Art Hill, Professor and Chair, Department of food Science, University of Guelph, focuses his teaching and research on cheese technology, dairy chemistry and dairy processing. Research relates to gelation and cheese making properties of milk and milk adjuncts, and milk analysis. Some...
Robert Lencki
User Details
Position / Title:
Associate Professor
Email:
Building:
Food Science Building 38
Room:
245
Phone Number:
519-824-4120 x54327
Fax Number:
519-824-6631 After obtaining his BASc in Chemical Engineering at the University of Toronto, Dr. Lencki worked for two years in the Foods Division of Proctor and Gamble developing new fats and oils, and baking processes. He then returned to academia to do an MSc at the University of Waterloo in Bioprocess Engineering, working specifically on on-line extraction of ethanol from fermentation broths. This was followed by a PhD at McGill University that focused on immobilized enzyme reactor design. After two years as a professor in the Chemical Engineering Department at Université Laval, Dr. Lencki came to the Department of Food Science at the University of Guelph where he is now an Associate Professor. Dr. Lencki is a member of the Biopolymers Separation Group in the Center for Food and Soft Materials and the University of Guelph. Current research interests involve the separation and modification of biomolecules in order to improve the functionality of both foods and ingredients. Some specific projects involve: examining the solution behaviour of proteins, polysaccharides and polyphenols in order to understand their association under both dilute and concentrated conditions (to better characterize membrane ultrafiltration and gel formation phenomena); the study of how phospholipids affect triglyceride crystal morphology (to improve butterfat fractionation and spreadability); casein micelle structure and its fractionation to produce functional ingredients; the development of diacylgycerol blends with suitable food functional properties (to create healthier fat products); and the modeling of produce respiration and gas transfer in modified atmosphere packaging (to extend the self-life of perishables).
Research:
1) Developing new methods for milk processing The standard manner by which raw milk is processed throughout the world involves pasteurization (to destroy all human pathogens) and homogenization (to reduce fat globule size to prevent creaming). In Canada, provincial laws require that all milk be pasteurized, because raw milk can harbour dangerous microbes such as M. paratuberculosis, L. monocytogenes and E. coli. Despite this danger, a growing number of consumers wish to drink raw milk because they feel that current processing methods alter the sensory and nutritional qualities of the milk. Pasteurization does destroy enzymes and immunoglobulins and several of these proteins are known to have health benefits. High temperatures also facilitate interactions between the whey protein beta-lactoglobulin and kappa-casein, which inhibits rennet activity and alters the texture of cheeses and yoghurt. Complex formation also hinders the production of protein peptides during aging, thereby altering the sensory qualities of the final cheese. Connoisseurs know that cheeses produced from raw milk are often superior in taste and texture to those coming from pasteurized milk. The homogenization step also alters the structure of the skim milk membranes (SMM) present in raw milk, thereby changing its mouth feel. This project specifically looks at how heat treatment and homogenization alters milk structure. We have recently published work that was the first to show that casein micelles have a fibril-like structure (J. Dairy Sci. 90:75-89 (2007)) and have proposed a new micelle stabilization mechanism that is consistent with this casein fibril model. WE are now focusing on several simple separation techniques (membrane filtration, precipitation, flotation) that can be used on raw milk to remove the various valuable yet unstable components before further processing. These fractions could then be used as valuable food ingredients or reintroduced into the milk after human pathogens have been destroyed to produce healthier and more functional dairy products. 2) Developing functional DAG fats Consumption of fats and oils (triacylglycerols or TAG) high in saturated or trans fatty acids, or over-consumption of any conventional fat or oil can have serious health consequences including (but not limited to) heart disease, diabetes and obesity. However, it has been demonstrated in both animal and human nutritional studies that, by replacing dietary TAG with 1,3 diacylglycerols (DAG), weight loss is promoted and blood lipids are improved. In Japan, DAG oil (marketed as EconaTM) is now the best selling premium oil, but the same product (EnovaTM) has had only limited success on this continent because it does not have physical properties that are appropriate for baked goods and plastic fats (i.e., butter and margarine), the main sources of dietary fat in the North American diet. This project explores whether, by engineering specific 1,3 DAG fat structures, blends can be made that have melting profiles and crystal microstructures similar to those typically found in commercial plastic fats. 3) Effect of phospholipids on fat crystallization Polar lipids such a monoacylglycerides, diacylglycerides, fatty acids, sterols, and phospholipids (PL) are naturally found in fats and are known to affect crystal structure. In fact, PL is routinely added to margarines and chocolate to obtain desirable functionality. However, it is not well understood how minor components like PL affect fat crystallization behaviour. Adding modifiers to obtain desirable crystal morphology is a common practice in many large-scale industrial crystallization processes. Better control of polar lipid concentrations in fat could potentially provide a very powerful tool for modifying and controlling crystal morphology, thereby improving the quality of fat-based food products.
