Panel 4: Technology

Panel leader: Maria Elena Torres

A METHOD TO OBTAIN MUCILAGE FROM ALGARROBO SEEDS

Magaly Vásquez
Eduardo Valenzuela
Héctor Canales
University of Chile

INTRODUCTION

The species of the genus Prosopis have the capacity for thriving on poor fertility soils and hot dry climates. This feature makes them suitable candidates for controlling desertification. The main application of algarrobo (Prosopis chilensis (Mol.) Stuntz) pods has been as animal fodder; thus, good knowledge of its chemical composition would enhance its possibilities for utilization. The aims, at the first stage, were:

• To devise a method for removing mucilage from algarrobo seeds.
• To measure the effect of concentration on the viscosity of the mucilage solution.

MATERIALS AND METHODS

The material used was algarrobo (Prosopis chilensis (Mol.) Stuntz emend Burk) fruit, the pods of which had an average of 21.0 ± 0.17 seeds, equivalent to 29.1% by weight. Seeds and mesocarps were analyzed gravimetrically by the Munson & Walker method (2) and chromatographically with Whatman paper No. 1, using as carrying solvent ethyl acetate, isopropanol and water (13:6:1), and 0.3% 2-tiobarbituric acid and 5% trichloracetic acid as developer, warming to 105°C for 15 min.

Mucilage was removed treating the seeds with 0.5% sodium hydroxide at 75° C for 4–10 min, and shaking. Alcali was subsequently washed off the seeds with drinking water, and then the seeds were left to soak for 24–48 h, changing the water periodically. Excess water was removed and the seedcoat, cotyledons and mucilage were separated. These components were heater-dried separately at 35° C. Mucilage was measured with a Thomas Wiley laboratory mill, mesh No. 60.

Mucilage solutions were prepared diluting the powder in the solvent. They were then mixed with a shaker at 45° C for 1.5 h, filtrating with glass wool to separate the unsolved particles. The viscosity of the various solutions was measured in terms of draining-off times at 25° C (3), using an Oswald viscosimeter.

RESULTS

Table 1 shows the findings of the chemical analysis.

TABLE 1
Proximal chemical composition of algarrobo seeds and mesocarp (g/100g)

* By difference

The chemical composition coincides in general with that reported by national authors (4) Nitrogen free extract was 58.0% by the Munson & Walker method. Total sugars were 57.39% expressed as glucose percentage. Non-reducing sugars amounted to 50.66%. The chromatographic analysis revealed saccharose as the predominant carbohydrate (5). The presence of sugars coincides with the sweet taste reported in literature (6, 7, 8).

Once the method for removing mucilage from the seeds was applied, the corresponding yield was 30.8% mucilage; 38.8% cotyledons; and 19.4% seedcoat.

The first trial on viscosity—made with a 1-ml graded pipette and 1% solutions—gave the results shown in Table 2.

TABLE 2
Draining time for algarrobo mucilage solution and carragenine at 25° C

* Mean ± S.D.

This test showed the algarrobo mucilage solution to be 6.9 times slower than water; carragenine solution, in turn, was 7.6 times slower.

The effect of concentration on viscosity was measured by trials using the Oswald viscosimeter, the findings of which are presented in Table 3.

TABLE 3
Draining times for algarrobo mucilage and carragenine solutions. Water was used as standard for comparison.

It may be observed that drainage becomes slower with increasing mucilage concentration. Draining times increase from 15.2 ± 0.04 s with 0.1% mucilage to 89.5 ± 0.77 s with 0.5% mucilage (p<0.01). 0.1% algarrobo mucilage is, in turn, 1.6 times slower than water, while carragenine compared against water takes 2.1 times. 0.1% mucilage showed a significant difference with 0.1% carragenine (p<0.01).

The other test performed was to measure the effect of pH on the mucilage solution (Table 4); pH commonly found in foodstuffs were used for the purpose.

TABLE 4
Draining times for mucilage solutions at various pH and 25° C.

In general terms, no significant changes derived from pH were observed. The pH 5.6 solution drained off more slowly (p<0.01) than pH 3.2 and pH 7.0 solutions, which showed no significant differences among themselves.

