Primary and Secondary Metabolites in Fruits and Vegetables; Analytical Solutions, Chemical Composition and Bioavailability Evaluation

Dear Colleagues,

In plants, basic functions are largely performed by primary metabolites. Primary metabolites are substances that are absolutely necessary for plant growth and development and play an important role in plant metabolism. Primary metabolites include sugars, organic acids and amino acids. Primary metabolites play an important role in maintaining the quality and determining the nutritional value of fruits. Sugars and organic acids also influence the taste and flavour of fruits and vegetables.

In addition to primary metabolites, plants also have substances called secondary metabolites that are formed from primary metabolites. According to their biosynthetic origin, they are divided into three main groups: terpenoids or terpenes, nitrogenous compounds and phenolic compounds. Nitrogenous compounds include compounds such as alkaloids, glucosinolates and cyanogenic glycosides. Nitrogenous compounds are synthesized from amino acids and contain nitrogen (N). The plant accumulates them in different parts of its composition and in different concentrations. They have a defensive function, protecting the plant from natural enemies and pathogens, and can be toxic to some insects and mammals. Terpenoids are composed of isoprene units, and are substances that are mainly involved in protecting the plant from stressful environmental factors; they are in communication between plants and other organisms. Phenolic compounds consist of an aromatic ring and hydroxyl groups and are the most abundant secondary metabolites in fruits and vegetables. Most phenolic compounds are esters or glycosides. Phenolic compounds provide protection to plants from stressors, are involved in flower and fruit pigmentation and also contribute to fruit flavour and aroma. Some phenolic compounds have allelopathic effects, meaning that they can inhibit or stimulate the growth of neighbouring plants. In addition, individual secondary compounds can also be growth regulators and germination inhibitors, or can simply provide a nitrogen reserve.

The content of primary and secondary compounds in fruits and vegetables is influenced by various factors such as variety, genotype, growing conditions, ripening stages, agricultural practices, postharvest storage conditions and processing methods. Many environmental factors, such as the availability and accessibility of nutrients and water, light and temperature, can influence the synthesis and accumulation of secondary metabolites. In addition to abiotic factors, there are also plant-damaging organisms in nature, such as herbivores, nematodes, fungi and bacteria, against which the plant also protects itself by synthesising certain secondary components.

Some compounds from secondary metabolites also have bioactive activity. This means that they cause reactions or trigger a response in living tissues. Compounds are biologically active if they have a direct effect on the organism, either positive or negative. Secondary metabolites are also useful to humans as they are commonly used as medicines, flavourings, spices and dietary supplements. The content of secondary metabolites depends primarily on the plant species and on their function in the life cycle of the plant. For humans, information about their content in fruits is extremely important, especially from the point of view of their beneficial or harmful effect when absorbed into the body. The beneficial effects of fruits and vegetables depend mainly on the concentration of phenolic acids, flavonoids, carotenoids, anthocyanins, vitamins and minerals. Clinical studies have shown that the consumption of fruits and vegetables high in anthocyanins and other phenolic substances can reduce the risk of obesity, cardiovascular diseases, degenerative diseases and various cancers. The reason for this lies in their antioxidant effect.

This Special Issue of Plants will focus on the diversity in the occurrence of primary and secondary metabolites in different fruits and vegetables, their content and function in plants and analytical methods for their precise extraction and analysis. At the same time, we are also interested in how the different environmental conditions of the site (drought, stress, nutrients, soil pH, etc.), different cultivation techniques (fertilisation, spraying, irrigation, etc.) and fruit processing technologies (pasteurisation, pressing, different substances, etc.) affect the preservation of their bioactive value. With the help of new results from the field of metabolites in fruits and vegetables, their usefulness in the field of phytochemistry, pharmacy, public health, the food industry and agriculture will be much greater. In addition, the improved effects of the extraction of metabolites from plant tissues and the preservation of their content in food require special attention so that in the technological processes of fruit and vegetable processing, their functional properties are not affected and the consumer receives a good-quality product.

Dr. Maja Mikulič-Petkovšek
Guest Editor

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• phytochemistry
• primary and secondary metabolites
• fruits and vegetables
• analytical techniques
• environmental factors
• production technology
• horticultural crops
• sugars
• organic acids
• polyphenolics
• cyanogenic glycosides
• glucosinolates
• terpenoids
• extraction
• drying
• natural product chemistry
• novel processing technologies
• flavonoids
• phenolic-rich extracts
• herbal medicine
• disease management
• development of innovative products
• fruit quality
• bioactive compounds
• final product
• stability of substances
• antioxidant properties
• health status
• resistant cultivars
• plant growth responses
• phenylpropanoid pathway
• enzymes
• biotic and abiotic stress
• storage
• postharvest technology
• nutrients
• sustainable approach
• plant biostimulators
• oxidative stress
• adaptive mechanisms
• plant diseases
• elicitors