SummaryIn experimental small-scale manufacture of Cheddar cheese a study was made of the movement of lactose, lactic acid, calcium and phosphorus between curd and whey, and of the effect of high acidity developed in the curd before whey separation, on the pH and physical properties of the cheese. It was found that while the curd particles remain in contact with the whey, the lactose fermented in the curd is replaced by lactose diffusing from the whey. Lactic acid produced in the curd diffuses into the whey rather slowly.When a high lactic acid level is attained rapidly the curd does not cheddar well, the pH of the cheese is low, the flavour is sour and bitter, the body is crumbly and the cheese is bleached. When a high lactic acid level is reached slowly, the curd also does not cheddar properly but the pH of the cheese may be within normal limits up to 3 weeks, at which age its body is coherent and its colour is normal. However, on maturing, the cheese becomes acid, the body crumbly and liquid separation occurs even at 2 months of age. This points to a risk in grading cheese at an early age.It is suggested that the abnormal behaviour in cheddaring of ‘high-acid’ curds is connected with an excessive loss of calcium. When high acidity is developed over an extended time in the whey, the curd retains more lactose but loses more phosphorus so that its buffering capacity is reduced. Cheese made from such curd becomes highly acid at maturity and this leads to the development of a bitter flavour.It is, therefore, concluded that both the rate of development of acidity, and the time the curd is in the whey, are critical factors in controlling the quality of Cheddar cheese.
Practical aspects of the weed taint problem in Ansti-alia have been dealt with in an earlier paper (Conochie, 1950). Various species of the genus Lepidium (chiefly X. hi/ssopifolium and L. honariense) at times provide the greater part of tbe berbafjo available to dairy stock in some districts of southern Queensland. The milk produced bas a faecal odour and a persistent nauseating fiavonr due to tbe presence of abnormal amounts of indole and skatole. Ilussong and Quam (1943) found that butter from the milk of cows feeding on Lepidium virginkum bad a higb indole content, but tbey were not able to produce tbe effect witb animals feeding under controlled conditions, nor did tbey investigate the pbysiological processes involved. Combs (1949) reported tbat the effect bad been produced under controlled conditions in 1935-37 witb botb L. virginicum and a species of tbe genus Ambrosia.There is a complete absence in tbe literature of basic information on the production, absorption and excretion of indole and skatole in the normal ruminant. In addition notbiiig is known of the effect of Lepidinm in tbe diet on these processes. A study of tbe subject was undertaken in the hope that it mifiht suggest some practical steps, such as the control of feeding practice, which would reduce the incidence of Lepidium taint under field conditions. Lepidium hyssopifolium, the most widespread species of the genus in Australia, was used in all tests.
METHODS.Millc indole and sTcatnle. The methml uaed for tlie estimation of milk indole was based on that of Clarke fi al. (1937). The p-dimethylaminolienzaldeliytle complex was iiieasuiTil in an Evelyn photoelectric coloriraeter with filter No. 540. Since skatole also forms a coloured comnlL'x with appreciable ahsorption at 540 rofi, results ohtained by the Clarke method will reflect both the iodole and skatole contents. As shown by the results quoted later, both substances are present in /.cpicHwHi-taintrd milk. However, results throughout this report are expressed as indole, calculated from the totai absorption.Separate values for indole and skatole were obtained in a few cases by measuring the absorption of the p-dimethylaminobenzaldehyde complex at 540 m/t and 570 m/i in a Beckman spectrophotometer. The absorption curves for the puro complexes of indole and skatole with pdimethylaminobenzaldehyde are shown in Fig. 1.
SummaryMicroscopical and chemical studies of seaminess in Cheddar cheese revealed that the white lines or seams characteristic of the defect are sections through layers of crystals lying between the milled curd particles. The crystals were identified from their X-ray diffraction pattern and by their refractive index as calcium orthophosphate dihydrate, CaHPO4. 2H2O. On each side of the adjoining curd surfaces in affected cheese there is a zone about 20 μm thick of strongly contracted protein which is almost devoid of crystals.Adding sodium chloride to cheddared curd increased the quantities of calcium, phosphorus and water released. The increases were proportional to the amount of salt applied within the range 0–2·5 g NaCl per 100 g curd.The solubility of calcium orthophosphate was found to rise from about 0·0025 M in water to a maximum of 0·008M in 2 M sodium chloride solution.It is postulated that calcium and phosphate ions released from the curd into the seam crystallize in the form of CaHPO4. 2H2O as the solubility of the compound is lowered by diffusion of salt from the surfaces into the curd particles.
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