Characterization of by-products of sunflower culture – commercial applications for stalks and heads

Industrial Crops and Products 10 (1999) 185 – 200 www.elsevier.com/locate/indcrop

Characterization of by-products of sunflower culture – commercial applications for stalks and heads V. Marechal, L. Rigal * Laboratoire de Chimie Agro-Industrielle, U. A. INRA 31A1010 ENSCT INPT, 118 route de Narbonne 31077 Toulouse Cedex 4, France Accepted 23 April 1999

Abstract The by-products of sunflower production were characterized. The sunflower heads contain a strong smelling essential oil (EO) (0.2%) and pectins (22%). The galacturonic acid (GA.A.) content of the pectins depends on the extraction conditions (water-soluble pectins: 67%, soluble in ammonium oxalate/oxalic acid: 74%, in hydrochloric acid: 33%). They are all slightly methylated (degree of methylation (DM) B 20%). The stalks may be readily separated into two parts: fiber (external part, 90%) and the pith (internal part, 10%). The mechanical properties of paper pulp obtained by thermomechanical treatment in a twin-screw extruder of the whole stalks or depithed stems were investigated. The pulps had high values of ring crush test (RCT) and concora medium test (CMT), which make them suitable for the manufacture of cardboard. Low-density materials can be also shaped with ground pith. The role of water-soluble substances in the cohesion of these materials is discussed. Its mechanical properties, which are comparable to those of polystyrene, were determined. They may find application in the packaging and packing industries. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Agromaterials; Commercial applications; Essential oil; Paper pulp; Pectin; Pith; Stalk; Sunflower; Sunflower head; Twin-screw extruder

Sunflower, the fourth source of oil-seeds worldwide with a production of 25 180×103 metric tons of seeds in 1995/1996, representing around 50 000× 103 ha of cultivated land is currently produced for its seeds. The rest of the plant, namely 3–7 tons of dry matter/ha (including 10% of head) is left in the fields, and represents a considerable biomass that could find applications. * Corresponding author. Tel.: +33-5-61175720; fax: + 335-61175730.

More than 500 years ago the North American Indians used medicinal decoctions of sunflowers (roots: snake bites; stems: treatment of inflammatory conditions). In the 1980s, Hungarian researchers at Budapest University showed that aqueous extracts of sunflower stalk had strong anti-inflammatory activity (Hollo 1987). Cosmetic preparations (He´lia D) based on aqueous extracts of sunflower stalk have been developed by Biogaˆl at Debrecen (Hungary). Other uses of sunflower have been described (see The Sunflower by Heiser, 1976).

0926-6690/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 6 - 6 6 9 0 ( 9 9 ) 0 0 0 2 3 - 0

186

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Most of the scientific studies on sunflower residues have been carried out on flower-head pectins. In the 1940s, Colin and Lemoine (1940) noted the presence of significant amounts of uronic acid in the pith, and numerous studies have been devoted to the chemical composition of sunflower pectins, their extraction, and distribution in the plant (Shewfelt and Worthington 1953; Zitko and Bishop 1966; Lin et al., 1976; Sabir et al., 1976), and their content in relation to maturity of the plant (Riaz and Uddin 1972; Lin et al. 1975; Campbell et al. 1978; Pathak and Shukla 1981). Compared to other pectins, sunflower pectins have, at natural state, a low degree of methylation (DM), which makes them gel at lower sugar concentration and they may thus find application in low-calorie foodstuffs. Compared with commercially available pectins with a low DM obtained by chemical demethylation, which leads to some depolymerization, the natural sunflower pectins form firm gels over a large range of pH (Kim and Sosulski 1978; Sosulski et al. 1978; Chang and Miyamoto 1992). However, these gels tend to break up as a result of the non-random distribution of methyl groups. Kim et al. (1978) improved the quality of the gels by following the demethylating step by an amidation. However, to our knowledge, sunflower pectins have yet to find commercial applications as gelling agents. Jimenez et al. (1991), Jimenez and Lopez (1993) have investigated the uses of sunflower stalk for the manufacture of paper pulp. The following studies were designed to develop a new method of fractionating by-products of sunflower cultivation in order to find application for the non-oil by-products.

