Sterol requirements of insects

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Vol. 37



The requirements for sterols seem, therefore, to be qualitatively the same for the six insect species under investigation, but there are obvious quantitative differences. From a comparison of the growth on three diets relatively deficient in sterols (summarized in Table 2) it can be concluded that Sitodrepa, Ptinus and Ephe8tia kuehniellarequire larger quantities of sterols than Tribolium, La8ioderma and Silvanus.

quire a sterol in the diet for growth. The quantitative requirements of sterols by different insects are different, but the qualitative requirements of the insects under investigation are the same. The specificity of the sterol requirements was studied.
We gratefully acknowledge a Government grant from the Royal Society,which, partly, made this investigation possible. We are also much indebted to Prof. I. M. Heilbron and Dr E. R. H. Jones (Imperial College of Science and Technology) and to Mr A. L. Bacharach and Dr E. Lester Smith (Glaxo Laboratories Ltd.) for the gift of a number of sterols.

SUMMARY The sterol requirements of six different insect species have been investigated; all the insects re-REFERENCES
Fraenkel, G. & Blewett, M. [1943 a]. J. exp. Biol. 20, 28. - [1943 b]. Biochem. J. 37, 686. [1943c]. Trans. R. ent. Soc. 93, 457.

Fraenkel, G., Reid, J. A. & Blewett, M. [1941]. Biochem. J. 35, 712. Richardson, C. H. [1926]. J. agric. Res. 32, 895.

Apparent Vitamin C in Foods
BY F. WOKES, JOAN G. ORGAN, JEANETTE DUNCAN AND F. C. JACOBY, Ovaltine Research Laboratories, King's Langley,Herts

(Received 12 August 1943)
Titration with 2:6-dichlorophenolindophenol is used to estimate vitamin C in a wide variety of foodstuffs, though the dye may react with substances besides ascorbic acid. Harris [1933] showed that dye-reducing substances can be produced by heating certain sugars with alkali. Johnson [1933] found with germinated peas that dye titrations indicated higher vitamin Ccontents than was shown by biological tests. In acid extracts part of the dyereducing power was due to a substance which reduced the dye more slowly than ascorbic acid. Bacharach, Cook & Smith [1934] found an increase in the dye-reducing power of malt extract heated to 1000 for j-2 hr. McHenry & Graham [1935] obtained increases of 50-170% by heating certain vegetables for a few minutes at 580 or bystanding these for a fgw hours at room temperature in 1 % HCI. Ahmad [1935] found that boiling cabbage for 10 min. with 20% CC13COOH increased the apparent vitamin C content by nearly 200 -. Reedman & McHenry [1938] found that the apparent vitamin C in heated potatoes resembled true vitamin C in both physiological and many chemical properties, Their suggestion that ascorbic acid might exist incombination with protein from which it was set free by heating was discredited by Harris & Ojliver [1942], who suggested three possible causes for the
results: (1) incomplete extraction from unheated tissues, (2) variations in sampling, (3) inhibition by heat of the ascorbic -acid oxidase in the foods examined. The possible -occurrence of non-specific dye-reducing substances in vegetable tissues wasconsidered of little or no practical importance, although it was admitted that germinated seedlings, malt extract, yeast and fermented juices might repay further study. During the last three years we have been accumulating evidence to show that the apparent vitamin C content of foods can become considerably higher than the true vitamin C value under manufacturing and storage conditions which mayoccur in practice. Preliminary reference to these findings was made by Wokes, Johnson, Duncan, Organ & Jacoby [1942] and by Wokes, Organ, Duncan & Jacoby [1943a]. The provisional term 'apparent vitamin C' was proposed to describe substances occurring in natural and processed foods which, although not possessing antiscorbutic activity, simulate vitamin C very closely in their chemical and...