Functional Properties of Cassava Tapioca Grits

Abstract

This study investigated the functional properties of tapioca grits produced from wet starches from 39 different cassava varieties (36 cassava mosaic disease resistant varieties CMD clones and 3 checks TMS 30572, 4(2) 1425 and 82/00058). There were significant differences (p < 0.05) for functional properties of tapioca grits from different cassava varieties. Dispersibility of tapioca ranged from 6–29%, water absorption capacity (WAC) ranged from 415.13–595.26%, swelling power ranged from 20.76–26.92%, solubility index ranged from 4.04–20.42%, color intensity ranged from 87.79–92.09%. Granule size of pre-gelatinized tapioca ranged from 12.50–22.50 μm. Significant differences (p < 0.05) were obtained on the effect of cassava varieties, viscometer speeds and temperature of tapioca meal. The viscosity of the tapioca meal decreased (37.90–0.72 Pa.s) with increasing shear rates at both 30 and 40°C, but higher for lower temperature respectively. Tapioca meal produced from cassava variety M98/0028 had the highest viscosity 37.90 Pa.s at 13.66 (s^-1).

Keywords:

• Tapioca
• Starch
• Properties
• Functional
• Rheological

INTRODUCTION

Cassava is an important root crop in many tropical countries, where the starchy and tuberous roots are eaten in various forms, including as starch and flour.[1] Cassava starch is the product obtained by steeping and wet milling of the root.[2] The major reasons for the importance of cassava starch has been its easy extraction, rapid sedimentation, clarity of paste, neutral flavor, light color and reasonably good adhesive strength.[3,4]

In Nigeria, tapioca refers to roasted cassava starch made from partially gelatinized cassava starch through application of heat treatment to moist starch in shallow pans.[5] It has a status of smuggled product in Nigeria.[6] Tapioca grits appears as flakes or irregularly shaped granules, which is usually soaked and cooked in water and sugar/milk added. Tapioca has continued to be popular in Nigeria as a breakfast meal and sometimes is eaten with akara balls (a product from cowpea) as a complement.

A number of reports are available in the literature on tapioca from cassava roots.[5,7] However, very scanty attempts have been reported on the quality properties of tapioca grits. Moreover, breeders at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, have developed some resistant cassava varieties to prevent the spread of cassava mosaic disease (CMD) in the country.[8] In a bid to find additional utilization to the newly bred cassava clones, research efforts have been focused on evaluating them for potential food and industrial applications. For example, Shittu et al.[9] evaluated about 43 CMD clones for flour making purpose. They classified the cassava clones based on the yield and some functional characteristics of their flour. Similar attempt is also required for some other cassava products like tapioca that have high commercial values. Generally, the rheological property of a food system is dependent on the composition, cooking system or the ingredients of the system.[10,11] This paper reports our findings on the functional and rheological properties of tapioca grits from some newly developed CMD resistant cassava varieties.

MATERIALS AND METHODS

Cassava Varieties

A total of 36 newly developed CMD- resistant clones of cassava with 3 susceptible (existing) cassava varieties were obtained from a trial plot of the IITA, high rainfall planting area, Onne, Rivers State, Nigeria. Onne (Lat 4.4^oN, Long 7.1^oE) has a mean annual rainfall of 2600 mm. The cassava varieties were planted during the rainy season (June 2003/2004 and 2004/2005) in a randomized complete block design with three replications. No fertilizers or herbicides were applied during the course of the experiment. Hand weeding was done when necessary. Harvesting was done at 12 months after planting (MAP). Only the two middle rows were harvested/plot and cassava roots processed were collected from only one replication. Processing of the harvested cassava roots commenced within 60 min after harvesting.

Preparation of Starch

The method described by Osunsami et al.[12] was used for the production of various cassava starches. The cassava roots were harvested from the farm and washed to remove dirt from the skin. Ten kg of freshly harvested cassava roots/clone were peeled manually using a stainless steel knife and washed thoroughly with potable water to remove dirt and adhering sand particles. The peeled roots were grated and sieved. The mixture was filtered through a fine mesh sieve (muslin cloth). The filtrate was allowed to settle for about 6 hours. The supernatant was decanted and sediment washed three times with potable water to obtain a white, odorless, and tasteless starch. The resultant wet starch was thinly spread over a black high density polyethylene (HDPE) according to Shittu et al.[9] in the open air for drying under ambient conditions (28–30°C, 70–80% RH) for five hours. The dried cake was milled using a locally fabricated hammer mill (IITA, Ibadan) fitted with a screen of 250 μm aperture size and packaged using food grade polyethylene bags and kept in the cold room (at about 4°C) for laboratory analysis.

