The hidden power of secondary metabolites in plant-fungi interactions and sustainable phytoremediation.

The global environment is dominated by various small exotic substances, known as secondary metabolites, produced by plants and microorganisms. Plants and fungi are particularly plentiful sources of these molecules, whose physiological functions, in many cases, remain a mystery. Fungal secondary metabolites (SM) are a diverse group of substances that exhibit a wide range of chemical properties and generally fall into one of four main family groups: Terpenoids, polyketides, non-ribosomal peptides, or a combination of the latter two. They are incredibly varied in their functions and are often related to the increased fitness of the respective fungus in its environment, often competing with other microbes or interacting with plant species. Several of these metabolites have essential roles in the biological control of plant diseases by various beneficial microorganisms used for crop protection and biofertilization worldwide. Besides direct toxic effects against phytopathogens, natural metabolites can promote root and shoot development and/or disease resistance by activating host systemic defenses. The ability of these microorganisms to synthesize and store biologically active metabolites that are a potent source of novel natural compounds beneficial for agriculture is becoming a top priority for SM fungi research. In this review, we will discuss fungal-plant secondary metabolites with antifungal properties and the role of signaling molecules in induced and acquired systemic resistance activities. Additionally, fungal secondary metabolites mimic plant promotion molecules such as auxins, gibberellins, and abscisic acid, which modulate plant growth under biotic stress. Moreover, we will present a new trend regarding phytoremediation applications using fungal secondary metabolites to achieve sustainable food production and microbial diversity in an eco-friendly environment.

Enhanced hydrophobic paper-sheet derived from Miscanthus × giganteus cellulose fibers coated with esterified lignin and cellulose acetate blend.

Biobased packaging materials derived from carbon-neutral feedstocks are sustainable alternatives to conventional fossil-based polymers. In this study, a method was developed to prepare paper-sheets derived from Miscanthus × giganteus cellulose fibers for potential food contact applications. The papers were hydrophobized with modified lignin from Miscanthus × giganteus biomass and commercial Kraft alkali lignin through hydroxyethylation with ethylene carbonate, followed by esterification with propionic acid. The esterified lignin (10 % w/w) and cellulose acetate (5 % w/w, based on lignin content) were dissolved in acetone and applied as a coating on the miscanthus paper sheets. The esterified lignins were characterized using FTIR, NMR, DSC, TGA, and elemental analyses. The uncoated and coated paper-sheets had contact angle values 52.4° and >130°, respectively, indicating an increased surface hydrophobicity of the coated paper samples. The water vapor transmission rate decreased significantly from 213.7 (uncoated paper-sheet) to 63.3 g/m2.d (coated paper-sheet). The tensile strength of the coated paper (64.6 MPa) was higher than the uncoated counterpart (57.1 MPa). Results from this study suggest that the esterified lignin coated miscanthus paper is a promising hydrophobic food packaging material alternative to conventional fossil-based thermoplastics.

Triggered and controlled release of bioactives in food applications.

Bioactive compounds (e.g., nutraceuticals, micronutrients, antimicrobial, antioxidant) are added to food products and formulations to enhance sensorial/nutritional attributes and/or shelf-life. Many of these bioactives are susceptible to degradation when exposed to environmental and processing factors. Others involve in undesirable interactions with food constituents. Encapsulation is a useful tool for addressing these issues through various stabilization mechanisms. Besides protection, another important requirement of encapsulation is to design a carrier that predictably releases the encapsulated bioactive at the target site to elicit its intended functionality. To this end, controlled release carrier systems derived from interactive materials have been developed and commercially exploited to meet the requirements of various applications. This chapter provides an overview on basic controlled and triggered release concepts relevant to food and active packaging applications. Different approaches to encapsulate bioactive compounds and their mode of release are presented, from simple blending with a compatible matrix to complex multiphase carrier systems. To further elucidate the mass transport processes, selected diffusion and empirical release kinetic models are presented, along with their brief historical significance. Finally, interactive carriers that are responsive to moisture, pH, thermal and chemical stimuli are presented to illustrate how these triggered release mechanisms can be useful for food applications.

A review on colorimetric indicators for monitoring product freshness in intelligent food packaging: Indicator dyes, preparation methods, and applications.

Intelligent food packaging system exhibits enhanced communication function by providing dynamic product information to various stakeholders (e.g., consumers, retailers, distributors) in the supply chain. One example of intelligent packaging involves the use of colorimetric indicators, which when subjected to external stimuli (e.g., moisture, gas/vapor, electromagnetic radiation, temperature), display discernable color changes that can be correlated with real-time changes in product quality. This type of interactive packaging system allows continuous monitoring of product freshness during transportation, distribution, storage, and marketing phases. This review summarizes the colorimetric indicator technologies for intelligent packaging systems, emphasizing on the types of indicator dyes, preparation methods, applications in different food products, and future considerations. Both food and nonfood indicator materials integrated into various carriers (e.g., paper-based substrates, polymer films, electrospun fibers, and nanoparticles) with material properties optimized for specific applications are discussed, targeting perishable products, such as fresh meat and fishery products. Colorimetric indicators can supplement the traditional "Best Before" date label by providing real-time product quality information to the consumers and retailers, thereby not only ensuring product safety, but also promising in reducing food waste. Successful scale-up of these intelligent packaging technologies to the industrial level must consider issues related to regulatory approval, consumer acceptance, cost-effectiveness, and product compatibility.

