Influence of some formulation and process parameters on the stability of lysozyme incorporated in corn flour- or corn starch-based extruded materials prepared by melt blending processing

• Corn flour-based materials containing lysozyme as antimicrobial agent were prepared.
• Glycerol and moisture contents had opposite effects on lysozyme stability.
• More than 60% of lysozyme activity was retained after extrusion at 90 °C.

In order to obtain an antimicrobial biodegradable material, corn flour was extruded with 1% of lysozyme. Since the limited stability of natural preservatives such as lysozyme is a common bottleneck to the elaboration of active biomaterials by melt blending processes, the influence of formulation and of extrusion processing temperature on its residual enzymatic activity was investigated. To assess the contribution of process parameters such as temperature, shear stress and of related formulation parameters such as glycerol and moisture contents, the stability of lysozyme following its extrusion or its thermoforming with plasticized corn starch or thermal treatments in aqueous glycerol solutions was also studied. Increasing glycerol content from 25% to 30% significantly limited inactivation of lysozyme during extrusion, while increasing initial moisture content of the mixture from 14.5% to 28.5% had the opposite effect. These observations open the possibility to prepare active materials retaining more than 60 ± 7% of initial lysozyme activity.

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