Citric acid production from beet molasses by cell recycle ofAspergillus niger

Summary Production of citric acid from beet molasses at a varying pH profile using cell recycle ofAspergillus niger was investigated. Best results in terms of citric acid concentration, yield, productivity and specific citric acid productivity were obtained with a substrate pH of 3.0.     

Pullulan production from brewery wastes by Aureobasidium pullulans

The production of pullulan from brewery wastes by Aureobasidium pullulans in shake flask culture was investigated. The maximum pullulan concentration (6.0g/l) was obtained after 72h of fermentation. The external addition of nutrients into the spent grain liquor improved significantly the production of pullulan. In this case, the highest values of pullulan concentration (11.0±0.5g/l), pullulan yield (48.2±1.5%), and sugar utilization (99.0±0.5%) were obtained in the medium (pH 6.5–7.5) supplemented with K₂HPO₄ 0.5%, l-glutamic acid 1%, olive oil 2.5%, and Tween 800.5%.     

The role of oxidative stress on carotene production by Blakeslea trispora in submerged fermentation

In aerobic metabolism, reactive oxygen species (ROS) are formed during the fermentation that can cause oxidative stress in microorganisms. Microbial cells possess both enzymatic and non-enzymatic defensive systems that may protect cells from oxidative damage. The antioxidant enzymes superoxide dismutase and catalase are the two key defensive enzymes to oxidative stress. The factors that induce oxidative stress in microorganisms include butylated hydroxytoluene (BHT), hydrogen peroxide, metal ions, dissolved oxygen tension, elevated temperature, menadione, junglone, paraquat, liquid paraffin, introduction to bioreactors of shake flask inocula and synthetic medium sterilized at initial pH 11.0. Carotenes are highly unsaturated isoprene derivatives. They are used as antioxidants and as coloring agents for food products. In fungi, carotenes are derived via the mevalonate biosynthesis pathway. The key genes in carotene biosynthesis are hmgR, ipi, isoA, carG, carRA and carB. Among microorganisms, Βlakeslea trispora is the main microorganism used for the production of carotenes on the industrial scale. Currently, the synthetic medium is considered the superior substrate for the production of carotenes in a pilot plant scale. The fermentation systems used for the production of carotenes include shake flasks, stirred tank fermentor, bubble column reactor and flat panel photobioreactor. This review summarizes the oxidative stresses in microorganisms and it is focused on the current status of carotene production by B. trispora including oxidative stress induced by BHT, enhanced dissolved oxygen levels, iron ions, liquid paraffin and synthetic medium sterilized at an initial pH 11.0. The oxidative stress induced by the above factors increases significantly the production of carotenes. However, to further reduce the cost of carotene production, new biotechnological methods with higher productivity still need to be explored.     

Ethanol production from deproteinized whey byβ-galactosidase coimmobilized cells ofSaccharomyces cerevisiae

Summary The performance of -galactosidase coimmobilized cells ofSaccharomyces cerevisiae was evaluated during shake flask fermentation of deproteinized cheese whey lactose to ethanol. The performance of the coimmobilized enzyme treatment was compared to that of a treatment using acid prehydrolyzed whey lactose (a readily available substrate). Enzyme coimmobilization resulted in a slower rate and a lower extent of substrate utilization, thus giving a lower maximum ethanol concentration (13.5 versus 16.7 g/l). It did result, however, in a better ethanol yield (95% vs. 89% theoretical). It appears that, compared to acid prehydrolysis of whey lactose, through -galactosidase coimmobilization we could succeed in obtaining substantial process simplifications, thus saving in equipment and operating cost, while gaining in ethanol yield at the cost of some reasonable loss in the rate and the extent of lactose utilization.     

Effect of the ratio of (+) and (−) mating type of Blakeslea trispora on carotene production from cheese whey in submerged fermentation

The effect of the ratio of (+) and (?) mating type of Blakeslea trispora on carotene production from deproteinized hydrolysed whey in shake flask culture was investigated. Also, the inoculum ratio of the two mating types on the morphology of the microorganism and the relationship between morphological changes of the fungus and product formation were studied. The concentration of carotenes was significantly affected by the ratio of (+) and (?) mating type of B. trispora. A ratio of 1:10 up to 1:100 of (+) and (?) type was found to achieve the highest carotene yields. The optimum ratio of the (+) and (?) mating types for the maximum pigment production (175.0 mg/g dry biomass at 8 days of fermentation) was found to be 1:10. The carotene content in B. trispora consisted of β-carotene, γ-carotene, and lycopene. At the maximum concentration of carotenes the proportion of β-carotene, γ-carotene, and lycopene (as percent of total carotenes) was 80, 12, and 8%, respectively. B.trispora growing in submerged fermentation is able to develop complex morphologies which have been classified into three major groups: freely dispersed hyphae, clumps and pellets. These parameters are strongly influence the production of carotenes.     

