Ronald D. Villanueva

Structure and functional performance of gigartinacean kappa -iota hybrid carrageenan and solieriacean kappa -iota carrageenan blends

Abstract Hybrids of kappa and iota carrageenans, known as kappa-2 carrageenans, of contrasting phycological origin and type of hybridization were compared chemically and functionally. Nuclear magnetic resonance spectrometry showed gigartinacean kappa-2 (hybridization was known to be a co-occurrence of kappa and iota structures in a chain) to contain 45% iota and 55% kappa, very similar to a 3:3 kappa:iota hand-made blend of solieriacean origin (hybridization was that kappa and iota occurring as separate chains). Gel permeation chromatographic data, however, demonstrated the gigartinacean extract to possess lower molecular weight compared to the solieriacean extracts, a hint to the variability in the origin of the two hybrid carrageenans. As texturing agents in water and milk systems, gigartinacean kappa-2 was found to produce inferior gels compared to its hand-made counterpart. However, both hybrids were found to exhibit similar functional performance as viscosity-enhancing/stabilizing agent in hot-processed chocolate milk preparations, and analogous inutility as viscosity build-up agent in cold-processed chocolate milk. A hand-made solieriacean kappa–iota blend can have the same properties as a gigartinacean kappa-2, but it depends on the actual application which blend performs comparable to kappa-2.

Stability of agar in the seaweed Gracilaria eucheumatoides (Gracilariales, Rhodophyta) during postharvest storage

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 318gcm(-2) until the third month of storage but decreased considerably 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.

Seasonal Variations in the Yield, Gelling Properties, and Chemical Composition of Agars from Gracilaria eucheumoides and Gelidiella acerosa (Rhodophyta) from the Philippines

Abstract The yield, physical, and chemical properties of agars from two Philippine red seaweeds, Gracilaria eucheumoides and Gelidiella acerosa, were investigated on a bimonthly basis. The yield of agar from Gracilaria eucheumoides was at a maximum during the early rainy season (May, 29%) and at a minimum during the summer month of March (20%). In Gelidiella acerosa, a peak in agar yield was also recorded in May (21%), with generally higher yields recorded during the rainy than in the dry season. Agar gel strengths fluctuated from 225 to 430 g cm−2 and from 160 to 820 g cm−2 for Gracilaria eucheumoides and Gelidiella acerosa, respectively, and both agars exhibited strongest gels in July. Significant seasonal variations were observed in the gelling and melting temperatures of agar from Gracilaria eucheumoides, but not from Gelidiella acerosa. Sulphate content only varied slightly in agar samples from Gracilaria eucheumoides, while a higher sulphate content was found in Gelidiella acerosa agar during the dry season. Moreover, the sulphate content in G. acerosa agar fluctuated inversely with the 3,6-anhydrogalactose content. A FT-IR analysis showed a fairly constant spectrum for temporal Gracilaria eucheumoides agar while peaks attributed to S–O vibrations intensified in Gelidiella acerosa samples which were recorded to contain high sulphate residues and possess low gel strengths. Diagnosis of the FT-IR spectra in the 1000–400 cm−1 frequency range was also conducted in comparison with agarose and Gracilaria chilensis agar.

Chemical characteristics and gelling properties of agar from two Philippine Gracilaria spp. (Gracilariales, Rhodophyta)

The chemical structure of agars extracted from Philippine Gracilaria arcuata and G. tenuistipitata were determined by NMR and infrared spectroscopy. Agar with alternating 3-linked 6-O-methyl-β-D-galactopyranosyl and 4-linked 3,6-anhydro-2- O-methyl-α-L-galactopyranosyl units was isolated from G. arcuata, while the agar from G. tenuistipitata possesses the regular agarobiose repeating unit with partial methylation at the 6-position of the D-galactosyl residues. Both agars exhibit sulphate substitution at varying positions in the polymer. Chemical analyses reveal higher 3,6-anhydrogalactose and lower sulphate contents in alkali-modified than in native agar from both samples. Also, alkali modification enhanced agar gel strength and syneresis. Native G. arcuata agar produces a viscous solution (2000 cP at 75 °C) with a high gelling point (>60 °C) that forms a soft gel even after alkali modification (gel strength: <300 g cm−2). On the other hand, the agar from G. tenuistipitata exhibits gel qualities typical of most Gracilaria agars.

Growth and survivorship of juvenile corals outplanted to degraded reef areas in Bolinao-Anda Reef Complex, Philippines

Abstract The worldwide decline of coral reefs due to natural and anthropogenic disturbances necessitates the development of techniques to restore damaged reefs. The potential use of sexually derived coral propagules as a tool in coral reef restoration has recently been actively investigated. This study was conducted to determine growth and survivorship of juveniles of the reef-building coral Acropora valida, outplanted at a degraded reef. These juveniles were products of sexual propagation, i.e. involving coral spawning, gamete fertilization, larval rearing and settlement, and juvenile rearing, at an outdoor hatchery facility. Six-month-old juvenile corals attached to rubble inserted into plastic masonry wall plugs (‘tox’) were outplanted to three experimental bommies at the Bolinao-Anda Reef Complex, northwestern Philippines. Cumulative survival of outplants was 67.5±7.6% during a study period of 183–190 days, with no apparent difference among bommies. The juveniles grew with a 37-fold increase in ecological volume – from 1.25±0.97 cm3 (1.1±0.3 cm mean diameter) at outplantation to 46.19±35.49 cm3 (3.8±1.1 cm mean diameter) at approximately 6 months. The results of this study substantiate the use of sexually derived coral propagules for reef restoration. Cost analysis revealed sexually produced corals to be more expensive than asexual counterparts. Further developments or refinements in the culture technology for sexually derived corals for reef restoration are needed to enhance cost-effectiveness.

