Food and Beverages

Statement of the Problem: Consumers´ demand for a preservation technology that retains fresh-like quality has resulted in a growing interest for non-thermal processing methods. Among them, UV-C light proved to reduce microbial contamination in various liquid foods. However, its efficacy in turbid systems is limited because suspended matter often contains absorbing molecules that can harbor microbial cells. To overcome this limitation, a hurdle approach should be addressed.

Objective: The objective was to obtain a carrot-orange juice blend (1:1 ratio (v/v)/pHadj:5.0/10.6 °Brix/absorptivity:0.32cm-1/7667 NTU particle size=D[3,2]:5.1±0.1 μm/D[4,3]:60.81±8.68 μm) processed by UV-C assisted by mild heat (H) and the addition of a natural antimicrobial extract with high Polyphenols Content (PC).

Methodology: For microbial challenge tests, the inoculated juice (Escherichia coli ATCC 35218, Saccharomyces cerevisiae KE162 or Pseudomonas fluorescens ATCC 49838) was recirculated in an annular UV-C reactor (254 nm; 1.6 L/min; 15 min; 10.6 kJ/m2; 50°C). For the antimicrobial extract (YME), yerba mate (Ilex paraguariensis) leaves were sonicated (20 kHz; 95.2 μm; ethanol; 25°C) freeze-dried and subsequently added to the juice (0.4% w/v). Native flora; sensory analysis; PC and total antioxidant activity (TAA) (Folin-Ciocalteu and DPPH methods) were also studied during juice storage (5ºC).

Findings: UV/H provoked 3.5-6.0 log-reductions of inoculated flora, while 0.6-2.9 log-reductions were achieved by single UV-C and H treatments. Native flora was reduced by 5 log-cycles without any recovery during 20 days (5ºC). Conversely, single treatments less reduced the native population. YME addition to the juice considerably increased PC (720±45 μg GAEq/mL) and TAA (5.5±1.0 μg Trolox eq/mL) compared to the non-additivated juice (PC=302±40 μg GAEq/mL; TAA=1.6±1.3 μg Trolox eq/ mL), values which remained constant during 50 day storage (5ºC). The additivated UV/H treated juice was described by consumers with optimal acidity, aroma, viscosity and sour flavor.

Conclusion & Significance: A method involving UV-C light and mild heat for the preservation of a turbid juice was found. Furthermore, YME addition increased juice antimicrobial capacity and bioactive compounds content.