The Study of Thermal Reversibility of the Freezing-defrost Process of Browned Onion

The features and dynamics of the freezing-defrost processes of the studied sample of browned onion were established and studied. At the research it was revealed, that at freezing temperature –20 °С the value of maximal freezing speed does not change.The process of defrost of browned onion was carried out using calorimeter with the reverse connection on temperature and PID-regulator, on the temperature curve of its freezing. It was determined, that the process of defrost of the studied sample needs more heat that is educed at freezing. The modes of stepped defrost that testify to the possibility of thermal reversibility of freezing process were experimentally established.The direct dependence of educed and consumed heat quantity on the mode of thermal processing of studied sample was revealed. The more moisture was eliminated from the food product, the less heat must be consumed for defrost. The analogous dependence is typical also for the freezing process.The received data can be used for determination of the rational modes of freezing and defrost of the browned onion

Effect of Sautéing of Onion on Its Storage at Low Temperatures

We studied dynamics of freezing and defrosting of sautéed onion, determined its acidic and peroxide number, which was stored during 30 days at temperature of –18 °C. The change in anatomical structure of frozen onion depending on thermal pre–treatment was examined.The technology of production of frozen vegetable mixes implies the use of thermal treatment; therefore, selecting the method of canning, which will make it possible to maximally preserve useful substances of chemical composition of a product, is relevant.As the object of experiment we used fresh and frozen sautéed onionIt was found as a result that at temperature of freezing – 20 °C, the value of maximum speed of freezing practically does not change; this indicates that the rate of cooling is not limited by thermal and physical properties of the sample. We also experimentally determined the increase in acid number in the process of refrigeration storage during 30 days and the decrease in peroxide number in the examined samples of sautéed and frozen onion.It was revealed that the cells of onion after sautéing changed their form and structure: they do not have a clear form and orderliness; the breaks are visible at the contours of the walls of cells. The luminescent formations after sautéing of onion change their form as a result of deformation of cellular membranesThe obtained data may be used for providing high quality of the frozen vegetable mixes for soups and for determining rational regimes of freezing and defrosting of sautéed onion in their composition. Adding sautéed onion to the frozen vegetable mixes is expedient and will not change organoleptic properties of a product; it will not accelerate the oxidation processes of fats, but will only help to preserve the integrity of shape and delicate consistency of onion in a soup prepared from such a mix