Effect of cellulose nanocrystals on thyme essential oil release from alginate beads: study of antimicrobial activity against Listeria innocua and ground meat shelf life in combination with gamma irradiation

Abstract : Thyme essential oil (EO) loaded alginate beads (1–3%) containing cellulose nanocrystals (CNCs) (0–40% polymer dry basis) were prepared in order to study EO release profile in simulating solvent and the antimicrobial effect against Listeria innocua via in vitro and in situ tests. Introduction of CNCs from 0 to 30% in alginate beads exhibited an increase of EO loading capacity from 0.12 to 0.17% and a kinetic release constant (k) decrease from 9.85 to 6.77 when beads were prepared with 3% thyme EO, respectively. These optimal concentrations were selected in order to assess the antimicrobial efficiency to eliminate L. innocua and to reduce the mesophilic total flora (MTF) on ground meat during storage. Results showed that ground meat containing active alginate beads showed a 2 log reduction of L. innocua during more than 10 days as compared to the control. The influence of gamma-irradiation treatment was studied on MTF of ground meat, allowing a 4 log reduction during 14 days when alginate beads containing 3% thyme EO were added. A synergy between thyme EO and irradiation was observed in terms of L. innocua elimination and shelf-life extension.