1. Materials and methods The tests were carried out on sunflower specimens from the INRA Plant Research Station at Auzeville (France). The studies on pectin content as a function of plant maturity were carried out on sunflower hybrids cultivated on a clay soil in the Gers De´partement (France) in 1995. Specimens were taken at around 18.00 h and were kept

at −20°C. The plants were harvested at various physiological stages of the flower head. The various plant organs were separated manually from each specimen. Minerals were determined according to the French Standard (ASTMD-1106) and calcium was determined by atomic absorption spectrometry. The essential oil (EO) was extracted by steam distillation for 6 h according to the method laid down in the French Pharmacopoeia. Proteins were assayed by the Kjeldahl method (Bradstreet 1967). The lipid, pectin, and hemicellulose fractions were obtained during successive extractions. The plant matter was homogenized and placed in a reactor containing 95% ethanol (EtOH) and heated at 70°C. The mixture was washed three times with EtOH for 15 min and after filtration the EtOH was evaporated leaving the lipid fraction. Matter insoluble in EtOH was extracted three times in water for 30 min at 20°C. The aqueous filtrates were then pooled and concentrated. The pectins were recovered after two sequences of purification: precipitation in EtOH and resolubilization in water. The excess EtOH was removed by evaporation under a partial vacuum. The pectins were freeze-dried. The water-insoluble residue was treated for 1 h at 70°C with a mixture of ammonium oxalate and oxalic acid (Ox) at pH 3. The filtrate was recovered and the pectins precipitated with EtOH, then dissolved in a solution of hydrochloric acid pH 1.5 and reprecipitated with EtOH. This treatment was carried out one more time to eliminate oxalate salts formed during the extraction. The purified pectins were dissolved in water and then freeze-dried. The residue not soluble in oxalate was taken up in a solution of HCl pH 1.5, and treated for 2 h at 70°C. the pectins were recovered and purified as described above for the water-soluble fraction. The final residue was extracted with 4% sodium hydroxide at 50°C for 1 h. The resulting hemicellulose fraction was filtered off and adjusted to pH 5 with acetic acid and precipitated with EtOH. The percentage of galacturonic acid (GA.A.) in the pectins was determined according to Blu-

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

menkrantz and Absoe-Hansen (1973). The DM was determined by gas phase chromatography according to the method described by Bartolome and Hoff (1972). Fifty milligrams of the dry pectin extract are dissolved in 5 ml of 0.5% disodium ethylenediamine tetraacetic acid (EDTA) in a 30 ml glass vial fitted with a rubber stopper. Five milliliters of 0.05% propanol and 5 ml of 1M sodium hydroxide are then added to the mixture. After stirring for 30 min at 30°C, the vial is cooled to 0°C. Seven milliliters of phosphoric acid and 7 ml of sodium nitrite are added to the vial, which is then sealed and placed on ice. After shaking for 45 min, the vapor phase is removed from the vial using a gas syringe and injected into the chromatography column. Propanol was employed as internal standard, and the column was calibrated by replacing the pectin extract solutions with solutions of methanol at different concentrations. The distribution of neutral sugars in the pectins was determined by high performance ionic chromatography after hydrolysis for 5 h with 0.5M sulfuric acid. Lignin, cellulose, and hemicelluloses of the fibers were quantified according to Van Soest and Wine (1963, 1968).

187

Total sugars were determined according to Dubois and Gilles (1956). The polysaccharides were hydrolyzed in 1N sulfuric acid at 100°C for 8 h and then assayed by high performance ionic chromatography. A modified twin-screw extruder (Clextral BC 45, Framatome, Firminy 42702, France) (Fig. 1) was employed to prepare the paper pulp. Seven sections, four of which (B, C, E, and F) are heated by induction belts and cooled by circulating water, formed the 1.4 m long barrel. The screw profiles of the two corotating screws used for the tests are illustrated in Fig. 1. All experiments were carried out with a reverse screw element which had peripheral slots grooved in the screw flight for leakage flow. Conical holes (1 mm entry, 2 mm exit) formed the filter element placed at the end of the barrel in order to extract the liquid phase from the slurry. The NaOH or ammonium oxalate/oxalic acid solution was injected at a single point using a volumetric pump. Sunflower biomass was fed in from a bin via a feeding screw and a chute at a constant flow rate. All the experiments were conducted at a fixed screw speed of 124 rpm. The pulp obtained was refined in a Sprout Waldron apparatus fitted with 30 cm discs (C 2976 pattern). The slabs were made in a standard Franck system. To determine

Fig. 1. Modified Clextral BC 45 twin-screw extruder: configuration and screw shapes.

188

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Fig. 2. Sunflower head pith under the scanning electron microscope.

required to break the slab, and the slope of the force/thickness of the slab as a function of vertical displacement of the bar, were measured to determine elasticity. The compression tests were carried out using a cylindrical ram (12 cm diam) with a rounded end, which was lowered at a rate of 0.3 mm s − 1. Two successive 1 mm deplacement from the initial surface of the slab were made, the second being to check for the residual deformation made by the first compression. Cohesion was measured in a traction test until breakage of the slabs (6 cm long, 2.5 cm wide, cut out from the cylindrical slabs) and stretched at a rate of 5 mm min − 1 from the two ends (gripped 3 cm apart). The breaking force was expressed as a function of the thickness.

