DETERMINATION OF OIL/STEAM INTERFACIAL TENSION AT ELEVATED TEMPERATURES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0223711
• Project Start Date: Oct 1, 2010
• Project End Date: Sep 30, 2015
• Program Code: [(N/A)]- (N/A)

Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695

Performing Department
Food, Bioprocessing, and Nutrition Sciences

Non Technical Summary
Foods are processed to affect chemical, biological, and/or physical change; often at elevated temperatures to accelerate the desired modifications. While some transformations take place volumetrically, many involve or occur at an interface. The proposed project seeks to quantify the role of surface and interfacial tension in heat and mass transfer at elevated temperatures with a focus on immersion frying. Compositional change in frying oil via degradative use leads to changes in heat and mass transfer rates that are not completely understood. Although these effects have been quantified by the project leader, the transport fundamentals involved were only theorized as data had previously been restricted to room temperature measurement. The objective for this project is to use a newly modified Du Nouy ring method and a pendant drop goniometer with controlled temperature and humidity chamber to measure oil-air and oil-steam interfacial tension over a range of temperatures (20C to 200C) and surfactant types and concentrations (0 to the critical micelle concentration). The oil-air interface is of importance for post frying oil migration while the oil-steam interface is critical to understanding heat and mass transfer during frying. Data will be used to quantitate the physio-chemical changes in oils as they affect heat and mass transfer rates in frying, thereby affording better process control. Our research goal is to better understand the fundamental properties involved such that processors can adjust formulations and/or processing methods to create healthier fried foods.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
501	5010	2020	70%
501	7299	2020	30%

Knowledge Area
501 - New and Improved Food Processing Technologies;

Subject Of Investigation
7299 - Research equipment and methods, general/other; 5010 - Food;

Field Of Science
2020 - Engineering;

Keywords

frying

oil

interfacial tension

surface tension

boiling

Goals / Objectives
The goal of the proposed research is to better understand the relationship between frying oil physical properties and frying heat and mass transfer. Three general objectives are proposed towards achieving the stated goal: 1.) Quantify the effects of temperature on unused frying oil viscosity and interfacial tension over the temperature range of 20-200C (years 1-3); 2.) Quantify the effects of changes in oil composition on viscosity and interfacial tension over the specified range of temperatures(years 2-4); 3.) Measure heat and mass transfer at the oil-product interface during frying over a range of oil compositions/qualities (years 3-5). Within objectives one and two, the interfacial properties will be studied for: a.) an oil-air surface; b.) an oil-steam interface; c.) and oil-solid interface. Our long-term research goal is to better understand interfacial properties at high temperatures and for a wide range of processes such that processors can make adjustments to formulations and/or processing methods to produce healthy, safe, and affordable foods.

Project Methods
Study of high temperature surface and interfacial tension will progress from simple to complex interfaces beginning with the unused oil-air interface, then the unused oil-steam interface, then oil laced with surfactants and/or viscosifiers against air and steam, and lastly testing of oil degraded by repeated frying against air and steam. These interfaces will be studied over the temperature range of 20-200C. The proposed research will initially use canola oil due to its stability and the availability of physical property data given by Miller et al. (1994). Additional oils will be studied as methods and properties are developed. Oil quality will be degraded following the methods outlined in Hubbard (2000) of continuous frying of finely cut potatoes. Quality of the degraded oil will be determined by analysis of total polar materials (TPM) using column chromatography (Hubbard, 2000). Glycerol monostearate (CAPMUL GMS-50 K, ABITEC Corporation, Columbus, OH) will be used to alter the interfacial tension of Wesson Pure Canola Oil (Hunt-Wesson, Fullerton, CA). Glycerol monostearate is a common degradation product produced during immersion frying, and has been shown to significantly reduce interfacial tension at an oil/water interface (Gil and Handel, 1995). Solutions will be prepared with a range of surfactant concentrations from zero to the critical micelle concentration (CMC), the point at which the surface tension is no longer reduced by further addition of surfactant. Interfacial tension measurements will be performed using a pendant drop method (Adamson and Gast, 1997) and a modified Du Nouy ring method over a temperature range of 20-200C and surfactant concentrations, 0-CMC. The newly modified Du Nouy method is proposed as a possible alternative to the considerably more expensive pendant drop method. Thus this research will seek to study the proposed objectives but also test this new method against the accepted pendant drop technique. Interfacial tension will be determined using a goniometer with an imaging system and attached environmental chamber, thus allowing study of high temperatures and humidity. An elevated temperature micro-syringe will be used in conjunction with an automatic pipetting system. Oil-air measurements using the Du Nouy ring will follow that detailed in ASTM (2004) D 971 - 99a with the addition of a controlled temperature isothermal sample cell. Oil viscosity will be measured over a temperature range of 20 to 200C recording data approximately every degree change in temperature. Oil viscosity will be changed through the use of fatty acid methyl esters (Allen et al., 1999). The procedure developed by Hubbard and Farkas (1999) to map over time the convective heat transfer coefficient and heat flux during the boiling stage of immersion frying will be used for this study. It is expected that the primary difficulty will be in determination of the interfacial tension at the oil-steam interface. This will be resolved through use of the Rame-Hart environmental chamber and high temperature syringe to maintain the desired conditions and form the pendant drop at the required temperature, respectively.

