Psychrometric Determination of Water Activity in the High aw Range

Prior, B. A.; Casaleggio, C.; Vuuren, H. J. J. Van

doi:10.4315/0362-028x-40.8.537

Cited by 24 publications

(5 citation statements)

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“…A standard curve for the a, determination of LiCl and Na2S04 solutions was prepared by using a Wescor psychrometer (Prior et al, 1977). The mass of LiCl required per kg of medium at 0.995 and 0.990 a , was 5 3 0 g and 14-00g, respectively.…”

Section: J P Mildenhall a N D B A Prior Methodsmentioning

confidence: 99%

Water Relations of Erwinia chrysanthemi: Intracellular and Extracellular Pectate Lyase Production

MILDENHALLl

Prior

1983

Microbiology

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When Erwinia chrysanthemi was grown in a sodium polypectate/yeast extract/salts medium adjusted with sorbitol to water activity (a,) values of 0.990 and 0.980, extracellular pectate lyase (PL) production was repressed, whereas intracellular PL levels were not affected. Inorganic solutes (NaCl, LiCl, KCl, Na2S04 and a NaCl/KC1/Na2S04 mixture) at 0.990 a, strongly stimulated the intracellular levels of PL (6-to 17-fold greater than the control), whereas extracellular levels were only slightly increased. Intra-and extracellular PL levels were not affected by LiCl, NaCl and KCl at 0.995 a,. A NaCl/sorbitol mixture (0-990 a,) completely inhibited extracellular but not intracellular PL production. Lowering of the a, of cultures during mid-exponential growth phase with NaCl(O.990 a,) resulted within 30 min in a 70-fold increase in intracellular PL activity. When sorbitol was used in similar experiments, extracellular PL production was inhibited to a greater extent than intracellular levels.

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Section: J P Mildenhall a N D B A Prior Methodsmentioning

confidence: 99%

Water Relations of Erwinia chrysanthemi: Intracellular and Extracellular Pectate Lyase Production

MILDENHALLl

Prior

1983

Microbiology

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“…The aw of the medium was adjusted to 0.960 with NaC1 (1.20 molal from the data of Robinson and Stokes 1959) or polyethylene glycol (PEG) 400 (BDH, Poole, Dorset, England; 1.02 molal as deter-mined psychrometrically by the method of Prior et al 1977). Antifoam (0.3 ml-l-1; Chemserve Antifoam A; Chemical Services, Johannesburg, RSA) was added to the medium to control foaming.…”

Section: Growth Medium and Control Of Water Activitymentioning

confidence: 99%

Water relations of polyol accumulation by Zygosaccharomyces rouxii in continuous culture

Zyl

Prior

1990

Appl Microbiol Biotechnol

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Glycerol and arabitol were the main polyols accumulated b y Zygosaccharomyces rouxii in continuous culture but the intracellular and extracellular concentrations of the polyols varied with the dilution rate and osmoticum used to adjust the water activity (aw) to 0.960. When the aw was adjusted with NaC1, glycerol was the main polyol accumulated intracellularly whereas glycerol and arabitol were accumulated when polyethylene glycol (PEG) 400 was used. The extracellular glycerol and arabitol concentrations at 0.960 aw (NaCI or P E G 400) were similar or decreased relative to cultures at 0.998 aw. Compared to steady-state cultivation at 0.998 a,~, the yeast retained at 0.960 aw (NaC1 or PEG 400) a greater proportion of the total glycerol intracellularly against an increased concentration ratio without significantly greater production of glycerol. Arabitol was only significant in osmoregulation when cultivated at 0.960 aw (PEG 400). The intracellular glycerol concentration was insufficient to balance the aw across the membrane, but an equilibrium could be achieved under certain conditions if arabitol was also osmotically active.

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“…The relationship of a, to concentrations of glycerol and arabitol was determined experimentally using a psychrometer (Prior et al, 1977) and the data was used to establish the formulae : a, (glycerol) = 1 -[0.000177 x concentration (g I-I)] and a, (arabitol) = 1 -[0.000116 x concentration (g 1-l)]. The intracellular a, was calculated from the product of a, (glycerol) and a, (arabitol).…”

Section: Organism Andmediummentioning

confidence: 99%

Accumulation of Polyhydroxy Alcohols by Hansenula anomala in Response to Water Stress

Eck¹,

Prior²,

Brandt³

1989

Microbiology

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The responseoftheyeast Hansenulaanomala toareduction inwater activity (a,)from0.998 to0.925 (adjusted with glucose or NaC1) was monitored. Natural abundance 3C NMR spectroscopy and HPLC analysis revealed that the type of carbon source determined which polyols were present intracellularly at 0.998 a,. At 0.95 a, (NaCl), glycerol was accumulated in all instances irrespective of the type of carbon source indicating the primary role of glycerol in osmoregulation. The carbon source had a bearing only on which other polyol(s) were accumulated. During growth on glucose at 0-95 a, (NaCl or glucose), glycerol was accumulated intracellularly in the exponential growth phase with a concentration ratio (intra-/extracellular) as high as 10000-fold whereas during the stationary phase arabitol accumulation occurred to a lower concentration ratio while the glycerol concentration decreased. The specific growth rate and cell volume decreased with increasing NaCl or glucose concentrations. This indicated that the yeast had no specific requirement for these compounds for optimum growth but tolerated high concentrations. Reducing the a, to 0.95 resulted in increasing intracellular concentrations of glycerol and arabitol whereas below 0.95 a, (NaC1 or glucose), the intracellular polyol concentration decreased while the polyol concentration ratios across the cell membrane increased. During the early exponential growth phase at 0-95 a,, glycerol was accumulated in sufficiently high concentrations to achieve an osmotic balance across the membrane whereas in the stationary phase the arabitol and glycerol concentration was insufficient to maintain the osmotic balance. t Present address: South

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Psychrometric Determination of Water Activity in the High aw Range

Cited by 24 publications

References 0 publications

Water Relations of Erwinia chrysanthemi: Intracellular and Extracellular Pectate Lyase Production

Water Relations of Erwinia chrysanthemi: Intracellular and Extracellular Pectate Lyase Production

Water relations of polyol accumulation by Zygosaccharomyces rouxii in continuous culture

Accumulation of Polyhydroxy Alcohols by Hansenula anomala in Response to Water Stress

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