Investigating the Acid- and Enzyme-Induced Coagulation of Raw Milk Using Dielectric and Rheological Measurements

Abstract

In this study, the enzyme-induced and acid coagulation of raw milk samples were investigated, and these two processes were monitored by determining the changes in dielectric and rheological behavior to see if any correlations could be found between these two properties. For the enzyme-induced experiments, 250 cm3 of raw milk sample and industrial chymosin were used, and during the acid coagulation, industrial thermophile yogurt culture was added to the same amount of milk. The apparent viscosity was monitored with a vibro viscometer, and the dielectric constant was measured in a frequency range of 200–2400 MHz with an open-ended dielectric assessment kit (DAK) connected to a vector network analyzer (VNA). Our experimental findings revealed that during both enzyme-induced and acid coagulation, two distinct phases could be found in terms of dielectric and rheological properties, and regardless of the molecular mechanisms behind the aggregation of casein micelles, a strong correlation (with R2-values ranging between 0.967 and 0.992) can be found between the extent of the apparent viscosity and dielectric constant, suggesting that dielectric measurements might be adequately used in these dairy processing technologies. These results verified the applicability of the non-destructive dielectric measurements in dairy technologies.

Monitoring the process of yogurt spoilage by dielectric measurements and spread plate method

“…The results of this research led to the conclusion that the dielectric constant at 1.5 kHz was correlated with the state of spoilage of different frozen fish, while the conductivity of the test materials varied independently of spoilage [9]. In one of our earlier studies we have shown that dielectric analysis can also be used during the coagulation of raw milk: strong correlation was found between the apparent viscosity and the dielectric constant of the milk samples during the acid-and enzyme-induced coagulation of the samples [10]. The results of these earlier studies have also shown that, although the suitability of dielectric measurement as an indirect but rapid method for indicating changes in the deterioration phenomena of foodstuffs or food raw materials (e.g.…”