Textural and Gelatinization Characteristics of White, Cream, and Orange Fleshed Sweet Potato Tubers (Ipomoea Batatas L.)

Figures & data

Figure 1 Different varieties of sweet potato tubers used in the study: (a) 362-7; (b) CO3-4; (c) SI 60; (d) Sree Arun; (e) SV 280; (f) SV 98; (g) Sree Varun. (Color figure available online.)

Table 1 Textural properties of sweet potato raw tubers

	Puncture test				Cutting/shearing test
Varieties	Stiffness, N/s	Firmness, N	Toughness, Ns	Piercing force, N	Piercing energy, Ns	Cutting force, N	Cutting energy, Ns
White fleshed varieties
SI 60	22.99 ± 1.17^b	90.19 ± 6.46^b	1302 ± 165.12^b	26.59 ± 2.08^d	265.13 ± 23.33^b	187.73 ± 39.38^cd	2518 ± 462.02^bc
SV 280	21.65 ± 3.38^b	95.06 ± 17.44^b	1334 ± 255.37^bc	24.59 ± 2.27^c	265.92 ± 25.95^b	137.79 ± 26.77^a	1809 ± 354.97^a
CO3-4	17.23 ± 4.8^a	106.01 ± 15.5^c	1452 ± 224.27^c	24.66 ± 3.41^c	272.88 ± 37.86^b	191.82 ± 42.43^cd	2485 ± 619.05^bc
Cream fleshed varieties
Sree Arun	18.13 ± 3.32^a	88.47 ± 9.15^b	1292 ± 157.41^b	25.34 ± 2.63^cd	255.23 ± 26.25^b	211.51 ± 44.75^d	2733 ± 468.51^c
Sree Varun	22.05 ± 4.25^b	89.76 ± 6.67^b	1285 ± 114.83^b	25.92 ± 2.74^cd	267.07 ± 24.14^b	167.84 ± 57.75^bc	2166 ± 739.48^ab
Orange fleshed varieties
362-7	22.93 ± 6.20^b	75.88 ± 8.85^a	1049 ± 186.42^a	20.13 ± 2.76^a	235.70 ± 23.13^a	154.79 ± 40.11^ab	1835 ± 653.85^a
SV 98	22.35 ± 4.09^b	93.49 ± 7.61^b	1353 ± 124.13^bc	22.23 ± 1.96^b	265.67 ± 20.60^b	169.78 ± 38.88^bc	2229 ± 571.47^b
Means with the same letters in a column are not significantly different (p < 0.05) by Duncan's multiple range test. ± denotes standard deviation.

Table 2 Biochemical properties of sweet potato tubers

Varieties	Moisture content, %	Starch, % db	Sugar, % db	Fiber, % db
White fleshed varieties
SI 60	73.02 ± 0.58^c	67.67 ± 0.^15c	14.86 ± 0.35^bc	1.71 ± 0.156^cd
SV 280	70.16 ± 0.27^a	68.38 ± 0.83^c	11.51 ± 0.69^a	1.66 ± 00^d
CO3-4	71.58 ± 1.21^b	67.67 ± 0.29^c	13.55 ± 0.62^b	1.99 ± 0.156^c
Cream fleshed varieties
Sree Arun	76.77 ± 0.27^e	64.00 ± 0.24^b	15.78 ± 0.25^cd	2.8 ± 0.142^a
Sree Varun	76.47 ± 0.27^e	63.49 ± 1.39^b	16.94 ± 0.17^de	2.5 ± 0.142^ab
Orange fleshed varieties
362-7	74.78 ± 0.36^d	59.13 ± 2.23^a	23.11 ± 0.01^f	1.55 ± 0.07^d
SV 98	75.99 ± 0.66^e	62.47 ± 1.65^b	18.38 ± 1.41^e	2.36 ± 0.142^b
Means with same letters in a column are not significantly different (p < 0.05) by Duncan's
multiple range test. ± denotes standard deviation.

