الفهرس 
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Abstract
The present study was concerned to estimate the capacity of six fungal isolates to produce ergosterol and to select the most potent one.
The production of ergosterol was carried out through two steps;first step was carried out on the shake flask to optimize the growth conditions of Saccharomyces boullardi ATCC236 to produce ergosterol and to investigate the suitable physiological and biochemical parameters required for ergosterol production .The second step include the production on the level of bioreactor.
• The fungal isolates were grown aerobically under submerged conditions in Erlenmeyer flasks (250ml) containing the components of fermentation medium. All experiments were carried out on an orbital shaking incubator at 30°C and agitated at 150rpm.
• The effect of different media composition on ergosterol production was studied. The fermentation medium No. II with a composition of ( gm/100ml); glucose 8 , corn syrup 8, urea 0.1, KH2PO4 0.6 MgSO4 0.1, NaNO3 0.2 was found to give a maximum ergosterol output (67.5mg/L). While, the weak ergesterol productivity ( 43 and 42.5mg/L) was accompanied with other used media No. I, III., respectively.
• On studying the effect of different medium volumes (25, 50,75,100,120ml) the maximum ergosterol output was obtained in 50ml of medium.
• Different fermentation periods(1,2,3,4,5,6,7,8,9 and 10 days) were studied. The optimum period was found to be after 8 days, as it gives the highest ergesterol production (84.76 mg/L)
• The effect of different pH values (4, 4.5, 5, 5.5, 6, 6.5, 7, 8, 9) on ergosterol production was studied. The maximum ergosterol yield was obtained at pH 9, where the productivity was accompanied with alkalinity.
• To overcome the shift in the pH value of the fermentation medium due to the different metabolic activities of the experimental producer, three types of buffered solutions were used to cover a pH range from 4 to 10. The best ergosterol output was obtained in buffered medium at pH 9.2.
• The fermentation process was carried out by inoculating 3ml from different inoculum ages (1,2,3,4 ,5 and 6 days) into the production medium. The yields of ergosterol were improved with an inoculum age of 4 and 5 days. The best ergosterol output was obtained by using an inoculum age of 6 days.
• The effect of different inoculum size on ergosterol production was studied by inoculating the fermentation medium with different inoculum sizes (2 ,3, 4, 6,8,10 and 12ml/ flask). The ergosterol production was negatively responded to the inoculum size used and the best ergosterol output was obtained at an inoculum size of 3ml/ 50ml of fermentation medium.
• On studying the effect of carbone source in the culture medium on ergosterol production, the glucose in the production medium was substituted by different carbone sources (lactose, ethanol, acetic acid, sucrose, starch and glycerol). The maximum ergosterol output (196.8mg/L) was obtained by using glucose as cabone source, while moderate yields (133.36 and 186.7 mg/L) were obtained by using lactose and ethanol, respectively.
• The effect of different glucose conc. (40, 60, 80, 100 and 120g/L) on ergosteral production was studied. The maximum ergosterol yield was obtained at a glucose conc.of (100g/L).
On studying the effect of different nitrogen sources (corn steep liquar, yeast extract, peptone, NH4SO4, NH4Br and urea) on the production of ergosterol. The best ergosteral yield (221.4 mg/L) was obtained by using corn steep liquar and a considerable ergosteral output (191.5mg/L) was obtained by using yeast extract as a nitrogen source.
• Different conc. of corn steep liquor (40,50,80,100, and 120mg/L) were investigated. The best engosterol output (221.4mg/L) was obtained at a conc. of 80g/L. A remarkable decrease of ergosterol yield (148.2 and 145.6 mg/L) was obtained at a conc. of 100, 120g/L, respectively.
• Some additives were added to the fermentation medium for ergosterol production. The maximum yield (230.62 mg/L) of ergosterol was obtained with the addition of ZnSO4 and the moderate yields (84.20, 115.82 mg/L) were obtained with the using of FeSO4 and CuSO4, respectively. The lowest yields (36.84, 42.7 and 52.65 mg/L) were obtained with the addition of NiSO4, CoCl2 and Sodium Citrate, respectively.
• On studying the effect of different agitation speeds (50, 100, 150, 200rpm) on the productivity of ergosterol. The best yield (289.27 mg/L) was obtained at an agitation speed of 200 rpm, which reflected the importance of O2 for the production of ergosterol.
• Different fermentation runs were carried out using 5 L laboratory stirred fermentor (B. brawn Cpu 200) with working volume of 3L containing the fermentation medium (gm%) glucose 10, corn steep 8, urea 0.1, KH2PO4 0.6, MgSO4 0.1 and NaNO3 0.2, pH was adjusted at 9. After sterilization at 121°C for 20min, the bioreactor was inoculated with 10% (v/v) of the previously prepared yeast culture. The cultivation was conducted under the following conditions, temperature 30 ±20C, agitation speed 400rpm, airflow 10 L/ min for 6 days.There is a gradual increase in ergosterol productivity during the first stages of fermentation and the best ergosterol output (342mg/L) was obtained after fermentation period of 72hr. The productivity decreased and reached to 179(mg/L) after 120 hrs.
• On studying the batch fermentation of S. boulardii ATCC236 for ergosterol production using a higher agitation speed of 600rpm with the same fermentation conditions as previously discussed. the productivity of ergosterol was increased to the maximum output (488mg/L) after 72hrs.
• On studying the fed batch culture of S. boulardiiATCC236 for ergosterol production using glucose feeding. the sequential addition of glucose after 48hr of fermentation process led to an increase in ergosterol contents and the maximum yield (887mg/L)was obtained after 72hr.
• On studying the fed batch culture of S.boulardii ATCC236 for ergosterol production using corn steep feeding. Adding corn steep liquor after 48hrs accompanied with a remarkable increase in the productivity of ergosterol. The best yield (1235mg/L) was obtained after72hr. At the longer fermentation time, a decrease in ergosterol out puts was noticed.