Aqualab

The pH of the black raspberry/red raspberry juice was determined by the official method (AOAC 981.12.) using a potentiometer (Thermo Fisher Scientific, Orion 3-star, USA), and the TSS was expressed as °Brix using a refractometer (ATAGO, Model PAL-α), water activity (a_w) was determined with an AquaLab (series 3, Decagon Devices, Inc., Pullman, WA, USA) at room temperature (25 °C) [9 ], and the titratable acidity (%TA) was determined by the burette method, against NaOH (0.1 N) solution by using phenolphthalein as the indicator (AOAC, 1990).

An initial characterization of the purchased breads was conducted on day 0 of the storage period. The pH value and total titratable acidity (TTA) were analyzed according to the guidelines of the International Association for Cereal Science and Technology (ICC) [22 ], using a pH meter (206-pH2, Testo SE & Co. KGaA, Lenzkirch, Germany) and a Titrator (Titroline 6000, SI Analytics GmbH, Mainz, Germany) equipped with 0.1 M NaOH (Merck KGaA, Darmstadt, Germany). Water activity (a_w-value) was measured with an electronic hygrometer (Aqua Lab, Decagon Devices, Pulmann, WA, USA). Using the chilled-mirror dew-point technique, the a_w-value was determined and previously calibrated with standard solutions of NaCl (6 M, VWR International GmbH, Darmstadt, Germany) and KCl (0.5 M, Carl Roth GmbH & Co. KG, Karlsruhe, Germany) of known activity. All measurements were performed at a sample temperature of 25 °C.

The pH values were monitored during fermentation and drying using a pH meter (WTW Microprocessor pH Meter, WTW GmbH), whereas the water activity was determined using an “Aqua Lab” device (CX‐2‐ Decagon Devices Inc.). Two independent samples were analyzed in triplicate.

The staling rate was assessed by determining both crumb and crust moisture content and water activity (a_w) of baked bread after cooling, and bread stored in perforated plastic bags at room temperature (25°C) after 1, 2, and 5 days from manufacture. Moisture was determined according to the ICC-Standard method 110/1 (1976), whereas a_w was measured with an Aqua Lab apparatus (Aqua Lab, Model 3TE, Decagon Devices, Inc., Pullman, WA, United States).

Milk powder was used in this study as a simplified model of dried food product. To obtain an inoculated milk powder (26% fat, Regilait, Saint-Martin-Belle-Roche, France), 50 mL cultures were centrifuged (3,400 g, 10 min at 25°C) and washed twice with 25 mL of PBS. In a final step, the supernatant was removed and cell pellets were weighed. Milk powder was added to the pellets at a 1:20 ratio (w_pellet:w_powder) and homogenized by means of a mortar for 30 min. Directly after inoculation, milk powder a_W was checked using an a_W meter (Aqualab, Decagon Devices, Inc, Dardilly, France) and found to be approximately 0.80. The cultivability of the bacteria was estimated using the spread plating method after incubation in TSA media for 24 h at 37°C and recorded as CFU/mL.