Effect of dissolved carbon dioxide on the sonocrystallisation and physical properties of anhydrous milk fat

The effects of dissolved CO₂ (0–2000 ppm) coupled with ultrasound (US; 20 kHz) on the physical properties of anhydrous milk fat (AMF) were examined. Carbonated AMF was sonicated at 28 °C for 5 s at various amplitudes and subjected to isothermal (28 °C) and non-isothermal (cooling from 28 to 5 °C) crystallisation conditions. AMF microstructure, thermal properties and hardness were evaluated after 48 h of storage. In general, carbonated AMF samples treated with the same US amplitude exhibited a slight decrease in endset-melting temperature, smaller fat crystals with denser fat crystal network. Dissolved CO₂ caused harder texture of sonicated AMF at 25 °C. However, when carbonated + sonicated AMF samples was stored at 5 °C, their texture appeared to be softer than that of the control sample. A protective effect of CO₂ against formation of primary oxidative products during 90 days of storage was evidenced in both non-sonicated and sonicated AMF.     

Inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide

This study assessed the inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide (HPCD) at 10–30 MPa and 20–50 °C for 20–70 min. The log reduction of microorganisms increased as raw bovine milk was exposed to higher pressures and temperatures and longer treatment times. The maximum reduction of aerobic bacteria (AB) was 4.96‐log at 25 MPa and 50 °C for 70 min. At lower temperatures and treatment times, a complete inactivation of yeasts and moulds (Y&M) and coliform bacteria (CB) was obtained at 25 MPa. Changes in microorganisms naturally present in raw bovine milk during storage were also assessed. There were 1.83‐log survival of AB, 0.65‐log survival of Y&M and a complete inactivation of CB in raw bovine milk when subjected to HPCD at 25 MPa and 40 °C for 50 min. Moreover, the AB, Y&M and the CB in raw bovine milk exhibited insignificant alterations during storage at 4 °C for 15 days, indicating a potential capability of HPCD to extend the shelf life of milk.     

Effect of carbon dioxide on the inactivation of florida spiny lobster polyphenol oxidase

Florida spiny lobster (Panulirus argus) polyphenol oxidase (PPO) exposed to CO₂ (1 atm) at 33, 38, and 43°C showed a decrease in enzyme activity with increased heating time. Enzyme inactivation by CO₂ was faster for PPO heated at 43 than at 33 or 38°C. Inactivation kinetics revealed PPO was more labile to CO₂ and heat in the range 33–43°C than to heat alone. Kinetic data also revealed that CO₂, in addition to pH changes, was involved in the loss of PPO activity. Studies using get electrophoresis showed no differences in protein patterns and isoelectric point between CO₂-treated and non-treated control. The pH of CO₂-treated PPO stock solution was brought back from 5.4 to 8.0 after 6 weeks of frozen-storage and no enzyme reactivation was observed.     

Effect of carbon dioxide on improving the keeping quality of raw milk

Fresh cows' milk samples were treated with CO₂ to give a calculated CO₂ content of 77mM. The treated samples as well as the control were stored at 7° and 20 ± 5°C for three days and analysed periodically. The increase in the total count as well as the counts of psychrotrophic, lactic acid and coliform bacteria during storage at 7°C was found to be inhibited by the addition of CO₂. The treated samples had higher titratable acidity and lower pH values than the controls but satisfied the clot-on-boiling test. The keeping quality of cooled milk can therefore be improved by the addition of CO₂.     

High pressure carbon dioxide inactivation of microorganisms in foods: the past, the present and the future

Thermal pasteurization is a well known and old technique for reducing the microbial count of foods. Traditional thermal processing, however, can destroy heat-sensitive nutrients and food product qualities such as flavor, color and texture. For more than 2 decades now, the use of high-pressure carbon dioxide (HPCD) has been proposed as an alternative cold pasteurization technique for foods. This method presents some fundamental advantages related to the mild conditions employed, particularly because it allows processing at much lower temperature than the ones used in thermal pasteurization. In spite of intensified research efforts the last couple of years, the HPCD preservation technique has not yet been implemented on a large scale by the food industry until now. This review presents a survey of published knowledge concerning the HPCD technique for microbial inactivation, and addresses issues of the technology such as the mechanism of carbon dioxide bactericidal action, the potential for inactivating vegetative cells and bacterial spores, and the regulatory hurdles which need to be overcome. In addition, the review also reflects on the opportunities and especially the current drawbacks of the HPCD technique for the food industry.     

