Thermal pretreatments of carrot pieces using different heating techniques: Effect on quality related aspects

During fruit and vegetable processing, different thermal processes (blanching, pasteurization, sterilization) based on different heating techniques can be used. In this context, it is important to evaluate the impact of blanching on quality related parameters. This paper describes a case study on carrot pieces, studying the effect of thermal pretreatments (high temperature blanching, low temperature blanching and low temperature blanching in combination with Ca2+-soaking) on enzyme activity (peroxidase (POD), pectinmethylesterase (PME)), structural properties (degree of methoxylation (DM), texture) and nutritional aspects (beta-carotene content). The thermal pretreatments were carried out by conventional heating as well as by microwave heating and ohmic heating, since these new heating methods can become important new technologies in food industry. It has been shown that, depending on the application, selecting the right pretreatment conditions can help to control the enzyme activity. To obtain a firm carrot texture after thermal processing, low temperature blanching seems to be the most appropriate pretreatment condition. This was supported by the micrographs and the analysis of the degree of methoxylation. Furthermore almost no influence of the pretreatments on the beta-carotene content of the samples could be noticed. For all quality parameters studied, no unambiguous effect of the heating technique could be detected. Thus, the time/temperature conditions of the thermal pretreatments determine the quality related aspects, independent of the heating technique used. Industrial relevance: With regard to consumer acceptance, a good quality control of fruit and vegetables is important. Food quality covers a wide range of parameters, including enzyme content, structural properties, nutritional properties, sensorial characteristics etc. This study gives an overview of the effect of blanching, which is a common preprocessing step in food processing, on quality related parameters in carrots. The data deliver integrated information on structural level as well as on nutritional level and on enzyme content. Moreover, novel thermal process technologies (microwave heating, ohmic heating), which gain more and more attention in food industry, are being considered as alternatives for conventional blanching. (C) 2009 Elsevier Ltd. All rights reserved.