PC and cassava starches were similar regarding gross chemical composition and basic physical ... agronomic yields achieved under low technology field.
TECNOLOGIA DE ALIMENTOS Acta Científica Venezolana, 50: 240–244, 1999
CHEMICAL, PHYSICAL AND MORPHOMETRIC PROPERTIES OF PERUVIAN CARROT (Arracacia xanthorrhiza B.) STARCH Elevina E. Pérez 1 , Rafael Borneo 1 , Carmelo G. Melito 2 and Juscelino Tovar 2 1. Instituto de Ciencia y Tecnología de Alimentos, Facultad de Ciencias, Universidad Central de Venezuela, P.O. Box 47069, Caracas 1041-A, Venezuela. 2. Instituto de Biología Experimental, Facultad de Ciencias, Universidad Central de Venezuela, P.O. Box 47069, Caracas 1041-A, Venezuela.
Recibido: 23/07/99 ; Revisado: 22/09/99 ; Aceptado: 05/10/99 ABSTRACT: Starch was isolated from Peruvian carrot (PC) -or arracacha- (Arraccacia xanthorrhiza B.) roots. Its chemical, physical, physicochemical and granular structural properties were compared to those of commercial cassava starch. Scanning electron microscopy revealed a granular size for PC starch ranging between 4 and 26 m in diameter, with spherical and truncated-egg shapes. PC and cassava starches were similar regarding gross chemical composition and basic physical characteristics but differed in pasting properties, with PC starch showing lower breakdown and consistency indices. The two starches also showed different water absorption and solubility patterns. Key Words: Arracacia xanthorrhiza, arracacha, cassava starch, Peruvian carrot starch, root starches. CARACTERISTICAS QUIMICAS, FISICAS Y MORFOMETRICAS DEL ALMIDON DE APIO CRIOLLO (Arracacia xanthorriza B.) RESUMEN: Se aisló el almidón de las raíces frescas de Arraccacia xanthorrhiza B., planta tropical conocida como apio criollo, arracacha o zanahoria blanca. Las propiedades químicas, físicas y morfométricas de este almidón se compararon con las de una muestra comercial de amplio uso industrial, el amidón de yuca. Observados mediante microscopía electrónica de barrido los gránulos de almidón de apio mostraron una mezcla de las formas esférica y oval truncada, con diametros entre 4 y 26 m. Los almidones de yuca y apio resultaron similares en cuanto a su composición química general y principales características físicas, pero se diferenciaron en sus patrones de solubilidad y poder de hinchamiento, así como en las propiedades de sus pastas, siendo la muestra de apio la que mostró valores menores de fragilidad y consistencia viscoamilográficas. Palabras clave: Arracacia xanthorrhiza, arracacha, apio , yuca, almidones de raíces
INTRODUCTION The Peruvian carrot (PC), or "arracacha", is an ancient South-American crop that, as many other species of tubering plants, store starch in their roots as an energy source for vegetative reproduction8 . PC has a short shelf life, which is largely due to the poor post-harvest handling and storage conditions prevailing in the countries where it is produced10 . In South America it is consumed after roasting or boiling by domestic methods and only minor industrial uses have been attempted. The high starch content of this root, which ranges between 20 and 25% (wet basis)8 , and the relatively high agronomic yields achieved under low technology field conditions14 make it suitable as a potential starch source for large scale uses. The present study was therefore undertaken to characterize starch isolated from arracacha roots grown in Venezuela, and examine some of its chemical, physical and morphometric properties. Figure 1. SEM Photomicrograph of peruvian carrot starch. Bar size 20 m.
241
Characterization of Peruvian carrot starch Tabla 1. Composition of Peruvian carrot (PC) and cassava (C) starches (% dry basis). Component Moisture Total starch Crude protein Crude fiber Ash Crude fat Fatty substances Bound fat Total sugars Reducing sugars Non reducing sugars Apparent amylose Apparent amylopectin Phosphorus Phosphate
PC Starch 14.00 97.87 0.05 0.25 0.13 0.07 0.10 0.03 1.6 1.5 0.1 38.5 61.5 0.063 0.194
0.12 0.01 0.02 0.01 0.02 0.02 0.02 0.06 0.06 0.03 1.3 1.5 0.01 0.01
Tabla 2. Chemical, physical and physicochemical properties of Peruvian carrot (PC) and cassava (C) starches.
C Starch 10.20 99.46 ND 0.11 0.10 NE 0.25 NE 0.08 0.07 0.01 37.3 62.7 0.010 NE
Properties
0.10
PC Starch C Starch
pH Acidity (meq/g.) 10 4 Absolute density (g/ml) Aw Syneresis
0.01 0.02 0.02 0.05 0.02 0.01 1.3 1.4 0.01
7
5.6
3
13
1.4032 0.602 None
1.445 NE None
1) Æ C; NE: Not evaluated.
* Available water, measured at 26 (
Values are means of at least 4 independent determinations standard deviation. * Calculated by subtraction. ND: Not detected; NE: Not evaluated.
MATERIALS AND METHODS Samples Peruvian carrot (Arracacia xanthorrhiza B.) roots were purchased from the local market in Caracas. Manually decorticated roots were used for the isolation of starch, following the general method described by Pérez et al.9 as modified recently for root materials10 . Commercial cassava starch was provided by Alfonzo Rivas & Co., C.A. (Caracas). Chemical properties Moisture, crude protein (N 6.25%), crude fiber, ash, and total, reducing and non reducing sugar contents of the isolated starches were determined by AACC methods1 . Total fatty substances were estimated according to Schoch15 . Crude fat content of the starch samples was estimated after extraction with hexane at 100Æ C according AOAC2 and bound lipids were calculated as the difference between fatty substances and crude fat. For assessing phosphorus and phosphate contents, the method of Smith17 was followed. Total starch was calculated as the dry matter content minus the sum of crude protein, fatty substances, crude fiber, total sugar and ash. Apparent amylose content was estimated after iodine complexation, using potato amylose as standard6 . Amylopectin content was calculated as total starch minus amylose. Physicochemical properties Density, pH and acidity (expressed as meq/g) were assessed after Smith17 . Available water (Aw) was measured using the Aqualab CX-2 equipment (Decagon Dev. Inc. Pullman, WA). Syneresis of starch gels was qualitatively
Figure 2. Solubility (A) and water absorption (B) of Peruvian carrot ( ) and cassava ( ) starches.
4
assessed after overnight storage at 30Æ C. Water binding capacity, swelling power and solubility determinations were carried out over the 65 - 90Æ C range, at 5Æ C intervals, according to Schoch16 . Apparent viscosity of 8% (w/w) starch suspensions was measured by means of the Brookfield viscosimeter; samples were heated at 30Æ C or 50Æ C and the assessment was performed using spindle NÆ 4 operating at 6, 12, 30 and 60 rpm17 . Pasting properties were determined with the Brabender Viscoamylograph according to AACC1 , and the breakdown, setback and consistency indices were calculated from the corresponding plots7 . Values were expressed in Brabender units (BU). Scanning Electron microscopy Granular shape and size were studied by scanning electron microscopy (SEM). Starch was sprinkled on adhesive tapes, attached to circular specimen stubs, coated with 200 Å of gold/palladium using a Hitachi E 102 Ion sputter, examined at 20.0 kV, and photographed in a Hitachi S 2400 scanning electron microscope. The starch granule diameter range was estimated by measuring 20-30 randomly selected granules from duplicated micrographs11 .
242
Pérez, Borneo, Melito y Tovar Tabla 3. Apparent viscosity of Peruvian carrot (PC) and cassava (C) starches as a function of shear stress. Shear stress PC C (rpm) starch starch 6 12 30 60
28500 15830 8370 5420
16830 11250 7000 5020
Values are expressed in centipoises (cps). Determinations were performed at 30 Æ C.
Figure 3. Swelling Power of Peruvian carrot starch.
RESULTS AND DISCUSSION Table 1 compares the chemical and physical features of isolated peruvian carrot (PC) starch and those of a widely used commercial root starch, i.e. cassava. Moisture content was higher in PC than in cassava starch; however, it fell within an acceptable range for extended shelf life. In spite of the fact that all minor components, such as crude protein, crude fiber, fatty substances, and total sugars were more abundant in PC starch, it showed a reasonable purity as evaluated from the total starch content (97.9%). The results also showed the presence of bound fat in PC starch, a constituent probably located within the granular structure. PC starch showed higher reducing and non reducing sugar content than cassava starch, which might be due to the difference in parental materials. Amylose and amylopectin values in PC starch were comparable to those found in the cassava reference, although the apparent amylose content in the latter seems higher than usual. This stresses the limitations of iodine-complexation techniques for analyzing heterologous starches. Phosphorus and phosphate concentration in PC starch were higher than in casava starch, but not too different from those reported for other starch preparations 3;18 . The diameter of PC starch granules ranged from 4 to 26 m, showing spherical to truncated egg-shape (Figure 1). Table 2 summarizes some of the physical and physicochemical properties of PC and cassava starches. PC was considerably less acidic than the cassava reference,
Figure 4. Relationship between Swelling Power and solubility of Peruvian carrot starch.
something that may contribute to the minor functional differences described below. The two samples showed similarities in pH and density values, as well as in their low syneresis tendency. All these properties were comparable to those of other root starches3;5;10;11 and, on the overall, revealed only slight differences between PC and cassava starches. Figure 2 depicts the water absorption and solubility patterns of PC and cassava samples. Water absorption of PC starch was slightly lower (Figure 2B). This difference may be due to unequal ratios of crystalline to amorphous regions within the granule4;10 . Thus, having a lower proportion of weakly bound amorphous material, PC would presumably imbibe less water. Similarly, the solubility patterns (Figure 2A) indicated that although PC starch leached more soluble matter into the solvent than cassava starch at low temperatures, the opposite behavior was observed
243
Characterization of Peruvian carrot starch
70Æ C,
above a fact that indicates a greater stability for PC starch. PC starch exhibited a marked two-stage swelling pattern (Figure 3), where an initially rapid swelling – between 70 and 80Æ C – was followed by a slower change after 85Æ C. PC starch displayed a rapid release of soluble matter into the liquid, particularly above a swelling power of 40 (Figure 4). The observed differences in physicochemical features between PC and cassava starches may be explained by slight inherent structural and molecular dissimilarities. Tabla 4. Rheological properties of Peruvian carrot and cassava starches.
Parameter Gelatinization temperature range (Æ C) Initial Final Viscosity (B.U.) Initial Peak viscosity (P) Final viscosity (95Æ C;30 min.) (H) Cooled to 50 Æ C (C) Final viscosity (50Æ C;30 min.)
61 70.5
0 760
0 900
740 540
380 400
620
420
20
520
Setback (C-P)
-220
-500
Consistency (C-H)
-200
20
Breakdown (P-H)
Interestingly, in PC by using other physical starch the viscosity peak was reached during the holding time at 95Æ C and the preparation exhibited lower breakdown and consistency indices than cassava starch. Again, differences in the pasting characteristics of both starches seem to reflect stronger molecular associations stabilizing cassava starch granules. The more marked setback registered for PC starch gels (Table 4) might be indicative of differences in molecular size between this and cassava starch. Apparent viscosity measurements support this appreciation, since PC starch consistently developed greater viscosity than the cassava sample (Table 3). CONCLUSION
PC Starch C Starch
60 95
methods10 .
Data collected in Table 3 suggest that PC and cassava starches display a characteristic pseudoplastic nonNewtonian fluid behavior at 30Æ C5 . A similar tendency was observed at 50Æ C (data not shown), but apparent viscosity values were significantly lower. The visco-amylographic properties of the starches were also studied (Table 4). At the concentration analyzed, no difference was found in the initial pasting temperatures, but the final points differed significantly, with a much higher value for the PC sample. Such a wide temperature range for the gelatinization of PC starch has also been noticed
Peruvian carrot starch shows spherical and truncated-egg granules that range between 4 and 26 mm. Isolated to 98% purity, its chemical composition is similar to other root starches. It is also comparable to cassava starch in most physical properties. Some differences in rheological features were observed between PC and cassava starches, which may be due to inherent structural and molecular dissimilarities. The relatively high and stable viscosity developed by PC starch during cooking, together with its limited retrogradation/syneresis proclivity could make it suitable in the formulation of instant products, such as dehydrated soups and puddings. Since these possibilities might be magnified through a number of modification techniques, complementary studies on physical and chemical modifications of PC starch and its digestibility features are in progress. ACKNOWLEDGMENTS Financial support from Consejo de Desarrollo Científico y Humanístico de la Universidad Central de Venezuela (Grants 03-10-2725-92 & 03-10-0107-93), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICIT, Grant S1-2501) and International Foundation for Science (IFS, Grant E/2009-2) is gratefully acknowledged.
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