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

Glucose-triacylglycerol (TAG) mixed substrates were used to modulate the physical and mechanical properties of medium-chain-length poly(hydroxyalkanoates) (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 cell productivity was not reached in any of the cultures until 72 h post-inoculation. 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, mixed substrates resulted in mcl-PHAs with compositions that varied slightly over time. PHA-glc/C and PHA-glc/S were composed of 7 mol % and 8 mol % 3-hydroxydodecenoic acid (C(12:1)), respectively at 72 h. These concentrations were 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-hydroxytetradecenoic 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 respective TAG, as glucose resulted in almost no C(14:)(X) monomers. The molar masses of each of the polymers remained relatively constant between 24 and 96 h. At 72 h, the number-average molar masses (M(n)) of PHA-glc/C and PHA-glc/S were 178,000 and 163,000 g/mol, respectively, which were also intermediate to the M(n) of PHA-glc (225,000 g/mol) and the respective PHA-TAG (PHA-C = 153,000 g/mol; PHA-S = 75,000 g/mol). These physical differences caused variations in the mechanical properties of mcl-PHA films, thus providing a new and effective method of modifying their properties.

Viscoelastic properties of linseed oil-based medium chain length poly(hydroxyalkanoate) films: effects of epoxidation and curing.

Medium-chain-length poly(hydroxyalkanoate) (mcl-PHA) polymers derived from linseed oil (PHA-L) have a relatively small molar mass and contain a high concentration of unsaturated side-chains. As such, these polymers are amorphous and take on the consistency of a viscous liquid at room temperature. In order to increase the application potential of this material, the side-chain olefinic groups of PHA-L were converted to epoxy derivatives (PHA-LE) using m-chloroperoxybenzoic acid (m-CPBA). Epoxidation resulted in a 37% conversion of olefinic to epoxy groups. The epoxy groups enhanced the PHA-LE film susceptibility to crosslinking upon exposure to air. PHA-LE films began to crosslink and stiffen in less than 25 days, whereas PHA-L films began to crosslink between days 50 and 75. The PHA-LE films showed an increase in tensile strength (TS, from 4.8 to 20.7 MPa) and Young's modulus (YM, from 12.9 to 510.6 MPa) between 25 and 100 days. In contrast, PHA-L had a TS of 25.0 MPa and YM of 767.8 MPa after 100 days. Epoxidation helped induce crosslink formation; however, aging for 100 days ultimately resulted in crosslinked films from both PHA-L and PHA-LE with higher strength and durability than the original materials.

Lipase-catalysed production of biodiesel fuel from some Nigerian lauric oils.

Fatty acids esters were produced from two Nigerian lauric oils, palm kernel oil and coconut oil, by transesterification of the oils with different alcohols using PS30 lipase as a catalyst. In the conversion of palm kernel oil to alkyl esters (biodiesel), ethanol gave the highest conversion of 72%, t-butanol 62%, 1-butanol 42%, n-propanol 42% and iso-propanol 24%, while only 15% methyl ester was observed with methanol. With coconut oil, 1-butanol and iso-butanol achieved 40% conversion, 1-propanol 16% and ethanol 35%, while only traces of methyl esters were observed using methanol. Studies on some fuel properties of palm kernel oil and its biodiesel showed that palm kernel oil had a viscosity of 32.40 mm2/s, a cloud point of 28 degrees C and a pour point of 22 degrees C, while its biodiesel fuel had a viscosity of 9.33 mm2/s, a cloud point of 12 degrees C and a pour point of 8 degrees C. Coconut oil had a viscosity of 28.58 mm(2)/s, a cloud point of 27 degrees C and a pour point of 20 degrees C, while its biodiesel fuel had a viscosity of 7.34 mm2/s, a cloud point of 5 degrees C and a pour point of -8 degrees C. Some of the fuel properties compared favourably with international biodiesel specifications.

Heat resistance and fatty acid composition of Listeria monocytogenes: effect of pH, acidulant, and growth temperature.

The objective of this study was to determine the influence of pH, acidulant, and growth temperature history on the heat resistance and fatty acid composition of Listeria monocytogenes Scott A. Cells were grown to late exponential phase (OD600 = 0.6) at 10, 19, or 37 degrees C in brain heart infusion broth acidified to pH 5.4 or 7 with either acetic or lactic acid. Thermal death times at 60 degrees C subsequently were determined by using a submerged-coil heating apparatus. The surviving cell population was enumerated by spiral-plating heated samples onto tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. The thermal resistance of cells cultured at a particular temperature was significantly lower (P < 0.05) when lactic acid was used to acidify the medium of pH 5.4. Regardless of acid identity, D values significantly decreased (P < 0.05) with increased growth temperature when the pH of the growth medium was 5.4, whereas D values significantly increased (P < 0.05) with increased temperature at pH 7. At pH 5.4 adjusted with lactic acid, D values were 1.30, 1.22, and 1.14 min for cells grown at 10, 19, and 37 degrees C, respectively. At pH 5.4 adjusted with acetic acid, L. monocytogenes failed to grow at 10 degrees C; the D values were 1.32 and 1.22 min when the cells were grown at 19 and 37 degrees C, respectively. At pH 7, the D values were 0.95, 1.12, and 1.28 min with lactic acid and 0.83, 0.93, and 1.11 min with acetic acid at 10, 19, and 37 degrees C, respectively. The most abundant fatty acids (44 to 82%) were branched-chain saturated fatty acids (anteiso-and iso-C15:0 and iso-C17:0) regardless of pH, acidulant, or growth temperature. However, there was an increase in C15:0 isomers at the expense of iso-C17:0 when the growth temperature was lowered from 37 to 10 degrees C. While variable changes in longer-chain fatty acids were found, the percentage of longer-chain (C16 and C18) fatty acids was greatest when L. monocytogenes was grown at 37 degrees C regardless of pH or acidulant. This study demonstrates that the heat resistance of L. monocytogenes depends upon its growth conditions.

Fatty acid turnover rates in the adipose tissues of the growing chicken (Gallus domesticus).

The purpose of this study was to investigate the mobility of fatty acids in adipose tissue of the chicken and to determine whether adipose tissue dynamics are altered by dietary repartitioning agents. To this end, the turnover rates of fatty acids and triglycerides were estimated in adipose tissue of growing chicks by using isopentadecanoic acid (IPDA) and elaidic acid (EA) as marker dietary fatty acids. The half-life of IPDA in abdominal and sartorial adipose tissues of birds over 6 to 10 wk of age were 20 +/- 4 and 23 +/- 6 d, respectively. The half-life for the remaining total carcass lipids was 23 +/- 3 d. The corresponding half-life for EA in abdominal fat tissue of birds over 2 to 7 wk of age was 18 +/- 3 d, a half-life not significantly different from the IPDA half-lives. On the other hand, a thyromimetic repartitioning agent (L-94901) fed to birds at the 2 ppm level from 2 to 7 wk of age significantly decreased the half-life of EA in abdominal fat tissue to 6 +/- 2 d. The data suggest that fatty acids were released from a more labile adipose site and subsequently reincorporated into abdominal and sartorial tissues and that fat mobilization occurred at the same time as did adipose tissue deposition in the growing chicken.