2. Results

2.1. Physiological characterization

Fig. 3. Stalk pith under the scanning electron microscope.

the applicability of the pulp for manufacture of corrugated cardboard, we selected a weight of 130 g/m2. Shaping of the agromaterials: after absorption of water, 8 g of ground pith were placed in a cylindrical mould and dried for 30 min at 150°C. The samples thus consisted of 10 cm diameter slabs, were analyzed using a TAXT2 texture analyzer (Rhe´o) for flexion and compression, and an Instron press for cohesion. For the flexion tests, the slabs were supported on two bars placed 6 cm apart and a third bar equidistant between the two was lowered at a rate of 0.3 mm s − 1. The force

The sunflower head consists of three main parts: the neck (part between head and stalk), which is not readily separated at harvest, the bracts (lower part) and the pith (core of head). The relatively unstructured pith consists of a tangle of filaments (Fig. 2), sometimes with resin in the core. The crushed sunflower head has a strong and not disagreeable smell. The external part of the stalk is fibrous and makes up 90% of the dry weight (DW) of the total stems. The fibers are long and brown in color, and are readily separated from the white elastic and low density pith (35 kg m − 3 versus 430 kg m − 3 for the fibers). The fibrous structure of the pith in the stalk is quite different from that in the head, which is more organized in a honey-comb arrangement (Fig. 3).

2.2. Chemical characterization A pleasant smelling EO can be extracted by steam distillation of the flower heads. It comprises 0.2% of the initial dry matter. Another characteristic of the sunflower head is its high pectin content with a large proportion of polygalacturonic acids (Table 1). Pectin content depends on the

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

189

Table 1 Chemical composition of sunflower head [expressed in % with respect to dry weight (DW) of matter]a Content (%) Dry weight

88

Ash

16.7

Essential oil

0.2

Proteins

5.3

Lipid fraction

8

Total pectins Extracted in water at 20°C Extracted in ammonium oxalate

Extracted in HCl Polysaccharides extracted with NaOH Lignin Cellulose

Characteristics

Fatty acids: palmitic, stearic, Waxes: 0.5% of dry matter of sunflower head

21.7 1.9

DW, 87%; ash, 8.1%; DM, 1%; GA.A., 67%; Ca, 0.8%

17.0

DW, 95.68%; ash, 2.1%; DM, 15%; GA.A., 74%; Ca, 1.3%

2.8 16.8

Sugars: arab. (32%); gal. (31%); glu. (16%); rham. (7%); fru. (7%); xyl. (5%); man. (1%) DW, 93.54%; ash, 18.7%; DM, 6%, GA.A., 33%; Ca, 13.0% DW, 85%; ash, 40.5%; uronic acids, 19%; total sugars: 23.5% sugars, xyl.(60%); glu. (14%); gal. (11%); rham. (8%)

6.3 19.6

a Abbreviations: arab., L(+)-arabinose; fru., rham., L(+)-rhamnose; xyl., D(+)-xylose.

D(−)-fructose;

variety of sunflower and its stage of maturity (Fig. 4), and may make up 20 – 25% of the dry matter for a healthy mature plant. In our specimens, 22% of the pectins were extracted from the initial organic matter by successive treatment with water, ammonium oxalate and HCl as described in the Section 1 section. These pectins are weakly soluble in water and differ from other pectins by their low DM. This is thought to be a result of demethylation occurring during the development of the plant (Fig. 5 and Tieman, 1992 on the tomato). Alkaline extraction of the head after treatment with water, oxalate and HCl, leads to isolation of an fraction with a high uronic acid and L(+ )-rhamnose content. It was assumed to be a mixture of pectins and hemicelluloses (Table 1). The composition of fibers of sunflower stalk (Table 2) resembles that of other annual plants such as corn and paper sorghum. They are characterized by a high cellulose and hemicellulose content. Acid hydrolysis (Fig. 6) indicated that they were of the galacto-arabino-xylan type.

gal.,

D(+)-galactose;

glu.,

D(+)-glucose;

man.,

D(+)-mannose;

The pith from sunflower stalk, which is quite unlike that of the stalk fibers, has a high pectin content and low levels of hemicelluloses and lignin (Table 3), which distinguishes it from the stem piths of corn, sorghum and kenaf (Table 2). Large amounts of uronic acids and L(+)-rhamnose were obtained on acid hydrolysis of the alkaline extract of heads. This alkaline extract would also appear to be a mixture of pectins and hemicelluloses.

