7marine macroalgae-villasenor.pmd I.M. Villaseñor 61 SCIENCE DILIMAN (JANUARY-JUNE 2016) 28:1, 61-67 Marine Macroalgae: A Review Irene M. V illasenor University of the Philippines Diliman ISSN 0115-7809 Print / ISSN 2012-0818 Online INTRODUCTION There is an abundance of marine algae along the Philippine coastline (36, 289 km) (Hurtado et al. 2013). These algae are used for food, feeds, and medicine, among others. The most popular seaweeds that are utilized as food products are those belonging to the Caulerpa, Euchema, and Gracilaria species (Montaño 2002). Sargassum sp, brown seaweed, is traditionally used as a f ish wrapper, vegetable, fertilizer, flower inducer, insect repellant, animal feed, and as a drink with reported health benef its (Montaño et al. 2006). Some Philippine seaweed exhibit antimicrobial (Mabugay et al. 1994) and cytotoxic activities against selected human cancer cell lines (Tantengco et al. 2015). Kappa- carrageenan gel can also be used to sequester paralytic shell f ish poison (PSP) (Cañete and Montaño 2002). The potential of seaweed resources as biofuel was also explored with the identif ication of the seaweed species Sargassum spp. , Turbinaria spp. , Hydroclathrus spp. , Caulerpa spp. , and Ulva spp. as possible sources of biomass for biofuel production (Marquez et al. 2014). AGAR The worldwide production of the gelling agent agar mainly relies on the red algae of the order Gracilariales and Gelidiales for raw material (Villanueva et al. 2010). Chemical Property The alkali-modified agar from Gracilaria edulis has a basic repeating unit of alternating 3-linked 6-O-methyl-beta-D-galactopyranose and 4-linked 3,6-anhydro-alpha-L- galactopyranose with partial methylation at O-2 of the anhydrogalactose and partial M a r i n e M a c r o a l g a e : A Rev i ew 62 sulfation at the O-4- of the methylated galactose residue (Villanueva and Montaño 1999). Agar with the regular agarobiose repeating unit was also isolated from Gracilaria arcuata and Gracilaria tenuistipitata. Agar from G. tenuistipitata has partial methylation at the 6-position of the D-galactosyl residues. Both agars from G. arcuata and G. tenuistipitata exhibit sulphate substitution at varying positions in the polymer (Montaño et al. 1999). Another potential source of agar is the red algal order Ceramiales. The native agar from Laurencia flexilis has the same basic repeating unit with minor sulfation at 4-position of the 3-linked galactose residues. It has low sulfate and high 3, 6-anhydrogalactose levels (Villanueva et al. 2010). Physical Property G. arcuata produces a soft agar gel, while the agar from G. tenuistipitata exhibits gel qualities typical of most Gracilaria agars (Montaño et al. 1999). Alkali modif ication enhanced agar gel strength and syrenesis. The gel strength of G. edulis was considerably enhanced with the addition of sodium, potassium, and calcium ions (Villanueva and Montaño 1999). The native agar from L. flexilis formed a gel with moderate gel strength and higher gel syneresis (Villanueva et al. 2010). Compared with Gracilaria spp. and Gracilariopsis bailinae, Gracilaria firma exhibited the highest growth rate and agar gel strength, and a high resistance to epiphytes when grown under controlled flow-through culture conditions (Araño et al. 2000). In another study, the gel strength and the gelling and melting temperatures of gels prepared from Gracilaria eucheumoides, Gracilaria firma, Gracilaria salicornia, L. flexibilis, and Gracilariopsis heteroclada increased, whereas the syneresis index decreased upon the addition of sucrose (Romero et al. 2000). Gel strength of agar from G. eucheumoides was optimum when extracted at 900C, 10% alkali (NaOH) concentration, and 2-hour duration. However, the agar yield was higher when the extraction was performed at a lower temperature, higher alkali concentration, and shorter treatment time. Higher 3,6-anhydrogalactose content and lower sulphate level were obtained at higher temperature and alkali concentration, and longer duration of the treatment (Villanueva et al. 1997). A seasonal assessment generally showed that the highest biomass and maximum agar yields from Gelidiella acerosa (Roleda et al. 1997a), G. eucheumoides (Villanueva I.M. Villaseñor 63 et al. 1999), and G. edulis (Romero et al. 2007) are obtained during the rainy season. The three studies, however, have different conclusions regarding the quality and chemistry of the agars obtained. The overall gel quality (gel strength, viscosity, gelling, and melting temperatures) in G. acerosa was highest during the dry season (Roleda et al. 1997a), while the agar from G. edulis exhibited the highest gel strength, deformation, cohesiveness, and melting temperature when collected during the onset of the rainy season (Romero et al. 2007). Both agars from G. eucheumoides and G. acerosa exhibited the strongest gels in July (Villanueva et al. 1999). Signif icant seasonal variations were also observed in the gelling and melting temperatures of agar from G. eucheumoides. The sulphate content of agar from G. acerosa was the lowest during