Nutritive Value of Ca INFLUENCE OF TEMPERATURE AND TIME OF STORAGE ON VITAMIN CONTENT N. B. GUERRANT, 0. B. FARDIG', hl. G. VAVICH2, AND H. E. ELLENBERGER Pennsyluania State College, State College, Pu.
A
study was made of the effects on vitamin content of storing commercially canned foods for 2 years at various temperatures. Among the vitamins concerned were ascorbic acid, carotene, thiamine, riboflavin, and niacin. Representative samples of these canned foods were assayed at definite intervals during the storage period. Both time and temperature of storage had an adverse effect on the vitamin content, the degree of effect depending on the particular food and on the specific vitamin. Ascorbic acid and thiamine retention was affected more severely by temperature of storage than by the storage period, while the reverse was true for riboflavin and niacin. Carotene retention was not seriously affected by storage conditions. Canned foods stored at 50" F. showed better retention of vitamin than canned foods stored at higher temperatures.
the present studies were limited primarily t o canned vegetables. Anion@;the canned products selected for the studies mere: green and bleached asparagus, green beans, lima beans, carrots, yellow and n-hite corn, Alaska and sweet peas, spinach, apricots, and prunes. With certain products two sizes of cans ( S o . 2 and No. 10) were involved. I n the case of canned foods t h a t are packed in more than one locality in the United States, samples were obtained from as many producing areas as possible; these areas have been broadly designated as eastern, midwestern, and western (for details see Table I). Canned sweet peas were also selected as a typical canned food for use in a study of the effect of commercial warehouse storage in various localities on vitamin retention. The investigation involved only regular commercially canned products processed from uniform lots of raw stock. All products were of fancy or extra standard quality. These canned foods were selected in quantity as they came from the canning line, and the cans were numbered in sequence, processed under the usual conditions, cooled, packed in cartons, and sent directly t o State College. The time required t o reach State College depended, to some extent, on the locality in which the product was packed and the distance it had t o be shipped. For the eastern samples, usually not more than 2 days and never more than 5 days elapsed between the time the product was packed and when
I
N A previous publication (1)i t was shown t h a t the vitamin content of canned foods is affected adversely by prolonged storage at higher temperatures. The temperatures employed in these preliminary studies ranged from 30" t o 110" F. and the storage period was 1 year. The use of the higher storage temperature (110" F.) was dictated by army interest in the Dossible effect of troDical temDeratures in certain n-ar theaters. Because the number of products investigated in the earlier studies was limited and some of the storage TABLE I. DESCRIPTION AXD VITAMIN COXTEKT OF CANNED FOODS USEDIN temperatures employed nere somewhat STORAGE STUDIES higher than those usually encountered Vitamin Content When Placed in Storage, in the commercial v-arehouse storage, 3Ig. per 100 G. Can Contents Date Date Ascorbic CaroCode Can Thia- Ribothe investigation r a s extended to inStored acid tene Size Packed mine flavin Siacin Product NO. clude a wider range of canned foods, :rn Samples Easte stored at more practical temperatures 2 5/10/44 5/15/44 22. 50 0.47 0.12 Green asparagus 101 0.11 1.09 and for a more extended period. It 5/10/44 5/15/44 10.60 0.19 10 0.06 0.05 Green asparagus 102 0.82 2 0.09 0.82 6/ 6/44 6/ 8/44 10,50 0.31 0.05 Alaska peas 109 was also recognized t h a t the storage 0.10 6/ 6/44 6/ 8/44 11.80 0.30 0.06 0.86 Alaska peas 110 10 conditions employed in such studies 0.13 7/ 6/44 7/10/44 0.33 0.07 1.29 115 2 9.77 Sweet peas 0.04 8/10/44 0.33 125 2 5.50 8 / 8/44 , . Green beans , . . would involve constant temperatures 8/10/44 0.34 126 4.81 8 / 8/44 . . . 0.04 Green beans 10 8/25/44 2.41 0.51 131 8/23/44 2 ... 0.07 0104 Lima beans and, therefore, would not be exactly 0.04 0.56 8/25/44 132 2.96 8/23/44 10 ... 0.07 Lima beans comparable t o those encountered in 6.62 9/ 7/44 133 9/ 5/44 2 . . . 0 04 0 . 0 7 0.83 Yellow corn 6.52 0.02 9/ 7/44 ... 0.07 0.96 134 9/ 5/44 10 Yellow corn a commercial warehouse storage where 0.02 0.35 3.98 0.11 2 10/17/44 10/19/44 21.80 143 Spinach the temperature of storage usually fluctuMidwest Samples ates with seasons and with night and 22.20 0.48 0.07 0.10 111 2 6/16/44 6/21/44 Green asnarazus dag. Hence, i t seemed advisable to at0.31 0.11 0.07 0:95 7/ 1/44 7/10/44 2 10.10 Alaska pkas 113 0 19 0.07 1.56 7/12/44 2 11.30 0.40 117 7/ 8/44 Sweet peas tempt also to determine vitamin reten0,52 0.05 8/26/44 8/15/44 2 5.77 0.05 Green beans 129 0.91 0.04 5.42 0.06 9/ 7/44 8/29/44 135 2 0.11 Yellow corn tion in canned foods stored under actual 1.25 0.02 9/26/44 9/11/44 7.59 2 0.05 139 White corn warehouse conditions. .. , . ,. 0:06 12/ 5/44 12/ 12/44 2 145 Diced carrots 11/27/44 8.84 .. 11/21/44 146 10 ... Diced carrots . . 1
.
EXPERIMENTAL CONDITIONS
PRODUCTS STUDIED. Inasmuch as a conparable investigation of vitamin retention in commercially canned fruits and fruit juices ( 7 ) was being planned, 1 Present address, Bristol Laboratories, Syracuse, N. Y. 2 Present address, University of Arizona, Tucson. Aril.
.
Spinach Spinach Bleached asparagus Bleached asparagus Green asparagus Sweet peas Apricots Apricots Green beans Yellow corn Prunes Diced carrots
103 104 105 106 107 119 121 123 127 137 141 147
2258
21/2 IO 2 10 2 2 2 1/2 2'/2
2 2 2 '/Z 2
Western Samples 5/16/44 5 / 5/44 5/16/44 5 / 5/44 5/16/44 6/ 3/44 5/17/44 5/29/44 5/16/44 6 / 3/44 7/11 144 7/20/44 7/28 /44 7/19/44 8/11/44 7/31/44 8/15/44 8 1 4/44 9/ 8;'44 8/31/44 10/ 4/44 10/17/44 2 / 2/45 1/16/45
.
I
22.70 22.00 21.80 20.40 29.50 10.60 5.83 4.44 6.36 7.85 I
.
.
...
4.23 3.55 ..t
...
0.45 0.38 1.40 1.60
...
...
0.67 11.20
0.10 0.11
0 : iz 0.06
0.32 0.33 0.82 0.79 1.08 0.98
0:05 0.03
0:04 0.08 0.02
0:34 1 .09 0.44
0.03 0.03 0.09 0.07
..
0.08 0.08
..
..
..
..
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948 RETENTION
OF A S C O R B I C ACID
R E T E N T I O N OF C A R O T E N E
MiDWEST
EAST
2259
WEST
EAST
MIDWEST
WE51
SPINACH 103
:eo
ALASKA PEAS 109 '"BLEACHED ASPARAGUS lffi
IO0
.. SWEET PEAS 117
SWEET PEAS 119
-%-$-;I
-.-
STORED AT 5 O F
80
LIMA BEANS 131 O " B l 2
I5
24
0 4 0 1 2 M O N T H S IN
18 24 STORAGE
0
4
8
1
2
18
24
MONTHS
iN
s?oRA$E
"
24
Figure 1. Effect of Time and Temperature of 'Storage on Reduced Ascorbic Acid Content of Commercially Canned Foods
Figure 2. Effect of Time and Temperature of Storage on Carotene Content of Commercially Canned Foods
it was placed in storage; for the western samples this interval was somewhat longer. On being received a t the laboratory, the canned products were removed from the shipping cartons, checked and inspected, and segregated into comparable samplings, and those samplings destined t o be stored were placed in storage a t once. The groups of cans constituting the samples were selected in such a manner as to ensure equal distribution of the product as it came from the canning line. The cans of food constituting the control sampling were opened immediately, examined, and subjected to analysis. A typical pack of sweet peas was selected as the canned food to be used in the warehouse storage studies. All peas used in this phase of the investigation were from the same batch of raw stock and were packed in No. 2 tins on the same canning line. Representative samplings of this pack were stored in nine warehouses located in different geographical areas, while other samplings were maintained under control storage a t the temperatures previously indicated. Although the canned peas were not placed in the warehouses until late November, they were sampled and assayed during the latter part of July, shortly after being packed, and again when placed in storage. The results of these assays indicated favorable retention of the vitamins during the interim between packing and storage. STORAGE CONDITIONS.Three constant temperature rooms were used as storage space and maintained at 50 ', 65 and 80 F., respectively, throughout the storage period. These temperatures were suggested by a committee of the canning industry after due consideration of available warehouse temperature data, temperatures prevailing in localities where the major portion of the annual canned food production is stored, and available information on the effects of temperature on retention of canned food quality. It was believed that data obtained under these conditions of storage would be of value in setting up satisfactory
and economical storage conditions for canned foods even when employed on a commercial scale. Records kept of the range of temperatures within the three storage rooms throughout the storage period by means of recording thermometers showed fluctuations not exceeding 1 2 " F. The nine warehouses involved were regular commercial storage units, located in various parts of the country and selected in an attempt to duplicate average warehouse conditions prevailing in these localities. The properly labeled canned products were placed in storage in the fiber cases in which they had been shipped t o the laboratory. Representative samplings of the foods were removed from storage on specified dates for examination and for vitamin assays a t the end of 4, 8, 12, 18, and 24 months of storage. Samplings of peas from the various warehouses were assayed after 12, 18, and 24 months of storage. All samplings consisted of six No. 2 or No. 21/2 or two No. 10 cans. ASSAYMETHODS. The contents of each sample can were removed from the can and examined as to quality and solid-liquid distribution. The combined liquids and the thoroughly mixed combined solids were reconstituted in their original proportions to form composite samples for use in the various vitamin determinations. These composite samples were prepared for assay and assayed for reduced ascorbic acid, carotene, thiamine, riboflavin, and niacin by the procedures previously reported (2). The data obtained in these studies have been reduced to tabular and graphic form and are presented in Table I and in Figures 1 to 6, inclusive.
O,
O
VITAMIN CONTENT OF CANNED FOODS WHEN PLACED IN STORAGE
Examination of the data presented in Table I shows that the vitamin content of the canned foods used in the present investiga-
2260
INDUSTRIAL AND ENGINEERING CHEMISTRY LAST
RETENTION OF THIAMINE MIDWEST
--
60
'.....___-...-.80
'.-
70
Vol. 40, No. 12
.torage. Apricots, on the other hand, ret,ainrii COIIiiderably less of the vit,aniin when h-t,ored at 8 0 " P.for 2 years than when stored a t 50" or 6a F. for thc same period. The percentage of ascorbic acid retained was found to vary considerably with different packs of the same product. Green asparagus (East, No. 102) showed good retention of this vitamin when stored a t all three temperatures, whereas ascorbic acid retention by other packs of both green and bleached asparagus (East,, Midwest, arid West, Nos. 101, 111, 107, 105, and 106) was definitely affected by the storage temperat,ures. The efficiency of ascorbic acid retent,ion by green asparagus 102 a t all temperat,ures over and above that observed in asparaguf 101 (both from the same raw stock) may be attributed t o differences in size of can constituting the t ~ v opacks, but, such a relationship does not hold when m consider the percent,age of ascorbic acid retained by bleached asparagus packs 105 and 106. Pcrhaps the efficiency of ascorbic acid retention by this sampling of green asparagus (pack 102) may be more logically attributed to its previous thermal treatment. Asparagus pack 102 (No. 10 cans) contairied only about one half (10.6 against 22.5 mg.) as much of the vitamin when placed in storage as did the 101 pack (No. 2 cans). Furthermore, the apparent increase in ascorbic acid content of asparagus pack 102 on prolonged storage at 80" F. suggests the formation of ferrous iron or of other reducing substances which interfere in the usual procedure for determining reduced ascorbic acid. The formation of these interfering matcrials is usually associat,ed with previous prolonged thermal treatment. In other words, the favorable retention of ascorbic acid by this particular pack of asparagus may have been due t o differences in canning conditions and perhaps to the fact t-hat the product was subjected to a more severe heat t,reatmcnt, which resulted in the destruct,ion of a considerable portion of the reduced ascorbic acid initially present and rendered the remainder less subject t o oxidation owing t o the reduced oxygen t,ension.
-
There appears t o be no consistent difference in the percentage of reduced ascorbic acid retained by the V E L L C V / CORN 133 respective products from the different geographical 'm :._.___. areas. The minimum percentage of ascorbic acid 5 i c 9 E G 47 59.F SICRED AT 65'F retained by the nine products investigated (apricots, -------_ green beans, yellow corn, sweet peas, spinach, lima 60 beans, white corn, Alaska peas, and asparagus) a t the 1 E L l G W CORN 134 '' WHITE CORN 139 '' " " l2 Is 24 O If( end of 2 years of storage, in the order listed, was 48, M O N T h S IN STORAGE 67, 73, 74, 75, 76, 77, 79, and 79. I n each instance Figure 3. Effect of Time and Temperature of S turage on 'Thiamine this minimum retention was observed in products Content of Commercially Canned Foods that had been stored at 80 F. A n examination EFFECT ori CAROTEXE RETESTTOK. of the data presented in Figure 2 shows that carotene retentions, as tior].\vas \?,ell within t,he ranges recently reportcd for a wide selecthe result of the storage conditions, were c o n d e r a b l y highcr than tion of commercially canned product,s (3-6,8, y). In fact, a those found for ascorbic acid. K i t h respect to most products, majorit,y of the products were of higher vitamin content than the the adverse effect of storage temperature on retention of this average values reported by the above authors. Although the vitamin was less inarlred bhan was the effect of time of storage. specific variety of raw product involved in each instance in the This is in agreement with previous findings ( I ) . Although expresent investigation was not known, the vitamin contents of perimental conditions were not exactly comparable, the results f,he products from the three geographic areas Rere found to be here reported indicate somewhat lower carotene retentions from remarkably similar. From the standpoint of the initial vitamin comparable products a t the end of a 9-month storage period content, a product originating in one geographic area showed no than were reported bp McConnell et d . ( 6 ) . For the eight consistent advantage over t h a t from another geographic area. products under investigation (yellow corn, spinach, apricots, Likewise, Tvhere comparisons of the data were possible, the asparagus, diced carrots, sweet peas, prunes, and Alaska peas) contents of No. 2 cans did not always show higher vit,amin conthe minimum percentage of carotene retent,ion observed during tents than corresponding No. 10 cans. the %year storage period was, in the order listed, 70, 70, 72, 74, 82, 82, and 84. The retention of carotene by these products EFFECT OF STOR.46E AT CONSTAXT TEMPERATURES during~ the 24-month storage somewhat greater R ~ ~i~~~~ 1~ ~ ~ period, although ~ ~ ~ E~~~~~ON R~~~~~~A~~~~~~~ than reported by hfoschette et d. ( 7 ) for tomatoes, tomato juice, indicates t h a t in general retention o f reduced ascorbic acid by and peaches, is of the same general magnitude as the retention the canned foods decreased with time and temperature of storage. periods' observed for The adverse effect of each factor on ascorbic acid retention WZLS EFFECT O N THIAMIXE RETEXTIOS.An examination of the found to vary with different canned foods. data presented in Figure 3 reveals t h a t the time and temperature The retention of ascorbic acid from lima beans showed a marked Of thiamine of storage had a very marked effect On the decrease as time of storage progressed but showed no appreciable retained by the canned foods. difference in vitamin retention attributable to the temperature of
-.
79 59
.;
.
2269
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1948 RETENTION
O f RIBOFLAVIN
RETEWTION CAS-
N ,D :it 5 i
t * S i
,
,
GL PRUNES
I
,
141
OF NIACIN %Ci7
N.lOl"'EST
,
1
."
LIMA BEANS 132 to0
30 LIMA BEANS
0
4
e
i
z
131
la
GREEN BEANS 119
24
o d e 1 2 ie 24 0 4 8 1 2 M O N T H S IN S T O R A G E
,E
w
Figure 4. Effect of Time and Temperature of Storage on Riboflavin Content of Commercially Canned Foods
The degree of retention of this vitamin a t the end of 2 years of storage ranged from 46% for green asparagus (No. 107) siored a t 80" F. to 97% for sweet, peas (No. 117) stored at' 50" F. I n general, the effect of temperature of storage on thiamine retention was more marked than was the effect of time of storage. Each of the 26 packs of canned foods examined relative t o thiamine retention, after being stored a t the three temperatures for 24 months, showed the lowest vitamin retention where the product had been stored at t.he higher temperature (80" F.). With most of the foods investigated, the effect of temperature of storago on thiamine retention was very definite, in that samplings stored a t the lower temperature (50' F.) likewise showed the highest retention of the vitamin while samplings stored at the intermediate temperature (65 F.) had intermediate thiamine values. Of the eight canned foods investigated (asparagus, green beans, yellow corn, Alaska peas, lima beans, spinach, white corn, and sweet peas) the minimum percentage of thiamine retention observed in all packs a t the end of 2 years of storage, in the order listed, was 46, 54, 58, 62, 62, 70, 71,and 72. Here again the percentage of the vitamin retained during the first 12 months of storage appears t,o be considerably less than would be indicated by the data of Moschette et al. ( 7 ) . However, the latter studies concerned acidic products.
Figure 5. Effect of Time and Temperature of Storage on Niacin Content of Commerciall, Canned Foods
Of the eight products placed in storage (green beans, lima beans, ydlow corn, Alaska peas, spinach, asparagus, prunes, and sweet peas), the minimum percentage of riboflavin retained at the end of the storage period was, in the order given, 27, 52, 56, 60, 63, 69, 73, and 77%, while the maximum riboflavin retention for the same products in the order given was 84, 94, 75, 92, 90, 88, 86, and 93%. With one exception (yellow corn 137) these higher percentages of riboflavin retention were all observed among portions of the respective packs which had been stored a t the lowest temperature (50 F.), But, here again, the effect of can size or of geographical area in which the product was grown on riboflavin retention was not evident.
EFFECT ON RIBOFLAVIN RETENTION. The data presented in Figure 4 show t h a t with the majority of the canned foods under investigation, riboflavin content decreased with increases in both time and temperature of storage. However, the time effect appears t o have been the more pronounced of the two factors.
EFFECTON NIACISRETENTION.The effect of time and temperature of storage on niacin retention appears t o have been very irregular and inconsistent (Figure 5). These inconsistencies are evident in t h e niacin values obtained for the different products as well as for the different packs of 'the same product. For example, green asparagus 101 showed good retention of the vitamin while green asparagus 102 retained somewhat less than 80% of its niacin content during storage. Perhaps some of the inconsistencies in the niacin data here presented may be attributed t o the method of assay, which may not have been equally applicable to all types of canned foods. As a whole, the time effect on niacin retention appears t o have been more marked than the temperature effect.
The riboflavin content of certain packs of yellow corn, green beans, and lima beans was especially affected by the length of storage period. I n fact, each of the 22 packs of canned foods investigated was found t o have a definitely lower content of riboflavin at the end of 18 months than at the end of 12 months of storage and the majority of the packs showed a further decrease in riboflavin content following a n additional 6 months in storage. On the other hand, the poorest riboflavin retention a t the end of the 24-month storage period by the products studied was found in each instance in that portion of the pack which had been stored at the highest temperature (80" F,).
Of the nine products investigated relative to niacin retention (asparagus, green beans, Alaska peas, yellow corn, white corn, prunes, spinach, sweet peas, and lima beans), the minimum percentage of vitamin retention observed at the end of 2 years under the conditions of storage was, in the order listed, 71, 73, 79, 81, 85, 86, 90, 91, and 94%. On the other hand, the maximum niacin retention observed for these products ranged from 91% for white corn (No. 139) t o 108y0 for spinach (NO. 143). I n several instances there were some evidences of increased niacin content with prolonged storage. Moschette et al. ( 7 ) have indicated somewhat similar findings regarding the effect of storage on the niacin
INDUSTRIAL AND ENGINEERING CHEMISTRY
2262 MEAN
VARIATION (HIGH
IN
d
TEMPERATURE LOW)
C H A N G E IN
VITAMIN
CONTENT
DURING STORAGE
LOCATION OF STOR4GE 70
NEW W R K .
60
NY
M
40
- - - --
CAROTENE ASCORBIC ACID
an
+Y
-.
THiAMlNE
80 70
- --
ST LOUIS. MO
60
50 40 *I$ 90
rum cl 2 70
NEW ORLEAW LA
2 60
LU8O VI 70
1
WASHINGTON, p .-.
$9 90
80 70
-
-
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YUBA CITY
CALI5
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-
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D J F M AMJ J A S O N D J FMA M J J A S 0 N 0 1945 1946
0
6
12
I8
24
M O N T H S IN STORAGE
70
Vol. 40, No. 12
was satisfactory. Of the three vitamins studied, thiamine retention was affected most adversely by storage with respect to canned peas stored in all nine v-arehouses. On the other hand, carotene retention was least affectcd. While the loss of thiamine was not cxtremely serious under any of the conditions of warehouse storage (23% or less), there does appear t o be a relationship between vitamin loss and temperature of storage. For instance, the peas stored at Xew Orleans, La., and Yuba City, Calif., lost slightly more thiamine than those stored in other warehouses. The mean average temperatures recorded in these two warehouses were somewhat higher than temperatures recorded in the other seven warehouses and the fluctuations in the temperature (high and low for the respective months) were somewhat greater. However, if one examines the data as to the effect of the more adverse conditions of warehouse storage on the retention of the three vitamins in peas and compares these values with vitamin retention values for peas stored under constant temperatures (Figures 1, 2, and 3), it appcars that the minimum vitamin retentions in warehouse storage were comparable to those occurring \>hen the product was held for a similar period a t 80" F. Vitamin retentions from peas which had been stored in some of the other warehouses were more comparable to those retentions occurring at a constant temperature of 65" F. Thus it would appear that the fluctuation of storage temperature, within the ranges studied, does not result in appreciably lower vitamin retention than does storage under constant temperature. SUMMARY
An investigation has been made of the effect of 4, 8, 12, 18, and 24 months' storage a t 50", 65", and 80" F. on the reduced ascorbic acid, Carotene, thiamine, riboflavin, and niacin content of 32 different packs of content of canned peaches. The temperature effect on niacin re11 different canned foods of known origin, the majority of which tention was not as clear-cut as with other vitamins, in t h a t the were grown and packed in three different geographical areas, minimum niacin retention was not always found in those portions of The investigation also involved a study of the effect of comthe pack t h a t had been stored a t the highest temperature (80' F.) mercial warehouse storage on the ascorbic acid, carotene, and nor was the maximum niacin retention always found among those samplings stored at the lower temperature (50 ' F.). Howthiamine content of sweet peas over a similar period. ever, niacin retention in all products investigated was satisfactory The data obtained substantiate those previously reported for under the experimental conditions described. similar products ( 1 ) . I n general, vitamin retention was reasonably satisfactory under practically all conditions of storage. EFFECTOF WAREHOUSESTORAGEO N VITAMINRETENTION. Both time and temperature of storage had an adverse effect on T h e data presented in Figure 6 give the location of storage and the vitamin content of the canned foods, the degree of effect indicate t h e mean average (high and low) monthly temperature in depending on the particular food and vitamin. Retention of asthe nine warehouses employed during this phase of the storage corbic acid and thiamine was affected more markedly by teminvestigation, as well as the percentage change in the ascorbic perature of storage than by the period of storage, while the reacid, carotene, and thiamine content of the canned peas during the verse was true for riboflavin and niacin. Of the five vitamins 24-month storage period. investigated, carotene was least affected by storage conditions. The canned peas used in this phase of the investigation were of Canned foods stored a t 50' F. retained a higher percentage of better than average quality. They contained, initially, 27.6 each of the five vitamins than those stored a t the higher temperamg. of reduced ascorbic acid per 100 grams, 10.7 mg. after proctures. The minimum ascorbic acid retention observed a t the essing, and 10.1 mg. when placed in storage. They were packed end of 24 months' storage ranged from 48y0 for apricots t o '79% during the month of July and placed in storage during the latter for green asparagus; the minimum carotene retention ranged from part of November. Stability of the three vitamins during the 70oj, for yellow corn to 84y0for Alaska peas; and the minimum interim between packing and being placed in warehouse storage Figure 6. Effect of Warehouse Storage on Reduced ascorbic Acid, Carotene, and Thiamine Content of Commercially Canned Peas
December 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
thiamine retention ranged from 46% for green asparagus t o 72% for sweet peas. T h e lowest riboflavin retention observed at the end of the 2-year storage period was 27% in green beans, while the lowest riboflavin retention observed in sweet peas was 77%. The minimum niacin retention ranged from 71% for green asparagus t o 94% for lima beans. No consistent evidence was obtained that a food grown and packed in one geographical area retained a higher percentage of its vitamin content than t h a t grown and packed in another area. Samples of a representative pack of commercially canned sweet peas, after being stored for 2 years in nine different commercial warehouses located in various parts of the country, retained high percentages of their ascorbic acid, carotene, and thiamine contents, the degree of retention appearing t o depend on the average temperature within the warehouses in which the samples had been stored. ACKNOWLEDGMENT
The authors are indebted t o members of the Research Committee of the NCA-CMI Nutrition Program for their assistance in selecting and collecting the various packs of canned foods used in this investigation.
2263
LITERATURE CITED
(1) Guerrant, N.B.,Vavioh, M. G., and Dutoher, R. A., IND. ENG. CHEM.,37, 1240 (1945). (2) Guerrant, N.B.,Vavich, M. G., Fardig, 0. B., Ellenberger, H. A., Stern, R. M., and Coonen, N. H., Ibid., 39, 1000 (1947). (3) Hinman, W.F.,Higgins, M. M., and Halliday, E. G., J . Am. Diutet. Assoc., 23, 226 (1947). (4) Ives, Margaret, Wagner, J. R., Elvehjem, C. A,, and Strong, F. M., J. Nutrition, 28,117 (1944). (6) Ives, Margaret, Zepplin, Marie, Ames, S. R., Strong, F. M., and Elvehjem, C. A,, J. Am. Diutet. Assoc., 21,357(1945). (6) McConneil, J. E. W., Esselen, W. B., Jr., and Guggenberg, N., Fruit Products J.,24,133 (1945). (7) Moschette, D. S., Hinman, W. F., and Halliday, E. G., IND. ENG.CHEM.,39,994 (1947). (8) Pressley, Anne, Ridder, Clara, Smith, M. C., and Caldwell, Emily, J,Nutrition, 28,107 (1944). (9) Thompson, M. L., Cunningham, Elizabeth, and Snell, E. E., Ibid., 28, 123 (1944). RECEIVED January 2, 1948. Authorized for publication December 19, 1947, as Paper 1420 in the Journal Series of the Pennsylvania Agrioulturnl Experiment Station. Investigation supported in part by a grant from the National Canners Association-Can Manufaoturers Instituta Nutrition Fund. The 27th of a series of papers dealing with the general subject.
Heating Rates of Food in Glass and Other Containers D. G . MERRILL Hartford-Empire Company, Hartford, Conn.
A simple empirical formula is given for the approximate heating rate of cylinders of finite length which considers the conductivity of the material and the surface-heat transfer coefficient. This formula is of general application except for short heating times. Data from confirming experiments are given for solids and for containers in which the container wall is considered as included in the boundary surface. Constants are derived for application to the heating of food in glass containers so that established methods for computing sterilization process time in tin may be extended to glass. The interrelationships of surface heat transfer, internal conditions, and container proportions are discussed in their effect on lag factor j .
M
ETHODS for calculating the sterilizing process time for foods packed in tin have been well established. When the necessary constants for a given food have been determined by experiment, these methods permit extending the results by computation to the various sizes of cans and t o other variations in condition which affect the heating rate. T h e existing formulas, however, are not entirely applicable t o the conversion of the constants which express rates of heat penetration where glass containers are involved. This is because of t h e relatively large resistance to heat transfer offered by the greater thickness and lower conductivity of the glass wall, as compared t o t h a t of the metal container. This factor of wall resistance is considered below, and vhile its inclusion tends t o make the computations more complex, the use of graphical methods will keep them from becoming too unwieldy. I n the method given by Ball (2) for food packed in tin the assumption is made that the metal container and surface films offer no resistance t o heat flow-Le., there is an instantaneous
change of surface temperature which is equivalent t o a n infinite surface-heat transfer rate. This simplifying assumption is justified by confirming experiments, when contents are of such consistency that internal heat transfer is mainly b y conduction. Schulta and Olson ( I d ) point out, however, t h a t with liquid foods this method is unreliable and they use, under these conditions, a formula-in which the heat flow at the surface is the controlling influence. Neither of these methods provides for computation of heat penetration where both surface and internal heat flow resistances are significant and this becomes of special importance for the glass container because the glass offers a n appreciable resistance to heat flow into the contents, which varies with the thickness of the glass. The problem involved is, therefore, that of the temperature distributionin a cylinder of finite length during heating in which both the conductivity of the material and the coefficient of heat transfer at the surface are of finite value and approximately constant. The solution of this problem leads t o involved equations which are not suitable for convenient numerical computation. There are available, however, charts such a s those of Gurney and Lurie (6),Grober (5), and Bachmann (1) which facilitate estimating temperature distribution in simple solids including the infinite slab, the cylinder of infinite length, and t h e sphere. The cylinder of finite length is not included but examination of the curves for slab and infinite cylinder leads t o a suggested form for a n approximate formula. HEATING CURVES DEFINED BY f AND j
The formula sought is one which may be applied t o sterilizing computations by the method of Ball (2,9). I n this method heating and cooling curves are approximated by straight lines in
