For many pure liquids, an increase in temperature causes a linear decrease in the surface tension. Figure 4. 9) as a direct function of temperature for data obtained from both the goniometers: Eq.\ 9. where is the liquid-gas surface tension (), is the oil’s molar mass (), is the oil’s density (), is the Eötvös constant (), is the oil’s critical temperature (), and is the temperature () at which is estimated. The surface tension data was also modeled using the predicted density values obtained from the Rackett equation and fitting them in the Eötvös equation. Same Eötvös constant values could be used to fit the data for all oils studied with one equipment. Deep fat frying is one of the oldest and the most commonly used techniques to process foods, which involves submerging a food in hot oil (150–200°C) for a short period of time until it reaches a safe minimum internal temperature. There was a difference in values for the surface tension measured with KRÜSS vs ramé-hart equipment mainly because of the numerical method used by each equipment in calculating surface tension from the Young’s equation. United States Department of Agriculture. The experimental and predicted data were observed to follow a similar trend with increase in temperature (Fig. Measurements were performed in triplicate. Archimedean method has been successfully used to determine density of liquids at high temperatures (molten igneous rocks) [21]; however it has not been used to measure densities of food oils. Comparison of the average density values between five vegetable oils at different temperatures. We use cookies to improve your website experience. [13] There is an increasing consumer trend for less greasy and healthier products. Surface tension was modeled as a function of temperature using the semi-empirical Eötvös equation (Eq. of vegetable oils (crambe, rapeseed, corn, soybean, milk- of each vegetable oil, and for the purity and the manufac- weed, coconut, lesquerella) and eight fatty acids in the turers of the fatty acids used in the experimental pro- range from Cg to CZZ The viscosity measurements were cedures. The environmental chamber and the high temperature syringe, both equipped with a temperature control system (P/N 100–50; ramé-hart instrument co.; Succasunna NJ, USA) and SOLO Temperature Controller Configuration software (AutomationDirect; Cumming GA, USA) were used. [29,30] Prior to each measurement, the oil was placed inside a beaker and heated under constant agitation until the desired temperature was reached. Understanding of transport rate of oil at high temperatures (up to 200°C) when different types oils are used can be used for varied applications such as a better/more accurate prediction of the oil absorption rates during frying, and understanding of drying rate during spray drying. The value determined for was 69.67 g. Measurements were performed at room temperature (22 ± 1°C), 40°C and at increasing intervals of 20°C until the smoke point of each oil was reached (200°C; except for olive oil, 180°C). This finding agrees with the result from Xu et al. Density values of five vegetable oils from room temperature to the smoke point of each oil. [15] Mass transfer during frying is characterized by the simultaneous movement of water in the form of vapor from the food into the oil, and the movement of oil into the food. Oil: Temperature (°C) Absolute viscosity … [25] The Pendant drop technique is commonly used to measure the IFT of hydrocarbons and crude oils at high temperature [26,27] but has not been used to measure the surface tension of food oils at high temperatures. Intercept (), slope () and correlation coefficient () values corresponding to the empirical equation to predict density of each vegetable oil. [20], and Noureddini et al. 1). Conversions between dynamic and kinematic viscosities were done using the following equation: 12. where is the kinematic viscosity (), is the dynamic viscosity (), and the density () at the selected temperature. The main mechanisms proposed to govern the oil absorption during frying are water escape and oil uptake; capillary pressure; vapor pressure and vacuum effect; diffusion, adherence and drainage of oil on the food surface. A generalized method was developed to estimate the liquid density of vegetable oils and fatty acids. [4,24] Surface tension of oils is measured at room temperature, however, frying process is conducted at temperatures between 150–180°C. Density was modeled using the modified Rackett equation, surface tension using the Eötvös equation, and viscosity by the modified Andrade equation. Comparison between viscosity experimental values of A) Canola oil, and B) Soybean oil and their corresponding predicted values by the modified Andrade equation. By closing this message, you are consenting to our use of cookies. In order to predict the density of a vegetable oil using this equation, it is necessary to know the critical temperature, critical pressure, molecular weight, and Rackett parameter of each fatty acid present in the oil (Table 1), as well as the molar ratios at which the fatty acids are present. Overall, the Eötvös equation overestimates the surface tension value at lower temperatures (23 and 40°C) and underestimates the surface tension at higher temperatures (140–200°C). 6). Rackett parameter is estimated using these values and is a measure of the molar volume of a saturated pure liquid. [ 20 ] , and Noureddini et al. is includes pumping, ow measurement, … Decane was purchased from TCI America (Portland OR, USA). 5). The correlation for vegetable oils was based on fatty acid critical properties and composition of the oil. Table 10. The values of , and were obtained using the method of least squares (Table 11). Oil viscosity depends on oil type as well as frying temperature and oil quality. The buoyancy was determined by: Eq.\ 2. where and are the mass of the reference object plus immersed wired suspended in vacuo, and in the test fluid respectively. Vegetable oils primarily consist of fatty acids in the form of triglycerides. Regardless of the oil type, there was a significant decrease (p < 0.05) in viscosity as the temperature increased (Fig. Registered in England & Wales No. The difference in Eötvös constant with respect to equipment was mainly because of the differences in numerical method used for surface tension calculation by the equipment, which affected the fit of the model. Oil viscosity depends on oil type as well as frying temperature and oil quality. Canola oil (Wesson, ConAgra Foods Inc.; Omaha NE, USA), extra virgin olive oil (Filippo Berio, SALOV North America Corp.; Lyndhurst NJ, USA), soybean oil (Crisco, The J.M. Statistical analysis using General linear model (GLM) showed significant effect (p < 0.05) of temperature and oil type on density. Absolute Viscosities of Vegetable Oils at Different Temperatures and Shear Rate Range of 64.5 to 4835 s −1. Rackett Equation, On the Interfacial Behavior of Ionic Liquids: Surface Tensions and Contact Angles. Table 4. Correlations were developed for viscosity with temperatures using empirical equations as well as relating fatty acid composition to the viscosity change. We would like to thank Dr. Owen Jones, Dr. Rituraj Borghain, Dr. Oswaldo Campanella and Dr. Cordelia Running for granting us access to use the equipment and facilities in their lab. Smucker Co.; Orrville OH, USA), peanut oil (LouAna, Ventura Foods, LLC; Brea CA, USA) and corn oil (Mazola, ACH Food Companies, Inc.; Memphis TN, USA) were purchased from a local market. All the oils used in the study showed Newtonian behavior at the range of temperatures studied. [34] where no effect of oil type on surface tension was observed, and the effect could be attributed to the presence of long-acyl chains in all oils, whose surface tensions are not very different from each other. [35] The , and were calculated as the sum of the corresponding property for each fatty acid present in the oil weighted with its correspondent molar fraction; was calculated using Eq. Table 6. According to the US Department of Agriculture [12], world vegetable oil consumption has increased from 151.68 to 177.16 million metric tons from 2011/12 to 2015/16. [32] Eq.\ 5. Table 1. Density is an important factor which influences oil absorption as it affects the drainage rate after frying and also the mass transfer rate during the cooling stage of frying. The trends for all the three physical properties were similar to those reported in literature, and thus results could be corroborated. Dynamic viscosity measured was then converted into kinematic viscosity (υ, Eq. The heating profile for the temperature controller was set up as: heat from 23°C until the smoke point of each oil (200°C, except olive oil 180°C) in increments of 20°C and holding at each temperature for 5 min.