In this study, lipase-producing lactic acid bacteria (LAB) were isolated from traditional fermented foods and screened for their growth characteristics and lactone-producing ability in a fast-ripened cheese slurry model. The selected strains were used as an adjunct starter culture for making Cheddar cheese. Sensory evaluation and gas chromatography-mass spectrometry (GC-MS) were used to compare changes in the flavor and lactone content of Cheddar cheese made with and without an adjunct starter during ripening at 4, 10 or 14 ℃ for up to 150 days. The results showed that Pediococcus acidilactici 4D and Lactococcus garvieae Y3, two strains with the ability to produce lipase, exhibited better lactone production performance. Sensory evaluation showed that compared with Cheddar cheese without adjunct starter, the cheese added with P. acidilactici 4D had the highest milky and fruity aroma intensity after 90 days of ripening at 10 and 14 ℃, respectively. The cheese added with L. garvieae Y3 showed the highest milky aroma intensity after 120 days of ripening at 14 ℃. Four lactones were identified by GC-MS. The contents of δ-decalactone and δ-dodecalactone in Cheddar cheese with P. acidilactici 4D or L. garvieae Y3 were higher than those in Cheddar cheese without adjunct starter at all three ripening temperatures, and both strains could promote the formation of δ-octolactone. In addition, γ-butyrolactone was identified only in Cheddar cheese fermented by L. garvieae Y3. By exploring the effects of ripening temperature and time on the formation of lactones, it was found that the optimal ripening temperature was 14 ℃. The total lactone content of cheese added with P. acidilactici 4D reached the highest level at 90 days of ripening, while that with L. garvieae Y3 reached the highest level at 120 days.

The flavor and quality of fermented foods are fundamentally influenced by microbial involvement. Microorganisms are the primary driving force behind the fermentation process, which is facilitated by microbial growth and reproduction, and especially by complex intra- and inter-species interactions, leading to the production of abundant nutritional components and unique flavor compounds. Numerous studies have been conducted on the community succession and individual contribution of microorganisms in fermented foods. In recent years, microbial interactions have gradually become the focus of research. This review delves into the core mechanisms by which microorganisms shape the flavor of fermented foods, with a focus on how quorum sensing (QS) regulates the metabolic activity and how group behavior of microorganisms and nutritional interactions promote the construction of microbial communities. It further examines the positive effects of different interaction types (mutualism, commensalism, amensalism, and competition) on the flavor profile of fermented foods. The review concludes by highlighting current problems and challenges, with the aim of providing insights for future research on microbial interactions and their impact on the flavor of fermented foods.

The difference in the volatile flavors of five different Chinese acid-curd cheeses including milk fan, milk cake, Qula (yak milk cheese), Hurood cheese and milk knot was analyzed by sensory evaluation, gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS). The results of sensory evaluation showed that the five cheeses had a significant difference in flavor. Among them, dairy fan, with strong milky, fruity and bread-like aromas, had the best overall aroma performance and the highest preference score. The combination of GC-IMS and GC-MS expanded the detection range of volatile flavor compounds, and could more comprehensively reflect the volatile compounds in different Chinese acid-curd cheeses. The sensory evaluation results were verified by GC-IMS analysis. All five samples had their own characteristic peak areas, and the characteristic peak areas of dairy fan and Qula were significantly larger than those of the other samples. GC-MS analysis showed that the proportion of acids in dairy fan, Hurood cheese and Qula was the highest, the proportion of esters in milk cake was the highest, and the proportion of alcohols in milk knot was the highest. The calculation of odor activity value (OAV) combined with the results of principal component analysis (PCA) showed that ethanol, ethyl butyrate, ethyl caproate, 2-heptanone and δ-caprylactone were the major contributors to the flavor of dairy fan. Phenethyl formate, phenethyl acetate, caprylic acid, lauric acid and n-decanoic acid were the major contributors to the flavor of Qula. Dodecyl aldehyde was identified as the characteristic flavor compound of dairy cake. Partial least squares analysis (PLSA) revealed the correlation between aroma properties and volatile flavor compounds. Dairy fan has the potential to be developed and promoted in China because of its excellent flavor and consumer preference.

Raw almonds are rich in aldehydes, alcohols and other odorants contributing to fresh fruity and hay-like aromas. The flavor of almonds can change significantly due to various chemical reactions during thermal processing and storage, which can greatly affect its flavor quality. In this context, this review summarizes the major aroma compounds in raw almonds and the major aroma compounds formed by the Maillard reaction, the oxidation of fatty acids, and the degradation of amino acids and soluble sugars in roasted almonds, and it compares the effects of different thermal processing methods and conditions on the aroma compounds and aroma properties of almonds. In addition, this review summarizes the changes of the major aroma compounds and off-odor compounds in almonds during storage and the rational storage methods and conditions. Finally, possible future directions for research on almonds and other nuts are outlined. This review could provide a theoretical basis and reference for flavor quality control of almonds and other nuts during thermal processing and storage.

Foods contain a variety of macromolecules such as proteins as well as trace flavor compounds and the binding effect between aroma compounds and the protein matrix has an important impact on the release and perception of the overall flavor of foods. In this paper, we systematically review the mechanism, determination methods, mathematical models and influential factors of the binding effect between proteins and aroma compounds, and summarize the binding interactions between proteins and aroma compounds including non-covalent bonding, covalent bonding and mass transfer effect, and presents a systematic comparison of the application of multispectral techniques such as fluorescence, circular dichroism and Fourier transform infrared spectroscopy to the investigation of the protein-aroma compound binding effect. Moreover, we summarize several common theoretical models and emerging molecular docking and molecular dynamics simulation methods available for research on the binding interactions between proteins and aroma compounds, and review the influential factors of the release and retention of aroma compounds bound to the protein matrix from three perspectives: protein, aroma compounds and food ingredients. Furthermore, we discuss the major problems existing in the current research and put forward some suggestions for future research directions in order to provide a scientific basis and reference for the controllable release of aroma compounds bound to proteins in foods.