The effects of carbonation treatment (1 to 5 MPa, 30 min) plus heat treatment (30 to 80°C, 30 min) in the presence of various fatty acid esters (FAEs; 0.05 and 0.1%, wt/vol) on counts of viable Bacillus subtilis spores were investigated. FAEs or carbonation alone had no inactivation or growth inhibition effects on B. subtilis spores. However, carbonation plus heat (CH; 80°C, 5 MPa, 30 min) in the presence of mono- and diglycerol fatty acid esters markedly decreased counts of viable spores, and the spore counts did not change during storage for 30 days. The greatest decrease in viable spore counts occurred in the presence of monoglycerol fatty acid esters. Under CH conditions, inactivation and/or growth inhibition occurred at only 80°C and increased with increasing pressure. The greatest decrease in spore counts (more than 4 log units) occurred with CH (80°C, 5 MPa, 30 min) in the presence of monoglycerol fatty acid esters. However, this treatment was less effective against Bacillus coagulans and Geobacillus stearothermophilus spores.

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The effects of carbonation with heating (CH) on germination of Bacillus subtilis spores were investigated. Treatment conditions for CH and heat treatment alone were set to obtain an approximate 1 log reduction in viable count. Pre-treatment of spores with CH at 80℃ and 5 MPa for 30 min significantly decreased their heat resistance to a subsequent heating process at 90℃ for 30 min, as compared with pretreatment by heat alone at 90℃ for 30 min. Treatment with CH also decreased refractility and enhanced DAPI staining when compared with heat treatment alone, thus suggesting that CH effectively initiates and stimulates germination of B. subtilis spores.

Deterioration of food quality and freshness is mainly due to microbial growth and enzyme activity. Chilled fresh food, especially meat and seafood, as well as pasteurized products, rapidly lose quality and freshness during packing, distribution and storage. Real‐time food quality monitoring using on‐package indicator films can help consumers make informed purchasing decisions. Interest in the use of intelligent packaging systems for monitoring safety and food quality has increased in recent years. Polysaccharide‐based films can be developed into on‐package indicator films due to their excellent film‐forming properties and biodegradability. Another important component is the use of colorants with visible color changes at various pH levels. Currently, natural pigments are receiving increased attention because of their safety and environmental friendliness. This review highlights the recent findings regarding the role of natural pigments, the effects of incorporating natural pigments and polysaccharides on properties of indicator film, current application and limitations of on‐package indicator films based on polysaccharides in some foods, problems and improvement of physical properties and color conversion of indicator film containing natural pigments, and development of polysaccharide‐based pH‐responsive films. © 2022 Society of Chemical Industry.

The heat inactivating effect of low-pressure carbonation (LPC) at 1 MPa against Escherichia coli was enhanced to 3.5log orders. This study aimed to investigate the mechanisms of this increase in heat inactivation efficiency. The increased inactivation ratio was found to be the result of LPC-induced heat sensitization. This sensitization was not due to any physical damage to the cells as a result of the treatment. Following the depletion of intracellular ATP, the failure of the cells to discard protons caused an abnormal decrease in the intracellular pH. However, in the presence of glucose, the inactivation ratio decreased. In addition, a further increase in inactivation of more than 2log orders occurred in the presence of the protein synthesis inhibitor chloramphenicol. Hence, the decreased heat resistance of E. coli under LPC was most likely due to a depletion of intracellular ATP and a decreased capacity for protein synthesis.

This study aimed to evaluate the synergistic effects of nisin combined with cinnamaldehyde (Nis+Cin) and nisin combined with carvacrol (Nis+Car) on food-borne bacteria. The minimum inhibitory concentrations for Nis, Cin and Car ranged from 2,500 to 10,000 IU/mL, 0.78-6.25 mg/mL and 0.78-3.13 mg/mL, respectively. Nis+Cin displayed a total synergism against all test bacteria, showing a marked release of bacterial intracellular constituents. In a food model, high protein concentration, low starch and oil concentration as well as low pH, positively influenced the antimicrobial activity. Moreover, in sandwich spread, Nis+Cin enhanced the inhibition of S. typhimurium at the greatest level by reducing cell numbers by more than 4 log CFU/g from 6 days of storage. These results suggest that the dose used for each antimicrobial compound can be minimized by combination, thereby decreasing the possibility of antimicrobial resistance and also reducing food processing costs.

Effect of low-pressure carbonation (LPC) on heat inactivation of yeast and bacterial vegetative cells was investigated. Microbial cell suspensions were carbonated at 0.6 MPa and 12℃ for 15 min and subsequently heated for 1 min at temperatures ranging from 50℃ to 70℃ at 1 MPa. As a control experiment, suspensions were heat treated for 1 min under atmospheric pressure without LPC. The heat inactivation effect on yeast was not significantly changed by LPC; however, the heat inactivation efficiency on several bacteria was enhanced. The promoted inactivation was also observed for heat treatment under atmospheric pressure after LPC. The enhanced inactivation was not notable by heat treatment followed by LPC. The results suggest enhanced heat inactivation against bacteria under LPC, and the increased heat inactivation of bacteria may be due to LPC-mediated sensitization to heat.

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