Aplicación combinada de sonicación y aceites esenciales en la conservación de zumos naturales de fruta

Résumé

ABSTRACT Objectives: To study the effect of sonication combined with moderate temperatures and natural antimicrobials on the inactivation of Saccharomyces cerevisiae, Escherichia coli O157: H7 5297 and Listeria monocytogenes LM82, in natural juices and their survival under refrigeration conditions. To study the effect of these treatments on the physical-chemical properties, the content of bioactive compounds, the antioxidant activity and the natural microflora of natural juices and the stability of some quality parameters and bioactive compounds under refrigeration conditions. Methodology: Minimal inhibitory concentration of cinnamon leaf essential oil against S. cerevisiae was determined using absorbance measurements based on the microtiter plate assay. It has been evaluated and modelled the survival of S. cerevisiae in Trypticase Soy Broth (TSB) and natural orange juice processed by combined use of thermo-ultrasound (24 kHz; 105 m; 33,31 W/mL; 30 minutos; 30º, 40º, 50ºC) and cinnamon leaf essential oil. Thermo-ultrasound treatments were applied with a UP200H ultrasonic processor (Hielscher Ultrasound Technology) using a S3 probe. It were selected the best conditions of inactivation in TSB to study the inactivation of S. cerevisiae in natural orange juice. Experimental data were fitted by using the "Shoulder+log-linear" and "Weibull" models (GInaFiT). The maximum concentration of cinnamon leaf essential oil accepted by consumers in natural orange and pomegranate juices was determined by sensory analysis. The inactivation of S. cerevisiae in natural orange and pomegranate juices untreated (control) and treated with mild temperature (50ºC), cinnamon leaf essential oil, thermo-ultrasound (24 KHz; 33.31 W/mL; 30 minutes; 50ºC), or thermo-ultrasound plus cinnamon leaf essential oil and its survival under refrigerated conditions (5ºC, 28 days) were studied. Freshly squeezed orange juice was sonicated (for 1, 10, 20 and 30 minutes at 24 kHz frequency) to evaluate its impact on selected physico-chemical characteristics and bioactive compounds, such as total phenols, flavonoids, DPPH radical scavenging activity, total carotenoids, ascorbic acid, pH, °Brix and color parameters. Additionally, the effects of sonication treatments on the microbial load were also evaluated. It has been used response surface methodology to study the effect of thermo-sonication and essential oil on orange and pomegranate juice quality parameters. Natural fresh orange and pomegranate juice samples were continuously sonicated at a constant frequency of 24 kHz for a range of processing temperatures (50-60°C), amplitude levels (0-100%) and CLEO (0-320 mg/L). Color parameters (CI, TINT, %YE, %BLUE, %RED), pH, ºBrix, total phenols, flavonoids, carotenoides, anthocyanins content were measured. Response surface methodology (RSM) based upon a three-factor, three-level Box-Behnken experimental design was used to determine the effect of independent variables. Minimal inhibitory concentration of essential oils against L. monocytogenes LM82 and E. coli O157:H7 5297 was determined using absorbance measurements based on the microtiter plate assay. It has been evaluated the survival of L. monocytogenes LM82 and E. coli O157:H7 5297 in natural apple juice processed by combined use of thermo-ultrasound and essential oils. The resistance of L. monocytogenes LM82 and E. coli O157:H7 5297 cells to the combined action of thermal treatment and ultrasound, was analyzed in natural apple juice with cinnamon leaf essential oil at 40ºC. Conclusions: Results of the present study indicate that sonication coupled with mild temperatures and natural antimicrobial may be employed as a suitable technique for fruit juice processing, and may be applied to improve their safety and nutritional quality. Box-Behnken design and RSM was demonstrated to be an effective technique to model the effect of sonication on juice quality while minimising the number of experiments required.