Production of fermentable media from vine‐trimming wastes and bioconversion into lactic acid by Lactobacillus pentosus

Trimmings of vineshoots, an agricultural waste with little use, were hydrolysed with dilute sulphuric acid (1–5%) in order to obtain sugar solutions suitable as fermentation media. The operational conditions for hydrolysis were selected on the basis of both the generation of hemicellulosic sugars (mainly xylose) and glucose and the concentrations of reaction byproducts affecting fermentation (furfural, hydroxymethylfurfural and acetic acid). Hemicellulosic hydrolysates were supplemented with nutrients and fermented with Lactobacillus pentosus, without any previous detoxification stage, to produce lactic acid. Under the best operational conditions assayed (3% H₂SO₄ and 15 min), 21.8 g lactic acid l^?1 was produced (Q_P = 0.844 g l^?1 h^?1, Y_P/S = 0.77 g g^?1), which represents a theoretical yield of 99.6%. Acetic acid was the primary byproduct formed from xylose, at about 25% of the lactic acid level. Copyright © 2004 Society of Chemical Industry     

Production of detoxified sorghum straw hydrolysates for fermentative purposes

Sorghum straw can be hydrolysed to obtain monosaccharide solutions, mainly containing xylose. The usual biotechnological application of xylose is its bioconversion to xylitol. The global process from straw to xylitol can give an added value to the sorghum straw. The process has the following sequential steps: reduction of size, acid hydrolysis, neutralization, detoxification, fermentation, recovery and purification. This work deals with the optimization of the detoxification process of sorghum straw hydrolysates with activated charcoal. The variables evaluated were pH (1–5), contact time (20–60 min) and activated charcoal charge (20–33 g kg^?1). Mathematical models were obtained through a factorial experimental design. The models suggest that optimal conditions for detoxification are pH 1, contact time of 29 min and a charcoal charge of 33 g kg^?1. These conditions allowed hydrolysates with 54.2 g xylose L^?1, 13.5 g glucose L^?1, 12 g arabinose L^?1, 0.2 g furfural L^?1 and 0.0 g acetic acid L^?1 to be obtained. The results suggest that performing the detoxification step before the neutralization step gave the best outcome. Fermentations by Candida parapsilosis NRRL Y‐2315 were performed and it was confirmed that the treated hydrolysate is suitable for xylitol production, yielding up to 17 g L^?1 of this polyol. Copyright © 2006 Society of Chemical Industry     

Prehydrolysis ofEucalyptus wood with dilute sulphuric acid: operation at atmospheric pressure

MilledEucalyptus globulus wood samples were subjected to acid hydrolysis using H₂SO₄ as catalyst. The reactions were carried out in a stirred, reflux-operated batch reactor. The effects of both catalyst concentration (in the range 3.5–10%) and hydrolysis time (0–11 h) on the concentration of arabinose, glucose, xylose, acetic acid and furfural were studied. The kinetics of xylan hydrolysis followed general trends similar to those described in earlier studies. Almost quantitative xylose recovery was achieved after 11 h of reaction time in experiments with 10% H₂SO₄. The furfural concentrations were low (0–0.44 g/L) in all the cases studied. Additional aspects relative to the selectivity of the prehydrolysis are discussed.     

Effect of added glucose and xylose on the fermentation of perennial ryegrass silage inoculated with Lactobacillus plantarum

Perennial ryegrass (Lolium perenne L) was ensiled in laboratory silos after addition of glucose or xylose at rates of 0, 25, 35 and 45 g kg^?1 fresh grass. In addition, an inoculum of Lactobacillus plantarum, supplying 10⁶ organisms g^?1 fresh grass, was applied to all treatments. Silos were opened after 7, 21 and 100 days and the silage was subjected to chemical and microbiological analysis. AH silages were well fermented with pHs between 3·60 and 3·70 and low NH₃-N concentrations (<95 g kg^?1 total nitrogen) and an absence of butyric acid. Glucose was virtually completely consumed within 21 days but 0·30–0·50 of the xylose doses remained after 100 days. Lactic acid concentrations were not increased by the addition of sugars, but the glucose treatments were associated with very high concentrations of ethanol, 60–100 g kg^?1 DM, and the xylose additions produced very high concentrations of acetic acid, 60–135 g kg^?1 DM. Most(>0·80) of the glucose that disappeared could be accounted for in ethanol formation but the xylose consumed could be accounted for only if the lactic acid produced in its fermentation was metabolised further to acetic acid; indeed, for the two higher doses of xylose, the concentrations of lactic acid were reduced from the control value of 177 g kg^?1 DM to 140 and 120 g kg^?1 DM, respectively. The results indicate that the provision of extra sugar, as hexose or pentose, allows yeasts to assume a more prominent role in the fermentation with consequent wasteful fermentation of sugars. Furthermore, the suggestion is that xylose may indirectly, via a stimulation of lactate-assimilating yeasts, encourage further metabolism of lactic acid to acetic acid.     

Desulphiting dried apricots by exposure to hot air flow

Sulphited dried apricots were exposed to hot air flows at 40, 50 and 60 °C and the removal of SO₂ was investigated as their moisture content fell from an initial value of 193.2 g kg^?1 to a final value of 80–90 g kg^?1. A first‐order kinetic model was found for the removal of SO₂ between 40 and 60 °C. Temperature quotients (Q₁₀) for the removal of SO₂ were 2.84 between 40 and 50 °C and 4.93 between 50 and 60 °C; the activation energy (E_a) was 114.40 kJ mol^?1 between 40 and 60 °C. Analysis of the kinetic data also suggested a first‐order reaction for non‐enzymatic browning, with Q₁₀ values of 2.34 between 40 and 50 °C and 5.36 between 50 and 60 °C and an E_a value of 109.36 kJ mol^?1 between 40 and 60 °C. Exposure of dried apricots to a 60 °C air flow resulted in a rate constant for brown pigment formation that was 12 and 5 times higher than those at 40 and 50 °C respectively. © 2002 Society of Chemical Industry     

Simultaneous lactic acid and xylitol production from vine trimming wastes

Hemicellulosic hydrolyzates from vineshoot trimmings obtained by dilute sulfuric acid hydrolysis were evaluated for xylitol production by Debaryomyces hansenii NRRL Y‐7426. Bioconversion was not efficient, however, since a mixture of products (mainly ethanol) was achieved. Taking into account that hexoses (such as glucose or mannose) can inhibit xylose metabolism by repression and inactivation of the xylose transport system or catabolic enzymes and that these hemicellulosic hydrolyzates are characterized by a high glucose concentration, a novel technology was developed, sequentially transforming glucose into lactic acid by Lactobacillus rhamnosus followed by fermentation of xylose into xylitol by Debaryomyces hansenii after L. rhamnosus removal by microfiltration. Optimal conditions were achieved using detoxified concentrated hemicellulosic hydrolyzates, after CaCO₃ addition in both stages of fermentation and using nitrogen purges after sampling in order to reduce the oxygen dissolved. Under these conditions 31.5 g lactic acid L^?1 (Q_LA = 1.312 g L^?1 h^?1 and Y_LA/S = 0.93 g g^?1) and 27.5 g xylitol L^?1 (Q_Xylitol = 0.458 g L^?1 h^?1 and Y_Xylitol/S = 0.53 g g^?1) were produced. Finally, lactic acid was selectively recovered using the resin Amberlite IRA 400 (0.0374 g of lactic acid g^?1 of dry resin), allowing a further recovery of xylitol by sequential stages of adsorption, concentration, ethanol precipitation, concentration and crystallization to obtain food‐grade xylitol according to a developed process. Copyright © 2007 Society of Chemical Industry     

Xylitol bioproduction from wheat straw: hemicellulose hydrolysis and hydrolyzate fermentation

A 2² central composite design with five center points was performed to estimate the effects of temperature (120, 130 and 140 °C) and acid loading (100, 150 and 200 mg g^?1) on the yield of monomeric xylose recovery from wheat straw hemicellulose (Y_S/RM). Under the best hydrolysis condition (140 °C and 200 mg g^?1), a Y_S/RM of 0.26 g g^?1 was achieved. After vacuum concentration and detoxification by pH alteration and active charcoal adsorption, the hydrolyzate was used as source of xylose for xylitol bioproduction in a stirred tank reactor. A xylitol production of 30.8 g L^?1 was achieved after 54 h^?1 of fermentation, resulting in a productivity (Q_P) of 0.57 g L^?1 h^?1 and bioconversion yield (Y_P/S) of 0.88 g g^?1. The maximum specific rates of xylose consumption and xylitol production were 0.19 and 0.15 g g^?1 h^?1, respectively. Copyright © 2006 Society of Chemical Industry     

