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
The subjects ate a n average of 1 0 4 g. of protein, 79 g. of fat, and 338 g. of carbohydrate daily, an amount of food sufficient t o supply 2,4 j5 cal. of energy. Of the 98 g. protein consumed daily, the 6 9 g. derived from the seal meat were found t o be 9 4 . 6 per cent digested. All the subjects except one reported t h a t they were in normal physical condition during the experimental period; the one exception reported a tendency towards constipation a t t h e termination of the period, a condition not infrequently resulting from diets t h a t are very completely digested. The general conclusion t o be drawn from these experiments is t h a t seal-meat protein like t h a t of other meats is well digested. As is always the case in this experimental work, discussion of t h e food and ration is always avoided with the subjects. However, from conversation which was overheard, i t was apparent t h a t they did not note any unusual flavor and thought these meat cakes were “Hamburg steak.” SUMMARY
The results obtained in the digestion experiments with kid, rabbit, horse, and seal meats are summarized i n Table 11. The coefficients of digestibility there given for the protein, t h e f a t , and the carbohydrate of t h e entire ration and for t h e protein of the meats alone itre the averages of the coefficients of the digestibility obtained in the individual experiments with the different meats. The amounts of meat eaten are included as a matter of dietary interest. DIGESTION EXPERIMENTS WITH MEATS AMOUNT OF MEATEATEN c DigestiAver. Max. bility DIGESTIBILITY OB ENTIRE RATION per per of Meat CarboMan Man Protein KIND Protein Fat hydrate per per Alone OF No. of Per Per Per Day Day Per MEAT Expts. cent cent cent Ash Grams Grams cent .Kid ..... , 3 91.7 95.5 98.6 87.9 163 166 94.4 .Rabbit. , . 5 90.0 95.8 97.9 80.1 205 217 91.8 94.5 98.5 83.2 Horse. ... 7 94.3 306 414 96.4 92.9‘ 98.0’ 88.21 Seal.. 6 91.9 230 281 94.6 1 Average of four experiments.
The total ration in all the tests was very well utilized -the carbohydrates, especially, being very completely absorbed, from which i t is apparent t h a t these meats did not decrease the digestibility of the other constituents of the diet. I n every case the average amount of meat eaten daily was in excess of t h a t included in the ordinary diet of the average person, and in no instance were any physiological disturbances noted. The digestibility of the protein of t h e four kinds of meat studied was essentially the samk as t h a t of other and better-known meats.
pears are held a t a lower temperature t h a n peaches, and, if both are held a t the same temperature, t h e peaches may be injured. The question arises whether fruit which has been frozen or only partly frozen can be distinguished from fruit not subjected t o these low temperatures. Extreme cases of frozen fruit can, of course, always be recognized after thawing b y the mushiness and darkening of the pulp, b y t h e modified taste, and by the rapidity of rot. Between t h e extreme frozen condition and the non-frozen condition, cases arise t h a t cannot be judged by such obvious indications. Chemical and histological methods of examination suggest themselves for such cases. CHEUICAL METHODS O F DETECTION9
Before discussing chemical methods of detection i t is necessary t o have in mind the physical effects of ice crystals upon cells, as are fully described in the studies of Schander and Schaffnit.‘ These include progressive disintegration effects, such as the growth of ice crystals, the instreaming of water from adjacent cells, the concentration of cell saps, cell plasmolysis, the destruction of inner plasma membranes with attending loss of osmotic function, the infiltration of electrolytes, and the coagulation of the proteins of t h e protoplasm. From this description it may be concluded t h a t such free mingling of materials can rapidly give rise t o those products which are normally slowly formed by ripening and by over-ripening. Changes in fruits after gathering are described b y Otto and Kooper2 as increasing the amount of invert sugar and producing losses of water, cane sugar, acidity, and nitrogen. Contino3 observes a loss of pectin. Prinsen-Geerligs4 observes conversion of starch t o sucrose and decrease of acids. Tannic acid6 appears and disappears. Many fruits lose water during ripening,B but the total water content may be increased by “metabolic water.” The specific gravity7 of good fruit increases on storing, while t h a t of frozen fruit decreases. With apple after ripening and storage there is a slight increase in invert sugar followed by a continual decrease, and sucrose also gradually decreases.8 Since the concentrations of acids vary during ripening and over-ripening, their variation after freezing and thawing was considered as a possible means of detection of the prior frozen state. However, the work of Bigelow and Dunbars indicated t h a t the concentrations of acids are too low and the acids themselves too varied t o be of value. Other components conLandw. Jahrb , 6’2, 1, Chem. Zentr., 2 (1918), 397. Z Z . Nahr. Genussm., 19 (1910), 10, 328. Staz. sper. ugrav. ital., 46, 60. 4 Intern. Sugar J . , 10 (1908), 372. . 6 Basset, el al., J . A m . Chem Soc., 33 (1911), 416; Science, 33 (1911). 624: Tonegretti, Staz. sper agrar. itat,, 48 (1911), 369; Gerber, Compt rend., 124, 1106; Behrens, Centr Bakt. Parasitenk., 4, Part 11, 7770. Babcock, University of Wisconsin, Research Bulletin 22, 87. 7 Webber, et al., California Agricultural Experiment Station, Bulletin 804 (1919). 245. 8 Neidig, et al., Idaho Agricultural Experiment Station, Report 1917, 1
A CHEMICAL METHOD FOR THE DETECTION IN FRUIT OF A PRIOR FROZEN CONDITION By William M. Dehn and M . C. Taylor CHEMICAL LABORATORY, UNIVERSITY OF WASHINGTON, SEATTLE, WASH.
