Ginger Milk Curd (GMC), a traditional Chinese cheese of Guangdong, remains not fully elucidated regarding the changes of volatile organic compounds (VOCs) across its different processing stages. This study employed electronic nose (E-Nose), electronic tongue (E-Tongue), gas chromatography-ion mobility spectrometry (GC-IMS) and ultra-high performance liquid chromatography-Q-Exactive HF-X mass spectrometer (UHPLC-Q-Exactive HF/MS) to investigate the alterations in VOCs and low molecular weight metabolites throughout the processing of GMC. The results revealed significant alterations in VOCs, resulting in flavor transitioning from the original flavor to fruity, sweet, green, and citrus flavor. The E-Nose and E-Tongue effectively differentiate the aroma and flavor characteristics of samples at four key processing stages. Among them, GMC contains higher levels of alcohols, aldehydes, ketones, and sulfides compared to samples from other stages, and it shows significant differences in umami, saltiness, and astringency taste characteristics. 71 volatile compounds were identified via GC-IMS, with 13 key volatile compounds, including 1-octen-3-one, 1,8-cineole, dimethylsulfide, and methyl 2-methylbutanoate, contributing to the flavor variations in GMC. Meanwhile, protein degradation, lipid oxidation, and the Maillard reaction were identified as key factors significantly impacting the levels of metabolites and VOCs. The enhancement of flavor characteristics in GMC was attributed to the rise in taste-active peptides, aromatic amino acids, and free fatty acids during processing.

Dairy products contain complex types and contents of proteins, lipids, and lactose. The Maillard reaction (MR) occurs between proteins and reducing sugars during the processing and storage of dairy products. Maillard reaction products (MRPs) have garnered attention for their potential antioxidant activity. MRPs include melanoidins, reductones, and volatile heterocyclic compounds, which affect flavor and color. Relevant literature was identified through a structured search of PubMed and Web of Science; studies were included if they investigated MRPs in dairy products and reported antioxidant-related outcomes. This review offers a comprehensive overview of the MR in dairy products, systematically investigating the influence of protein, reducing sugars, and their ratios, as well as reaction conditions (process technology, temperature, time, pH, and water activity) on the formation and antioxidant activity of MRPs. The review also covers current applications and the future potential of MRPs as natural antioxidants in dairy products. Although MRPs effectively delay lipid oxidation and enhance stability in dairy products, research on their molecular structure and antioxidant mechanisms remains insufficient. Future research should focus on understanding the multifactorial synergistic effects within the complex dairy matrix, elucidating the molecular structure and extraction of antioxidant substances, and developing regulatory techniques to balance the antioxidant properties of MRPs with the safety concerns of potential harmful byproducts.

Double-Layer Steamed Milk Custard (DLSMC) is a famous traditional Chinese dessert. This study aimed to analyze the flavor and the changes in metabolites during different stages of DLSMC preparation, including raw buffalo milk, thermo-processing, first and second-layer milk skin formation. Electronic nose and electronic tongue were employed to preliminarily assess the overall flavor characteristics between these stages. The results indicated that DLSMC demonstrated increased sweetness, saltiness, and umami compared to raw buffalo milk, along with heightened levels of nitrogen oxides, methane, alcohols, aldehydes, ketones, and sulfur-containing compounds. Thus, the thermo-processing and second-layer milk skin formation were pinpointed as critical for flavor alterations. Additionally, headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) detected a total of 46 volatile organic compounds (VOCs), with 8 compounds identified as key flavor components. Untargeted metabolomics revealed 98 differential metabolites, including amino acids, lipids, and nucleotides, that were significantly linked to changes in key flavor compounds. Indeed, the fluctuations in the levels of amino acids, lipids, and nucleotides play a crucial role in influencing flavor changes during the production of DLSMC made from buffalo milk.