The influence of the components of potato starch / psyllium husk flour films on microorganisms in the context of its potential use

Abstract Films were prepared by solution casting from potato thermoplastic starch plasticised with glycerol and containing 0, 2, 6, or 10 g of Plantago ovata husk flour (PF) per batch. The control film without PF was designated TPS, while the modified films were designated TPS/PF_2G, TPS/PF_6G, and TPS/PF_10G, respectively; the designations 2G, 6G, and 10G indicate the mass of PF added, expressed in grams. These additions corresponded to 0.25, 0.75, and 1.24% (w/w) of the total wet film-forming mixture. The films were evaluated for microstructure, water contact angle (WCA), effects on selected bacteria ( Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Bacillus subtilis ) and microscopic fungi ( Saccharomyces cerevisiae, Aspergillus niger, and Candida albicans ), and biodegradability under laboratory conditions. The effects of the films and PF extracts prepared using a 30% glycerol–water solution on microorganisms were assessed by agar diffusion methods. Biodegradation was evaluated indirectly by monitoring changes in film structure during soil incubation and directly by measuring soil respiratory activity after the addition of film samples. PF increased the initial WCA from 87.16° for TPS to 114.60° for TPS/PF_10G and slowed its subsequent decrease. Neither the films nor the PF extracts exhibited antimicrobial activity. All film formulations promoted Bacillus growth and sporulation to a similar extent. Increasing the PF content delayed both biodegradation, assessed as the loss of film surface area, and mineralisation, measured as CO₂ release. These findings indicate that PF can be used to modify the stability and biodegradation rate of thermoplastic starch films in soil. The absence of inhibitory effects on the tested microorganisms supports further investigation of these materials for biodegradable packaging and carriers for agricultural or pharmacology applications.