Agri-food waste as a source of bioactive compounds

Fungal postharvest diseases of fresh fruits cause significant economic losses while reliance on conventional synthetic fungicides for their control raises important environmental and safety concerns. 

Likewise, growing issues about the accumulation of agri-food industrial waste and by-products are increasingly driving the search for new strategies for their valorization to boost the circular bioeconomy and increase sustainability.

This review examines the antifungal potential of extracts obtained from underutilized agri-food by-products and their main bioactive compounds, such as phenolics, terpenes, alkaloids, and glucosinolates.

The key optimization parameters for the recovery of bioactive compounds using both conventional and green extraction methods are described.

The antifungal activity of these extracts has been demonstrated against major pathogens causing fruit postharvest decay, including Botrytis cinerea, Penicillium spp., Monilinia spp., and Colletotrichum spp. While in vitro studies prove the inhibition of fungal growth and spore germination, in vivo applications show significant potential to reduce decay of commercially important fruits such as citrus, apples, strawberries, and grapes.

Therefore, the use of these extracts within non-polluting integrated postharvest disease management strategies represents a promising, sustainable, environmentally friendly alternative for decay control.

Remaining challenges include identifying new applications, broadening the spectrum of activity, assessing potential synergies with other alternative control methods, and advancing in regulatory approval and scale-up for commercial implementation.

Introduction

Approximately one-third of global fruit and vegetable production is lost after harvest due to senescence and inadequate handling, with fruit decay caused by biotic agents being a major contributor to substantial economic losses (Dwivedi et al., 2024).

Among the diverse fungal pathogens contributing to postharvest losses, several stand out due to their economic impact and broad host range.

Botrytis cinerea Pers. emerges as a predominant threat causing gray mold in a wide range of fruit crops. This polyphagous fungus inflicts substantial losses on grapes, berries, pome fruits, pomegranates, and stone fruits, among others (Richards et al., 2021). 

Similarly, Alternaria species, especially A. alternata (Fr.) Keissl., causing black rot or black spots in pome and stone fruits, persimmons, pomegranates, citrus, and many tropical fruits, are generalist pathogenic fungi responsible for significant economic losses (Troncoso-Rojas and Tiznado-Hernández, 2014).

Colletotrichum species, responsible for anthracnose diseases, further contribute to postharvest decay by affecting a wide variety of temperate, subtropical, and tropical fruits, including apples, grapes, citrus, avocados, mangoes, and bananas (Shi et al., 2021).

Monilinia species, particularly M. fructicola (G. Winter) Honey and M. laxa (Aderh. & Ruhland) Honey cause brown rot, leading to severe losses in stone and pome fruits (Adaskaveg and Förster, 2022, Spadaro et al., 2020).

These widespread pathogens generally infect unripe fruit in the field, remain latent or quiescent, and resume development after harvest, posing significant challenges to fruit quality and marketability, particularly under favorable environmental conditions during storage and transportation.

Pathogens that infect fhrough peel wounds

In addition to these prominent latent pathogens, other postharvest diseases are caused by pathogens that infect the fruit through peel wounds inflicted on mature fruit near, during, or after harvest.

Examples of important diseases caused by wound pathogens are citrus green and blue molds, caused by Penicillium digitatum (Pers.: Fr.) Sacc. and Penicillium italicum Wehmer, respectively, and citrus sour rot, caused by Geotrichum citri-aurantii (Ferraris) E.E. Butler (Smilanick et al., 2020).

Penicillium expansum Link, the causal agent of blue mold in many temperate fruits such as pome and stone fruits, is especially important because it produces mycotoxin patulin, posing additional health risks (Wang et al., 2021).

Rhizopus stolonifer (Ehrenb.) Vuill., the cause of soft rot on berries, grapes, stone fruits, and many subtropical and tropical fruits, is another polyphagous and aggressive pathogen able to cause, under certain conditions, very important postharvest economic losses (Bautista-Baños et al., 2014).

Control methods, and challenges

The use of synthetic chemical fungicides is currently the primary method to control postharvest fungal diseases.

These postharvest fungicides encompass a wide range of compounds of different chemical nature with different modes of action. They can be easily applied in fresh produce packinghouses as aqueous solutions, coating emulsions in drencher or packing line facilities, and storage room fumigants.

