MOTTLED COLOUR IN CHEESE.

New Zealand Journal of Agriculture, Volume 42, Issue 4, 20 April 1931, Page 244

MOTTLED COLOUR IN CHEESE.

INVESTIGATIONS IN SOUTH AUCKLAND DISTRICT.

W. H. Udy,

Chief Chemist, Hamilton Dairy Research Laboratory.

A considerable amount of coloured cheese made in- New Zealand suffers'in . grade due to an unevenness of colour. ! This is shown 'in the form of a seamy or a mottled appearance on drawing a plug. ‘ The discoloration varies in intensity and hue, being sometimes almost white.. . Sometimes the. discoloration apparently follows the surfaces of the curd-particles. ’ ■ .7

Investigation of this defect has been made from time to time in the New Zealand Co-operative Dairy Company’s Research Laboratory, at Hamilton, and the main cause of the defect is looked upon as being due to development in the cheese of organisms which cause a reduction of the cheese colour. The defect occurs more commonly in the hot weather, and generally develops on holding the cheese in storage. A large number of organisms have been studied as to their effect on cheese-colour, and a gram negative bacillus has been isolated from discoloured cheese which readily bleaches cheese-colour in annatto agar media.

The need for good-quality milk and sanitary conditions of cheesemanufacture are suggested as the most important means of overcoming this defect.

Effect of Exposure to Sunlight.

As the. result of observations .by a factory-manager recently investigations have been made as to the effect of direct sunlight on the milk and curd in the vat,, and it has been found that this is an important cause of mottled colour. As little as five minutes’ direct sunshine . playing on the. surface of milk with annatto added, in a vat while setting, gave the surface a distinctly lighter colour than the remaining curd. Thirty minutes’ direct sunshine' gave an almost white surface. This curd, , after cutting and mixing into the remainder of the curd, gave, a definite mottleness. ;

Direct sunlight playing on the curd in-the whey after cutting also, proved effective. Sunlight shining down through several inches of whey on to curd at the bottom of a tinned container for half an hour gave distinct discoloration. Moist whey-soaked curd exposed to direct sunlight showed distinct discoloration' in five minutes, . and was quite bleached in thirty minutes. ’ This bleaching penetrated to a considerable depth into the curd particle. -

Direct sunlight playing on the milk in the vat during setting, or on the curd in. the whey or later, is therefore proved to -be a cause of mottleness in colour.

A survey was made of the amount of exposure of milk and curd to sunlight and the incidence of mottled colour at a number of different cheese-factories during the* 1930-31 - summer month's. It was found that exposure in the vats to . direct sunlight was common. In one factory with six vats two only of the vats were exposed to an appreciable amount of sunlight, and of a large number of vats graded down for mottled colour practically all were from these two vats.

• In discussing the action of sunlight in discolorizing cheese-curd it has to be remembered that light is made up of different rays, only some of which are chemically effective. A large proportion of these effective rays will pass through clear glass, but coloured or dust-covered glass would greatly diminish this proportion. Diffused sunlight ■ willhave very little action. The trouble due 'to exposure, to .sunlight should therefore' be readily overcome' by painting the glass so .that only diffused light is used.

Food Values and I' odine-metabolism Research. — The Chairman’s address at the last meeting, of the Research. Council, ' in Wellington, included the following reference to this subject : “ Good progress has been made in a. number of investigations into (1) the nutritive value of cheese protein and its vitamin efficiency, (2) the Vitamin C content of milk, and (3) iodine metabolism, by various workers conducting their researches under- the direction of Dr. J. Malcolm at the Otago University.Such work is fundamental to-our dairy -industry and has immediate practical , application. To indicate some of the findings will exemplify this point. It has been found that pasteurization. does not adversely affect the Vitamin D content of New Zealand cheese, and that summer cheese is an excellent source of this vitamin; As contrasted with butter, where apparently a considerable loss occurs during milk - separation in winter months, the* seasonal fluctuation in Vitamin D content of cheese is much less. It has also been demonstrated that a definite relationship exists - ; between calcium and ■■ iodine in so far as these participate in food metabolism within the bodies of animals consuming any particular diet.” ... .. - . . . .