Wpływ procesu rozmrażania mikrofalowego truskawek na zawartość wybranych składników w suszu

Celem pracy było określenie wpływu parametrów rozmrażania mikrofalowego na zawartość wybranych składników: antocyjanów i polifenoli ogółem. Badanie prowadzono, wykorzystując mrożone truskawki odmiany Senga Sengana, zebrane w latach 2010, 2011, 2012. Truskawki rozmrażano, stosując następujące moce mikrofal: 0,9; 1,2 i 1,8 W-(g rozmrażanych owoców)-1. Rozmrożone truskawki suszono w laboratoryjnej próżniowej suszarce komorowej w temperaturze zadanej 60°C, przy ciśnieniu 4 kPa. Antocyjany oznaczano, korzystając z pomiarów absorbancji w spektrofotometrze według metodyki Wrolstada, a polifenole ogółem, korzystaj ąc ponownie z metody spektrofotometrycznej zaproponowanej przez Singleton i Rossi. Analizy statystyczne przeprowadzono osobno dla wybranych mocy mikrofal w każdym badanym roku zbioru. Zmiana mocy mikrofal miała istotny wpływ na zawartość składników bioaktywnych rozmrożonych truskawek. Zwiększanie mocy mikrofal powoduje obniżenie zawartości polifenoli ogółem i antocyjanów. Do rozmrażania truskawek należy stosować moc mikrofal na poziomie 0,9 W-(g rozmrażanych owoców)-1. Suszenie próżniowe istotnie zmniejszyło zawartość antocyjanów i polifenoli ogółem.

The objective of this study was to determinate the effect of microwave thawing parameters on the anthocyanins and total polyphenols content in strawberries. Strawberries of the Senga Sengana variety were harvested in years 2010, 2011, 2012 then they were frozen and stored until the day of the experiment in temperature -19°C. Strawberries harvested in 2010 were stored 31 months, strawberries harvested in 2011 were stored 19 months, and strawberries harvested in 2012 were stored 7 months. Strawberries were thawed using microwave oven (Samsung, model MW87W), following microwave powers were used: 0.9, 1.2 and 1.8 W-(g thawed strawberries)-1.Thawing was continued until the temperature inside the fruit was (+5°C). After thawing strawberries were dried in laboratory vacuum dryer (60°C, 4 kPa). The contents of total polyphenols and anthocyanins in microwave thawed strawberries were compared before vacuum drying and after this process. Anthocyanins in strawberries were indicated using Wrolstad [1993] methodology. Extracts of dried and thawed material were prepared. Absorbency was measured with wave light: X = 510 and 700 nm. Total polyphenols were indicated using Singleton and Rossi [1965] methodology. Total polyphenols were indicated in spectrophotometer Helios у UV-VIS Thermo Electron, weave light: X = 750 nm. Separated statistics were carried out for different microwave powers in each analyzed year of harvesting. Because experiment results did not have normal distribution, to determine significant differences Kruskal-Wallis's test was used. Statistical analysis was performed at the a = 0.05 significance level using Statistica 10 software (StatSoft, Inc.). The lowest total polyphenols and anthocyanins retention was indicated in microwave thawed strawberries (1.8 W-(g thawed strawberries)-1) harvested in the year 2011, stored for 19 months. The highest content of considered biologically active compounds was obtained for thawed strawberries harvested in the year 2012, and stored only for 7 months. The biggest total polyphenols and anthocyanins retention in microwave thawed strawberries after vacuum drying was also indicated in strawberries harvested in 2012. Vacuum drying leads to statistically significant loss of anthocyanins and total polyphenols in strawberries. Anthocyanins content in thawed strawberries was significantly greater (8.29-17.99 mg-(100 g d.s.)-1 than anthocyanins level in strawberries after drying (6.17-12.68 mg-(100 g d.s.)-1). Total polyphenols level in thawed strawberries was significantly greater (19.15-34.68 mg-(100 g d.s.)-1 than total polyphenols level in strawberries after drying (18,10-33,12 mg-(100 g d.s.)-1). Anthocyanins and total polyphenols contents were greater when microwave power used for thawing strawberries were lower (these differences were statistically significant). For thawing frozen strawberries it is appropriate to use microwave power 0.9 W-(g thawed strawberries)-1. For microwave power 1.8 W-(g thawed strawberries)-1 the content of bioactive compounds was statistically significant lower for Senga Sengana strawberries harvested in each analyzed year. The power of the microwave 1.2 W-(g thawed strawberries)-1 caused statistically insignificant reduction in the content of bioactive compounds in relation to the power 0.9 W-(g thawed strawberries)-1.