A PHENOMENOLOGICAL MODEL OF MILK COAGULATION

A model of additional stabilization for the milk colloid system by means of the micelle electric charge arising owing to dissociation of micellar calcium caseinate is offered. The model allows comprehending the unique role of calcium in milk clotting and describing some features of coagulation temperature dependence, as well as explaining the nature of rennet, acid, heat-acid and heat-calcium coagulation within uniform concepts

STUDY OF CALCIUM ROLE IN COLLOIDAL STABILITY OF RECONSTITUTED SKIM MILK UNDER RENNET COAGULATION CONDITIONS

The role of calcium in rennet coagulation of milk is unquestionable in production technology of many cheeses. Therefore, understanding the possible mechanism of calcium influence on the colloidal stability of casein micelles may be the key to control the process of milk coagulation. It is evident that calcium ions are involved in maintenanceof milk coagulation stability, but the molecular mechanism of how these ions influence micellar caseins system is not fully known. Thus, the role of calcium in maintenance of the colloidal stability of milk is quite an urgent problem. Methodologically, the research was based on analysis of coagulation process of reconstituted skim milk, enriched with ions of calcium, magnesium and sodium. Milk whey separated from the clot after coagulation was investigated for sodium, magnesium, calcium and phosphorus. A simple quantitative model, which includes kinetic description of the proteolysis process and the thermodynamics of the dissociation process of the functional groups of micellar caseins, was worked out to analyze experimental results. Kinetic and thermodynamic methods of describing the process of stability loss in micellar system were combined in one model, using the concept of solvent quality which is defined by the second osmotic virial coefficient. The experiments showed that calcium and magnesium ions chemically connect to casein micelles. Using reasonable assessments for thermodynamic and kinetic parameters, we managed to get quite adequate description of the experimental data on the coagulation of reconstituted skimmed milk enriched with calcium and magnesium ions. It was stated that the equilibrium constants for the dissociation of magnesium and calcium caseinates should differ by more than two orders of magnitude. The authors demonstrated principal possibility of using the model to describe the rennet, acid and mixed acid-rennet clotting of milk

Study of implants for intraoperative hyperthermia

At the present time hyperthermia is recognized as one of the most promising methods in the combined treatment of malignant tumors. Nevertheless, for the most of existing methods for heating of tumor tissues it is rather difficult to realize the exact localization of heat exposure. The aim of this study is to compare two types of implants for intraoperative local tumor bed hyperthermia carried out using induction heating in an alternating magnetic field of the sub-MHz range. Composite implants of the first type are created on the base of a self-curing plastic mass mixed with electrically conductive ferromagnetic particles. The second type of implant is a hollow object with thin walls that follows the shape of the tumor. Implants of this type are filled with a liquid metal non-magnetic alloy with melting point below room temperature. The model implants were heated in a self-designed inductor with a short cylindrical coil 35 cm in diameter. Biological tissues were modeled using an ultrasound gel. Experimental results show that both types of implants were heated in an external alternating magnetic field with a fi-equency of 90 kHz and an amplitude not exceeding 4 kA/m up to temperatures that allow both traditional hyperthermia (tissue heating to 41-45 °C) and thermal ablation therapy (tissue heating to temperatiu-es above 50 °C). Good agreement between the experimental data and model numerical calculations was obtained. © 2021 Izdatel'stvo Meditsina. All rights reserved

Characterization of Ferromagnetic Composite Implants for Tumor Bed Hyperthermia

Hyperthermia therapy (HT) is becoming a well-recognized method for the treatment of cancer when combined with radiation or chemotherapy. There are many ways to heat a tumor and the optimum approach depends on the treatment site. This study investigates a composite ferromagnetic surgical implant inserted in a tumor bed for the delivery of local HT. Heating of the implant is achieved by inductively coupling energy from an external magnetic field of sub-megahertz frequency. Implants are formed by mechanically filling a resected tumor bed with self-polymerizing plastic mass mixed with small ferromagnetic thermoseeds. Model implants were manufactured and then heated in a 35 cm-diameter induction coil of our own design. Experimental results showed that implants were easily heated to temperatures that allow either traditional HT (39 degrees C-45 degrees C) or thermal ablation therapy (>50 degrees C) in an external magnetic field with a frequency of 90 kHz and amplitude not exceeding 4 kA/m. These results agreed well with a numerical solution of combined electromagnetic and heat transfer equations solved using the finite-element method