Effects of conventional and ultrasound blanching on enzyme inactivation and carbohydrate content of carrots

Abstract

There is a growing interest in the use of ultrasound (US) as an alternative to conventional processes. Although US has previously been applied as a pretreatment of fruits and vegetables, no investigation has been done on the usefulness of US for carrot blanching, paying special attention to its effect on enzyme inactivation and leaching losses. In the present paper, the influence of US (in bath and with probe) on peroxidase (POD) and pectinmethylesterase (PME) inactivation and on the loss of total soluble solids and carbohydrates by leaching has been evaluated. Results of this preliminary study have also been compared with those obtained after conventional (hot water and steam) blanching of carrots. The highest enzyme inactivation was obtained with the conventional treatments performed at high temperatures and with the US probe treatments with heat generation. Carrots blanched by US probe for 10 min at a temperature up to 60 °C showed characteristics similar to those conventionally treated at 60 °C for 40 min. Although the efficiency of US was limited for total inactivation of POD and PME, this treatment resulted to be advantageous in terms of time for blanching at mild temperatures. US probe treatments could also be considered as an advantageous alternative to low-temperature long-time (LTLT) conventional treatments for those applications in which partial inactivation of PME is required for the better preservation of carrot structure.