Preparation of Tapioca

Wet starch was produced using the method described by Osunsami et al.[12] and used in the production of tapioca. The moist starch (m.c. 0.4 g/100 g sample) was roasted in a flat hot pan with constant stirring at 120–150°C for 20 minutes. Vegetable oil was used to rub the pan before roasting to prevent stickiness and burning.[13] The end of the roasting was determined by squeezing the resultant tapioca on the palm to test for dryness. After roasting, the tapioca was spread on a tray to cool and sample taken to the laboratory for analysis.

Functional Properties

The starch damage was determined using the extractability method of McDermott.[14] The extractant and iodine solutions were first prepared before the determination. Samples of 0.5 g were weighed into dry 100-ml conical flasks and placed in a water bath at 30°C to equilibrate. To each sample 20 ml of extractant, pre-heated at 30°C, was added and shaken for 10 s every three minutes. The slurry was filtered through 11 cm diameter Whatman No.1 filter paper into test tubes. Then 2 ml of the filtrate was pipetted into a 25 ml volumetric flask already containing 15 ml of distilled water, 1.0 ml of iodine solution was added, made up to the 25 ml mark with distilled water (21 ± 0.5°C), mixed and left for 10 minutes. Absorbance was read on a spectrophotometer already standardized with blank at 600 nm wavelength: degree of starch damage = 0.286 + 50.3 (Absorbance).

Swelling and solubility of starches were determined as described by Ruales et. al.[15] It involved weighing 1 g of tapioca into a 50-mL centrifuge tube, then 50 mL of distilled water was then added and mix gently. The slurry was heated in a water bath at 70–100°C respectively for 15 min. During heating, the slurry was stirred gently to prevent clumping of the flour. On completion of 15 min, the tubes containing the paste were centrifuged at 3000 rpm for 10 min. The supernatant was decanted immediately after centrifuging. The weight of the sediment was determined. The moisture content of the sedimented gel was thereafter determined to get the dry matter content of the gel.

Least gelation capacity was determined according to Sathe and Salunkhe.[16] 2–20% suspension (w/v) in 5 mL distilled water were prepared in test tubes. The test tubes containing the suspensions were heated in a boiling water bath for 1 h. The tubes and content were then cooled rapidly under running cold water. The test tubes and content were further cooled for 2 h at 4°C. The tubes were then inverted to see if the content would fall or slip off. The least gelation concentration is that concentration when the sample from the inverted test tube does not fall or slip off.

Method employed for water absorption capacity was described by Sosulski.[17] Fifteen mL-distilled water was water to 1 g of tapioca grits in a pre-weighed centrifuge tube. The centrifuge tube and content was agitated on a STUART scientific orbital shaker (Redhill, Surrey, UK) for 2 min and centrifuged at 4000 rpm for 20 min on a STUART scientific, SPECTRA (Merlin 503, Redhill, Surrey, UK) centrifuge. The clear supernatant was discarded and the centrifuge tube was weighed with the sediment. The amount of water bound by the grit was determined by difference and expressed as the weight of water bound by dry flour (100 g). Color was determined as described by Francis.[18] The average granule size and starch structure were determined based on method described by Kawabata et al.[19] using a light microscope (Laborlux S, Lectz Wetzlar Germany 513558) and computerized microscope (Olympus DP 50, BX51, Japan), respectively.

Rheological Measurements

Tapioca sample (45 g) was weighed into a 600-ml beaker; 225 ml of water (i.e., 1:5) was added to the sample and allowed to soak overnight. The soaked sample was cooked for 5 min in 300 ml of water with constant stirring. All viscosity measurements were carried out immediately after cooking the tapioca meal. The viscosity of difference samples were measured in triplicates at different speeds (10, 20, 30, 50, and 60 rpm) for 20 sec. Viscosity was determined by calculation following the procedure developed by Mitschka[20] and Adebowale[11], at two temperatures (40°C and 30°C) with spindle number 6, using a digital rotational Brookfield Viscometer (Brookfield Engineering Laboratories, Middlebow, USA, Model DV-E). Since the viscometer does not give direct shear rate and shear stress values for disc-type spindles, shear rate and shear stress values were obtained from the torque-rpm readings by calculation following the procedure developed by Mitschka.[19] The method involves taking measurements of many pairs of torques (α_i) with a spindle for fixed values of viscometer speed N _i (rpm). Values of α_i were converted to shear stresses τ_i (Pa) using Eq. 1.