the dry season (Roleda et al. 1997a), which is in contrast to the results obtained by Villanueva et al. (1999). G. acerosa exhibited a higher sulphate content and lower 3,6-anhydrogalactose during the dry season, while the sulphate content in agar samples from G. eucheumoides varied slightly. The agar from G. edulis contained the lowest amount of sulfate and mono-O-methylated residues (Romero et al. 2007). Vegetative plants of G. acerosa yielded higher agar content with high gel strength compared to tetrasporic plants (Roleda et al. 1997b). Pressure cooking, compared to the traditional method of boiling, extracted more agar from G. acerosa but lowered its quality (Villanueva et al. 1998). Agar samples from G. acerosa pretreated with acetic acid (0.5% for 1 hour at 16-200C) and autoclaved at 15-20 psi for one hour gave the highest agar yield and strength (Roleda et al. 1997c). Gamma irradiation increased the yield but decreased gel strength in agar samples from G. acerosa (Villanueva et al. 1998). Irradiation did not signif icantly change the sulphate level but decreased the 3,6-anhydrogalactose content of agar. CARRAGEENAN The carrageenophytes include four genera, six species, and 21 morphotypes/ varieties/cultivars under the family Solieriaceae (Hurtado et al. 2013). Kappaphycus alvarezii, Eucheuma denticulatum, and Kappaphycus sp. sacol variety are the carrageenan-containing red seaweeds currently farmed in the Philippines (Aguilan et al. 2003). Vegetative regeneration is the only farming method for Eucheuma and Kappaphycus, thereby necessitating the development of an alternative method of generating sporelings (Azanza-Corrales et al. 1996). M a r i n e M a c r o a l g a e : A Rev i ew 64 Chemical Property The polysaccharide extracted from the seaweed Kappaphycus striatum (Schmitz) Doty (sacol variety) is composed mainly of 3-linked beta-D-galactopyranosyl-4- sulfate residues alternating with 4-linked 3,6-anhydro-alpha-D-galactopyranosyl (kappa carrageenan), 3,6-anhydrogalactopyranosyl-2-sulfate (iota-carrageenan), and 6-O-methylgalactopyranosyl-4-sulfate (methylated carrageenan) (Villanueva and Montaño 2003), and mu-precursor residues (Aguilan et al. 2003) as minor components. By contrast, E. denticulatum predominantly contains iota-carrageenan with signif icant amounts of nu-precursor residues (Aguilan et al. 2003). Another seaweed varietry locally called “endong” has a similar appearance to K. alvarezii (Doty) Doty ex Silva var. tambalang Doty A . However, ‘’endong’’ mostly contains carrageenan of the iota type (Villanueva et al. 2009). It was subsequently named as E. denticulatum (Burman) Collins & Hervey var. endong Trono & Ganzon- Fortes var. nov. (Ganzon-Fortes et al. 2012). Seaweed farmers are advised to separate their harvests of “endong” and “tambalang”. Physical Property Among the carrageenophytes, Kappaphycus sp. sacol variety is fast growing and has improved resistance against the “ice-ice” disease (Aguilan et al. 2003). ‘’Ice-ice’’ disease causes the depolymerization of kappa-carrageenan, leading to decreased average molecular weight, carrageenan yield, gel strength and viscosity, and increased syneresis index (Mendoza et al. 2002). As an alternative to industrial alkali treatment, postharvest batch culture with low nutrient concentrations produced native carrageenans in E. denticulatum (“spinosum”) that had significantly higher gel strengths (Villanueva and Montaño 2014). In another study, K. alvarezii, Kappaphycus sp. , and K. striatum were cultivated in tanks containing f ish farm effluent. Fish farm effluent has high ammonium content (Villanueva et al. 2005). All three carrageenophytes reduced the ammonium content of the f ish farm effluent and showed improved carrageenan content. However, the carrageenan quality was not signif icantly enhanced (Rodriquez and Montaño 2007). A study by Mendoza et al. (2006) showed that the mature tissues of K. striatum sacol green variety yielded greater amounts of carrageenan; by contrast, the young tissues exhibited higher gel strength, cohesiveness, and viscosity, and lower average I.M. Villaseñor 65 molecular weight. The minor iota carrageenan and methlylated carrageenan units in the major kappa-carrageenan decreased in quantity with age. Villanueva et al. (2011) recommended that the harvest time for K. alvarezii var. alvarezii to be after eight weeks of culture, while for K. striatum var. sacol, Kappaphycus sp. “aring-aring” and Kappaphycus sp. “duyan” to be nine weeks. The highest optimization index, in terms of biomass, carrageenan yield, and gel strength, was observed during these weeks. Gigartinacean and solieriacean are hybrids of kappa-iota carrageenans with a co- occurrence of kappa and iota structures in a chain in the former and as separate chains in the latter. Gigartinacean hybrid has a lower molecular weight and produced inferior gels compared to solieriacean. Both hybrids exhibited similar functional performance as viscosity enhancing/stabilizing and build-up agents (Villanueva et al. 2005). 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