Effect of carbon dioxide on the growth of Bacillus cereus spores in milk during storage

The effects of the addition of 11.9 mM CO2 on the growth of Bacillus cereus spores inoculated into sterile homogenized whole milk at 101 and 106 spores/ml and stored at 6.1 degrees C, was examined weekly for 35 d. Colony-forming units from CO2 treated inoculated milks decreased over 35 d at a rate similar to that of untreated inoculated milk, as defined by linear regression. Plate counts for treated and control milks inoculated at 10(1) cfu/ml were not significantly different on sampling d 0, 14, 21, and 28. Plate counts at d 7 were significantly different and counts at d 35 were at undetectable levels for both treated and control milks. Plate counts for milk inoculated at 10(6) cfu/ml were not significantly different on d 0, 28, and 35; they were significantly different on d 7, 14, and 21. There was no consistency as to whether the control or test milks were higher in counts on days when the differences were significant. Added CO2 reduced the pH of the milk from an average value of 6.61 to an average value of 6.31; however, this drop did not correlate with changes in any other parameter measured. These data suggest that moderate levels of CO2 do not enhance the outgrowth of B. cereus spores over long-term storage and do not increase the risk of foodborne illness due to the organism.     

高压二氧化碳杀菌机理研究进展

高压二氧化碳（HPCD）技术作为一种新型非热杀菌技术,越来越受到研究者的关注,但目前对其杀菌机理尚未明确。本文分析了目前国内外有关HPCD杀菌机理的研究进展,并分析了HPCD对微生物细胞内几个作用靶点包括细胞壁、细胞膜、细胞质、蛋白质、酶和核质的影响,以期为进一步研究和应用提供理论依据。     

CO2对乳性质的影响及在乳品杀菌中的研究进展

综述了在不同条件下，在牛乳中充入CO2，同时与未处理的原料乳做对照。通过对牛乳蛋白和脂肪的水解情况、细菌的生长参数、CO2注入温度对牛乳pH值和冰点的影响等方面研究CO2对牛乳的处理效果。结果表明，经CO2处理的牛乳具有很好的抑菌效果，尤其在低温条件下，能够有效抑制乳中细菌的生长，保证乳品的质量，延长乳制品的货架期，具有很好的市场前景。     

High carbon dioxide pressure inactivation kinetics of Escherichia coli in broth

The inactivation kinetics of Escherichia coli by high pressure carbon dioxide was investigated. Inactivation rates increased with increasing pressure (25, 50, 75 and 100 atm), temperature, and exposure time. Microbial inactivation followed first order reaction kinetics, with inactivation rates (k) and decimal reduction times (D) that varied from 0·0848 to 0·4717 min⁻¹and from 4·90 to 27·46 min, respectively, at treatment temperatures (20, 30 and 40°C). The inactivation rates of E. coli were described by the apparent activation volume (ΔV^*) and a ‘pressure z value’, and they were greatly dependent on both temperature and pressure.     

High pressure inactivation of microorganisms inoculated into ovine milk of different fat contents

High hydrostatic pressure inactivation of Escherichia coli, Pseudomonas fluorescens, Listeria innocua, Staphylococcus aureus, and Lactobacillus helveticus were studied. These microorganisms were inoculated at a concentration between 10(7) and 10(8) cfu/ml in Ringer solution and in ovine milk adjusted to 0, 6, and 50% fat content to evaluate the baroprotective effect of fat content on inactivation of microorganisms. Treatments of pressurization consisted of combinations of pressure (100 to 500 MPa) and temperature (4, 25, and 50 degrees C) for 15 min. Gram-negative microorganisms were more sensitive than were Gram-positive ones (more destruction P. fluorescens > E. coli > or = List. innocua > Lb. helveticus > S. aureus). Pressurizations at low temperature (4 degrees C) produced greater inactivation on P. fluorescens, List. innocua, and Lb. helveticus than at room temperature (25 degrees C), whereas for E. coli and S. aureus the results were opposite. Ovine milk per se (0% fat) showed a baroprotective effect on all microorganisms, but percentage of fat (6 and 50%) did not show a progressive baroprotective effect in all pressurization conditions or for all microorganisms.     

