Abstract
Current treatment routes are not suitable to reduce and stabilise bacterial content in some dairy process streams such as separator and bactofuge desludges which currently present a major emission problem faced by dairy producers. In this study, a novel method for the processing of desludge was developed. The new method, elevated pressure sonication (EPS), uses a combination of low frequency ultrasound (20 kHz) and elevated CO2 pressure (50 to 100 bar). Process conditions (pressure, sonicator power, processing time) were optimised for batch and continuous EPS processes to reduce viable numbers of aerobic and lactic acid bacteria in bactofuge desludge by ≥3-log fold. Coagulation of proteins present in the desludge also occurred, causing separation of solid (curd) and liquid (whey) fractions. The proposed process offers a 10-fold reduction in energy compared to high temperature short time (HTST) treatment of milk.
Highlights
There are a number of treatments commonly applied to reduce the viability of bacteria in raw milk to generate products fit for human consumption
We describe the development of elevated pressure sonication (EPS), a novel technology for the treatment of desludges (Bains and Leeke 2015)
Power sonication is a technique used to pasteurise many dairy products (BermúdezAguirre and Barbosa-Cánovas 2011); it is used at high frequency to kill bacteria to acceptable limits
Summary
There are a number of treatments commonly applied to reduce the viability of bacteria in raw milk to generate products fit for human consumption. Alternative routes of bacterial deactivation or removal from dairy streams, either industrially or in academic research settings, include centrifugation/bactofugation, reduction in pH (in casein manufacture), sonication, pulsed electric fields and high pressure treatments, each of which have different impacts on the microbiological safety and chemical and sensory properties of the product (Sampedro et al 2005; Ortega-Rivas and Salmerón-Ochoa 2014). These techniques are typically used in combination to reduce viability of spoilage and pathogenic bacteria to acceptable limits in the final product. Rapid decompression treatment has been reported in the literature (Foster et al 1962; Fraser 1951; Hemmingsen and Hemmingsen 1980), but this is only suitable for bacteria that contain gas vacuoles and is not broadly applicable for food processing
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