Microbial spoilage in bread, primarily driven by its high moisture and nutrient content, significantly impacts both its quality and shelf life. This study assesses the potential of compound sourdough, fermented with Lactobacillus sanfranciscensis and Propionibacterium freudenreichii, as a natural preservative in bread. Composite sourdough was incorporated at ten different levels (5%-50%) to examine its effects on fermentation behavior, physicochemical properties, sensory attributes, staling, and microbial stability. The results indicated that with increasing sourdough incorporation, organic acid concentrations, including lactic and propionic acids, rose significantly, while pH decreased, reaching its lowest point at a 50% sourdough addition. At lower sourdough levels (5%-20%), fermentation performance improved, as evidenced by a reduction in fermentation time, lower baking loss, and an increase in specific volume and height-to-diameter ratio. However, higher sourdough levels (25%-50%) impaired fermentation due to excessive acidity, which inhibited yeast activity. Sensory evaluation revealed that moderate sourdough incorporation (5%-20%) enhanced bread texture, making it softer and more elastic, with overall higher sensory scores. In contrast, excessive sourdough levels (25%-50%) resulted in increased hardness, reduced springiness, and deteriorating taste. Additionally, appropriate sourdough levels improved bread’s storage properties by enhancing moisture retention, reducing hardness, and slowing staling. On the other hand, excessive sourdough accelerated moisture loss and staling, resulting in firmer bread. Higher sourdough ratios also contributed to improved mold inhibition and extended shelf life, with the 50% addition extending the shelf life to 15 days, although this led to a significant compromise in quality. Ultimately, the study concluded that a 20% sourdough addition strikes an optimal balance between antimicrobial efficacy and the preservation of overall bread quality. This study optimized the compound sourdough ratio to balance fermentation, bread quality, and shelf life, offering a sustainable preservation solution for industrial production.