Ethanol production from nonsterilized carob pod extract by free and immobilized Saccharomyces cerevisiae cells using fed-batch culture

The production of ethanol from carob pod extract by free and immobilized Saccharomyces cerevisiae cells in batch and fed-batch culture was investigated. Fed-batch culture proved to be a better fermentation system for the production of ethanol than batch culture. In fed-batch culture, both free and immobilized S. cerevisiae cells gave the same maximum concentration (62 g/L) of final ethanol at an initial sugar concentration of 300 g/L and F = 167 mL/h. The maximum ethanol productivity (4.4 g/L h) was obtained with both free and immobilized cells at a substrate concentration of 300 g/L and F = 334 mL/h. In repeated fed-batch culture, immobilized S. cerevisiae cells gave a higher overall ethanol concentration compared with the free cells. The immobilized S. cerevisiae cells in Ca-alginate beads retained their ability to produce ethanol for 10 days. (c) 1994 John Wiley & Sons, Inc.     

Solid-state fermentation of carob pods for ethanol production

The production of ethanol from carob pods by Saccharomyces cerevisiae in solid-state fermentation was investigated. The maximal ethanol concentration (160±3 g/kg dry pods), ethanol productivity (6.7 ± 0.2 g/kg per hour), ethanol yield (40 ± 1.8%), biomass concentration (7.5 ± 0.4 x 10⁸ cells/g carob pulp) and fermentation efficiency (80 ± 2%) were obtained at an inoculum amount of 3%, a particle size of 0.5 mm, a moisture level of 70%, a pH of 4.5 and a temperature of 30°C. Under the same fermentation conditions both sterilized and non-sterilized carob pods pulp gave the same maximum ethanol concentration.     

Autolysis of Blakeslea trispora during carotene production from cheese whey in an airlift reactor

The phenomenon of autolysis in Blakeslea trispora during carotene production from deproteinized hydrolyzed whey in an airlift reactor was investigated. The process of cellular autolysis was studied by measuring the changes in carotene concentration, dry biomass, residual sugars, pH, intracellular protein, specific activity of the hydrolytic enzymes (proteases, chitinase), and micromorphology of the fungus using a computerized image analysis system. All these parameters were useful indicators of autolysis, but image analysis was found to be the most useful indicator of the onset and progress of autolysis in the culture. Autolysis of B. trispora began early in the growth phase, continued during the stationary phase, and increased significantly in the decline phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes. The biosynthesis of carotenes was carried out in the exponential phase, where the phenomenon of autolysis was not intense.     

Pretreatment of beet molasses to increase pullulan production

Pretreatment of beet molasses with cation exchange resin, sulphuric acid, tricalcium phosphate, potassium ferrocyanide, and ethylenediaminetetraacetic acid and disodium salt (EDTA) to increase the production of pullulan was investigated. Among the above techniques used for the removal of heavy metals, sulphuric acid treatment gave better results regarding polysaccharide concentration, polysaccharide yield, and sugar utilization. Aureobasidium pullulans grown on beet molasses produced a mixture of pullulan and other polysaccharides. The pullulan content of the crude polysaccharide was 30–35%. The addition of nutrients improved the production of polysaccharide. A maximum polysaccharide concentration (32·0±1·0 g litre⁻¹) was achieved in molasses solution (70 g litre ¹ initial sugar concentration, pH 6·5–7·5) treated with sulphuric acid and supplemented with K₂HPO₄ 0·5%, -glutamic acid 1%, olive oil 2·5% and Tween 80 0·5%. In this case, the highest values of biomass dry weight (33·8±1·0 g litre⁻¹), polysaccharide yield (63·5±2·5%), and sugar utilization (97·5±1·5%) were obtained at pH 6·5, 3·5, and 4·5–7·5, respectively.     

The effect of pH on production of citric and gluconic acid from beet molasses using continuous culture

Summary The effect of pH on the production of citric and gluconic acid, from beet molasses byAspergillus niger, was studied using continuous culture. At pH values above 2.5 gluconic acid was the major product, citric acid being the predominant product at low pH values. The optimum specific activities of citrate synthase, aconitase, NAD-linked isocitrate dehydrogenase, and NADP-linked isocitrate dehydrogenase occurred at pH 4 and of glucose oxidase at pH 5.