Triggered and controlled release of active gaseous/volatile compounds for active packaging applications of agri-food products: A review.

Gaseous and volatile active compounds are versatile to enhance safety and preserve quality of agri-food products during storage and distribution. However, the use of these compounds is limited by their high vapor pressure and/or chemical instability, especially in active packaging (AP) applications. Various approaches for stabilizing and controlling the release of active gaseous/volatile compounds have been developed, including encapsulation (e.g., into supramolecular matrices, polymer-based films, electrospun nonwovens) and triggered release systems involving precursor technology, thereby allowing their safe and effective use in AP applications. In this review, encapsulation technologies of gases (e.g., CO2 , ClO2 , SO2 , ethylene, 1-methylcyclopropene) and volatiles (e.g., ethanol, ethyl formate, essential oils and their constituents) into different solid matrices, polymeric films, and electrospun nonwovens are reviewed, especially with regard to encapsulation mechanisms and controlled release properties. Recent developments on utilizing precursor compounds of bioactive gases/volatiles to enhance their storage stability and better control their release profiles are discussed. The potential applications of these controlled release systems in AP of agri-food products are presented as well.

Toxicity of Five Plant Volatiles to Adult and Egg Stages of Drosophila suzukii Matsumura (Diptera: Drosophilidae), the Spotted-Wing Drosophila.

The environmental impact of methyl bromide (MB) has resulted in its phase out as an insecticidal fumigant except for critical use exempted categories. Consequently, there is an urgent need to develop an environmentally sustainable MB alternative fumigant. trans-Cinnamaldehyde (TC), benzaldehyde, allyl isothiocyanate (AITC), hexanal, and ethyl formate (EF) are naturally occurring plant volatiles with insecticidal properties. This study assessed the toxicity of these plant volatiles to adult and egg stages of the spotted-wing drosophila (SWD) (Drosophila suzukii Matsumura). The plant volatile treatments had a significant effect on adult SWD mortality. The descending order of toxicity to adult SWD was benzaldehyde > AITC > TC > hexanal > EF at a headspace concentration of 0.50 µL/L air for 24 h. All the volatiles, at a concentration of 4.00 µL/L air, significantly inhibited larval emergence from SWD eggs in artificial diet compared to the control. At a 0.50 µL/L air level, among the volatiles tested, only AITC exhibited 100% inhibition against larval emergence from SWD eggs in blueberry fruits after 24 h exposure. In summary, this study shows that all volatiles tested elicited varying degrees of toxicity toward SWD adults and eggs. However, AITC was the most efficacious volatile and the one with the greatest promise as a post-harvest fumigant for both adult and egg stages of SWD.

Synthesis and Characterization of Ethyl Formate Precursor for Activated Release Application.

Ethyl formate (EF) is a generally recognized-as-safe flavoring agent commonly used in the food industry. It is a naturally occurring volatile with insecticidal and antimicrobial properties, promising as an alternate fumigant to methyl bromide which is undesirable due to its ozone depletion in the stratosphere and toxic properties. However, EF is highly volatile, flammable, and susceptible to hydrolytic degradation. These properties present considerable end-use challenges. In this study, a precursor of EF was synthesized via the condensation reaction of adipic acid dihydrazide and triethyl orthoformate to form diethyl N,N'-adipoyldiformohydrazonate, as confirmed by Fourier transformed infrared and solid-state nuclear magnetic resonance spectroscopies. Differential scanning calorimetry analysis showed that the precursor had a melting point of 174 °C. The physical properties of the precursor were studied using scanning electron microscopy and dynamic light scattering analysis, which showed that the precursor was made up of agglomerated particulates with irregular shapes and sizes. The resulting precursor was nonvolatile and remained stable under dry conditions but could be hydrolyzed readily to trigger the release of EF. The release behaviors of EF from the precursor was evaluated by citric acid-catalyzed hydrolysis, showing that 0.38 ± 0.008 mg EF/mg precursor was released after 2 h at 25 °C, representing about 98% of the theoretical loading. Both EF release rate and its total release amount decreased significantly (p < 0.05) with decreasing temperature and relative humidity. The conversion of the highly volatile EF into a solid-state precursor, in conjunction with the activated release strategy, can be useful for controlled release of EF for fumigation and other applications in destroying insect pests and inhibiting the proliferation of spoilage microorganisms.