Correlations between growth parameters of spoilage micro-organisms and shelf-life of pork stored under air and modified atmosphere at -2, 4 and 10 degrees C

The correlations of the growth parameters (the initial cell number (N(0)), maximum cell number (N(max)), maximum specific growth rate (mu(max)), lag-phase (lambda)) of typical spoilage micro-organisms (lactic acid bacteria (LAB), coliforms, pseudomonads, Brochothrix thermosphacta) growing on sliced pork to the sensory shelf-life and microbial shelf-life were investigated. The changes in sensory quality and proliferation of micro-organisms on pork shoulder were studied at different atmosphere conditions (air and 40%CO(2)/59%N(2)/1%O(2)) and temperatures (-2, 4 and 10 degrees C). Microbial counts were fitted to the modified-Gompertz equation to obtain the growth parameters of different micro-organisms. B. thermosphacta and coliforms were predominant bacteria associated with spoilage of pork under all temperatures and air conditions. However, pseudomonads could only dominate under regular atmosphere condition. Using multiple linear regression, high correlations were found between the lag-time (lambda) of LAB (0.9814, 0.9830), B. thermosphacta (0.9895, 0.9849), or the maximum specific growth rate (mu(max)) of coliforms (-0.9583, -0.9695) and the microbial shelf-life and sensory shelf-life, respectively. The mu(max) and lambda of micro-organisms correlated well with microbial and sensory shelf-life. The shelf-life of pork is mainly correlated with the growth parameters of mu(max) and lambda than by N(max).     

Real-time viable-cell mass monitoring in high-cell-density fed-batch glutathione fermentation by Saccharomyces cerevisiae T65 in industrial complex medium

An on-line monitoring of viable-cell mass in high-cell-density fed-batch cultivations of Saccharomyces cerevisiae grown on an industrial complex medium was performed with an in situ capacitance probe fitted to a 50-l fermentor. Conventional off-line biomass determinations of several parameters, including dry cell weight (DCW), optical density at 600 nm wavelength (OD(600)), packed mycelial volume (PMV) and number of colony forming units (CFU), were performed throughout the bioprocess and then compared with on-line viable-cell concentrations measured using a capacitance probe. Capacitance versus viable biomass and all off-line biomass assay values were compared during glutathione fermentation in industrial complex culture media. As a result, the relationship between the number of colony forming units and capacitance with a correlation coefficient (R) of 0.995 was achieved. Simultaneously, compared with those determined by at-line indirect estimation methods including oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER), the specific growth rates estimated by on-line capacitance measurement could be more reliable during glutathione fermentation. Therefore, it is concluded that a capacitance probe is a practical tool for real-time viable biomass monitoring in high-cell-density fed-batch cultivation in a complex medium.     

Production of intracellular phytochemicals in Chlorella under heterotrophic conditions

A heterotrophic synchronous culture (HSC) of Chlorella regularis S-50, a strain with a high growth rate, and one for its mutant were established by alternately culturing for 6 h on medium containing glucose and for 3 h on medium without glucose. The changes in cellular components and respiratory activity during the course of cell cycling in the HSC were investigated. The synchronized daughter cells (small cells) produced by the HSC contained 2-3 times as much intracellular phytochemicals (carotenoids, chlorophyll, tocopherols, and others typical of green plants) as the glucose-metabolizing cells or the non-synchronous cell mass. To attain the HSC at high cell density, the effects of glucose and oxygen on growth rate, synchronous growth, and production of intracellular phytochemicals were revealed. During the increase in cell mass, when a glucose concentration of 0.5-10 g l(-1) in the culture fluid was maintained by glucose feeding, and the (Qo2)(max) in cells was kept constant by supplying oxygen, cell mass increased synchronously with a specific growth rate, mu, of over 0.2 h(-1). In the HSC, when the late glucose-metabolizing cells were aerated by supplying oxygen to maintain over a half of the (Qo2)(max) under glucose-deficient conditions, intracellular phytochemicals increased rapidly in parallel with cell division. On the basis of these results, the HSC system at high cell density was attained by a glucose-limited fed-batch culture that involves three controlled conditions; glucose concentration, glucose feeding time, and oxygen supply. The system maintained synchronous growth for more than three generations until the cell density reached about 90 g l(-1) with a mu of 0.2 h(-1). In the HSC system, synchronized daughter cells were obtained at a cell productivity of 84 g l(-1) (30 h)(-1). The cell yield for glucose was 0.45. A weight of 100 g of dry cells contained 710 mg carotenoids, 350 mg lutein, 50 mg alpha-carotene, 60 mg beta-carotene, 3.3 g chlorophylls, 23 mg tocopherols, and others, with 63 g of protein rich in essential amino acids. Industrial-scale HSC systems made it possible to steadily produce Chlorella, containing 10-50 times as much phytochemicals as green and yellow vegetables, regardless of the weather.     

