Multi-Response Optimization of Sequential Mild Heating and UV-C Radiation Hurdle Technology for Decontamination and Quality Retention of Traditional Tunisian Coarsely Milled Barley (Chorba Chiir)

Low-moisture cereal products, such as traditional Tunisian coarsely milled barley, represent a vital global and regional dietary staple. However, their post-harvest processing is challenged by contamination with highly resilient endogenous spore-forming bacteria. This study investigated a sequential mild-thermal and UV-C hurdle technology, combining oven temperature (Factor A; 60, 80 and 100 °C) thermal treatment time (Factor B; 2, 6 and 10 min) with UV-C radiation (Factor C; 214.8, 644.4 and 1074.0 mJ/cm2), using a three-factor, three-level Box–Behnken experimental design coupled with response surface methodology (RSM). Three responses were evaluated: microbial logarithmic reduction (Y1), water activity aw (Y2), and total color difference ΔE (Y3). Statistical analysis confirmed that thermal factors (A: oven temperature and B: thermal treatment time) served as the primary drivers of microbial inactivation, while UV-C light acted primarily at the immediate solid surface, inducing localized photothermal micro-evaporation that significantly affected surface water activity without degrading bulk chromatic properties. Multi-response optimization established an optimal processing window at an oven temperature of 94.5 °C, a thermal treatment time of 8.30 min and, a UV-C dose of 1074 mJ/cm2. Experimental validation under these optimal conditions yielded a highly reliable 1.385 ± 0.013 Log CFU/g reduction in naturally occurring, heat-resistant spore-forming bacteria. Concurrently, the product maintained an exceptionally dry state (aw = 0.34 ± 0) and preserved its natural visual attributes (ΔE= 2.77 ± 0.08). The low validation relative standard errors (RSE < 10% for physical attributes; 15.6% for microbial reduction) demonstrated a good predictive precision and industrial feasibility of the quadratic models.