement: The primary effect is t o make a better appearing product, but secondly i t appears t o be a factor in insuring the sterility of some products.
The only possible influence t h a t this procedure could have, would be t h a t of shock to the bacterial cell. This might possibly devitalize the cell in such a way t h a t it would be more easily destroyed by a subsequent heating, or, perhaps, perish slowly, or not be able t o grow under such rather unfavorable conditions as exist in sealed containers. Of course, this initial period top of the furnace from a sight feed pressure oiler and of heating during blanching will destroy many organisms vaporized from a length of chain hung in the upper in the vegetative stage, but a glance a t Table X will part of the furnace. Curves showing t h e composition show t h a t the organisms in the spore stage are the only of the gas produced b y the cracking of these liquids ones which are of importance in canning. and by carbonizing coal by the above method a t various If the shock of cold is of value in sterilization it temperatures and equal rates of feed of volatile matter should be more widely known t h a n it is a t present, as are contained in Fig. I. i t could be used in many lines of investigation other CONCLUSIONS t h a n t h a t of food canning. The question of blanching and cold dipping is of The paraffin hydrocarbons when cracked b y the method herein described give gases which a t the same particular importance in the canning of foods, as in this case the cooling can be made much more rapid temperature have practically the same composition. The aromatic hydrocarbons without side chains t h a n is possible after t h e material is packed in jars. gave a totally different form of gas curves. They do For this reason we conducted quite extensive experinot begin to decompose a t such low temperatures as ments upon this problem during our preliminary work t h e paraffins do and when they do break down they upon canned vegetables in the summer of 1917. The process consists of a short period of heating in boiling apparently yield only hydrogen and methane. After eliminating the nitrogen- and the oxygen- water or steam, followed b y rapid cooling. The containing constituents of the coal gas produced, this product is later subjected t o the sterilizing process. gas is similar to t h a t produced from paraffin oils and This procedure is of much practical importance in not a t all similar t o the gas produced from the aromatic improving the physical condition of the product and in causing shrinkage before the material is added t o bodies examined. The above results indicate t h a t coal is made u p in the jars. The experiments were conducted t o estabgeneral of straight chain compounds. The best evi- lish its value as an aid t o sterilization. dence of this t h a t has been put forward to date is the I n much of this preliminary work we used large fact t h a t “low temperature” coal t a r consists practically test tubes and half-pint bottles with large mouths. entirely of straight chain oils. Some of these were plugged with cotton, while others CHEMICA~ ENGINEERING LABORATORY were sealed with rubber stoppers. This was not from COLUMBIA UNIVERSITY an idea of economy in cost of material so much as an NEW YORKCITY economy in laboratory space and time, as rubber stoppers usually cost more t h a n jars. Several dozen THE INFLUENCE OF COLD SHOCK IN THE test tubes, however, occupy no more space in the STERILIZATION OF CANNED FOODS steamer than would be occupied by one dozen pint By L. D. BUSUNELL jars. Also, heat penetrates them much more rapidly Received March 29, 1918 and we were able in this way to save a t least half an hour on each experiment. The results which we obINTR0DCCTION The influence of rapid cooling, after heating, is a tained were comparable in every way to results which matter of considerable importance in the canning we obtained by the use of jars. The tubes are somewhat more difficult t o seal, industry. I t s value in t h e blanching of foods was but if they are completely filled before heating begins first mentioned by Benson’ who reports in part as and are sealed at once by a sterile solid glass rod as follows : soon as the heating period is completed, practically When a food product has been blanched in boiling hot water no trouble is experienced by the stoppers being blown or live steam, remove quickly from this and plunge immediately out on second heating. Better results are obtained into cold water. The influence of this method upon bacteria, b y using stoppers with one hole and plugging this with 1 “Home Canning Club Instruction to Save Fruit and Vegetable Waste,’’ Office of Farmers’ Cooperative Demonstrations, Northern and Western States, Washington, D. C., 1915, p 4.
1 “Bacteriological Examination of Canned Foods,” Research Laboratory National Canners’ Association, Bull. 1 4 (1917), 7.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
June, 1918
a sterile glass rod, t h a n by fitting t h e tubes with solid stoppers. T h e rods should fit very firmly, otherwise they may be drawn into t h e t u b e or leak air on cooling. The stoppers should be pushed well into t h e t u b e before t h e heating begins. I n all t h e vegetables t h e time allowed for heat t o penetrate in test tubes was j min.; in bottles, 15 min.; in pint jars, 3 0 min. This time was always allowed t o elapse before sterilization was supposed t o have begun.
