Evaluation of Phosphatase Inactivation Kinetics in Milk Under Continuous Flow Microwave and Conventional Heating Conditions

Figures & data

Figure 1 A schematic diagram of continuous-flow microwave heating and isothermal holding system set-up. (Figure provided in color online.)

Figure 2 Time-temperature profile (dotted line) and corresponding lethal rate profile (solid line) for milk under isothermal water bath heating condition.

Figure 3 Survival curves of ALP in milk during isothermal in a water bath as a function of a) uncorrected time and b) corrected heating times. (Figure provided in color online.)

Figure 4 Temperature sensitivity curves for ALP in milk during conventional batch heating treatment showing uncorrected (dotted line) and corrected (solid line) heating times. (Figure provided in color online.)

Table 1 Thermal kinetic parameters (D- and z-values) of ALP in milk at various temperatures under conventional isothermal water bath heating condition

	D-values (s)
Exit temperature of		CUT + CDT
the second oven (°C)	Uncorrected	Corrected
60	1250.0	1250.0
65	188.7	182.7
70	28.1	16.6
75	8.9	1.7
z value (°C)	6.88	5.18

Figure 5 Time-temperature profiles for milk at inlet of oven 1 (T₁), outlet of oven 1 (T₂), outlet of oven 2 (T₃) and outlet of the holding coil (T₄) in continuous-flow microwave heating system at initial temperature 20°C and flow rate 480 ml/min. (Figure provided in color online.)

Figure 6 Time-temperature profile of milk during continuous-flow microwave heating (dotted line) and computed effective times (solid line) at exit temperature °C. (Figure provided in color online.)

Table 2 Thermal kinetic parameters (D- and z-values) of ALP in milk at various temperatures under continuous-flow microwave heating

	D-values (s)
Exit temperature of
the second oven (°C)	Time-uncorrected	Time-corrected
65	91.7	17.6
67	53.8	6.3
70	19.5	1.7
z value (°C)	7.39	4.92

Figure 7 Survival curves of ALP in milk during continuous-flow microwave heating as a function of corrected heating times. (Figure provided in color online.)

Figure 8 Survival curves of ALP in milk during continuous-flow thermal holding as a function of corrected heating times. (Figure provided in color online.)

Table 3 Thermal kinetic parameters (D- and z-values) of ALP in milk at various temperatures during continuous-flow isothermal holding (holding coil volume = 100 ml)

	D-values (s)
Exit temperature of
the second oven (°C)	Time-uncorrected	Time-corrected
65	73.0	128.2
67	47.4	45.7
70	16.8	13.5
z value (°C)	5.18	5.15

Figure 9 Temperature sensitivity curves for inactivation rates of ALP under different conditions. (Figure provided in color online.)

Table 4 Thermal kinetic parameters (D- and z-values) of ALP in milk under conventional isothermal water bath heating, continuous-flow MW heating and continuous-flow thermal holding conditions

	D-values (second)
	Conventional water	Continuous-flow	Continuous-flow
Temperature (°C)	bath heating	thermal holding	MW heating
60	1250.0
65	182.7	128.2	17.6
67		48.5	6.3
70	16.6	13.5	1.7
75	1.7
Ratio of D-values (compared with MW heating)	10.4–9.8	7.3–7.9
z-value (°C)	5.18	5.15	4.92