Fig. 4. Amount of pectins extracted as a function of maturity of plant (expressed in galacturonic acid content).

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

190

Fig. 5. Degree of methylation of the three fractions as a function of maturity of sunflower heads.

2.3. Fractionation of sunflower head The sunflower head was fractionated in two stages: (i) steam distillation of the EO; (ii) extraction of pectins. Steam distillation of 5 kg of dried head for 6 h

Fig. 6. Kinetics of hydrolysis by 1N sulfuric acid at 100°C of polysaccharides of depithed sunflower stalk extracted with 1% NaOH at 90°C for 1 h (final composition: xyl. 69%, gal. 16%, arab. 10%, rham. 4%, glu. 1%)

at 100°C with vigorous agitation confirmed the yields obtained in the laboratory: 0.2% of oil with

Table 2 Distribution of hemicellulose/cellulose/lignin in various plant materialsa Hemicelluloses

Cellulose

Lignin

References

Hard wood

25

48

24

Thompson, 1981

Soft wood

25

43

29

Thompson 1981

Wheat straw

34

38

14

Lawther et al., 1995

Kenaf Whole stalk Depithed stalk Pith

23 (pent.) 16 22

39 45 37

10 8 14

Cunningham et al., 1986 Cunningham et al., 1986 Cunningham et al., 1986

Sorghum Canes Depithed canes Pith

24 (pent.) 22–34 32

27 31–44 37

Corn Whole stalk Depithed stalk Pith

27 (pent.) 26 (pent.) 26 (pent.)

46 48 48

17 16 13

Sunflower Depithed stalk (DW, 88%; ash, 3.8%; proteins, 1.4%)

32

41

17

a

Pent., pentosans.

9 7–14 9

Cunningham et al., 1986 Manolas, 1993 Manolas, 1993

McGovern et al., 1987 McGovern et al., 1987 McGovern et al., 1987

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

191

Table 3 Chemical composition of pith from sunflower stalk [expressed as % with respect to dry weight (DW) of matter]a Content (%) DW

88

Ash

16.6

Proteins

0.9

Lipid fraction

4

Total pectins 17.6 Extracted in water 4.7 at 20°C Extracted in ammo- 11.7 nium oxalate extracted in HCl 1.2 Polysaccharides extracted in NaOH

4.4

Lignin

3.2

Cellulose

Characteristics

waxes: 0.3%

DW, 86%; ash, 19.9%; DM, 4%; GA.A., 46%; Ca, 9.3% DW, 85%; ash, 3.7%; DM, 9%; GA.A., 82%; Ca, 2.3% DW, 90.1%; ash, 14.1%; DM, 8%; GA.A., 43%; Ca, 12.7% DW, 89%; ash, 49.4%; uronic acid, 17%; total sugars, 24.5%; sugars: xyl. (25%); glu. (24%); gal. (20%); rham. (16%); arab. (10%); man. (6%)

45.4

a Abbreviations: arab., L(+)-arabinose; gal., xyl., D(+)-xylose.

D(+)-galactose;

respect to the initial weight of dry matter. The EO has a spicy odor resembling that of leather, with some accents of labdanum. It has a strong and highly individual smell and could find application in the perfume industry. Extraction of sunflower pectin with aqueous ammonium oxalate is speeded up by raising the temperature from 70 to 100°C (Fig. 7). Eighty percent of the pectins were extracted within 5 min at 100°C. No degradation of pectins was observed after reaction for 6 h. A two-way factorial design for the study of the influence of temperature and concentration of ammonium oxalate on the percentage of GA.A. extracted, indicated that the ammonium oxalate concentration could be reduced from 20 g l − 1 to 11 g l − 1 independent of temperature and with no appreciable loss in yield (Table 4). Eleven grams per liter is thus the theoretical maximum concentration required for extraction of pectins containing 80% non-methylated GA.A.s, assuming that one equivalent of ammonium oxalate is required for two equivalents of GA.A.

glu,

D(+)-glucose;

man.,

D(+)-mannose;

rham., L(+)-rhamnose;

The pectin can be extracted at the same time as the steam distillation of the EO. For a contact duration of 6 h, a 19% yield in pectins with respect to DW of flower head was obtained (Table 5). The EO was found to have the same olfactory qualities as the oil extracted as described above and in identical yield.

Fig. 7. Kinetics of extraction of pectin from sunflower heads of sunflower at 70 and 100°C.