Carbohydrates associated with leaf protein

Heating leaf protein of agricultural crops with 2 N H₂SO₄ removed 5–10% of its dry weight as carbohydrate, of which less than half was reducing sugar; arabinose, galactose, xylose and sometimes a little glucose were found for all the crops studied. Pronase released soluble carbohydrate from red clover and wheat protein as large fragments which gave pentose, mainly arabinose, on heating with 0.2 N H₂SO₄, and galactose and glucose on heating with 2 N H₂SO₄. Similar results on graded acid hydrolysis were shown by a fraction from red clover liquor, the soluble material remaining after heat-precipitation of the protein.     

活性炭吸附结合TiO2光催化分离纯化杨木预水解液中的木糖

利用活性炭吸附和TiO₂光催化降解脱除杨木预水解液中的溶解木素,探讨了不同活性炭类型（木质基磷酸活化活性炭、食品质303活性炭、煤质活性炭）、活性炭用量、吸附时间、光催化时间、TiO₂用量对预水解液中木素、总木糖、糠醛、羟甲基糠醛（5-HMF）以及乙酸等有机组分含量的影响,优化确定了活性炭吸附和TiO₂光催化降解条件。研究结果表明,木质基磷酸活化活性炭对木素的吸附脱除效果最好,在活性炭用量为1.0%和吸附时间为10 min时,总木糖得率为93.1%,木素、糠醛、5-HMF、乙酸脱除率分别为75.1%、29.3%、22.4%、3.5%。单一TiO₂光催化处理,在TiO₂用量1.0%和光催化时间10 h条件下,总木糖得率为89.0%,木素、糠醛、5-HMF、乙酸脱除率分别为40.2%、24.2%、32.1%、3.1%。活性炭协同TiO₂光催化处理预水解液的较优工艺条件为：木质基磷酸活化活性炭用量1.0%、光催化时间6 h和TiO₂用量0.1%~0.5%,此条件下预水解液中木素的脱除率为84.4%~86.7%,总木糖得率为88.2%~89.8%,糠醛脱除率为53.8%~65.1%,5-HMF脱除率为48.6%~51.7%,乙酸含量变化不明显 。     

Sorption of volatile compounds into electron beam irradiated EVA film in the vapour phase

In order to investigate the sorption of volatile compounds by electron beam irradiated ethylene/vinyl acetate copolymer (EVA) films, permeation measurements in the vapour phase were carried out. The diffusion coefficients of octane, ethyl hexanoate, octanal, octan-1-ol and d-limonene increased with an increase in the irradiation dose. The sorption of all volatile compounds in this study was depressed in electron beam irradiated film: the decreases in solubility coefficients for 20 Mrad EVA film were 15% for octane and ethyl hexanoate, 45% for octan-1-ol and octanal, and 50% for d-limonene. The enthalpy change in sorption (ΔH) of ethyl hexanoate was ?13·4 kJ mol^?1 for 50 g kg^?1 EVA film at a dose of 20 Mrad compared with ?27·6 kJ mol^?1 for the unirradiated one. In a homologous series of aliphatic alcohols, sorption was significantly depressed with increasing carbon chain length. Judging from both heat-seal strength and sorption behaviours, the most appropriate irradiation dose for the practical usage of irradiated EVA film was less than 15, 10 and 5 Mrad for 50, 95 and 150 g kg^?1 EVA film, respectively.     

Revalorisation of vine trimming wastes using Lactobacillus acidophilus and Debaryomyces hansenii

