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In deseeded opuntia juice medium batch and continuous cultivation ofCandida utilis produced 12 and 19.9gl−1 yield of the SCP respectively. Its biological value(72), digestibility coefficient(70) and protein score(58) indicated it to be a good protein.

Submerged batch cultivation under controlled environmental conditions of pH 3.8, temperature 30°C, and KLa≥200 h−1 (above 180 mMO2 l −1 h−1 oxygen supply rate) produced a maximum (12.0 g·l −1) SCP (Candida utilis) yield on the deseeded nopal fruit juice medium containing C/N ratio of 7.0 (initial sugar concentration 25 g·l −1) with a yield coefficient of 0.52 g cells/g sugar. In continuous cultivation, 19.9 g·l −1 cell mass could be obtained at a dilution rate (D) of 0.36 h−1 under identical environmental conditions, showing a productivity of 7.2 g·l −1·h−1. This corresponded to a gain of 9.0 in productivity in continuous culture over batch culture. Starting with steady state values of state variables, cell mass (CX−19.9 g·l −1), limiting nutrient concentration (Cln−2.5 g·l −1) and sugar concentration (CS−1.5 g·l −1) at control variable conditions of pH 3.8, 30°C, and KLa 200 h−1 keeping D=0.36 h−1 as reference, transient response studies by step changes of these control variables also showed that this pH, temperature and KLa conditions are most suitable for SCP cultivation on nopal fruit juice. Kinetic equations obtained from experimental data were analysed and kinetic parameters determined graphically. Results of SCP production from nopal fruit juice are described.

Candida utilis was grown in batch and continuous culture on prickly pear juice as sole carbon and energy source. In batch culture the maximum specific growth rate (mum) and the substrate yield coefficient (Yps) varied according to sugar concentration. When the fermentation was carried out with 1% sugar, mum and Ys were 0.47/h and 42.6%, respectively. The best yields occurred in a chemostat at the pH range of 3.5 to 4.5 and temperature of 30 C. A beneficial effect on Ys was observed when the dilution rate (D) was increased. At a D of 0.55/h, the productivity was 2.38 g/liter per h. The maintenance coefficient attained a value of 0.09 g of sugar/g of biomass per h. Increases of D produced higher protein contents of the biomass. The information obtained indicates that protein production with Candida utilis, using prickly pear juice, should be carried out a high dilution rates where the Ys and protein content of the cell mass are also higher.