483
5 min. T h e time of spoilage was noted b y t h e appearance of clouding of t h e liquid surrounding t h e peas and by presence of growth on t h e surface. We have always noted these signs when spoilage appeared in containers sealed with cotton only. TABLG11 Blanched Min.
Heated Min.
Cooled Rapidly Cooled Slowly Time of Spoilage Time of Spoilage Hrs. Hrs.
E X P E R I 11E N T A L
I-The method of heating for a short time followed by a plunge into cold water was tried on several kinds of culture media containing varying numbers of spores of both aerobic and anaerobic bacteria. The tubes were subjected t o a short heating in t h e steamer, followed by plunging them into cold water, and b y a second a n d longer heating. This method failed in every case t o shorten the timenecessary t o sterilize, either in t h e streaming steam or in t h e autoclave. E X P E R I M E N T 2-The same procedure was followed as in Experiment I , except t h a t t h e tests were made in duplicate; half of t h e tubes were cooled rapidly in ice water and half allowed t o cool slowly t o this temperature. The time required was from 1 5 t o 30 min. I n no case was t h e reduction in number more marked in t h e tubes cooled rapidly t h a n in those cooled slowly. E X P E R I X E N T 3-Several pure cultures obtained from spoiled canned goods were used in this experiment. T h e cultures were grown in broth for several days and equal amounts placed in test tubes as near t h e same thickness of wall and t h e same diameter as could be obtained. These were then placed in streaming steam for IO min. Half of t h e tubes were plunged into ice water and t h e remaining half allowed t o cool slowly t o t h e same temperature. These tubes were then all placed in t h e steamer and steamed for 30 min. and plates made. Table I shows t h e results obtained. EXPERIMENT
TABLEI hT0.
1 2 3 4
5 6 7 8
Original Per Cc. 38,000,000 1,000,000 90,000,000 40,000,000
70,000,000 268,000,000 1,580,000,000 600,000,000
Cooled Rapidly Per Cc. 2,600,000 0 14,000,000 7,000,000 200,000
4,300,000 60 20
Cooled Slowly Per Cc. 2,500,000 100
11,000,000 600,000
200,000 1,300,000 0 0
This table shows t h a t t h e shock of cold did not influence t h e thermal death-point of pure cultures, as all t h e above data, except, perhaps, No. 4, are easily within t h e limits of experimental error. E X P E R I M E N T 4-111 this experiment we tried t h e influence of cold shock upon t h e time necessary t o sterilize peas. T h e peas were treated in every way as in ordinary canning and blanched for different periods of time. I n order t o avoid contamination in handling and t o insure rapid cooling in the ice water, t h e peas were placed in test tubes of medium size, covered with water, and t h e tubes plugged with cotton. T h e tubes were heated in streaming steam for different periods of time. No time was allowed for penetrating, which was found later t o be about
10 20
90 90
72 72
120 120
I n this case there is no evidence t h a t t h e length of blanching time or t h e rapidity of cooling influenced in any way t h e ease with which t h e spores were subsequently killed b y heat. I n fact, those cooled more slowly seem t o be least easily destroyed if t h e time of spoilage is a n indication. We may account for this on the basis of germination of t h e spores during the slow process of cooling, as this usually requires several minutes (see Table IV). E X P E R I N E N T j-Table I11 shows the influence of cold shock followed by intermittent heating. In this case green beans were used and t h e conditions of t h e experiment were similar t o those in Experiment 4? except t h a t blanching was continued for 1 5 min. in the steamer. Heated 15 min. twice 30 min. twice 60 min. twice 90 min. twice
1 day 1 day 1 day 1 day
TABLEI11 Time between Last Heating and Spoilage Cooled Rapidly Cooled Slowly Spoiled after 60 hrs. Spoiled after 48 hrs. Spoiled after 60 hrs. Spoiled after 60 hrs. Good after 10 days Good after 10 days Good after 10 days Good after 10 days
This experiment also shows t h a t spores are not devitalized b y cold shock and t h a t blanching for rather long periods followed by cold dipping does not aid in sterilization. E X P E R I M E N T 6-This experiment was devised t o test t h e possibility of spore germination between t h e time of blanching and heating. Fresh peas were used. The conditions of the experiment are as in Experiment j , except t h a t the blanching was for 5 min. Blanched Heated r Min. Min. 10 Sp. 5 60 Sp. 5 60 Sp. 5 180 Sp. = Spoilage.