BACKGROUND: Mild acid treatments of vine‐shoot trimmings result in the hydrolysis of hemicellulosic sugars that can be utilised by Lactobacillus acidophilus CECT‐4179 (ATCC 832) and Debaryomyces hansenii NRRL Y‐7426 as carbon sources to obtain food additives. Since the high content of glucose in these hydrolysates reduces the effective bioconversion of xylose into xylitol by D. hansenii, the use of Lactobacillus acidophilus, one of the main probiotic species, allows this problem to be solved by the selective consumption of glucose. In order to use both sugars (glucose and xylose), hemicellulosic vine‐shoot trimming hydrolysates can be sequentially fermented by both micro‐organisms. RESULTS: It was found that, in the first step, L. acidophilus generated almost exclusively lactic acid (32.7 g of lactic acid L^?1, Q_LA = 1.363 g L^?1 h^?1, Y_LA/S = 0.72 g g^?1) by homofermentative degradation of sugars (mainly glucose), and in the second step, the remaining hemicellulosic sugars were transformed primarily into xylitol by Debaryomyces hansenii (31.3 g of xylitol L^?1, Q_Xylitol = 0.708 g L^?1 h^?1, Y_Xylitol/S = 0.66 g g^?1). Furthermore, L. acidophilus proved to be a strong cell‐bounded biosurfactant producer. Cell extracts were able to reduce the surface tension (ST) of PBS in 18 mN m^?1 units. Lactobacillus acidophilus cells showed no difference in viability before or after PBS extraction of biosurfactants, achieving values of 0.9 × 10⁹ colony‐forming units (CFU) mL^?1 in both cases. CONCLUSIONS: These results have made a serious contribution to the re‐evaluation of a useless and pollutant residue, producing a wide range of natural food additives. Copyright © 2008 Society of Chemical Industry     

A simple,rapid and novel method based on salting-out assisted liquid–liquid extraction for ochratoxin A determination in beer samples prior to ultra-high-performance liquid chromatography coupled to tandem mass spectrometry

A novel, simple, easy and cheap sample treatment strategy based on salting-out assisted liquid-liquid extraction for ochratoxin A (OTA) ultra-trace analysis in beer samples using ultra-high-performance liquid chromatography-tandem mass spectrometry determination was developed. The factors involved in the efficiency of pre-treatment were studied employing factorial design in the screening phase and the optimal conditions of the significant variables on the analytical response were evaluated using a central composite face-centred design. Consequently, the amount of salt ((NH₄)₂SO₄), together with the volumes of sample, hydrophilic (acetone) and nonpolar (toluene) solvents, and times of vortexing and centrifugation were optimised. Under optimised conditions, the limits of detection and quantification were 0.02 µg l^?1 and 0.08 µg l^?1 respectively. OTA extraction recovery by SALLE was approximately 90% (0.2 µg l^?1). Furthermore, the methodology was in agreement with EU Directive requirements and was successfully applied for analysis of beer samples.     

Improvement of wine aromatic quality using mixtures of lysozyme and dimethyl dicarbonate,with low SO2 concentration

The use of sulphur dioxide (SO₂) in the treatment of foodstuffs presents some problems as it could lead to pseudo-allergies in some people. The aim of this research work was to study the addition of different preservative mixtures and their influence on the concentration of volatile compounds and sensorial quality in wine. To do so, vinifications were carried out using Garnacha must to which lysozyme, dimethyl dicarbonate (DMDC) and mixtures of these with SO₂ were added at different doses (25 and 50 mg l^?1). The results were compared with a control sample to which only SO₂ had been added (50 mg l^?1). In general, mixtures of SO₂ with lysozyme and DMDC favoured the formation of volatile compounds in the wines. Wines obtained from the mixtures of lysozyme and DMDC with 25 mg l^?1 of SO₂ had better sensorial quality than the wines obtained with 50 mg l^?1 as the only preservative used.     

Isolation and characterization of collagen from bigeye snapper (Priacanthus macracanthus) skin

Acid‐solubilized collagen (ASC) and pepsin‐solubilized collagen (PSC) were isolated from the skin of bigeye snapper (Priacanthus macracanthus) with yields of 64 and 11 g kg^?1 wet weight, respectively. Both ASC and PSC were characterized as type I collagens with no disulfide bonds. Peptide maps of ASC and PSC digested by V8 protease and lysyl endopeptidase showed some differences in peptide patterns and were totally different from those of calf skin collagen. The maximum solubility was observed at pH 4 and 5 for ASC and PSC, respectively. A sharp decrease in solubility of both collagens in acetic acid was found with NaCl concentration above 30 g l^?1. Thermal transitions of ASC and PSC in deionized water were observed with T_max of 30.37 and 30.87 °C, respectively, and were lowered in the presence of acetic acid (0.05 mol kg^?1 solution). Therefore, ASC was a major fraction in bigeye snapper skin and it exhibited some different characteristics to PSC. Copyright © 2005 Society of Chemical Industry     

