Now showing items 1-6 of 6

    • Article

      Agar yield, gel strength and sulfate content in Gracilariopsis heteroclada farmed in brackishwater canals 

      TR de Castro - The Israeli Journal of Aquaculture-Bamidgeh, 1996 - Society of Israeli Aquaculture and Marine Biotechnology
      This paper aimed at determining the optimum NaOH pretreatment strength and duration and the monthly variations in gel strength, agar yield and sulfate content of agar from Gracilariopsis heteroclada (Zhang et Xia) farmed in brackishwater canals in Leganes, Iloilo, Philippines, during the dry season (October to March). The highest gel strength (641 g/cm2) and lowest sulfate content (7.66 µg/mg SO4) were obtained following pretreatment with 5% NaOH for 30 min. The agar yield from this treatment was 32.4% and negatively correlated with percent alkali used (r = -0.92465, p<0.05) and gel strength (r = -0.72711, p<0.05). The sulfate content was also negatively correlated with gel strength (r = -0.40911, p<0.05). The gel strength (274-622 g/cm2), agar yield (18.1-38.1%) and sulfate content (11.4-22.9 µg/mg) showed monthly variations. Water temperature ranged 30-35°C, salinity 26-32 ppt, and rainfall 39.4-561 mm. The agar yield was negatively correlated with temperature (r = -0.57286, p<0.05) and rainfall (r = -0.66435, p<0.05). Results showed that agar from G. heteroclada has very good potential for use as a raw material in the production of food, drug and industrial grades of agar because of its superior gel strength.
    • Article

      Assessment of stocks of a natural Gracilaria population on Panay Island, Philippines 

      TR de Castro, NG Guanzon Jr. & MR Luhan - Botanica Marina, 1991 - Walter de Gruyter
      Two peaks in biomass were recorded from natural beds of Gracilaria sp. at Leganes, Iloilo and Batan, Aklan study sites. The major peak occurred in February 1989 for both areas. The minor peak occurred in September 1988 at Batan and October 1988 at Leganes. Highest biomass at Ivisan, Capiz occurred in May 1988. Lowest biomass was recorded in June at Batan and December 1988 at Leganes. At Ivisan, no biomass was recorded from November 1988 to February 1989. Correlation analysis showed no relationship between biomass and temperature or pH at all study sites. However, salinity was negatively correlated with biomass at Leganes and Batan. Rainfall was inversely correlated with biomass. Based on salinity data gathered from the three study sites, Gracilaria sp. is euryhaline and can tolerate a wide range of salinity. The results show a marked seasonality in the biomass of Gracilaria sp.
    • Article

      Effects of gel depth and gel surface area on agar gel strength 

      TR de Castro - The Philippine Scientist, 1993 - San Carlos Publications, University of San Carlos
      Agar is a high priced phycocolloid extracted from red seaweeds (Rhodophyta) called agarophytes. It is a mixture of polysaccharides whose basic monomer is galactose (Armisen and Galatas 1987). Agar has many uses in the food and pharmaceutical industry, and the measure of its commercial value is based on its physical properties. One of the most important physical properties of commercial agar products is its gel strength (Chandrkrachang and Chinadit 1988). Gel strength is the force required to rupture the gel and it is measured through the use of gel testers available in the market, such as the Nikkan-sui, Rowerbal, and the Marine Colloids gel testers. Each instrument has built-in specifications for optimum use and results. Standard procedures used in the preparation of 1.5% agar gels for gel strength determination usually require 1.5 g of sample. Replication of samples in laboratory testing is however standard requirement and replication is constrained when sample extracts are scarce.

      This paper discusses the effects on gel strength of different gel depths and gel surface areas. It aims to identify the minimum size of vessel and depth of gel that will give optimum results using a Marine Colloids Model GT-2 gel tester.
    • Article

      Evaluation of agar from three species of Gracilaria from Panay and Guimaras islands 

      TR de Castro - The Philippine Scientist, 1993 - San Carlos Publications, University of San Carlos
      Agar from three species of Gracilaria, G. changii G. coronopifolia, and Gracilariopsis heteroclada, collected form Panay and Guimaras islands was evaluated. Each species was pretreated with NaOH solution before extraction. Highest agar yields were obtained following alkaline pretreatment at the lowest concentration (1% NaOH) for all species. Highest gel strengths were obtained at different alkaline pretreatment conditions: 644 ± 3.4 g cm-2 at 3 % NaOH for 60 min for G. changii, 641 ± 11.9 g cm-2 at 5 % NaOH for 30 min for G. heteroclada, and 170 g cm-2 at 5 % NaOH for 30 min G. coronopifolia. Agar gelling temperatures ranged from 38.5-40ºC and agar melting temperature ranged from 80.5-85 ºC. Specific viscosity was highest for agar from G. changii at 18 cps. Moisture and ash contents ranged from 8.04-15.20 % and 4.32-4.98%, respectively. Based on the result for this study, G. heteroclada and G. changii are two species which merit further studies for their prospective commercial value to the different industries using agar.
    • Article

      Growth of Gracilaria sp. (Gracilariales, Rhodophyta) in brackishwater ponds at different stocking densities. 

      TR de Castro & NGJ Guanzon - The Israeli Journal of Aquaculture-Bamidgeh, 1993 - Society of Israeli Aquaculture and Marine Biotechnology
      The specific growth rate (% per day) and net production rate (g per m2 per day) of Gracilaria sp. cultivated in net cages in a brackishwater pond were determined at different stocking densities (200, 250, 300 and 350 g/net cage of 0.5 m2). The mean specific growth rates for the duration of the culture period were highest at stocking densities of 200 and 250 g per cage (P<0.05). The highest mean net production rate was obtained at a stocking density of 250 g per cage. The highest monthly mean specific growth rates and mean net production rates for all treatments were obtained in April, July and November; these were not significantly different from each other nor from the month of March (P>0.05), but were significantly different from the other months (P<0.05). Production was better during the dry season. Correlation analysis showed that water temperature, salinity, pH and total rainfall had no effect on the specific growth rate and net production rate (P>0.05). Results indicate that Gracilaria sp. can be grown in cages in brackishwater ponds at stocking densities of 200 and 250 g/net cage (400 and 500 g per m2, respectively).
    • Article

      Improvised filter unit for agar extraction/filtration 

      TR de Castro - The Philippine Scientist, 1993 - San Carlos Publications, University of San Carlos
      Agar is a high-priced phycocolloid usually extracted from red seaweeds (Rhodophyta). It has many uses in the food and pharmaceutical industry (Chapman 1970, Armisen and Galatas 1987). Worldwide production of agar has reached 5000t and the demand is still increasing because of new applications (Santelices and Doty 1989). In laboratory-scale extraction of agar the filtration system preferred is a stainless steel pressure filter (Aguilar-Santos and Doty 1978, Hoyle 1978). Commercial-scale extraction, however, uses filter presses of varying designs, each according to the particular need (Armisen and Galatas 1987). In small laboratories with limited facilities, an improvised extraction/filtration unit can be devised for routine laboratory work on agar processing. In the course of extraction/filtration trials conducted at SEAFDEC/AQD, a simple but efficient extraction/filtration unit was designed. It took into consideration the volume of the sample, the temperature during extraction, and the ease of using the unit.