ifoam'96 Book of Abstracts 11th IFOAM Scientific Conference 11-15 August 1996, Copenhagen, Denmark

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Posters

Factors Affecting the Renneting Properties of Milk. P2; 59

1Institute of Anatomy, Physiology and Hygiene of Domestic Animals, GER-53115 Bonn; 2Institute of Organic Agriculture, GER-53115 Bonn; 3Department of Organic Livestock Farming, GER-49090 Osnabrueck; 4Institute of Grassland and Environmental Research, UK-Aberystwyth SY23 4LL.

For successful cheese processing under conditions of organic agriculture excellent renneting properties of the raw milk used is an important precondition. The objective of this experiment was to investigate how the renneting properties of the milk are influenced by the metabolic status of the cow, the udder health and the genetic protein polymorphism.
Milk and blood samples from 185 dairy cows on three farms in Germany (two organic /one in conversion) were collected within the first seven weeks of lactation. To assess the metabolic status of the cow various screening parameters in the blood (urea, glucose, protein, aspartate-aminotransferase, cholesterol) and in the milk (urea and acetone) were determined. The udder health was assessed by measuring the pH and the lactate-dehydrogenase activity of the milk. Furthermore the true and casein protein content of the samples and the genetic polymorphism of thealpha-s1-, the beta- and kappa-casein, and of the beta-lactoglobulin were analysed.
Renneting properties as the rennet clotting time (RCT) and the curd firmness ten minutes after RCT (A10) were measured as changes in milk viscosity. For this purpose a new computer based apparatus based on cantilever beam technic was constructed. For milk samples with a RCT lower than 20 minutes multiple regression models were calculated. For the RCT within this grade 45.5% of the variations could be explained by the pH of the milk. A10 was mostly affected by the casein content (39%) and the RCT (33%) of the milk. A10 and casein content were significantly (ANOVA/ p 0.05) higher in samples with a cholesterol level below 2.6 mmol/l, milk urea values above 5.0 mmol/l or acetone concentrations below 0.08 mmol/l. Significant positive effects on A10 and RCT were determined in samples with kappa-casein BB or beta-casein A1B muster.
Methods for improvement of milk quality in organic agriculture were discussed.
The project was funded by the European Union (Contract: AIR 3-CT 92 0776).