Qixin Zhong Research

Research Areas in Food Ingredient Science Technology

We study the distribution of antimicrobials in food matrices with the goal to eventually model and control mass transfer required to rationally design delivery systems. We explore novel antimicrobials and combinations of antimicrobial mechanisms to improve the efficacy of antimicrobials as intervention strategies. By collaborating with food microbiologists, we also study biophysical principles of antimicrobial activities.

We fabricate colloidal particles to encapsulate antimicrobials and control their release properties. These colloidal particles are formed with various principles from food biopolymers (sols) or mixtures of oils and surfactants (emulsions, microemulsions, and nanoemulsions). The encapsulated natural antimicrobials are added in foods or used as alternative solutions for postharvest washing fresh produce to address disadvantages of conventional antimicrobials.

We also study antimicrobial coatings to inhibit pathogens potentially contaminating fresh produce and to preserve quality during shelf-life storage. Colloidal particles encapsulating antimicrobials can overcome topographical barriers on produce surface and control mass transfer of antimicrobials to achieve long-term efficacy against pathogens. Antimicrobial coatings also can control postharvest physiology to reduce the loss of produce quality.

Antimicrobial preservatives are used in or on food products to inhibit the growth of pathogenic and spoilage microorganisms to ensure microbial safety and quality. The molecular structures of antimicrobials determine they may separate out of the aqueous phase and bind with food components due to attractive hydrophobic and/or electrostatic interactions. These physical phenomena require delivery systems to evenly distribute antimicrobials at the application site and reduce the interference of food components so as to enhance the availability of antimicrobials to interact with microorganisms.

Physically, delivery systems are one-, two-, or three-dimensional structures engineered according to physical, chemical, and biochemical principles based on a specific application. These structures are fabricated so as to minimize negative effects of environmental stresses or respond to physical, chemical, biochemical, and biological conditions at the application site. For food applications, these structures shall be prepared with ingredients at a level approved by regulatory agencies. For practical applications, technologies shall be scalable and inexpensive, ingredients shall be affordable and sustainable, structures shall be small enough to prevent adverse effects on texture (sandiness; viscosity), appearance (turbidity in transparent products; color), and dispersion stability, and, most importantly, delivery systems must not cause negative effects on the health and well-being of humans and animals.

We study delivery systems for a wide variety of bioactives, including phytochemicals, enzymes, amino acids, bioactive lipids, dietary fibers, and probiotics. Structures in our studies include biopolymer-bioactive complexes, coacervates, biopolymer particles, microemulsions, emulsions, nanoemulsions, solid lipid nanoparticles, and films. Lipophilic compounds are dissolved in the lipid phase of emulsion droplets with single or double layers. We also fabricate solid/oil/water emulsions to deliver water-soluble compounds and probiotics. In addition to characterizing functions of these delivery systems, structures at different length scales are studied to interpret novel functions.

Diets are the foundation of human nutrition and health. With the increasing scientific evidences of bioactive dietary components and beneficial bacteria promoting health, there are great needs of technologies to incorporate these ingredients in food products to maintain food quality, prevent the activity loss during processing and storage of foods and post-ingestion, and deliver bioactives to the target site. Delivery systems are studied to address these needs to produce functional foods.

We study strategies of stabilizing solid particles in sols during food processing and storage. Examples include physical (complexation and preheating), biochemical (transglutaminase cross-linking), and chemical (glycation with reducing saccharides using the Maillard reaction) methods to minimize thermal aggregation of whey proteins, formation of biopolymer complex particles to disperse alcohol-soluble plant storage proteins (prolamins) such as those of corn (zein), and adsorption of polysaccharides on protein particles. These studies are needed in production of beverages.

We fabricate novel oil/water/surfactant mixtures in forms of emulsions, microemulsions, and nanoemulsions. Examples include engineering interfaces using combinations of surfactants with synergistic functions, especially without the need of high mechanical energy. These systems are used to deliver flavorings, antimicrobials, and bioactive compounds.

We also engineer foams with superior stability. This is studied by overcoming destabilizing mechanisms of liquid drainage, disproportionation, and coalescence to prevent the collapse of air bubbles. The stability of foams is important to products such as whipped creams and ice creams.

Colloidal particles have a dimension typically from several nanometers to about 1 micrometer, but the dimension of colloidal systems can be well over 1 micrometer if they share common physical phenomena. Colloidal particles are native to many food products, with milk being a common example because of the dimensions of casein micelles and fat globules. Colloidal science is significant to the manufacturing of many food products that have solid (a sol), liquid (an emulsion), or gaseous (a foam) particulates dispersed in a liquid or solid continuous phase. Research goals are to create colloidal systems with unique sensory and functional properties and maintain these properties during shelf-life storage.

Proteins can self-assemble due to chemical and physical forces during heating, antisolvent precipitation, or a pH cycle, and the prepared particles can be designed with novel gelation, stabilizing, and thickening properties enabling new applications. Complex particles composed of proteins, polysaccharides, and small molecular surfactants can be fabricated to be stable (for dispersion in beverages) or unstable (for gelation in semi-solid products) against aggregation. These particles with unique surface properties also can be used to prepare (Pickering) emulsions and foams.

We also study amyloid-like fibrils self-assembled from peptides after acid hydrolysis of proteins as materials for potential food applications. Dispersions with these fibrils provide a zero-shear viscosity several magnitudes higher than conventional protein dispersions (Biomacromolecules 14: 2146; Soft Matter 11: 5898). Fibrils produced from different food proteins have unique mechanical properties (Young’s modulus) for novel food and non-food applications (Soft Matter 11: 5898). Fibrils and the derived rods also have potential applications as surfactants and encapsulating materials.

Many food ingredients are used to provide rheological, interfacial, and mechanical properties that are needed to produce food products with unique quality attributes. Rheological properties are important to thickening, gelation, and stabilizing functions that are correlated to viscosity, viscoelasticity, and yield stress. From the materials perspective, self-assembled structures of food molecules with and without assistance of external forces can be fabricated utilizing physicochemical and biochemical properties of food molecules to enable the desired functional properties.

We are interested in understanding molecular, nanoscopic, microscopic, and macroscopic structures of food biopolymers and food products to interpret their functions relevant to processing, storage, sensory, digestion, and biological properties. Analytical tools and theoretical frameworks in colloidal and biopolymer sciences are used to correlate molecular interactions, multi-length scale structures, and physical properties of food biopolymers and food products. The new science gained from these studies can be used to guide technological developments to improve and design functional properties of food biopolymers and food products.

Food biopolymers, proteins, and polysaccharides are common ingredients in food preparation. Food biopolymers also form structures of native and processed food products to determine quality and the digestion and bioavailability of major and minor nutrients and bioactives important to health. Understanding physical, chemical, biochemical, and biological properties of food biopolymers and food products therefore is important to improve their functional properties for optimized nutritional and health benefits.

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Dr. Qixin Zhong

qzhong@utk.edu

865-974-6196

Research Areas in Food Ingredient Science Technology

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