CHANGES OF PECTIN QUANTITY IN FRESH AND FROZEN APPLE PRODUCTS

摘要

Recently more and more innovations enter the manufacture of food products and one of them is food hydrocolloids. Food colloids open a lot of different possibilities in dessert production, which are used to perform certain functions. Pectin is a traditional agent for jams and jellies, but its application extends to fruit products for the food industry. In food product technology pectin is added as gelling agent and stabilizer. The three apple varieties - 'Antonovka', 'Baltais Dzidrais' and 'Zarja Alatau' harvested in Latvia State Institute of Fruit Growing were used for the experiment. Photometric measurement was used to determine the composition of pectin. Pectin was isolated from the apple mass by leaching with ethanol, and from the residues - by extracting with diluted sodium hydroxide solution. By adding carbasol and sulphuric acid to the extract, through different intermediate stages carroty condensation product formed, which was photometrically measured at 525 nm. Pectin, pH and soluble dry matter were determined in fresh and frozen apple mass from apples of three ripeness stages. On the basis of worked out functional analysis of colloids, it is possible to optimize regulation of heat processes for different ripeness stages of apples. It is established that ripeness stage influences pectin quantity in fruits, but there are no data about pectin quantity changes in frozen fruits. By fruit ripening under the impact of enzyme protopectinase, protopectin hydrolyzes and transforms into pectin, which flows from the intercellular spaces into protoplasm of cells. Therefore ripe as well as heat treated fruits are soft and loose. It is important to measure pectin in frozen apple mass, in order to determine its potential jellying power. For each kind of product appropriate conditions have to be chosen for freezing, as well as the condition of products before freezing has to be taken into consideration in order to reduce the harmful influence on their quality to the minimum. The results of the research indicate that pectin quantity in frozen apple mass has decreased substantially. This susceptibility of sugar containing products to temperature fluctuations possibly is due to their high concentration of unfrozen water and lower melting temperature. It is possible to calculate the mass fraction of ice depending on temperature and moisture content in product what is very important for prognosticating the product quality. The aim of the research is to compare changes of pectin quantity in fresh and frozen apple products depending on storage time. The research is related to application possibilities of the current colloids, which are used in food industry at present.