Influence of pure solute on its activity during refrigeration of products
Annotation
A calculation method for determining water activity in food products at the temperatures below freezing point taking into account protein denaturation and dehydration of pure solute accompanying it and its penetration into solution of tissue juicesis presented. It was proved that it is possible to use ethanol water solution as an analogue of tissue juiceswhen making calculations. The temperature of starting freezing determined by initial ethanol solution concentration, relative contents of pure solute against quantity of dry matter s,and common moisture of solution and pure solute in relation to product weight Whave been acceptedas the characteristics reflecting physics-chemical product peculiarities. The classic formula of water activity familiar from the theory of solutions has been modified by a correction which takes into account additional ingress of pure solute into solution of tissue juices due to proteins dehydrogenation at their denaturation. Expressions for determining pure solute mass at the temperatures equal or above freezing point, transition of relative pure solute contents from general water mass in product into contents of pure solute from solution water mass. An example of calculating water activity for conventional product of animal origin with tst= –1°C; W = 0.8,and the ingress use of averaged magnitude s= 0.27 kg c/kg m obtained by D.G. Rjutov,and also experimental results byS. Charma and P. Mudi forrelative content of pure solute from general water mass at the temperatures below the start of freezing are exemplified. It has been found outthat water activity at the temperatures from –1 to –40°Сdiminishes by 25% and its diminishing is not proportional to the temperature drop. The greatest drop of water activity up to 85% takes place at the temperature range from –1.0 to –6.7°Сwhen basic ice formation takes place and the share of frozen out moisture is ~84%. The ingress of pure solute into solution of tissue juices due to protein denaturation does not influence much the water activity in the product. Its increase amounts on average to 0.9% in comparison withan ideal variant of denaturation absence duringrefrigerationof products.