In Vitro Antioxidant, Antibacterial and Mechanisms of Action of Ethanolic Extracts of Five Tunisian Plants against Bacteria

Quality of Refrigerated Squid Mantle Cut Treated with Mint Extract Subjected to High-Pressure Processing

Squid (Loligo vulgaris) is commonly prone to spoilage, leading to a short shelf-life. High-pressure processing (HPP) can play a role in maintaining the quality and freshness of squid. Along with HPP, food preservatives from natural sources such as mint extract (ME), which are effective, safe, available, and cost-effective, are required. The present study aimed to investigate the combined effect of ME and HPP on the quality of refrigerated squid mantle cuts (SMC) over a period of 15 days. The time-kill profiles of ME and planktonic cell inactivation by HPP were assessed. ME (400 mg/L) inhibited bacterial growth, while planktonic cells treated with HPP (400 MPa) exhibited a reduction at 5 min. Physicochemical and microbial qualities of SMC treated with ME (0, 200, 400 mg/L) followed by HPP (0.1, 200, 400 MPa) for 5 min were monitored during refrigerated storage. Samples treated with ME (400 mg/L) and HPP (400 MPa) exhibited lower weight loss, cooking loss, pH changes, volatile base content, microbial counts, and higher textural properties than other samples. Based on next-generation sequencing results, Brochothrix campestris from family Listeriaceae was the predominant spoilage bacteria in treated sample after 12 days of storage. Therefore, ME and HPP combined treatments exhibited effectiveness in extending the shelf-life of refrigerated SMC.

Biological activities and determination of the mode of action of Tunisian Globularia alypum and Cistus monspeliensis ethanolic extracts

This study was designed to evaluate the antioxidant and antimicrobial activity of ethanolic extracts (EEs) of Cistus monspeliensis and Globularia alypum. C. monspeliensis showed the highest values of phenolic compounds. Further, it was shown that EE of C. monspeliensis displayed the highest DPPH (IC50 = 8.3 ± 1.08 mg/mL). The chemical profiles demonstrated a total of 12 and 13 phenolic compounds for C. monspeliensis and G. alypum, respectively. EEs of both plants possessed broad-spectrum antimicrobial activity when tested against Escherichia coli and Staphylococcus aureus. Treatment of studied strains with these extracts at their MICs reduced considerably the bacterial viability. The extracts did not induce total bacterial lysis, as determined by the measurement of optical density at 620 nm. Strains treated with EEs at Minimum Inhibitory Concentrations showed significant loss of tolerance to NaCl. Our results contribute to understanding the antibacterial mechanism of ethanolic extracts of the studied medicinal plants.

Natural Antimicrobials: A Reservoir to Contrast Listeria monocytogenes

Natural environments possess a reservoir of compounds exerting antimicrobial activity that are forms of defence for some organisms against others. Recently, they have become more and more attractive in the food sector due to the increasing demand for natural compounds that have the capacity to protect food from pathogenic microorganisms. Among foodborne pathogens, Listeria monocytogenes can contaminate food during production, distribution, or storage, and its presence is especially detected in fresh, raw food and ready-to-eat products. The interest in this microorganism is related to listeriosis, a severe disease with a high mortality rate that can occur after its ingestion. Starting from this premise, the present review aims to investigate plant extract and fermented plant matrices, as well as the compounds or mixtures of compounds produced during microbial fermentation processes that have anti-listeria activity.

Evaluation of Phytochemical Screening, Pigment Content, In Vitro Antioxidant, Antibacterial Potential and GC-MS Metabolite Profiling of Green Seaweed Caulerpa racemosa

Exploration of seaweeds to unravel their bioactive metabolites from the perspective of wider applications gained substantial importance. The present study was performed to investigate the total phenolic, flavonoid, tannin content, antioxidant activity and antibacterial potential of various solvent extracts of green seaweed Caulerpa racemosa. The methanolic extract showed higher phenolic (11.99 ± 0.48 mg gallic acid equivalents/g), tannin (18.59 ± 0.54 mg tannic acid equivalents/g) and flavonoid (33.17 ± 0.76 mg quercetin equivalents/g) content than other extracts. Antioxidant activity was determined by using 2,2-diphenylpicrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay with different concentrations of C. racemosa extracts. The methanolic extract showed higher scavenging potential in both the DPPH and ABTS activity with the inhibition value of 54.21 ± 1.39% and 76.62 ± 1.08%, respectively. Bioactive profiling was also identified by using Gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared (FT-IR) techniques. These studies revealed the presence of valuable bioactive compounds in C. racemosa extracts and these compounds might be responsible for antimicrobial, antioxidant, anticancer and anti-mutagenic properties. Major compounds identified in GC-MS were 3,7,11,15-Tetramethyl-2-hexadecen-1-ol, 3-hexadecene and Phthalic acid. In terms of antibacterial activity, C. racemosa has promising antibacterial potential against aquatic pathogens Aeromonas hydrophila, Aeromonas veronii and Aeromonas salmonicida. Further evaluation studies focusing aquatic related aspects would reveal the novel bioproperties and applications of C. racemosa.