低温液化二氧化碳生产技术和设备

采用低温液化工艺和技术装备，生产高纯度低压液体二氧化碳是扩大二氧化碳应用市场提高二氧化碳销量的重要措施。     

Sterol ester production using lipase-catalyzed reactions in supercritical carbon dioxide

Synthesis of sterol and stanol esters is of importance, due to their recent recognition and application in the food and nutriceutical industries as cholesterol-lowering agents. In this study, several enzymes were evaluated to determine the best catalyst and optimal conditions for the reaction between various fatty acids and cholesterol or sitostanol in supercritical carbon dioxide (SC-CO₂). Using an analytical supercritical fluid extraction (SFE) unit, the lipase derived from Burkholderia cepacia, Chirazyme L-1, was determined to be the most selective for facilitating the desired reactions. Fatty acids C₈-C₁₈, pressures between 20.7 MPa and 31 MPa, a temperature range of 40-60 °C, along with variable flow rates, and initial static hold times were used to evaluated the feasibility of the above reaction. The yield of the cholesterol esters, as measured by supercritical fluid chromatography (SFC), ranged from 90% for caprylic acid to 99% for palmitic acid, while the corresponding reaction between sitostanol and the same fatty acids produced yields of 92% for caprylic acid and 99% for palmitic acid, respectively. The extraction apparatus was modified to provide a continuous flow of the reagent fatty acid and sterol/stanol over the enzyme bed, thereby allowing continuous production of the desired esters which averaged a 99% yield under optimal conditions.     

Predictive modelling and validation of Listeria innocua growth at superatmospheric oxygen and carbon dioxide concentrations

The effect of superatmospheric oxygen and carbon dioxide concentrations on the growth of Listeria innocua, which was used as a model organism for the pathogen Listeria monocytogenes, was evaluated. The bacteria were grown on a nutrient agar surface at 7 degrees C. Three carbon dioxide levels (0%, 12.5% and 25%) were combined with different levels of high oxygen concentrations (above 20%) based on a mixture design. The applied oxygen concentrations did not significantly influence the growth. High CO2 concentrations, on the contrary, reduced the maximum specific growth rate and prolonged the lag time. An overall model to describe the growth of L. innocua under high carbon dioxide conditions was constructed based on nine growth experiments, using a weighted one-step regression procedure. The influence of carbon dioxide on lag time and maximum specific growth rate was described using Ratkowsky-type models and inserted in the Baranyi equation. The model described the growth very well. To assess the validity of the model, 14 additional experiments were carried out. There was a good correlation of the model predictions and observed validation data.     

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.     

中压法回收生产高纯度食品级液体二氧化碳的研究

分析了酒精厂二氧化碳形成机理，比较各种二氧化碳生产方法的优缺点。重点介绍中压法回收生产高纯度食品级液体二氧化碳的生产方法及压缩、净化、液化和灌装技术。     

Effects of stunning with different carbon dioxide concentrations and exposure times on suckling lamb meat quality

Forty-nine Manchega breed male suckling lambs were used to determine the effect of different stunning methods (using two different CO₂ concentrations and exposure times) on lamb meat quality. The lambs were allocated to five stunning treatments including four CO₂ treatments [80% CO₂ for 90 s (G1); 90% CO₂ for 90 s (G2); 90% CO₂ for 60 s (G3); 80% CO₂ for 60 s (G4)] and an electrically stunned control group (G5). The gas-stunning treatments did not cause neither haematomas nor blood splash in the carcasses. Meat quality was evaluated by testing pH, colour (L^∗, a^∗, b^∗, chroma, hue values), water holding capacity (WHC), cooking loss (CL), shear force (SF), drip loss (DL) and total aerobic bacteria. Statistical differences in pH at 24 h post-mortem, colour, WHC and CL were not found among groups. After 7 days post-mortem, there were statistical differences among groups in pH (highest in G4 and G5) and in DL (highest in G1). There were differences in SF due to stunning method evident after 72 h and 7 days ageing. The statistical differences (P < 0.01) among groups on total aerobic bacteria at 24 h (lower and higher values in G2 and G5, respectively) disappeared at 7 days post-mortem. As G2 as G3, could be recommended to stunning suckling lambs since a highest stability with ageing time on meat quality was found using 90% CO₂.     