Progress 10/01/11 to 09/30/12

Outputs
OUTPUTS: Immersion frying is a widely used cooking technique that involves heating foods in oil above 100C. During frying, the heating profile of the product causes rapid moisture loss at its surface resulting in crust formation without burning. The rate of heat transfer, moisture loss and oil uptake are all affected, in part, by interfacial tension between the oil, steam and food surface. Understanding the relationship between frying oil temperature and the oil-steam interfacial tension may yield insight into the mechanism of boiling heat transfer and thus moisture loss. The pendant drop method was used to determine oil-air and oil-steam interfacial tension for five cooking oils (Canola, corn, olive, peanut, and soybean) at temperatures up to 200C. Initial oil and air values started at room temperature and oil and steam values started at 110C. The pendant drop method relates density difference, force of gravity, drop shape, and drop radius of curvature to interfacial tension. To determine interfacial tension, the density of the oil must to be known at each temperature. Density was determined from room temperature to the smoke point of each oil using the Archimedean method. This method relates fluid density to the buoyancy and volume of a submersed object of known physical properties. PARTICIPANTS: Aydar, Alev: Masters Degree student in Food Science. Degree awarded December 2012 O'Meara, Meghan: Masters Degree student in Food Science. Degree awarded December 2012 TARGET AUDIENCES: Food industry with focus on snack foods, fast foods, and fried foods. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
All oils demonstrated a nearly linear decrease in density with increasing temperature (R2>0.99) from a high of 915.7 kg/m3 (soybean at 22C) to a low of 801.5 kg/m3 (peanut at 200C). Density trends for all oils were similar but density values were statistically different. Coefficient of variations of triplicate measurements at each temperature were less than 0.13%, indicating that the method demonstrated high precision for measuring the density of food oils at high temperatures. All interfacial tension values decreased linearly as temperature increased (R2>0.99) from a high of 32.14 mN/m (Canola oil at 23.5C) to a low of 20.04 mN/m (fresh peanut and fresh corn oil at 200C). Interfacial tension trends were similar for all oils but values were statistically different between oils at a given temperature (p<0.0001). No significant difference was found between the oil-steam and oil-air interfacial tension values e.g. 25.21 mN/m, 25.29 mN/m, respectively, for Canola at 120C. The coefficient of variation for quadruple measurements at each temperature ranged from 0.06 to 0.85%, indicating a precise method.

Publications

• O'Meara, M. and Farkas, B.E. and Dungan, S. 2012. Oil/Steam and Oil/Air Interfacial Tension at Elevated Temperatures. Paper 077-62, Abstract. National IFT Annual Meeting, Las Vegas, NV, USA, June 25-June 28.

Progress 10/01/10 to 09/30/11

Outputs
OUTPUTS: Results were shared through a presentation at the annual Institute of Food Technologists connference in Las Vegas: O'Meara, M. and Farkas, B.E. and Dungan, S. 2012. Oil/Steam and Oil/Air Interfacial Tension at Elevated Temperatures. Paper 077-62, Abstract. National IFT Annual Meeting, Las Vegas, NV, USA, June 25 - June 28. PARTICIPANTS: Farkas, B.E.: Principle Investigator O'Meara, M.: Masters Student, completed 2012 Aydar, A.: : Masters Student, in progress. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Immersion frying is a widely used cooking technique that involves heating foods in oil above 100C. During frying, the heating profile of the product causes rapid moisture loss at its surface resulting in crust formation without burning. The rate of heat transfer, moisture loss and oil uptake are all affected, in part, by interfacial tension between the oil, steam and food surface. Understanding the relationship between frying oil temperature and the oil-steam interfacial tension may yield insight into the mechanism of boiling heat transfer and thus moisture loss. The pendant drop method was used to determine oil-air and oil-steam interfacial tension for five cooking oils (Canola, corn, olive, peanut, and soybean) at temperatures up to 200C. Initial oil and air values started at room temperature and oil and steam values started at 110C. The pendant drop method relates density difference, force of gravity, drop shape, and drop radius of curvature to interfacial tension. To determine interfacial tension, the density of the oil must to be known at each temperature. Density was determined from room temperature to the smoke point of each oil using the Archimedean method. This method relates fluid density to the buoyancy and volume of a submersed object of known physical properties. All oils demonstrated a nearly linear decrease in density with increasing temperature (R^2>0.99) from a high of 915.7 kg/m^3 (soybean at 22C) to a low of 801.5 kg/m^3 (peanut at 200C). Density trends for all oils were similar but density values were statistically different. Coefficient of variations of triplicate measurements at each temperature were less than 0.13%, indicating that the method demonstrated high precision for measuring the density of food oils at high temperatures. All interfacial tension values decreased linearly as temperature increased (R^2>0.99) from a high of 32.14 mN/m (Canola oil at 23.5C) to a low of 20.04 mN/m (fresh peanut and fresh corn oil at 200C). Interfacial tension trends were similar for all oils but values were statistically different between oils at a given temperature (p<0.0001). No significant difference was found between the oil-steam and oil-air interfacial tension values e.g. 25.21 mN/m, 25.29 mN/m, respectively, for Canola at 120C. The coefficient of variation for quadruple measurements at each temperature ranged from 0.06 to 0.85%, indicating a precise method. The results indicate that oil-air interfacial tension may be used as an estimate for oil-steam interfacial tension. Additionally, the method and data generated through this research may be used in analysis of processes involving food oils at high temperatures including frying and atomization of biodiesel fuels.

Publications

• No publications reported this period