The evaluation of D- and L-lactic acid production by lactic acid bacteria is of critical importance, particularly for strains intended for use in infant and young child foods. Additionally, compliance with relevant regulatory standards necessitates the detection of D-lactic acid. Additionally, regulatory requirements exist in this regard. This study aimed to develop and validate a method for simultaneously measuring D-lactic acid and L-lactic acid produced by lactic acid bacteria. The method validation of the HPLC analysis was performed in terms of accuracy, precision, specificity, limit of quantification (LOQ), linearity, range, and robustness, and the measurement uncertainty was also evaluated. The method demonstrated a limit of detection (LOD) of 0.25 µg/mL and LOQ of 0.8 μg/mL for D-/L-lactic acid. For six validated bacterial strains, mean recoveries ranged from 93.50% to 105.37%, with intra-assay relative standard deviations (RSD) of 0.90–2.64% and inter-laboratory RSD of 2.56–10.16%. Excellent linearity, accuracy, and precision were observed across the concentration range of 0.8–200.0 μg/mL. Results confirmed no interference from culture media batch variations, and sample stability was maintained for 48 h. Additionally, relative expanded uncertainties were determined as 10.48% and 7.64%. The developed method was suitable for the identification and quantification of D- and L-lactic acid in lactic acid bacteria fermentation broth samples. This method was applicable for assessing the production of D-/L-lactic acid by food cultures.

Daqu is a key starter used in Baijiu production, and its microbial composition and associated metabolic functions play critical roles in fermentation performance and flavor development. This work aimed to reveal how Daqu-making temperature regulates microbial community divergence and subsequent metabolite formation via multi-omics analysis so as to provide theoretical guidance for Daqu quality control. In this study, physicochemical analysis, metagenomic sequencing, and metabolomic profiling were combined to investigate the microbial community structure, functional differentiation, and metabolite characteristics of nine Daqu samples collected from six major Baijiu-producing regions in China. The temperature during Daqu preparation was found to be a primary factor driving microbial community assembly and functional specialization. Medium-temperature Daqu exhibited higher saccharifying activity (up to 867 U) and greater microbial diversity with the enrichment of amino acid metabolism-related pathways, indicating enhanced protein degradation and amino acid utilization for the formation of flavor precursors. In contrast, high-temperature Daqu showed stronger capacities for carbohydrate degradation and conversion, particularly in starch and sucrose metabolism, which were closely associated with the enrichment of thermotolerant fungi and bacteria. LEfSe analysis identified 47 distinct microbial biomarkers (LDA score > 3.0), which could differentiate between medium- and high-temperature Daqu. Redundancy analysis indicated that environmental factors (moisture and acidity) together with functional properties (fermentation, esterification, liquefaction, and saccharification) act as key drivers of microbial functional patterns. Metabolomic analysis further revealed that medium-temperature Daqu had higher abundances of esters and fatty acids, whereas high-temperature Daqu had higher proportions of alcohols and ketones. Taken together, these results provide a multi-omics perspective on temperature-driven microbial functional differentiation in Daqu and offer a scientific basis for quality-oriented regulation and process optimization in Baijiu production.

Inroduction: Burkholderia cepacia is a representative member of the Burkholderia cepacia complex (Bcc) and is widely distributed in water and soil environments. It has a propensity to form biofilms in water-based products, making it a significant contaminant in the pharmaceutical, cosmetic, and food industries and posing threats to product quality control and public health. Therefore, rapid and accurate species-level identification of B. cepacia is of great importance. Methods: To achieve rapid and accurate species-level identification of B. cepacia , we performed a pan-genome analysis based on 138 high-quality genome sequences covering B. cepacia and its closely related Bcc species with taxonomic positions validated by average nucleotide identity (ANI) analysis. A conserved core gene encoding a glycosyl hydrolase family 18 (GH18) protein was identified as a species-specific molecular marker. A specific primer pair comprising SEQ ID NO.2 and SEQ ID NO.3 was designed based on this marker and validated with both genome sequences and bacterial pure cultures. Results: The GH18-encoding gene is highly conserved across 115 B. cepacia strains (sequence identities ranging from 90.3 to 100.0%) and is absent in all other Bcc species examined. The primer pair exhibited high inclusivity and exclusivity for B. cepacia . The established PCR method achieved a detection limit of 5 pg/μL for pure genomic DNA and 10 ³ CFU/mL in artificially contaminated water-based personal care and medical device products. Discussion: The identification of this conserved core gene provides a promising basis for the rapid and accurate species-level detection of B. cepacia . Given the widespread occurrence of B. cepacia in water and soil environments and its ability to form biofilms in water-based products, such a species-specific molecular marker may help improve contamination monitoring and quality control in the pharmaceutical, cosmetic, and food industries, thereby contributing to public health protection.