The formation and structural characteristics of melanoidins from fermenting and distilled grains of Chinese liquor (baijiu)

Chemical, structural and antioxidant properties of melanoidins in fish sauce

BACKGROUND

Melanoidins, as a functional component, exhibit antioxidant properties. However, the antioxidant mechanism of melanoidins in fish sauce remains poorly understood. The present study focused on the structural characteristics, microstructure and antioxidant activity of melanoidin substances in fish sauce.

RESULTS

Ultrafiltration and color difference analysis were utilized to confirm the main molecular weight composition of melanoidins. The ultrafiltration component > 10 kDa in fish sauce exhibited the darkest and reddest color, along with the highest content of melanoidins (699.5 mg g-1). The spectral characteristics were consistent with typical melanoidins. Gas chromatography-tandem mass spectrometry and Fourier transform infrared spectroscopy analyses revealed that the melanoidins contained a significant number of oxygen-containing groups, amino compounds, carbohydrates, aromatic compounds and carbonyl compounds (CO), pyrrole (CN), among others. In total, 129 alkanes, 71 esters, nine olefins and two alkynes were identified. The melanoidins (> 10 kDa component) had the strongest antioxidant activity, including a reducing power of 0.8, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity of 67.7% and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of 92.4%. Additionally, the melanoidins (> 10 kDa component) had the highest total phenolic content at 48.2 μg gallic acid equivalents mL-1.

CONCLUSION

Melanoidins are important factors affecting the antioxidant activity of fish sauce. There were differences in the structural properties of melanoidin fractions with different molecular weights. © 2024 Society of Chemical Industry.

Upcycling of melanoidin-rich Chinese distilled spent grain through solid-state fermentation by Aspergillus awamori

This study investigated the upcycling of distilled spent grain (DSG), a melanoidin-rich by-product of the Chinese liquor industry, via fungal solid-state fermentation (SSF). Two fungi, Aspergillus oryzae and Aspergillus awamori, were tested, with A. awamori growing better on DSG than A. oryzae. SSF with A. awamori increased the concentration of water-soluble protein and phenolic compounds in DSG extracts by 46.5 % and 52.5 %, respectively, and reduced melanoidin level by 73.5 % w/w of DSG, suggesting A. awamori could metabolize melanoidins. Submerged fermentation (SmF) using isolated DSG melanoidins as sole carbon and nitrogen sources confirmed this observation. After 3 days of fermentation, A. awamori and A. oryzae biomass reached 2.5 g/L and 1.5 g/L, quenching melanoidin color by 24.4 % and 12.4 %, respectively. SmF by A. awamori also released free arabinose, glucose, and xylose. Data highlighted the possibility of converting melanoidins into edible mycelia resources, potentially applicable to various melanoidin-rich food by-products.

Unraveling the mysteries of melanoidins: insights into formation, structure, and health potential in fermented blacken foods

Fermentation is widely known for its ability to enhance the food nutritional ingredients, and its products are with improved texture, flavor, and nutritional. Fermented blacken foods (FBF) are a unique group of foods characterized by their darker hue while retaining nutritional benefits. Despite their popularity, research on melanoidins, the compounds responsible for the characteristic color and health-promoting properties of FBF, remains limited. This review summarizes the formation, extraction, purification, structural features, and health benefits of melanoidins in FBF. The relationship between preparation methods, and physicochemical properties and bioactivities was elucidated. The formation of melanoidins in FBF, influenced by the Maillard reaction (MR) and microbial metabolic activity is analyzed, highlighting the dynamic nature of melanoidin synthesis in fermentation systems. Furthermore, the review addresses the characteristics of FBF production processes and the role of microorganisms and enzymes in melanoidin formation. Melanoidins in FBF exhibit diverse chemical compositions and molecular structures, influenced by precursor molecules, reaction pathways, and environmental factors. These compounds contribute to the sensory attributes, stability, and bioactivity of FBF including antioxidant, antimicrobial, and prebiotic properties. This review underscores the importance of melanoidins in FBF and their influences on food quality, nutrition, and health.

Comparison of characterization and composition of melanoidins from three different dried apple slices

The composition of melanoidins in dried apple that affects quality remains unclear. The composition and structure of melanoidins in dried apple slices by hot air drying (HAAM), instant controlled pressure drop drying (DICAM), and vacuum freeze-drying (FDAM) were investigated. It showed that the melanoidins were highly heterogeneous mixtures with a light-yellow color and blue-green fluorescence, belonging to polysaccharide-type melanoidins. Specifically, HAAM had a large molecular weight (929.5 g/mol) and wide molecular weight distribution, with more double-bond conjugated systems. DICAM (610.9 g/mol), possessing the strongest fluorescence intensity, was mainly composed of compounds with fewer π-conjugated structures and more electron-donating groups. As a control, the low level of Maillard reaction in FDAM resulted in the formation of the smallest molecular weight (458.6 g/mol) with weak fluorescence intensity. Moreover, 10 compounds were tentatively identified in apple melanoidins. This study provides the foundation for the future functional preparation of apple melanoidins.

