Internal Temperature Distribution During Individual Quick Blanching

Kinetic parameters for thermal inactivation of cut green beans lipoxygenase calculated using unsteady‐state methods

“…Average thermal diusivities obtained were the following: 1.525´10 ±7 m 2 s )1 (25±73.9°C), 1.555´10 ±7 m 2 s )1 (25±85.2°C) and 1.575´10 ±7 m 2 s )1 (25±92.65°C), the ®rst and the third being signi®cantly dierent (P < 0.05). These values are similar to those compiled by Holdsworth (1997) for pea pure e, 1.54±1.59´10 ±7 m 2 s )1 , potato pure e, 1.39±1.46´10 ±7 m 2 s )1 (at 60±100°C) and tomato pulp, 1.46±1.50´10 ±7 m 2 s )1 (at 28°C) and those determined by Lund et al (1972) for carrots, 1.56´10 ±7 m 2 s )1 (in the range 20± 100°C) and Garrote et al (2000) for potatoes, 1.62´10 ±7 m 2 s )1 (in the range 20±150°C). Table 2 shows the estimated values for green beans thermal conductivities as a function of green bean temperature.…”

“…Average thermal diffusivities obtained were the following: 1.525 × 10 –7 m 2 s −1 (25–73.9 °C), 1.555 × 10 –7 m 2 s −1 (25–85.2 °C) and 1.575 × 10 –7 m 2 s −1 (25–92.65 °C), the first and the third being significantly different ( P < 0.05). These values are similar to those compiled by Holdsworth (1997) for pea purée, 1.54–1.59 × 10 –7 m 2 s −1 , potato purée, 1.39–1.46 × 10 –7 m 2 s −1 (at 60–100 °C) and tomato pulp, 1.46–1.50 × 10 –7 m 2 s −1 (at 28 °C) and those determined by Lund et al . (1972) for carrots, 1.56 × 10 –7 m 2 s −1 (in the range 20–100 °C) and Garrote et al .…”

“…If we compare the inactivation rate constants for both lipoxygenases, at 82 °C k pea =1.32 s –1 is lower than k green bean =92.9 s –1 , but at 100 °C, k pea =3295 s –1 is greater than k green bean =1094 s −1 . It is also interesting to compare the thermal resistance of lipoxygenase and peroxidase, the latter being used as an index of appropriate blanching; Lund et al . (1972) determined a k 100°C =1.4 s –1 and E a =167.4 KJ mol −1 for carrot labile peroxidase.…”

“…If we compare the inactivation rate constants for both lipoxygenases, at 82°C k pea 1.32 s ±1 is lower than k green bean 92.9 s ±1 , but at 100°C, k pea 3295 s ±1 is greater than k green bean 1094 s )1 . It is also interesting to compare the thermal resistance of lipoxygenase and peroxidase, the latter being used as an index of appropriate blanching; Lund et al (1972) determined a k 100°C 1.4 s ±1 and E a 167.4 KJ mol )1 for carrot labile peroxidase. It was observed that this E a is very similar to that obtained for green bean lipoxygenase, but the rate constant is much lower; the estimated temperature at which the rate constant of green bean lipoxygenase equals the value of k 100°C 1.4 s ±1 for peroxidase is 57.5°C, revealing that lipoxygenase is much less resistant to heating treatment than labil peroxidase.…”

Predicting the end point of a blanching process

“…The fact that the mass average temperature of the piece is always greater than the center temperature during exposure to steam, suggested a new method of blanching (Lund, Bruin Jr., & Lazar 1972). Lazar, Lund, and Dietrich (1971) described the individual quick blanching method, which is based on the equilibration of preheated food pieces to the mass average temperature.…”