Particle size and concentration of ground rice on tribological properties and in vitro starch digestibility of rice porridge

Figures & data

Figure 1. Appearance of gelatinized ground rice in porridge (a – b) and light micrographs (c – f) for difference particle sizes and concentrations of ground rice in porridge (20X magnification). (a) 10% w/v concentration of small-sized particles, (b) 10% w/v concentration of large-sized particles, (c) 5% w/v concentration of small-sized particles, (d) 5% w/v concentration of large-sized particles, (e) 10% w/v concentration of small-sized particles, and (f) 10% w/v concentration of large-sized particles.

Figure 2. Particle size distribution of (a) ground rice (before cooking) and (b – d) gelatinized ground rice (after cooking) with different concentrations; (b) small-sized, (c) mixed-sized, and (d) large-sized particles in ground rice in porridge.

Table 1. Averaged particle size (D [4,3]), yield stress, and viscosity at shear rate of 50 s⁻¹.

Sample type	Rice particles in porridge	Averaged particle size (µm, D [4,3])	Yield stress (mPa)	Viscosity (mPa.s) at 50 s^−1
Raw	Small sized	111 ± 4i	-	-
	Mixed sized	255 ± 5f	-	-
	Large sized	378 ± 14c	-	-
5%	Small sized	201 ± 1g	6,515 ± 176e	345 ± 1g
	Mixed sized	355 ± 3d	43,521 ± 3,271b	1,740 ± 28e
	Large sized	506 ± 5a	54,904 ± 3,230a	1,880 ± 99e
7.5%	Small sized	201 ± 3g	7,176 ± 562e	1,120 ± 99f
	Mixed sized	292 ± 3e	47,609 ± 926b	2,395 ± 106d
	Large sized	404 ± 1b	55,196 + 4,961a	2,610 ± 141d
10%	Small sized	179 ± 6h	20,490 ± 1920d	3,380 ± 156c
	Mixed sized	242 ± 16f	31,887 ± 136c	5,220 ± 42b
	Large sized	366 ± 2cd	42,279 ± 1835b	5,995 ± 247a

Values shown as mean±SD values.

Different lowercase letters in same column indicate significant differences (p < 0.05) based on ANOVA.

Values for yield stress were predicted using a Herschel-Bulkley model at shear rates of 0.2–20 s⁻¹, Coefficient of determination > 0.9.

Figure 3. Viscosity (a – c) and shear stress (d – f) versus shear rate of the porridge with different particle sizes and concentrations of ground rice over a shear rate range of 0.1–1,000 s⁻¹ at 37°C.

Figure 4. Stribeck curves of porridge with different particle sizes and concentrations of ground rice; (a) small-sized, (b) mixed-sized, and (c) large-sized particles.

Figure 5. In vitro starch digestion of porridge with different particle sizes and concentrations, measured as area under curve (AUC) of cumulative released glucose.

(a) during gastric phase (G-phase) and (b) during intestinal phase (I-phase). Values with different superscript letters indicate significant differences (p < 0.05).

¹AUC was calculated based on the cumulated released glucose (g) per 100 g of ground rice at each time increment.