Effect of high intensity ultrasound on antioxidant activity and microbiological quality of strawberry juice

Tijekom ovog istraživanja proizveden je sok od jagode različitim tehnološkim postupcima koji uključuju prethodnu obradu jagode blanširanjem, zatim bistrenje, depektinizaciju ili oba postupka zajedno. Nakon pripreme sokova isti je termički obrađen u cijevnom izmjenjivaču topline ili ultrazvukom visokog intenziteta, frekvencije od 20 kHz sa sondama promjera 12 i 7 mm. Obrada ultrazvukom visokog intenziteta provodena je u trajanju od 3, 6 i 9 minuta pri temperaturi soka od 25°C, 40°C i 55°C te amplitudama za sondu promjera 12 mm (60, 90 i 120 μm), a za sondu promjera 7 mm (53, 79,5 i 106 μm). Za planiranje i dizajniranje eksperimenta korišten je centralno kompozitni plan, a optimiranje procesnih parametara te statistička obrada rezultata provedena je metodom odzivne površine. Učinak ultrazvuka visokog intenziteta na sokove jagoda praćen je ispitivanjem mikrobiološke ispravnosti soka (ukupni broj bakterija, kvasci, plijesni, enterobakterije, E. coli i Salmonella spp.) nakon obrade te nakon 10, 20 i 30 dana skladištenja pri temperaturi od +4 °C, zatim mjerenjem ukupne boje na kolorimetru te određivanjem sadržaja antocijana na HPLC-u. Sva navedena ispitivanja provedena su i u uzorcima soka jagode termički obrađenim u cijevnom izmjenjivaču topline kao i u matičnom soku. Svrha ovog rada bila je dobivanje kompletne slike o učinku ultrazvuka visokog intenziteta na mikrobiološku ispravnost, promjenu parametara boje te sadržaja biološki aktivnih spojeva (antocijana) u soku od jagode.During this research strawberries juice were produced with various technological processes involving previous blanching strawberries, then clearance, depectinization or both processes together. After preparing the same juice is thermally processed in a tubular heat exchanger or with high-intensity ultrasound with frequency of 20 kHz and with a probe diameter of 12 and 7 mm. High-intensity ultrasound treatment was conducted in the period of 3, 6 and 9 minutes at a temperature of juice from 25 °C, 40 °C and 55 °C and amplitudes of the probe diameter of 12 mm (60, 90 and 120 mm), and the probe diameter 7 mm (53, 79.5 and 106 mm). For planning and design of experiments, a central composite design and optimization of process parameters and statistical analysis of results was performed using the response surface methodology. Effect of high intensity ultrasound on the juices of strawberries was monitored by examining microbiological correctness of the juice (total number of bacteria, yeasts, molds, enterobacteria, E. coli and Salmonella spp.) after treatment and after 10, 20 and 30 days of storage at a temperature of +4 °C and then measuring the total color on the colorimeter, the content of anthocyanins in the HPLC. All these tests were carried out in strawberry juice samples which were treated in tube heat exchanger as well as the raw (not treated) juice. The purpose of this study was to obtain a complete picture of the effect of high intensity ultrasound on the microbiological correctness, change the color parameters and content of bioactive compounds (anthocyanins) in strawberry juice