Glucose/lipid mixed substrates as a means of controlling the properties ofmedium chain length poly(hydroxyalkanoates)

Glucose-triacylglycerol (TAG) mixed substrates were used to modulate the ph ysical and mechanical properties of medium-chain-length poly(hydroxyalkanoa tes) (mcl-PHAs). Pseudomonas resinovorans NRRL B-2649 grew and produced mcl -PHAs on glucose and TAGs (coconut oil, C; soybean oil, S) after 24 h in a shake flask culture. However, with the exception of coconut oil, maximum ce ll productivity was not reached in any of the cultures until 72 h post-inoc ulation. Here, 50:50 mixtures of glucose and coconut oil (glc/C) or glucose and soybean oil (glc/S) resulted in intermediate cell productivities with a maximum of 57% and 48% of the CDW at 72 h, respectively. In addition, mix ed substrates resulted in mcl-PHAs with compositions that varied slightly o ver time. PHA-glc/C and PHA-glc/S were composed of 7 mol % and 8 mol % 3-hy droxydodecenoic acid (C-12:1), respectively at 72 h. These concentrations w ere intermediate to the C-12:1 concentration of PHA-glc and respective PHA- TAG. Also, significant amounts of 3-hydroxytetradecanoic acid (C-14:0), 3-h ydroxytetradecenoic acid (C-14:1), and 3-hydroxytetradecadienoic acid (C-14 :2) were present in PHA-glc/C and PHA-glc/S, which were derived from the re spective TAG, as glucose resulted in almost no C-14:X monomers. The molar m asses of each of the polymers remained relatively constant between 24 and 9 6 h. At 72 h, the number-average molar masses (M-n) of PHA-glc/C and PHA-gl c/S were 178 000 and 163 000 g/mol, respectively, which were also intermedi ate to the M-n of PHA-glc (225 000 g/mol) and the respective PHA-TAG (PHA-C 153 000 g/mol; PHA-S = 75 900 g/mol). These physical differences caused va riations in the mechanical properties of mcl-PHA films, thus providing a ne w and effective method of modifying their properties.