Effects of temperature, pH, water activity and CO2 concentration on growth of Rhizopus oligosporus NRRL 2710

Abstract

Aims: To investigate the effects of temperature, pH, water activity (a w ) and CO 2 concentration on the growth of Rhizopus oligosporus NRRL 2710. Methods and Results: Hyphal extension rates from mycelial and spore inocula were measured on media with different a w ($ 1AE0, 0AE98 and 0AE96) and pH (3AE5, 5AE5 and 7AE5) incubated at 30, 37 or 42°C in atmospheres containing 0AE03, 12AE5 or 25% (v/v) CO 2 . The effects of environmental conditions on hyphal extension rate were modelled using surface response methodology. The rate of hyphal extension was very sensitive to pH, exhibiting a pronounced optimum at pH 5AE5-5AE8. The hyphal extension rate was less sensitive to temperature, a w or CO 2 , exhibiting maximum rates at 42°C, a w $ 1AE0 and 0AE03% (v/v) CO 2 . Conclusions: The fastest hyphal extension rate (1AE7 mm h )1 ) was predicted to occur at 42°C, pH 5AE85, a w $ 1AE0 and 0AE03% CO 2 .Significance and Impact of the Study: The present work is the first to model the simultaneous effects of temperature, pH, a w and CO 2 concentration on mould growth. The information relates to tempe fermentation and to possible control of the microflora in Tanzanian cassava heap fermentations.

Studying and modelling the combined effect of temperature and water activity on the growth rate of P. expansum

“…R 2 values show that a w and temperature account for 98% of the growth-rate variation observed in the glycerol model and 97% of that observed in the sorbitol model (Box and Draper, 1987). Similar models have been established for other food spoilage pathogens such as Rhizopus oligosporus NRRL 2710 (Sparringa et al, 2002) and P. chrysogenum (Sautour et al, 2001a,b;El-Halouat and Debevere, 1997). The results of our study are in accordance with those of Sautour et al (2001a), who report no significant difference between a glycerol and a sorbitol model based on germination of P. chrysogenum and show that a w has a greater effect on germination than temperature.…”

Production of fibrolytic enzymes by Aspergillus japonicus C03 using agro-industrial residues with potential application as additives in animal feed

“…Soy bran with crushed corncob (1:3 w/w) increased xylanase activity by 8.5% as compared with the control. This residue possibly increased the aeration of the medium, stimulating growth and enzyme production [21,22]. In addition, other researchers have recognized corncob as a useful and cost-effective medium ingredient because it is largely produced as a by-product during corn processing [23,24].…”

Evidence of thermostable amylolytic activity from Rhizopus microsporus var. rhizopodiformis using wheat bran and corncob as alternative carbon source

“…The crushed corncob (2:2), rice straw and corncob (1:3, 2:2) increased the amylase activity in 5.3-30% as compared to the control. These residues also increased the aeration of the medium, stimulating growth and enzyme production [24,25].…”