ISBN 978-3-8439-5184-5

978-3-8439-5184-5, Reihe Lebensmitteltechnologie

Britta Graf
Microwave technology for heating liquid and concentrated milk products in technical scale

166 Seiten, Dissertation Universität Hohenheim Stuttgart-Hohenheim (2022), Softcover, A5

Zusammenfassung / Abstract

Microwave technology involves short heat transfer with high heating rates, allowing gentle heating. In this thesis it is hypothesized that heating of liquid and pasty, concentrated milk suspensions by means of a single-mode microwave heating plant in technical scale results in reduced fouling and minimal product changes. As alternative microwave application a microwave-assisted extruder for high protein food material is developed. Finally, a novel process for shelf-stable milk involving microfiltration and microwave heating, resulting in long shelf life and increased product properties, is developed.

Reconstituted milk concentrates were heated with a continuous microwave heating plant in technical scale. Product properties were retained and deposit formation was reduced by 90 %. Thermophilic spores were inactivated up to 3 log stages. A microwave-assisted extruder for high-protein food material was developed and tested and the gel-sol transition temperature of the material was succesfully reached. Considerations for scale-up concluded that mass flows of up to 2,000 kg/h with microwave powers up to 86 kW (f = 915 MHz) and screw diameters of 236 mm are realizable. Customized phase treatment (CPT) was developed for shelf-stable milk with retained roduct properties. Skim milk was microfiltered (pore size 0.1 μm) and CPT of the obtained phases (retentate and permeate) was performed. Direct UHT milk showed particle formation and age-gelation during storage. Apparent plasmin activity was elevated in direct UHT milk (0.31 - 0.37 pkat/mL) compared to indirect and CPT milk (0.03 - 0.04 pkat/mL). The shelf life of CPT was comparable to indirect UHT milk.

The results of this thesis indicate that continuous microwave heating is a feasible alternative technology for heating liquid and concentrated milk products. Fouling and product hanges are reduced in comparison to indirect heating. Microwave technology demonstrates great potential within food processing.