The Effect of Come-up Time on Fractal Dimension of Lime Juice in Thermal Processing by Conventional and Infra-red Methods

Juice cloud and turbidity are considered as desirable properties in lime and other citrus juices. The turbidity is influenced by the presence of pectin in citrus juice. Pectin methylesterase (PME) causes cloud loss due to its function in desterification of the pectin. Thermal processing is commonly used to inactivate this enzyme. As the first stage of the heating process¡ the come up time (CUT) plays a considerable role in PME inactivation. The aim of this study was to investigate the PME inactivation¡ turbidity and fractal dimension (FD) changes during lime juice thermal processing using conventional (water bath) and infrared (IR) heating at 60¡ 70¡ 80 and 90 oC. The results showed that by rising juice temperature¡ the PME inactivation and the turbidity increased during both thermal treatment methods. Therefore¡ the cloud particles remained suspended and less particles aggregation took place to form fractal structures¡ resulting in a homogeneous distribution of cloud particles and FD reduction. Due to shorter CUT¡ the samples heated by IR showed higher PME retention and FD in comparison with conventional processing.