Rheological Properties of Extruded Milk Powders

Figures & data

Table 1 Composition (g/100 g sample) of nonfat dry milk (NDM), whey protein concentrate (WPC), and whey protein isolate (WPI), from manufacturers' specifications.

	Moisture	Protein	Fat	Lactose	Ash
NDM	3.2	36.2	0.8	52.0	7.9
WPC	4.8	77.6	7.0	7.0	3.0
WPI	2.8	89.6	2.5	1.8	3.3

Table 2 Addition of water during extrusion process.

Setting	Water addition (mL/min)
20	25 ± 2
30	39 ± 3
40	52 ± 3
50	72 ± 3
60	86 ± 4
70	97 ± 3

Table 3 Grams of moisture per 100 g sample in extruded nonfat dry milk (NDM), whey protein concentrate (WPC), and whey protein isolate (WPI) samples, with pooled standard deviations (PSD).

	NDM	WPC	WPI	NDM	WPC	WPI	NDM	WPC	WPI
Pump setting	Extruded at 50°C			Extruded at 75°C			Extruded at 100°C
20		35.4	43.8		30.9	38.4		30.5	34.4
30	43.4	46.6	53.8	36.9	39.1	46.7	40.9	35.6	42.7
40	50.3	50.6	60.7	43.8	51.0	58.4	48.0	46.4	53.8
50	52.0	56.8	65.1	48.1	54.4	62.6	54.2	54.5	53.7
60	52.7	53.8	67.6	50.8	59.0	66.1	57.1	59.5
70	56.4			54.5			58.9
PSD	2.0	4.4	7.9	4.0	1.8	3.2	2.9	3.7	2.1

Table 4 Water solubility index values for extruded nonfat dry milk (NDM), whey protein concentrate (WPC), and whey protein isolate (WPI) samples, with pooled standard deviations (PSD).

	NDM	WPC	WPI	NDM	WPC	WPI	NDM	WPC	WPI
Pump setting	Extruded at 50°C			Extruded at 75°C			Extruded at 100°C
20		10.30	12.91		41.64	36.52		38.14	50.93
30	16.93	11.82	12.85	16.16	37.76	26.00	16.89	43.07	45.28
40	15.84	12.50	11.55	16.50	28.38	26.53	16.57	39.84	33.01
50	15.68	11.88	11.20	16.64	19.62	26.21	17.21	33.81	47.42
60	16.46	11.38	11.08	16.59	16.05	25.46	16.53	28.70
70	16.04			16.63			15.11
PSD	3.48	3.04	0.99	3.60	3.94	2.72	4.28	8.17	10.26

Figure 1 Relationships between percent moisture and log of the elastic modulus (log G′) in nonfat dry milk samples extruded at 50°C (circles, solid line), 75°C (squares, dashed line), and 100°C (triangles, broken line). R² values for the 50, 75, and 100 °C linear regression lines are 0.77, 0.88, and 0.41, respectively.

Figure 2 Relationships between log of the elastic modulus (log G′) and extrusion temperature of extruded nonfat dry milk samples, normalized to 50% moisture, with standard deviation bars.

Figure 3 Relationships between percent moisture and log of the elastic modulus (log G′) in whey protein concentrate samples extruded at 50°C (circles, solid line), 75°C (squares, dashed line), and 100°C (triangles, broken line). R² values for the 50, 75, and 100°C linear regression lines are 0.86, 0.81, and 0.20, respectively.

Figure 4 Relationships between log of the elastic modulus (log G′) and extrusion temperature of extruded whey protein concentrate samples, normalized to 50% moisture, with standard deviation bars.

Figure 5 Relationships between percent moisture and log of the elastic modulus (log G′) in whey protein isolate samples extruded at 50°C (circles, solid line), 75°C (squares, dashed line), and 100°C (triangles, broken line). R² values for the 50, 75, and 100°C linear regression lines are 0.76, 0.92, and 0.70, respectively.

Figure 6 Relationships between log of the elastic modulus (log G′) and extrusion temperature of extruded whey protein isolate samples, normalized to 50% moisture, with standard deviation bars.

Table 5 Loss modulus values for extruded nonfat dry milk (NDM), whey protein concentrate (WPC), and whey protein isolate (WPI) samples, with pooled standard deviations (PSD).

	NDM	WPC	WPI	NDM	WPC	WPI	NDM	WPC	WPI
Pump setting	Extruded at 50°C			Extruded at 75°C			Extruded at 100°C
20		0.55	0.40		0.30	0.24		0.29	0.21
30	0.23	0.70	1.18	0.24	0.22	0.20	0.27	0.28	0.27
40	0.21	0.45	0.31	0.23	0.23	0.27	0.22	0.21	0.28
50	0.21	1.02	0.76	0.21	0.24	0.28	0.21	0.20	0.27
60	0.22	0.84		0.20	0.52	0.41	0.20	0.22
70	0.20			0.21			0.20
PSD	0.02	0.06	0.07	0.02	0.04	0.04	0.04	0.04	0.07