The possibility of obtaining a sufficiently purified mucilage opens prospects for this substance as a hydrocolloid, apt for utilization in food fabrication as thickening agent, and stabilizer for suspensions and foams (9, 10, 11).

The conclusions arrived at are as follows:

• A method to remove mucilage from algarrobo seeds was devised.
• At constant temperature, an increase in mucilage concentration provokes higher viscosity.
• There is potential for algarrobo mucilage utilization as thickening agent.

REFERENCES

1. ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS. Official Methods of the OAOC. 10th Ed. Washington D.C., The Association, 1965.

2. SCHMIDT-HEBBEL H. Avances en Ciencia y Tecnología de los Alimentos, Alfabeta Impresores, pp. 32–38, 1981.

3. MULLER H.G. Introducción a la Reología de los Alimentos, Zaragoza, Editorial Acribia, pp. 155–161. 1973.

4. CIUDAD C., RODRIGUEZ O. Tabla auxiliar química proximal de alimentos. Instituto de Investigaciones Agropecuarias. Estación Experimental La Platina, 1^a edición, 1982.

5. BECKER R., MYER D., SAUNDERS R. Farming the desert Prosopis species (Mesquite) pods as a food crop. League for International Food Education 17(1): 2, 1984.

6. SERRA M.T. Arboles y arbustos forrajeros en Chile. Primer encuentro “Estado de la Investigación sobre Manejo Silvo-pastoral en Chile”, p. 6–12 November, Talca 1983.

7. BECKER R., GROSJEAN O. A compositional study of pods of two varieties of Mesquite (Prosopis glandulosa, P. velutina). J. Agric. Food Chem. 28:22–25, 1980.

8. LOOSER G. La importancia del algarrobo (Prosopis chilensis) en la vegetación de la Provincia de Santiago, Chile. Revista Universitaria, Universidad Católica de Chile. 47:103–116, 1982.

9. GLICKSMAN M. Hydrocolloid Utilization in Fabricated Foods. Cereal Foods World. 21(1): 17–26, 1976.

10. MEER W. Plant Hydrocolloids. In: Graham H. Ed. Food Colloids Wetsport. Conn, The Avi Publishing Co. p. 522–539, 1977.

11. SCHMIDT-HEBBEL H. Aditivos y contaminantes de Alimentos. Edited by Fundación Chile. Editorial Universitaria, p. 58–60, 1979.

PHYSICAL AND MECHANICAL PROPERTIES OF TAMARUGO AND ALGARROBO WOOD FROM THE TAMARUGAL PAMPA

Emilio Cuevas
Iván Ulloa
Ramón Rosende
Juan Donoso
Faculty of Agricultural, Veterinary and Forest Sciences
University of Chile

Practically all of the characteristics and properties of wood are derived from its organic origin, its cellular structure and the chemical composition of its constituent tissues.

Wood is composed of complex-structured cells formed by a distinctive mix of cellulosic polymers, hydrocarbons and lignin, the organization of which integrates a reinforced cellular structure. This accounts for the combination of elasto-plastic reactions of the wood when faced to external stress, being superior in strength, at equal weights, to concrete and steel. It is noteworthy that, at equal volume, wood weighs nearly five times less than concrete, four times less than brick, over five times less than aluminum and over fifteen times less than steel.

The preferentially parallel-to-the-axis orientation of the cells in a tree and the predominantly crystaline structure of cellulose provide the wood with great strength for traction efforts. The presence of lignin in the external layer of the cell wall and medium lamella offers a lateral support to the cell and contributes to the stability and compression capacity of the material.

Due to the structure and organization of the cellulose in the cell walls, the tapered shape of the ligneous cells and their longitudinal-radial arrangement, resulting from the radial symmetry of the stem, the wood behaves as an orthropic material. That entails a different reaction depending on the axis: tangential, radial and longitudinal. On the other hand, wood is a hygroscopic substance, which, together with its orthropic nature and the contraction phenomenon —which becomes evident when the moisture content falls below the saturation point of the fibers—, gives rise, with the change in moisture, to dimensional variations and deformations that affect the processing and utilization of the wood.