Effect of aeration and agitation on growth rate of Thermus thermophilus in batch mode

The growth kinetics of Thermus thermophilus HB27 was investigated in rich medium (Thermus medium) under batch cultivation at 65 degrees C in 3-l fermentors. The growth and oxygen consumption rates were highly dependent on the aeration and agitation rates. Volumetric mass transfer coefficient (K(L)a, h(-1)) and hence oxygen transfer rate (OTR, mol m (-3) h(-1)) into the fermentation broth increased with increased aeration and/or agitation rates. A K(L)a and OTR of 175.4 h(-1) and 31.7 mol m(-3)h(-1) respectively, corresponding to 500 rpm agitation and 2 vvm aeration with a mixture of air and oxygen, were required to avoid oxygen limitation. The maximum growth rate (mu(max), h(-1)), doubling time (t(D), h), and dry cell weight determined for T. thermophilus HB27 growing under these conditions were 0.27 h(-1), 2.67 h, and 3g/l respectively. This cell yield is higher than any previously published reports for growth of Thermus cultures, including studies that employed pressurized bioreactors.     

Alteration of cellular metabolism by consecutive fed-batch cultures of mammalian cells

The metabolism of myeloma cells was altered to reduce lactate production in consecutive fed-batch cultures. The glucose concentration was maintained at low levels (0.28-0.55 mM) by employing a dynamic nutrient feeding method based on on-line measurement of the oxygen uptake rate (OUR) to estimate the metabolic demand of the cells. This strategy has been previously reported to be applied to cultures of hybridoma cells, in which the production of lactate was significantly reduced by thus maintaining the glucose concentration at low levels. However, for this cell line, a single fed-batch culture was not sufficient to alter the cellular metabolism, even at a glucose concentration of 0.28 mM. Two consecutive fed-batch cultures were employed to ensure that the cells were cultivated under a low glucose concentration for a sufficiently prolonged period of time to allow a switch of the cellular metabolism from a glycolytic (high lactate production) to oxidative (low lactate production) state.     

Growth of Salmonella choleraesuis subspecies diarizonae serovar 61:k:1,5,(7) in broth and fresh mutton

Three serovars of Salmonella choleraesuis (IIIb 61:k:1,5,(7), Enteritidis and Dublin) were grown in broths of pH 5.5 and 6.2 and incubated at 4, 6, 8 or 12 degrees C. Growth in the broth, measured by means of an increase of absorbance, was not observed below 8 degrees C. At 8 and 12 degrees C, the maximum growth rate (mu(max)), lag period and maximum absorbance level (max(abs)) varied according to serovar and pH. In general, serovar IIIb 61:k:1,5,(7) and serovar Enteritidis grew better than serovar Dublin. The effect of pH on lag period, seen for serovar IIIb 61:k:1,5,(7) and serovar Enteritidis at 8 degrees C, was absent at 12 degrees C, while the effect of pH regarding the mu(max) and the max(abs) was observed also at 12 degrees C. Furthermore, the growth serovar IIIb 61:k:1,5,(7) in normal and dark, firm and dry meat at 8 degrees C with ambient air in competition with the natural microbial flora was tested in minced meat and chops. Slow growth of serovar IIIb 61:k:1,5,(7) was observed in minced meat. The low virulence and the ordinary growth capabilities indicate that serovar IIIb 61:k:1,5,(7) will probably not represent a serious hazard to the public health.     

Modelling the effect of ethanol on growth rate of food spoilage moulds

The effect of ethanol (E) on the radial growth rate (mu) of food spoilage moulds (Aspergillus candidus, Aspergillus flavus, Aspergillus niger, Cladosporium cladosporioides, Eurotium herbariorum, Mucor circinelloides, Mucor racemosus, Paecilomyces variotii, Penicillium chrysogenum, Penicillium digitatum, Rhizopus oryzae and Trichoderma harzianum) was assessed in Potato Dextrose Agar (PDA) medium at a(w) 0.99, 25 degrees C. In order to model this effect, the Monod type equation described previously by Houtsma et al. (Houtsma, P.C., Kusters, B.J.M., de Wit, J.C., Rombouts, F.M., Zwietering, M.H., 1994. Modelling growth rates of Listeria monocytogenes as a function of lactate concentration. Int. J. Food. Microbiol. 24, 113-123.) was re-parameterised: mu = mu(opt)[K(E(max)-E)/K E(max)-2KE+E(max)E]; E(max) (%, wt/wt): ethanol concentration at which no growth occurs, K (%, wt/wt): ethanol concentration at which mu = mu(opt)/2, mu(opt) (mm day(-1)): growth rate at 0% ethanol. The model was capable of describing curves, mu vs. E, with either a concave shape (KE(max)/2) with a good accuracy (root mean square error (RMSE) < or = 0.136) with the notable exception of R. oryzae and T. harzianum. After growth rate data were square-root transformed to stabilise the variance, E(max) was estimated in the range 3% to 5% for all moulds with the exception of T. harzianum (E(max) 2.14%) and P. variotii (E(max) 6.43%). Ethanol would appear an effective additional barrier to inhibit fungal growth in food products and would represent an interesting alternative to the use of preservatives.     

The search of antioxidants in plant root's extracts of the carline thistle

The carrying out tests of water-extracts of carline thistle (plant pink, Caryophyllaceae) in Kazakhstan (extract 1) and gathered in the Primorye region (extract 2). The method of spectral and thin layer chromatography silicagel plates contain phenolys components. It is found out that both extracts contain the same bonds with the max, uptake of long waves lambda = 282 hm and lambda = 260 hm. Besides, extract 2 has significant quantity of substances with the max, uptake lambda = 272 hm and substance with the max, uptake lambda = 330 hm. When determining with the help of standard tap the chemical nature of the substances, which have antioxidant characteristics, we settled out that antioxidant of soapwort possibly can be coffee acid and nonpolar flavonoid of unstated nature.     

Consumption of oxygen by the muscles of beef animals and related species. II. Consumption of oxygen by post-rigor muscle

The oxygen consumption rate (o.c.r.) of post-rigor beef muscle, unlike the pre-rigor o.c.r., is virtually unaffected by the degree of comminution of the muscle. It has a constant enthalpy of activation (ΔH*) of 18.2 ± 0.3 kcal/mol, which is nearly double the value for pre-rigor muscle and is close to the enthalpy of activation of the mitochondrial NAD⁺-linked oxidation of pyruvate (～19 kcal/mol). The latter mitochondrial rate (m.r.) appears to be the step which determines the post-rigor o.c.r., unlike the pre-rigor state where the rate of turnover of ATP (a.t.r.) is rate-determining, except below 15 °C. This is because the potential post-rigor a.t.r. is too high for the mitochondrial electron-transport chain to keep pace with it under the prevailing conditions of low pH. The post-rigor o.c.r. can be doubled at all times of storage up to 6 weeks by addition of an ATP supplement. The o.c.r. declines exponentially from the second day of storage onwards and reaches about 10% of its initial level after about 6 weeks storage of the muscle at 2 °C. This is shown to parallel the decline in the m.r. on storage and is evidently due to partly irreversible impairment of mitochondrial function and not to loss of NAD⁺. The respiratory quotient (r.q.) in the post-rigor state is 1.0 at low pH and falls to ～0.5 on raising the pH to 7.2, due to initial production and subsequent oxidation of α-glycerol phosphate and pyruvate in equal amounts. There are species differences in the magnitude of the post-rigor o.c.r., possibly due to differing mitochondrial contents. The exponential decay of the o.c.r. during storage goes far to explain the increasing depth of penetration of the oxymyoglobin layer which forms on exposing a surface of meat to air or oxygen and which gives the exposed meat an attractive bright red appearance.     

