Former Food Products (FFPs) as alternative feed ingredients: assessment of undesirable substances from the original food matrix

One of the key principles of the circular economy is the valorisation of agri-food waste through its reintegration into the food chain, transforming industrial by-products into valuable resources [1]. In this context, former food products (FFPs), which are foodstuffs no longer suitable for human consumption but still rich in nutritional and energetic value, are promising alternative ingredients for animal feed [2]. The use of FFPs in feed production involves multiple processing steps (i.e., unpacking, grinding, mixing, drying), which, if not performed correctly, may compromise the quality and safety of the final product. Areas of concern include microbiological and chemical contamination, gastrointestinal effects on the animal and the presence of external materials like packaging residues. FFPs, being low in moisture or heat-treated, are generally microbiologically stable; nevertheless, microbial analysis must confirm their hygienic quality, as inadequate handling can lead to contamination [3]. More studies demonstrated negligible microbiological risks and no adverse effects on gastrointestinal health, microbiota, growth performance and meat quality from post-weaning to finishing pigs fed diets partially replacing common feed materials with FFPs [4, 5]. Additionally, FFPs did not impair the metabolic health or ruminal fermentation of early-lactating cows [6]. Visual inspection methods have also confirmed that the residual content of packaging materials in processed FFPs remains below national regulatory tolerance thresholds [7,3]. FFPs may also contain compounds naturally present in the original food matrix, which can represent another area of concern, particularly when FFPs include chocolate and cocoa-based confectioneries, which are well-documented sources of methylxanthines such as caffeine and theobromine. These compounds can exert bioactive effects on animals when present in high concentrations, potentially affecting the cardiovascular, nervous, and gastrointestinal systems. This study investigated the presence of theobromine and caffeine in 12 FFPs, 1 feed control sample, and 2 cocoa by-product samples. High-performance liquid chromatography coupled with UV detection (HPLC-UV) was employed to quantify the levels of these alkaloids. This assessment is especially pertinent in the context of Directive 2002/32/EC, which establishes species-specific thresholds and maximum levels for undesirable substances in animal feed, including theobromine, to guarantee animal health and feed safety. Based on the results, FFPs with an inclusion rate of 30% into feed diets lead to a theobromine concentration below the established European maximum limit for ruminants and pigs (300 ppm and 200 ppm, respectively). This confirms the potential of FFPs as a safe alternative ingredient for feed, with great potential in preventing food waste and reducing the environmental impact of the agro-food sector.