Aqueous chlorine dioxide mediated tempering of wheat grains: Evaluation of tempering potential, kinetics, and mechanism of Salmonella inactivation.

Abstract

The study evaluated the potential of aqueous chlorine dioxide (ClO2) for tempering wheat. Wheat kernels were tempered to 17 % moisture using aqueous ClO2 (20.6-102.8 mg kg-1) for 0-24 h in a 2-factor mixed level full factorial design (5 × 8 = 40 runs). The highest reduction of 4.1 log10 CFU/g was obtained at 102.8 mg kg-1 at 24 h; while all exposures ≥12 h of 82.2 mg kg-1 achieved >3 log reduction. The biphasic inactivation model was the best fit to describe ClO2 induced Salmonella inactivation. The fast phase (k1) and slow phase (k2) rate constants ranged from 0.88 to 2.20 h-1 and 0.056 to 0.139 h-1, respectively. Consequently, the time required to attain 3 log reduction at concentrations of 20.6, 41.2, 61.7, 82.2 and 102.8 mg kg-1 were 79.2, 49.4, 24.8, 12.7, and 5.2 h, respectively. The inhibition zones widened from 10.0 (20.6 mg kg-1) to 20.6  mm (102.8 mg kg-1). Cell death through membrane damage, leakage, and DNA integrity confirmed that oxidative damage was the dominant lethal mechanism for Salmonella inactivation. Furthermore, the yield of straight grade flour from ClO2 tempered (82.2 and 102.8 mg kg-1) wheat was 1.3-3.4 % higher compared to untreated wheat. Particle size distribution of all flours remained virtually identical, with ClO2 and ClO2-1residues remaining within LOD. Tempering with ClO2 enhanced the lightness (L*) of the flour, increasing ΔL* by +2.4 to 2.9. Overall, ClO2 tempering with 82.2 mg kg-1 of wheat offered >3 log reduction within 12 h of tempering time while maintaining flour properties similar to control.