FINE CHEMICAL STRUCTURE OF CARRAGEENAN FROM THE COMMERCIALLY CULTIVATED KAPPAPHYCUS STRIATUM (SACOL VARIETY) (SOLIERIACEAE, GIGARTINALES, RHODOPHYTA)1

The polysaccharide extracted from Kappaphycus striatum (Schmitz) Doty (sacol variety), a recently farmed eucheumoid seaweed, was characterized by Fourier transform infrared and NMR spectroscopy. The extract is composed mainly of 3‐linked β‐d‐galactopyranosyl‐4‐sulfate residues alternating with 4‐linked 3,6‐anhydro‐α‐d‐galactopyranosyl residues (κ‐carrageenan). Minor components include 3,6‐anhydrogalactopyranosyl‐2‐sulfate residues (ι‐carrageenan) and 6‐O‐methylgalactopyranosyl‐4‐sulfate residues (methylated carrageenan). The substitution pattern of carrageenan in the tribe Eucheumatoideae and the family Solieriaceae is revisited in terms of chemotaxonomic affiliation.

Tissue age as a factor affecting carrageenan quantity and quality in farmed Kappaphycus striatum (Schmitz) Doty ex Silva

Abstract Carrageenan yield and quality from young and old tissues of Kappaphycus striatum “sacol” green variety were investigated using native and alkali-modified carrageenan extraction procedures. Dried apical (young) and basal (old) segments were pooled to produce 5 g of dried samples of each for carrageenan extraction. Mature tissues yielded greater amounts of carrageenan than young tissues. The latter exhibited higher gel strength, cohesiveness, viscosity properties and lower average-molecular weight than the mature, old tissues. FT-IR and 13C and 1H NMR analyses showed that both young and old tissues contained mostly the kappa-type repeating disaccharide sequences of 3-linked β-D-galactopyranose 4-sulfate (G4S) and 4-linked 3,6-anhydro-α-D-galactopyranose (DA). Moreover, the study showed that, as the algal thalli aged, the iota carrageenan (G4S-DA2S) and methlylated (G6M) carrageenan units (these were minor substituents in the major kappa-carrageenan repeating disaccharide unit) decreased in quantity. These differences suggest that the timing of galactan biosynthesis may be related to certain physiological and structural functions during the growth of the alga.

Highly methylated agar from Gracilaria edulis (Gracilariales, Rhodophyta)

The structure and gelling properties of alkali-modified agar from Gracilaria edulis were investigated. 1H and 13C NMR experiments revealed a basic repeating unit of alternating 3-linked 6- O-methyl-β-D-galactopyranose and 4-linked 3,6-anhydro-α-L-galactopyranose. Partial methylation at O-2 of the anhydrogalactose moiety was also revealed. Meanwhile, the O-4 of the methylated galactose residue was detected to exhibit partial sulfation by NMR and FT-IR spectroscopy. The gel strength and syneresis index of the extracted agar were considerably enhanced by the addition of sodium, potassium, and calcium ions. The ion-driven gelation and peculiar sulfate position conferred the agars similarity to κ-carrageenan.

Growth, agar yield and quality of selected agarophyte species from the Philippines

Abstract Three local agarophyte species (Gracilaria firma, Gracilaria sp. and Gracilariopsis bailinae) were grown under controlled outdoor flow-through culture conditions. Growth rates and agar characteristics of the three species were determined. Gracilaria firma showed superior growth and agar quality among the three species. It exhibited the highest growth rate, highest agar gel strength and was observed to be highly resistant to epiphytes. Growth experiments under various light and ammonium combinations showed that the highest photon flux density level (900 μ mol m−2s−1) and moderate ammonium (150 μM NH4Cl) concentration gave the highest growth rates for all species. The single and interactive effects of light and ammonium enrichment on growth and agar characteristics of the three species were highly significant.

Agar from the red seaweed, Laurencia flexilis (Ceramiales, Rhodophyta) from northern Philippines

The worldwide production of the gelling agent agar mainly rely on the red algae of the order Gracilariales and Gelidiales for raw material. We investigate here the potential of a species from another red algal order, Ceramiales as an agar source. The agar from Laurencia flexilis collected in northern Philippines was extracted using native and alkali treatment procedures and the properties of the extracts were determined using chemical, spectroscopic and physical methods. The native agar, 26% dry weight basis, forms a gel with moderate gel strength (200 g cm−2). Alkali‐treatment did not enhance the gel strength, indicating insignificant amounts of galactose‐6‐sulfate residue, the precursor of the gel‐forming 3,6‐anhydrogalactose (3,6‐AG) moieties. Furthermore, the Fourier transform infrared and chemical analysis showed low sulfate and high 3,6‐AG levels, not affected significantly by the alkali treatment. Nuclear magnetic resonance spectroscopic analysis revealed 3‐linked 6‐O‐methyl‐D‐galactose and 4‐linked 3,6‐anhydro‐L‐galactose as the major repeating unit of the native extract, with minor sulfation at 4‐position of the 3‐linked galactose residues. The native and alkali treated agars have comparably high gelling and melting temperatures, whereas the former exhibits higher gel syneresis. Laurencia flexilis could be a good source of agar that possesses physico‐chemical and rheological qualities appropriate for food applications. Due to the inability of alkali treatment to enhance the key gel qualities of the native extract, it is recommended that commercial agar extraction from this seaweed would be done without pursuing this widely‐used industrial procedure.