Physicochemical and functional properties of Canna edulis starch

(Running title: Properties of Canna edulis starch)

S.N.Moorthy, B. Vimala and Archana Mukherjee.
Central Tuber Crops Research Institute, Sreekariyam, Trivandrum, 695 017, INDIA

Abstract

Key words: Canna edulis, starch, rheology, swelling, arrowroot.

Introduction

Apart from the major root crops like cassava, sweet potato, aroids and yams, many types of rhizomatous and tuberous root crops are grown in different countries including India. Queensland arrowroot (Canna edulis) is a perennial herb grown in many countries for its edible rhizome (Joseph and Peter, 1985) . According to Hermann (1994), the bakery products prepared from canna starch are much lighter, and crisper than those from wheat. This Institute has three accessions of Canna edulis classified from the leaf colour as green, purple and dark purple. Only the tubers of dark purple accession are consumed since the others are fibrous and contain large quantity of phenols. This paper describes the physicochemical and functional properties of starch isolated from these three accessions.

Materials and methods

The rhizomes were harvested at ten months stage, washed, peeled and pulped in a Remi blender with 10 vol. of water. The pulp was mixed with 5 vol. water , strained through a 150 mesh sieve and allowed to settle. Resuspension and resettling were carried out several times and the deposited cake was dried in sunlight and stored in moisture proof containers.

Starch granule size was measured microscopically using ocular and stage micrometer at X120 . Dry matter and starch contents were determined by AOAC (1975) procedures and total and soluble amylose contents by the methods of Sowbhagya and Bhattacharya (1971) and Shanty et al. (1980) respectively, X-ray diffraction analysis on a Phillips X-ray diffractometer using CuKα radiation. Viscosity measurements of the starch pastes at 3,4 and 5% concentrations were carried out on a Brabender Viscograph model 801020 using 350 mcg cartridge with heating at 1.50C /min. Viscosity of a 1% starch solution was measured on a Redwood No 1 Viscometer. A 10% solution was studied in the Rapid Visco Analyser ( Model 4, Newport Scientific) in triplicate with heating from 50 to 950C at 120C/min, holding at 950C for 2 min, cooling back to 500C at 120C/min. Swelling volume was determined as described by Moorthy (1994). The clarity and paste stability were measured on 1% solutions. Phosphorus was determined by the vanadomolybdate method (Jackson, 1967)

Results and Discussion

There was a large variation in the dry matter content of three accessions (Table 1) from 20-35%. Kay (1987 ) reported 28-33% for Canna edulis tubers. The starch content also varied, but the value for dark purple accession was close to that of cassava and sweet potato.

The starch granules are quite large 35.5 to 43.5μm. Previous reports vary considerably. Fujimoto et al. (1990) obtained an average size of 45.8μm, but Soni et al. (1990) found 13 to 17 μm; a maximum granule size of 140μm was given by Kay (1987). Photomicrographs showed that granules are oval and polyhedral as reported by Kay (1987) and Soni et al. (1990)

The X-ray diffraction pattern is of type ‘B’, as reported by Fujimoto et al. (1990), as is yam starch. The amylose content is 24-30 %, similar to the 27% of Ishii et al. (1991), but lower than the 38% of Soni et al. (1990) . All these values are higher than most other tuber crops (Moorthy, 1994). The soluble amylose is nearly 40% of the total, as in all the other tuber starches.

The solution viscosity is 65 – 100 sec (Table 1), higher than other tropical tuber starches: cassava starch normally has a value 50-60 sec for a 2% solution (Moorthy 1985). The Brabender data are higher than those reported by Nagahama and Troung (1994 : 650 BU for 6% paste) and Soni et al. (1990: 500 BU for 5% paste) and also higher than other tuber starches The starch exhibits very low viscosity breakdown. On cooling, the paste is non-cohesive in texture and sets into a strong gel free from syneresis. Thus the starch will be valuable in food applications. For C. edulis starch, Perez et al. (1998) obtained a peak viscosity of 300BU for a 4% paste and negative breakdown and high setback. We confirmed the low breakdown, but we did not observe the high setback .

All three accessions continue to gelatinise even after 950C, showing that the starch possesses strong associative linkages. A similar result was reported by Soni et al. (1990), while Nagahama and Troung (1994) found that gelatinisation occured at 710C . These characteristics resemble yam starch. The RVA patterns do not coincide with the Brabender (Table 1), as they indicate a similar but noticeable breakdown for all three starches with a lower setback for the purple accession. In contrast to the Brabender data, Perez et al. (1998) obtained high viscosity breakdown and low setback for their C. edulis starch. The solution properties (Table 1) show that all the accessions have lower swelling volumes than the 23.5 ml/g at 800C reported by Nagahama and Troung (1994). The clarity and solution stability are high as for yam and cassava starches. The phosphorus contents in are high as reported by Nagahama and Truong (1994), whereas Soni et al. (1990) found much lower values.

These Canna edulis starches resemble yam in most functional properties. The starch has good potential in food applications because of the high viscosity and gel strength especially in canned foods that require high paste stability (Smith, 1982).

Table 1 : Dry matter, starch content, granule size and amylose content in the starch

Accession Dry matter (%) Starch (%) Total amylose (%) Soluble amylose (%) Granule size (μm)
Dark purple 35.71±1.21 27.03±0.98 24.16±01.09 10.02±0.56 35.5±10.19
Purple 28.18±0.88 20.0±0.78 30.3±0.99 11.98±0.81 43.5±11.98
Green 20.33±1.01 12.33±0.71 27.62±1.10 11.05±0.78 36.9±12.38

Table 2: Brabender Viscosity properties of Canna starch

  Solution Viscosity (sec) Peak Viscosity (BU) Viscosity at 95 0C (BU) Viscosity after holding at 950C (BU) Pasting temperature(0C)
Starch Conc.   4 4 4 4
Dark Purple 65 700 720 950 72 – 97
Purple 80 650 700 750 79 – 95
Green 100 700 780 900 76 – 95

Table 3 : RVA viscosity properties of Canna starch

Starch Peak Viscosity* Trough Viscosity* Final Viscosity* Pasting Temperature**
Dark purple 3952 2652 3571 74.65
Purple 4187 2830 3466 74.20
White 3888 2665 3550 75.55

* cP units, mean of three replications
** 0C

Table 4 : Swelling volume, clarity, stability and P content of the starch

  Swelling volume ml/g Clarity Absorbance Paste Stability (h) P content ppm
Dark purple 12.25 0.152 68 876
Purple 14.33 0.20 72 801
Green 10.85 0.202 64 507

References

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  16. Simplified colorimetric method for determination of amylose content in rice, Staerke/Starch, 23 , 53-56.

Table 5. Physicochemical properties of the Canna edulis starch

Accession Dark purple Purple Green
Dry matter (%) 35.71±1.21 28.18±0.88 20.33±1.01
Starch (%) 27.03±0.98 20.0±0.78 12.33±0.71
Total amylose (%) 24.16±01.09 30.3±0.99 27.62±1.10
Soluble amylose (%) 10.02±0.56 10.02±0.56 11.05±0.78
Granule size (μm) 35.5±10.19 43.5±11.98 36.9±12.38
Viscosity (sec) 1% 65 80 100
Brabender Peak Viscosity (BU) 4% 700 650 700
Viscosity at 95 0C(BU) 4% 720 700 780
Viscosity after holding at 950C (BU) 4% 950 750 900
Pasting temperature(0C) 4% 72-97 79-95 76-95
RVA Peak Viscosity (cP) 3952 4187 3888
Trough Viscosity (cP) 2652 2830 2665
Final Viscosity (cP) 3571 3466 3550
Pasting Temperature (0C) 74.65 74.2 75.55
Swelling volume (ml/g) 12.25 14.33 10.85
Clarity (Absorbance) 0.152 0.2 0.202
Paste stability (h) 68 72 64
P content ( ppm) 876 801 507