Study of oat bran as substrate for obtaining functional ingredients containing Lactobacillus acidophilus

The production of a functional ingredient (FI) containing Lactobacillus acidophilus (ATCC 4356) immobilised in oat bran was designed and optimised. The effects of the independent variables, incubation time and hydration level, were analysed and optimised to simultaneously maximise the cell count and growth, as well as the yield of the obtained FI and the resistance of the probiotic to simulated gastric conditions after 7 days of storage at 25 °C, minimising pH and nutrient loss (proteins and carbohydrates) in the washing water. The optimal design conditions found were 60 h of incubation and 13 mL of water/g oat bran. The growth kinetics of L. acidophilus was determined for the optimal system, showing no lag phase and the maximum specific growth rate (µ_max) of 1.1 ± 0.1 h^- 1. The system with an optimal hydration level (13 mL/g oat bran) and 36 h of fermentation was selected for being scaled-up in one order of magnitude. A reduction in cell growth, in the FI yield, and an increase in the value of the titratable acidity of the recovered supernatants were observed. During the fermentation, the acids produced were mainly lactic acid followed by acetic acid. It must be highlighted that the fermentation process proposed, reduced the initial oxalic acid content in oat bran. The production of FI based on oat bran containing L. acidophilus represented a sustainable process that also improved the nutritional aspects of the raw material. Oat bran could be by itself an adequate support for L. acidophilus storage stabilisation.