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Method for improving the quality of frozen foods by assisting the freezing process and reducing the size of the ice crystals

Final ReportSummary - MINICRYSTAL (Method for improving the quality of frozen foods by assisting the freezing process and reducing the size of the ice crystals)

Freezing is a very widespread process within the food processing industry, being used not only to manufacture products that are consumed in frozen state, such as ice cream, frozen yoghurts, sorbets, etc, but also as a very important means of preserving fresh foodstuffs. However, freezing animal and plant tissues causes many irreversible physical and chemical changes within the food matrix, often leaving the final product with lower eating quality than when it was in the fresh state. Ice crystals represent one of the key contributors to quality degradation in frozen foods. As they grow in size, they exert additional stresses on fragile cellular structures and can damage emulsions and lead to negative product characteristics such as poor appearance, unacceptable texture and physical and nutritional product damage. In short, smaller ice crystals promote a better quality product and control of the crystal size distribution in the final product is one of the most important aspects for many freezing operations.

As quality issues take increasing precedence among European Union (EU) consumers, a key challenge facing frozen food manufacturers is how to reposition their products as health-friendly. Consumers not only instinctively believe that fresh food tastes better than frozen food- they also see frozen foods as cheap and inferior. In response, the MINICRYSTAL project addressed promising research in the ability of high powered ultrasound (HPU) to initiate ice nucleation and to control crystal size distribution in the frozen product during solidification of liquid food. Past research has also shown promise for HPU to shorten the freezing process and lead to a product of better quality. Thus, MINICRYSTAL's main goal was to design and to develop a prototype HPU system for its industrial validation in food freezing facilities which was easy to operate and easily integrated with commercially available freezing equipment.

The MINICRYSTAL project started in October 2008 with a kick-off meeting in Barcelona to address this context. Nine partners from five countries, which included three research organsiations and six small and medium-sized enterprises (SMEs), jointly assessed the research programme. The consortium focused in particular on a thorough validation of the proposed technology and anticipated MINICRYSTAL processes for different test foods under laboratory conditions. In order to study the effects of ultrasound-assisted immersion freezing in as much depth as possible, a number of equipment features and flexible designs have been developed throughout the scales of few to several kg per batch process. Also, the results of the initial sector diagnosis and laboratory work were highly promising. This was a solid basis for a flexible scale-up step under complex design considerations and a parallel validation approach with higher through-put levels and laboratory accuracy at the same time.

The research pursued on power ultrasound application on different food freezing processes suggested an improvement in freezing rate, a better preservation of the food micro-structure, as well as a reduction in drip loss. Within the prolonged laboratory research phase, it was possible to show significant improvements (P < 0.05) in the freezing rate up to 19 - 22 % for carrots, and up to 25 % for meat sample under specific operating conditions. Despite rather high variability in results due to naturally variable foods, the observed effect were clearly attributed to the ultrasound treatment on the basis of supporting trials with model foods (tylose and agar samples). Good reproducibility for this more homogenous and standard samples was obtained. Furthermore, significant reductions (P < 0.05) in drip loss of 25 % under specific operating conditions were obtained for carrots, and improvement in the range of 19 - 28 % were observed for chicken and beef samples. As higher drip loss indicates higher damage of the sample structure and thus inferior quality, the microstructure was investigated by making use of the isothermal freeze substitution technique for preparing the samples for microscopy. The MINICRYSTAL treated samples presented a higher proportion of smaller crystals than the control sample (immersion freezing without ultrasound application). Additional studies have been performed to measure mass transfer and to control salt uptake in the food samples. Finally, recommended sound parameters for carrots and chicken and beef samples have been specified.

