Xiufang Bi

High-pressure CO2 (HPCD) is a non-thermal technology that can effectively inactivate the vegetative forms of pathogenic and spoilage bacteria, yeasts, and molds at pressures less than 30 MPa and temperatures in the range of 20≡C to 40≡C. However, HPCD alone at moderate temperatures (20-40≡C) is often insufficient to obtain a substantial reduction in bacterial spore counts because their structures are more complex than those of vegetative cells. In this review, we first thoroughly summarized and discussed the inactivation effect of HPCD treatment on bacterial spores. We then presented and discussed the kinetics by which bacterial spores are inactivated by HPCD treatment. We also summarized hypotheses drawn by different researchers to explain the mechanisms of spore inactivation by HPCD treatment. We then summarized the current research status and future challenges of spore inactivation by HPCD treatment.

High hydrostatic pressure (HHP) is used for microbial inactivation in foods. Addition of carbon dioxide (CO2 ) to HHP can improve microbial and enzyme inactivation. This study investigated microbial effects of combined HHP and CO2 on Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae, and evaluated sensory attributes of treated feijoa fruit puree (pH 3.2). Microorganisms in their growth media and feijoa puree were treated with HHP alone (HHP), or saturated with CO2 at 1 atm (HHPcarb), or 0.4%w/w of CO2 was injected into the package (HHPcarb+CO2 ). Microbial samples were processed at 200 to 400 MPa, 25 °C, 2 to 6 min. Feijoa samples were processed at 600 MPa, 20 °C, 5 min, then served with and without added sucrose (10%w/w). Treated samples were analyzed for microbial viability and sensory evaluation. Addition of CO2 enhanced microbial inactivation of HHP from 1.7-log to 4.3-log reduction in E. coli at 400 MPa, 4 min, and reduction of >6.5 logs in B. subtilis (veget...

High-pressure CO2 (HPCD) is a non-thermal technology that can effectively inactivate the vegetative forms of pathogenic and spoilage bacteria, yeasts, and molds at pressures less than 30 MPa and temperatures in the range of 20≡C to 40≡C. However, HPCD alone at moderate temperatures (20-40≡C) is often insufficient to obtain a substantial reduction in bacterial spore counts because their structures are more complex than those of vegetative cells. In this review, we first thoroughly summarized and discussed the inactivation effect of HPCD treatment on bacterial spores. We then presented and discussed the kinetics by which bacterial spores are inactivated by HPCD treatment. We also summarized hypotheses drawn by different researchers to explain the mechanisms of spore inactivation by HPCD treatment. We then summarized the current research status and future challenges of spore inactivation by HPCD treatment.

ABSTRACT High hydrostatic pressure (HHP, 600 MPa/1 min) and high-temperature short-time (HTST, 110 °C/8.6 s) treatments of mango nectars were comparatively evaluated by examining their effects on natural microorganisms, acid invertase, 5-hydroxymethylfurfural (HMF), sugars, pH, titratible acid (TA), viscosity, and cloud, immediately after treatments and during 16-week storage at 4 and 25 °C. At both stages of the experiment, the counts of yeast and mold in treated mango nectars were less than 1.00 log10CFU/mL, while total aerobic bacteria were less than 1.70 log10CFU/mL. Both HHP and HTST treatments caused a significant decrease in fructose, glucose and total sugar, as well as a significant increase in HMF and cloud of mango nectars, while changes in sucrose, pH, and TA were insignificant. During the 16-week storage, however, fructose, glucose, TA and HMF increased, while sucrose, total sugar, pH and cloud decreased significantly. The kinetic data of changes in sucrose, fructose and glucose fitted well into a combined model. The activity of acid invertase was reduced by 91.4% in HTST-treated mango nectars and, increased by 8.57% after HHP treatment. In both cases, these levels remained stable during storage. There was no significant change in the viscosity in mango nectars after HHP treatment, while a significant increase after HTST treatment. Both HHP- and HTST-treated mango nectars showed a gradual decrease in the viscosity during storage. Industrial Relevance Mango (MangiferaindicaL.) is one of the important tropical fruits, and its processed products are of high commercial and economic importance. This work presents a comparison on HHP- and HTST-treated mango nectars after processing and during storage, on natural microorganisms, acid invertase, 5-hydroxymethylfurfural, sugars, pH, titratible acid, viscosity, and cloud. The available data would provide technical support for the evaluation and application of HHP or HTST in the mango nectar industry, and also for the establishment of criteria for commercial production of high quality mango nectars with safety requirements.

The effects of high pressure carbon dioxide (HPCD) treatment on natural microorganisms, indigenous enzyme activity, damage to cell membranes and hardness in fresh-cut carrot slices were investigated. 1.86log10 cycle reduction for aerobic bacteria (AB) and 1.25 for yeasts and molds (Y&M) were achieved at 5MPa and 20°C for 20min. The residual activity (RA) of peroxidase (POD), polyphenol oxidase (PPO), and

ABSTRACT The individual and combined effects of high pressure carbon dioxide (HPCD) and nisin (200 IU/mL) on the inactivation of Escherichia coli O157:H7 suspended in physiological saline (PS, pH 5.60), phosphate-buffered saline (PBS, pH 5.60 or 7.00) or carrot juice (pH 6.80) were evaluated. The pressure in this study was 5 and 8 MPa, the temperature was 25 °C–45 °C, and the treatment time was 5–65 min. Inactivation of cells in PS (pH 5.60) by HPCD followed first order kinetics, the k (the inactivation rates) increased while the D (decimal reduction time) decreased in the presence of nisin, however, the acid solution dissolving nisin rather than nisin itself played a prominent role in this combination effect with HPCD in PS buffer. The inactivation kinetics of cells in PBS (pH 5.60 or 7.00) and carrot juice (pH 6.80) by HPCD followed slow-to-fast two-stage kinetics and was fitted by the modified Gompertz equation. The M (the time at which the absolute death rate is maximum) significantly decreased in the presence of nisin. HPCD enhanced the sensitization of E. coli to nisin and the time for the complete inactivation was shortened by 2.5–5 min in PBS buffer and carrot juice by combination of HPCD and nisin (HPCD + nisin) than by HPCD alone. Regression coefficients (R2) and mean square error (MSE) were used to evaluate the model performance, indicating that the models could provide a good fitting to the experimental data.

High-pressure CO2 (HPCD) is a pasteurization method that inactivates microorganism and enzymes through molecular effects of CO2 under pressures below 50 MPa without exposing foods to adverse effects of heat. Thermal pasteurization can impart undesirable changes on organoleptic and nutritional quality of the foods, which can reduce sensory perception and consumer acceptance of the foods. As a novel nonthermal processing technique, HPCD does avoid drawbacks such as loss of flavor, denaturation of nutrients, production of side toxic reactions, as well as changes in physical, mechanical, and optical properties of the food materials involved in the processing. This review gives a survey and analysis of recent publications regarding the effects of HPCD on the flavor, texture and color of processed foods, and possible mechanisms explaining HPCD technique on the flavor, texture, and color of the foods were discussed.