TABLEIV --Incubation min. 20 min. 48 hrs. Sp. 48 hrs. 48 hrs. Sp. 48 hrs. 48 hrs. Sp. 72 hrs.
a t 3 S 0 C.40 min. 80 min. Sp. 48 hrs. Sp. 48 hrs. Sp. 120 hrs. Sp. 48 hrs. Sp. 96 hrs. Good 7 days
Table I V shows t h a t t h e incubation period has b u t little influence upon t h e ease of sterilization. I n t h e column showing incubation for 80 min. and heating for 180 min., t h e product did not spoil. This might have been due t o t h e fact t h a t t h e spores had all changed t o the vegetative stage, b u t this is not likely, because heating for 60 min. will easily kill all in t h e vegetative stage and this, together with t h a t heated 1 2 0 min., spoiled. This would seem t o indicate t h a t t h e incubation period, due t o slow cooling, will not explain why, in some cases, t h e organisms cooled slowly are more easily killed, or a t least grow more slowly, t h a n those cooled more rapidly. I n several instances, however, we have observed spoilage t o take place more
434
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
rapidly, a n d in some cases more spoilage follows blanching t h a n when no blanching is practiced. E X P E R I M E N T 7-This, together with some of t h e following experiments, was conducted t o determine t h e necessity of complete sterilization t o insure t h e keeping of canned foods. We believe t h a t it is usually considered necessary t o sterilize completely t o avoid spoilage unless some substance is added t o alter t h e physical or chemical nature of the product. We have repeatedly received inquiries concerning this point a t the laboratory. Also, many conflicting reports have reached u s as t o the time necessary t o process t o insure keeping, certain people losing t h e entire pack, while others, under very similar conditions a n d methods of treatment, lose very little.
Blanched 1 .O Per cent Salt 2.0 Per Heated Sp. Sp. 48 hrs. 60 min. 1 d a y . . . . . . . . . . . . . . . . . Sp. 120 min. 1 d a y . . . . . . . . . . . . . . . . . . . . . Sp. 48 hrs. Sp. 180 min. 1 d a y . . . . . . . . . . . . . . . . .. . . . Good 10 days Sp. 15 min. 2 days. . . . . . . . . . . . . . . .. . . . Sp. 48 hrs. Sp. 30 min. 2 days . . . . . . . . . . . . . . .. . . . Sp. 48 hrs. Sp. 60 min. 2 days. . . . . . . . . . . . . . . . . . . . Sp. 48 hrs. Good 90 min. 2 days . . . . . . . . . . . . . . . . . . Sp. 60 hrs. hrs. 15 min. 3 days. . . . . . . . . . . . . . . . . . . days 30 min. 3 days. . . . . . . . . . . . . . . . .. . . . SGPdod Good 60 min. 3 days. . . . . . . . . . . . . . . . . . . SP. 40 hrs. Good '90 min. 3 days. . . . . . . . . . . . . . . .. . . . Good 10 days
?:
gg:
The first 1 There are two reasons for using cotton plugs in this work. is t h a t spoilage takes place very rapidly, if i t takes place a t all: the second is t h a t cotton acts as a bacterial filter and a t the same time allows air to enter.
No. 6
TABLEVI Heated Min. 60
120 180
Cooled Rapidly Cotton Seal Rubber Seal Sp. 48 hrs. Good 5 days Sp. 60 hrs. Good 5 days Good 5 days Good 5 days
Cooled Cotton Seal Sp. 48 hrs. Sp. 72 hrs. Sp. 96 hrs.