Received June 10, 1920
Modern methods of cold storage of fruits sometimes raise the question whether too low temperatures have been employed, resulting in abnormal deterioration when the fruit is removed from storage. For example,
22. 0 THISJOURNAL, 9 (1917), 762. A full bibliography is given That the acid concentration may increase through rotting was shown by Hawkins, A m J . Botany, 2 (1915), 71.
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sidered and abandoned were starch,l oxidases,' waterj3n i t r ~ g e ne, t~c 5 That the changes in sucrose concentration could be used was suggested by such observations as the following: Sugars exercise the greatest protective action against freezing;6 sucrose disappears in rotting and is transformed t o invert sugar during the stages of ripening and over-ripening ; sucrose and invert sugar are differently localized* in the tissues of the fruit. The method described below makes use of the fact that freezing brings about a very rapid transformation of sucrose t o invert sugar, the result, of course, of the free mingling of sucrose with inverting acids or invertase, or both. * M E T H O D O F ANALYSIS One half of the fruit t o be examined is analyzed directly and the other half is frozen with cracked ice and salt. Each sample of the fruit may be cut into halves, or, with very small fruit, two approximately equal samples may be set aside for the analysis. The directly analyzed portion involves the estimation of invert sugar before and after hydrolysis, yielding ,4 and B; the frozen portion is also analyzed for invert sugar before and after hydrolysis, yielding C and D. In other .words, the ratios of invert sugar t o sucrose before and after freezing are compared. I n all cases the estimations are made by weighing the cuprous oxide formed after reduction. The respective solutions are measured out in triplicate in ro cc. samples, treated with IO cc. each of Fehling solutions I and 11, diluted t o a known volume (100 cc., for example), and boiled for a known time, say 5 min. The precipitates are filtered hot on weighed Gooch crucibles, washed with water and then with alcohol, and dried t o constant weight at about 110' C. When the solutions are prepared in the manner described below no difficulty is met in filtering rapidly on the Gooch crucibles, and the first two analyses will usually agree. SOLUTION A-The fruit is mashed in a mortar with water containing sufficient free alkali t o maintain t o the end an alkaline reaction, transferred t o a flask or beaker, and boiled until a complete extract of t h e material is obtained. Since the percentage of invert sugar is not sought,g but only its ratio t o sucrose, no weighing of fruit and maintaining of constant volumes need be made. A portion of the solution is filtered hot, then cooled and made slightly acid, and again 1 Neidig, Prinsen-Geeligs, etc , LOC cit. Some fruits, as for example, peaches, are practically devoid of starch. 2 Gore, U. S. Dept. Agr., Bureau of Chemistry, Bulletin 144; Yoshida, J . Chem. SOL, 48, 472; Bcrtrand, Co?npt rend., 118, 1215, Lindet, Ibid., 140, 370; Martinand Ibid , 121, 512; Appleman, Butan Gas. 50, 182. 3 Webber, LOG. cit 4 Bassett, LOC. at. 5 Windisch and Schmidt, Z . Nahr Genussm., 11, 584 5 Maxinov, Ber. botan. Ces., SO (1912). 52, 293 7 Hawkins, LOC cit Acids and reduclng sugars 8 DeMoussy, Compt. r e n d , 161 (1915), 443. Are expressed t o the greatest extent with high pressure on the fruits, whereas non-reducing sugars are obtained with slight pressure. 8 Knowledge of the concentrations of i n v x t sugar and sucrose in the entire fruit is of no value in this connection since these vary wlth the variety and age of the fruit. The final per cent of inversion could be obtained on this basis, if so desired, but the method would be greatly complicated without yielding added value
filtered-to separate colloids which would have a fatal effect on subsequent filtering. Enough solution is set aside for analysis (A) and the remainder is treated as follows: SOLUTION B-A known volume of the solution is treated with a known volume of concentrated hydrochloric acid, estimated t o be sufficient t o hydrolyze the sucrose1 when immersed in a boiling water bath for 20 to 30 min. After cooling and filtering, t h e solution is made alkaline, and analyzed for total reducing sugar, corrections for change of volumes being made In t h e final calculations. SOLUTION c-After freezing2 and thawing, the second half of the fruit is treated exactly as for Solution A . SOLUTION *This solution is prepared from C as Solution B is prepared from A. A sound apple, frozen for 16 hrs., then thawed o u t and left standing for 24 hrs., was analyzed with t h e result indicated in Table I . Sotu- ---Sample-TION (1)
TABLE I AVERAGE Invert Sucrose
Percentage Inversion 31 4 -
If t h e value 79.1 for sucrose is indicated by S, and the value 37.7 is indicated by s, the percentage of inversion (3 7.47) resulting from-freezing (and thawing and autolysis t o the time of analysis) can be calculated by the following, easily derived forinula, in which the constant 1.052 is the ratio of molecular weights of two molecules of hexoses t o one molecule of sucrose. Per cent of inversion
(S - s) s 3. I .052SS
With other fruit, as, for example, the peach, similar changes resulted. The data in Table I1 were obtained with sound peaches frozen 1 2 hrs. and thawed 3 hrs. SOLU--SamplTION
TABLEI1 AVERAGE Invert Sucrose
0.3063 0.2080 o.3342 0.2080
1 0 0 : 75.51
Samples of this same supply of sound peaches analyzed 2 wks. later under the same conditions gave the following data: TABLEI11 AVER(2) AGE Invert Sucrose o.2286 0 . 2 2 7 6 0.2276 0,3184 0.5459 0 . 5 4 6 0 ) ::::$;]0.2369 0.2668