Estimation of the Antifungal Threshold of Thyme Essential Oil for Bread Preservation, Ensuring Consumer Acceptance and Product Quality

The replacement of synthetic preservatives with natural alternatives is increasingly important in bakery production. This study examined the antifungal activity of thyme essential oil (TEO) against bread spoilage molds and its impact on product quality and consumer acceptance. TEO was tested at concentrations from 0 to 200 ppm against <i>Aspergillus flavus</i> and <i>Penicillium expansum</i> in bread and a model system, with mold responses modeled using the Gompertz equation. Because TEO affects the sensory qualities of bread, the kinetic parameters of mold growth were used to estimate the minimum inhibitory concentration (MIC), thereby ensuring a mold-free shelf life without significantly altering sensory properties. Bread samples were analyzed for pH, moisture, water activity, texture, specific volume, and sensory attributes (odor, flavor, texture, and acceptability). Residual thymol and carvacrol (measured using GC-MS) were also evaluated. The retention of thymol and carvacrol in baked bread was 75-80%. The tested TEO concentrations did not alter the moisture content, pH, or water activity of bread, while the specific volume was reduced and the width-to-height ratio increased as the TEO concentration increased. At concentrations below 100 ppm, TEO enhanced bread softness, while higher levels (>150 ppm) slightly increased hardness. Sensory testing showed no significant differences in color or texture (<i>p</i> > 0.05). At 50 ppm, TEO imparted a subtle thyme aroma and flavor, improving the sensory profile. At 100 and 150 ppm, the aroma and flavor became more pronounced and were well accepted. However, at 200 ppm, the thyme aroma and flavor decreased overall acceptance. In bread, the MIC of TEO for <i>A. flavus</i> ranges from 104.2 ppm (200 h delay) to 120.8 ppm (250 h), and for <i>P. expansum</i>, from 106.6 ppm (200 h) to 123.6 ppm (250 h). The MICs (100-125 ppm) fall within sensory acceptable scores, indicating that TEO can delay mold growth while maintaining bread quality. Moderate levels of TEO extended the mold-free shelf life of bread by providing microbial control and preserving its sensory properties.