High level secretion of recombinant human serum albumin by fed-batch fermentation of the methylotrophic yeast, Pichia pastoris, based on optimal methanol feeding strategy

The dynamic programming method was applied to obtain the optimal specific growth rate, mu, in the fed-batch fermentation using the recombinant human serum albumin (rHSA)-producing yeast, Pichia pastoris. Based on the relationship between the specific production rate, varrho, and the specific growth rate, mu, a simple mathematical model describing the growth and rHSA production was constructed and used for calculations. Two constraints, final volume and maximum methanol feed rate, were adopted for calculations and the optimal mu resulted as follows. That is, mu was initially at the maximum value, mu(max), then decreased gradually. Finally, mu decreased to the mu(min) that gave a maximum varrho. The decline of mu was revealed to be caused by the constraint for maximum methanol feeding rate, F(max), and F(max) was constant until mu decreased to mu(min). We tried to realize the optimal mu in the fed-batch fermentation by manipulating the methanol feeding rate and obtained it. However, the observed varrho was differed from the expected one. The discrepancy between the expected varrho and observed varrho after the change of mu suggests the inapplicability of the relationship between mu and varrho to dynamic situations where mu changes. To confirm this, simulation and fed-batch fermentation runs were carried out at a methanol feeding rate that would cause a continuous change in mu. The rHSA production was simulated well, suggesting the applicability of the relationship between mu and varrho in such situations. Discontinuity in the change in methanol feeding rate of the optimal feed pattern at the time mu changed is considered to be the cause for the discrepancy between the expected and observed varrho. Therefore, a new methanol feeding strategy that could mimic the changes in mu and varrho of the optimal strategy without a discontinuity in the feeding rate was sought using a mathematical model of fermentation by trial and error. This modification in the methanol feeding rate resulted in a considerably improved varrho and 18% increase in total rHSA production compared with those obtained by the optimal strategy.     

Dynamic in vivo (31)P nuclear magnetic resonance study of Saccharomyces cerevisiae in glucose-limited chemostat culture during the aerobic-anaerobic shift

The purpose of this work was to analyse in vivo the influence of sudden oxygen depletion on Saccharomyces cerevisiae, grown in glucose-limited chemostat culture, using a recently developed cyclone reactor coupled with (31)P NMR spectroscopy. Before, during and after the transition, intracellular and extracellular phosphorylated metabolites as well as the pHs in the different cellular compartments were monitored with a time resolution of 2.5 min. The employed integrated NMR bioreactor system allowed the defined glucose-limited continuous cultivation of yeast at a density of 75 g DW/l and a p(O(2)) of 30% air saturation. A purely oxidative metabolism was maintained at all times. In vivo (31)P NMR spectra obtained were of excellent quality and even allowed the detection of phosphoenolpyruvate (PEP). During the switch from aerobic to anaerobic conditions, a rapid, significant decrease of intracellular ATP and PEP levels was observed and the cytoplasmic pH decreased from 7.5 to 6.8. This change, which was accompanied by a transient influx of extracellular inorganic phosphate (P(i)), appeared to correlate linearly with the decrease of the ATP concentration, suggesting that the cause of the partial collapse of the plasma membrane pH gradient was a reduced availability of ATP. The complete phosphorous balance established from our measurement data showed that polyphosphate was not the source of the increased intracellular P(i). The derived intracellular P(i), ATP and ADP concentration data confirmed that the glycolytic flux at the level of glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase and enolase enzymes is mainly controlled by thermodynamic constraints.     