The effects of defaunation on the metabolism of lactic acid in the rumen

Two experiments examined the effects of defaunation on the ruminal metabolism of lactate. Three rumen-cannulated sheep given a diet of molassed sugar beet pulp and barley (80:20) were used to study the effects of defaunation (with manoxol-OT) on the metabolism of lactic acid produced endogenously from rumen fermentation. Defaunation increased mean ruminal concentrations of lactate from 3.4 mmol litre^?1 to 8.9 mmol litre^?1 but other rumen measurements remained virtually unchanged: pH, 6.3 and 6.3; molar proportions of acetic acid, 645 and 645 mmol mol^?1; propionic acid, 189 and 197 mmol mol^?1 and butyric acid 142 and 115 mmol mol^?1 for the faunated and defaunated states respectively. In a second experiment, two groups each of four rumen-cannulated sheep were used to study the effect of defaunation on the ruminal metabolism of added Na-D, L lactate. One group of four was defaunated using a rumen-washing technique whilst the other group of four remained faunated. The animals were given a diet of rolled barley and hay (60:40) and were given a series of intraruminal doses of Na-D, L lactate from 0 to 100 g day^?1, increasing by 20 g day^?1 every third day. Disappearance of added lactate was much more rapid in faunated animals: at the 100 g day^?1 dose rate, L-lactate concentrations had fallen from a peak of 6 g litre^?1 to >1 g litre^?1 after 3 h whereas in defaunated sheep the peak of 6.5 g litre^?1 was reduced to >1 g litre^?1 only after 7 h. In faunated animals lactate addition caused an increase in the ruminal concentration of total volatile fatty acids (VFA) from 147 to 217 mmol litre^?1 between the zero and 100 g day^?1 dose rates, accompanied by an increase in the molar proportion of propionic acid from 190 to 320 mmol mol^?1. However, in defaunated animals there was only a small increase in total VFA concentrations from 94 to 106 mmol ml^?1 with no change in the molar proportion of propionic acid and a small increase in butryric acid from 140 to 180 mmol mol^?1.     

Urea and Heat Unfolding of Cold-Adapted Atlantic Cod(Gadusmorhua)Trypsin and Bovine Trypsin

The reversible unfolding reactions for phenylmethylsulphonyl fluoride (PMSF)-modified trypins from Atlantic cod (cod PMS-trypsin) and cattle (bovine PMS-trypsin) were monitored by fluorescence spectrophotometry as a function of urea concentration and temperature. For urea unfolding at 25°C, the free energy change at zero concentration of urea (ΔG(H₂O)) for cod PMS-trypsin was 11(±4·4) kJ mol⁻¹ compared with 18(±1·14) kJ mol⁻¹ for bovine PMS-trypsin, while the mid-point concentration for urea unfolding curve ([urea]_1/2) was 3·0(±0·57) M and 4·1(±0·16) M, respectively. From studies of enzyme heat unfolding, the mid point temperature of the thermal unfolding curve ( T _m ) was 46(±1·4)°C for cod PMS-trypsin compared with 57(±2)°C for bovine PMS-trypsin. The standard free energy change (Δ G° ) for reversible thermal unfolding of cod PMS-trypsin was 9(±1) kJ mol⁻¹ compared with 19(±1) kJ mol⁻¹ for bovine PMS-trypsin. Values for the enthalpy (Δ H _m ), entropy (Δ S _m ) and heat capacity (Δ C _p ) for heat unfolding are compared. Results from urea and thermal unfolding studies show that cod PMS-trypsin has a significantly lower conformational stability than bovine PMS-trypsin.     

Production of fungal biomass from cormel process waste‐water of cocoyam (Xanthosoma sagittifolium (L) Schott) using Aspergillus oryzae obtained from cormel flour

Aspergillus oryzae obtained from spoilt cormel flour was subjected to mutation treatments using X‐rays, solar radiation and bleach. Exposure of A oryzae spores to X‐radiation of 50 kV at 20 mA s and other treatments induced both mutation and lethality in the organism. Following selection and screening of viable colonies on a medium containing cormel process waste‐water as the only carbon source, two strains, A oryzae No 15 and A oryzae No 8, which significantly (P ≤ 0.05) produced more biomass at a higher growth rate than the wild parent, were chosen for single‐cell protein production. Nutrient content of the single‐cell protein produced by the mutants was comparable to that of the wild type. Addition of 3.0 g each of (NH₄)₂SO₄, NH₄NO₃, NH₄Cl, and urea in 1 l of Xanthosoma process waste‐water increased the growth rate of mutants, with the highest increase observed with urea. Medium amended with urea also produced fungal biomass with the highest protein level of 7.97 g l^?1 for A oryzae No 8 strain compared with a protein yield of 3.97 g l^?1 obtained in the control. Total biomass produced after 54 h was 22.47 g l^?1 for A oryzae No 15 strain when urea was added, whereas only 15.20 g l^?1 was produced when no nitrogen source was added. The optimal temperature for single‐cell protein production was found to be 35 °C and the optimal pH was 3.50. A speed of 100 rpm gave the largest quantity of fungal biomass for the mutants tested. Copyright © 2003 Society of Chemical Industry     

REVISED CONFORMATIONAL STABILITY PARAMETERS FOR BETA-LACTOGLOBULIN ISOTHERMAL DENATURATION BY UREA

Isothermal unfolding studies for beta‐lactoglobulin (β‐Lg) usually apply a denaturation model suitable for a single submit protein. A method is described for correcting such results in retrospect. This leads to accurate estimates for the Gibbsfree energy of stabilization of native β‐Lg aimer. The denaturation of β‐Lg aimer is described by a dissociation coupled unfolding (DCU) process; Dimer → monomer → unfolded state. The Gibbs free energy change for DCU (ΔG°_DCU) was 80 kJ mol^?1 at pH 7 and 97 kJ mol^?1 for β‐Lg at pH 2.6. With the addition of a range of salts (pH 6.85) then ΔG°_DCU increased to 105 kJ mol^?1. The literature is replete with denaturation studies employing β‐Lg as the principal protein. In many instances, it would be prudent to reevaluate stability data for β‐Lg in line with techniques outlined here.     

Comparison of the contribution to soil organic matter fractions,particularly carbohydrates,made by plant residues and microbial products

Soil was incubated with ¹⁴C-ryegrass or ¹⁴C-glucose, fractionated and the distribution of radioactivity in six fractions and in their constituent sugars was compared. The fractions were (1) the light fraction (d < 2.00), (2) heavy fraction which was subdivided into (3) HCl soluble, (4) humic acid, (5) fulvic acid, and (6) humin. Sugars were released from soluble fractions by hydrolysis with 0.5M H₂SO₄, and from insoluble fractions by hydrolysis with 2.5M H₂SO₄ and 12M H₂SO₄ followed by 0.5M H₂SO₄. The light fraction contained the greater part of the radioactivity and the sugars in both types of incubation. The proportion of the radioactivity accounted for by sugars in the light fraction of the ryegrass incubation, initially 44%, decreased to 30% after 6 months incubation and to 19% after a year. In one of the glucose incubations, done with soil that had been dried prior to remoistening to 25% w/w and incubating, the proportion was 17% after incubation for one month; in the other, done on soil that had not been given a drying treatment and had a 35% w/w moisture content, it was 32%. In the ryegrass incubation, the sugars with the greatest specific activities were present in the light fraction. In contrast, in the glucose incubation, sugars in the HCl-soluble, fulvic and humic fractions had the highest specific activities. Carbon from ryegrass contributed more to the humic acid and humin fractions of the soil than did the carbon from glucose, whereas carbon from glucose made a greater contribution to the acid-soluble organic matter.     

The yeast flora of ensiled whole-crop maize

The yeast flora in samples of 13 different whole-crop maize silages was shown to be predominated by Candida krusei, C. lambica, Saccharomyces dairensis, S. exiguus, C. holmii or C. milleri. All these strains fermented glucose but, except for the latter three species, not sucrose, α-trehalose or raffinose. Under conditions resembling those in silage, i.e. at pH 4.0 in the presence of a complex nitrogen source, all strains assimilated lactic and acetic acids. This result suggests that the predominant yeasts in silage should not be distinguished into lactate utilisers and lactate non-utilisers. All strains, except those of Saccharomyces dairensis, tolerated acetic acid (5 g litre^?1) and grew at pH 4.0 in a mineral salts medium containing lactic acid (10 g litre^?1), acetic acid (5 g litre^?1) and yeast extract (1 g litre^?1). Growth in this medium was completely inhibited by the cationic detergent Arquad C33W (20 mg litre^?1), propionic acid (5 g litre^?1), benzoic acid (5 g litre^?1) or salicylic acid (10 g litre^?1).