Modeling and simulation of cephalosporin C production in a fed-batch tower-type bioreactor

Immobilized cell utilization in tower-type bioreactor is one of the main alternatives being studied to improve the industrial bioprocess. Other alternatives for the production of beta -lactam antibiotics, such as a cephalosporin C fed-batch p recess in an aerated stirred-tank bioreactor with free cells of Cepha-losporium acremonium or a tower-type bioreactor with immobilized cells of this fungus, have proven to be more efficient than the batch profess. In the fed-batch process, it is possible to minimize the catabolite repression exerted by the rapidly utilization of carbon sources (such as glucose) in the synthesis of antibiotics by utilizing a suitable flow rate of supplementary medium. In this study, several runs for cephalosporin C production, each lasting 200 h, were conducted in a fed-batch tower-type bioreactor using different hydrolyzed sucrose concentrations, For this study's model, modifications were introduced to take into account the influence of supplementary medium flow rate. The balance equations considered the effect of oxygen limitation inside the bioparticles. In the Monod-type rate equations, eel concentrations, substrate concentrations, and dissolved oxygen were included as reactants affecting the bioreaction rate. The set of differential equations was solved by the numerical method, and the values of the parameters were estimated by the classic nonlinear regression method following Marquardt's procedure with a 95% confidence interval. The simulation results showed that the proposed model fit well with the experimental data,and based on the experimental data and the mathematical model an optimal mass flow rate to maximize the bioprocess productivity could be proposed.

A note on carcass characteristics of rabbits fed on a restricted system

Thirty four 65 days old New Zealand White female rabbits. weighting 1900 +/- 40 g, were separated in 3 groups and caged individually. One group was slaughtered when 70 days old (reference group, n=14). The second group was slaughtered 50 days later after ad libitum feeding (n = 6), and the third group was slaughtered also when 120 days old, but after restricted feeding since 70 days old i.e. 50% of the spontaneous feed intake of the 65-70 days period (restricted group n=14). Whole carcass weight and carcass cuts weights were measured after 24 hours storage at +4 degrees C. For each of the 3 groups in the previous order, slaughter live weight was 1992 - 2988 and 1887g; Chilled carcass percentage were 47.9 - 51.0 and 50.1. Feed restriction decreased the loin proportion of the carcass lower than that of the reference group (27.0 - 26.1 and 22.8% for the 3 groups in the same order) but increased the posterior limbs proportion (36.5 - 36.6 and 40.1).

Growth and metabolism of pacu (Piaractus mesopotamicus Holmberg 1887) juveniles fed diets containing different protein, lipid and carbohydrate levels

To verify the potential of lipids and carbohydrates to spare dietary protein and to understand the intermediary metabolism of interaction of these nutrients in pacu juveniles, an experiment was carried out to evaluate pacu physiological and performance parameters. The experimental design was completely randomized with 12 treatments in a 2 x 2 x 3 factorial arrangement, consisting of diets containing two digestible protein levels (200 and 230 g kg(-1) PD), two lipid levels (40 and 80 g kg(-1)) and three carbohydrate levels (410, 460 and 500 g kg(-1)). Fish-fed 230 g kg(-1) digestable protein (DP) showed increased glycaemia, decreased hepatic glycogen, as well as a smaller intake index and better feed conversion ratio. The higher dietary lipid level (80 g kg(-1)) reduced protein intake and serum protein concentration, increased liver and body fat content, but did not affect growth. At a lipid level of 80 g kg(-1), the increase in dietary carbohydrate levels promoted greater weight gain (WG), crude protein intake (CPI) and better feed conversion ratio (FCR). For fish fed diets containing 40 g kg(-1) lipid, the best energy-productive values (EPV) were obtained at 460 g kg(-1) carbohydrate. Increased levels of the main nutrients in the diets reduced the levels of serum triglycerides, while the increase in energy concentration increased the hepatosomatic (HSI) and glycaemia index values. Pacu used lipids as effectively as carbohydrates in the maximization of protein usage, as long as dietary protein was at a level of 230 g kg(-1) DP. The physiological parameters indicated that the best balance between the DP, dietary lipid and carbohydrate levels within the ranged this trial was obtained at 230, 40 and 460 g kg(-1), respectively, without lower growth.

Food intake and digestive efficiency in temperate wool and tropic semi-arid hair lambs fed different concentrate: forage ratio diets

This work was conducted to evaluate food intake and digestive efficiency of temperate wool and tropic semi-arid hair lambs, according to different concentrate: forage ratios in diet. Twenty-four lambs, averaging 90 +/- 1.8 days old and a mean body weight of 20 +/- 0.69 kg, 12 of them wool lambs, F, from Ideal x Ile de France crossing, and 12 others pure Santa Ines hair lambs, were distributed into a four replication 3 x 2 factorial arrangement consisting of three diets and two genotypes. Experimental diets consisted of: D1 = 60% concentrate mix (C) and 40% Cynodon sp. cv. Tifton-85 hay (F), D2 = 40% C and 60% F, and D3 = 20% C and 80% F. D1 was formulated for a daily gain of 300g per animal. Increasing forage levels in diets resulted in linear reductions (P < 0.01) in DM, OM, CP, TCH and metabolizable energy (ME) intake, and a linear increase (P < 0.01) in NDF ingestion. Tropic semi-arid hair lambs had higher DM, OM, NDF, CP, and TCH intake than temperate wool lambs. Although there were no genotype effects in OM and GE coefficient of digestibility, hair lambs showed more efficient (P < 0.05) digestibility of DM, CP, NDF and TCH. Increases in forage levels of diets corresponded to a negative linear effect (P < 0.01) in the apparent digestibility of DM, OM, CP, TCH and GE, while apparent digestibility of NDF increased linearly (P < 0.01). Total endogenous nitrogen (fecal plus urinary N) for F(1) Ideal x Ilede France wool and Santa Ines hair lambs were, respectively, 182 and 312 mg/kg(0.75) per day. Thus, Santa Ines tropic semi-arid hair lambs showed to be more responsive than F(1) Ideal x Ile de France temperate wool lambs to low quality fibrous diets. (C) 2004 Elsevier B.V. All rights reserved.