超高压处理对泡豇豆杀菌效果的影响

为了探求超高压杀菌在四川泡菜工业中的应用,提高其微生物安全,以泡豇豆为供试材料,研究了泡豇豆含盐量、处理压力、处理时间对超高压杀菌效果的影响,并考察了超高压处理对泡豇豆保藏性能的影响。实验结果表明:含盐量为4.2%的泡豇豆超高压杀菌效果优于含盐量6.7%,超高压技术更适用于低盐泡菜的杀菌;压力越大、处理时间越长,微生物致死率越高,但压力较时间对杀菌效果的影响更大;对样品分别采用300、400MPa处理30min,菌落总数降低的对数为5.45、5.52,且均无霉菌和酵母菌检出;300～400MPa处理可以使大肠菌群数有效得到降低,且能有效提高泡豇豆的保藏性能。     

Determination of thermal inactivation kinetics of microorganisms with a continuous microflow apparatus

Use of a continuous microflow submerged microcoil (CSMC) apparatus was compared with the capillary tube (CT) method for measuring the thermal inactivation kinetics of Pseudomonas fluorescens at 61 degrees C for 3 to 29 s. Inocula were continuously pumped through a microbore (< or = 0.0762 cm inside diameter) thin-walled stainless steel capillary tube submerged in a heated oil bath. The heating time was set by changing the flow rate, tube dimensions, or both. With the use of microthermo-couples, the time for the inocula to reach within 1 degree C of the set temperature was <3 s, and shorter than that with capillary tubes or vials. Inactivation curves (61 degrees C) for P. fluorescens prepared by the CSMC method were not different from curves prepared by the CT method, as determined by analysis of variance (P > 0.05). Inactivation of Bacillus cereus spores (105 degrees C) and native microflora found in raw milk (72 degrees C) over heating times of 3 to 42 s were determined by CSMC. CSMC can measure thermal inactivation kinetics of microorganisms efficiently and simply at high temperatures and in short times. Survivors can be enumerated in 1-ml volumes of heat-treated samples, making it useful for determining inactivation kinetics of low numbers of microorganisms, such as those found in high-quality raw milk. Inactivation kinetics were generally more accurately described by the Weibull function (R2 > or = 0.97) than the linear kinetic model.     

Mathematical modeling of Escherichia coli inactivation under high-pressure carbon dioxide

Inactivation curves of Escherichia coli under high carbon dioxide pressures (2.5, 5.1, 7.6 and 10.1 MPa) at different temperatures (20, 30, 40 and 45 degrees C) were analyzed using the modified Gompertz model. The phase disappearance (time for complete inactivation of all cells, lambda) and the inactivation rate (mu) of E. coli were inversely related. Inactivation rates (mu) of E. coli were higher at 45 degrees C under 10.1 MPa CO2 pressure than at 25, 30 and 40 degrees C under 2.5, 5.1 and 7.6 MPa CO2 pressure. Increased pressure and temperature had significant effects on the survival of E. coli. The temperature dependence of the inactivation rate constant was analyzed based on the Arrhenius, linear and square-root models. The temperature sensitivity (high E(mu)) determined based on the Arrhenius model was higher at high temperatures. E(mu) (activation energy) value was -186.56 Kjoule/mol at 10.1 Mpa, and -137.24, -167.25 and -183.80 Kjoule/mol at 2.5, 5.1 and 7.6 MPa, respectively. Results of this study enable the prediction of microbial inactivation exposed to different CO2 pressures and temperatures.     

