| Popis: |
Natural antimicrobial agentsderived from herbs and plants have been used for millenia in medicine and food preservation. Indeed, essential oils (EO) and plants extracts (PE), in addition to contributing to flavour and taste, can act against food microbiota thus enhancing its stability. Moreover, recently, the consumers’ demand for naturalproducts – free of chemical preservatives - has been strongly increased. Fruit-based juices are susceptible to spoilage microorganisms,mainly yeasts and lactic acid bacteria, which negatively affect their organoleptic and nutritional properties making the product unacceptable to consumers. The aim of this study was to evaluate the effects ofnatural compounds, i.e. EO of Satureja montana and PE of Cotinus coggygria, in combination with mild thermal treatments on shelflife of carrot-orange juice and its microbial stability. In particular, viability of two spoilage microrganims Saccharomyces cerevisiae and Lactobacillus plantarumwas addressed. The EO and PE were preliminarly characterized by gascromatographic analises whichshowedthat S. montana was composed mainly by carvacrol and o-cimene, while the main components of C. coggygria were sulfuretin and fustin. Both S. montana EO and C. coggygriaPE displayed a good antimicrobial activity against S. cerevisiae, with minimum inhibitory concentration (MIC) values of 0.351 mg/ml and 0.094mg/ml, respectively. On the other hand, Lactobacillus plantarum was more resistant thanS. cerevisiae(MIC >0.5 mg/ml). The freshcarrot-orange juice was added with the S. montanaEO or C. coggygriaPE at MIC/4 concentrations for S. cerevisiae. Following its deliberatecontamination with the spoilage microrganisms (4 LogCFU/ml), samples were heat treated (60 °C for 2 or 5 min) and stored at room temperature for 9 days or 4°C for 50 days. Changes insurviving spoilage microbiota, pH, colour and antioxidant activity were monitored over storage. Overall, the results highlighted the possibility of stabilizing a juice with a high pH (5.4)by applying the "Hurdle Technology". The natural compounds enhanced the efficacy of heat treatments in inactivating/damaging the spoilage biota and delaying its recovery over storage. Moreover, no significant changes in the pH and color of the juices were found during storage, while limited variations in the antioxidant activity were detected |