192

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Table 4 Complete 22 factorial plan to investigate the influence of temperature and concentration of the extracting solution on the percentage of extracted galacturonic acids with respect to initial dry weight (DW) of the plant matter (% GA.A.) Concentration X1* − + − + Main effect of temperature Main effect of concentration Interaction effect

U1*(g l−1)

Temperature X2

U2 (°C)

11 20 11 20

− − + +

70 70 100 100

Responses % GA.A 19.6 19.5 22.9 23.1 6.9 0.1 0.3

* X, coded value; U, true value. Table 5 Yield for simultaneous extraction of pectins and essential oil Operating conditions

100°C, 6H, 20 g l−1 ammonium oxalate/oxalic acid at pH 3.5

2.4. Fractionation of sunflower stalk Sunflower stems can be split up into two parts mechanically, by crushing and separation in a cyclone system. The first consists of external fibers and pith whose particle distribution is illustrated in Fig. 8. The thermomechanical properties (TMC) of the paper pulps obtained by treatment with alkali (4% NaOH at 55°C) of the fibers (depithed stalks) in the twin-screw extruder (Fig. 1) were somewhat better than those obtained using the whole stalks (Table 6). The shear and breaking indices, and the breakage lengths were higher for a lower volumic mass. Increase in concentration of sodium hydroxide led to a slight improvement in pulp quality from whole stalks. The percentage of precipitated polysaccharides was somewhat higher for whole stems, although determination of the various sugars showed that they consisted mainly of hemicelluloses. Pectins did not appear to be removed by this treatment, and were thought to be responsible for the lower quality of the pulp made from whole stalks. However, the mechanical characteristics were equivalent to those from the chemically treated pulp

Yield (% dry matter) Essential oil

Pectins

% GA.A.

0.2

19

74

(12.2% NaOH, 147°C) obtained from sunflower stalks by Jimenez and Lopez (1993) using a batch reactor (Table 7). However, we obtained higher yields of refined pulp than these authors (75–80% versusB 50%). An alternative to mechanical fractionation of the stalks for removal of pith is a two-stage chemical treatment in the twin-screw reactor: (i) extraction of pectins with ammonium oxalate; (ii) thermomechanical treatment with sodium hydroxide of the residue. The fact that the

Fig. 8. Distribution of pith and fiber fractions from sunflower stalks crushed in an Electra type VS1 eight-hammer crusher with a 15 mm grid

Table 6 Quality of pulps from sunflower stalk processed in a twin-screw reactor* Plant matter

Whole stems

Whole stems

Depithed stems

Whole stems

Residue de 4(1) Whole stems 4(1) then 4(2)

Operating conditions in twin-screw reactor

1

2

3

4(1)

4(2)

Yield of refined product (%) Extraction yield of polysaccharides (% organic matter) Composition of polysaccharides (%) Percentage of total sugars Percentage of uronic acids Composition of sugars (%)

Characteristics of slabs Draining index, °SR Weight, g/m2 (NF Q 03019) Volume/mass, cm3/g Density, g/cm3 Breaking strain, kN/m (ISO 1924) Breaking length, m

86

NaOH 4% 512

83

NaOH 5% 512

130

NaOH 4% 512

81

OXa 750

33

NaOH 4% 512

175

175

175

140

100

55

55

55

55

55

78

76

79

72

70

5.0

5.9

3.1

4.5

9.9

56

62

57

28

58

23

19

22

62

22

Xyl., 84.5; Gal., 6.6; Gluc., 5.6; Arab., 3.3

50 131.8 1.59 0.63 4.33 3350

N.D.b

54 132.6 1.5 0.67 5.21 4010

Xyl., 87.8; Gal., 4.6; Gluc., 4.3; Arab., 3.3

50 131.2 1.71 0.59 5.07 3940

Gal., 36.3; Arab., 25.2; Rham., 25.4; Gluc., 8.0; Xyl., 3.3; Man., 1.6

N.D.b

81

Overall result

50 4.5+5.8

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Input flow rate of organic matter (g min −1) Extracting solution Input flow rate of liquid (ml min −1) Screw rotation speed (rpm) Temperature °C

4c

51 135.5 1.53 0.65 5.3 3990 193

194

Plant matter

Whole stems

Whole stems

Depithed stems

Whole stems

Residue de 4(1) Whole stems 4(1) then 4(2)

Operating conditions in twin-screw reactor

1

2

3

4(1)

4(2)

Stretch to break point, % Shear strength, mN (NF EN 21974) Shear index, mNm2/g Resistance to breaking, mN (NF Q 03 053) Breaking index, kPam2/g Concora medium test (CMT), N Ring crush test (RCT), kN/m

1.0 395

1.35 393

1.47 458

1.73 518

3.00 149

2.96 187

3.49 206

3.82 243

1.13 224

1.41 231

1.57 234

1.79 228

1.46

1.42

1.33

1.40

a

Ammonium oxalate/oxalic acid pH 3.5. N.D., not determined. c Overall result of experiment 4(1) followed by 4(2). * Arab., L(+)-arabinose; gal., D(+)-galactose; glu., D(+)-glucose; man., b

D(+)-mannose;

rham., L(+)-rhamnose; xyl.,

D(+)-xylose).

