Poly(γ-glutamic) acid (PGA) production from confectionery waste using Bacillus species

Abstract

Approximately 9 million tonnes of food waste is generated annually in South Africa. Its treatment, including treatment of confectionery waste, is costly because of the high chemical oxygen demand (COD) loads; as a result much of this waste is sent to landfill. South Africa’s confectionery industry contributes to a significant proportion of the country’s economy. Among the confectionery waste entering landfills are defective material, expired sweets and returns. This high COD waste can create breeding grounds for pathogenic microorganisms and anaerobic methanogens, causing negative environmental impacts. Part of the Department of Science and Technology (DST) Waste Research, Development and Innovation (RD&I) roadmap initiative is to minimise waste entering landfills by identifying waste sources from which to produce value that will contribute to social and economic growth. Confectionery waste has a high sugar content which can be used for feedstock to bioprocesses. By placing this bioproduction into a waste biorefinery framework, bio-based raw materials can be used to produce competitively priced products with low environmental impact, thereby optimising remediation and value generation simultaneously. Ongoing research at the Centre for Bioprocess Engineering Research (CeBER) at the University of Cape Town has shown that a wastewater biorefinery approach can use wastewater as feedstock for the generation of products of value. Previous studies have investigated potential products of value based on nutrient loads found in wastewater as well as the nature of the product. Among the organisms selected was the Bacillus species, producing the potential product poly-γ-glutamic acid (PGA), an extracellular poly-amino acid when there is an excess of nutrients. Similarly, this product could potentially be produced from sugar-rich waste candy. The aim of this study was to explore the use of hard candy waste as a feedstock for PGA, and Bacillus licheniformis JCM 2505 was selected as it was characterised in terms of the nutrients needed. The most attractive attribute of this strain was that it did not need L-glutamic acid to synthesise PGA but could do so from sugar. L-glutamic acid is costly. Using a cheaper nitrogen alternative would make the process more cost effective. To investigate this potential, the confectionery waste was characterised to identify the nutrients, namely, sugars, organic nitrogen and key trace elements needed for cell function and PGA production. Results showed that the nitrogen content and trace element concentrations were insignificant, as it was determined that the waste consisted mostly of sucrose. This therefore had to be supplemented with a basal medium containing the supplementation needed for cell function and PGA production. The growth of B. licheniformis was profiled in Erlenmeyer shake flasks using candy waste supplemented with the basal medium, with sucrose supplemented with basal medium as a control. The results showed similar trends on candy waste and sucrose.