Implications of the use of As-rich groundwater for agricultural purposes and the effects of soil amendments on as solubility

An agricultural site in Segovia province (Spain) contains high levels of arsenic (As) of geological origin in its groundwater, which is used intensively for irrigation. Crops, irrigation waters, and soils were analyzed to evaluate the occurrence of As in this area and its potential impact on the food chain. High As mobility was found in the agricultural soils, related to the application of As in the irrigation waters (14.8-280 μg As L(-1)) and the general alkaline and sandy character of these soils, which imposes a low capacity for As sorption and therefore enhances plant uptake. The use of amendments can also affect the solubility of As in these soils. Evidence for this was evaluated based on a study of the effect of organic (compost) and inorganic (iron oxides-rich rolling mill scale and phosphate fertilizer) amendments. Arsenic solubility in soil and plant uptake were high, but not significantly affected by organic matter or phosphate addition, while As immobilization was associated with addition of iron oxides with the rolling mill scale, although this did not result in a decrease of As uptake by the tested plants.     

利用代谢网络模型和线性规划法在线预测谷氨酸发酵中产物浓度

在好氧型的谷氨酸发酵实验中发现，溶解氧（DO）对发酵性能有很大的影响，谷氨酸的生成方式也因此有很大不同：较低的DO水平能够延长产酸期、提高谷氨酸的最终浓度，但是代谢副产物——乳酸也有较大程度的积蓄；而DO水平过高，虽然代谢副产物不会生成积蓄，但菌体消亡过快导致产酸期缩短、谷氨酸的最终浓度降低．同时，谷氨酸的生成方式与发酵过程中摄氧率（OUR）和CO2的释放率（CER）有着非常紧密的关联．作者利用代谢网络模型并结合使用线性规划优化法，通过在线测定OUR和CER，比较准确地在线推定出发酵过程中谷氨酸的质量浓度变化。与传统的非构造式动力学模型相比，上述预测方法具有建模简单、模型物理意义明确、通用性能好等优点，为后续过程的在线控制和优化提供一种全新和有效的途径。     

Factors influencing luxury uptake of phosphorus by microalgae in waste stabilization ponds

Phosphorus removal in waste stabilization ponds (WSP) is highly variable, but the reasons for this are not well understood. Luxury uptake of phosphorus by microalgae has been studied in natural systems such as lakes but not under the conditions found in WSP. This work reports on the effects of phosphate concentration, light intensity, and temperature on luxury uptake of phosphorus by WSP microalgae in continuous culture bioreactors. Increasing temperature had a statistically significant "positive effect" on intracellular acid-insoluble polyphosphate concentration. It is likely that elevated temperature increased the rate of polyphosphate accumulation, but because the biomass was not starved of phosphate, the stored acid-insoluble polyphosphate was not utilized. Increasing light intensity had no effect on acid-insoluble polyphosphate but had a "negative effect" on the acid-soluble polyphosphate. A possible explanation for this is that the faster growth rate at high light intensity results in this form of polyphosphate being utilized by the cells for synthesis of cellular constituents at a rate that exceeds replenishment. The variability in the phosphorus content of the microalgal biomass shows that with this new understanding ofthe luxury uptake mechanism there is the potential to optimize WSP for biological phosphorus removal.     

Kinetics analysis of growth and lactic acid production in pH-controlled batch cultures of Lactobacillus casei KH-1 using yeast extract/corn steep liquor/glucose medium

This study was performed to determine the optimal conditions of yeast extract, corn steep liquor and glucose concentration for the growth and lactic acid production of Lactobacillus casei KH-1 and to assess the effect of these conditions using a response surface methodology. A Box-Behnken design was used as an experimental design for the allocation of treatment combination as 17 pH-controlled batch cultures. The growth and product parameters were estimated by Gombertz, Leudeking and Piret models from experimental data, and analyzed statistically with response surfaces. The effects of yeast extract, corn steep liquor and glucose were significant for the maximum specific growth rate, mu(max) and the maximum biomass concentration, X(ma). The interaction of corn steep liquor and glucose indicated that the positive or negative effect of glucose on mu(max) in corn steep liquor below or above 2.1% could be explained by the glucose-dependent availability of a nutrient on mu(max) Although the experiment was achieved in pH-controlled batch culture for L. casei KH-1, the growth- and non-growth-associated production rate parameters, a and b, were significant in the response surface model. The growth and lactic acid production of L. casei KH-1 were strongly affected by glucose and the importance of the media composition was demonstrated. The estimated optimal conditions of the growth and lactic acid production of L. casei KH-1 were 1.276% and 0.697% for yeast extract, 3.505% and 1.708% for corn steep liquor, and 2.390% and 2.215% for glucose, respectively.     

