Stability of agar in the seaweed Gracilaria eucheumatoides (Gracilariales, Rhodophyta) during postharvest storage Jumelita B. Romero a,b, * , Ronald D. Villanueva b,1 , Marco Nemesio E. Montaño b a Mindanao State University-Tawi-Tawi, Sanga-Sanga, Bongao, 7500 Tawi-Tawi, Philippines b The Marine Science Institute, College of Science, University of the Philippines Diliman, 1101 Quezon City, Philippines article info Article history: Received 14 January 2008 Received in revised form 9 March 2008 Accepted 11 March 2008 Available online 14 April 2008 Keywords: Agar Agar textural properties Gracilaria eucheumatoides Molecular weight Storage stability abstract The status of the cell-wall polysaccharide of the red seaweed, Gracilaria eucheumatoides upon postharvest storage was assessed in this study. The yield, chemical composition, physical and textural properties of alkali-treated agar extract was determined at different time intervals within 31 months of storage at dried state after harvest. Minimal fluctuation in agar yield was observed, ranging from 22.9% to 29.0%. The gel strength of agar extracts averaged 318 g cm 2 until the third month of storage but decreased con- siderably thereafter. The relative viscosity and molecular weight of the extracts varied inversely with storage time. Results indicated that both physical and textural parameters of agar generally decreased with storage time, likely due to depolymerization as indicated by decrease in molecular weight. Agar extracted from seaweeds up to 3 months of storage could be considered to exhibit gel quality suitable for food applications. Prolonged storage of the seaweed harvest is not recommended. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Agar, a cell-wall polysaccharide, is extracted from selected mar- ine red algae (Rhodophyta) including those of the genus Gracilaria. Agar consists of an agarobiose repeating unit composed of a 3-O- linked b-D-galactopyranose residues alternating with 4-O-linked 3,6 anhydro-a-L-galactopyranose in a linear sequence which may be pyruvated, methylated, or sulfated (Rees, 1969). These chemical substituents are responsible for the varying gel properties of the polysaccharide in aqueous solutions. Agar is widely used for medical, pharmaceutical, industrial and laboratory experimental purposes (Okazaki, 1971), primarily due to its excellent gelling ability (Selby and Whistler, 1993). Many studies focused on the properties of the agar extract with respect to extraction procedures, seaweed species, season, geo- graphical origin and environmental parameters (Freile-Pelegrín and Robledo, 1997; Montaño et al., 1999; Villanueva et al., 1999; Marinho-Soriano, 2001; Marinho-Soriano et al., 2001; Marinho- Soriano and Bourret, 2003; Freile-Pelegrín and Murano, 2005; Pereira-Pacheco et al., 2007; Romero et al., 2007; Orduña-Rojas et al., in press). After the harvest of the seaweed resource, the quantity and quality of agar may further be affected (aside from extraction conditions) by the storage conditions and duration prior to extraction. This is due to possible degradation of agar in the sea- weed during storage. To date, there is limited report exploring this postharvest phenomenon (only Freile-Pelegrín, 2000). In this study, the physical characteristics and chemical compo- sition of agar extracted from Gracilaria eucheumatoides (=G. euche- umoides) upon postharvest storage were determined at different time intervals up to a period of thirty-one months. Physico-chem- ical profile of agar from stored seaweeds would provide informa- tion for seaweed processors as regards to the acceptable storage duration of algal raw material before extraction. 2. Methods G. eucheumatoides samples were collected at Bolinao, north- western Philippines (16°27 0 N, 119°55 0 E) in September 1996. These were cleaned of epiphytes, washed with freshwater and oven-dried at 60 °C. Twenty grams of the dried seaweed were indi- vidually packed in perforated plastic bags (a total of 27 bags) and stored at room temperature (25–32 °C) until processed. The perfo- ration would allow the seaweed samples to be subjected to ambi- ent relative humidity (71–85%, http://www.pagasa.dost.gov.ph/ cab/climate.htm). The duration of the experimental storage is from September 1996 to April 1999. Algal sample in each bag represents an experimental unit. Three bags (n = 3) were sampled randomly after packing (storage time: 0 mo) and after 1, 3, 6, 9, 12, 24, 28 and 31 mo of storage. The seaweed in each bag was immediately processed or extracted for agar after sampling. 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.03.017 * Corresponding author. Address: Mindanao State University-Tawi-Tawi, Sanga- Sanga, Bongao, 7500 Tawi-Tawi, Philippines. Tel.: +63 919 6955600. E-mail address: jbromero05@yahoo.com (J.B. Romero). 1 Present address: REQUIMTE-CEQUP, Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, s/n 4200- 465 Porto, Portugal. Bioresource Technology 99 (2008) 8151–8155 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech