Use of response surface methodology for selection of nutrient levels for culturing Paecilomyces variotii in eucalyptus hemicellulosic hydrolyzate.

Eucalyptus hemicellulose was hydrolyzed by treating eucalyptus wood chips with sulfuric acid. The hydrolyzate was used as the substrate to produce single-cell protein by growing Paecilomyces variotii IOC-3764 for 72 or 96 h. The influences of rice bran, ammonium sulfate and fermentation time were verified by a 23 full-factorial central composite design. At the optimum process conditions, the cell concentration was 12.06 g/l, which was obtained when the microorganisms were cultivated for 89 h in a medium composed of 10 g/l rice bran, 2.0 g/l nitrogen and 1.1 g/l sodium phosphate. The mathematical model Y = 10.65 + 2.40X2 + 2.36X3 + 1.16X2X3 - 2.10X2(2) - 1.06X3(2) describes biomass production by P. variotii in eucalyptus hemicellulosic hydrolyzate with a determination coefficient of R2 = 0.9561, where X2 and X3 are ammonium sulfate and fermentation time, respectively.

The effect of media composition on the thermal resistance of Bacillus stearothermophilus.

Spores of Bacillus stearothermophilus ATCC 7953 were developed at 62 degrees C on 32 media composed of various amounts of 11 components: D-glucose, L-glutamic acid, yeast extract, peptone, sodium chloride, magnesium sulfate, ammonium phosphate, potassium phosphate, calcium chloride, ferrous sulfate and manganese sulfate. Statistical models were used and demonstrated a strong interaction of yeast/peptone/ammonium phosphate, contributing positively to the best sporulation yield (6-7 log10 spores). The most influential medium components on the thermal resistance (at 121 degrees C) of spores in suspension (calcium acetate, pH 9.7) were yeast extract (positively) and potassium phosphate (negatively), both creating the positive interaction, for spores from a 6-day incubation period. However, the strong negative effect of sodium chloride decreased the D-value from 1.81 min to 0.57 min upon increasing the incubation period (62 degrees C) from 3 days to 6 days. The D-glucose and peptone exhibited greater effects than the yeast extract and potassium phosphate interaction on D-values for 3-day spores on strip, just as the highly joint-positive peptone/sodium chloride effect maintained the thermal resistance of 6-day spores on strips. The spores on strip system showed less stability than the spores in suspension. The most stable spore system confirmed D-values at 121 degrees C at a range between 1.5 min and 1.9 min, which were obtained by keeping sodium chloride and potassium phosphate at minimum concentrations and yeast extract and peptone at maximum concentrations, regardless of the 3- to 6-day sporulation.

Bacillus stearothermophilus sporulation response to different composition media.

To evaluate the effectiveness of 11 commonly used ingredients to improve Bacillus stearothermophilus ATCC 7953 sporulation, with high spore yields in a short period of incubation, 32 composition media were set up by a fractional factorial 2IV11-6 design at two levels: D-glucose (0.018-0.25%), L-glutamic acid (0.040-0.10%), yeast extract (0.050-0.40%), peptone (0.30-0.50%), sodium chloride (0.001-1.0%), magnesium sulfate (0.001-0.20%), ammonium phosphate (0.010-0.035%), potassium phosphate monobasic (0.050-0.25%), calcium chloride (0.001-0.05%), ferrous sulfate (0.0003-0.002%), manganese sulfate (0.001-0.50%). The largest variation on Log10 CFU response took place due to sodium chloride main effect, by changing it from low to high levels. Magnesium sulfate, calcium chloride, and ferrous sulfate were split and exerted no detectable main effect influence on sporulation. Setting up two 16 runs for sodium chloride effect, in each of which the remainder levels were kept constant, other components contribution was studied. At low sodium chloride, best average 7.25 Log10 CFU yielded by fastening yeast extract and peptone at high level, and remainders at low level. Considering high level of sodium chloride, peptone, yeast extract and ammonium phosphate kept at high level and remainders at low level confirmed the best sporulation yield. Adjusted models evidenced a strong influence of joint yeast/peptone effect, associated to ammonium phosphate contributing positively. The reduced incubation period from 15 days to 3-6 days at 62 degrees C was attained for all 32 experimental runs.

Thermal resistance of Bacillus stearothermophilus spores on strips previously treated with calcium.

Moist thermal resistance parameters of spores of B. stearothermophilus ATCC 7953, inoculated in aqueous suspensions and on strips, were evaluated at 118 degrees C and 121 degrees C, by the proposed serum-bottle-mini-autoclave method. The present work studied the effect of alkaline calcium exchange-inducing storage treatments on the viability and moist heat-resistance of B. stearothermophilus spores, stored at -18 degrees C, following impregnation into filter paper strips which had been previously treated by immersion in alkaline 0.02 M calcium acetate. The thermal resistance of B. stearothermophilus spores on strip at set work conditions as biological indicator exhibited an average medium D (121 degrees C) of 1.92 min for concentrations of 10(5)-10(6) spores per strip over 360 days of storage in a freezer. The serum-bottle-mini-autoclave measuring system resulted in reasonably accurate and reproducible BIs calibration, before using them in an equipment validation program. The calcium acetate-strip system demonstrated a very high stability (Ea = 49.95 kcal/mol) to keep the spore viability and thermoresistance over steam cycles and storage. The heat activation kinetics of spores were also studied.