High-cell-density fermentation for ergosterol production by Saccharomyces cerevisiae

The direct feedback control of glucose using an on-line ethanol concentration monitor for ergosterol production by high-cell-density fermentation was investigated and the fermentation parameters (e.g., pH, dissolved oxygen, ethanol concentration, oxygen uptake rate, carbon dioxide evolution rate and respiratory quotient) were analyzed. Controlling glucose feeding rate in accordance with ethanol concentration and adjusting pH with ammonia during the fermentation process were effective fed-batch methods for ergosterol production. The fermentation parameters well described the variation of the whole fermentation process. Cultivation in a 5 l fermentor was carried out under the following conditions: culture temperature, 30 degrees C; pH, 5.5; agitation speed, 600 rpm; fermentation time, 60 h; controlling ethanol concentration below 1% and keeping respiratory quotient (RQ) at approximately 1.0. Under these conditions, the yeast dry weight reached 120 g/l and the ergosterol yield reached 1500 mg/l.     

固态发酵中的传感器检测技术

固态发酵(SSF)中各种变量的检测对发酵过程的控制具有重要意义,但由于其培养基来源的多样和复杂性,使得这些参数不易测定。本文综述了固态发酵中采用不同传感器对环境参数(温度、pH、水分含量和水活度)和碳素平衡(生物量、底物浓度、CO2)的检测方法,并对目前固态发酵在线检测中的新技术应用,以及具有应用潜力的检测方法(X射线、磁共振成像技术等)进行了介绍。     

Assessment of nitrogen status of soils for cereal crops: Use of plant and soil analysis to diagnose nitrogen status of spring barley

The results of field experiments with spring barley at two locations in 1978 and 1979 were used to evaluate early season measurement of soil mineral N, plant N and chlorophyll, and nitrogen stress as indicators of straw and grain yields and N uptake at maturity. A new definition of N stress based upon rates of N uptake is proposed. Plant N and chlorophyll contents early in the season were positively related (P< 0.001) to final N uptake. Early season N stress (based on growth rate) was negatively related (mainly P< 0.001) to grain yield and, less strongly, to N uptake. There appeared to be some advantage in using rate of N uptake rather than growth rate to define N stress for the purpose of predicting crop final N uptake.     

Modeling and predicting the simultaneous growth of Listeria monocytogenes and natural flora in minced tuna

The growth kinetics of Listeria monocytogenes and natural flora (NF) in minced tuna from 2 to 30 °C were examined, and a simultaneous growth model was developed. The inhibiting effect of the NF on the growth of L. monocytogenes was examined by inoculating different levels of NF isolated from the minced tuna. The kinetic data were fitted to the Baranyi model and estimated the growth parameters such as specific growth rate (μ(max)), maximum population density (N(max)), and lag time. The temperature and inoculated NF dependency on the μ(max) of L. monocytogenes and NF were described by modified Ratkowsky's square-root model. As the initial NF level increased, the slopes of the square-root models were decreased for both L. monocytogenes and NF. The N(max) of L. monocytogenes was described as a function of temperature and inoculated NF level. Simultaneous growth prediction of L. monocytogenes and NF under constant temperature conditions was examined by using the differential equations based on the Baranyi model with the effect of interspecies competition substituted into the developed μ(max) and N(max) models. The root mean square errors between the model prediction and the observation for L. monocytogenes and NF were 0.42 and 0.34, respectively. Predictive simulation under fluctuating temperature conditions also demonstrated a high accuracy of simultaneous prediction for both L. monocytogenes and NF, representing the root mean square errors of 0.19 and 0.34, respectively. These results illustrate that the developed model permits accurate estimation of the behavior of L. monocytogenes in minced tuna under real temperature history until consumption.