Slowly Rubber Seal Good 5 d a y s Good 5 days Good 5 days
for 5 min., dipped into cold water, a n d placed in similar tubes. All were then covered with salt solution of various strengths, plugged with cotton, and processed as indicated in Table VII. I n filling t h e t u b e with blanched beans a sterile funnel a n d forceps were used so t h a t they did n o t come into contact with t h e hands of the operator. They were, however, cooled in running water from t h e tap. Table VI1 shows results obtained. These results show t h a t blanching does not increase ease of sterilization a n d t h a t salt, except in amounts too large t o be permissible, has no influence upon t h e keeping quality. E X P E R I M E N T I o - I n this experiment a n a t t e m p t was made t o show t h e influence of blanching upon sweet corn. The corn was of excellent quality a n d freshly picked. Test tubes were used throughout t h e experiment. T h e corn, after blanching for 5 min. in steam, was cut from t h e cob with a sterile knife a n d poured into large, sterile glass bottles, a t the end of t h e blanching period. T h e unblanched corn was treated in a similar manner except t h a t no preliminary heating was applied. Tables VI11 and I X show t h e
TABLEVI1 5 Minutes cent Salt 4.0 Per Sp. 48 hrs. Sp. 48 hrs. Good 48 hrs. Sp. 48 hrs. 48 hrs. 60 hrs. Good 10 days 48 hrs. SGPdod 48 hrs. Good 10 days Good 10 days
T h i s experiment shows t h a t no improvement in keeping quality is t o be expected from blanching and cold dipping. Exclusion of air, however, does have a very marked influence upon keeping quality. This point will be discussed more in detail later.
IO,
EXPERIMENT 8-This is a n experiment similar t o Experiment 7 except t h a t vinegar was used in place of salt, 1 5 cc. of vinegar being added t o each 1000 cc. of water used. (Five cc. of t h e vinegar required 4 cc. N / 2 o NaOH t o neutralize t o phenolphthalein.) Table VI shows t h e results obtained. T h e results are similar t o those in Experiment 7 . EXPERIMENT 9-The following experiment was devised t o see if blanching increased t h e ease of sterilization over a similar product packed without blanching. I n this experiment fresh green beans were used. These were snapped into small pieces a n d divided into two lots. One lot was placed directly into large, clean test tubes which had been autoclaved shortly before use A second lot was blanched in a steamer
TABLEV Heated Cooled Rapidly Cooled Slowly Min. Cotton Seal Rubber Seal Cotton Seal Rubber Seal 60 Sp. 48 hrs. Good 5 days(a) Sp. 48 hrs. Good 5 days 120 Sp. 96 hrs. Good 5 days Good 5 days Good 5 days Sp. 72 hrs.(b) Sp. 60 hrs. Good 5 days 180 Sp. 72 hrs. (a) We have found t h a t a product which will keep for 5 days a t 35' C. will usually keep indefinitely. We have some of these rubber-sealed bottles which are still good after 6 mos. ( b ) Rubber stopper became loosened and leaked air.
I n some of our work we have been surprised t o note the ease with which certain foods, supposed t o be very difficult t o sterilize, would keep indefinitely if properly sealed. Also t o find t h a t most organisms isolated from the product after prolonged heating were aerobic in nature. T o determine this point we devised the method of sealing one set of tubes with rubber and a duplicate set with cotton plugs.' I n this experiment small beets were used. They were first dipped in boiling water and the skins removed. They were then blanched for I O min. in streaming steam. Upon removal from t h e steamer they were divided into two lots. One lot was dipped immediately into cold water a n d t h e second cooled very slowly t o the same temperature. These were then packed in large, wide mouth bottles and processed a s indicated below. N o exceptional precautions were taken t o prevent contamination. I n this case 1 5 g. of salt were added t o each 1000cc. of liquid used. Table V shows t h e results of this experiment. Spoilage was determined by t h e appearance of t h e material after standing a t 3 5 O C. for t h e time mentioned.
Vol.