(1)

Values of log τ_i were then plotted against log N _i. The slope of the graph (n) was then calculated. The corresponding values of the shear rates (s^-1) were then calculated using Eq. 2.

(2)

The conversion factors of 2.35 and 0.36 were used for kατ and k_Nγ for spindles #6 as reported by[11,19].

Data Analyses

Descriptive analysis and two-way analysis of variance (ANOVA) were performed to explore the general trend of the experimental data. Mean separation were performed on the analysed data using Duncan's multiple range test with the aid of SAS version 9.1 software[21].

RESULTS AND DISCUSSION

Table 1 shows the functional properties of tapioca from cassava starch from CMD resistant varieties. There were in general significant differences (p < 0.05) in the functional properties of tapioca grits from cassava varieties. Dispersibility of tapioca ranged from 6–29%, water absorption capacity (WAC) values ranged from 415.13–595.26%, swelling power ranged from 20.76–26.92%, while solubility index ranged from 4.04–20.42% showing a decrease in solubility, while color intensity values ranged from 87.79–92.09%. Values of water absorption capacity (415.13–595.26%) are within values (231–610%) reported by Sanni et al.[6] for tapioca grits. The variability in the values may be due to seasonal, maturity and environmental factors for cassava varieties used for the tapioca studies respectively. Water absorption capacity is important in bulking and consistency of products as well as in baking applications. Granule sizes are reported to influence water absorption. Small granules have higher solubility and hence enhanced water absorption capacity.[22]

Table 1 Functional properties of tapioca grits from 39 CMD-resistant varieties

CMD variety	Dispersibility(%)	Water absorption capacity (%)	Swelling power (%)	Solubility (%)	Color
30572	19.00	488.49	23.42	9.22	91.61
4(2)1425	21.00	478.46	24.14	11.21	90.18
82/00058	20.00	479.82	23.47	6.30	90.86
91/02324	20.00	548.73	23.12	9.44	90.71
92/0067	23.00	448.00	25.73	15.88	87.79
92/0325	18.00	455.97	23.64	9.45	89.47
92/0326	29.00	503.34	21.90	7.07	88.71
92B/00061	20.00	428.41	22.90	5.82	89.61
92B/00068	20.00	478.99	22.81	6.56	87.80
94/0026	18.00	479.59	24.19	15.83	89.38
94/0039	25.00	442.57	21.96	9.43	90.25
94/0561	29.00	519.03	21.51	7.49	90.83
95/0166	23.00	466.37	23.20	9.11	90.78
95/0289	29.00	415.13	22.47	12.63	91.31
96/0523	19.00	540.25	23.14	10.65	92.09
96/0603	20.00	599.26	26.23	20.42	90.66
96/1089A	21.00	472.55	24.17	8.45	89.51
96/1632	29.00	554.60	20.76	6.63	91.93
96/1642	24.00	460.15	26.92	20.42	90.25
97/0162	16.00	473.73	23.39	10.03	91.29
97/0211	21.00	504.59	23.39	11.20	89.57
97/2205	21.00	477.99	26.17	6.35	87.82
97/3200	19.00	453.17	23.33	5.71	91.55
97/4763	21.00	428.24	22.74	7.47	91.81
97/4769	28.00	438.55	23.75	12.05	91.26
97/4779	29.00	439.56	24.20	15.13	91.72
98/0002	18.00	536.39	23.25	7.49	91.96
98/0505	20.00	493.03	22.13	9.26	91.64
98/0510	21.00	459.04	23.91	8.49	90.55
98/0581	22.00	525.30	20.99	4.04	91.02
98/2101	18.00	435.43	21.46	8.18	91.22
98/2226	19.00	562.73	23.35	8.20	91.60
99/2123	19.00	431.93	21.68	8.49	91.24
99/3073	6.00	523.85	23.52	8.09	90.64
99/6012	19.00	495.05	22.98	15.83	91.46
M98/0028	19.00	474.45	23.69	11.19	90.70
M98/0040	21.00	475.21	23.06	12.63	87.82
M98/0068	18.00	461.78	23.90	9.47	90.03
TME419	18.00	472.48	29.01	16.07	88.58
Range	6.00–29.00	415.13–599.26	20.76–29.01	4.04–20.42	87.79–92.09
Mean	21.03	482.62	23.48	10.19	90.44
Std Error	0.71	6.75	0.26	0.62	0.20
Std Dev	4.42	42.15	1.62	3.89	1.26
CV	19.50	17.76	2.61	15.10	1.59
P of variety	**	**	**	**	**
** Significantly different at P < 0.05.

