Analysis, Characterization and Antioxidant Properties of Natural Products

1. Introduction

Natural products, derived from plants, animals, microorganisms and marine organisms, constitute a natural chemical repository characterized by both structural diversity and biological activities. Their functions, including antioxidant [1], anti-inflammatory [2], neuroprotective [3] and metabolic regulatory effects [4], have made them core research subjects in the fields of food, medicine, health products and daily chemicals [5,6]. As public demand for healthy, natural and safe products continues to rise, research on the precise separation and analysis, structural characterization, activity evaluation and industrial application of natural products has been deepening [7]. There is an urgent need for systematic technical methodologies and scientific conclusions to support the development of this field [8].

Against this background, we have organized and launched a Special Issue titled “Analysis, Characterization and Antioxidant Properties of Natural Products” in the journal Applied Sciences. This Special Issue focuses on key scientific and technical issues across the entire research chain of natural products, and solicits and selects high-quality research findings covering novel extraction and purification processes, advanced analytical and characterization techniques, antioxidant activity mechanisms, functional product development and application evaluation. It aims to provide an academic exchange platform for researchers worldwide and promote the translation of natural product research from basic science to industrial application.

2. Contributions in This Special Issue

This Special Issue collects a total of 5 representative research papers, covering multiple subfields including plant active ingredients, food functional components, lipid resources and delivery systems, which fully demonstrate the cutting-edge technologies and application value of natural product research.

2.1. Green Extraction and Antioxidant Activity Optimization of Resveratrol from Japanese Knotweed

Ultrasonic-assisted solvent extraction was employed to systematically investigate the effects of extraction time, temperature, ultrasonic frequency and solvent system on the extraction efficiency of resveratrol and polyphenols from Japanese Knotweed. The optimal extraction conditions were determined as 10 min, 50 °C, and 80 kHz for resveratrol, and 20 min, 25 °C, and 37 kHz for polyphenols. The methanol–water mixed solvent was verified as the optimal extractant, providing a green and efficient scheme for the resource utilization of the invasive plant Japanese Knotweed and the industrial production of resveratrol [9].

2.2. Comparative Analysis of Antioxidant Profiles Between Cold-Drip and Hot-Brew Coffee

Combining high-performance liquid chromatography with post-column derivatization and the cupric ion reducing antioxidant capacity (CUPRAC) method, the effects of different brewing processes on coffee antioxidant components were accurately analyzed. It was found that hot-brew coffee exhibited a significantly higher concentration of antioxidant substances than cold-drip coffee, and characteristic differences existed in the antioxidant fingerprints of coffee from different brands, offering a scientific basis for coffee quality evaluation and healthy consumption [10].

2.3. Thermal Stability and Antioxidant Mechanism of Thymoquinone in Black Cumin Seed Oil

Spectroscopic and chromatographic hyphenated techniques were used to monitor the content variation of thymoquinone in black cumin seed oil under thermal storage conditions. It was discovered for the first time that sealed heating could increase the content of thymoquinone, and polyphenols were confirmed as the key contributors to the antioxidant activity of the seed oil, providing a novel strategy for the storage, preservation and functional enhancement of black cumin seed oil [11].

2.4. Construction of NMN Liposomes and In Vitro Blood–Brain Barrier Transport Study

An in vitro blood–brain barrier model was established using hCMEC/D3 cells, revealing that the transmembrane transport mechanism of nicotinamide mononucleotide (NMN) was concentration-dependent passive transport. ANG peptide-modified liposomes could significantly improve the blood–brain barrier penetration ability of NMN, offering key technical support for the targeted delivery of NMN in the field of neurodegenerative diseases [12].

2.5. Quality Evaluation and Intelligent Identification of 26 Edible Plant Essential Oils

Combining gas chromatography, colorimetric analysis, infrared spectroscopy, and machine learning algorithms, the fatty acid composition, oxidative stability, color, and pigment characteristics of essential oils were systematically analyzed, enabling accurate discrimination between pulp essential oils and seed essential oils with a classification accuracy of 96%. High-quality essential oil resources with balanced n−6/n−3 ratios, such as flaxseed oil and chia seed oil, were screened out [13].

