Industrial Waste-Derived Nanoparticles and Microspheres Can Be Potent Antimicrobial and Functional Ingredients

Rapeseed oilcake or press-cake is generated as bulk waste during oil extraction from oilseeds. Owing to its high protein content, further processing of oilcakes into vegetable protein generates large quantities of fibrous residue (“oil-and-protein” spent meal) as by-product, which currently has very limited practical utility. Here, we report hydrothermal carbonization of this industrial waste to convert it into carbon nanoparticles, bestowed with multitude of functionalities. We demonstrate that these nanoparticles can be assembled into micrometer-sized spheres when precipitated from water by acetone. These microspheres, with their added feature of hemocompatibility, can be potentially utilized as an encapsulation vehicle for the protection of thermolabile compounds (such as protein); however, the secondary and tertiary features of the protein were marginally perturbed by the encapsulation process. The synthesized carbon nanoparticle was found to be an effective biocidal agent, exhibiting bacterial cellular damage and complex formation with the bacterial plasmid (evident from ethidium bromide exclusion assay), which are critical for cell survival. The results show the ability to convert industrial biowaste into useful nanomaterials for use in food industries and also suggest new scalable and simple approaches to improve environmental sustainability in industrial processes. 1. Introduction Since the early 1990s, carbon nanoparticles (CNPs) have garnered considerable interest in plethora of applications. Unfortunately, application of CNP in food and its packaging materials is still in its infancy. Several methods are currently in use to synthesize CNP in the sizes from 30？nm to several micrometers, such as arc plasma technique, self-assembly template approach, reduction of supercritical carbon dioxide with bimetallic lithium and potassium, pyrolysis of carbon sources, hydrothermal reaction, and chemical vapour deposition [1]. However, most of these methods either use complicated equipment or require rigorous reaction conditions or are time-consuming. Sometimes the catalysts involved in the synthesis may be occasionally encapsulated in the CNP [2], thus questioning the purity of the product. The higher cost for the production of CNP and its associated lethality limits its mass production. Endeavor to follow the dictates of sustainable development urges the global scientific community to opt for bioresources that are conferring safe “green” credentials. Biomass from food industries has been long recognized as an obvious renewable feedstock for production of