&
cent Salt 48 hrs. 48 hrs. 10 days 48 hrs. 48 hrs. 60 hrs. 10 days 48 hrs. 10 days 10 days 10 days
Packed without Blanching 1.0 Per cent Salt 2 . 0 Per cent Salt 4.0 Per cent Salt Sp. 72 hrs. Sp. 72 hrs. Sp. 72 hrs. Good 10 days Sp. 72 hrs. 72 hrs. Good 10 days Good 10 days SGPdod 10 days Sp. 48 hrs. Sp. 48 hrs. Sp. 48 hrs. Sp. 48 hrs. Sp. 48 hrs. Sp. 48 hrs. Good 10 davs Sp. 48 hrs. Sp. 48 hrs. Good 10 da$s Good 10 days Sp. 48 hrs. Sp. 48 hrs. Sp. 60 hrs. 4 days Good 10 days Sp. 4 days 48 hrs. Good 10 days Good 10 days Good 10 days Good 10 days sdb.od hd,s;s
g::
?:
influence of heating upon t h e keeping quality of corn treated by various methods. The plus sign indicates spoilage. The minus sign indicates t h a t t h e product was good after I O days in t h e warm room. These results show t h a t there is no influence due t o blanching, very little due t o small amounts of salt, very little due t o small amounts of acid, a n d a great deal due t o larger amounts of acid and t o sealing.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
June, 1918
TABLEVIII-CORN BLANCHED 5 MINUTES Sealed with Sealed with Cotton Stopper Rubber Stopper
I.
'0 0
60 min. 1 d a y . . . . .
k
TABLEIX-CORN Nor BLANCHED Sealed with Sealed with Cotton Stopper Rubber Stopper
b
&
0
.
120 min. 1 d a y . . . . . . 180 min. 1 d a y . . . . . . 15 min. 2 d a y s . , . . , 30 min. 2 d a y s . . . . . 60 min. 2 days.. . . . 90 min. 2 davs., . . . 15 min. 3 da$s.. . . 30 min. 3 days.. . . . 60 min. 3 days.. . . . 90 min. 3 days.. . . . 15 min. twice 1 day 30 min. twice 1 day 60 min. twice 1 day 90 min. twice 1 day 15 min. twice 2 davs
.
15 min. twice 30 min. twice 60 min. twice 90 min. twice
3 days 3 days 3 days 3 days
-
It is interesting t o note t h e influence of heating twice a day upon t h e keeping quality. We devised this method for t h e sterilization of culture media. Occasionally we resort t o this method in the summer time when the temperature of t h e laboratory remains nearly t h a t of the incubator for t h e entire 2 4 hrs. Several types of spore-forming aerobes not only change from the spore t o t h e vegetative stage, but change again into t h e spore stage in 24 hrs. These types grow b u t very little a t low temperature a n d do not show in t h e media for several days if t h e room is cold. T h u s the incubation of t h e product with two applications of heat each 24 hrs. usually aids greatly in t h e sterilization. These types also grow b u t little in t h e absence of free oxygen and are the types which we have obtained most commonly from spoiled vegetables in cottonsealed tubes. This method may be of considerable value in canning of vegetables b u t we have not done enough work t o advocate its use. E X P E R I U E N T I I-This experiment shows something of the influence of heating upon t h e reduction in numbers of bacteria in sweet corn. T o determine these numbers the tubes were shaken for several minutes before the sample was taken. The kernels'were usually reduced t o a pulp by the shaking process SO the results may be considered fairly representative Number before heating Number after heating Min.
30
60 90 120
150 170 180
g z. m, g 2 2 2. 2 m, + + + +- --- + - - - - - - - - - - - - - - - - - + + - - - - - - - + + - - - - - - - - O F - - - - - - - - - - - + - - - - - - - + + - - - - - - - - - - - - - - - + + - - - - - - - - - - + + + 1111 - - $ - - - - - - - - - + - - - - - - - - -
0 0 Heated N 60min.lday..,.., 120 min. 1 d a y . . ,. . . + - + 1 8 0 m i n . l d a y, . . . . . 1 5 m i n . 2 d a y s. . . . . 30min.Zdays . . . . . - 60 min. 2 days ..... 90min.Zdays - 15 min. 3 days ..... 30min.3days. , . . . 6 0 m i n . 3 d a y s .,... 90min.3days. . . . . - 15 min.twice 1 day 3 0 min. twice 1 day - 60 min. twice 1 day 90 min. twice 1 day - - 15min.twice2days - 30min.twice2days - - 60min.twiceZdays -- 90min.twice2days - - l J m i n . t w i c e 3 d a y s - -30min.twice3days 60min.twice3days - - 90min.twice3days - - -
-
TABLEX Per Cc. 4000
43 5
Per cent Destroyed
...
30 15 10 7 6 4
1
1
of t h e numbers present. Every test will give slightly different numbers. We have in some cases found more and in some less, b u t this is a fair illustration for a good quality of corn. I n this case t h e material was in a jar sealed only with cotton. T h e temperature surrounding the jar was 98O C. (boiling point of water a t this altitude).
