Mineral and Protein Contents of some Marine Algae froin the Coastal Areas of Northern Sri Lanka

Protein and mineral contents of twenty-five spxies of marine algae from the coastal areas of Northern Sri Lanka are reported. Specics such as Centroceros clavulatum, Ulva lactuca, Hypnea muscifor~nis, Acanthophora delilei and Gracilaria edulis are found to have high protein content which are comparable to that in food materials such as cereals, eggs and fish. Algae such as Gracilaria edulis, Laurencia obtusa, Sargassumpolycystum, Ulva lactuca and Gracilaria crassa and Thalasia hemprichi (angiosperm) have fairly large amounts of nitrogen, phosphorus and potassium and hence could be used as fertilizers.


Introduction
Marine algae and sea gasses are two of the important groups of marine plants occurring in the sea.They contain several inorganic elements and a complex mixture of organic substances synthesised from them.Due to the presence of these chemical substances marine algae find a variety of uses, some of which are briefly indicated below.
Marine algae are used 3 to prepare alginic acid and agar.Fresh dried and processed seaweeds are utilised as human food 1 1 , 1 4 9 1 5 in Japan, Indonesia, China,.Philippines, India and other south east Asian countries.Seaweeds such as Porphyra, Ulva, Chlorella, Gracilaris and Chondrus are commonly used as ingredients for soups and as meat flavourings.' 5 143 Countries like Japan have large industries based.on edible seaweeds.The algal carbohydrates are not easily digestible and hence.the food value of the seaweeds depends on the minerals, trace elements, proteins and vitamins present in them.The seaweed meal is nutritjous due to its high mineral and protein content.Seaweeds are used 11, 14, 15 to stock feed sheep and cattle in maritime districts.
Seaweeds contain reasonable quantities of nitrogen, phosphorus andpotassium.and they are extensively used, either directIy or in the form of compost with cowdung.as manure for vegetables in India.13 In seaweeds, the minerals and trace elements.occur in water soluble form 13 and hence these could be easily taken up by the plants.The carbohydrates and other organic constituents of the seaweeds are.reported 1 3 to increase the moisture holding capacity of soils.The marine algae are also a good source of potash and soda.
During certain seasons fairly large quantities of seaweeds are found in the coastal areas of the Jaffna Peninsula.In order to make the best use of these seaweeds a knowledge of their chemical composition is essential.Therefore as an initial step, a study of the mineral, protein and vitamin contents of the seaweeds found in Northern Sri Lanka was started.Our results on the estimation of the moisture, ash and protein contents and of the amounts of some inorganic elements present in twenty five species of seaweeds are given below.

Experimental Methods and Materials
The seaweeds were collected from Mandaitivu, Nainativu and Keerimalai, washed well and air dried for three days.The moisture contents were determined by drying them in an oven at 10S°C to constant weight.The ash contents were determined by ashing weighed quantities of samples at 4500C in a mufle furnace until constant weight was obtained.The total nitrogen was determined by the Kjeldhal method and protein content was calculated by multiplying the total nitrogen content by 6.25.

31. Preparation of Test Solutions
Seaweed samples of known weights were ashed at 450°C and dissolved quantitatively in a known volume of 0.6M HCl and the resulting solutions were used to determine the amounts of sodiilm, potassium, calcium, magnesium and trace elements.

Determination of the amounts of Sodium and Potassium
Sodium and potassium were determined using a Corning Model 400 flame photometer using appropriate interference filters.The flame intensities for sodium were corrected for interference by calcium by the standard addition method.l7

Determination of the amounts of Calcium and Magnesium
The amount of calcium present in seaweeds was determined12 by titrating a known volume of the test solution with standard EDTA with Patton-Reeder's indicator and using potassium cyanide as the masking agent.
The amount of magnesium present in seaweeds was estimated as follows: The total amount of magnesium and calcium present was determined by titrating known volumes of test .solutionwith standard EDTA solution with Eriochrome Black T as indicator and using potassiun~ cyanide as masking agent.12The amount of magnesium is obtained by subtracting the amount of calcium present from this value. .

Determination of Iron in Seaweeds
The test solution was prepared in 0.6M HC1 as described above.The amount of iron present in the test solution was determined8 by measuring the density of the colour produced by the addition of 1,10orthophenanthroline on a Corning model A4inzral and Protein Contents of'sorne Marine AIgae

Determination of Trace Eiements
Amounts of trace elements copper, manganous, nickel, zinc, cadmium, cobalt and chromium were determined using the test solution [prepared as described above] on a Varian Model 1275 atomic absorption spectrophotometer.

Determination of the amount of Lead in Seaweeds
Samples of known weight were subjected to wet oxidation with concentrated nitric acid and concentrated sulphuric acid by the reported procedure.10 The resulting solution was used to prepare the test solution.The amount of lead present was determined 10 using Corning Model 252 colorimeter after complexingwith dithizone.