Swelling power of 20.76–29.01% for tapioca falls within the range of 10.3–36.5% reported by Sanni et al.[6] Starch swells on heating in water and the extent of swelling depends on the starch. The swelling power of aqueous suspension of starch is an indication of the strength of the hydrogen bonding between the granules.[22] Cassava has swelling power property in line with its observed viscosity.[23] The swelling of granules and the concomitant solubilization of amylose and amylopectin gradually induce the loss of granular integrity and gives rise to a viscous paste.[24] The swelling power of the samples reflects the extent of associative forces within the tapioca, therefore, the higher the swelling power, the higher the associative forces. The lower swelling power of tapioca was probably caused by damage to the granules during processing. The major factor that controls the swelling behavior of a starch is the strength and character of the micellar network within the granule.[25] In agreement with the above statement, Hari et al.[26] reported that the stronger the internal molecular structure, the higher the temperature required for gelatinization. Generally, wet starch loss its micellar network after subjected to heat treatment during tapioca processing.

Solubility reflects the extent of intermolecular cross bonding with the granule.[26] Solubility values of 4.0.4–20.42% for tapioca agreed with that reported by Onitilo et al.[27] Cassava starch has a higher solubility compared to the other tuber crops, and the higher solubility can be attributed partly to the high swelling it undergoes during gelatinization.[23] Least gelation concentration can be described as a measure of the minimum amount of starch or blends of starch that is needed to form gel in a given volume of water. The higher the least gelation concentration, the higher the amount of the starch needed to form a gel.[13,28] The color intensity of the starches ranging from 87.79–92.09% for tapioca indicates whiteness. Starch extracted under perfect condition is pure white in color and it is an important criterion for starch quality.[3] The color of starch will determine its clarity when gelatinized. Cassava starch is quite transparent and hence has good clarity. The high clarity makes it excellent for food applications. Clarity depends on the associative bonds between the starch molecules in the granule. Cassava starches thus have a better clarity than cereal starches due to weaker associative forces.[23]

Table 2 represents the granule size of the tapioca produced from different cassava varieties. Granule size of pre-gelatinized tapioca ranged from 12.50–22.50 μm with truncated shape unlike the wet starch that has round shape and granule size of 14.38–22.50 μm. In general, there were no significant differences in the size of tapioca (gelatinized wet starch) and native starch. Native and pre-gelatinized granules of cassava starch observed by light microscopy (LM) presented diameters ranging from 12.50–22.50 μm. Granules before heat treatment presented essentially, spherical or truncated hemispherical shapes, which resulted from the dissociation of the compound starch granules during extraction from cassava tubers. The truncated area is characterized by flat, convex, or concave surfaces (Plate 1). Granules gelatinization of native starch to tapioca, light microscopy (LM) images showed some intact granules, granules that have partially lost their granular integrity and completely disrupted granules (Plate 2). After heat treatment, the degree of damaged granules with pores and fissures were more (Plate 2) resulting in the collapse of the granular structure thereby forming structures of irregular and flat shapes. Observations from light microscopy confirm that a thermal disorganization of the starch granules involving several stages occurs during heating.[1, 23] This confirms the study of Ghiasi et al.[29] concerning wheat starch granules where native starch granules partially or totally lost their redial organization after heating was observed. This observation was also reported by Perez et al.[30] that granules of the modified starch (tapioca) were fused together affect heat or physical treatment.

