Cadmium bioremediation of cocoa by Bacillus xiamenensis Luk70 in post-harvest processing

Abstract Cadmium (Cd) levels in chocolate pose serious health risks due to the toxicity of this trace element. This research introduces a post-harvest bioremediation approach using Bacillus xiamenensis Luk70 biomass; a Gram-positive, spore-forming, motile bacterium with high tolerance to abiotic stress, to decrease Cd levels in fermented cocoa beans. The process involved applying an equal ratio (kg:liter) of bacterial biomass solution to fermented cocoa beans under ambient conditions. The effects of cocoa bean fermentation percentage, treatment time, nib pH, and bacterial biomass composition (vegetative cells and spores) were systematically evaluated. Cd concentrations in cocoa nibs were reduced by a factor of 1.45–1.77 within the first 12 h of treatment. The lowest final Cd concentration obtained was 1.43 ± 0.20 mg kg⁻¹, which complies with EU limits for chocolate with 55% cocoa solids. A negative correlation was observed between nib pH and Cd reduction, whereas higher degrees of fermentation and longer treatment times improved removal efficiency. Sensory evaluation revealed that the treated cocoa liquor preserved its sensory attributes comparable to those of the untreated control. A cost analysis based on pilot-scale bacterial biomass production estimated the treatment cost at USD 0.83 per kg of wet cocoa beans, equivalent to 28.6% of the national average price of wet beans in Colombia as of 2024. While there are promising solutions for cadmium removal from cocoa, it's essential to consider the economic costs and potential impacts on the cocoa supply chain and its producers to ensure responsible and sustainable practices.