Significance of UV and acidic water tempering treatments on inactivating pathogenic E. coli on hard red winter (HRW) wheat grains and whole wheat flour quality

• UV treatment alone reduced STEC by up to 2.3 logs post-exposure. • Hurdle approach showed synergism against STEC during wheat tempering. • STEC inactivation during tempering followed a concave shape. • The combined treatment did not adversely affect whole wheat flour quality. Non-thermal hurdle approaches could improve decontamination efficacy in food products without compromising quality. This study evaluated the effects of UV-C and acidic water tempering treatments in reducing the Shiga toxin-producing E. coli (STEC) contamination on wheat grains and its potential effects on the wheat flour produced. Hard red winter (HRW) wheat grains were inoculated (high: 6.4 ± 0.1 log CFU/g and low: 4.7 ± 0.2 log CFU/g) with STEC O121 / O26 and treated with UV-C (255 to 280 nm; 0 to 80 mins exposure time) alone or in combination with acidic water (5% lactic acid - LA) tempering (18 h). UV-C exposure (280 nm) from 10 – 80 mins resulted in STEC load reductions (P < 0.0001) ranging from 1.4 – 2.3 logs and 0.4 – 1.3 logs at high and low inoculation levels, respectively. Combining both acidic water tempering and UV-C (280 nm, 40 mins) resulted in an STEC load reduction of 2.3 – 3.6 logs within 12 h of tempering. The combined treatment (UV-C and LA) showed a synergistic effect (O/E ratio > 1; 1.1 – 1.3) against pathogenic E. coli as shorter times were needed (≈ 6 h) for a 3-log reduction relative to the individual treatments. This was supported by the lower (P < 0.05) predicted time required for a 3-log reduction (9.4 to 13.0 h) relative to the individual treatments (≥ 28.9 h). The LA/UV tempering treatment produced whole wheat flour with comparable color profile, particle morphology, solvent retention capacity, and pasting properties to whole wheat flour produced with conventional tempering (water). This study showed the potential of UV-C and acidic water tempering as an effective hurdle approach combination for mitigating E. coli contamination on wheat grains without affecting quality. These findings can be used as basis for addressing enteric pathogen contamination of whole wheat flour.