Preparation, identification, and molecular docking of novel angiotensin-converting enzyme inhibitory peptides derived from rice-based distillers' spent cakes

BACKGROUND

Rice-based distillers' spent cake (RDSC), a by-product of the Chinese liquor (Baijiu) industry, is a potential source of angiotensin-converting enzyme (ACE) inhibitory peptide. Since ACE plays a crucial role in controlling hypertension, inhibition of ACE has been widely emphasized. The ACE inhibitory active peptide derived from by-products of food has been recognized as a safer and cheaper inhibitor.

RESULTS

Aimed to discover ACE-inhibiting active peptides in RDSC. Hydrolysis of RDSC by alcalase for 4 h followed by ultrafiltration yielded low-molecular-weight (< 3 kDa) fractions. Subsequently, a comprehensive method using a combination of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) and LC-Q-Exactive-MS to identify the novel short peptides (3-5 amino acids residues; n = 7) and medium-sized peptides (more than 6 amino acids residues; n = 6). In vitro activity assay showed that the peptides KPFFPGL, GFPRPLL, GPPGVF, and VGK exhibited the highest activity with inhibitory concentration of 50% (IC50) of 11.63, 12.34, 19.55, and 33.54 μmol L-1. Molecular docking reveal that the active and inactive sites (Glu123, Asp121, Arg522, and Lys118) play important roles in enhancing the ACE inhibitory activity of peptides.

CONCLUSION

Here we report a comprehensive method that effectively extracted and identified the bioactive peptides from RDSC. Four highly active novel peptides may be the most promising candidates for functional foods against hypertension, provide significant information for enhancing value of rice-based distilled by-products. © 2024 Society of Chemical Industry.

Isolation, structural characterization and biological activity evaluation of melanoidins from thermally processed cocoa beans, carob kibbles and acorns as potential cytotoxic agents

The aim of this study was to determine the chemical structure and biological activity of melanoidin fractions derived from cocoa beans, carob kibbles, and acorns roasted at different temperature-time conditions. The results showed that plant origin and roasting conditions had significant effects on the chemical composition, structural features, and morphology of melanoidins. All tested melanoidins exhibited significant antioxidant properties in three in vitro assays. In addition, they show significant in vitro anti-inflammatory activity by reducing lipoxygenase. The results from MTT assay showed that the all studied melanoidins had a cytotoxic effect against SW-480 cells in a dose- and time-dependent manner. Furthermore, the most pronounced activity was observed for acorn melanoidins. This is a unique finding, as the specific cytotoxic effect has not been reported for cocoa, carob and acorn melanoidins, and opens up a great opportunity to develop a potential novel cytotoxic agent against deadly colon cancer in the future.

Formation, Evolution, and Antioxidant Activity of Melanoidins in Black Garlic under Different Storage Conditions

Melanoidins (MLDs) are formed through the reaction of carbonyl compounds and amino compounds in the Maillard reaction (MR) during the heating or storage of food. In this study, the formation, chemical composition, and structural characteristics of black garlic (BG) MLDs stored at different temperatures (4 °C, 20 °C, and 35 °C) over a period of 6 months were investigated. The initial products of the MR formed more often at 4 °C and 20 °C, while higher temperatures (35 °C) promoted the reaction in the middle and late stages of the MR. The higher temperature promoted an increase in molecular weight and MLD content, which can be attributed to the increase in protein and phenolic content. Elemental analysis confirmed an increase in nitrogen (N) content and the continuous incorporation of nitrogen-rich substances into the skeleton. Amino acids, particularly aspartic acid and threonine, were the primary N-containing compounds involved in MLD formation. Additionally, the infrared analysis revealed that the changes in MLDs during storage were characterized by amide I and amide II groups. The MR enhanced the yields of heterocyclic compounds (from 56.60% to 78.89%), especially that of O-heterocyclic compounds, at the higher temperature according to Py-GC-MS analysis. Furthermore, the higher temperature enhanced the molecular weight, maximum height, and roughness of MLDs compared to the control. The antioxidant ability of MLDs was positively correlated with storage temperatures. In summary, temperature had an impact on the formation, evolution, and antioxidant activity of MLDs.