B. C. ROY SARKAR AND K.
C.
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sulphate. This was necessary for removing the sterols which would otherwise interfere with the
estimation owing to their gradual precipitation. It was found that even without any carotene
supplements there was a basal excretion of 0.22 µg. per animal per day. But this pigment was not
carotene as it had not typical selective absorption in the visual region of the spectrum. The apparent
excretion of carotene on various supplements at 1-2 µg. level of dosage varied from 40 to 52 per cent
in the case of both the standard of reference and that supplied from the fodders. A biolgical assay
of this faecal pigment showed about 25 per cent active carotene, so that the true carotene excretion
was 10-13 per cent of the original ingestion. It might be mentioned here that livers of animals re-
ceiving various carotene supplements were free from reserves of vitamin A as tested by the antimony
reaction. Probably the absorbed carotene from the various sources was equally utilized.
(4) Relative efficiency of the standard carotene and preformed vitamin A
This was studied essentially by assaying the standard carotene, which has been shown to be
quite as potent as the green fodder carotene, against cod-liver oil, standardized by the spectrographic
method [Coward, 1938]. E 1%
1c.m 328 mµ was taken to be 1600. The results of the bio-assays
are given in Table III. It is evident from the data that the standard carotene was half as active
as an equal weight of vitamin A. As the ratio of the growth rate on fodder carotene to that on standard
TABLE III
Relative efficiency of standard carotene and cod-liver oil Vitamin A at minimal levels of dosage
No of
assay
1
2
Date of assay
5. 5. 43 (summer) . . . . . . . . . . .
4. 1. 43 (winter) . . . . . . . . . . .
Average .
Growth rate per week (g)
Vitamin A at 1
µg. level of
dosage
9.33
8.08
8.76
Carotene at 2 µg.
level of dosage
8.98
8.38
8.68
cartotene varied from 0.95 to 1.08 (average 1.01), the vitamin A equivalence of a microgram of the
different fodder carotene varied from 0.48 to 0.54 µg. giving an average of 0.51 µg. (Table I). A
similar relationship has been observed by other workers. It may be pointed out here that separate
analyses showed no trace of vitamin A in the faeces and livers of the cod-liver oil-fed groups of rats.
It might be presumed that both carotene and vitamin A were completely utilized after absorption
if no change into inactive forms took place anywhere in the process of digestion and assimilation.
On this basis, the efficiency of transformation of ß-carotene into vitamin A can be calculated as
follows. Taking into consideration the fact that the standard of reference was composed of 80 per
cent ß- and 20 per cent α-carotene, and assuming that 87 per cent of the carotene ingested at a level
of 2 µg. was absorbed, 1 µg. of carotene appears to be as active as 0.639 µg. of cod-liver oil vitamin
A. If E 1%
1c.m 328 m.µ is taken as about 1900 instead of 1600 used previously
[Morton, 1942], 1 µg. of carotene would be equivalent to 0.538 µg. of vitamin A, a value which is
about half the theoretical one if a symmetrical breakdown of the ß-carotene molecule yielding two
molecules of vitamin A occurred. It would also appear that 1 µg. of vitamin A possesses an
activity of 3.1 i.µ. showing a conversion factor of i.µ./E=1631.6.
SUMMARY
1. With the object of determining the vitamin A value of carotene in different green fodders,
an investigation has been undertaken to study (i) the relation between the chemically determined
carotene and its biological activity as compared with that of standard carotene, (ii) the purity of
apparent carotene from different sources, (iii) absorption of carotene in rats, and (iv) the relative
efficiency of the standard carotene and preformed vitamin A.
S