Following, a pre-industrial MINICRYSTAL treatment bath was built, which can be operated together with commercial cooling units. The prototype was composed of a treatment bath with respective sonication gear, a flexible transport belt system and electronic software control, which can be operated together with commercial cooling units. Following the building, functionality testing and verification of the recommended settings, the MINICRYSTAL prototype was installed in a pilot-plant area in Bremerhaven. A thorough validation regime for the test foods beef, chicken and carrot was deployed. The trials delivered performance results on drip and cooking losses of MINICRYSTAL-treated samples against various control samples (blast frozen, bath-treated without sonication), brine contents, temperature profiles, texture measurements and sensory analysis. Some similar observations were made as within the laboratory level, e.g. lower drip loss in beef samples, whereas with the higher through-put higher deviation in results occurred as expected (e.g. salt up-take, characteristic freezing time, texture shear force measurement). MINICRYSTAL-treated samples nevertheless were generally rated better than blast frozen samples. It was further possible to treat skin-packed food batches as well to proof alternative concepts and use models for exploitation. Finally, standard MINICRYSTAL-treated samples were evaluated in a sensory lab by consumers and by trained panelists.

Overall, the MINICRYSTAL system showed a robust, safe performance with many beneficial effects on specific food applications. Especially, the treatment of chicken breast can be considered as a success story with excellent commercial value for food business operators and high consumer appeal of the end products. For other food applications, further optimisation work is required, but beneficial technological effects were observed (e.g. up-take of solids, weight increase, improved firmness in carrot texture) which have great potential for commercial applications. The highly complementary expertise and broad experience of the partners led to the identification of potential new applications for the developed MINICRYSTAL system in three key areas (food, biomedical sector and related transfer fields). Due to the commercial interests of the SMEs at hand, further details remain confidential and are subject towards further work and intellectual property rights protection.

The system itself offers interesting aspects also from a process engineering point of view: the isolation of the system is valuable in terms of energy-saving and structuring of the work flow and shifts as temperature increases very slowly when the cooling unit is not under operation. Given a singular supply, this can be translated into intermittent operation and energy savings; given a central supply, this context can be used to feed more lines and expand production capacity.

In a socio-economic context, the possibility to make freezing processes 'greener' is very appealing as sustainability issues become more and more important to consumers, businesses and authorities. Therefore, the future exploitation potential of the system is highly appraised.

The research and technology development (RTD) performers have put together respective results and data analysis to visualise and to demonstrate the functionality and benefits of the MINICRYSTAL system. Demonstration session materials, which contain the contacts to two SMEs leading the exploitation (Mr Mario Plasencia: via e-mail; Mr Steve Goode: via e-mail).

List of partners

RTD perfromers:
- Verein zur Förderung des Technologietransfers an der Hochschule Bremerhaven e.V.
Fischkai 1, D-27572
Claudia Krines (R&D Director Food) via e-mail

- Innovació i Recerca Industrial i Sostenible ; Parc Mediterrani de la Tecnologia
Edificio Institut de Geomàtica
Avda. Carl Friedrich Gauss nº 11; E-08860
Colm Digby (General Manager) via e-mail

- University College Dublin
National University of Ireland
Belfield, Dublin 4
Da-Wen Sun (Professor of Refrigeration and Computerized Food Technology) via e-mail


- Fresh Seal, Ltd.
St. Georges Road, Unit 1 Industrial, Telford TF2 7QZ
United Kingdom
George Vanezi (Marketing Manager) via e-mail

- Aktive Arc Sarl.
Les Loges, La Vue des Alpes, CH-2052
Mr Mario Plasencia (Operation Director) via e-mail

- Biotronics Ltd.
Unit 1 Moreton Farm
Moreton Eye, Leominster, Herefordshire HR6 9NE
United Kingdom
Steve Goode (Managing Director) via e-mail

- Rangeland Foods Holding Ltd.
Lough Egish Food Park, Castleblayney, Co. Monaghan. Rep. of Ireland
Jim Lucey (Director) via e-mail

- Gemüsebearbeitung GmbH
Hinterm Holze 10, Twistringen 27239
Birte Kattau-Behnert (Safety&Quality Assurance) via e-mail

- Hebold Mixing and More GmbH.
Peter-Henlein-Str. 12, 27472 Cuxhaven
Lodewijk Postmus (Director) via e-mail