SummaryA relatively simple method is described for the manufacture of Cheddar cheese under controlled bacteriological conditions. This method is shown to give the required degree of asepsis and to permit the manufacture of cheeses of uniform and normal composition.The composition, bacteriology and flavour of 28 ‘aseptic’ cheeses and of 18 ‘nonaseptic’ control cheeses made by this method are discussed. Thirty-nine of these cheeses were made using singly 3 strains of Streptococcus cremoris and 2 strains of Str. lactis as starter and 7 were made using gluconic acid lactone in place of starter. The effect of inoculating the milk with a strain (25·2) of ‘Lactobacillus plantarumcasei’ and a strain (L1) of micrococcus was also investigated.
1. The levels of vitamin A alcohol and ester, carotene and xanthophyll in the blood plasma of six cows, grazed out-of-doors on pasture under typical New Zealand conditions, have been followed throughout one lactation. The same constituents have also been followed in the milk fats of these animals and in commercial factory butters over the same season.2. The seasonal trend in the vitamin A and carotenoid content of New Zealand milk fat is a reflexion of the changing level of these substances in the blood plasma.3. The decreased level of carotene, xanthophyll and vitamin A ester in the blood plasma over the summer months is consistent with a decreased absorption or utilization of carotenoids over this period.4. Throughout the year the vitamin A in the milk fat is predominantly in the ester form with no increase in vitamin A alcohol indicative of any increased utilization of hepatic vitamin A reserves.The author is indebted to the Department of Scientific and Industrial Research for a grant towards this investigation; to Mr M. R. Patchell and the farm staff of The Dairy Research Institute (N.Z.) for assistance in the collection of milk and blood samples; to Dr F. H. McDowall, Mr A. K. R. McDowell and the staff of the Chemistry Laboratory, The Dairy Research Institute (N.Z.), for the preparation of the fat samples and for the supply of factory butters. The assistance of Miss Fay Frecklington and Miss Jane Monroe with part of the experimental work is also acknowledged.
In a previous communication (Kon, McGillivray & Thompson, 1955) we reported some of our findings on the metabolism of vitamin A and carotene administered intravenously to rats and calves partially deficient in vitamin A, and to rabbits with normal vitamin A reserves. These findings, in agreement with those of Bieri & Pollard (1954) and Bieri (1955), showed that carotene, when administered intravenously as an aqueous dispersion, could be converted into vitamin A by rats and rabbits at a site other than the intestine. The vitamin first appeared in the blood as the alcohol, whereas after oral administration the initial increase is mainly as ester (Thompson, Ganguly & Kon, 1949). With calves, however, no evidence of conversion of the intravenously administered carotene was found, which indicates a possible species difference (cf. Church, MacVicar, Bieri, Baker & Pope, 1954). One problem encountered in this work was the high toxicity for calves of the injected Tween dispersions and hence the relatively lower doses of carotene that could be used. It seemed important, therefore, to investigate further the conversion in rats given similar carotene levels. Studies were also made of the conversion in rats not deficient in vitamin A. In vitamin A-deficient rats the metabolism of other carotenoid pigments similarly administered was studied, together with the effects of hypo-and hyperthyroidism and of complete hepatectomy on the conversion of carotene. EXPERIMENTALThe methods and materials used were essentially as described in the earlier paper (Kon et al. 1955) with the additions or modifications listed below. Preparation of carotenoid pigmentsCarotene. Unless otherwise stated, crystalline carotene (L. Light and Co. Ltd) containing about 88% p-carotene was used. For comparing the activity of a-and /%carotene this material was separated by chromatography on magnesium oxide into c( and / 3 fractions.Lycopene. Lycopene was extracted from tomatoes by means of acetone in the cold and purified by chromatography on alumina.
In 1947, Barnicoat(i) reported results of an investigation carried out during the 1935-6 season into the vitamin A and carotene content of New Zealand butterfat. These results explored, as he pointed out, a somewhat novel field in that they related to the butterfat from animals fed outdoors on pasture throughout the year, the complicating effects due to stall feeding being eliminated. Under these conditions a uniformly" high vitamin A potency might have been expected, but Barnicoat found marked seasonal fluctuations in both carotene and vitamin A, the variations with season being, however, in the opposite direction to those recorded in the literature for European and American butters (e.g. (3)). In the case of butters from two representative New Zealand dairying districts (Waikato and Manawatu) maximum levels of both carotene and vitamin A occurred in the late winter and spring (July-October) giving a total vitamin A potency of 42-53 i.u./g. fat. These values decreased through the late spring and summer reaching a minimum level of 33-37 i.u./g. fat in late summer (February) and then rising again through the autumn. The changes in potency were shown to be seasonal rather than lactational. Results, to be published shortly by McDowall & McDowell (4), of an extensive investigation covering other New Zealand dairying districts and extending over several seasons, confirm the trends observed by Barnicoat, while similar fluctuations have been reported by Farrer, Balding, Warren & Miller (5) for a number of districts in Australia where dairying conditions are comparable to those existing in New Zealand. Morgan & Pritchard(2) and Baumann & SteenbockThe clearly denned seasonal fluctuations apparent in European and American butterfat have been shown to depend largely on variations in the carotene content of the feed available to the cows (e.g. (6,7)) and Barnicoat suggested that the decrease in vitamin A potency of New Zealand butterfat over the summer period might result from a lowering of the carotene content of the grass associated with the hardening up of the pasture following the spring flush.Little information was available regarding the carotene content of typical New Zealand pastures, but a limited number of assays carried out by the writer on mixed pastures mainly of ryegrass and clover during 1949-50, and a more extensive investigation by Cawley (8), indicated an average value of about 550 fig./g. dry matter over the autumn, winter and spring periods, with a variation of about + 100/xg./g. The values decreased during the summer to an average in midsummer of about 200/xg./g. with individual determinations ranging from 152 to 510 /Ltg./g. In all the above cases analyses were carried out on samples of pasture as near as possible representative of what would be consumed
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