Uv vis du 640

US-treated yeasts were inoculated in YPG broth to 3 log CFU/mL; the medium was supplemented with NaCl (2–5%-stress conditions for the strains used in this research) and incubated at 25 °C (yeast optimal temperature) or 37 °C (temperature of human body; probiotic properties for yeasts). Growth was evaluated after 24 and 48 h at an absorbance of 600 nm using a spectrophotometer UV–Vis DU 640 Beckman (Fullerton, CA, USA).
The results were modelled as the growth index [28 (link)] modified by Racioppo et al. [19 (link)]:
where Abs_s is the absorbance of US-treated strain and Abs_c is the absorbance of the control (untreated microorganism, combination A1).
GI was analyzed as suggested by Bevilacqua et al. [28 (link)] and modified as follows:

GI < 25%: complete inhibition;

25% < GI < 75%: partial inhibition;

GI > 75%: no inhibition.

A new class was added to point out a positive effect on yeast growth:

GI > 120%: growth enhancement.

Growth profile of alicyclobacilli was assessed as follows:
The samples were inoculated to 6 log cfu/ml with either cells or spores and incubated for 7 days: growth was assessed every day by measuring absorbance at 420 nm through a spectrophotometer UV-VIS DU 640 Beckman (Fullerton, CA).
Results from phenotyping were converted into quali-quantitative codes (0, no growth or no enzymatic activity; 1, growth or positive enzymatic activity) and used as input data to run a cluster analysis through the add-in component of Excel XLSTAT (Addinsoft, Paris, France).