Production of polyhydroxyalkanoates (PHA) by mixed cultures has been widely studied in the last decade. Storage of PHA by mixed microbial cultures occurs under transient conditions of carbon or oxygen availability, known respectively as aerobic dynamic feeding and anaerobic/aerobic process. In these processes, PHA-accumulating organisms, which are quite diverse in terms of phenotype, are selected by the dynamic operating conditions imposed to the reactor. The stability of these processes during long-time operation and the similarity of the polymer physical/chemical properties to the one produced by pure cultures were demonstrated. This process could be implemented at industrial scale, providing that some technological aspects are solved. This review summarizes the relevant research carried out with mixed cultures for PHA production, with main focus on the use of wastes or industrial surplus as feedstocks. Basic concepts, regarding the metabolism and microbiology, and technological approaches, with emphasis on the kind of feedstock and reactor operating conditions for culture selection and PHA accumulation, are described. Challenges for the process optimization are also discussed.
"This technique imposes selective pressure on highly diverse mixed microbial communities (MMC) to select microorganisms with a certain production capacity (Ciesielski et al., 2008). To enrich the bacterial community with these bacteria that effectively produce PHAs, selective pressure is applied in the form of changing periods of presence and absence of the external carbon substrate (feast/famine phases) (Serafim et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: The development of processes for the production of biopolymer materials is being stimulated by a combination of factors. These factors include the negative effects of petrochemical-derived plastics on the global environment, depletion of global fossil fuel supplies, and the growing demands of an ever-increasing population for the products deemed necessary for an affluent modern lifestyle. In particular, polyhydroxyalkanoates have attracted attention as environmentally friendly alternatives to the synthetic polymers that are commonly used. Polyhydroxyalkanoates are polyesters produced and accumulated in intracellular granules by many microorganisms. Because they are biodegradable and biocompatible and can be produced by fermentation of renewable feedstocks, they are considered attractive substitutes for petroleum-derived polymers. To create bacterial polyesters, crude and waste plant oils, which can be difficult to dispose of, can be recovered and used as feedstock. This paper gives an overview of the potential for the production of polyhydroxyalkanoates with useful physicochemical properties by bacteria grown on renewable resources such as plant oils.
Journal of Cleaner Production 10/2015; 106:408-421. DOI:10.1016/j.jclepro.2014.09.040 · 3.84 Impact Factor
"For this category of food products, as their shelf life is short, there is no need for long-lasting packaging materials, making biodegradable materials interesting environmental-friendly solu- tions. Among the different biodegradable materials commercially available, poly(hydroxy-3-butyrate-co-3-valerate) (PHBV), is a bacterial polyester presenting the advantage of being bio-sourced and potentially prepared from food industry by-products (Serafim et al., 2008). Its main drawbacks are its high cost (3–5 D /kg, Chanprateep, 2010) and its barrier properties which are too high to fit respiring products needs (Shogren, 1997). "
[Show abstract][Hide abstract] ABSTRACT: Abstract Lignocellulosic fibres obtained by dry grinding of three different solid agro-residues, i.e. wheat straw, brewing spent grains and olive mills, were compared regarding their potential use as fillers in poly(3-hydroxybutyrate-co-valerate) (PHBV) for food packaging applications. Differences found in their composition might have influenced their grinding ability, as observed with the difference of sizes, i.e. 109 μm, 148 μm and 46 μm, respectively. Thereafter, composites structure was characterized regarding their morphology, fibre/matrix interaction, matrix molecular weight and crystallization behaviour. Poor fibre/matrix adhesion, degradation of PHBV polymer chains, and decrease of PHBV’s crystallinity were evidence. Consequently, mechanical properties were degraded in presence of the fibres. Water vapour transfer rate of composites was increased with wheat straw fibres introduction while it was decreased for olive mills-based materials. Regarding the food packaging applications, PHBV/wheat straw fibres composites appeared as promising materials to reach the requirements of respiring food products, whereas PHBV/olive mills composites would be more adapted for water sensitive products.
"For example, it has been recently demonstrated that sustainable packaging materials can be obtained by designing composite structures from constituents all derived from food industry by-products in order to fulfil mass transfer properties requirements for an optimal preservation of a targeted food type . Among the matrices used for the preparation of biocomposites, polyhydroxy-co-3-butyrate-co-3-valerate (PHBV), a bacterial aliphatic copolyester, has been reported to be produced from food industry by-products  and to provide a complete biodegradability in composting, backyard or landfill conditions, as well as recyclability  . In addition, PHBV is easily process-able using either extrusion or injection processes   . "
[Show abstract][Hide abstract] ABSTRACT: The present work aims at investigating the impact of wheat straw fibres (WSF) size, morphology and content on the process-ability and functional properties (mechanical properties and water vapour permeability) of PHBV-based composites. For that purpose, three types of fibres obtained by successive grindings (from the micrometric up to the millimetric scale) were used. It was shown that the highest possible filler level was all the more high when decreasing fibre size (over 50wt% in the case of micrometric fibres), due to reduced film heterogeneity and improved fibre wetting by the polymer. As regards functional properties, increasing fibre size and/or content led to a significant degradation of ultimate tensile properties, while the Young’s modulus was not significantly affected. At the same time, water vapour transmission rate was significantly increased from 11 up to 110 g.m-2.day-1, which could extend the applicability of PHBV/WSF composites as food packaging materials to respiring fresh products.
Composites Part A Applied Science and Manufacturing 02/2015; 72. DOI:10.1016/j.compositesa.2015.02.006 · 3.07 Impact Factor
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