2.2. Experimental Design

The potential boosting effect of A. platensis on all the chosen strains and the commercial mix acidifying starter cultures was evaluated following the experimental design reported in Figure 1. Three different growth substrates were considered: Tryptic Soy Broth (TSB) (Oxoid), reconstituted skim milk powder (SSM) (Oxoid, Ltd., Basingstoke, United Kingdom), and a commercial soy-based beverage (SBB).

Schematic representation of the experimental design of this study: (A) Strains fermentation in TSB and SSM, (B) Commercial mix culture fermentation in SSM and SBB.

TSB, reconstituted to 30 g/L (w/v), was sterilized at 121 °C for 20 min. SSM, reconstituted to 10% (w/v), was sterilized at 100 °C for 10 min. SBB, composed by water, hulled soya beans (8%), sugar, calcium carbonate, acidity regulator (Potassium phosphates), flavouring, salt, stabiliser (Gellan gum), vitamins (B2, B12, D2), iodine (Potassium Iodide), was aseptically opened and immediately used.

The dehydrated organic A. platensis, kindly provided by S.A.Ba.R (Novellara, RE, Italy), was rehydrated in water (5% w/v) and then sterilized at 121 °C for 20 min.

Sterilized A. platensis (SP) (5%) was added at 0.25% and 0.50% (w/v) to each substrate (Figure 1).

Yeast extract (Oxoid) (YE) a common LAB growth stimulant, was evaluated as positive control (C+). It was rehydrated in water (5% w/v), sterilized at 121 °C for 20 min and added at 0.25% and 0.50% (w/v) to each substrate (Figure 1).