Wpływ dodatku substancji ochronnych na zakres temperatury krioskopowej i przebieg procesu zamrażania soku z ziemniaka

Celem pracy było określenie wpływu dodatku substancji ochronnych (krioprotektantów), takich jak: alkohol, chlorek sodu oraz kwas askorbinowy, na zakres temperatury krioskopowej i przebieg procesu zamrażania soku z ziemniaka. Zamrażanie prowadzono w kriostacie, w temperaturze –20°C. Temperaturę krioskopową oraz długość poszczególnych etapów procesu zamrażania odczytano z krzywych mrożenia. Wykorzystując bilans masowy procesu zagęszczania, obliczono zawartość wody wymrożonej w badanych próbach. Badania dowiodły, że dodatek wszystkich substancji ochronnych spowodował obniżenie temperatury krioskopowej zamrażanych próbek. Najniższą temperaturę krioskopową (–2,6°C) zanotowano dla soku z dodatkiem NaCl. Całkowity czas zamrażania wszystkich badanych próbek uległ skróceniu w wyniku dodatku substancji ochronnych. Najwięcej wody (91,69%) uległo wymrożeniu w próbie soku z dodatkiem NaCl, co koreluje z obniżeniem temperatury krioskopowej.

The growing interest in potato juice properties is connected with the need of invention of the best methods of its preservation and storage. The aim of this study was to determine the influence of cryoprotective substances such as alcohol, sodium chloride and ascorbic acid on the cryoscopic temperature range and the course of freezing process of the potato juice. Freezing was carried out in two variants using a cryostat temperature of –20°C. The freezing process was carried out by immersion in a cryostat (HUBER CC-505, Germany). The cylindrical vessel (0.05 m diameter and 0.13 m high, 250 ml potential capacity) with 200 ml of the solution was placed in a bath freezing apparatus, in the presence of the cooling liquid SilOil (HUBER, Germany), at the temperature of –20°C. The process was monitored using two thermocouples. Temperature of the cooling liquid and temperature of the solutions were tested to achieve –15°C in the center of the vessel. Records were taken every 60 seconds by the MPI-LAB temperature recorder (Metronic Instruments) connected to the computer. In order to determine the time of particular stages of the freezing process (cooling time, phase change and final freezing) and to determine the freezing point, recorded data were used to prepare freezing curves in Microsoft Excel 2010. On those freezing curves tangent lines were applied to each straight section, which allowed for estimation of the freezing point and time of particular stages. Representative of frozen water in the samples was defined based on the mass balance in cryoconcentration process. Measurements were performed in triplicate. In order to correlate the influence of particular substances on freezing point and time of particular freezing stages, one-way ANOVA analysis of variance and also Tukey significant difference test (α = 0.05) was carried out using R Commander 3.1.3. The study shows that the addition of all protective substances caused lowering of cryoscopic temperature values (the lowest –2.6°C) for the sample with the NaCl addition. The total time of freezing for all samples with the additives, frozen at a temperature of –20°C, was nearly by 20% reduced. The shortest time of freezing was noticed for the sample of juice with the addition of sodium chloride (9 minutes shorter in comparison to the sample without additives). The most water (91.69%) froze in the sample of potato juice with the addition of NaCl, which clearly correlate with the freezing point depression. This study can play a key role, especially when designing new product (such as potato juice) preservation.