The above studies closely focus on the core directions of the Special Issue. They not only reflect the innovative applications of advanced technologies including chromatography, spectroscopy and machine learning in natural product analysis, but also center on characteristic active substances such as resveratrol, thymoquinone, NMN, coffee antioxidant components and plant essential oils. Covering the full-scenario demands of resource utilization, process optimization, activity mechanism, targeted delivery and quality evaluation, these studies provide solid theoretical and technical support for the scientific development and high-value utilization of natural products.

3. Challenges and Future Perspectives

Natural product science is in a critical development stage with innovations in analytical technologies, in-depth biological mechanism research and expanded application scenarios. Despite preliminary progress in this Special Issue, scientific issues and technical bottlenecks remain to meet the needs of the grand health industry and green sustainable development. Future research will focus on the following directions:

3.1. Develop New In Situ, Real-Time and Non-Destructive Analytical Technologies

Current off-line and destructive detection methods fail to reflect the real status and dynamic changes of natural products in organisms. Future research should integrate micro–nano sampling, in situ spectroscopy and other technologies to realize rapid screening, accurate quantification and dynamic tracking of active components, and establish a standardized antioxidant activity evaluation system to solve the problem of incomparable experimental results [14].

3.2. Deepen Structure–Activity Relationships and Molecular Mechanisms of Natural Products

Existing studies lack systematic interpretation of “structure–activity–target–pathway” networks. Future research will combine computational chemistry, molecular docking and multi-omics technologies to clarify the antioxidant mechanisms of core active components (e.g., polyphenols, quinones) and identify their functional targets, providing a theoretical basis for targeted screening and product design [15].

3.3. Break Through Green and Efficient Preparation Technology Bottlenecks

To solve low extraction efficiency, solvent pollution and active ingredient degradation, efforts should be made to develop green extraction technologies (ultrasonic/microwave assistance, supercritical fluid extraction, etc.) combined with precise separation technologies. In addition, resource-based utilization of low-value resources (agricultural and forestry by-products, etc.) should be promoted to improve economic and environmental benefits [16].

3.4. Promote Innovative Development of Targeted Delivery Systems and Functional Products

Poor water solubility, low stability and bioavailability limit the application of natural active ingredients. Future research will focus on novel delivery systems (nanoliposomes, microcapsules, etc.) to improve their stability and bioavailability, and extend related research ideas (e.g., NMN liposomes crossing the blood–brain barrier) to more active substances [17].

3.5. Integrate AI and Big Data to Empower Natural Product Development

With machine learning and chemometrics, natural product component databases, activity prediction models and quality discrimination models will be established to realize rapid candidate screening, intelligent process optimization and accurate quality identification, shortening R&D cycles and reducing costs [18].

3.6. Strengthen Safety Evaluation and Standardized System Construction

Due to complex components and batch variations of natural products, a full-chain standard system covering raw material traceability, quality control and safety toxicology is urgently needed. Quality markers and detection methods for products from different sources should be improved to ensure safe application in food, pharmaceuticals and cosmetics [19].

4. Conclusions

Research on natural products will continue to evolve toward precision, greenness, functionality, intelligence and standardization, and will keep driving the interdisciplinary integration of analytical science, materials science, life science and the food and pharmaceutical industries. We look forward to the emergence of more cutting-edge achievements in the future, which will transform natural bioactive substances into genuinely safe, effective and accessible health products. At the same time, we aim to realize the sustainable utilization of biological resources and contribute scientific strength to human health and ecological protection.

Finally, we sincerely thank all contributing authors for their diligent research, the peer reviewers for their rigorous evaluation, and the editorial office of Applied Sciences for their full support. The successful publication of this Special Issue would not have been possible without the concerted efforts of all parties. We look forward to continuing to work hand in hand with colleagues worldwide to jointly promote innovative breakthroughs in the field of natural product research.