This approach effectively reduces losses and postharvest spoilage, offering a convenient and relatively low-cost solution (Chen et al., 2021). Nevertheless, their use in agriculture has sparked concerns about their environmental impact, potential hazards for both aquatic and terrestrial organisms, and the emergence of resistant pathogenic fungal strains (Sharma et al., 2019).

Concerns about mycotoxins and foodborne pathogens further underscore the need to explore viable alternatives to control postharvest fungal diseases.

Additionally, potential restrictions on preharvest fungicide application may lead to high levels of fungal inocula that can produce latent infections and cause decay after harvest.

Despite setbacks, such as the rejection of the Sustainable Use Regulation (SUR) in 2022 and subsequent withdrawal by the Commission in early 2024 due to widespread sectorial protests, evidence indicates that chemical pesticides contribute significantly to pollution, biodiversity loss, compromised water quality, degraded soils, pest resistance, and chronic illnesses.

Therefore, the imperative for cost-effective alternatives remains pressing, particularly given the economic losses reported by European farmers due to uncontrolled pests and unfair competition from regions with different regulatory standards.

Need of safe alternatives

Over the past years, there has been an intensive research effort to find safe alternatives to mitigate postharvest losses of horticultural produce caused by fungal infections.

Various approaches have been explored, including natural or low-toxicity chemical compounds such as organic and inorganic GRAS (generally recognized as safe) salts, plant extracts, essential oils, antagonistic microorganisms used as biological control agents, nano technology and genetic engineering approaches (Rahman et al., 2024, Torres-Palazzolo et al., 2024).

Despite these endeavors, the discovery of effective alternatives and, above all, their practical implementation have proven to be a challenge (Chowdhury et al., 2022).

Waste-to-resource approach

While global food security remains a major concern, it is compounded by the underutilization and discarding of by-products and residues from major agri-food industries, which also greatly contribute to food loss and waste.

Research efforts have thus focused on effectively valorizing these residues, with an emphasis on extracting valuable bioactive compounds.

This waste-to-resource approach aligns closely with the growing focus on environmental sustainability and waste valorization, fitting within the framework of the circular bioeconomy (Mir-Cerdà et al., 2023).

Moreover, the extraction of value-added compounds to be used as natural antimicrobials is in harmony with the objectives outlined in the European Union (EU) Green Deal strategy, which proposed to reduce the use of synthetic pesticides in agriculture by 50 % by 2030 (Liobikienė and Miceikienė, 2023).

Potential of agri-food by-products as novel antifungal agents

Regardless of the growing body of research on the valorization of agri-food by-products, their potential as novel antifungal agents for the control of postharvest diseases of fresh horticultural produce remains highly unexplored.

Most studies have focused on the characterization and extraction of bioactive compounds for high-value applications in the food, pharmaceutical, and energy sectors, while their direct use as natural antifungal treatments for fresh fruit has received limited attention.

Aims of this review

This review aims to provide a comprehensive overview on the exploitation of agri-food by-product extracts rich in bioactive compounds as postharvest treatments to mitigate fungal decay of fresh fruits.

To this end, the review examines the major classes of bioactive compounds (viz., phenolics, terpenes, alkaloids, and glucosinolates) present in agri-food by-products and the key parameters influencing their extraction efficiency using both conventional and green technologies.

Particular attention is given to the potential of these extracts to control postharvest diseases, highlighting results obtained in in vitro tests against major postharvest pathogens and evidence observed in in vivo trials with important fruit commodities.

By integrating current knowledge on extraction optimization, bioactivity, and potential applications, this review highlights the potential of the valorization of agri-food waste to develop, within a circular bioeconomy framework, novel sustainable and non-polluting strategies to reduce postharvest losses and extend the shelf life of fresh fruits.

Source

From waste to health: Valorization of agri-food by-products for the control of fresh fruit fungal postharvest decay
Ricardo Lima de Souza, María B. Pérez-Gago, Lluís Palou
https://doi.org/10.1016/j.postharvbio.2025.114054
https://www.sciencedirect.com/science/article/abs/pii/S0925521425006660