Effect of Radio Frequency Heating on Yoghurt, II: Microstructure and Texture

Abstract

Radio frequency (RF) heating was applied to stirred yoghurt after culturing in order to enhance the shelf-life and thereby meet industrial demands in countries where the distribution cold chain cannot be implicitly guaranteed. In parallel, a convectional (CV) heating process was also tested. In order to meet consumers’ expectations with regard to texture and sensory properties, the yoghurts were heated to different temperatures (58, 65 and 72 °C). This second part of our feasibility study focused on the changes in microstructure and texture caused by post-fermentative heat treatment. It was shown that there were always microstructural changes with additional heat treatment. Compared to the dense and compact casein network in the stirred reference yoghurt, network contractions and further protein aggregation were observed after heat treatment, while at the same time larger pore geometries were detected. The changes in microstructure as well as other physical and sensorial texture properties (syneresis, hardness, cohesiveness, gumminess, apparent viscosity, G’, G’’, homogeneity) were in good agreement with the temperature and time of the heat treatment (thermal stress). The RF heated products were found to be very similar to the stirred reference yoghurt, showing potential for further industrial development such as novel heating strategies to obtain products with prolonged shelf-life.

Effect of Radio Frequency Heating on Yoghurt, I: Technological Applicability, Shelf-Life and Sensorial Quality

“…As can be seen in Figure 3 , the electric conductivity of the yoghurt was directly proportional to the temperature. Generally, the measured electric conductivity was slightly higher than the literature values for milk, most likely due to the contribution of lactic acid to conductivity [ 11 ].…”

“…This section presents the results of the RF and CV heating of yoghurt products after culturing and describes the technological applicability, shelf-life, pH, color and sensorial changes. The details of the textural and microstructural changes are given elsewhere in the second part of this two-part study [ 11 ].…”

“…It was therefore decided not to undertake an RF heating series at 72 °C, and this is the reason why no temperature-time profile at 72 °C is shown in Figure 4 . Further details concerning syneresis and the texture analysis of the few yogurt samples that were heated to 72 °C are described in the second part of this two-part study [ 11 ].…”

“…A second, separate part of this feasibility study will focus on the changes in microstructure and texture caused by a post-fermentative heat treatment [ 11 ].…”

Radio Frequency Heating of Milk–Effects on Quality, Safety, and Shelf Life Assessed Using Artificial Senses and Chemometric Tools

“…Therefore, the aim of this work was to study the impact of different RF heating protocols on quality and safety aspects of raw bovine milk, using artificial senses coupled with chemometric tools. Other authors have investigated the effect of RF heating on dairy products, such as yogurt [20,21] and powder milk [22]; however, this is the first study using electronic senses to achieve this task. Consisting of an array of sensors, exhibiting various selectivity and pattern recognition systems that analyze the sensor responses, this process is inspired by the neurophysiology of the smell and taste [23].…”