4c

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Table 6 (Continued)

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

195

Table 7 Various parameters of paper pulp from different sources

Source of pulp

Yield of refined product (%) Draining index,°SR Volume/mass, cm3/g Breaking length, m Shear index, mNm2/g Breaking index, kPam2/g Concora medium test (CMT), N Ring crush test (RCT), kN/m

Whole stalk

Wood

Sunflowera NaOH (12.2%), 147°C

Recycled paperb

Broom sorghumc Non-resinous woodb

Whole stalk

Depithed stalk

Pith

48 51.5 – 6335

31 1.82 3680

44 1.70 4945

2.05 4301

1.44 4960

1.6 3660

6.39

7.90

4.96

5.12

3.57

2.21

2.25

2.62

2.29

2.26

2.03

1.34

285 1.44

145 1.11

200

216

1.60

1.29

177 1.18

187 1.25

a

Jimenez and Lopez (1993). Choudens et al. (1996); Choudens and Angelier (1996). c Rigal et al. (1996), N’Diaye (1996). b

precipitate from the first stage contained pectins was indicated by the high uronic acid and sugar contents. A combination of these two processes in the twin-screw reactor led to a lower yield (50%), although 10% of the initial dry matter could be recovered in the form of a precipitate containing pectins and hemicelluloses. The quality of the pulp obtained in this process was higher than that of the other pulps, with higher shear and breakage indices. This showed the value of removing pectins from the raw material. Overall, the mechanical properties (CMC and RCT) were superior to those obtained from sorghum or recycled paper (Table 7), and were comparable to paper pulp from non-resinous wood. Paper pulp from sunflower may thus find application in the manufacture of corrugated cardboard. The low density of the pith may also be exploited in the manufacture of light materials without any requirement for additives or mold-drying process. The mechanical characteristics of the materials obtained were found to depend on the amount of water employed in fabrication (Table

8). The water appeared to solubilize a fraction of free carbohydrates and pectins in the pith (Table 9). This may account for the superior mechanical properties of materials based on sunflower pith compared to those from piths of other plants (Table 10). The pectins from sunflower have marked adhesive properties giving rise to a paper to paper joint that is stronger than the paper itself (Table 11). An aqueous solution of carbohydrates leads to a natural enduction of the surface of the pith particles forming a glued joint during a simple contact assembly process (Fig. 9). However, cohesion is poor if insufficient water is employed for solubilization (Table 8). A water/pith ratio of between 2 and 3 appeared to be optimal. At ratios above 4, there was a marked decrease in cohesion stemming from extrusion of water during fabrication with a consequent loss of binding material. It should be noted that solubilization of the binding materials leads to a shrinkage of the parenchymal structure, which may be responsible for the increase in density at low water contents. The decrease in density at higher water/pith ratios was

196

Flexion to breakage

Compression by 1 mm

Cohesion

Materials shaped under zero pressure

Density

Breaking strength/thicknes (kg mm−1)

Slope (kg mm−2) Strength (kg)

Residual sag (mm)

Thickness (mm)

Strength/thickness (kg/mm)

8 g pith+0 g H2O 8 g pith+8 g H2O 8 g pith+16 g H2O 8 g pith+24 g H2O 8 g pith+32 g H2O Pith rinsed in water Raw stalk Packing polystyrene

0.11 0.33 0.32 0.30 0.22 0.26 0.27 0.02

0.1 1.2 1.7 1.5 1.5 0.5 0.2 0.5

0.1 0.4 0.5 0.4 0.8 0.2 0.1 1.2

0.17 0.31 0.26 0.30 0.30 0.31 0.43 0.26

8.9 3.0 3.0 3.2 4.2 3.3 – –

0.2 3.4 5.4 5.3 1.8 0.6 – –

1.0 5.2 4.8 4.6 3.4 2.7 2.1 0.7

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Table 8 Mechanical properties of agromaterials-influence of water content

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

197

Table 9 Galacturonic acid (GA.A.) and free sugar contents of the fractions of different piths extracted in water for 10 min at 20°C (water/pith= 70)a

Sunflower Kenaf Sorghum Corn

GA.A.

Arab.

Rham.

Gal.

Glu.

Sacc.

Xyl.

Man.

Fruct.

Total neutral sugars

1.6 0.14 N.D. 0.11

5.7 2.1 0.1 9.8

8.4 0 0 0

4.3 5.0 0.2 5.8

41.6 68.4 24.5 39.5

3.0 10.0 41.1 22.1

1.7 4.2 4.6 10.2

1.2 2.5 0.7 0

34.1 7.8 28.8 12.7

0.16 0.12 12.6 0.11

a Sugars are expressed as % of total neutral sugars, GA.A. and total neutral sugars are expressed as % of dry weight of pith. Abbreviations: N.D., not determined; arab., L(+)-arabinose; rham., L(+)-rhamnose; gal., D(+)-galactose; glu., D(+)-glucose; Sacc., saccharose; xyl., D(+)-xylose; man., D(+)-mannose; fru., D(-)-fructose.

assumed to be a result of swelling of the cellulose by excess water. A high fiber content leads to a reduction in number of contact points between the pith particles, with a decrease in adhesive properties and a loss of mechanical strength. It is, therefore, preferable to use as pure pith as possible. Overall, agromaterials fabricated from sunflower pith have a similar density to that of expanded polystyrene and superior flexion parameters. The results of compression tests, indicating the tendency to crushing show that materials from sunflower pith are more resistant than expanded polystyrene. Although they have higher density than expanded polystyrene, agromaterials based on sunflower pith show considerable promise for the manufacture of biodegradable packing and packaging materials.

sulting fractions could be utilized for the manufacture of cardboard, and low density agromaterials. Pectins can then be extracted from mixtures of the pith with the heads after extraction of the EO.

Table 11 Mechanical strength of joints glued with pith pectin extracted with ammonium oxalate Support

Breaking strength of glued joint (N)

Paper/paper Cardboard/cardboard Wood/wood

\mechanical strength of paper 195 108

3. Conclusion Based on these preliminary results, we have drawn up a scheme for fractionation of byproducts of sunflower cultivation (Fig. 10). It combines applications for the sunflower heads, the pith, and fibers from the stalks. Harvesting could be modified to enable recovery of heads along with the seeds in the first pass of the harvester. A second pass with the combine harvester with a lower cut would pick up the stalks. The fibers and pith could be separated with suitable cyclone type equipment. The re-

Fig. 9. Glued joint under the scanning electron microscope

198

Flexion to breakage

Compression by 1 mm

Cohesion

Materials fabricated under zero pressure from piths from various sources (8 g pith+8 g H2O)

Density

Breaking strength/ thicknes (kg mm−1)

Slope (kg mm−2) Strength (kg)

Residual sag (mm)

Strength/thickness (kg/mm)

Sunflower Kenaf Sorghum Corn

0.33 0.11 0.16 0.18

1.2 0.3 0.5 0.6

0.4 0.2 0.2 0.4

0.31 0.39 0.26 0.25

3.4 1.5 4.0 2.5

5.2 1.6 2.1 2.4

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Table 10 Parameters of various agromaterials from different plant sources

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

199

Fig. 10. Possible commercial uses of various sunflower products

Acknowledgements We would like to thank Messrs Puech and Gelfi for supply of the raw materials.

References Bartolome, L.G., Hoff, J.E., 1972. Gas chromatographic methods for the assay of pectin methylesterase, free methanol, and methoxy groups in plant tissues. J. Agri. Food Chem. 20 (2), 262–266. Blumenkrantz, N., Absoe-Hansen, G., 1973. New method for quantitative determination of uronic acids. Anal. Biochem. 54, 484 – 489. Bradstreet, R.B., 1967. The Kjeldahl method. Academic Press, London, p. 167. Colin, H., Lemoine, S., 1940. La matie`re uronique de la moelle de tournesol. Compt. Rend. Acad. Sci. 211, 44–47. Campbell, S.J., Sosulski, F.W., Sabir, M.A., 1978. Development of pectins in sunflower stalks and heads. Can. J. Plant Sci. 58, 863 – 868. Chang, K.C., Miyamoto, A., 1992. Gelling characteristics of pectin from sunflower head residues. J. Food Sci. 57 (6), 1435 – 1438. Choudens, C., Angelier, R., Brochier, B., Labalette, F., 1996. Manufacture of unbleached high-yield pulps for packaging papers by the bivis process from fibre sorghum. First European Seminar on Sorghum for Energy and Industry, Toulouse, Proceedings, 1–3 April.

