CONICET | Buscador de Institutos y Recursos Humanos

The market for functional foods, particularly those that incorporate probiotic bacteria, is constantly expanding, a fact that involves new technological challenges. The development of probiotic dietary supplements in powder requires feasible techniques at industrial scale such as spray drying. However, the process involves thermal stress to the cell with loss of viability and or metabolic activity. Previous studies showed that the fermentation conditions strongly affect robustness of lactic starter cultures. The aim of this study was to evaluate the effect to stirring on growth, acidification and tolerance to heat stress of the probiotic Lactobacillus rhamnosus CRL1505.Bach cultures were performed in CERELA medium (Under patenting process, pH 6.3) without pH control, under (150 or 400 rpm) or without stirring (control) at 37ºC. An active culture (16-h old) was inoculated (1%, w/v) and fermentation proceeded for 24h. Samples were aseptically withdrawn at 0, 4, 6, 8, 10, 12 and 24h. Growth (OD620nm and plate-dilution method), pH, lactose consumption (HPLC) and organic acid produced (HPLC) were evaluated. The heat stress tolerance (60ºC/ 5 min.) of cells harvested at a late stationary phase was also determined. Slight differences in growth between stirred (1.8 109 uf/ml) and static (8.4 108 uf/ml) cultures were observed, after 24 h. Lactic acid production increased more rapidly under aerated conditions than in static cultures. Acetic acid and ethanol formation was detected only in agitated cultures (9-16 mM), The cells grown with agitation were significantly more resistant than cells grown in static condition to heat stress. After 5 minutes at 60ºC, viable counts for stirred cultures were 3.2-fold higher than for static cultures regardless the stirring rate. These results are encouraged for drying probiotic cultures by spray.