Effect of Freezing Rate and Starch Granular Morphology on Ice Formation and Non-Freezable Water Content of Flour and Starch Gels

Figures & data

TABLE 1 Physicochemical properties and swelling and solubility at 120°C of all studied flour and starch samples

Parameter	RF	WRF	TS	PG
Moisture (%)	7.08 ± 0.63^a	6.79 ± 0.55^a	6.58 ± 0.32^a	4.26 ± 0.20^b
Amylose (%)	28.13 ± 0.60^a	4.12 ± 0.32^d	17.48 ± 0.55^c	19.00 ± 0.35^b
Protein (%)	6.30 ± 0.04^a	6.16 ± 0.03^b	N/D	N/D
Swelling (g/g)	14.25 ± 0.36^b	23.16 ± 0.78^a	23.90 ± 3.33^a	14.71 ± 1.94^b,*
Solubility (%)	11.55 ± 0.26^d	25.01 ± 3.29^c	48.70 ± 4.24^b	63.47 ± 1.73^a

Amylose was measured using an amylose/amylopectin assay kit, Megazyme, Ireland. Protein was measured using Kjeldahl method. N/D: non-detectable.

^a,b,c,dmeans values followed by the same superscript letter within the same row are not significantly different (p ≥ 0.05).

*means the remaining starch granules in PG that could absorb large amount of water and then sediment upon centrifugation.

FIGURE 1. DSC cooling (a, c, e) and the second heating (b, d, f) thermograms of rice flour (RF), waxy rice flour (WRF), and tapioca starch (TS) at various water contents.

FIGURE 2. DSC cooling (a, c, e) and the second heating (b, d, f) thermograms of rice flour (RF), waxy rice flour (WRF), and tapioca starch (TS) at various water contents.

FIGURE 3. Normailized ice melting enthalpy by weight of water as functions of Wc of RF- (square), WRF- (triangle), and TS (diamond)-water systems at the studied freezing rate of –100°C/min (filled symbol) and –10°C/min (unfilled symbol).

TABLE 2 Non-freezable water weight content (W_NFW) of starch-water systems determined by the method described in Lui and Cowman^[26]

Sample	1st heating temperature (°C)	Freezing rate (°C/min)	WNFW (g/g dry starch)	R^2
RF	120	–100	0.32	0.9906
WRF	120	–100	0.37	0.9924
TS	120	–100	0.40	0.9958
RF	120	–10	0.31	0.9944
WRF	120	–10	0.38	0.9979
TS	120	–10	0.39	0.9978
TS	70	–100	0.28	0.9983
TS	60	–100	0.27	0.9999
PG	70	–100	0.39	0.9969

FIGURE 4. Optical micrographs of iodine-stained granules; tapioca starch (TS) granules after heated to 60, 70, and 120°C (a–c, birefringence shown in inset in a), rice flour (RF) and waxy rice flour (WRF) after heated to 120°C (d–e), and pregelatinized tapioca starch (PG) after heated to 70°C (f).