-
-,
0
+
-
0
0
-
-
0
-
-
- - - - - - - - - - - - - - - - - - - - - - - -
Table X shows t h a t over 99 per cent of the organisms are killed in 5 min. a t this temperature, b u t t h a t 0.03 per cent survived even after 3 hrs. This is probably enough t o cause spoilage. in a container sealed with cotton, b u t not in one sealed with rubber. E X P E R I M E N T I 2-This experiment shows the influence of heating upon the thermal death-point of organisms found on sweet corn treated in various ways. Table X I tends t o show t h a t the total number of bacteria which may be cultivated from a product after a short heating is very small. The few remaining, however, may bring about spoilage if they develop. This apparently is not always t h e case, as t o o few are present t o establish the initial growth which seems t o be necessary. I n comparing t h e relationship of
Heated Water Before heating. .. . 20,OQO 60 min .... ... 34 120 min.. .. 8 180 min.. .. . . . . 4 15 min. twice 1 day 50 30 min. twice 1 day 20 60 min. twice 1 day 8
.. .. .. .... .. .. . . . . .
TABLEX I Number of Bacteria per Cc. 0.05 0.1 0.3 1.0 2.0 3.0 Per Per Per Per Per Per cent cent cent cent cent cent Salt Salt Salt Acid Acid Acid 20,000 20,000 20,000 20,000 20,000 20,000 38 27 24 32 24 18 8 4 3 6 3 1 2 1 0 3 1 0 44 32 28 32 28 21 19 10 12 14 10 8 6 2 6 2 1 0
bacterial counts to the keeping quality of the product it is often found t h a t certain containers may show a few organisms upon culture media and yet show n o signs of spoilage, especially if acid is present or t h e tube has been properly sealed t o exclude air. It is very difficult t o make comparisons between two lots of this kind of material as the organisms are so unevenly distributed throughout the mass; for this reason averages of several trials should be used in compiling tables. Many tests in this laboratory have led t o the belief t h a t keeping is not due, in a great many cases, t o absolute sterilization. We have had jars of vegetables t h a t are easily spoiled by bacteria, which have kept under conditions of incomplete sterilization. Others t h a t had been heated for a long time and plugged carefully with cotton have spoiled in a few days. We have kept some of the sealed jars for I O rno.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
43 6
with no signs of deterioration, either in flavor, odor, or appearance, and have been able to cultivate both aerobes and anaerobes from them after t h a t time. Under-processing in favor of sealing as a preserving agent should not be advocated, b u t we feel sure t h a t many products have been placed on the market which were under-processed and have not spoiled. We hope t o determine this point later. Table X I 1 shows a comparison between numbers of bacteria destroyed b y sterilization and t h e keeping quality. This table is a compilation from Tables I X and XI. The two tables were not made on t h e same date or from t h e same lots of corn. We have, however, made several tests of this sort with similar results. Unfortunately no counts were obtained from sealed tubes, but they probably would differ b u t very little from those sealed with cotton. TABLE XI1 1.0 Per cent Salt 38 8 2 44 19 6 2
Heated Water 60 min. 1 d a y . . 34 120 min. 1 day 8 180 min. 1 d a y . , , , 4 15 min. twice 1 day 50 30 min. twice 1 day 20 60 min. twice 1 dav.. 8 90 min. twice 1 da$ 4
...... ........ . . ... .. ....
... 60 min. 1 d a y . , ...... + 120 min. 1 d a y . . ...... +
+ + Sealed with Rubber + + + -
-
180 min. 1 d a y . , . . . . . . 15 min. twice 1 day.. . 30 min. twice 1 day.. . 60 min. twice 1 day ... 90 min. twice 1 day ... 60 min. 120 min. 180 min. 15 min. 30 min. 60 min. 90 min.
Number of Bacteria 0.05 2.0 Per Per cent cent Salt Acid 27 32 4 6 1 3 32 32 10 14 2 2 1 0 Sealed with Cotton
........ + ......... ... .-
1 day 1 day.. ...... 1 day., twice 1 day twice 1 day twice 1 day.. . twice 1 day..