Determination of Phosphoras in Seaweeds
Dried seaweed samples [ 1-2g J were weighed accurately, ashed with magnesium nitrate,e the ash was dissolved in 2(NH& SO, (101n1) and the solution made up to 50ml.The amount of phosphorus present in this solation was determined6 by measuring the density of the colour produced on complexing with vanadomolybdate reagent on a Corning Model 252 colorimeter using 430,470 and 490nm filters.

Determination of Total Sulphur in Seaweel
The amount of total sulphur in seaweeds was determined by the reported method.6Accurately weighed szmpIe (1-2g) of seaweed was treated wit11 concentrated nitric acid (10ml) and the mixture was allowed to stand overnight at room temperature.The resulting mixture was evaporated to dryness and the residue was ashed in a muffle furnace at 450° C. The ash was dissolved in a minimum volume of 25% nitric acid and the solution made up to 50ml in a volumetric flask.A known volume of this solution was treated with an excess of standard barium chloride.The unreacted barium chloride was determined by titration with standard EDTA.The amount of sulphate was estimated by the method OF difference.

Determination of the amount of Chloride in Seaweeds
Accurately weighed powdered seaweed (1.2g) was ashed at 450° C with an equal weight of sodium carbonate.The ash was dissolved in minimum amount of 25% nitric acid and the solution made up to 50ml in a volumetric flask.The amount of chloride present in this solution was determined by Vollard method.16

Results and Discussion
The amounts of moisture, ash, total nitrogen and protein found in twenty five species of the seaweeds from the coastal areas of Northern Sri Lanka are given in Table 1.The results show that some of the algae such as Gracilaria edulis, Gracilaria confervoides, Hypnea musc$ormis, AcantlwpItora delilei, Centroceros clavulatum and Ulva Iactuca have between 13-26% protein and this amount is comparable or even somewhat higher than the reported4 protein content of food materials like cereals, eggs and fish.Algal proteins are r e p ~r t e d l ' , ~~, ~~ to have many of the essential aminoacids including iodine containing aminoacids and hence the above seaweeds, are a good source for protein rich food.Also, the above species of seaweeds could be added to foods which are deficient in protein.In India Gracilaria edulis is in the preparation of soup.It is interesting to note that generally the seaweeds from the Keerimalai area have a higher protein content than those from the Mandaitivu coast, which in turn have a higher protein content than those from Nainativu coast.Amounts of the minerals sodium, potassium, calcium and magnesium present in twenty five species of seaweeds were determined by the methods indicated above and our results are given in Table 11.Gracilaria edulis, Gracilaria crassa, Laurencia obtusa, Turbinaria ornata and Sargassum tenerrimum have fairly large amount of potassium.Jania natalensis, Acetabularia crenulata, Padina pavonia, Sturvea anastamosm, Tlialasia henzprichi, Pocockiella variegaia, Laurencia obtusa, IJypnea musciformis and Ulva reticulata have reasonably large quantity of calcium.It is interesting to note that Jmia natalensis, which is capable of accumulating calcium and depositing it in the form of a calcareous skeleton, has the highest amount of calcium.Jania natalensis, Chaetomorpha sp, Padina pavonia, Laurencia obtusa, Ulva reticulata and Thalasia hemprichi have more than 1 % magnesium.All values are expressed in g/lODg of air dried samples of seaweeds.

Magnesium Mineral and Protein Contents of sonze-Marine Algae 18s
Our results on the colorimetric estimation of the amounts of iron and phosphorus are shown in Table 111.i t is seen that species such as Gracilaria edulis, Padina pavonia, Pocockiella variegata, Cl~aetomorpha sp, Sargassum polycystum and Jania natalensis are rich in iron.A130 the seaweeds from the Nainativu and Mandaitivu areas generally have more iron content than those from Keerimalai area Gracilaria edulis, Gracilaria crassa, Gracilaria confervoides, Hypnea musciformis.Codium sp, Chaetomorplza sp, Ulva lactuca and Thalmia hemprichi have relatively large amounts of phosphorus.

