Effect of thermal treatment on microbiological, physicochemical and structural properties of high pressure homogenised hazelnut beverage

Abstract

The aim of this study was to investigate the effect of low (65, 72 and 85 degrees C) and high (105, 110 and 115 degrees C) temperature heat treatment on the microbiological, physical and chemical properties of high pressure homogenised hazelnut beverage. The total number of aerobic bacteria decreased with heat treatment and was not detected after 72 degrees C and higher heat treatments. The pH value of hazelnut beverage did not change significantly as a function of temperature (P>0.05). The total soluble content and soluble protein values of the low or high heat treated hazelnut beverage were significantly decreased after the heat treatments considered non-thermal treated ones, and also serum separation was adversely affected (P<0.05). Changes in colour components showed an increase in browning of hazelnut beverage by thermal treatment. The viscosity values of the samples significantly increased depending on the temperature except for the 65 degrees C treatment (P<0.05), and Herschel Bulkley's model was sufficient to describe the flow behaviour. Heat treatment at 85 degrees C for 5 min and higher temperatures led to an increase in particle size due to protein denaturation. Our results showed that the ideal temperature-time parameters were determined as 20 min at 72 degrees C and 1 min at 105 degrees C, based on microbiological results and better physicochemical properties.