++ + --
per Cc. 0.1 Per cent Acid 24 3 1 28 10 1 0
--
-
-
0.3 Per cent Acid 18 1 0 21 8 0 0
-
-
These results show t h a t in several cases spoilage did not occur even when there were, no doubt, a few organisms present. This is shown particularly in t h e case in which acid is used. The influence of sealing is also very marked. Even in cases in which considerable spoilage occurred in cotton-sealed tubes no spoilage appeared in tubes properly sealed with rubber. EXPERIMENT 13-This experiment was devised t o show influence of rubber alone upon the keeping quality. i
TABLE XI11
0.2 0 . 0 5 0'.1 2.0 0.5 1.0 Per Per Per Per Per Per cent cent cent cent cent cent Water Salt Salt Salt Acid Acid Acid Heated Plugged with one-hole rubber stoppers, the hole being plugged with cotton 15 min. 1 day . . . . . . . . . . . . . . 4. 30min.lday.............. 460 min. 1 d a y . . . . . . . . . . . . . . Plugged with one-hole rubber stopper and glass rod 15 min. 1 d a y . . . . . . . . . . . . . . + 30 min. 1 d a y . . . . . . . . . . . . . . 60 min. 1 day.. . . . . . . . . . . . . Plugged with cotton only 15min.lday.............. 430 min. 1 d a y . . . . . . . . . . . . . . 60 min. 1 day . . . . . . . . . . . . . . f
+ _+ +
+ + + - _+ - - - -- -
-
-
_ - _ - _-- - ++ + + + + - -
Since we had obtained such marked results by sealing tubes with rubber as compared t o sealing with cotton it was considered possible t h a t the rubber stoppers might contain some substance toxic t o t h e bacterial cell and thus prevent growth. Beets were used in this case and were packed in large mouth bottles and treated as indicated in Table X I I I . The
Vol.
IO,
No. 6
plus sign means spoilage. The minus sign means good after I O days. We may conclude from Experiment 13 t h a t i t was not the influence of t h e rubber alone t h a t could account for t h e preserving action in rubber-sealed containers. Table XI11 serves again t o emphasize the great value of sealing and t h e use of acid in t h e canning industry. CONCLUSIONS
I-Blanching is of no value in reducing t h e time necessary t o properly process canned foods. 2-Small amounts of salt are of little value in preventing the growth of bacteria in canned foods. 3-Small amounts of organic acid (acetic acid) have a distinctly retarding action upon t h e growth of bacteria in canned vegetables. T h e use of small amounts should be advocated in all cases in which it will not injure t h e texture, flavor, or appearance of the product. 4-In many cases an unsterile product will keep indefinitely if properly sealed. This, however, is not t r u e in all cases and sealing should not be expected t o take t h e place of proper processirig because of t h e danger of loss due t o spore-forming anaerobes. DEPARTMENT OB BACTERIOLOGY KANSAS STATEAGRICULTURAL COLLEGE MANHATTAN, KANSAS
DETECTlON O F ADDED COLOR IN BUTTER OR OLEOMARGARINE By HERBERTA. LUBS Received December 12, 1917
I-OBSERVATIONS
ON
SOME
QUALITATIVE
TESTS
FOR
THE D E T E C T I O N O F A D D E D C O L O R S I X F A T S
A study of the various methods described for t h e detection of added colors in butter and butter substitutes reveals a number of misleading statements which might lead a more or less inexperienced analyst t o false conclusions. For example, certain tests described in t h e literature lead t o the false conclusion t h a t some aniline colors are vegetable colors, and vice versa. Furthermore, certain azo colors cannot be detected by methods which are supposed t o reveal their presence. Some of t h e tests described in the literature for t h e detection of added color are perfectly satisfactory when certain compounds are present, but fail t o reveal the presence of added color when other dyes are used, and for this reason some changes must be made in the procedure, These modifications will be discussed under the tests in question. The analyst should make a combination of tests with t h e modifications subsequently recommended t o obtain reliable results. L O W ' S TEST-According t o Low,' if a fat containing an azo color is shaken with a mixture of four p a r t s of glacial acetic acid and one part of concentrated sulfuric acid the acid layer will settle o u t with a winered color. I t is quite true t h a t in some cases a winered color is obtained, but in other cases a yellow, brown, or even a blue color is imparted t o t h e acid layer in the presence of various azo colors. For 1
J. A m . Chem. Soc.,
20 (1898), 889.
