Michael R. Johns

Effect of C/N ratio and aeration on the fatty acid composition of heterotrophicChlorella sorokiniana

The effect of the carbon to nitrogen (C/N) ratio of the medium and the aeration rate on the lipid content and fatty acid composition ofChlorella sorokiniana was investigated using heterotrophic, batch culture. Both parameters had a significant effect. A C/N ratio of approximately 20, was found to indicate a change from carbon to nitrogen limitation forC. sorokiniana. Cell lipid content was at a minimum at this value and increased at both higher and lower C/N values. Low C/N ratios favoured a high proportion of trienoic fatty acids at the expense of monoenoic acids. Aeration enhanced cell growth, fatty acid yield and the synthesis of unsaturated dienoic and trienoic fatty acids, but reduced cell lipid content. The results demonstrate that the fatty acid composition and lipid content of heterotrophically-grown microalgae can be favourably manipulated by varying culture conditions.

Developments in wastewater treatment in the meat processing industry: A review

A review of progress in the treatment of wastewater from slaughterouses is presented. Significant progress in issues such as nutrient removal and high-rate anaerobic treatment are highlighted. Nevertheless, few data concerning waste minimisation and source reduction in slaughterhouses, which offers the most cost-effective route to waste management in the industry, exist. The information presented enables a better understanding of the problems encountered with the effluent from the industry and common pitfalls with its treatment.

Effect of pH and nitrogen source on pigment production by Monascus purpureus

The effect of pH and nitrogen source on pigment production by Monascus purpureus 192F using glucose as the carbon and energy source, was studied in pH-controlled, batch fermentor cultures using HPLC analysis to determine individual pigment concentrations. A maximum of four pigments were detected in fungal extracts. These were the yellow pigments monascin and ankaflavin, the orange rubropunctatin and the red pigment monascorubramine. Monascorubramine was present as the major product in all instances. Fungal growth and ankaflavin synthesis were favoured at low pH (pH 4.0), whereas production of the other pigments was relatively independent of pH. The nature of the nitrogen source affected fungal growth and pigment production, independent of pH. Ammonium and peptone as nitrogen sources gave superior growth and pigment concentrations compared to nitrate. Ankaflavin was not detected in nitrate cultures. The highest red pigment production was obtained using a glucose-peptone medium at pH 6.5, due to the secretion of red pigments into the medium under these conditions.

Production of pigments byMonascus purpureus in solid culture

SummaryThe effect of physical and nutritional factors on the production of pigments byMonascus purpureus FRR 2190 was studied using cultures grown on both rice and a synthetic medium that was solidified with carrageenan and extruded into rice-like particles. Pigment yield was highly sensitive to physical parameters. Optimal pigment formation in rice cultures occurred at an initial pH of 6 and an initial moisture content of 56%. Lower moisture contents led to a large decrease in pigment concentration. Red and yellow pigment production on solidified gel media was increased up to three-fold compared to that of liquid cultures of the same medium composition, particularly when peptone was used as the sole nitrogen source. Solid state rice cultures gave the highest pigment yields.

Heterotrophic growth of Chlamydomonas reinhardtii on acetate in chemostat culture

The possibility of using heterotrophic chemostat culture to achieve relatively high cell densities of Chlamydomonas reinhardtii by avoiding the inhibition of growth by the substrate, acetate was investigated. Continuous culture gave significant improvement in cell dry weight concentration and productivity compared to batch culture. It is postulated that this was due to low acetate concentration in the continuous culture. The highest cell concentration obtained was 1·5 g/litre at a feed acetate concentration of 3·4 g/litre. At acetate concentrations up to this level, the modified Monod model successfully predicted the steady-state cell concentration and cellular productivity. However, no further increase in cell concentration was achieved, despite the use of higher feed acetate concentrations (i.e. 5·1 g/litre), in which, steady-state acetate concentrations were below the inhibition level (i.e. 0·4 g/litre). This inhibitory effect was probably due to sodium rather than to acetate per se in the cultures.

Screening of diatoms for heterotrophic eicosapentaenoic acid production

Nine strains of diatoms (representing four species) were screened for their ability to produce eicosapentaenoic acid (EPA) when cultured heterotrophically on glucose. Four strains were able to produce EPA heterotrophically using glucose as its carbon and energy source. Of the four,Nitzschia laevis was the best EPA producer, yielding 0.017 g g−1 dry cell weight.N. laevis was the only species tested which synthesised more EPA heterotrophically than photosynthetically. This study shows thatN. laevis is a potential source of EPA production using heterotrophic culture conditions with glucose as the carbon and energy substrate.

Effect of pH, agitation and aeration on hyaluronic acid production byStreptococcus zooepidemicus

SummaryThe optimum pH for both the rate of production and yield of hyaluronic acid (HA) byStreptococcus zooepidemicus from glucose medium was 6.7±0.2 under anaerobic conditions. High agitation rates (600 rpm) gave superior results compared to 300 rpm. Aeration of the culture (0.3 VVM) improved the HA yield, but not the rate of production and lead to some acetate and CO2 being formed, in addition to lactate and HA.

A strategy for high cell density culture of heterotrophic microalgae with inhibitory substrates

Substrate inhibition is one of the major problems preventing high cell densities of microalgae in heterotrophic culture, so the possibility of overcoming the problem by various culture techniques was examined. It was found that perfusion culture may be the most appropriate technique for high cell densities in heterotrophic culture using inhibitory substrates. An experimental example in which a hollow fibre cell recycle system (HFCRS) was employed to achieve high cell densities of Chlamydomonas reinhardtii on acetate under heterotrophic conditions of growth was demonstrated. The cell density in the HFCRS was much higher than that reported in the literature for this species.

Mutarotation of D-fructose in aqueous-ethanolic solutions and its influence on crystallisation

Abstract The mutarotation of d -fructose in aqueous-ethanolic solutions was studied between 24 and 50 °C. The ethanol:water mass ratios of the solvent were 3:1, 6:1, and 9:1. The principal tautomers found in the solution were β- d -fructopyranose. β- d -fructofuranose, and α- d -fructofuranose, as is found with aqueous solutions of d -fructose. The furanose tautomers were more strongly favoured in the aqueous-ethanolic solutions, comprising approximately 60% of the fructose in solution for the range of solvent conditions studied, in comparison to 27% in aqueous solution at 24 °C. The rate of mutarotation from β- d -fructopyranose to the furanose tautomers was fivefold slower in solutions of ethanol:water ratio of 9:1 than in aqueous solutions. The tautomeric composition of d -fructose in aqueous-ethanolic solutions was shown to affect the crystallisation of the sugar, due to the slow rate of mutarotation of furanose forms to β- d -fructopyranose.

Solid‐state fermentation in rotating drum bioreactors: Operating variables affect performance through their effects on transport phenomena

Aspergillus oryzae ACM 4996 was grown on an artificial gel-based substrate and on steamed wheat bran during solid-state fermentations in 18.7 L rotating drum bioreactors. For gel fermentations fungal growth decreased as rotational speed increased, presumably due to increased shear. For wheat bran fermentations fungal growth improved under agitated compared to static culture conditions, due to superior heat and mass transfer. We conclude that the effects of operational variables on the performance of SSF bioreactors are mediated by their effects on transport phenomena such as mixing, shear, heat transfer, and mass transfer within the substrate bed. In addition, the substrate characteristics affect the need for and the rates of these transport processes. Different transport phenomena may be rate limiting with different substrates. This work improves understanding of the effects of bioreactor operation on SSF performance.