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Over the last few years marine algae has attracted many researchers worldwide to isolate high value bioactive compounds for food and pharmaceutical industries due to its broad spectrum of various biological activities such as antioxidant, antibacterial, antifungal, anticancer, anti-inflammatory and antidiabetic (Thomas & Kim, 2011; Eom, Kim, & Kim, 2012; Hamed, Ozogul, Ozogul, & Regenstein, 2015; El Shafay, Ali, & El-Sheekh, 2016; Sathya, Kanaga, Sankar, & Jeeva, 2017; Davoodbasha, Edachery, Nooruddin, Lee, & Kim, 2018). Algae are the fastest growing plants in the world and generally divided into macroalgae and microalgae based on morphology. The macroalgae or “seaweeds,” are more abundant, multicellular plants growing up to 60 meters long in ocean. Microalgae are microscopic, mostly existing as small cells of about 2–200 µm and dwell in fresh, sea and even wastewater systems (Sirajunnisa & Surendhiran, 2016). Generally, marine algae are categorized into three main groups namely Rhodophyceae (red algae), Chlorophyceae (green algae), Phaeophyceae (brown algae) for the attribution of different pigments like phycobilins, chlorophyll and fucoxanthin respectively (Kadam, Tiwari, & O’Donnell, 2013; Barbosa, Valentão, ; Andrade, 2014). Asian countries like China, Japan, and Korea used seaweeds for medicinal and food purposes since prehistoric times (Thomas ; Kim, 2011).
Many research reports revealed that marine algae could act as a potential alternative source of antimicrobial agents because of their functional groups with excellent antibacterial activity include phlorotannins, fatty acids, polysaccharides, peptides, terpenes, polyacetylenes, sterols, indole alkaloids, aromatic organic acids, shikimic acid, polyketides, hydroquinones, alcohols, aldehydes, ketones, and halogenated furanones, alkanes, and alkenes (Barbosa et al., 2014; Shannon ; Abu-Ghannam, 2016; Sathya et al., 2017; Pina-Pérez, Rivas, Martínez, ; Rodrigo, 2017; Zouaoui ; Ghalem, 2017). Screening for under exploited bioactive compounds from marine algae with antimicrobial properties to be employed in food applications. Hence, the research has moved towards finding natural antimicrobial compounds against food pathogens to replace synthetic compounds. Various primary bioactive compounds from marine algae are shown in Fig.1. Antimicrobial agents from terrestrial plants such as spices and herbs and their antimicrobial activity against food pathogens have already been well documented in literature. There are more than 100,000 species of algae existing on earth (Sirajunnisa ; Surendhiran, 2016). However, information about their potential activity against food pathogens is sparse since it is a recent field of research worldwide. Recently, some research reports have been published on antimicrobial potential of bioactive compounds extracted from marine algae against food pathogens and obtained notable positive results by various researchers globally. For instance, Rajauria et al. (2012) reported that methanol extract of polyphenolic compounds from the Irish brown seaweed Himanthalia elongates showed potent bactericidal activity against Gram-positive Listeria monocytogenes and Enterococcus faecalis and Gram-negative Pseudomonas aeruginosa and Salmonella abony at a concentration of 60 mg/mL. Dussault et al. (2016) reported that low concentrated algal extracts (?500 µg/ml) from Padina and Ulva sp. showed potential antimicrobial activity against Gram-positive foodborne pathogens such as Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. A summary of antimicrobial agents from marine algae and their antimicrobial activities against food pathogens is shown in Table 1.
