In situ monitoring of solid fat content by means of pulsed nuclear magnetic resonance spectrometry and ultrasonics

Abstract

An ultrasonic technique was developed to study the crystallization process of edible fats on-line. A chirp wave was used instead of the conventional pulser signal, thus achieving a higher signal-to-noise ratio. This enabled measurements to be made in concentrated systems [~20% solid fat content (SFC)] through a 8.11-cm thick sample without significant signal loss. Fat samples were crystallized at 20, 25, and 30°C at a constant agitation rate of 400 rpm for 90 min. The crystallization process was followed by ultrasonic spectroscopy and a low-resolution pulsed nuclear magnetic resonance spectrometer. Specific relationships were found between ultrasonic parameters [integrated response, time of flight (TF), and full width half maximum] and SFC. TF, which is an indirect measurement of the ultrasonic velocity (v), was highly correlated to SFC (r 2 > 0.9) in a linear fashion (v = 2.601 SFC + 1433.0).Paper no. J10957 in JAOCS 82, 305-312 (May 2005). KEY WORDS:Full width half maximum, integrated response, p-NMR, solid fat content, time of flight, ultrasonic velocity.Sensing and measurement of food properties is crucial to the improvement of the quality of food and profitability of food manufacturing operations. Instrumental measurements can reduce the dependence on time-consuming chemical and sensory analysis. Measurements should provide some information about the food (e.g., temperature, composition, structure, concentration) that will be useful in controlling final product quality. The response time is crucial, so although laboratory tests on finished product are valuable, measurements made on-line of the freshly made or in-process foods are better. On-line sensors used in the food industry must also be inexpensive and robust to survive in the frequently hot and wet environment of a food-processing plant. The technique should also be both nondestructive and amenable to hygienic design principles (ideally, noninvasive). It should also provide a relatively simple output to an operator or an automated control system (1). Ultrasonic technology has advantages over many techniques because it can be applied to systems that are optically opaque, concentrated, and electrically nonconducting. In addition, ultrasonic measurements are rapid and precise, are nondestructive and noninvasive, can be fully automated, are nonhazardous, and are particularly suitable for on-line monitoring.Ultrasound techniques exploit the interaction of high-frequency sound with matter to generate information about material physicochemical properties. Such techniques have been established and used in numerous fields such as medicine, oceanography, and materials science. A number of publications have demonstrated the usefulness of ultrasound in food research, including particle size determination, creaming, crystallization, and aggregation phenomena in emulsions (2,3). Ultrasound also has been used to characterize the rheological behavior of solid fat dispersions and xanthan/sucrose mixtures (4,5) and to calculate the percentage of frozen material in foods...

New technologies to determine solid fat content on‐line

“…Ultrasonic technology, on the other hand, proved to be an accurate technique to measure SFC on-line since no corrections needed to be made. Previous data (1) showed that this technique can be used even for high SFC values and that measurements do not depend on sample motion. Transducers can be placed in the pipe walls where the fat is being crystallized, and therefore the crystallization process can be followed in real time.…”

“…SFC was measured on-line by means of an ultrasonic technology developed previously in our laboratory (1,2). Figure 5 shows the comparison between the SFC obtained by the mq20, NMR-MOUSE, and ultrasonic technology for both samples (A and B) diluted 50% with canola oil and crystallized at 30°C.…”

“…Sometime after the SFC plateau was reached, ultrasonic measurements could not be performed owing to the high attenuation of the signal. This attenuation depends on crystal size and the final SFC, which depends indirectly on the crystallization temperature and the chemical nature of the sample that is being crystallized (1,2).…”

“…Crystallization experiments at 30°C, SFC determinations, and ultrasonic experiments were carried out with two fat samples (1). Interesterified hydrogenated palm oil was used as sample A and partially hydrogenated palm oil and palm stearin as sample B.…”

“…This fact has encouraged scientists to develop new techniques that can be used to measure SFC values online. Recent work has proven that ultrasonic technology can fulfill this promise (1,2). Ultrasound techniques have been used in numerous areas, such as medicine, oceanography, and materials science.…”