Additionally, wood, unlike other materials, presents a high degree of variation in its properties, due to the fact that it is a product of the tree metabolism and of the action of external factors which condition its growth. This variation becomes evident, in a decreasing degree, in wood from different trees of the same species and in wood from different parts along and across the stem.

From the above data, it is evident that good knowledge on the characteristics and properties of each wood species is mandatory to obtain quality products to meet ever increasing demands and requirements.

This work presents a partial characterization of tamarugo (Prosopis tamarugo Phil.) and algarrobo (Prosopis alba Gris.) wood from the Tamarugal Pampa. It is part of a project wider in scope with which the CORFO Agricultural Society has encharged the Faculty of Agricultural, Veterinary and Forest Sciences of the University of Chile. The authors, academicians from the Wood Technology Department, express their aknowledgment to both institutions for the opportunity to conduct this research and to be present at this International Round Table.

PURPOSES

The research was programmed to carry out a systematic analysis of the basic physical and mechanical properties of tamarugo and algarrobo wood, aiming at the collection of data contributing to a guideline for their utilization. The following properties were determined: density, contraction, static bending, compression parallel to grain, hardness and toughness.

BACKGROUND AND SCOPE

The data regarding the technological characteristics of tamarugo and algarrobo wood are very scant. One of the few references corresponds to Ortiz J. (1966), who only included some comments regarding the general characteristics of the wood and the more recommendable uses. A contribution by Contreras D. (1982) is also aknowledged, whereby some physical properties are cited from advance reports of the authors of this work.

As to other species of the genus Prosopis, there are not many technological publications available. A review of the literature only reveals a few references, some of which include the value of certain properties, but others do not go beyond very general considerations. The most relevant bibliographical citations refer to the following species:

• Prosopis africana. Sallenave, P. (1955); Bolza E., Keating W. G. (1972).
• Prosopis alba. Tortorelli L. (1956); Gobierno de la Provincia de Santiago del Estero, Argentina (1970); National Academy of Sciences. (1980).
• Prosopis algarrobilla. Tortorelli L. (1956); Gobierno de la Provincia de Santiago del Estero (1970).
• Prosopis caldenia. Record S.J., Hess R.W. (1949); Tortorelli, L. (1956); Gobierno de la Provincia de Santiago del Estero, Argentina (1970).
• Prosopis chilensis. Record S.J., Hess R.W. (1949); National Academy of Sciences (1980).
• Prosopis cineraria. National Academy of Sciences (1980).
• Prosopis juliflora. Record S.J., Hess R.W. (1949); Hills, W. E. (1962); National Academy of Sciences (1980) Falker P. (1982).
• Prosopis kuntzei. Record S.J., Hess R.W. (1949); Tortorelli L. (1956); Gobierno de la Provincia de Santiago del Estero (1970).
• Prosopis nigra. Record S.J., Hess R.W. (1949); Tortorelli L. (1956); Gobierno de la Provincia de Santiago del Estero (1970).
• Prosopis ñandubay. Record S.J., Hess E.W. (1949).
• Prosopis pallida. National Academy of Sciences (1980).
• Prosopis pubescens. Record S.J., Hess R.W. (1949).
• Prosopis ruscifolia. Tortorelli L. (1956); Gobierno de la Provincia de Santiago del Estero. (1970).

One of the predominant characteristics of the population of Prosopis established at the Tamarugal Pampa is the variability in growth habits, the tortuosity and abundant ramification of the stem of both species, together with the occurrence of multiple stems which become intertwined, giving rise to a shrub-like vegetation difficult to exploit and with a low potential of commercial timber.

From another standpoint, it must be kept in mind that the Prosopis formations at Regions I and II are growing in a marginal environment where human settlements are also struggling to make a living, relying heavily on the available resources.

This conforms a very complex picture as regards the utilization possibilities of the wood, which, nevertheless, can be attractive providing that compatibility is achieved between the more interesting uses and the preservation and propagation of the resource, in harmony with meeting the minimum needs of the rural population.

