Corn-milling pretreatment with anhydrous ammonia.

Exposure to anhydrous ammonia has been suggested as a pretreatment for corn milling. Batches of corn were exposed to ammonia under controlled conditions. The amounts of ammonia absorbed and reacted with the corn were measured. The amounts were not more than are needed as nutritional supplement for yeast fermentation to ethanol. Loosening of the hull was observed qualitatively, and subsequent shearing in a disk mill followed by steeping for 2, 4, 6, or 8 h showed that germ could be recovered at higher yield and after a shorter steeping time compared to untreated control batches. Quality of oil was not affected by treatment with ammonia.

Dry-grind process for fuel ethanol by continuous fermentation and stripping.

Conversion of a high-solids saccharified corn mash to ethanol by continuous fermentation and stripping was successfully demonstrated in a pilot plant consuming 25 kg of corn per day. A mathematical model based on previous pilot plant results accurately predicts the specific growth rate obtained from these latest results. This model was incorporated into a simulation of a complete dry-grind corn-to-ethanol plant, and the cost of ethanol production was compared with that of a conventional process. The results indicate a savings of $0.03 per gallon of ethanol produced by the stripping process. The savings with stripping result from the capacity to ferment a more concentrated corn mash so there is less water to remove downstream.

Changes in membrane fatty acid composition of Pediococcus sp. strain NRRL B-2354 in response to growth conditions and its effect on thermal resistance.

Membrane fatty acid composition and thermal resistance (D value) of Pediococcus sp. were determined for mid-exponential-phase (ME) and stationary-phase (ST) cells grown in tryptic soy broth (TSB) and tryptone-glucose-yeast extract (TGY) at 28 and 37 degrees C. As the cells entered the stationary phase of growth, the unsaturated fatty acid, C18:1 n11c, produced during the exponential phase of growth was converted to its cyclic form, C19:0 Delta9c. This shift in membrane fatty acid composition was accompanied by an increase in the D values of this bacterium. Data from this study suggest that the membrane fatty acid composition of Pediococcus sp. is dependent on the growth conditions and that membrane fatty acid composition plays a critical role in thermal resistance. Thermal inactivation curves of Pediococcus sp. cells grown in TGY at 28 degrees C indicated the presence of a cell population that is heterogeneous in thermal resistance. The growth of this bacterium in TGY at 37 degrees C and in TSB at 28 and 37 degrees C resulted in cell populations that were uniform in thermal resistance with a lag time for thermal inactivation. Thermal inactivation curves of ME and ST cultures were similar. The data presented here suggest that the cell population's uniformity of thermal inactivation is independent of the growth phase of the culture.

Effects of ethanol concentration and stripping temperature on continuous fermentation rate.

The operation of a pilot plant consisting of a 14-1 fermentor, 10-cm packed column and condenser for continuous fermentation and stripping of ethanol was stable for more than 100 days. The feed consisted of a non-sterile solution of 560 g/l glucose with 100 g/l corn steep water. Fouling of the packing in the column with attached growth of yeast cells was controlled by in situ washing at intervals of 3-6 days. A computer simulation of the pilot plant was developed and used to analyze the data. The productivity of the continuous fermentor varied from 14 g ethanol to 17 g ethanol l-1 h-1. The yield was equal to the maximum theoretically possible: 0.51 g ethanol/g glucose consumed. Results are fit to linear models for the effects of ethanol concentration on specific growth rate and cell yield, and for the effect of stripping temperature on specific growth rate.

Control of packed column fouling in the continuous fermentation and stripping of ethanol.

By recycling the contents of a 14 L fermentor through a stripping column to continuously remove ethanol and reduce product inhibition, continuous complete conversion of nutrient feed containing 600 g/L glucose was achieved in a small pilot plant. Ethanol was recovered from the carbon dioxide stripping gas in a refrigerated condenser, and the gas was reheated with steam and recycled by a blower. Productivity of ethanol in the fermentor as high as 15.8 g/L/h and condensate production of up to 10 L/day of almost 50% by volume ethanol were maintained for up to 60 days of continuous operation. Weekly washing of the column packing in situ was required to prevent loss of performance caused by attached growth of yeast cells, which restricts the gas flow rate through the stripping column. (c) 1996 John Wiley & Sons, Inc.

Continuous fermentation and stripping of ethanol.

Recycling the contents of a continuous fermentor through a stripping column is proposed as a means of reducing product inhibition and lowering the cost of fuel ethanol production. A 2-L fermentor and 10-cm packed column were continuously operated for 150 days without contamination. Some fouling of the packing with attached yeast cells was observed which partially blocked the column. Cell yield was lower than in a simple continuous fermentor. Complete conversion of 200 g/L glucose feed and 90% conversion of 600 g/L glucose feed were achieved. Data were analyzed by computerized process simulation. Cost analysis indicated that, with heat recovery to reduce heating and cooling costs, the continuous fermentor/stripper is possibly a lower-cost alternative to conventional fermentation and distillation.

Preparation of casein using carbon dioxide.

The effects of pressure, temperature, residence time, and mass of skim milk on some characteristics of casein, prepared by precipitation with high pressure CO2, were examined in a batch reactor. For a 500-g milk sample, precipitation occurred at pressures > 2760 kPa and temperatures > 32 degrees C. Residence time was not significant and was held at 5 min. Yields were maximum at 2750 to 5520 kPa and at 38 to 49 degrees C for a 500-g milk sample. The resulting whey had a pH of 6.0. The casein product had an acceptable appearance and had greater solids, ash, and Ca contents than commercial acid caseins. Particle size distribution studies showed that the mean particle size was sensitive to precipitation pressure and temperature and was similar to that of acid caseins produced under laboratory conditions. The HPLC studies of the casein and whey fractions showed that precipitation by CO2 did not result in fractionation of casein or whey proteins to their component proteins.

Effect of cultural conditions on production of eicosapentaenoic acid by Pythium irregulare.

The effect of culture conditions upon lipid content and fatty acid composition of mycelia of Pythium irregulare was investigated with particular attention to increasing the yield of 5,8,11,14,17-eicosapentaenoic acid (20:5; omega-3)(EPA). All experiments were done by shake flask culture using a yeast extract + malt extract medium. The maximum growth rate was obtained at 25 degrees C, but maximum EPA production was obtained at 12 degrees C. The highest EPA production was 76.5 micrograms EPA/ml 13 days fermentation at 12 degrees C. Addition of glucose during fermentation increased the yield considerably. The highest yield was 112 micrograms/ml, obtained at 13 days fermentation with spiking on day 11. Fermentation time could be shortened by initial incubation at 25 degrees C for 2 days, followed by incubation at 12 degrees C for 6 days. The culture also produced arachidonic acid and other omega-6 polyunsaturated fatty acids. EPA production was also obtained with lactose or sweet whey permeate, a by-product of cheese manufacture that contains lactose as the main carbohydrate.