Table 2 Granular size of tapioca grit from 39 CMD-resistant varieties

CMD variety	Granular size of wet cassava starch (microns)	Granular size of tapioca grits (microns)	Shape of wet cassava starch	Shape of tapioca grits
30572	18.13	16.25	Round	Truncated at one end
4(2)1425	17.50	15.00	Round	Truncated at one end
82/00058	15.63	15.00	Round	Truncated at one end
91/02324	16.25	17.50	Round	Truncated at one end
92/0067	16.88	22.50	Round	Truncated at one end
92/0325	19.38	17.50	Round	Truncated at one end
92/0326	15.00	17.50	Round	Truncated at one end
92B/00061	16.25	13.75	Round	Truncated at one end
92B/00068	16.25	16.25	Round	Truncated at one end
94/0026	18.75	12.50	Round	Truncated at one end
94/0039	18.75	16.25	Round	Truncated at one end
94/0561	16.88	15.00	Round	Truncated at one end
95/0166	19.38	18.75	Round	Truncated at one end
95/0289	18.13	16.25	Round	Truncated at one end
96/0523	15.00	17.50	Round	Truncated at one end
96/0603	15.00	17.50	Round	Truncated at one end
96/1089A	15.00	12.50	Round	Truncated at one end
96/1632	22.50	15.00	Round	Truncated at one end
96/1642	14.38	20.00	Round	Truncated at one end
97/0162	18.13	15.00	Round	Truncated at one end
97/0211	14.38	17.50	Round	Truncated at one end
97/2205	17.50	20.00	Round	Truncated at one end
97/3200	16.88	13.75	Round	Truncated at one end
97/4763	15.00	15.00	Round	Truncated at one end
97/4769	16.25	15.00	Round	Truncated at one end
97/4779	15.00	20.00	Round	Truncated at one end
98/0002	16.88	17.50	Round	Truncated at one end
98/0505	19.38	20.00	Round	Truncated at one end
98/0510	15.63	17.50	Round	Truncated at one end
98/0581	17.50	13.75	Round	Truncated at one end
98/2101	19.38	16.25	Round	Truncated at one end
98/2226	16.88	17.50	Round	Truncated at one end
99/2123	18.13	17.50	Round	Truncated at one end
99/3073	18.13	22.50	Round	Truncated at one end
99/6012	15.63	17.50	Round	Truncated at one end
M98/0028	18.13	17.50	Round	Truncated at one end
M98/0040	16.25	17.50	Round	Truncated at one end
M98/0068	15.63	17.50	Round	Truncated at one end
TME419	15.63	16.25	Round	Truncated at one end
Range	14.38–22.50	12.50–22.50
Mean	16.96	16.86
Std Error	0.28	0.37
Std Dev	1.76	2.33
CV	3.09	5.42
P of variety	**	**
** Significantly different at P < 0.05.

Plate 1 Typical native starch granule observed before heat treatment.

Plate 2 Typical tapioca granule observed after heat treatment [gelatinization].

Tables 3 and 4 shows the viscosity of tapioca meal from different CMD cassava varieties measured at different temperature (30°C and 40°C) and shear rate (13.66–81.96 s^-1 ). The viscosity of the tapioca meal decreased with increasing shear rates at both 30°C and 40°C, but higher for lower temperature respectively. At 30°C, tapioca meal produced from cassava variety M98/0028 had the highest viscosity 37.90 Pa s at 13.66 s⁻¹ followed by viscosity value of 24.5 Pa s at 27.32 s⁻¹ for tapioca meal from 94/0166, with viscosity values of 19.38 Pa s at 40.98 s⁻¹, 14.39 Pa s at 68.30 s⁻¹, and 12.65 Pa s at 81.96 s⁻¹ for tapioca meal from M98/0028. Tapioca meal produced from cassava variety 4(2)1425 had the lowest viscosity values of 3.10, 2.15, 1.7, 1.29, and 1.18 Pa s at 13.66–81.96 s⁻¹. At 40°C, tapioca meal produced from 92B/0068 had the highest viscosity value of 25.30 Pa s at 13.66 s⁻¹, followed by those made from 98/2101 with viscosity of 15.25 Pa s at 27.32 s⁻¹, and those meal made from cassava variety 94/0166 with viscosities of 12.80, 9.36, and 8.47 Pa s respectively at 40.98, 68.30, and 81.96 s⁻¹. Tapioca meal produced from cassava variety 4(2) 1425 had the lowest viscosity values of 2.07–0.72 Pa s at 13.66–81.96 s⁻¹, respectively.