EXPERIMENTAL PROCEDURE

Test Material

The wood for the trials was collected from the Refresco Farm, Region I, Tamarugal Pampa, which, at the time of the research, was under the administration of CORFO. Currently it is in the hands of the National Forestry Corporation (CONAF). Four plots were selected, two for the extraction of 50- and 22-year-old tamarugo and two for the extraction of algarrobo of the same ages. Six trees were selected per species and age class, among those with better stem shape and diameter, and a size to make it possible to obtain a piece at least 1.2 m long from them. Five such pieces in each of the groups were used for the trials, and the sixth was left as reserve.

Each of the pieces was painted on the ends to avoid excessive moisture loss. The identity of the material was controlled by the use of different colors according to the species and age class, as well as correlative numbers for the trees in each of the four groups.

The pieces were transported to Santiago and separated into three portions: one 0.70 m long and two 0.25 m each. Three little beams were prepared from the first portion, two of them 30 mm in cross section and 700 mm in length, and another one 25 mm in cross section and 700 mm in length. A small beam 55 mm in cross section and 250 mm long was made from one of the 0.25 m cylinders.

Test specimens were then made from the small beams; the 30-mm-cross-section beams provided specimens for density, contraction, static bending and compression parallel to grain tests; from the beams 25 mm in cross section specimens were prepared for toughness tests; and from the 55-mm-section ones, specimens were obtained for hardness tests.

Conditioning of the Test Specimens

The specimens for the mechanical properties tests were stabilized to a moisture content of 12% as a previous stage to carrying out the trials.

The specimens for physical properties were subjected to conditioning immediately after the initial green weight and volume had been established.

The conditioning was conducted in a chamber where constant temperature and relative air humidity conditions had been established (25° C and 67%, respectively), with the purpose of remitting the findings to a uniform moisture content, which, additionally, corresponds to the balance moisture reached by wood in vast areas of the world and is the standardized percentage moisture used internationally for laboratory trials.

Methodology

The physical properties were tested by the Australian test method, which uses a single type of specimen to make the density and contraction determinations.

This method is an adaptation of American (ASTM) and British (BSI) standards —very similar among themselves—, and is statistically as valid as them, as has been demonstrated by systematic research (Kelsey K.E., Kinston R.S.T., 1953; 1957). Additionally, at the time the trials were conducted, the Chilean Official Standard was adopted, complying fully with the stipulations of the Australian test method.

The specimens (40 in number, with two replications per tree; 2.5 cm in cross section and 10 cm long) were each measured tangentially and radially in three points and longitudinally in one point, and weighed in green conditions. They were subsequently conditioned to 12% moisture content (M.C.), reconditioned in saturated vapor at 100° C, again conditioned to 12% M.C., and, finally, dried up to anhydrous state. Measuring and weighing were repeated at each of these stages. It was thus possible to determine their density and contraction.

Density, expressed in g/cm³, was referred to anhydrous weight and volume (anhydrous density); to 12% M.C. weight and volume (density at 12% or normal); and to anhydrous weight and green or saturated volume (basic density).

The value of the anhydrous density makes it possible to compare with the findings of other research on the same or different species. The density at 12% is equivalent to the dry conditions up to balance moisture content typical of the general timber use conditions. The basic density value makes it possible to determine dry weight yield of the fibrous material contained in a given volume of green wood; it is a useful parameter as well for comparative purposes, since the density of the wood at any moisture content above the fiber saturation point can be calculated empirically from it. It is thus easy to compute the weight of a given volume of wood at any saturated moisture content.

Contraction, expressed as a percentage of the initial green dimension, was determined tangentially, radially and volumetrically up to moisture contents of 12% and anhydrous.

The contraction values used for practical purposes are those related to the moisture loss of the wood from green to 12% M.C.

The magnitude of collapse —when present— was determined by the difference in contraction up to 12% M.C., before and after reconditioning.

The mechanical properties were evaluated using the ASTM Standard D 143, with the modification recommended regarding the wood from trees smaller than 0.30 m in diameter, conducting all the tests with wood at 12% M.C.

Fiber stress at proportional limit was determined in static bending and compression parallel to grain, which corresponds to the effort under which the load-deformation curve leaves the straight line.

