This research proposal responds to the NRI Competitive Grants Program solicitation "75.0 Nanoscale Science and Engineering for Agriculture and Food Science" in priority areas (2) "Novel nanoscale processes, materials, and systems with improved delivery efficacy, controlled release, modification of sensory attributes"; and (3) "Understanding nanoscale phenomena and processes to support the development of nano-based technologies for food and agricultural product quality monitoring". <P>
We focus on the development of a new nanotechnology-enabled process to produce nanoscale energy-saving biopolymer films for frozen foods applications. Our approach is based on the layer-by-layer (LbL) method to form nanoscale biopolymer multilayer films, which will then be used to immobilize extracellular ice nucleators (ECIN). <P>
This proposed research will cover both basic understanding and practical applications. We hypothesize that the ice nucleating activity of ECIN will be maintained after its immobilization on natural biopolymer film surfaces, and the resulted films can change the temperature history of foods during freezing process, resulting in energy saving due to the reduction of supercooling and freezing time.<P>
We also hypothesize that ECIN can reduce the quality deterioration of frozen food caused by freeze/thaw cycles during storage. In this proposal, the following specific objectives will be addressed: <OL> <LI> Determination of the optimum physicochemical conditions to obtain ECIN with optimum ice nucleating activity; <LI> Development of strategy for the formation of nanoscale ECIN coating on hydrophilic natural polysaccharide-based multilayer films; <LI> Development of strategy for the formation of nanoscale ECIN coating on hydrophobic edible food protein-based materials. By coating the ECIN to the biopolymer film surface, the stability of ECIN is expected to improve significantly. In addition, the coated ECIN is re-usable.
NON-TECHNICAL SUMMARY: Freezing is one of the best methods for food preservation. With a frozen food market volume higher than 25.6 billion kg/year, even 1 ?C decrease in freezing temperatures can provide massive energy savings. Freezing requires relatively low temperatures (commercial freezers typically work at -18 ?C). The use of a biogenic ice nucleator is a unique application of biotechnology, as it directly improves freezing processes. Our previous results suggest that, with the application of biogenic ice nucleators, some current food freezing processes may be modified to operate at higher subzero temperatures to provide guaranteed freezing, energy savings and improvement of efficiency and product quality. Therefore, in this proposal, it will be desirable to integrate these unique ice-nucleation active components into new packaging materials or edible biopolymer coating materials for frozen food applications. The integration of extracellular ice nucleators (ECIN) into biopolymer thin films is expect to create novel edible films or novel biodegradable packaging materials. The use of such new materials in frozen foods potentially presents large benefits in terms of: (1) Quality: when such films are in contact with food systems, more nucleation sites will generate more, smaller crystals, changing the crystal size and distribution. This can result in quality improvement of model and real food systems. The changes in the temperature history of the food will certainly affect its quality as well. In addition, it is possible that the addition of ECIN will cause changes in the distribution of frozen water as a function of time and location. So far, no experimental data were found in terms of the effect of ECIN on the storage stability of frozen foods (e.g. the stability following freeze/thaw cycles, temperature fluctuations, or freezers operated at higher temperatures). (2) Economics: foods will freeze at higher temperature and the freezing time will be significantly reduced. These were well documented in model systems and small food systems, and energy savings are expected. Immobilized ECINs are stable and reusable. (3) Intellectual Merit: Biopolymer multilayers formed through electrostatic layer-by-layer deposition offer unparalleled compositional flexibility and a host of promising applications. These biopolymer multilayer films can be used to form nanostructured interfacial layers with specific functionalities, such as hydrophobility, surface morphology, mechanical properties, thickness, gas permeability, and environmental (temperature, pH, pressure etc.) responsiveness. The understanding of the kinetics of polysaccharide layer-by-layer formation, as well as the adsorption on multilayer polymer surfaces will facilitate the optimization of the immobilization of ECIN on polymer film surfaces.
APPROACH: Our experimental strategies in this project focus on the formation of nanoscale biopolymer multilayer films that can be used in the formation of nanoscale ECIN coating, as well as the fundamental understanding of the effects of physicochemical conditions on the multilayer formation and ECIN immobilization. First, we will determine the optimum physicochemical conditions to obtain ECIN with optimum ice nucleating activity. Second, we will develop the strategy for the formation of nanoscale ECIN coating on hydrophilic natural polysaccharide-based multilayer films, where carrageenans, a group of negatively-charged polysaccharides extracted from red seaweed, and chitosan, the only positively-charged polysaccharide from natural sources, will be used to form natural polysaccharide-based multilayer films, which will serve as the substrates for ECIN immobilization. Finally, we will develop strategy for the formation of ECIN coating on hydrophobic edible food protein-based biomaterials. Here we will use the corn zein as the example of hydrophobic edible food protein-based biomaterials.