Teaching:
FOOD*3160 Food Processing I This course builds on the basic engineering principles learned in FOOD*2620 (mass and energy balances; heat, mass and momentum transfer) in order to understand the operation of modern food processing plant facilities. The course will begin with a brief review of the mathematical and problem skills that are used by food engineers, followed by a general discussion of how food processes are design. The standard equipment used, and the underlying principles for their design, will then be examined for various high temperature (blanching, pasteurization, sterilization, evaporation, drying, extrusion) and ambient temperature (size reduction, homogenization, emulsification, centrifugation, filtration, extraction, irradiation) unit operations. Laboratories will be used to illustrate the operation and design of a variety of food processing apparatuses, whereas calculations and the development of problem solving skills will be emphasized in several tutorial sessions. FOOD *3170 Food Processing II This course builds on the basic engineering principles learned in FOOD*2620. As a continuation of the high and ambient temperature unit operations covered in FOOD*3160, low temperature unit operations in food processing will first be examined. This will be followed by a discussion on the design and operation of the ancillary equipment (e.g., refrigeration, material science and transport, measurement and control, sanitation, and water treatment systems) that are key to the operation of food processing plants. Finally, HACCP and how these various unit operations are integrated into a functioning food process will be examined. Laboratories will be used to illustrate various food processing unit operations, whereas calculations and the development of problem solving skills will be emphasized in several tutorial sessions. A feasibility study will also be undertaken so that groups of students can apply the knowledge obtain in the course to the design of various food processes.
Publications:
(for a complete list, see CV) Lencki, R.W. 2007. Evidence for fibril-like structure in bovine casein micelles. J. Dairy Sci. 90:75-89. Caseins are present in mammalian breast milk in the form of micelles containing thousands of associated proteins. Numerous models have been proposed for casein micelle structure and computer modeling has provided some clues as to how the various caseins interact to form these structures. Nevertheless, the principle mechanism by which caseins interact has remained elusive. This work was the first to demonstrate that amyloid fibril-like structures appear to be an important stabilizing mechanism in native bovine casein micelles. Because of their high stability, fibrils are generally avoided in in vivo proteins because excessive accumulation of these structures can lead to pathological disease. As a result, they are not often found in nature: the egg stalk of Chrysopa flava and a number of insect silks are rare examples. On the other hand, fibril-like structures in mammalian milk could have several advantages: Protein destabilization and aggregation inside the cow’s udder would have serious consequences to the animal’s health and milk production. Thus, maintaining a stable casein structure until it reaches the calf’s stomach is crucial. Furthermore, fibrils are often associated with metal ions. The presence of these structures could therefore increase micellar chelation capacity, leading to higher levels of colloidal calcium phosphate solubilization. Torrestiana-Sanchez, B., Balderas-Luna, L., Brito-De la Fuente, E., Lencki, R.W. 2007. The use of membrane-assisted precipitation for the concentration of xanthan gum. J. Membrane Sci. 294:84-92. Our research group was the first to suggest that simultaneous membrane filtration and precipitation could be a useful unit operation for polysaccharide purification. Xanthan gum, a valuable food ingredient, is expensive to produce because a large amount of solvent is needed for precipitation. It is also difficult to concentrate via membrane filtration because of its gel-forming properties. This work demonstrates that large increases in flux can be achieved by adding KCl and isopropanol to xanthan solutions before ultrafiltration. These solutes modify the specific resistance of the fouling layer by altering the phase separation and aggregation behavior of xanthan on the membrane surface. By combining the precipitation and ultrafiltration steps, the amount of solvent required in the separation process can be reduced by more than 40%, thereby greatly improving process economics. Yu, J., Lencki, R.W. 2004. Effect of enzyme treatment on the fouling behaviour of apple juice during microfiltration. J. Food Eng. 63:413-423. Changes in fouling layer surface morphology can alter unclarified apple juice microfiltration flux by several orders of magnitude. Surprisingly, we also observed that some enzyme treatments can create fouling layers that are rigid and porous but also have a high flux resistance. Depending on treatment conditions, high-resistance closed-cell or low-resistance open-cell structures can form. Thus, fouling layer flux resistance can sometimes be more strongly affected by pore tortuosity than gel void volume. Craven, J., Lencki, R.W. 2007. Rapid determination of diacylglycerols in milk fat fractions using solid-phase extraction. Lipids. 42:473-482. Analysis of complex lipid solutions containing elevated levels of diacylglycerols (DAG) is challenging because there is considerable overlap with the triacylglycerols (TAG) fraction during analysis by gas chromatography (GC). Current methods involve separating the TAG fraction by thin layer chromatograph (TLC) before GC analysis but this technique is time-consuming and produces only miligram quantities of the various fractions with a relatively poor yield. The technique developed in this work uses solid-phase extraction (SPE) to quantitatively separate TAG from DAG. This method can be used simply as a means of separating gram quantities of DAG or as a new rapid pre-treatment before GC analysis. Because the health benefits of DAG versus TAG have received a great deal of recent attention, this technique will be used extensively in future DAG research. Lencki, R.W., R.W. Neufeld, T. Spinney. Microspheres and method of producing same. US Pat. 4,822,534 (April 18, 1989); Can. Pat. 1,321,048 (August 10, 1993). Although these patents have expired, this emulsion/internal gelation microencapsulation method has become a standard technique for producing alginate beads. A publication describing the procedure (Appl. Microbiol. Biotechnol. 38:39-45 (1992)) has been cited 82 times.
CV:
