June, 1921
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
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The Relation of Moisture Content to the Deterioration of Raw-Dried Vegetables upon Common Storage1p2 By H. C. Gore and C. E. Mangels BUREAUOF CHEMISTRY. U.
s.
DEPARTMENT OP AGRICULTURE, WASHINGTON, D.
The simplest and one of the best ways of drying many kinds of vegetables is t o wash, trim, and cut t h e m finely, and dry in a current of warm air. Carrots, onions, turnips, tomatoes, celery, parsnips, and cabbage yield excellent products when dried in this way. Unless, however, the products are dried t o below certain moisture contents they will not retain their original color and flavor during storage a t ordinary temperatures. Fading of the natural colors occurs, accompanied by darkening of t h e tissues and changes in flavor and aroma. For example, sliced carrots, dried without taking special precautions t o dry thoroughly, lose their brilliant color and distinctive flavor. Turnips, cabbage, and onions similarly dried slowly darken upon keeping a t room temperatures, becoming finally as dark a s tobacco, and a t the same time suffer serious losses in distinctive flavor. Spinach fades and acquires a hay-like flavor unless dried very thoroughly a n d kept in air-tight containers. If the products have been cooked before drying the deterioration is less rapid, but no less certain. Microdrganisms cannot be concerned in this deterioration, because the moisture content is almost invariably well below t h a t a t which yeasts, molds, and bacteria will grow. The purpose of the work described below has been two-fold: 1-To demonstrate that the moisture content bears a definite relation t o the rate of deterioration. 2-To determine the critical moisture content for each of the important dried vegetables below which the changes in color and flavor on keeping at ordinary temperatures are very slow.
A steam-heated commercial dryer was used. A substantial quantity of each vegetable (about 100 lbs.) was cut finely, spread on trays, and dried in a current of warm air until i t reached a moisture content below t h a t a t which i t would spoil as a result of invasion b y microorganisms. A portion of the material, usually one-fourth t o one-fifth, was then removed, the remainder further dried, again sampled, and the operation repeated until four or five samples of different moisture content were secured. This set of samples, called a "moisture series," was kept a t room temperatures ranging from 70" t o 90' F. in the dark in tightly sealed, glass fruit jars. The moisture content of each jar of material was determined by drying t o constant weight in vacuum a t not over 70" C. As the products were finely divided before drying, the samples taken for moisture were not ground before drying. Notes made on the stored samples from time t o time are given below. The principal indication of deterioration was change in color. Changes in aroma and flavor also occurred, but usually were less clearly evident. 1
Received January 21, 1921. by permission of the Secretary of Agriculture.
* Published
c.
TABLE I-CARROTS (Dried December 31, 1917)
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A dried 6 hrs. a t 122O F.; B, 6 hrs. at 122' F. 2 hrs. a t 140'F.; 3 hrs. at 140' F.; D, 6 hrs. a t 122' F. 3 hrs. at C 6 hrs. at 122O F. 140. F. 1 hr. a t 158' F. Days of A B C D 4.99 Per cent 4.54 Per cent Stor- 11.11 Per cent 7.39 Per cent Hz0 Hz0 HzO aee HzO 40 No color change No change No change No change Strong carrot odor No change 68 Distinct fading No change No change of color noticeable 86 Color faded. Color slightly Odor and flafaded vor still distinctive 235 Carrot color Color faded. Color faded Like C faded. SamNo darkening. slightly less ple darkened Odor and flathan B vor still distinctive 690 Color faded and Color faded a n d Color faded. Sample lost browned. Disdarkened No darkening tinctive aroma and flavor lost 942 Distinctive color, Color faded. Sample lost Distinctive flavor, and flavor still aroma lost present
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TABLE11-TURNIPS (Dried January 2, 1918)
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A dried 6 hrs. at 122' F.; B,10hrs. a t 122OF.; C, 10 hrs. at 122' F. 1 hr. at 140' F.; D, 10 hrs. a t 122' F. 2 hrs. a t 140' F. Daysof A B C D 6.57 Per cent 5.00Percent 4.55 Per cent Stor- 11.51 Percent Hz0 Hz0 HzO HzO aae 33 Browned disNo change No change No change tinctlv. Strone turniG odor 65 Darker than Darkened very No change No change above. Still slightly. Very has strong little odor turnip odor 80 No change No change 233 Color dark Darkened and Sliahtlv darkSame as C brown. Strone has strone &ed. Turturnip od& nip odor turnip odor 588 Color dark Color brown. Slightly Same as C brown. Lacks Slight turnip browned distinctive odor flavor 940 Same as previous Same as previous Same as previous Same as C examination examination examination
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TABLE 111-ONIONS (Dried January 6, 1918) A dried 10 hrs. a t 113' F . ; B, 20 hrs. a t 113" F.; C, 24 hrs. at 113O F.; D , 24 hrs. a t 113' F. 0.5 hr. a t 113°-1220 F. Daysof A B C D 6.64 Per cent 5.74 Per cent 5.34 Per cent Stor- 9.65 Per cent HzO age HzO HzO Hz0 No change 29 Slight darkenNo change No change enmg. Onion odor 76 Same as previous No change No change No change 227 Color light Sample lost. Slightly yellow. Like C brown. FlaJar defective Flavor good vor poor 554 Color dark Distinctly brown. Flabrowned. Flavor and vor poor odor good 905 Same as previous Color light examination brown. Flavor deteriorated, but still distinctive
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TABLE IV-SPINACH (Dried May 13, 1918) B dried 1.25 hrs. a t 140' F.; C, 1.5 hrs. a t 140' F.; D , 2.5 hrs. a t 140" F.; E, 3 hrs. at 140' F. Daysof B C D E 5.38 Per cent 3.81 Per cent Stor- 8.90 Per cent 2.03 Per cent Hz0 HzO HzO age HzO Color slightly Color unchanged. Like D 103 Flavor poor, hav-like faded. FlaFlavor fair vor fair 778 Color slightly Same as pre- Color very Like D browned. Flavious examislightly faded. Flavor fair vor poor, haynation like
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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
TABLEV-CABBAGE (Dried January 2, 1918) A dried 6 brs. a t 122O F . ; B , 10 hrs. a t 122'F.; C,10 hrs. a t 122' P. 1 hr. a t 140° F . ; D , 10 hrs. a t 122' F. 1 hr. at 140' F . 1 hr. at 150'160' F. C D Daysof A B Stor- 11.15 Per cent 5.49 Per cent 3.54 Per cent 3.00 Per cent HzO HpO Hz0 Ha0 age 33 Slightly browned . .. ...... 80 Browned. Pe- N o change N o change N o change culiar taste and odor 232 Quite dark. Un- Slightly darkSlightly darkSame as C ened. Flavor pleasant aroma ened. Flavor good good 588 Same as previous Distinctly Same as previous Same as C browned examination examination 940 Same as previous Distinctly Same as previous Same as C examination examination browned. Unpleasant aroma
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D I S C U S S I O N O F RESULTS
The results of the observations clearly demonstrate the extremely important influence of low moisture content on the retention of distinctive color and flavor by raw dried vegetables upon keeping in air-tight containers a t ordinary temperatures. Carrots of 11.11 per cent moisture content faded distinctly during 68 days' storage, while carrots of 7.39 per cent moisture kept well for this period. Turnips of 11.51 per cent moisture
Vol. 13, No. 6
content browned distinctly and developed a peculiar turnip-like odor in 33 days, while turnips dried t o 5.00 per cent moisture had not changed in 80 days. The same general facts were noted in case of the samples of onions, spinach, and cabbage. The moisture content below which t o dry for satisfactory retention of color and flavor during common storage in air-tight containers can be approximated from the results given in the tables. SUMMARY
The moisture content of dehydrated raw vegetables was found t o be a factor of considerable importance for successful storage in air-tight containers a t ordinary temperatures. The initial moisture contents a t and below which the distinctive color and flavor are well retained for 6 mo. or more are as follows: Carrots, 4.99 t o 7.39 per cent; turnips, 5.00 per cent; onions, 5.74 t o 6.64 per cent; spinach, 3.81 t o 5.38 per cent; cabbage, 3.00 t o 3.34 per cent.
Manganese in Commonly Grown Legumes] By J. S.Jones and D.E.Bullis DIVISIONOF CHEMISTRY, OREGONEXPERIMENT STATION, CORVALLIS, OREGON
Whatever may be the function of manganese in plant nutrition there is no doubt of its common occurrence in soils and of its utilization in limited amounts by plants generally. I n the course of some analytical work on the legumes t h a t are characteristic of various parts of Oregon, the frequent development of a blue or bluish green color in the ash determinations was noted. This color we took t o be indicative of manganese in the legumes burned-possibly in unusually large amounts-but this latter surmise proved t o be wrong. The color could be developed almost a t will by raising the temperature of the combustion furnace to a point just below incipient fusion of the ash, and exceedingly small amounts of manganese were sufficient t o produce it. The explanation is the formation of a n alkali salt of manganic acid. Because of other determinations t o be made on the ash i t was undesirable t o ignite a t the high temperature required for the formation of the bluish green melt, hence the ash determinations neither proved nor disproved the presence of manganese in all samples of the several kinds of legumes under examination. Although the literature makes it plain t h a t manganese is utilized t o a n appreciable extent by plants generally, analytical data indicative of actual amounts found in plants as a whole or in their several parts are not of frequent occurrence. Jadin and Astruc,zreporting on some vegetable substances used as fodders, claim 0.36 mg. of manganese per kg. of dry material in potatoes and varying amounts in other fodders, up t o 80 mg. per kg. in poplar leaves and meadow grasses. The green or chlorophyll-containing parts were always richest in manganese. McHargue3 found, in many kinds of seeds and nuts, the largest amounts of manReceived January 3, 1921. Compt. rend., 166 (1912), 300; 169 (1914), 268. 8 J . Am. Chem. SOL, 86 (1914), 2932.
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ganese in those parts of the seed coats t h a t immediately surround the cotyledons. He found, too, t h a t manganese is relatively high in those parts which secrete large amounts of oxidizing enzymes. His inference is t h a t manganese serves as a catalyst t o the enzymes. Headden' found in the grain of wheat amounts ranging around 40 p. p. m. of.dry matter. He concluded t h a t manganese is present in the wheat kernel in practically the same amounts as iron, and t h a t fertilizers and irrigation waters do not affect t o any appreciable extent the amount of manganese stored by the wheat plant in its seeds. The meagerness of quantitative data for this element whose function in plant nutrition is imperfectly understood, and our plans for using certain of the legumes in animal nutrition investigations made i t worth while t o determine for the commonly grown legumes the extent t o which they utilize manganese in growth. Incidentally, t h a t portion of the work which determined the relative amounts of manganese in the several parts of these legumes gives additional support t o the theory t h a t its primary function is catalytic, inasmuch as by far the largest amounts were found in the leaves. ;METHOD
OF A N A L Y S I S
Manganese in organic material is usually determined colorimetrically, following its leaching from the ash and its conversion t o permanganate. For t h e conversion lead oxide is used alone, or ammonium persulfate is used with silver nitrate as a catalyst. It is frequently recommended, too, t h a t the material t o be ashed should first be mixed with some oxidizing agent, such as nitric acid or ammonium nitrate. Five grams of rather finely ground material were ashed in a silica dish without mixture with any kind of oxidizing agent. The practically pure white ash was taken u p with a 1
J . AgY. Res., 6 (1915), 349.
