A comparative metabolomic investigation in fruit sections of Citrus medica L. and Citrus maxima L. detecting potential bioactive metabolites using UHPLC-QTOF-IMS

The current study focused on targeted and non-targeted metabolomics of Citrus fruit parts (exocarp, mesocarp, endocarp, and seeds) to gain a comprehensive metabolomic insight. Sections of the Citrus fruit were preliminarily examined for proximate compositions (moisture, ash, fibre, fat, and protein). Whereas ultrasonication-assisted solvent extraction revealed a higher phenolic and flavonoid content at 80% (v/v) ethanolic medium, with the highest amount in the exocarp. Using targeted metabolomics, hesperidin (3307.25 mg/100 g), naringin (4803.73 mg/100 g) were detected in C. medica and C. maxima at greater levels, respectively. Further quantitative analysis revealed the presence of phenolic acids (gallic acid, trans-ferulic acid, p-coumaric acid, trans-cinnamic acid), and polymethoxyflavones (nobiletin, and tangeretin) and detected in the order of exocarp > mesocarp > endocarp > seeds. Using an untargeted metabolomics approach, metabolite discriminations among Citrus fruit sections were illustrated by Venn-diagram, heatmap, PCA, o-PLSDA, correlation matrices, and S-plot. UHPLC-QTOF-IMS revealed 48 metabolites including phenolics, vitamins, and amino acids. Furthermore, the METLIN database leads to the identification of 202 unknown metabolites. The metabolite biosynthesis and corresponding metabolite presence in Citrus fruit sections were confirmed using pathway enrichment and mass fragmentation analysis. Finally, potential biological activities were determined using in silico PASS software approach, and free radical scavenging potential was confirmed using in vitro assays for future preventive and therapeutic applications of the identified metabolites.

Bioactive Molecules of Mandarin Seed Oils Diminish Mycotoxin and the Existence of Fungi

Mandarin is a favorite fruit of the citrus family. Mandarin seeds are considered a source of nontraditional oil obtained from byproduct materials. This investigation aimed to assess the biomolecules of mandarin seeds and evaluated their antimycotic and antimycotoxigenic impact on fungi. Moreover, it evaluated the protective role of mandarin oil against aflatoxin toxicity in cell lines. The two types of extracted oil (fixed and volatile) were ecofriendly. The fatty acid composition, tocopherol, sterols, and carotenoids were determined in the fixed oil, whereas volatiles and phenolics were estimated in the essential oil. A mixture of the two oils was prepared and evaluated for its antimicrobial impact. The reduction effect of this mixture was also investigated to reduce mycotoxin secretion using a simulated experiment. The protective effect of the oil was evaluated using healthy strains of cell lines. Fixed oil was distinguished by the omega fatty acid content (76.24%), lutein was the major carotenoid (504.3 mg/100 g) and it had a high β-sitosterol content (294.6 mg/100 g). Essential oil contained limonene (66.05%), α-pinene (6.82%), β-pinene (4.32%), and γ-terpinene (12.31%) in significant amounts, while gallic acid and catechol were recorded as the dominant phenolics. Evaluation of the oil mix for antimicrobial potency reflected a considerable impact against pathogenic bacteria and toxigenic fungi. By its application to the fungal media, this oil mix possessed a capacity for reducing mycotoxin secretion. The oil mix was also shown to have a low cytotoxic effect against healthy strains of cell lines and had potency in reducing the mortality impact of aflatoxin B₁ applied to cell lines. These results recommend further study to involve this oil in food safety applications.

Valorization and extraction optimization of Citrus seeds for food and functional food applications

Valorization of food byproducts has attracted recently considerable attention. Citrus fruits provide considerable non-edible residues reach 80% in juice production. They are considered agri-wastes to comprise peel, pulp and seeds. Previous investigations have focused on peel and pulp to recover value-added products. The review presents for the first-time phytochemical composition of Citrus seeds' products, i.e., oil and extracts. Fatty acids, phytosterols and tocopherols amounted as the major bioactives in Citrus seeds, in addition to limonoids, dietary fibers and flavonoids. Besides their nutritional values, these chemicals have promising applications including production of biodiesel, food enhancers and antioxidants, especially from mandarin and grapefruit seeds. Optimum conditions of the different Citrus seeds' valorization are discussed to improve extraction yield and lessen environmental hazards of solvent extraction. This review presents the best utilization practices for one of the largest cultivated fruit seeds worldwide and its different applications.

Changes in chemical composition and biological activity of essential oil from Thomson navel orange (Citrus sinensis L. Osbeck) peel under freezing, convective, vacuum, and microwave drying methods

Thomson navel orange peel is a by-product of citrus processing, which contains high levels of bioactive compounds advantageous to human health, nevertheless due to its high moisture content it is exceedingly perishable. Drying is among the most common preservation methods, which could prolong the plants shelf-life via reducing their moisture value. Taking this into account, depending on their type and conditions, drying techniques could degrade plant heat-sensitive metabolites and lead to quality decline. Therefore, the goal of this paper was to investigate the influence of seven drying methods named sun, shade, oven, vacuum oven, microwave, and freeze-drying with different drying conditions on the physical properties, for example, bulk density and color (L*, a*, b*, ΔE, and browning index (BI)) and essential oil characteristics such as extraction yield, chemical composition, antioxidant (total phenolic content (TPC), DPPH, and FRAP essays), and antimicrobial (MIC and MBC) activities of Thomson peel and determine the superior drying procedure. Results showed that freeze-dried sample had the highest retention of L* (48.54) and b* (49.00) values, lowest BI (216.11) as well as highest EO extraction yield (6.90%), TPC (60.10 GAE/100 g), FRAP (0.52% at 80 mg/ml), and lowest IC50 (5.00 mg/ml), MIC and MBC compared with other drying treatments. Therefore, it could be inferred that freeze-drying is the most efficient drying approach in respect of preserving both physical and EO attributes of Thomson peel.

Post-harvest processing and valorization of Kinnow mandarin (Citrus reticulate L.): A review

Kinnow is a prevalent fruit crop of the mandarin group and belongs to the Rutaceae family. It is nutritionally rich in vitamin C, vitamin B, β-carotene, calcium, phosphorous and other health beneficing compounds. The fruit is grown commercially for fresh consumption and since the processing techniques are less prominent, a plentiful amount of harvested fruit goes for waxing and grading operations. To reduce the post-harvest losses, appropriate processing techniques need to be followed as considerable fruit waste is generated while processing. The foremost fruit wastes viz. peel and seeds are rich source of bioactive compounds and can be utilized for the extraction of aromatic compounds, essential oils and low-methoxyl pectin. Overall utilization of kinnow and its components through various technological interventions will not only enhance the profitability of processing industries but also assist in reducing the pollution load on the environment. The prevailing bitterness in kinnow juice has constrained its processing, value-addition, popularity and acceptability. Limited work has been done on kinnow processing leaving scarce relevant literature published on the post-harvest management. Efforts made by researchers worldwide, regarding the post-harvest application of kinnow and its by-products for product development, value addition and waste utilization is presented and discussed in this paper. This compiled information is envisioned to encourage the cottage food processing units in order to improvise the overall benefits along with achieving complete utilization of kinnow.