Effect of processing conditions on the microbiological quality and antioxidant properties of a beet leaves extract obtained by ultrasound

CORREA DE CARVALHO, MÁRCIA; ZARBO COLOMBO, ANTONELLA A; NUTTER, JULIA; JAGUS ROSA JUANA; AGÜERO MARÍA VICTORIA

Río de Janeiro

Simposio; 14° Simposio Latinoamericano de Ciencia de los Alimentos, SLACA.; 2021

 Bioactive compounds extraction from underutilized beet leaves (BLs)constitutes a promising strategy to improve the sustainability of agri-foodchain. In previous studies, the ultrasound-assisted aqueous extraction (withand without temperature control) of antioxidants compounds was optimized. Thepresent study aimed to evaluate these two optimized treatments on themicrobiological quality and antioxidant properties of the extracts obtained andthe stability of these attributes during refrigerated storage. BLs were washedand cut into small peace (0.04cm2). Extractions under conditionspreviously optimized were carried out: Thermosonication (TS, 90W, 1:17 ratio,16min) and Sonication (S, 90W, 1:10 ratio, 16min, with ice bath). Extractswere centrifuged (10.000rpm, 10min) and the supernatant was stored underrefrigerated conditions. The microbiological quality of extracts (mesophilicaerobic bacteria (BAM), enterobacteria (EB) and molds and yeasts (M&Y)) wasdetermined. Total polyphenols and betalains were spectrophotometrically quantified.Temperature reached by TS and S treatments were 89 and 45°C, respectively. TScaused a significant decrease (2.1 log) for BAM and for EB and M&Y (countsunder detection limit). Maximum polyphenols was found in TS (27.17 mgGAE/gDW),probably due to the high temperature reached that favored polyphenolsextraction. Betaxanthins after TS resulted lower than after S, and this isattributed to different degradation and transformation mechanisms associatedwith high temperatures. Betacyanins were not affected by temperature. On theother hand, BAM, EB and M&Y counts from TS extracts remained belowdetection limit during storage. Interestingly, microbial counts in S extractsremained constant during 2 days, differently from control that showed increasesfrom the beginning of storage. Probably sonication exerted some physical damageto microorganisms and a longer period was needed for adaptation torefrigeration. Polyphenols presented stability for both TS and S. A decrease of44 and 87% was observed for betalains for the TS and S, respectively, probablydue to degrading enzyme inactivation during TS. Termosonication allows toobtain extracts with appropriated microbiological and antioxidant propertiesand stability during storage.