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Kinetics of pectinaceous substances’ transformation reactions of autumn grades’ apples during storage at low positive temperatures
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Annotation
Apples are the main raw material for the preparation of pectin polysaccharide which is widely used in many food industries as a structure-forming agent and a biologically active additive-dietary fiber. The choice of autumns grades’ apples as a major source of pectin as a functional ingredient and the time of the aplles’ refrigerating storage allowing to preserve pectinaceous substances to the maximum is substantiated. The apples of Antonovka Novaya, the Bashkirsky Krasavets, Hybrid Zhukova, Dushistoye, Kitayka, Kordonovka, Systrarosa and Shtrifel grades grown up in a collection garden of the Pavlovsk experimental station of VNIIR of N.I. Vavilov are chosen as objects for the research (harvested in September, 2016 and 2017). Apples stored in polymeric containers in the refrigerator in the conditions of natural convection at a temperature (3±1) °C. After harvesting and periodically in the course of storage determined. Organoleptic indicators of quality are analyzed, the content of protopectin (water-insoluble fraction of pectinaceous substances), pectin (soluble fraction), and the sum of pectinaceous substances by a carbazole method are tested. The dependences between the change in the total content of pectinaceous substances, pectin, and protopectin and the duration of the storage at low positive temperatures for the grades of apples under investigation are detrmined. The regression equations characterizing these dependences are shown. The constants of protopectin and pectin hydrolysis reaction rate during refrigerating storage of autumn grades’ apples are calculated. It is shown that the minimum rate of protopectin and pectin hydrolysis of is characteristic for Kordonovka and Antonovka Novaya grades, maximum one – for Kitayka and Dushistoe grades. Reduction of protopectin and pectin amount is followed by softening consistence and decreasing turgor which are determined by organoleptic indicators on the 60th – 120th day of storage depending on the grade. To obtain pectin in industrial conditions it is recommended to use Hubrid Zhukova, Kordonovka and Antonovka Novaya grades kept at the temperature of (3±1)°C for not more than 60 days (Hubrid Zhukova grade) and 90 days (Kordonovka and Antonovka Novaya grades) as a source of raw materials.
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