Polysaccharides. Marine algae contain many different kinds of polysaccharides as their storage compounds and show good antibacterial, antiviral and antioxidant properties. Many of them are soluble dietary fibers (Chojnacka, Saeid, Witkowska ; Tuhy, 2012) and could be converted into nontoxic bioactive oligosaccharides by simple hydrolysis (Pina-Pérez et al. 2017). For example, sulphated polysaccharides from seaweed, Chaetomorpha aerea containing alginates, fucoidans and laminaran showed potent antimicrobial activity against food pathogens, E. coli and Staphylococcus aureus, at an MIC of 50 mg/mL of extract (De Jesus Raposo, de Morais, ; de Morais, 2015). Kadam et al. (2015) recorded the remarkable effect of ultrasound assisted extraction of laminarin from two Irish brown seaweeds Ascophyllum nodosum and Laminaria hyperborean against essential food pathogens such as Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella typhimurium. Another report published by Pierre et al. (2011) that carrageenans and the sulphated exopolysaccharide from the red microalga Porphyridium cruentum are effectively inhibiting one of the most important foodborne pathogen, Salmonella enteritidis. Treating Helicobacter pylori, one of the most dangerous foodborne pathogen responsible for gastric ulcer, is a big challenge till now affecting 50–80% of the worldwide population (Pina-Pérez et al., 2017). Chua et al. (2015) successfully inhibited the growth ` of H.pylori using sulphated polysaccharide fucoidan isolated from edible brown alga, Fucus vesiculosus, at the concentration of 100 µg /mL. Moreover, Araya et al. (2011) demonstrated that fucoidan showed no toxic effects on human trials with the daily intake of 6g which revealed the possibilities of applying in food industries.
Phenolic compounds. Phenolic compounds also known as Polyphenols are a group of tannin compounds that contain hydroxyl (?OH) substituents on an aromatic hydrocarbon moiety. Polyphenols in marine algae include phenolic acids, flavonoids, isoflavones, cinnamic acid, benzoic acid, quercetin, lignans, catechins, anthraquinones, phlorotannins (Chojnacka et al., 2012; Kadam et al., 2013; Pina-Pérez et al., 2017). Among various polyphenols, phlorotannins showed excellent, potent free radical scavenging properties than polyphenols derived from terrestrial plants due to eight interconnected phenol rings (Sathya et al., 2017). Phlorotannins found in many brown seaweeds such as Ecklonia cava, E. kurome, E. stolonifera, Eisenia aborea, Eis. bicyclis, Ishige okamurae and Pelvetia siliquosa have medicinal and pharmaceutical benefits and have shown strong anti-oxidant, antiinflammatory, antiviral, anti-tumor, anti-diabetes and anti-cancer properties (Eom et al., 2012). Phlorotannins are polymers of phloroglucinol units (1,3,5-trihydroxybenzene) with molecular weight ranging between 126 Da and 650 kDa (Kadam et al., 2013). In recent studies it was described that phlorotannin had excellent antimicrobial activity against food pathogens which could help devise a roadmap to replace synthetic chemicals for food preservation.
A research group led by Kim et al. (2017) investigated that antimicrobial activity of phlorotannin extracted from edible brown seaweed, Eisenia bicyclis acted against Listeria monocytogenes, one of the essential food contaminants in the meat processing industry. They evidenced that phlorotannins had excellent anti-listerial activity in the range between 16 and 256 µg/ml. Choi et al. (2010) recorded the potent antimicrobial activity of eckol rich phlorotannin from E.cava against food pathogens methicillin-resistant S. aureus (MRSA) and Salmonella sp. in the range between 125 and 250 µg/mL. Moreover, some research results concluded that phlorotannin showed no cytotoxic effects on animal models with oral administration (Nagayama, Iwamura, Shibata, Hirayama, ; Nakamura, 2002; Eom et al., 2012) which is highly suitable for food applications. A team led by Al-Saif et al. (2014), investigated the effects of flavonoids including rutin, quercetin, and kaempferol extracted from marine alga G.dendroides. They recorded the antibacterial activity of these compounds against some critical food contaminants such as E. coli, S. aureus and E. faecalis at the concentration of 10.5 mg/kg (rutin), 7.5 mg/kg (quercetin) and 15.2 mg/kg (kaempferol). Besides, marine algae can be directly added into human foods such as breads, pizza, cheese, pasta and meat products (Pina-Pérez et al., 2017) and used for edible coatings to preserve food products (Sánchez-Ortega et al., 2014; Pina-Pérez et al., 2017) which would add additional benefits of using marine algae in food industries.

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