Exploration and Development of Valorisation Routes for Citrus and Potato Waste using Green Methodologies

This thesis aimed to establish biorefinery schemes for two large-volume waste feedstocks (citrus juicing waste and potato waste) adhering to the 12 principles of green chemistry and in accordance with the Sustainable Development Goals set out by the United Nations. A citrus waste biorefinery based around microwave technology was developed, with multiple products. Citrus oil was extracted via microwave-assisted steam distillation (2.4% dry weight) with comparable quality citrus oil extracted via conventional steam distillation. High-methoxyl pectin was extracted under acid-free conditions with microwaves (15.36% dry weight). Pectin showed good gelling capabilities and passed industrial food standard tests. The cellulosic residue remaining after microwave extractions showed good water binding capacity for use as a rheology modifier. Collaboration with Brazilian company Agroterenas generated a map of processing and waste treatment at a modern citrus juicing plant. Industrial citrus juicing waste from Agroterenas was subjected to microwave-assisted pectin extraction (21.19% dry weight). The impact of Huanglongbing disease (HLB) on pectin content was explored with a reduction of 38% in infected oranges. Proteins were successfully extracted from waste potatoes and identified by SDS-PAGE followed by MALDI-TOF/TOF-MS. The protease inhibitors present in the protein were isolated and purified for potential application as appetite suppressants. The purified protease inhibitors were subjected to crystallisation screening with the aim of gaining a crystal structure of the protein. While crystals were obtained, work is needed to obtain a crystal with good diffraction. Complexation studies were performed on the protease inhibitor and its target enzymes, trypsin and chymotrypsin. A stable complex was isolated via size exclusion chromatography and analysed via SDS-PAGE and LC-MS/MS demonstrating that all three proteins were present. Finally, pectin from citrus waste was tested in a materials application. Porous, carbonaceous materials created from the pectin dubbed ‘Pecbon’ were tested in CO2 capture and compared to activated carbon. Pecbon carbonised to 800 C (P800) was found to adsorb 2.050.24 mmol/g CO2 showing similar performance to activated carbon (2.120.05 mmol/g).