Date o f Phosphorus
The amounts of nitrogen, potassium and phosphorus present in selected species of seaweeds are shown in Table IV.It is interesting to note that Gracilaria edulis, Laurencia obtusa, Padim pavonia, U l v ~ lactuca, Thulasia hemprichi, GI-ucilaria cmssa, Sargarsum polycystum and Sargassum~tenerirnwn have fairIy l a ~g e amounts of nitrogen, phosphorus and potassium and hence these could be used as fertilizers.Also other species which are rich in nitrogen, phosphorus or potassium could be mixed together t o form a good fertilizer.Seaweeds also contain trace elements.These arc a group of elements which are needed in infinitdy small amounts and these are very essential for the growth of plants and animals.Some of the important trace elements are Fc, Cu, Zn, Mn, Co, B and Mo.Some of the trace clements form complexes with enzymes and catalpse in metabolic reactions.The element copper is found in the enzyme polyphenol oxidasc and the respiratory pigment of invertebrates, homocyanin.The enzymes such as tyrosinase, laccase and ascorbic acid oxidase use copper to catalyse reaction^.',^Copper and cobalt are essential for health and productivity of animals.These two elements are associated with iron in the production of haemoglo bin.',' The element cobalt, in addition to being an essential element of Vitamin BI2 is important in the metabolism of sulphur containing aminoacids.Elements such as Zn, Mn, Mo, Cr and Cd are also involved in the biological processe~.~~Even though the trace elements have a vital function for human and animals they become toxic if present in relatively large amounts.The general recommendedl0 limits for some of the elements are given below.cadmium and lead are non-nutritive toxic elements.Seaweed species analysed have low cadmium level (1-4 ppm).However the level of lead is rather high.The statutory limit for Pb in food is 2 ppm.

Element
Sturvea anastornosuns, Jania natalensis and Padina pavonia have relatively large amounts of the toxic elements and these may be avoided as nutrients and fertilizers.Also it is apparent from the Table V that the seaweeds from the Mandaitivu coast are richer in trace elements than those from Nainativu.Chloride ion which is a micronutrient and sulphur which is a macronutrientz are also found in seaweeds.Table VI gives the values obtained for the amounts of ionic chloride and total sulphur present in some seaweeds.Our results show that Pocockiella variegata and Gracilaria edulis have relatively low amounts of ionic chloride.The species Thalasia hemprichi, Pocockiella variegata, Sargassum polycystum and Stoechospermum marginatum have relatively low amounts of sulphur.Some species of seaweeds such as Centroceros clavulatum, Gracilaria edulis, Gracila<ia confervoides, Acanthophora delilei and Ulva lactuca have relatively large amounts of protein and could be used for fortifying food items deficient in protein.Seaweeds such as Gracilaria edulis, Laurencia obtusa, Padina pavonia, Ulva lactuca, Thalmia hemprichi, Gracilaria crassa, Sargassum polycystum and Smgassum tenerri~nun?have fairly large amounts of the elements nitrogen, phosphorus and potassium and these could be used as fertilizers.Gracilaria edulis and Gracilaria crassa also have relatively large amounts of the trace elements.Attempts should be made to cultivate the above species of algae so thzt they could be profitably used.

TARLE 2 .
Amounts of Sodium, Potassium, Calcium and Magnesium present in Seaweeds.

TABLE 1 .
Moisture, Ash, Nitrogen and Protein contents of Seaweeds.All values are expressed as g/100g of air dried samples of seaweeds

TABLE 3 .
Amounts of Iron and Phosphorus present in seaweeds.All values are expressed in mg/kg of air dried samples of seaweeds.

TABLE 4 .
The amounts of nitrogen, potassium and phosphorus present in selected species of seaweeds.All values are expressed in rng/kg of air dried samples.
Zn, Mn, Ni, Cd, Co and Cr present in twenty three species of marine algae were determined using Varian Model 1275 Atomic Absorption Spectrophotometer.The amount of lead present in these samples were determined calorimetrically after complexing with dithizone.No detectable amount of cobalt or chromium was found in any of these twenty three species.Our results, which are given in TableV, show that (i) Padina pavonia and Sturvea anastomosans have relatively large amounts of copper while the species Stoechospermum marginatum, Sargassum polycystum and Thalasia lzemprichi have reasonable amounts of copper, (ii) the element zinc is found in relatively large amounts in Sturvea anasfomosans, Dictyofa species, Padina pavonia, Stoechospermum marginatum and Hypnea musciformis (iii) Manganese is found in relatively large amounts in red algae (iv) the species Sturvea anastornosam, Gracilaria edulis, Centroceros clavulatum, Jania natalensis, Hormophysa triquetra, Sargassum polycystzrm and Thalasia hemprichi have relatively high Ni content (v) the element Pb is found in relatively large amount in Sturvea anmtornosans, Gracilaria crassa, Gracilaria salicomia, Jania natalensis, Padina pavonia, Hormophysa triquetra and Sargassum polycystum and (vi) Cadmium is found in the range 1 -4 ppm.

TABLE 5 . Amounts of Copper, Zinc, Manganous, Nickel, Lead and Cadmium present in seaweeds. All values are expressed as mg per kg (i.e. ppm) of air dried samples of seaweeds. (Date of collection is the same as in the Tables 1 & 2).
(

TABLE 6 .
Amounts of ionic chloride and total sulphur present in seaweeds.All values are expressed in g/100g of air dried seaweeds.