Table 3 Viscosity at different shear rate for tapioca meal from CMD cassava varieties at 30°C

CMD variety	Viscosity (Pa s) at different shear rate (s^−1)
	13.66(s^−1)	27.32(s^−1)	40.98(s^−1)	68.30(s^−1)	81.96(s^−1)
30572	16.73	10.68	8.42	6.77	6.44
4 (2)1425	3.10	2.15	1.70	1.29	1.18
82/00058	10.33	7.07	15.51	4.29	3.99
91/02324	26.10	16.95	15.69	11.64	10.91
92/0067	18.90	12.57	10.51	8.42	8.00
92/0325	28.93	18.48	14.29	11.11	10.67
92/0326	21.97	15.78	13.00	9.83	9.37
92B/0061	28.80	17.92	15.36	12.26	11.49
92B/0068	31.00	21.47	17.06	12.67	10.88
94/0026	20.27	12.95	10.40	7.59	6.55
94/0039	21.37	15.53	11.89	9.40	8.73
94/0561	8.80	5.25	4.20	3.24	2.97
94/0166	29.37	24.50	17.48	14.04	11.27
95/0289	17.27	11.45	9.26	6.81	5.98
96/0523	13.03	9.48	7.56	5.59	4.99
96/0603	23.40	15.43	12.69	10.91	10.10
96/1089A	23.03	14.78	13.52	10.37	9.08
96/132	12.53	3.28	6.55	4.83	4.75
96/1642	11.80	7.37	5.96	4.81	4.51
96/4769	26.70	7.82	14.30	10.62	9.79
97/0162	11.73	9.50	8.48	7.17	6.07
97/0211	21.77	14.43	11.57	8.84	8.26
97/2205	23.60	14.87	11.97	8.96	8.25
97/3200	9.53	5.37	3.77	2.66	2.17
97/4763	16.77	11.38	9.31	7.45	7.03
97/4779	25.30	16.33	12.11	9.20	8.45
98/0002	17.50	12.18	10.92	8.19	7.62
98/0505	18.03	11.52	9.49	7.52	6.79
98/0510	19.93	13.50	10.36	7.75	7.20
98/0581	24.03	16.93	12.88	10.49	9.63
98/2101	29.67	18.42	16.77	12.39	12.26
98/2226	17.90	11.93	9.14	7.26	6.65
99/2123	22.53	14.50	11.49	9.19	8.67
99/3073	20.20	14.23	11.53	8.73	8.15
99/6012	26.63	18.33	13.59	10.47	9.46
M98/0028	37.90	24.00	19.38	14.49	12.65
M98/0040	20.60	12.90	10.43	7.52	6.92
M98/0068	24.77	16.48	13.85	11.89	11.41
TME419	19.07	12.18	10.05	7.36	6.73
Range	3.10 – 37.90	2.51 – 24.50	1.70 – 19.38	1.29 – 14.49	1.18 – 12.65
Mean	20.54	13.33	11.34	8.56	7.85
Std Error	1.14	0.81	0.62	0.49	0.44
Std Dev	7.09	5.09	3.86	3.03	2.75
CV	50.28	25.89	14.87	9.18	7.57
P of variety	**	**	**	**	**
**Significantly different at P < 0.05.

Table 4 Viscosity at different shear rate for tapioca meal from CMD cassava varieties at 40°C

