Using acoustic wave sensors to follow milk coagulation and to separate the cheeses according to the milk origin

Abstract

Optimum coagulation temperature and cutting time are usually empirically defined. The use of inexpensive acoustic wave sensors to monitor milk coagulation allows monitoring the process in real time, since its early stages. Besides, data are collected with minimum disturbance, which is an advantage over other methodologies, namely rheology. Coagulation of milk was followed by measuring both the frequency and equivalent circuit resistance of a piezoelectric quartz crystal. Three types of milk, ewe, goat and cow, were coagulated using different rennets at three different temperatures. Maximum observed coagulation rate, either with plant or animal rennet, increased with temperature both for ewe and goat milk. Maximum coagulation rate was higher with plant rennet than with animal rennet at 25 o C and 32 o C, while the opposite was found at 50 o C. The time needed to attain maximum coagulation rate was always smaller with ewe´s milk than with goat's milk, and maximum coagulation rate was higher with the former. Cow's milk was much more difficult to coagulate and needed twice the rennet quantity used for ewe and goat milk. Cheese obtained with the mentioned types of milk and different rennets shows different flavours, usually perceived by experts and connoisseurs, and that an electronic nose built in our laboratory was also able to distinguish. One sensor was enough to separate cheeses made from cow, ewe and goat milk. Besides, the addition of a second sensor allowed to separate the cheeses by rennet among the ones produced with the same milk.

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

“…This setup allowed for the monitoring of the pH-dependent formation of casein clusters and milk gel networks. Furthermore, it allowed for the evaluation of the impact of temperature and rennet type on the gelation of the milk [ 68 , 69 ].…”

Low and High-Intensity Ultrasound in Dairy Products: Applications and Effects on Physicochemical and Microbiological Quality

“…Of all the fermented dairy products, yogurt is the most representative of them, and viscosity is one of the attributes that most influences its quality and sensory acceptance [ 26 ]. Rheological parameter (storage (G′) and elasticity (G″) modulus) evaluations are conducted through viscometers and rheometers, which are considered destructive techniques [ 73 , 74 , 75 ]. In this sense, Izbaim et al [ 73 ] characterized the yogurt fermentation process by means of ultrasound (5 MHz), relating the ultrasonic velocity with the modulus G′ of the medium.…”

“…During their formation, gels present a very short deformation region in which their viscoelastic parameters remain constant. For this reason, the monitoring of their formation, with rheological techniques, must be carried out at very small strains, since external forces break their structures [ 75 ]. In this sense, AT-cut quartz crystals have been used as sensors at very low strains in the analysis of biomolecular interactions in liquid solutions.…”

Control and Monitoring of Milk Renneting Using FT-NIR Spectroscopy as a Process Analytical Technology Tool

“…For the dairy industry, in-line mechanical and/or optical devices have been proposed instead of the gold standard lactodynamograph based on the oscillation recording of a small stainless-steel pendulum immersed in milk [2]. For instance, acoustic wave sensors [4], small angle neutron scattering techniques [5], and ultrasonic analyses [6,7] have been evaluated. Spectroscopic sensors are among the most promising process analysers in food industry [8] and different PAT solutions have been proposed for their implementation in cheese manufacturing [9].…”