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The investigation of the occurrence of soft curd in cheese manufacture in South Australia (Linklater, 1956) has called for the measurement of seasonal variations in curd tension. In the course of this work an improved instrument for the measurement of curd tension has been developed.
Pilot scale trials have shown that it is practicable to vacuum press large quantities of curd in a single hoop. By extrusion of the cheese from the large hoop into a cutter unit it is possible to divide the cheese into smaller blocks of any pre-determined weight, with high accuracy. A commercial-sized prototype capable of holding all the curd from a 1,000 gallon vat is being developed.
It is suggested that the use of large hoops in place of a multiplicity of conventional rindless hoops will enable appreciable cost and labour savings to be made in addition to more accurate sizing of rindless cheese.
A new process has been developed which effectively pasteurises and deodorises cream at processing, capital and installation costs considerably lower than those of the existing steam injection, vacuum deodorising methods currently used in Australian dairy factories.
For removal of those taints which are eliminated during normal factory processing the experimental pilot plant was operated at 280°F, at cream throughputs which varied from 700 gal. per hour to 2,500 gal. per hour. It would appear that commercial plants with much greater throughput are feasible.
For release of weed taints not removed by normal processing (e.g. Coronopus) the pasteurisation temperature was raised to 340°F. Higher temperatures have also been attained with the pilot plant.
The pilot plant described in Part I effectively UHT pasteurised (280°F) and deodorised choice, first and second grade creams at 11,000 lb per hour using 0.9 lb steam per 10 lb cream treated, as compared with 3.5 to 5.7 lb steam per 10 lb cream for the steam injection pasteurisation/vacuum deodorising methods currently used in Australian butter factories.
No dilution occurs at pre-heating temperatures in excess of 200°F as shown by the identical fat contents (Babcock) of the cream entering and leaving the process; but at lower pre-heating temperatures dilution does occur (less than 2% from 190-199°F; less than 4% from 180-189°F; less than 6% from 170-179°F).
Heat saved by regeneration due to the high temperature (212°F) of the processed cream returned to the plate heat exchanger, is greater than the heat in the steam flowing to the machine, that is, more heat is applied by regeneration than by steam injection.
As at least 50% of the heat in the steam flowing to the pilot plant was recovered for use elsewhere in the factory (e.g. boiler feed or hot water system), the net steam cost was not more than one eighth of that for current plants.
Authors: K. Kumetat, R. Beeby and Audrey K. Morris
Precise details of the processes used in the manufacture of the recently developed "instant", or readily dispersible, milk powders are rather difficult to ascertain because of the highly competitive nature of the milk powder market. This paper discusses some of these processes.
Authors: I.B. Powell, G.K.Y. Limsowtin and D.M. Gray
Restriction enzymes provide an important mechanism of bacterial resistance to phage infection. Restriction systems exist in many cheese starter strains of Lactococcus lactis. There is evidence that some phages that infect L. lactis have evolved to minimise the effectiveness of these restriction systems, but it is not generally known whether this is achieved by chemical modification of phage DNA to mask restriction enzyme cleavage sites or whether the DNAs of these phages simply have few (or no) sites. Evidence from limited DNA cloning (Powell and Davidson 1986) and sequencing (e.g. Lubbers et al. 1995; Chandry et al. 1997) indicates that the DNAs of the phages studied have remarkably few sites, presumably an evolutionary response to restriction systems in host strains.
There is mounting evidence that the structure and function of mozzarella cheese are influence by physico-chemical changes that occur during the first weeks after manufacture. Analyses of the expressible serum obtained from mozzarella cheese by high-speed centrifuguation show that intact caseins (αs1-, αs2-, β-, para- κ-) and casein-associated minerals (Ca, Mg, Zn) become more soluable during ageing, with an accompanying increase in the water-holding capacity of the cheese. This behaviour is salt-dependent and may be indicative of salt-induced solvation and swelling of the casein fibres that form the structural matrix of the cheese. The distribution of casein-associatied minerals between the protein matrix and the serum phase is influenced by cheese pH, with lower pH favouring greater solubility. Soluble calcium is of particular interest, because it strongly inhibits salt-induced solvation of casein and does not contribute to cheese structure.
Authors: P.S. Kindstedt, A. Zielinski, M. Almena-Aliste and C. Ge
A post-manufacture method to increase or decrease the pH of mozzarella cheese by exposing shredded cheese to volatile ammonia or acetic acid, respectively, was developed and used to evaluate the effect of cheese pH on melting characteristics and calcium distribution. This approach enabled the cheese pH to be varied over a wide range without causing large collateral and confounding changes in cheese composition. Low-moisture part-skim mozzarella cheeses melted to a progressively more fibrous and elastic consistency, and the apparent viscosity increased in a linear manner with increasing pH in the range of ca. 5.0 to 7.0. In contrast, cheeses lost the ability to flow and melt at pH values less than 5.0, causing a large increase in the apparent viscosity with decreasing pH in the range of 5.0 to 4.7. Water-soluble calcium increased with decreasing cheese pH, especially in the pH range of 5.0 to 4.7. The results demonstrate that the pH of mozzarella cheese is a strong determinant of structure and functional characteristics, independent of other important parameters. A better understanding of the effect of pH on mozzarella cheese at different stages of ageing could lead to new strategies to tailor and control functional characteristics.
Cluster analysis has been used to classify cheddar cheese produced in eight different countries according to the country of origin. The classification was made on the basis of a range of selected semi-volatile compounds. A hierarchical cluster analysis of cheese semi-volatile composition showed the existence of two distinct groups. One group consisted predominantly of Australian cheeses, while the other group mostly contained cheeses produced elsewhere, suggesting that the semi-volatile composition of a cheese can be used to determine its country of origin. 'Crisp' and 'fuzzy' clustering techniques also confirmed the presence of the two distinct groups.
A method is described for the specific determination of lactose in cheese using a coupled enzyme system. The rate of utilization of lactose in a ripening Cheddar cheese was followed and the initial lactose content of a number of Cheddar cheeses is reported. The method was also applied to the determination of lactose in milk.
A rapid high-temperature method was developed for determining moisture on 1 g samples of cheese by treating before drying with 0.5 ml 6% tri-sodium citrate solution. Heating at 190°C was conducted on a thermostatically-controlled hot-plate for 5 to 6 minutes, using throw-away rectangular aluminium foil dishes and stirrers. Agreement with the standard method on 28 to 30 samples of varying age was highly significant.
The present study was undertaken to evaluate a simple test for the rapid detection of coliforms in flavoured milk, ice-cream and skim milk powder. In the test, a concentrate of the product obtained by centrifugation is mised with an equal quantity of double-strength broth before incubation at 37°C. One hundred and one samples were examined for Most Probably Number (MPN) of coliforms by resumptive coliform test at 37°C and checked for the earliest time required to detect the coliforms by the rapid test. Coliform levels at 1 to 10/mL could be detected in 8.33-10.37 h while higher counts, 11 to 100/mL and 101 to 1000/mL, could be detected in 7.67 h and 5.83 h respectively. MacConkey, BGLB and VRB broths gave comparable results. The MPN of coliforms and the rapid detection time were significantly and highly negatively correlated. On inoculation with pure cultures of coliforms and non-coliforms, the rapid test proved to be specific for coliforms and did not exhibit either false-positive or false-negative reactions. Since the rapid test does not require any additional equipment than what is normally present in the quality control laboratory, the test may be conveniently adopted in dairy plants for processed milk and milk products as well as for the line-testing programme. This rapid test is much cheaper than the conventional presumptive coliform test.