CMD variety	Viscosity (Pa s) at different shear rate (s^-1)
	13.66(s^−1)	27.32(s^−1)	40.98(s^−1)	68.30(s^−1)	81.96(s^−1)
30572	9.80	6.77	5.31	4.11	4.25
4(2)1425	2.07	1.45	1.13	0.82	0.72
82/00058	7.80	5.13	3.89	2.93	2.67
91/02324	14.40	9.78	8.00	6.09	5.71
92/0067	13.90	9.62	7.77	5.79	5.40
92/0325	13.13	9.35	7.78	5.91	5.36
92/0326	19.50	13.45	11.43	8.24	7.30
92B/0061	16.07	9.70	7.66	5.94	5.51
92B/0068	25.30	15.00	12.04	8.92	8.19
94/0026	15.27	9.53	7.22	5.11	4.54
94/0039	17.33	11.15	8.53	6.91	6.25
94/0561	5.60	3.65	2.81	2.09	2.00
94/0166	20.57	14.32	12.80	9.37	8.47
95/0289	11.67	7.10	5.49	4.20	3.86
96/0523	7.67	5.57	4.37	3.36	2.97
96/0603	17.70	11.90	9.27	7.47	6.79
96/1089A	15.80	11.05	9.60	7.31	7.23
96/132	8.90	5.80	4.95	3.80	3.44
96/1642	9.40	5.18	4.07	3.07	2.86
96/4769	19.60	13.38	10.58	7.98	7.29
97/0162	8.10	6.00	4.70	3.97	3.47
97/0211	15.40	9.55	7.93	6.07	5.52
97/2205	16.47	10.62	8.36	6.43	6.00
97/3200	3.60	2.68	1.71	1.14	0.97
97/4763	13.00	9.02	7.58	5.78	5.43
97/4779	14.80	9.97	8.42	6.15	5.29
98/0002	16.17	10.92	8.38	6.29	5.81
98/0505	12.50	8.30	6.72	5.52	4.53
98/0510	13.87	8.77	7.17	5.43	5.47
98/0581	19.70	12.57	9.78	7.70	7.32
98/2101	19.23	15.25	11.62	8.29	7.67
98/2226	11.97	7.92	6.29	4.83	4.73
99/2123	13.63	9.65	8.17	6.26	5.46
99/3073	16.10	11.07	8.74	6.44	6.20
99/6012	17.17	11.28	8.84	7.31	7.26
M98/0028	23.07	15.22	11.73	8.66	8.37
M98/0040	16.47	9.25	7.81	5.85	5.09
M98/0068	19.77	13.27	11.23	8.59	7.51
TME419	13.80	8.97	7.22	5.37	4.72
Range	2.07–25.30	1.45–15.25	1.13–12.8	0.82–9.37	0.72–8.47
Mean	14.26	9.47	7.62	5.78	5.32
Std Error	0.82	0.54	0.45	0.33	0.31
Std Dev	5.09	3.39	2.80	2.09	1.94
CV	25.95	11.49	7.86	4.36	3.78
** Significantly different at P < 0.05.

As shown in Figures 1 and 2, the viscosity of tapioca meal decreased with increasing shear rate irrespective of the temperature. The relationship between viscosity and shear rate for the tapioca meals indicated that tapioca meal is a non-Newtonian fluid material. Non-Newtonian flow can be elucidated by imagining any fluid to be a mixture of molecules with different sizes and shapes; as the molecules pass by each other as a result of applied force (shearing), the size, shape and cohesiveness will determine how much force is required to initiate motion.[10] At each specific rate of shear, the alignment may be different and more or less force may be required to maintain motion, which explains lowest interaction for tapioca meal from TMS 4(2)1425.

Figure 1 Pseudoplastic behaviour of tapioca meal from selected CMD cassava varieties at 30°C.

Figure 2 Pseudoplastic behaviour of tapioca meal from selected CMD cassava varieties at 40°C.

Significant differences (p < 0.05) were obtained on the effect of cassava varieties, shear rates and temperature of tapioca meal. Viscosity is a principal parameter when any flow measurement of fluids, such as liquids, semi-solids and gases are made. This property is particularly critical during handling, processing and storage.[31] Viscosity measurements are made in conjunction with product quality and efficiency. The reduction in viscosity with increasing shear rate or viscometer speed has been related to the increased alignment of the constituent molecules as shear rate increases.[10,32] Investigation of the effect of temperature on viscosity is very essential in evaluating materials that will be subjected to varying temperatures during processing or consumption, such as tapioca meal. Viscosity increased with decreasing temperature irrespective of cassava variety, and speed. In this study, an increase in temperature decreased the viscosity of tapioca meal. This observation agrees with earlier studies33–35 on akamu and other foods.[36,37] Sopade and Fillibus[35] likened this inverse relationship between viscosity and temperature to the incidence of a freer molecule to molecule interaction at elevated temperatures. And since viscosity can be described as a resistance to flow, such a freer interaction is expected to minimize the resistance.

CONCLUSIONS

The results from this work on tapioca showed that varieties have significant effect on the functional and rheological properties. Tapioca grits from different cassava varieties showed increased values in dispersibility and water absorption capacity. Tapioca grits from cassava TME 419 had the highest swelling power suitable for tapioca production. Most tapioca grits produced from various cassava varieties displayed pure whiteness. The viscosity of the tapioca meal decreased with increasing shear rates at both 30°C and 40°C with cassava clones M98/0028 and 94/0166 possess highest values for viscosity.

ACKNOWLEDGMENTS

This publication is an output from Integrated Cassava Project (CMD and CEDP) funded by the Federal Government of Nigeria, USAID, SPDC, Oil Companies and State Government in South-South and South-East Nigeria. The authors are grateful to Crop utilization Laboratory of the International Institute of Tropical Agriculture for the support.