Curcumin-mediated photodynamic treatment efficiently inhibits Bacillus cereus and extends the shelf-life of flat rice noodles

The complicated challenges posed by the high prevalence of Bacillus cereus (B. cereus) and the shortened shelf life of flat rice noodles (FRN) are still not effectively solved. In this study, we explored a promising alternative of curcumin-mediated photodynamic treatment (PDT) for the inhibition of B. cereus and the preservation of FRN quality. We optimized the processing parameters of PDT for FRN sterilization, using illumination at 30000 lx, a curcumin solution at 40 μmol/L, and an exposure time of 18 min, through single-factor experiments and central composite response design.

After treatment, PDT significantly inhibited B. cereus (P < 0.05) in FRN at low and medium contamination levels both at 4 and 30 °C, reducing it to below the maximum acceptable enumeration. Moreover, PDT inhibited the rapid proliferation of B. cereus during the first 48 and 24 h at 4 and 30 °C, respectively, preventing the bacterial population from exceeding the acceptable limit for FRN. For authentic FRN samples, the results of preservation effects indicated that PDT notably inhibited the growth of hygienic indicator bacteria, putrefactive bacteria, and foodborne pathogenic bacteria during the entire storage period at 4 °C. During this bacterial guarantee period, PDT significantly slowed the accumulation of acidity and the loss of rice aroma and flavor substances in FRN. Although it mildly caused texture profile and color deterioration, the alterations remained within the acceptable range. Moreover, negligible loss of carbohydrates, proteins, and fats were observed in the PDT-treated sample. Microbiome analysis indicated that PDT reduced the relative abundance of the dominant spoilage species Lactobacillus and Lactococcus in FRN. In conclusion, PDT is an emerging non-thermal sterilization process for controlling the risk of pathogens in FRN and preserving its quality. We proposed an integrative strategy in which curcumin-mediated PDT combined with chilled storage could effectively prevent and control B. cereus contamination in FRN and enhance preservation for FRN.