The modulus of rupture (static bending) is a measure of the capacity of the beam to support a load applied slowly for a short period of time. Its value is very important to evaluate the capacity of a given species.

The maximum crushing strength (compression parallel to grain) is a measure of the maximum load accepted by a piece of wood subjected to a slowly applied load parallel to the fiber. It gives an indication of the capacity of the wood for uses as a short pillar.

The hardness represents the strength of the wood against wear and cleavage.

Toughness is a measure of the energy necessary to break the wood by the impact of a pendulum falling from a pre-determined height. It makes it possible to select wood for uses which require high strength against impacts.

RESULTS AND DISCUSION

Table 1 summarizes the average values found in the physical and mechanical tests. Tables 2 and 3, in turn, include separate values for density and contraction, and Tables 4 and 5 the values for the mechanical properties. These last four tables include average figures, accompanied, in each case, by the respective values of the standard deviations (St. dev.) and coefficient of variation (C.V.).

The findings confirm the high density of both species, which exceed the values for all the commercial species in the country, the greater being that of tamarugo, comparable to that of the highest-density wood in the country, Amomyrtus luma (Mol.) Legr. et Kaus, whose basic density is 1.05 g/cm³ and, at 12% M.C., 1.15 g/cm³ (Torricelli 1942; Pérez 1978).

Table 3 shows that the contraction values for practical use (up to 12% M.C.) are relatively low if compared with commercial species of medium to high density, such as coigüe (Nothofagus dombeyii) or eucalyptus. The magnitude of contraction for both species before reconditioning (BR) is 13.2% and 12.0% tangentially, and 5.8% and 4.9% radially, respectively. After reconditioning (AR), contraction is reduced to 4.8 and 7.4% tangentially and 2.0 and 3.7% radially, respectively (Cuevas 1969).

Collapse is not evident in algarrobo wood, even though a reduction in contraction is observed after the reconditioning process. This recovery in the dimensions of the wood is attributable to a relaxation of the tensions within the wood.

In tamarugo, on the contrary, collapse is observed, since, together with a manifest recovery in the dimensions of the wood after reconditioning, a significant drop in density is evident, as illustrated by Tables 1,2 and 3.

As to mechanical capacity, it may be observed that it increases with the age of the tree in both species, a fact, in turn, related to the increase in wood density. It is also evident that tamarugo has greater mechanical capacity than algarrobo, as a result of the former's greater density.

The comparison of the findings in this study with those of other species growing in Chile (Pérez 1978) shows algarrobo wood, particularly that from 50-year-old trees, to match the mechanical capacity of species with greater strength.

Tamarugo wood, in turn, exceeds largely the values for most of the commercial species in the country.

The characterization of the wood of Prosopis alba Gris. growing in Argentina (Tortorelli 1956) indicates that its density varies from 0.75 and 0.85 of the lower values obtained in this study for the static bending strength and compression parallel to grain.

Sallenave (1955) gives values that are very similar to those for tamarugo found in this study, in static bending tests and compression parallel to grain conducted with P. africana.

When analyzing the findings of the mechanical properties, the great variation observed in the wood from both species must be kept in mind —as repeatedly stated in this paper—, resulting from its growth habit, the extreme environmental conditions under which it grows and the peculiar characteristics of its anatomical and chemical structure.

The findings warrant, nevertheless, the utilization of the wood from both these species, particularly tamarugo, in tool handles, handicraft items and others with similar requirements, due to their characteristic hardness and impact strength.

CONCLUSIONS

The analysis of the findings evidences some common characteristics for these species, among which are their decorative aspect, resulting from the differentiation between sapwood and heartwood and from the constitution of the ligneous tissue; their high density, providing the wood with great mechanical capacity; their dimensional stability, and the good quality which may be obtained from planed or machined products.

The literature mentions local uses for these species, such as fuelwood, charcoal, hubs and rays of cartwheels, poles, tool handles and construction materials. There are still beams and lintels made with algarrobo wood at the San Francisco temple in La Serena. Likewise, there are houses in Illapel and other towns in the area where thin pieces of algarrobo heartwood act as nails to join larger pieces or serve as base for pillars (Ortiz 1966). The structure of the building which housed the Caldera train station (the first railway in Latin America), is also joined with algarrobo pieces.

