15B-15 |
Milk gel formation by combined acidification and renneting: New insights into coagulation dynamics, gelation phenomena and gel properties |
C. C. TRANCHANT1, D. G. Dalgleish2, and A. R. Hill2. (1) School of Food Science, Nutrition & Family Studies, Univ. of Moncton, Moncton, NB E1A 3E9, Canada, (2) Dept. of Food Science, Univ. of Guelph, Guelph, ON N1G 2W1, Canada Despite its important bearing on the technology of a number of cheeses, the subject of milk gel formation by combined continuous acidification and renneting has been noticeably under-researched. Most investigations of milk coagulation have dealt with acid coagulation and rennet coagulation separately. A more complete and unified understanding of combined acid-rennet coagulation would be particularly valuable to improve the control of industrial processes and product quality. A comprehensive study was undertaken to determine the effects of varying the proportion of acidifying starter versus rennet on milk gel formation and viscoelastic properties. Four starter levels and four rennet levels were used. Reconstituted skim milk (standard and pre-treated RSM; initial pH 6.4) was set at temperatures ranging from 25-40°C. Gel development was monitored using small deformation dynamic rheometry (Nametre and Carri-Med Rheometers), with complementary measurements of pH and k-casein hydrolysis over time. Systematic qualitative and quantitative analyses of gelation curves showed that rennet concentration had a predominant influence on the evolution of gel viscoelastic properties over time. This influence plateaued above a certain concentration of rennet. Rennet concentration had a predominant influence on key coagulation parameters, including coagulation time; values of consistency (and elastic modulus, G'), pH and time at different stages of gel development; maximum rate of consistency (and G') development; and loss tangent (G''/G'). Innovative use of time-derivative data revealed the existence of three distinct patterns of coagulation, which were related to different degrees of renneting and distinct mechanisms of coagulation. These patterns were not recognized in the past. The findings have a direct bearing on process control, including optimization of yield and quality of cheeses such as Cheddar and cottage cheese. Insights into the relationships among coagulation conditions (sequence of acidification vs. renneting), molecular/supra-molecular properties, and macroscopic properties of acid-rennet casein gels may also foster product innovation and diversification.
Session 15B, Dairy Foods: Chemistry, microbiology and sensory analysis of various cheeses
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