Phenolic compounds and extracts with bioactive properties can be obtained from many kinds of plant materials. These natural substances have gained attention in the food research as possible growth inhibitors of foodborne pathogenic and spoilage bacteria. Many phenolic-enriched plant extracts and individual phenolics have promising anti-quorum sensing potential as well and can suppress the biofilm formation and toxin production of food-related pathogens. Various studies have shown that plant phenolics can substitute or support the activity of synthetic food preservatives and disinfectants, which, by the way, can provoke serious concerns in consumers. In this review, we will provide a brief insight into the bioactive properties, i.e., the antimicrobial, anti-quorum sensing, anti-biofilm and anti-enterotoxin activities, of plant phenolic extracts and compounds, with special attention to pathogen microorganisms that have food relation. Carbohydrase aided applications to improve the antimicrobial properties of phenolic extracts are also discussed.

https://www.mdpi.com/2076-3921/9/2/165/pdf

Plant Phenolics and Phenolic-Enriched Extracts as Antimicrobial Agents against Food-Contaminating Microorganisms

Potential application of grape (Vitis vinifera L.) stem extracts in the cosmetic and pharmaceutical industries: Valorization of a by-product

Plant extracts are a rich source of natural compounds with antimicrobial properties, which are able to prevent, at some extent, the growth of foodborne pathogens. The aim of this study was to investigate the potential of polyphenolic extracts from cladodes of Opuntia ficus-indica (L.) Mill. to inhibit the growth of some enterobacteria and the biofilm formation by Staphylococcus aureus. Opuntia ficus-indica cladodes at two stages of development were analysed for total phenolic content and antioxidant activity by Oxygen Radical Absorbance Capacity (ORAC) and Trolox equivalent antioxidant capacity (TEAC) (in vitro assays) and by cellular antioxidant activity in red blood cells (CAA-RBC) (ex vivo assay). The Liquid Chromatography Time-of-Flight Mass Spectrometry (LC/MS-TOF) analysis of the polyphenolic extracts revealed high levels of piscidic acid, eucomic acid, isorhamnetin derivatives and rutin, particularly in the immature cladode extracts. Opuntia cladodes extracts showed a remarkable antioxidant activity (in vitro and ex vivo), a selective inhibition of the growth of Gram-positive bacteria, and an inhibition of Staphylococcus aureus biofilm formation. Our results suggest and confirm that Opuntia ficus-indica cladode extracts could be employed as functional food, due to the high polyphenolic content and antioxidant capacity, and used as natural additive for food process control and food safety.

Antimicrobial and Antibiofilm Activity against Staphylococcus aureus of Opuntia ficus-indica (L.) Mill. Cladode Polyphenolic Extracts

Apple is among the most consumed fruits in the world and the expansion of their processing is increasing the generation of waste such as apple pomace. It finds some applications in food and feed systems, anaerobic digestion, and composting; however it most ends in landfills or in informal disposal. Therefore, waste management strategies that address this waste accumulation need to be explored. This review provides a state-of-art of valorization strategies adopted for recovery of value added products from apple processing-derived waste and discusses on their development stage. The research community has laid most of its efforts on incorporation of apple pomace into feed and food systems and in the development of pectin- and phenolics-extraction methods. Incorporation of apple pomace in feed and food systems is still negligible due to its low protein and high fiber contents. Therefore, coupling apple pomace with microbial conversion for nutritional upgrade could change this scenario. Some environmentally-friendly techniques have been developed for extraction of pectin and phenolics, but major developments are needed on their integration to attain tailored extraction of several compounds. Recovery of value added routes of apple pomace towards production of bio-chemicals are characterized by lack of deep research studies and of a holistic approach. Integrated approach with techno-economic analysis, life-cycle assessment, and inter-sectorial initiatives will possibly reveal the most promising valorization routes.

A critical review on the development stage of biorefinery systems towards the management of apple processing-derived waste

Silicon (Si) is considered a non-essential element similar to cadmium, arsenic, lead, etc., for plants, yet Si is beneficial to plant growth, so it is also referred to as a quasi-essential element (similar to aluminum, cobalt, sodium and selenium). An element is considered quasi-essential if it is not required by plants but its absence results in significant negative consequences or anomalies in plant growth, reproduction and development. Si is reported to reduce the negative impacts of different stresses in plants. The significant accumulation of Si on the plant tissue surface is primarily responsible for these positive influences in plants, such as increasing antioxidant activity while reducing soil pollutant absorption. Because of these advantageous properties, the application of Si-based nanoparticles (Si-NPs) in agricultural and food production has received a great deal of interest. Furthermore, conventional Si fertilizers are reported to have low bioavailability; therefore, the development and implementation of nano-Si fertilizers with high bioavailability could be crucial for viable agricultural production. Thus, in this context, the objectives of this review are to summarize the effects of both Si and Si-NPs on soil microbes, soil properties, plant growth and various plant pathogens and diseases. Si-NPs and Si are reported to change the microbial colonies and biomass, could influence rhizospheric microbes and biomass content and are able to improve soil fertility.

Effects of Silicon and Silicon-Based Nanoparticles on Rhizosphere Microbiome, Plant Stress and Growth.