Mathematical modeling of Saccharomyces cerevisiae inactivation under high-pressure carbon dioxide

High-pressure carbon dioxide inactivation curves of Saccharomyces cerevisiae at different temperatures were analysed using the modified Gompertz model. Comparable lambda and mu values were obtained under pressure treatment as function of temperature. The phase of disappearance (lambda) and the inactivation rate (mu) of S. cerevisiae were inversely related. Higher mu values were obtained at 50 degrees C than at 40, 30 and 20 degrees C under 10.0 MPa CO2 pressure. Increased pressure and temperature had significant effects on the survival of S. cerevisiae. Arrhenius, linear and square-root models were used to analyse the temperature dependence of the inactivation rate constant. For the Arrhenius model the activation energy (E(mu)) was 56.49 kJ/mol at 10.0 MPa, and 55.70, 53.83 and 52.20 kJ/mol at 7.5, 5.0, and 2.5 MPa, respectively. Results of this study enable the prediction of yeast inactivation exposed to different CO2 pressures and temperatures.     

Titanium dioxide (TiO2) photocatalysis technology for nonthermal inactivation of microorganisms in foods

BackgroundMicrobial contamination is a serious challenge in the food industry. With the increasing demand for fresh, nutritious and healthy food, novel techniques for microbial inactivation are highly needed. By absorbing photoenergy, titanium dioxide (TiO₂) based photocatalyst can produce reactive oxygen species (ROS) that are capable of inactivating microorganisms.Scope and approachThis review summarizes recent research developments of TiO₂ photocatalysis (TPC) for antibacterial applications in liquid, gas and solid systems in the food industry. Basic principles of TPC, the mechanism of photocatalytic inactivation, and strategies for improving photoactivity are described, and applications of TPC for decomposing organic substances are presented. Furthermore, applications of combining TPC with other technologies are also discussed.Conclusionsand key findings: The review shows that TPC technology has the ability to inactivate foodborne microorganisms, but with some drawbacks such as catalyst deactivation and low utilization of visible light. Modification can widen the light response into visible range and improve the photoactivity. The combined technologies can enhance the effectiveness of microbial inactivation. However, further study is still needed to improve both photocatalytic disinfection efficiency and food quality maintenance.     

Extraction of ewe's milk cream with supercritical carbon dioxide

The extraction of ewe's milk cream by supercritical carbon dioxide in the pressure range 9–30 MPa (90–300 bar) and at temperatures of 40 °C and 50 °C was studied. The solubility of total fat increased with pressure at both temperatures until a plateau was reached. The extraction of cholesterol also increased with pressure until a plateau was reached and it was higher at 50 °C than at 40 °C when the pressure was ≥15 MPa (150 bar). The triglyceride composition of each extract, determined by GC, showed that extracts obtained at lower pressures were enriched in short-chain triglycerides and their concentration decreased as the pressure increased. In the other hand, long-chain triglycerides were enriched in the extracts obtained at higher pressures and their concentration rose with increasing pressure.     

牛乳液酪蛋白的CO2沉淀分离

以CO2为沉淀剂,从牛乳液中分离酪蛋白,考察了牛乳液浓度、CO2压力和温度对酪蛋白产率的影响.结果表明,在相对低温的条件下,用低压CO2处理低浓度牛乳液,可能得到较高的酪蛋白产率.据此提出了可供参考的牛乳酪蛋白分离工艺条件:牛乳液浓度为1/40纯乳;CO2压力为0.5MPa;温度为10～25℃.     

预测微生物学在高压二氧化碳杀菌动力学的应用进展

高压二氧化碳(HPCD)技术是目前越来越受关注的非热杀菌技术之一。目前有关HPCD杀菌预测模型的研究报道较少。利用食品预测微生物学方法和理论,通过研究各个因素对HPCD杀菌过程的影响,建立预测模型和回归方程,可以更好的理解HPCD杀菌动力学及机理,提高其杀菌效果,确保食品安全。本文就食品预测微生物学在HPCD杀菌动力学研究中的应用进行综述分析,并提出未来可能的研究方向。