The possibilities of utilization of tamarugo and algarrobo wood from the Tamarugal Pampa must take into consideration some essential factors. It is a resource which grows under marginal climatic conditions, where human settlements depending heavily on the available resources are located. Massive and intensive use of the resource is, therefore, ruled out. On the contrary, what is intended is a rational management to insure its persistence and, possibly, increase its present availability.

The report of the National Academy of Sciences of the USA (Firewood Crops, 1980) is very clear in this respect, although it refers exclusively to firewood production.

The authors of this paper are of the opinion that the wood of these species has valuable characteristics apt for a number of uses. However, due to the constraints described above, it is not possible to assimilate their utilization possibilities to those of commercial timbers in the nation. Ultimately, it is up to Government policies to set the guidelines for utilization of this resource.

Tamarugo wood for charcoal production at Canchones (Tamarugal Pampa).

REFERENCES

BOLZA E., KEATING W.G. 1972. African timbers. The properties, uses and characteristics of 700 species. CSIRO, Div. Build Res. Melbourne, Australia.

CONTRERAS D. 1982. Distribución, productividad y manejo de ecosistemas naturales y artificiales de tamarugo y algarrobo en Chile. Algaroba V. 2. Simposio brasileiro sobre Algaroba. Empresa Brasilera de Pesquisa Agropecuaria do Rio Grande do Norte S.A., Natal, Brazil.

CUEVAS E. 1969. Incidencia en los fenómenos de contracción y colapso en el secado de algunas maderas comerciales de Chile, Inst. Forestal. Informe Técnico N^o 36 pág. 145–155, Santiago, Chile.

FELKER P. 1982. The Mesquite Wood Workshop, Mesquite Messenger. 1 (1). Texas, USA.

GOBIERNO DE LA PROVINCIA DE SANTIAGO DEL ESTERO. 1970. Maderas santiagueñas, Ministerio de Economía, Direc. Gral. de Bosques. Argentina.

HILLIS W.E. 1962. Wood extractives. Academic Press New York, USA.

KELSEY K.E., KINGSTON R.S.T. 1953. An investigation of standard methods for determining the shrinkage of wood. J. For: Prod. Res. Soc. 3 (4): 49–53.

KELSEY K.E., KINGSTON R.S.T. 1957. The effect of specimen shape on the shrinkage of wood. For. prod. J. 7 (7): 234–235.

NATIONAL ACADEMY OF SCIENCES. 1980. Firewood crops: Shrub and tree species for energy production. Washington, D.C. USA.

ORTIZ J. 1966. Algunos forestales chilenos de la estepa septentrional. Ministerio de Agricultura. Direc. Agr. y Pesca. Bol Téc. N^o 23. Santiago, Chile.

PEREZ V.A. 1978. Manual de Construcciones en Madera. Inst. For. Manual N^o 10. Santiago, Chile.

RECORD S.J., HESS R.W. 1949. Timbers of the New World. Yale University Press. New Haven, USA.

SALLENAVE P. 1955. Propriétés physiques et mechaniques des bois tropicaux de l'Union Française. Centre Technique Forestier Tropical, Paris, France.

TORRICELLI A., TORRICELLI E. 1942. La madera. Imprenta La Sud América. Santiago, Chile.

TORTORELLI L. 1956. Maderas y bosques argentinos. Ed. Acme. Buenos Aires, Argentina.

TABLE 1
Average values for some physical and mechanical properties of 22- and 50-year-old tamarugo and algarrobo wood

TABLE 2
Average density values for 22- and 50-year-old algarrobo and tamarugo wood

* BR = Before reconditioning.
** AR = After reconditioning.

TABLE 3
Average contraction values for 22- and 50-year-old algarrobo and tamarugo wood

* BR = Before reconditioning.
** AR = After reconditioning

TABLE 4
Mechanical properties of 22- and 50-year-old algarrobo wood

TABLE 5
Mechanical properties of 22- and 50-year-old tamarugo wood