Carob-Agro-Industrial Waste and Potential Uses in the Circular Economy

Ceratonia siliqua L. is a typical Mediterranean tree species that has also been introduced to the temperate regions of Central America, Australia, and Africa. The carob fruit consists of the pulp and the seed (endosperm and germ), each one of which is used in a great variety of bakery products and beverages, as animal feed, food additives, syrups, ice creams, dietetic products, and for the photographic emulsion. For instance, the carob pulp is used to make carob syrup and molasses through the recovery of sugars, whereas the seed is used to produce Locust Bean Gum (LBG), which is used as a growth medium, and as a thickener, chemically known as E410. Currently, there is a strong interest in carob re-cultivation due to the tree's ability to withstand drought and adapt to climate change, further to its medical and food exploitation potential. In 2016 and 2017, the global carob production exceeded 170,000 tons, with the highest volumes of carob production coming from Spain, Portugal, and Italy, followed by Morocco, Turkey, Greece, Cyprus, Lebanon, and Algeria. Carob fruit harvesting and processing does not produce significant amounts of agricultural and industrial waste. Agricultural waste mainly includes traps for rodents, plastic packaging waste, and field residues such as stems and leaves. On the other hand, industrial processing from carob mills and the food industry produces waste such as solid residual parts and plant biomass (e.g., leaves), which can be composted or used as animal feed. In carob factories, during the roasting and milling processes, air pollutants such as particulate matter (PM) and biogenic volatile organic compounds (VOCs) are released. Carobs and their waste have been studied by various research groups as a source of phenolic compounds and carbohydrates, as an alternate source for the production of biofuels (e.g., biohydrogen and bioethanol), in food packaging applications, in wastewater treatment, as well as a soil organic amendment. Overall, carob and carob waste have promising applications as raw material for further investigation and utilization.