Optimization of poly(beta-hydroxybutyric acid) recovery from Alcaligenes latus: combined mechanical and chemical treatments

Recovery of the intracellular bioplastic poly(beta-hydroxybutyric acid) or PHB from fed-batch cultured Alcaligenes latus, ATCC 29713, was examined usi ng combinations of chemical and mechanical treatments to disrupt the cells. Chemical pretreatments used sodium chloride and sodium hydroxide. For salt pretreatment the cells were exposed to NaCl (8 kg m(-3)) and heat (60 degr ees C, 1 h), cooled to 4 degrees C, and mechanically disrupted. For alkalin e treatments, the cells were exposed to sodium hydroxide (0.025-0.8 kg NaOH per kg biomass) and mechanically disrupted at ambient temperature. A combi ned treatment with sodium chloride (8 kg m(-3)), heat (60 degrees C, 1 h), and alkaline pH shock (pH 11.5, 1 min) was also tested. Mechanical disrupti on employed a continuous flow bead mill (2,800 rpm agitation speed, 90 mi m in(-1) slurry flow rate, 512 mu m mean bead diameter, bead loadings of 80% or 85% of chamber volume). Disruption was quantified by protein release. Ov er most of the disruption period, the release of PHB was approximately prop ortional to protein release. Regardless of the pretreatment or bead load, t he disruption obeyed first order kinetics; hence, the rate of protein relea se was directly proportional to the amount of unreleased protein. Relative to untreated biomass, pretreatment always produced earlier protein release during milling. Pretreatment with a minimum of 0.12 kg NaOH per kg biomass was necessary to enable complete disruption within three passes (85% bead l oad). Untreated biomass required more than twice as many passes. Irrespecti ve of the chemical pretreatment, the bead loading strongly influenced the d isruption rate which was higher at the higher loading. Alkaline hydrolysis associated PHB loss was observed, but it could be limited to insignificant levels by immediate neutralization of disrupted homogenates.