Effect of different concentrations of carbon dioxide and low concentration of carbon monoxide on the shelf-life of fresh pork sausages packaged in modified atmosphere

This paper reports the effects of different concentrations of carbon dioxide and the presence of low levels of carbon monoxide on quality attributes throughout storage of fresh pork sausages. Four pork forelegs (initial pH 5.5-5.7) were used to prepare a total of 120 fresh sausages, which were packaged in different atmospheres containing (%O(2)/%CO(2)/%N(2)): 0/20/80; 0/60/40; 40/20/40; 40/60/0; 80/20/0; and 0.3% CO/30% CO(2)/rest argon. The packs were stored for 20 days at 2±1 °C in the dark. Three packs for each atmosphere were opened every 4 days for subsequent analysis of pH, colour CIE L*, a*, b*, TBARS formation, microbial psychotrophic aerobes and sensory discolouration and off-odour. Results showed that increasing concentrations of carbon dioxide promoted oxidation of both myoglobin and lipids, most probably due to its effect of lowering pH. Therefore, preservation of colour and odour of fresh pork sausages packaged in modified atmosphere was better achieved using atmospheres containing low CO(2) concentrations (20%) rather than high (60%). However, their shelf-life depended also on the concentration of O(2); 20% CO(2) with high O(2) (80%) enhanced the red colour, but shortened shelf-life, while 20% CO(2) in the absence of O(2) extended freshness to 16 days. The atmosphere containing 0.3% CO, together with 30% CO(2), maintained the red colour for 20 days, but failed to keep fresh odour longer than 16 days.     

Effect of carbon dioxide on growth and extracellular enzyme production by Pseudomonas fluorescens B52

The effect of carbon dioxide (30 mM.l-1) on growth and extracellular protease and lipase production by Pseudomonas fluorescens B52 growing in a simulated milk medium at 7 degrees C in fermenter was investigated. The addition of carbon dioxide was shown to have a differential effect with extracellular enzyme production, particularly lipase, being inhibited to a greater extent than bacterial growth and final cell numbers.     

Lactic acid production and rheological properties of yogurt made from milk acidified with carbon dioxide

The influence of milk acidification up to pH 6.0 with CO₂ on D ‐ and L ‐lactic acid production and lactose consumption by yogurt starter, changes in the pH, and rheological and sensory properties of yogurt were studied. A slight influence of CO₂ on lactic acid production during yogurt manufacture was detected. No significant changes in lactic acid concentration were observed during storage, although the final concentration was significantly lower in control than in pH 6.2 and 6.0 acidified samples. A great influence of CO₂ on D ‐lactic acid production was not observed. Yogurt manufactured from milk with lower pH values showed lower final pH values after 7 days of storage. The viscosity was similar in all analysed samples. No significant differences in sensory characteristics between unacidified and acidified yogurts were detected. © 1999 Society of Chemical Industry     

Toxin production by Clostridium botulinum in pasteurized milk treated with carbon dioxide.

The addition of carbon dioxide to milk at levels of <20 mM inhibits the growth of selected spoilage organisms and extends refrigerated shelf life. Our objective was to determine if the addition of CO2 influenced the risk of botulism from milk. Carbon dioxide was added to pasteurized 2% fat milk at approximately 0, 9.1, or 18.2 mM using a commercial gas-injection system. The milk was inoculated with a 10-strain mixture of proteolytic and nonproteolytic Clostridium botulinum spore strains to yield 10(1) to 10(2) spores/ml. Milk was stored at 6.1 or 21 degrees C for 60 or 6 days, respectively, in sealed glass jars or high-density polyethylene plastic bottles. Milk stored at 21 degrees C curdled and exhibited a yogurt-like odor at 2 days and was putrid at 4 days. Botulinal toxin was detected in 9.1 mM CO2 milk at 4 days and in all treatments after 6 days of storage at 21 degrees C. All toxic samples were grossly spoiled based on sensory evaluation at the time toxin was detected. Although botulinal toxin appeared earlier in milk treated with 9.1 mM CO2 compared to both the 18.2 mM and untreated milk, gross spoilage would act as a deterrent to consumption of toxic milk. No botulinal toxin was detected in any treatment stored at 6.1 degrees C for 60 days. At 6.1 degrees C, the standard plate counts (SPCs) were generally lower in the CO2-treated samples than in controls, with 18.2 mM CO2 milk having the lowest SPC. These data indicate that the low-level addition of CO2 retards spoilage of pasteurized milk at refrigeration temperatures and does not increase the risk of botulism from treated milk stored at refrigeration or abuse temperatures.     

Accumulation of carbon monoxide and carbon dioxide in stored canola

Production of carbon monoxide (CO) and carbon dioxide (CO(2)) from canola was studied in the laboratory and in commercial storage. Canola rapidly produced amounts of CO and CO(2) far exceeding those reported for dry cereal grain and dried peas and at levels dangerous to human health. In the laboratory, canola (5.8% m.c.) was stored in sealed flasks at 25, 35 and 45 degrees C for 12 weeks. Levels of CO, CO(2) and oxygen (O(2)) were then measured by gas chromatography. Average levels of CO and CO(2) increased with storage temperature. Levels of CO peaked at 6 weeks, exceeding 10,000 ppm v/v (1%) at 45 degrees C. CO(2) levels peaked at 11.9% after 10 weeks storage at 45 degrees C. In field measurements, CO levels in a steel bin (7000 tonne capacity) filled with canola ranged from 1100 to 800 ppm in the grain bulk before sealing, 1050-370 ppm in the grain bulk after sealing, and 290-440 ppm in the head space of the sealed bin. CO(2) concentrations were >3% in the grain bulk and averaged 1.5% in the headspace. CO production rate was estimated at 200 ng g(-1) day(-1). Canola storage poses a greater potential safety hazard than storage of cereals.     