Choudens, C., Angelier, R., 1996. The bivis process and the annual plants (wheat straw and fibre sorghum) for the manufacture of pulps for packaging papers. Fourth European Workshop on Lignocellulosics and pulp, Stresa, Proceedings, 8 – 11 September. Cunningham, R.L., Carr, M.E., Bagby, M.O., 1986. Hemicellulose isolation from annual plants. Biotechnol. Bioeng. Symp. 17, 159 – 168. Dubois, M., Gilles, K.A., 1956. Colorimetric method for determination of sugar. Analyt. Chem. 28 (3), 350 – 356. Heiser, C., 1976. The Sunflower. University of Oklahoma Press, Norman, Oklahoma, pp. 69 – 78. Hollo, J., 1987. Le tournesol en Hongrie: recherches, technologie et produits. Rev. Fr. des Corps Gras 34 (5/6), 259 – 266. Jimenez, L.A., Lopez, F.B., Sanchez, I.P., 1991. Characterization of cellulose pulp from agricultural residues. Tappi J. 74 (1), 217 – 221. Jimenez, L.A., Lopez, F.B., 1993. Characterization of paper sheets from agricultural residues. Wood Sci. Technol. 27, 468 – 474. Kim, W.J., Sosulski, F.W., 1978. Formulation and characteristics of low-ester gels from sunflower heads. J. Food Sci. 43, 746 – 749. Kim, W.J., Sosulski, F.W., Lee, S.C.K., 1978. Chemical and gelation characteristics of ammonia-demethylated sunflower pectins. J. Food Sci. 43 (5), 1436 – 1439. Lawther, J.M., Sun, R., Banks, W.B., 1995. Extraction, fractionation, and characterixation of structural polysaccharides from wheat straw. J. Agric. Food Chem. 43, 667 – 675.

200

V. Marechal, L. Rigal / Industrial Crops and Products 10 (1999) 185–200

Lin, M.J.Y., Sosulski, F.W., Humbert, E.S., Downey, R.K., 1975. Distribution and composition of pectins in sunflower plants. Can. J. Plant Sci. 55, 507–513. Lin, M.J.Y., Humbert, E.S., Sosulski, F.W., 1976. Extraction of pectins from sunflower heads. Can. Inst. Food Sci. Technol. J. 9, 70 – 74. Manolas, C., 1993. Fractionnement du sorgho a balai (broom Sorghum), Thesis, INP Toulouse. McGovern, J.N., Coffelt, D.E., Hunter, A.M., Ahuja, N.K., Wiedermann, A., 1987. Other fibers. In: The joint textbook committee of the paper industry (Editors), Pulp and Paper Manufacture, Vol. 3: Secondary Fibers and Non-wood Pulping, 3 ed, 119 – 121. N’Diaye, S., 1996. Fractionnement de la matie`re ve´ge´tale: Mise au point d’un proce´de´ Thermome´canochimique et Mode´lisation du fonctionnement du re´acteur bi-vis, Thesis, INP Toulouse. Pathak, D.K., Shukla, S.D., 1981. Quantity and quality of pectin in sunflower at various stages of maturity. J. Food Sci. Technol. 18, 116–117. Riaz, S., Uddin, M., 1972. Polysaccharide components of sunflower heads: I: the pectins. Pak. J. Sci. Ind. Res. 15, 167 – 170. Rigal, L., Mannolas, C., N’Diaye, S., Gaset, A., 1996. Fractionnement du Sorgho a` fibre: Valorisation de la moelle pour la fabrication d’agromate´riaux. Proce´de´s de de´moel-

.

lage en re´acteur bi-vis. First European Seminar on Sorghum for Energy and Industry, Toulouse, Proceedings,1 – 3 April. Sabir, M.A., Sosulski, F.W., Campbell, S.J., 1976. Polymetaphosphate and oxalate extraction of sunflower pectins. J. Agri. Food Chem. 24, 348 – 350. Shewfelt, A.L., Worthington, O.J., 1953. The extraction of pectin from sunflower heads. Food Technol. 7, 336 – 340. Sosulski, F.W., Lin, M.J.Y., Humbert, E.S., 1978. Gelation characteristics of acid-precipitated pectin from sunflower heads. Can. Inst. Food Sci. 43, 572 – 575. Thompson, N.S., 1981. Chemical from hemicellulose. In: Goldstein, I.S., (ed.), Organic Chemicals from Biomasss, CRC Press, Boca Raton, FL, 125 – 141. Tieman, D.M., 1992. An antisense pectin methylesterase gene alters pectin chemistry and soluble solids in tomato fruit. The Plant Cell 4, 667 – 679. Van Soest, P.J., Wine, R.H., 1963. Use of detergents in the analysis of fibrous feeds IV: determination of plant cell wall constituents. J. AOAC 46 (5), 830 – 835. Van Soest, P.J., Wine, R.H., 1968. Determination of lignin and cellulose in acid detergent fiber with permanganate. J. AOAC 51 (4), 780 – 785. Zitko, V., Bishop, C.T., 1966. Structure of a galacturonan from sunflower pectic acid. Can. J. Chem. 44, 1275 – 1282.