Table 3 Texture profile parameters of cooked tubers

Varieties	Hardness, N	Adhesiveness, Ns	Springiness	Cohesiveness	Chewiness
White fleshed varieties
SI 60	19.62 ± 5.54^b	−0.36 ± 0.30^bc	0.943 ± 0.273^a	0.270 ± 0.091^ab	4.95 ± 2.69^b
SV 280	17.23 ± 4.91^b	−0.63 ± 0.33^a	0.955 ± 0.202^a	0.272 ± 0.059^ab	4.56 ± 1.91^b
CO3-4	26.84 ± 11.14^c	−0.23 ± 0.20^bc	0.0.964 ± 0.21^a	0.218 ± 0.036^a	5.89 ± 3.56^b
Cream fleshed varieties
Sree Arun	9.36 ± 5.74^a	−0.47 ± 0.38^ab	1.020 ± 0.468^a	0.234 ± 0.046^ab	1.799 ± 1.093^a
Sree Varun	16.06 ± 8.41^b	−0.33 ± 0.25^bc	0.919 ± 0.182^a	0.276 ± 0.085^ab	4.21 ± 2.65^b
Orange fleshed varieties
362-7	16.12 ± 4.03^a	−0.154 ± 0.11^c	0.864 ± 0.24^a	0.289 ± 0.045^b	3.86 ± 1.03^b
SV 98	14.76 ± 3.18^ab	−0.35 ± 0.15^bc	1.046 ± 0.207^a	0.279 ± 0.068^ab	4.18 ± 1.14^b
Means with the same letters in a column are not significantly different (p < 0.05) by Duncan's multiple range test. ± denotes standard deviation.

Table 4 Values of constants in linear model relating degree of cooking and relative firmness of sweet potato tubers**

	Constants
Varieties	A	B	Modulus* (individual model)	Modulus*(general model)
White fleshed varieties
SV 280	108.12	108.12	0.0045	0.4624
SI 60	110.19	110.19	0.0044	1.441
CO3-4	107.41	107.41	0.0005	1.274
Cream fleshed varieties
Sree Arun	105.34	105.34	0.0040	2.909
Sree Varun	107.8	107.8	0.0012	0.6173
Orange fleshed varieties
362-7	111.74	111.74	0.0008	2.7569
SV98	108.81	108.81	0.0044	0.4338
General model	108.18	107.48	—	1.41
*If the modulus values are <5, the equation is extremely good fit, if between 5–10 they are a reasonably good fit, and if >10 they are a poor fit.
** Y = A - Bx, where Y = degree of cooking, x = relative firmness, and A and B are model constants.

Figure 2 Comparison of the observed and predicted values of degree of cooking by the linear regression equations.

Figure 3 Comparison of the observed and predicted values of the kinetic models for the thermal softening of sweet potato tubers.

Table 5 Values of constants in the first order and dual mechanism first order kinetic model to explain thermal softening of sweet potato tubers

	First-order model*			Dual mechanism first-order model**
Variety	k	k 0	r ^2	k 1	k 2	r ^2
White fleshed varieties
SV 280	0.730	0.086	0.94	1.561	0.198	0.98
SI 60	0.816	0.079	0.98	1.555	0.173	0.96
CO3-4	0.928	0.099	0.96	2.589	0.232	0.95
Cream fleshed varieties
Sree Arun	0.523	0.091	0.89	1.146	0.214	0.98
Sree Varun	0.690	0.080	0.98	1.068	0.153	0.98
Orange fleshed varieties
362-7	0.750	0.072	0.96	1.370	0.168	0.98
SV98	0.629	0.077	0.94	1.178	0.179	0.98
*First order kinetic model .
**Dual mechanism first order kinetic model:
,
where Ft = the firmness at heating time ‘t’ min, N; Fo = initial firmness of the product, N; ko = rate constant, min^−1. Fe = firmness at equilibrium or the non zero maximum retainable firmness, N; k and k 1 = constant and k 2 = rate constant, min^−1.

Figure 4 Viscometric properties of flours extracted from sweet potato tubers of different varieties. Columns with the same letters for each property are not significantly different (p < 0.05) by Duncan's multiple range test. The vertical line on each column/point represents error bars using standard deviation.

Figure 5 Gelatinization properties of sweet potato flours from different varieties. Columns with the same letters for each property are not significantly different (p < 0.05) by Duncan's multiple range test. The vertical line on each column/point represents error bars using standard deviation.

Figure 6 Dendrogram based on the textural attributes of raw sweet potato tubers.

Figure 7 Score plot of sweet potato varieties based on texture profile of cooked tubers and pasting and gelatinization properties of flour.