The Influence of High Voltage Electrical Discharge on the Physicochemical Properties and Microbiological Quality of Rose Hip Nectar (Rosa canina laxa)

Visokonaponsko električno pražnjenje je netermička tehnika koja se pokazala učinkovitom u inaktivaciji brojnih mikroorganizama i enzima, uz minimalne učinke na nutritivni sastav i senzorska svojstava hrane. U radu je istražen utjecaj procesnih parametara, frekvencije pražnjenja (50 i 100 Hz) i vremena obrade (10, 15 i 20 minuta) na fizikalno-kemijska svojstva i mikrobiološku stabilnost kašastog soka šipka (Rosa canina laxa). Rezultati obrada su uspoređeni sa neobrađenim i pasteriziranim sokom. Obrada plazmom nije značajnije utjecala na pad pH vrijednosti i porast električne vodljivosti sokova, kao niti na degradaciju bioaktivnih spojeva. Najveći stupanj degradacije askorbinske kiseline (gubitak od 55%) i fenolnih tvari (50%), kao i najveća ukupna promjena boje (10,47) zabilježena je u pasteriziranom soku. Ispitivanje mikrobiološke kvalitete ne/obrađenih uzoraka soka provedeno je neposredno nakon pripreme/obrade, te tijekom 6 i 12 dana skladištenja pri 4 °C. Broj aerobnih mezofilnih bakterija, bakterija roda Enterobacteriaceae i Escherichia coli u ispitivanim uzorcima soka bio je sukladan važećim mikrobiološkim kriterijima, a niti u jednom uzorku soka tijekom 12 dana skladištenja nije zabilježena prisutnost bakterija Salmonella spp. i Listeria monocytogenes. Najbolju mikrobiološku stabilnost (< 10 CFU/mL) u pogledu broja kvasaca i plijesni imali su pasterizirani sok i sok pripravljen od kaše blanširane nakon pasiranja, koji je nakon pripreme obrađen plazmom (100 Hz, 20 minuta).High Voltage Electrical Discharge is non-thermal technique, which turned out to be effectively for inactivation of microorganisms and enzymes, with minimal effects on nutritional composition and sensory properties of food. In this paper has been investigated the influence of process arameters, discharge frequencies (50 and 100 Hz) and processing times (10, 15 and 20 minutes) on physico-chemical properties and microbiological stability of rose hip (Rosa canina laxa) nectar. All results were compared with untreated and pasteurised nectars. Plasma treatment did not significantly affect on decrease of pH value and increase in electrical conductivity, as well as the degradation of bioactive compounds. Maximum degree of ascorbic acid degradation (loss of 55%) and phenolic compounds (50%), as well as the highest total colour change (10.47) in pasteurised nectar was observed. Microbiological quality testing of non/treated nectar samples immediately after preparation/ treatment and after 6 and 12 days of storage at 4 °C, was carried out. Aerobic mesophilic bacteria, Enterobacteriaceae and Escherichia coli count in all samples during 12 days were below the permitted levels. Salmonella spp. and Listeria monocytogenes were not detected in any of the nectar samples. The best microbiological stability in terms of the number of yeasts and moulds (< 10 CFU/mL) had pasteurised nectar and nectar prepared with blanched purée, treated with HVED (100 Hz, 20 minutes)