Investigation of bioactive compounds and their correlation with the antioxidant capacity in different functional vinegars

There are complex and diverse substances in traditional vinegars, some of which have been identified as biologically active factors, but the variety of functional compounds is currently restricted. In this study, it was aimed to determine the bioactive compounds in 10 typical functional vinegars. The findings shown that total flavonoids (0.21-7.19 mg rutin equivalent/mL), total phenolics (0.36-3.20 mg gallic acid equivalent/mL), and antioxidant activities (DPPH: 3.17-47.63 mmol trolox equivalent/L, ABTS: 6.85-178.29 mmol trolox equivalent/L) varied among different functional vinegars. In addition, the concentrations of the polysaccharides (1.17-44.87 mg glucose equivalent/mL) and total saponins (0.67-12.46 mg oleanic acid equivalent/mL) were determined, which might play key role for the function of tested vinegars. A total of 8 organic acids, 7 polyphenol compounds and 124 volatile compounds were measured and tentatively identified. The protocatechuic acid (4.81-485.72 mg/L), chlorogenic acid (2.69-7.52 mg/L), and epicatechin (1.18-97.42 mg/L) were important polyphenol compounds in the functional vinegars. Redundancy analysis indicated that tartaric acid, oxalic acid and chlorogenic acid were significantly positively correlated with antioxidant capacity. Various physiologically active ingredients including cyclo (Pro-Leu), cyclo (Phe-Pro), cyclo (Phe-Val), cyclo (Pro-Val), 1-monopalmitin and 1-eicosanol were firstly detected in functional vinegars. Principle component analysis revealed that volatiles profile of bergamot Monascus aromatic vinegar and Hengshun honey vinegar exhibited distinctive differences from other eight vinegar samples. Moreover, the partial least squares regression analysis demonstrated that 11 volatile compounds were positively correlated with the antioxidant activity of vinegars, which suggested these compounds might be important functional substances in tested vinegars. This study explored several new functionally active compounds in different functional vinegars, which could widen the knowledge of bioactive factor in vinegars and provide new ideas for further development of functional vinegar beverages.

2,5-Diketopiperazines: A Review of Source, Synthesis, Bioactivity, Structure, and MS Fragmentation

BACKGROUND

2,5-Diketopiperazines (DKPs), also called cyclic dipeptides, are the simplest peptide derivatives in nature that are formed by the condensation of two amino acids. They are an important category of bioactive substances with various structures.

OBJECTIVE

This review focuses on the natural sources, synthetic processes, biological properties and MS fragmentation regularity of simple DKPs, in order to provide a reference for exploring future scientific and therapeutic potentials of these compounds.

METHODS

Pertinent information was collected and organized from several electronic scientific databases (e.g., Web of Science, China Knowledge Resource Integrated, ScienceDirect, PubMed, Wanfang Data and Google Scholar), PhD and MS dissertations. There are 107 articles published from the early 20th century to 2021 that were reviewed in this work.

RESULTS

DKPs have been obtained from a broad range of natural resources, including fungi, bacteria, plants, and animals, and have been synthesized by chemical and biological methods. DKPs have various pharmacological activities, including anticancer, antibacterial, antithrombotic, neuron protective, analgesic, and other activities. Mass spectrometry is the most common method for the structural analysis of DKPs. DKPs can be quickly screened and identified by MS according to the mass spectrum fragmentation pattern.

CONCLUSION

As a category of relatively unexplored compounds, DKPs have been demonstrated to have various bioactivities, especially with antitumor and antibacterial activities. However, the existing research on DKPs is still in the early stage, and their application in drug development needs to be further studied.