Smart waste-derived materials for feed application: chestnut shells and vine pruning biochar

Carrier-assisted delivery is a key step for the successful targeted oral delivery of bioactive molecules in functional diets in livestock. The aim is to protect the biomolecule during gastric transit, and ensure its efficient release in the intestine. Biochar is the by-product of the thermochemical conversion of residual biomass in an oxygen-limited environment and has suitable physico-chemical and morphological properties to be a carrier. Two types of biochar were tested as carriers of egg white lysozyme (LY), selected as a representative of bioactive molecules both in terms of molecular size (MW 14.3 kDa) and antibacterial activity, for application in weaned pig feed. One biochar was derived from chestnut shells (CB) and the other from vine pruning (VB). An efficient and environmentally-friendly procedure for LY adsorption was developed, based on a solid/liquid process in mild conditions. The effects of the operating conditions, such as initial LY content, reaction time, and pH were also studied. The optimal conditions were found to be a maximum LY loading of 21–23 mgLY gCarrier−1. Both pristine and hybrid materials were extensively characterized by combining morphological and physico-chemical techniques to obtain information on LY allocation and interactions with the carriers. Preliminary experiments on lysozyme release were performed at pH = 3 and pH = 7, simulating the pH conditions of the stomach and intestine of the weaned pigs, respectively. The results showed a higher releasing capacity when the pH was increased from 3 to 7. Specifically, the release showed a slight increase from 0.8% to 1.2% as the pH shifted from 3 to 7 for CB, and from 1.5% to 2.3% for VB. These results confirmed that biochar can protect LY from the low pH, during the gastric transit, and that LY could be released in the gut. These two benefits are likely related to the homogeneous distribution of LY molecules at the carrier surface, which is facilitated by the interaction of charges of opposite signs.