2.2. Cheese whey fermentation procedure
Substrates for the selection of PHAs-accumulating bacteria and
for the PHA accumulation tests were obtained by carrying out two
different cheese whey fermentations. The first fermentation was
set up with fresh cheese whey (cheese whey 1 – FCW1) in order
to achieve a high percentage of lactic acid in the final fermented
medium thanks to the presence in the substrate of autochthonous
lactic bacteria. The second fermentation test was performed by
using sterilized cheese whey (cheese whey 2 – FCW2) (120 C for
20 min), subsequently inoculated with sporogenous acidogenic
bacteria coming from the liquid fraction of digestate (50 g TSS L1
;
35 g Volatile Suspended Solids – VSS – L1
) collected from an
anaerobic digestion plant, then heat-shocked at 100 C for 1 h
(1:5 ratio, inoculum: cheese whey).
The two 96-h fermentation tests were carried out in two glass
flasks with a working volume of 500 mL, mechanically stirred at
150 rpm, with a pH set at 5.5 corrected automatically by adding
3 mol L1 KOH in a lab-incubator kept at 37 C. The two flasks were
fluxed with N2 and kept closed to maintain anaerobic conditions
inside.
Before their use as substrates for PHA production, the two fermented
cheese wheys were heated in a closed bottle at 100 C
for 30 min, then cooled and centrifuged at 8385g for 10 min, keeping
the supernatant to be used as the substrate.
2.3.