The ultimate goal of my research is to develop methods for enhancing functional performance of dairy foods by controlling their mesoscopic scale structures. Milk consists of mesoscopic particles such as fat globules, casein micelles, and whey proteins that are dispersed in an aqueous medium. These particles are transformed into smaller particles or aggregate to form larger clusters during dairy food processing, significantly impacting stabilities, functionalities, eating qualities, and digestabilities of dairy foods. <P>The objective of the proposed project is to reveal general principles behind the formation of mesoscopic structures of whey proteins that are byproducts from the dairy industry. This is considered to be a sound approach for enhancing the utilization of whey proteins, thereby improving the sustainability of the dairy industry, because the application of whey protein is currently dominated by the use for protein fortification purposes. Whey proteins exhibit various physicochemical functionalities such as gelation and surface active properties that are known to be improved further by conjugating whey proteins with polysaccharide. In this project, whey protein-polysaccharide conjugates (WPPC) will be prepared using polysaccharide with varied molecular weights and the formation of two types of mesoscopic structures will be studied. <P>Output 1: Fabrication of micrometer-sized particles that morphologically mimic fat particles in foods for fat reduction. When heated in an aqueous solution, whey proteins denature and aggregate to form large structures with various morphologies, depending on pH and ionic strength among other factors. Particulate aggregates that resemble fat particles in foods are formed at pH near the isoelectric points of whey proteins; however, the formation of such particulate aggregates is a rapid process and difficult to be precisely controlled. Heat-induced aggregation of WPPC is expected to be significantly slower than that of whey protein alone. Therefore, correlations between aggregation kinetics, heating conditions, and polysaccharide structures of WPPC will be established and used to identify optimal conditions for producing micrometer-sized whey protein particles suitable for fat replacement. <br/>Output 2: Fabrication of nano-particles for the delivery of hydrophobic antimicrobials, micronutrients, and nutraceuticals in foods. Many functional compounds that have health benefits or promote food safety are hydrophobic and difficult to be uniformly distributed within food matrices. Whey proteins are capable of encapsulating hydrophobic compounds into mesoscopic particles and disperse them in aqueous media; however, these particles tend to aggregate during long-term storage and/or by the application of heat during manufacturing, leading to deteriorated food qualities. Conjugation of whey proteins with polysaccharide is expected to offer a solution because polysaccharide is considered to form a protective layer on the particle surface and prevent particles from aggregation. In this study, WPPC-based nano-particles will be developed for enabling uniform distribution of hydrophobic functional compounds in foods.
Obesity is increasing throughout the world as a result of chronic energy imbalance, posing many health risks, including cardiovascular diseases, diabetes, and some forms of cancer. Nevertheless, reduced fat food products tend to suffer in the market place because consumers are reluctant to sacrifice eating pleasure for health. The current strategy for fat reduction in foods is to replace fat with dietary fiber or gelatinized starch. These fat replacers do not provide the right texture or mouth-feel because their structures do not resemble those of fat. Fat in dairy foods typically exists as small particles with an average size around 1 micrometer. What is needed to enable fat reduction in foods without generating adverse effects on eating qualities is to develop a method for imitating the fat structure in foods. Whey proteins are water soluble proteins in milk serum. When heated in an aqueous solution, whey proteins denature and aggregate to form large clusters with various morphologies, including small particles that resemble the structure of fat in foods. However, it is difficult to obtain whey protein particles that give the right texture because they rapidly stick together and turn into large particles that give chalky or gritty mouth-feel. Our approach in this project is to manipulate polymer-polymer interactions between whey proteins and food polysaccharides for gaining control over the formation of whey protein particles and enabling the production of whey protein particles that mimic creamy texture characteristic of fat in food. Another promising application of whey proteins is the utilization as a vehicle for delivering hydrophobic functional compounds in food. Despite much work that has been done to reduce contamination of foodborne pathogens from farm to fork, outbreaks of foodborne illnesses are frequently reported. Many antimicrobials are hydrophobic or lipophilic and their limited solubilities in aqueous systems tend to cause significant reductions in their antimicrobial activities in foods. Whey proteins are capable of encapsulating hydrophobic compounds into particles and disperse them in aqueous media; however, these particles tend to aggregate during long-term storage and/or by the application of heat during manufacturing, leading to deteriorated food qualities. Our approach in this project is to form a protective polysaccharide layer on the surface of whey protein particles and prevent them from aggregation. The developed system will be also applicable for the delivery of health beneficial hydrophobic compounds such as ?-carotene, lycopene, and tocopherol and is expected to serve as a tool for improving health and human well-being. Whey proteins are byproducts from cheese manufacturing. To date, whey proteins are predominantly used for rather limited types of food applications such as a protein source in sports nutrition products. For the sustainability and growth of the cheese industry, it is desirable to develop a variety of application areas of whey proteins. The proposed research is expected to open up a number of novel application opportunities and significantly enhance the utilization of whey proteins.
1. Preparation of whey protein-polysaccharide conjugates (WPPC) WPPC is normally prepared by heating mixtures of whey proteins and polysaccharide in a dry condition. In this study, WPPC will be prepared using not only the standard protocol but also unconventional wet-heating methods. Dextran was chosen as the polysaccharide source. For dry-heating treatments, whey protein isolate (WPI) and dextran will be mixed at a certain weight ratio and heated at 80 degrees C for 2 hours in a dry condition. For wet-heating treatments, WPI and dextran will be dissolved in buffer solutions and heated at 60 degrees C for 24 hours.
2. Kinetics of heat-induced aggregation of WPPC WPPC will be dissolved in distilled water at varied WPPC concentrations, pH, and ionic strengths and heated in a water bath at varied temperatures for varied periods of time. Non-aggregated WPPC will be quantified based on the intensity of the refractive index of the non-aggregated fraction. The weight-average molecular weight of aggregated WPPC will be determined based on static light scattering measurements on heated WPPC solutions that contain both aggregated and non-aggregated fractions. The scattering wave vector dependence of scattered light intensities will be measured using a multi angle laser light scattering (MALLS) photometer and normalized after subtracting the contribution from the non-aggregated fraction. The weight-average molecular weight of the aggregated fraction will be evaluated as the structure factor at zero wave vector. Morphological developments during heat-induced aggregation of WPPC will be studied using atomic force microscopy (AFM).
3. Encapsulation properties of WPPC WPPC will be dissolved in a buffer solution, mixed with varied volume fractions of oil phases containing varied amounts of hydrophobic compounds, stirred using a high speed blender, further homogenized using a high pressure homogenizer, and spray-dried. The spray-dried powders will be re-hydrated in deionized water to prepare aqueous dispersions of nano-particles containing the hydrophobic compounds, adjusted to varied pH and ionic concentrations, and stored. Time-dependent changes in turbidity and particle size distribution will be monitored during the storage. Small amounts of the nano-dispersions will be sampled at periodic intervals during the storage for evaluating the release kinetics of the encapsulated hydrophobic compounds. Surface morphologies of nano-particles will be investigated using AFM.
4. Efforts and evaluation The results from this study will be disseminated primarily by publications in scientific journals in the field of the food/dairy science as well as presentations at meetings of organizations such as the American Dairy Science Association and the Institute of Food Technologists. Direct educational benefits include the training of graduate students, participation of undergraduate researchers in the project, and integration of research and educational activities to communicate research outcomes in a broad context. Industrial personnel will benefit from training opportunities provided through the Dairy Foods Short Courses hosted by the Department of Food Science.