Optimization of low-temperature blanching combined with calcium treatment to inactivate Escherichia coli O157:H7 on fresh-cut spinach

Aims: To develop a mild blanching method with calcium salts to ensure microbiological safety and quality of fresh-cut spinach.

Methods and results: The antimicrobial efficacy of eight calcium salts was evaluated on Escherichia coli O157:H7 at 45-65°C and calcium hydroxide (Ca(OH)2 ) showed the greatest synergistic antimicrobial effect with heat. Combinations of low temperature treatments (45, 55, 65°C), time (20, 40, 60 s) and Ca(OH)2 (0·25, 0·50, 0·75%) were applied for E. coli O157:H7 disinfection on fresh-cut spinach to develop a predictive model using a Box-Behnken experimental design. A suitable quadratic model was produced (R(2) = 0·98, P < 0·001) and the optimum condition (64·9°C with 0·52% Ca(OH)2 for 42·4 s) was drawn by reducing 6·6 log CFU g(-1) of E. coli O157:H7 on fresh-cut spinach. Blanching at 61·9°C with 0·52% Ca(OH)2 for 41·7 s can inactivate E. coli O157:H7 on spinach by 5·4 log CFU g(-1) . The new method was comparable to the CDC recommendation for safe spinach cooking (71·1°C, 15 s; 5·0 log CFU g(-1) reduction) with lower levels of weight loss of the spinach (P < 0·05).

Conclusions: This study suggests an efficient spinach blanching method for E. coli O157:H7 disinfection.

Significance and impact of the study: This blanching method will enhance microbiological safety of fresh-cut produce while minimizing the use of energy and chemicals.