The influence of mastitis and stage of lactation on the yield and quality of cheddar cheese

Abstract

Proc. Amt. Sm. Arlim. Prod. 1993 Vol. 20 THE INFLUENCE OF MASTITIS AND STAGE OF LACTATION ON THE YIELD AND QUALITY OF CHEDDAR CHEESE M.J. AULDISTA, B.J. SUTHERLANDB. J.J. MAYESB, G.H. McDOWELLA and G.L. ROGERS ASchool of Agriculture, La Trobe University. Bundoora, Vic. 3083 BCSIRO Division of Food Processing. Highett, Vic. 3190 CBonlac Foods Ltd., Longwarry, Vic. 3816 C Manufacturers of dairy products using milk from the seasonally-calving herds of Victoria have reported difficulty preparing products of high quality from late season milk (G.L. Rogers, unpublished data). This phenomenon probably is caused by changes in raw milk composition occurring as lactation progesses, in combination with changes associated with the high bulk milk cell counts (BMCC) of late lactation milk (Ng-Kwai-Hang et al. 1982). The present study was conducted to investigate the respective effects of mastitis, as determined by BMCC, and stage of lactation on the yield and quality of cheddar cheese. Cheese was manufactured in a pilot-scale factory from sub-samples of bulk milk (approximately 200 L) collected from commercial dairy farms in northern Victoria. Four types of milk were used: low BMCC early lactation (LE), low BMCC late lactation (LL), high BMCC early lactation (HE) and high BMCC late lactation (HL). All milk contained low numbers of bacteria, and was pasteurised and standardised to similar fat:protein ratios prior to manufacture. The trial was repeated 3 times within S days. After a period of equilibration, cheeses were analysed for yield and quality (Table 1). Table 1. Mean bulk milk cell counts (BMCC; x 1000 cells/ml), cheese yields (kg/l00 kg milk), coagulation times (minutes), concentrations of cheese components (%). recoveries from milk of protein and fat (%) and grade points for cheeses manufactured from low BMCC milk from early (LE) and late lactation (LL), and high BMCC milk from early (HE) and late lactation (HL) The differences in cheese yields must be viewed with caution due to slight differences in the chemical composition of the milks. Nevertheless the deleterious effects of mastitis on product yield and quality were clearly observed in milk from late lactation. Cheese made from LL milk was significantly superior to that made from I-IL milk for nearly all yield and quality parameters measured. Manufacturing cheese from LL milk was also detrimental to cheese vield and quality, as evidenced by the lower recoverv of fat and poor flavour score of this cheese compared to that manufactured from LE milk. It is concluded that the effect of stage of lactation is exaggerated by an elevated BMCC. Many of the problems encountered u processin, late lactation milk may therefore be overcome by containing mastitis at this time. NG-KWAI-HANG. K.F., HAYES, J.F., MOXLEY, J.E. and MONARDES, H.G. (1982). J. Dairy Sci. 65: 1993-S. 371