马铃薯片红外加热灭酶脱水试验及动力学

Experiment and dynamics of dehydration and inactivation of enzyme of potato slices by simultaneous infrared dry-blanching

该文研究了生产低油薯片的一种前处理工艺,并为后续的油炸工艺提供基础。试验考察了辐射距离、样品厚度、处理时间等工艺参数对马铃薯片水分比(moisture rate,MR)、脱水速率、多酚氧化酶(polyphenol oxidase,PPO)相对残留活性、颜色等指标的影响,并进行了酶钝化动力学模型的研究。试验证明,辐射距离由15.5 cm减少到9.5 cm,样品厚度1.3 mm减少到0.8 mm时,马铃薯片最大脱水速率由0.24 g,(g·s)增加到0.59 g(g·s),PPO失活递减时间从364 s减少到152 s,色差值△E由5.26减少到1.66,,因此,马铃薯片红外处理应尽量采取高温短时处理。一级动力学模型能较好地预测加工过程中马铃薯片PPO失活情况(R^2=0.926~0.988)。PPO相对残留活性低于10%时,马铃薯片的湿基含水率由初始的77.71%降至44.58%~62.04%,预示着灭酶的同时脱除部分水分。后续油炸试验时,可选辐射距离为9.5 cm,处理厚度分别为0.8和1 mm,相应的处理时间为150和180 s时,这可得到较高品质的产品,其中PPO相对残留活性分别为8.51%和2.44%,最终湿基含水率为55.44和61.49,色差值△E为1.66和2.24。研究结果为后续油炸试验前处理工艺提供了参考。

A simultaneous infrared dry-blanching and dehydration （SIRDBD） method utilizes infrared dry heat to blanch fruits and vegetables and simultaneously remove a certain amount of moisture. This study investigated the effects of three processing parameters, e.g. distance between infrared emitter and material （9.5, 12.5 and 15.5 cm）, thickness （0.8, 1 and 1.3 mm, and the diameter was 6 cm） and processing time which was determined based on the complete inactivation of polyphenol oxidase （PPO）, on blanching and dehydration of potato slices. The measured performance parameters were temperature, moisture ratio （MR）, drying rate, relative residual PPO and surface color change （AE）. In the test, the surface temperatures of all samples increased to predetermined temperatures within 1 min and then were kept at those temperatures for the rest of processing. In general, the tests showed that the radiation distance decreased from 15.5cm to 9.5 cm and the thickness of samples decreased from 1.3mm to 0.8 ram, which would lead to an increase of the maximum dehydrating rates of potato slices from 0.24 g/（g.s） to 0.59 g/（g.s）, a decrease of the reduction time of PPO inactivation from 364 s to 152 s, and a reduction of the color difference value ALE from 5.26 to 1.66. Therefore, the test results indicated that the thin slices and narrow distance between the infrared emitter and sample were desirable for the quick moisture reduction, fast inactivation of enzymes and less color change. The residual PPO activities after application of various processing conditions were between 0-8.51%, which corresponded to a moisture reduction from 37.96% to 55.42% （w.b.）, and a processing time from 150 s to 420 s. This indicated that infrared heating could blanch fruits and vegetables and simultaneously remove a certain amount of moisture. In addition, when the thickness of potato slices increased, the activation energies of potato slices decreased, but the effective moisture diffusivities increased. The reduced distance between infrared emitter and sample improved effective moisture diffusivities of potato slices. The effective moisture diffusivities of potato slices under different processing conditions were between 3.37× 10^-10 m^2/s and 6.36× 10^-1m^2/s （R2=0.974-0.983）, and the activation energies of potato slices ranged from 20.34 kJ/mol to 32.59 kJ/mol （R2=0.951-0.996）. First-order kinetics fitted well for PPO inactivation （R^2 was from 0.926 to 0.988）, and the predicted kinetic parameters provided useful information for the blanching processing. The rate constants of PPO inactivation under different infrared radiation conditions were between 0.0063 s-1 and 0.0151 s^-1, and the reduction times ranged from 152 s to 364 s. The best processing parameters for the infrared heating mode were 9.5 cm radiation distance, 0.8 and 1 mm potato slice thickness and 150 and 180 s corresponding processing time, which resulted in 8.51% and 2.44% residual of PPO, 55.44% and 61.49% moisture content （w.b.）, 1.66 and 2.24 AE, respectively. It has been concluded that SIRDBD method can be used as an alternative to manufacture blanched and partially dehydrated fruits and vegetables. For infrared dry-blanching, a narrow distance between infrared emitter and material with high temperature should is recommended.