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Authors: M.H. Nguyen, M.M.A.Khan, K. Kailasapathy and J.A. Hourigan
Cottage cheese whey, concentrated by nanofiltration, was evaluated for use in ice-cream manufacture. Ice-cream made from formulations in which 25% and 50% milk solids-not-fat were derived from the whey concentrate showed similar physico-chemical properties and acceptabilities to a control with no added whey concentrate. Trial ice-creams were softer, although their melting resistances were higher than that of the control. Lactase enzyme, added to control lactose crystallisation, did not result in improved sensory attributes and overall acceptabilities. It was necessary to adjust the pH of the whey concentrate to 6.5 prior to use in ice-cream formulation.
Variants of Streptococcus lactis C2 which had spontaneously lost the ability to ferment lactose (lac-) were isolated from a litmus milk culture. These lac- isolates were also prt- having lost their surface-bound proteinase activity. Examination of one of the lac- prt- isolates (lac- 1) for stability of the lac- characteristics showed that reversion to the lac+ phenotype occurred after extensive sub-culturing of the mutant in broth medium containing lactose. Growth rate experiments on the C2 lac-1 mutant in skim milk showed that the mutant was capable of attaining relatively high cell populations in milk without producing acid from lactose. The optimum growth conditions for batch culture of the C2 lac-1 mutant isolate were determined and this culture was used in the production of a frozen concentrate. This lac- mutant concentrate retained complete viability on thawing and provided a means by which high levels of C2 lac- starter could be incorporated into cheese milk without affecting acid production during cheese manufacture.
Streptococcus lactis C2 lac- prt- mutant concentrates were successfully used to increase the starter population in Cheddar cheese without producing an atypical product. High total starter populations caused an increase in the levels of free amino acids and up to 12 weeks advancement in flavour development in mutant-containing cheeses which had been stored at 8°C for 6 months. Experimental cheeses which contained mutant starter did not develop bitterness and had superior flavour scores to their corresponding control cheeses at all stages of maturation. Exposure of cheeses containing lac- prt- mutant to an initial storage at 20°C for one month increased proteolysis in these cheeses. This treatment had no detrimental effect on the flavour scores of these cheeses and varying degrees of advancement in flavour development were obtained.
Data from 56 samples of sweetened condensed milk (9 per cent fat, 31 per cent milk solids) made over a period of one year showed the following average relationship between total solids and refractive index measured at 25°C:
T.S - 376 x R.I - 480.1.
As a means of determining the total solids content refractive index measurement was not more reliable than determination of specific gravity by pycnometer.
Authors: J.A. Stewart, L.L. Muller and A.T. Griffin
Hydrochloric (HC1) acid casein whey was treated by ultrafiltration to increase the ratios of protein to lactose and minerals. The resulting liquid whey protein concentrate (WPC) or a spray dried WPC from Cheddar cheese whey was incorporated into calf milk replacer(s) (CMR) to give a final composition of about 24% protein, 18% fat (as tallow), 7-11% ash and 47-51% lactose. The proportion of the protein in the CMR provided by WPC was varied from 35% to 100%, the remainder coming from skim milk or buttermilk.
At the Ellinbank Dairy Research Station, Friesian bull calves from about 4-5 days old were fed the experimental CMR and their performance compared with matched calves fed CMR based solely on skim milk which was either of similar gross composition or contained about 35% protein, 18% fat (as tallow), 7% ash and 40% lactose.
Within each of four experiments there were no significant differences (P>0.05) amongst CMR in faecal index or liveweight gain to weaning. There was no evidence of anaphylactic shock.
On 16 dairy farms, 220 heifer calves were fed either a control ration of the farmer's choice or an experimental CMR in which 50% of the non-fat-solids and 35% of the protein came from ultrafiltered HC1 casein whey. The experimental CMR compared favourably.
It is concluded that WPC of appropriate protein content may be substituted for skim milk or buttermilk in a high fat (18%) CMR.
Dairy foods have long been promoted using health messages. People wanting to improve public health have promoted dairy foods, and people promoting dairy foods have used health messages. This paper considers three different types of health messages that are relevant for the promotion of dairy foods - nutrient content messages, low-fat messages and health claims. It also discusses some of the potential opportunities and challenges associated with the promotion of dairy foods in the future, as we learn more about the health effects of the complex mixture of compounds present in milk and as the regulatory framework around food fortification and health claims develops in Australia and New Zealand. The changes in legislation permitting the use of health claims on food labels and in advertisements aimed at consumers will expand the repertoire of messages available to communicate the benefits of dairy foods. However, health claims won't replace nutrient content and low-fat messages. All three types of health messages discussed in the paper are likely to be widely used to promote dairy foods in the future.
This paper investigates two of the most commonly used end product microbial indicator tests, Standard Plate Count and coliforms, that are used by the dairy industry in Australia. The use of these particular tests, as a component of dairy manufacturers’ food safety programs, is discussed. Their use as a tool to benchmark industry performance through an industry-wide Product Testing Program in the state of Victoria is also described, and the benefits derived from the program explored.
It has been shown that mesophilic starter bacteria remain active and are able to metabolize residual lactose or galactose following the thermal stress (43°C) used in the manufacture of Cheddar cheese by the short method. When salt-tolerant strains were used to manufacture short method cheese residual galactose content was reduced ex-press and absent at 1 week.
The variation in bacterial population throughout boxes of both salted and unsalted butters was investigated. Up to 60 samples taken from a box were each analysed for total bacterial count, spoilage organisms count and presumptive coliforms. Marked variation in results for each test was found with samples from any single box of unsalted butter, while for salted butter the total bacterial counts were also quite variable. The results are discussed with reference to quality control and investigational work.
Four Cheddar cheeses containing coliform bacteria were stored for three months at 7-10°C and relative humidity 50-70%. At monthly intervals, 18 random samples were taken from each cheese according to a statistically designed pattern of three nested surfaces, two positions (corner or side) and three depths. Most Probably Number (MPN) presumptive coliforms/g and MPN Escherichia coli presumptive type 1/g were determined for each sample at each sampling period.
Initial coliform and E. coli types 1 levels varied between cheeses, but all decreased significantly with time. In no cheese was E. coli type 1 the sole coliform type found. The numbers of coliforms and E. coli type 1 did not differ significantly between surfaces or between positions sampled. There were, however, significant differences in coliform counts between depth sampled.
Linear regression curves were obtained when the overall MPN coliforms/g and MPN E. coli type 1/g were plotted logarithmically against time. The surface position and depth sampled had no significant effects on the slopes of the regression lines.
The psychrotroph counts obtained for bulk raw milk samples by incubation of similar plates of the appropriate dilution at 5°C and 7°C with counting of each after 7 and then 10 days, were compared. With data expressed as log10, no significant difference was found between population counts obtained at 7°C after 7 days and at 5°C after 10 days. However, both of these counts differed significantly (P < 0.01) from those obtained at 7°C after 10 days and at 5°C after 7 days; likewise this latter pair of counts differed significantly.
Variation in the fatty acid composition of milkfat from seven cows was studied throughout a lactation. The cows were from a commercial pure-bred Jersey herd, maintained on a high plane of nutrition.
The C4:0 acid had a maximum value during the first month of lactation, values decreased during succeeding months, reaching a minimum value at the end of lactation. The C6:0 to C14:0 acids all exhibited similar variation, values increased during the first 4 to 8 weeks of lactation, remained relatively constant until the fifth or sixth month, then decreased again until the end of lactation. There was little variation in the C16:0 acid throughout lactation. The C18:0 and C18:1 acid contents were high in early lactation, they decreased until mid-lactation, increasing again to the end of lactation. Changes in the content of C18:2 and C18:3 acids were variable.
It is considered that the increased content of C18 acids with corresponding decreases in C6:0 to C14:0 acids at the end of lactation may be due to decreased energy intake as a result of feeding concentrates according to the level of milk production. Cows at the same stage of lactation exhibited significant differences in their fatty acid composition. Their individual pattern relative to the herd was repeated at a subsequent lactation and is considered to be controlled by genetic factors.