Optimization for Synergistic Effects of Combined Chlorine and Sonication on Bacillus cereus in Dried Laver Using a Predictive Reduction Model

Introduction: Dried laver (Porphyra tenera) is widely consumed in Korea and Japan. It is an important seaweed that is high in minerals and vitamins and has considered nutritional value and a pleasing taste to the people in two countries.  However, 12.0% of Bacillus cereus was detected in Korean dried laver and thus this pathogen is an emerging seafood pathogen with public significance. Combined treatment of chlorine and sonication can be potentially used in the seafood industry to reduce B. cereus for food preparation and manufacturing.

Purpose: This study was conducted to investigate the optimization for synergistic effects of combined chlorine and sonication for the reduction of B. cereus in dried laver using a mathematical predictive reduction model. 

Methods: The combination treatment of chlorine concentrations (0-200 ppm) and sonication time (0-100 min) at 1,200 W and 36 kHz was arranged by central composite experiment design (CCD). The Polynomial models were developed for predicting reduction values of B. cereus in dried laver by combined chlorine disinfection and sonication. Hunter “L” was measured by color difference meter. 

Results: The polynomial equation predicting the inactivation of B. cereus was as follows: Y = 0.001+0.006 X₁ -  0.013 X₂ - 1.8E-05X₁X₂ + 4.8E-05X₁²+ 1.1E-05X₂² (X₁: sonication time, X₂: chlorine concentration). The predictive reduction models by response surface methodology were fit well (R² = 0.9998) and expressed as adequate models by Prob > F-value (P < 0.0001). The optimized effect of combined chlorine and sonication for the reduction of B. cereus in dried laver was predicted at 57 ppm of chlorine and 10 min of sonication.  The reduction value was 1.8 log CFU/g.  There was no significant difference of Hunter “L” (lightness) between no treatment dried laver and combined chlorine and sonicated dried laver. 

Significance: Using a mathematical prediction model, combined treatment of 57 ppm of chlorine and 10 min of sonication provides an effective reduction of B. cereus in dried laver without changes in color.