Targeting carbon for crop yield and drought resilience

Current methods of crop improvement are not keeping pace with projected increases in population growth. Breeding, focused around key traits of stem height and disease resistance, delivered the step‐change yield improvements of the green revolution of the 1960s. However, subsequently, yield increases through conventional breeding have been below the projected requirement of 2.4% per year required by 2050. Genetic modification (GM) mainly for herbicide tolerance and insect resistance has been transformational, akin to a second green revolution, although GM has yet to make major inroads into intrinsic yield processes themselves. Drought imposes the major restriction on crop yields globally but, as yet, has not benefited substantially from genetic improvement and still presents a major challenge to agriculture. Much still has to be learnt about the complex process of how drought limits yield and what should be targeted. Mechanisms of drought adaptation from the natural environment cannot be taken into crops without significant modification for the agricultural environment because mechanisms of drought tolerance are often in contrast with mechanisms of high productivity required in agriculture. However, through convergence of fundamental and translational science, it would appear that a mechanism of sucrose allocation in crops can be modified for both productivity and resilience to drought and other stresses. Recent publications show how this mechanism can be targeted by GM, natural variation and a new chemical approach. Here, with an emphasis on drought, we highlight how understanding fundamental science about how crops grow, develop and what limits their growth and yield can be combined with targeted genetic selection and pioneering chemical intervention technology for transformational yield improvements. © 2017 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Growth and mycotoxin production by fungi in atmospheres containing 80% carbon dioxide and 20% oxygen

The effect of atmosphere containing 80% CO₂ and 20% O₂ on growth of Mucor plumbeus, Fusarium oxysporum, Byssochlamys fulva, Byssochlamys nivea, Penicillium commune, Penicillium roqueforti, Aspergillus flavus, Eurotium chevalieri and Xeromyces bisporus was investigated. Production of aflatoxin by A. flavus, patulin by B. nivea, roquefortine C by P. roqueforti, and cyclopiazonic acid by P. commune was also studied. Fungal growth was evaluated by three methods: colony diameter, hyphal length or mycelium dry weight and ergosterol content. Among the nine fungal species examined, two E. chevalieri and X. bisporus, did not grow under these conditions. In this study, fungi differed in their response to modified atmospheres in biomass, ergosterol content, mycotoxin production and morphology. Reductions of 57.8-96.9%, 73.7-99.6% and 91.5-99.9% were obtained in colony diameter, hyphal length and ergosterol content, respectively, under this atmosphere compared to air. Ergosterol content was more affected in most species than other measurements. Patulin, cyclopiazonic acid and roquefortine C were produced in this atmosphere, although levels were very low and aflatoxin was not produced at all. Growth was quite extensive as measured by colony diameters, but hyphal lengths were low and ergosterol production was also affected in all species of this study.     

初探微生物法处理农作物生产L-阿拉伯糖

L-阿拉伯糖是一种新型的功能性甜味剂,由于独特的生理功能应用于食品、医药、保健等各个领域.因此,针对L-阿拉伯糖进行介绍,并对其用微生物方法处理农作物生产L-阿拉伯糖的初步研究.通过试验研究得出以下结论:利用微生物菌株米曲霉、绿色木霉、康氏木霉3种菌处理农作物副产物玉米芯、麦秆、稻壳、花生壳后,将所得到的发酵糖液经过离心等处理后进行高效液相色谱(HPLC)和薄层层析方法检测,确定此糖液中含有目标物质L-可拉伯糖.     

Nitrogen and carbon dioxide adsorption by soils

High-resolution nitrogen (77 K) and carbon dioxide (273 K) adsorption at subatmospheric pressures has been studied for a range of model soils of various origins with different organic matter (OM) contents. It is demonstrated that N2 and CO2 molecules probe different regions of soil particles. Nitrogen is adsorbed primarily on the outer surface of soil particles, while CO2 has a higher affinity to OM domains. Low-pressure nitrogen adsorption reveals that soil particle surfaces consist of clay/mineral domains with discrete patches of OM. A linear correlation has been found between the CO2 uptake and the amount of organic carbon reduced per unit of the external surface area. A new method for discriminating the microporosity of soil particles and accessibility of OM has been proposed.     

The pros and cons of carbon dioxide dumping

Global warming concerns have stimulated a search for carbon sequestration technologies.