New experimental set-up for testing microwave technology to continuously heat fouling-sensitive food products like milk concentrates

Abstract

Microwave heating is an emerging alternative direct heating method to face deposit and particle formation upon heating fouling-sensitive food products. This study successfully demonstrated the implementation of a new set-up for continuous microwave heating at pilot scale (f = 2450 MHz, P = 0.6–6 kW). Reconstituted skim milk concentrate (DM = 27, 31.5 and 36 g/100 g) was heated (110–125 °C, 5 s holding time) through microwave technology and with a tubular heat exchanger in order to examine heat-related product changes and compare both technologies.The results showed significantly reduced whey protein denaturation (35–40% less β-lactoglobulin denaturation) and deposit formation (90% less fouling) of microwave heated reconstituted skim milk concentrate compared to tubular heating, whereas colour changes were insignificant for all experiments. Both methods resulted in comparable particle sizes at equal flow profiles, however, turbulent flow conditions were necessary in order to prevent elevated particle formation. Industrial relevanceMicrowave heating is a promising alternative heating method for fouling-sensitive dairy products. This study demonstrates that through short heat-uptake times gentle product handling is ensured, resulting in retained native product properties. Reduced fouling leads to extended running times, implying less and eventually shorter cleaning intervals. Moreover, compared to other direct heating methods like steam injection, no additional water/steam is added to the product. With its space-saving design and easy handling, continuous microwave heating is a rising technology with high industrial relevance.