Gelling properties of milk gels using rennet as a coagulant

Abstract: As the consumption of dairy is a common staple in the Nordic and European diet and culture, better understanding of the dairy industry as a whole, and especially the cheese industry is needed to aim for a more sustainable production. This project aims to offer an extended approach on the rennet coagulation of milk, analysing the gelling properties of skim milk samples at different pH values (5.5-6.7) with various additions of CaCl2 (1.0-10 mmol/L), as well as the impact of the presence of fat and the fat content (2%-3%) of the milk samples. Two trials were performed during this project, the Response Surface method trial, and the Effect of fat on gelation-trial. The Response Surface method trial contained skim milk samples with a varying degree of added CaCl2 at different pH, to investigate how pH and CaCl2, and the interaction of these factors affect the gelling properties of the skim milk. The Effect of fat on gelation-trial contains both skim milk and full fat milk samples, with varying fat content (2%-3%), to establish if the fat content, or the presence of fat had a significant impact on gelling properties of the milk. Methods used in order to measure the gelling properties of the milk samples during these trials include Rheometer to establish G’ at 30 min, Turbiscan to establish the Δ Back Scatter (ΔBS) and Malvern Master sizer to establish particle size. Statistical methods such as Minitab21 and its response surface method was used to not only plan the Response surface method trial, but also to generate contour plots, pairwise parson correlations and 2-Sample T-test. Matlab was also used to generate plots of gelation curves. The results concluded that pH is an important factor regarding gelling properties of rennet milk gels, as it had a significant effect on both gelation time and G’ 30 min. CaCl2 does not have a statistically significant effect on the variables of gelation time, G’ 30 min and ∆BS 30 min. The fat content and the presence of fat had no significant effect on the gelation time, G’ at 2x gelation time and G’ 30 min, while the fat content had a significant effect on the ∆BS 30 min. It was expected that the pH would be significant for gelling properties, but unexpected that CaCl2, fat content and presence of fat did not have a bigger impact on the results obtained. In order to verify the results presented in this report, more research and trials, especially on the impact of fat content, presence of fat and CaCl2 needs to be made.