Effect of texturization on microbial inactivation in UV-C treated orange juice: Predictive modeling and analysis of Alicyclobacillus acidoterrestris physiological and morphological changes.

Abstract

UV-C light is an alternative for preserving clear fruit-based drinks, replacing existing thermal treatments that degrade product quality and are ineffective against some microorganisms, including Alicyclobacillus acidoterrestris, a spoiling agent of concern in the juice sector. Texturizing agents are essential since consumers' preferences for these products strongly depend on the mouthfeel. However, the complexity of the treated texturized system may have an essential influence on UV-C effectiveness. The main goal of this study was to evaluate the effect of texturization on the UV-C inactivation of A. acidoterrestris spores (AA) and separate cocktails of Escherichia coli (ECC), yeast (YC), and Salmonella (SC) in orange juice. Binary combinations (0.0 to 0.3 % w/v) of carboxymethyl cellulose (CMC) and guar gum (GG) were added to orange juice (OJ). A multiple regression analysis identified suitable CMC and GG combinations with optimal viscosity (~ 20 mPa.s) and maximum suspended particles (%S), leading to two formulations: TOJ₁ (0.075 % w/v CMC + 0.15 % w/v GG at five °C) and TOJ₂ (0.045 % w/v CMC + 0.165 % w/v GG). A consumer field test confirmed the advantages of sweetness, bitterness, flavor, color, and body/viscosity, establishing it as the best formulation. UV-C assisted by mild heat (UV-C/H) inactivation in OJ and TOJ₁ was determined (1651 mJ/cm², 50 °C, 1.8 L/min). Single treatments (UV-C and H) were also performed to evaluate synergy. The UV-C/H induced damage on AA spores was measured by flow cytometry (FC) labeling with fluorescein diacetate (FDA) and propidium iodide (PI) for monitoring membrane integrity. The bacterial cocktails were the most sensitive to the UV-C treatments, followed by YC and AA. UV-C achieved moderate inactivation (1.6-4.6 log reductions) in non-texturized OJ, while UV-C/H significantly enhanced microbial sensitivity (3.4-7.5 log reductions). Texturization slightly reduced UV-C effectiveness, achieving 2.9-5.2 log reductions in TOJ₁. The Weibull model provided the best fit characterizing UV-C inactivation with evidence of subpopulations of different resistances. In TOJ₁ treated by UV-C/H, the flow cytometry study revealed membrane-compromised AA spores with a gradual increase of PI+ cells with treatment time. The scanning electron micrographs showed structural damage, less evident in the texturized system. The results suggest that UV-C can be used to process texturized orange juice and could be a promising alternative for controlling Alicyclobacillus spp. spores and other microbial strains in industrialized orange juice.