Yak milk from the high-altitude cold regions of the Qinghai-Tibetan Plateau possesses exceptional nutritional value (Li et al., 2024). Herders traditionally ferment this milk into distinctive products like Qula (dried yogurt), cheese, and butter. These products, especially Qula, are prized for their unique nutrition and flavor. Traditional Qula is a naturally fermented, cheese-like product with distinct regional production characteristics (Fig. 1). Qula is manufactured from fresh yak milk through sequential steps including preheating, fermentation, heating, whey drainage, hanging, and sun-drying. This process yields a delicately tangy, creamy product with a rich aromatic profile (Wang et al., 2022). Characterized by high protein content, low fat levels, and excellent storability, Qula constitutes a primary dairy protein source for local herders (Liu et al., 2013).

The fermentation microbiota plays a decisive role in shaping the flavor and quality of traditional fermented dairy products. In traditional Qula production, fermentation is initiated under relatively open conditions using a back-slopping starter culture—i.e., whey retained from previous batches that contains active microbial communities. This open fermentation process facilitates the ingress of environmental microbiota, leading to the formation of complex microbial consortia in the final product (You et al., 2023). Although conventional pure-culture methods have successfully isolated diverse taxa from Qula, including Leuconostoc, Enterococcus, Lactobacillus, Acetobacter, Clostridium, Bacillus, yeasts, and molds (Ao et al., 2012), these approaches are inherently limited in their ability to capture the substantial unculturable microbial fraction present in such complex ecosystems. In contrast, high-throughput sequencing enables culture-independent characterization of microbial communities with unprecedented depth, breadth, and efficiency. By effectively detecting rare and unculturable taxa, this sequencing approach provides a powerful tool for deciphering the structure, function, and dynamics of complex microbial ecosystems (Ilikkan and Bagdat, 2021). Previous high-throughput sequencing studies have delineated regional characteristics of the Qula microbiota. For instance, an investigation across the Qinghai-Tibetan Plateau identified Lactobacillus and Acetobacter as the dominant genera (Zhu et al., 2018). In contrast, analysis of Qula samples from Nyingchi revealed a predominance of Proteobacteria and Firmicutes at the phylum level, with Lactobacillus, Acinetobacter, Raoultella, Pseudomonas, Lactococcus, and Acetobacter constituting the key genera (Chi et al., 2021). The lactic acid bacteria (LAB) community in Sichuan Qula was reported to be dominated by Leuconostoc (40.8%), Lactobacillus (39.0%), and Streptococcus (13.2%) (Bao et al., 2012). Despite these regional surveys, the microbial succession dynamics throughout the entire Qula production process and their functional correlation with the formation of key flavor metabolites remain largely uncharacterized.

This study employed an integrated analytical framework combining high-throughput sequencing and headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC–MS) to systematically profile the microbial communities and volatile flavor compounds throughout the traditional Qula production process. Subsequently, principal coordinate analysis (PCoA) and microbial correlation network modeling were applied in a complementary manner to elucidate the relationships between the core microbiota and the characteristic flavor profiles. Together, these approaches aimed to decipher the mechanistic role of microbial succession in the formation of key flavor compounds, thereby providing a scientific foundation for the targeted optimization of Qula flavor quality.