This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

There was increasing demand for minimally processed products that had the attributes of freshly prepared food but still had an extended shelf-life and superior nutritional quality. Conventional pasteurization and commercial sterilization processes at the time which involved extended exposure to heat could not provide these desired attributes. This project explored the application of high power microwave heating (HPMH) technology as a means to alternatively pasteurise vegetables whilst maximizing product quality. The net result was significant profitable top-line growth for our business, greater local investment in raw materials and labour and an improved contribution to the satisfaction of Australian processed vegetable consumers.

The project was a collaborative effort between Simplot and the University of Wollongong (Faculty of Engineering).

The project which formed part of a larger project was composed of two key stages (I) Laboratory development work and (II) Prototype development and validation.

• Laboratory development work - This stage was primarily concerned with establishing the process conditions required to achieve successful blanching, leading to some design concepts.
• The prototype development and validation stage was concerned with developing a prototype processing system. The work focused on microwave aspects involved in achieving uniform heating, materials handling challenges and materials flow trials and ultimately the construction and validation of semi-continuous processing unit delivering 30-40kg product/hr.

Stage I yielded significant results on the (i) electrical properties of locally grown vegetables (ii) enzymes inactivation with varying process regimes (iii) energy and heat penetration modelling and (iv) preliminary understanding of vegetable quality after treatment with these varying microwave conditions.

Stage II yielded a prototype microwave blanching system and process which returned many key and positive results including:

• Close to 100 per cent enzyme (peroxidase) inactivation for a given processing time;
• High level of vegetable quality retention;
• Fast processing times, and;
• No textural loss during chilled storage. 

Future research needed to concentrate on developing and validating the technology and process on a larger commercial scale and ultimately, its implementation if the research was to be successful. From the results of this project a conceptual commercial design for validation had been proposed with the following features:

• Mechanised unloading, cleaning and processing movements;
• Throughputs exceeding 600kg/hr;
• Improved microwave E-field uniformity, yielding more uniform heating and improved energy efficiency.