This paper reports two strategies to mobilize phenolic antioxidants from lyophilized and oven-dried black grape (Vitis vinifera x (Vitis labrusca x Vitis riparia)) pomace, and apple (Malus domestica cv. Jonagold) and yellow pitahaya (Hylocereus megalanthus) peel, core, peduncle and seed mixtures: a solid-state Rhizomucor miehei NRRL 5282 fermentation-based process and a carbohydrate-cleaving enzyme treatment using R. miehei NRRL 5282 cellulase and Aspergillus niger pectinase cocktails. Both methods proved to be suitable to increase the extractable phenolic content and improve the antioxidant properties of the phenolics as determined by 1,1-diphenyl-2-picrylhydrazyl radical inhibition or ferric reducing antioxidant power analyses. During solid-state fermentation, maximal phenolic yields obtained in lyophilized grape, apple and pitahaya residues were 1956 ± 31, 477 ± 37 and 495 ± 27 mg gallic acid equivalents (GAE)/100 g dry matter (DM), respectively, while they were 1385 ± 71, 362 ± 27 and 615 ± 26 mg GAE/100 g DM in oven-dried samples, respectively. The major individual phenolics produced enzymatically from the substrates were identified by HPLC as gallic acid, 4-hydroxybenzoic acid, vanillic acid, (+)-catechin and (−)-epicatechin, with yields ranging from 0.58 ± 0.06 to 215.81 ± 17.17 mg/100 g DM depending on the substrate and the pretreatment. The obtained phenolic-enriched extracts could potentially be applicable as sources of natural antioxidants.

/pdf/mobilization-of-phenolic-antioxidants-from-grape-apple-and-5cjbk88l6j.pdf

Mobilization of phenolic antioxidants from grape, apple and pitahaya residues via solid state fungal fermentation and carbohydrase treatment

In this study, antimicrobial, anti-quorum sensing and anti-biofilm forming activities of phenolic-enriched extracts produced by enzyme-assisted extraction from oven-dried and lyophilized black grape (Vitis vinifera x (Vitis labrusca x Vitis riparia)), apple (Malus domestica cv. Jonagold) and yellow pitahaya (Hylocereus megalanthus) residues were investigated. Both disk-diffusion and minimal inhibitory concentration (MIC) assays showed increased antimicrobial capacity for many extracts after the carbohydrase treatments. The lowest MIC (12.5 mg/mL) was found for black grape samples against Bacillus cereus and Bacillus subtilis, and for apple and pitahaya samples against Pseudomonas putida. The percent quorum sensing inhibition effect on Chromobacterium violaceum has varied between 9 and 36%, 15 and 24% and 6 and 23% for black grape, apple and pitahaya extracts, respectively, depending on the enzyme treatment. Pseudomonas aeruginosa, P. putida and Staphylococcus aureus biofilms were the most sensitive to the extracts, while the Salmonella enterica, Listeria monocytogenes and Escherichia coli biofilms were modulated by certain enzyme-free and treated samples. The extracts can be good candidates for the development of natural preservatives.

Antimicrobial activity of grape, apple and pitahaya residue extracts after carbohydrase treatment against food-related bacteria

Lipase enzymes of the oleaginous fungal group Mortierella are rarely studied. However, considering that most commercial lipases are derived from filamentous fungal sources, their investigation can contribute to the cost-effective development of new biotechnological processes. Here, an extracellular lipase with a molecular mass of 30 kDa was isolated from Mortierella echinosphaera CBS 575.75 and characterized. The purified lipase exhibited an optimal p-nitrophenyl palmitate (pNPP)-hydrolyzing activity at 25 °C and pH 6.6–7.0 and proved to be highly stable at temperatures up to 40 °C and under broad pH conditions. The enzyme was active under low temperatures, retaining 32.5% of its activity at 10 °C, and was significantly stable in polar and non-polar organic solvents. The Km, Vmax, and kcat for pNPP were 0.336 mM, 30.4 μM/min, and 45.7 1/min for pNPP and 0.333 mM, 36.9 μM/min, and 55.6 1/min for pNP-decanoate, respectively. The pNPP hydrolysis was inhibited by Hg2+, N-bromosuccinimide, and sodium dodecyl sulfate, while ethylenediaminetetraacetic acid and metal ions, such as Ca2+, Mg2+, Na+, and K+ enhanced the activity. The purified lipase had non-regioselective activity and wide substrate specificity, showing a clear preference for medium-chained p-nitrophenyl esters. Besides its good transesterification activity, the enzyme appeared as a suitable biocatalyst to operate selective esterification reactions to long-chained alkyl esters. Adsorption to Accurel MP1000 improved the storage stability of the enzyme at 5 °C. The immobilized lipase displayed tolerance to a non-aqueous environment and was reusable for up to five cycles without significant loss in its synthetic and hydrolytic activities. These findings confirm the applicability of both the free and the immobilized enzyme preparations in future research.

https://www.mdpi.com/1422-0067/19/4/1129/pdf

Carolina Zambrano

Papers

Plant Phenolics and Phenolic-Enriched Extracts as Antimicrobial Agents against Food-Contaminating Microorganisms

Mobilization of phenolic antioxidants from grape, apple and pitahaya residues via solid state fungal fermentation and carbohydrase treatment

Antimicrobial activity of grape, apple and pitahaya residue extracts after carbohydrase treatment against food-related bacteria

An Organic Solvent-Tolerant Lipase with Both Hydrolytic and Synthetic Activities from the Oleaginous Fungus Mortierella echinosphaera

Fermentative and Enzyme-Assisted Production of Phenolic Antioxidants from Plant Residues