Fruit residues as a sustainable feedstock for the production of bacterial polyhydroxyalkanoates

Polyhydroxyalkanoates (PHA) are bio-based and compostable polyesters while at the same time exhibiting physical and mechanical properties similar to conventional fossil-based plastic materials. To make the biotechnical production of PHA economically feasible, the utilization of a low-value feedstock, such as lignocellulosic biomass (LCB), is a common strategy to reduce both, the production costs and the energy consumption. The main problem of using LCB is the need of time-consuming, expensive and even hazardous pretreatments due to the resistance of those substrates to direct bioconversion by microorganisms. Preprocessing of LCB might claim make up for more than 30% of the total PHA production costs. Amongst carbon-rich waste materials, agricultural and in particular fruit residues are highly promising substrates since they are abundant, easily available and most importantly contains high amounts of fermentable sugars. A PHA production system based on fruit residues that do not require elaborate pretreatment represents a cleaner and sustainable process while at the same time making use of an agricultural waste stream. In addition to these characteristics, fruit residues can be considered as a sustainable substrate for PHA production because they do not compete directly with food crops. Scaling up and optimizing this process to utilize by-products from the fruit industry together with the integration of strategies to reduce energy, water and mass resources will not only make the production of microbial bioplastics such as PHA an eco-friendly process, but also help transform our industry into a bioeconomy with circular product streams. In this study, the use of fruit residues as potential feedstock in PHA production processes was analyzed, including biochemical pathways, pretreatments, production yields and other biotechnological aspects.