Application of magnetized water to reduce oil absorption and improve sensory properties of fried potato

Introduction: Magnetic field-treated water, so-called “magnetized water”, has been a challenging subject over the last several decades in both academia and industry, despite the controversy and the lack of a complete understanding (Esmaeilnezhad et al. 2017). When water is exposed to a magnetic field with positive and negative poles, its molecules become magnetized. This water can have a positive effect on foods due to its hexagonal structure. In addition to the effect of the magnetic field on the shape of water molecules, this magnetic field can reduce the surface tension of water, increase the pH, increase viscosity, and reduce the formation of sediment (Esmaeilnezhad et al. 2017). Ignatov and Mosin (2014) reported that the effect of the magnetic field on water is a complex multifactorial phenomenon resulted in changes of the structure of hydrated ions as well as the physicochemical properties and behavior of dissolved inorganic salts, changes in the rate of electrochemical coagulation and aggregate stability (clumping and consolidation), formation of multiple nucleation sites on the particles of fine dispersed precipitate consisting of crystals of substantially uniform size. Nakagawa et al. (1999) reported essentially two different types of conceivable field effects. One is a direct field effect on the biochemical reactions; the other is indirect via changes in the surroundings. In the case of the former effect, the concern might be the possible genetic influence that a magnetized water can have on living organisms. In the case of the latter, however, the magnetized water effects can be considered like any other external parameter, such as temperature, pressure, or mechanical stirring.
When being applied to water, the magnetic field therein changes the rates of chemical reactions due to the occurrence of competing reactions of dissolution and precipitation of the dissolved salts, facilitates the formation and decomposition of colloidal complexes, and improves electro-coagulation followed by sedimentation and crystallization of scaling salts (Ignatov and Mosin 2014). A series of molecular dynamics simulations showed that the number of hydrogen bonds increases under the application of a magnetic field. In particular, as the strength of the magnetic field increases from 1 to 10 Tesla, the number of hydrogen bonds increases by approximately 0.34%, which indicates that the magnetic field enhances the water networking ability. A larger number of hydrogen bonds suggests that the size of the water cluster increases under a MF; hence, the structure of the water molecules is more ordered and stable under an applied magnetic field (Chang and Weng, 2006).
Antal et al. (2014) studied the effect of magnetic water on the characteristics of freeze drying of apples. The results showed that magnetic water pretreatment increases the drying speed and decreases the drying time of freeze-dried apples. The pretreated apple cubes had a crisper texture and this method improved the color of the dried apples. In another research, Moulaei et al. (2022) studied the effect of magnetic water on the quality characteristics of frozen dough and bread produced from it and stated that the intensity of magnetism has a great effect on the quality of frozen dough in terms of reducing dough defrosting and according to the amount of flour extraction can have a significant effect on the amount of yeast gas production. Also, it can improve the textural properties of bread and be effective in bread staleness. In terms of sensory characteristics, magnetic water can improve the porosity, chewiness and taste of bread.

Fried food products are highly popular among consumers due to their unique textural characteristics (Asadnahal et al., 2022). Various agricultural products like potato absorb a lot of oil when fried in edible oils. The more oil absorbed by these products, the lower their shelf life and quality, and the lower the acceptance of the final product by the consumer. High absorption of oil by fried products can be reduced by applying different pretreatments (Kurek et al. 2017; Salehi 2020).
In this research, the use of magnetized water to reduce oil absorption and improve the sensory and appearance characteristics of fried potato slices was investigated.
Material and methods: In this research, first, potato slices with a thickness of 0.5 cm were prepared and divided into three groups. One group was immersed in water for 20 min. The second group was placed in the water that had already been magnetized by the device for 20 min. The third group was immersed in the magnetized water inside the device and exposed to the magnetic field for 20 min. After 20 min, the samples were removed, the surface moisture was removed, and they were fried at 150°C for 5 min. Finally, the samples were examined for moisture content, oil absorption, hardness, color parameters, color change index, surface changes, and sensory properties.
The moisture content of fried samples was measured by an oven at 105°C for 5 h (Shimaz, Iran) (Hosseini, 2006). The texture determination of the fried potato slices was performed on a STM-5 texture analyzer (Santam, Iran). A puncture test was performed using a cylindrical flat-end punch (diameter 2.5 mm). The test parameters were: pre-test and test speed, 1 mm/s. The test was repeated three times (Li et al. 2022). To examine the changes in color indexes including lightness (L*), redness (a*), yellowness (b*) and colour changes (ΔE) as well as changes in the area of the samples, images were taken after the frying process. The sample photos were captured using HP Scanner (Hp Scanjet 300). L* (lightness-darkness that ranges from 0 to 100), a*(redness-greenness that ranges from -120 to 120) and b* (yellowness-blueness that ranges from -120 to 120) were measured in this study. A hedonistic test was used to estimate the general level of liking for the fried potato slices. Twenty panelists were selected and recruited to descriptively analyze the texture of fried potato slices.
Data are presented as mean ± standard deviation for triplicate measurements. Statistical analysis was performed by one-way analysis of variance (ANOVA) at 95% level of significance, using SPSS software (version 21). In addition, means were compared with Duncan's multiple range test at 95% level of significance.
Results and discussion: The results of this study showed that the oil absorption of fried potato slices was significantly reduced when magnetized water pretreatment was used (p<0.05). The lowest oil absorption (14.85%) was related to the sample treated by magnetized water. The samples exposed to magnetized water and magnetic field had a higher moisture content, which also helps to reduce oil absorption by the product. Regarding moisture content, a significant difference was observed between the control sample and the other two samples (p<0.05), and the moisture content being higher in the treated samples. The texture analysis showed that the use of magnetic water pretreatment reduces the hardness of the fried product. The hardness of the control sample (placed in normal water), pretreated by magnetic water and exposed to magnetic field was equal to 1.67 N, 1.01 N, and 1.32 N, respectively. Antal et al. (2012) reported that the use of magnetic water pretreatment reduced the drying time, created a softer texture (reduced hardness) and increased the rehydration of vacuum-dried apples.
Statistically, there was no significant difference between the redness and yellowness of the samples (p>0.05); However, in terms of the lightness index, the control sample and the sample placed in the magnetic field had a statistically significant difference (p<0.05). The surface color changes of the samples placed in magnetic water were less and the rate of reduction in size of these samples during the frying process was minimal. The surface change of the control sample (placed in normal water), pretreated by magnetic water and exposed to magnetic field was equal to 14.54, 10.77, and 12.97%, respectively. Regarding the acceptability values of appearance, odor, texture, taste and overall desirability, potato slices pretreated with magnetized water received the highest values.
Conclusion: Deep frying has gained increasing attention as it produces attractive sensory and organoleptic properties in products, such as crispy texture, unique aroma and taste, attractive appearance, and faster and easier cooking. As is known, the effect of magnetic field on water bears a complex and multifactorial character that in the final result affects the structure of water and hydrated ions as well as the physico-chemical properties and behavior of dissolved inorganic salts. In general, the treatment of potato slices with magnetized water reduced the oil absorption, improved the size and appearance color, reduced the hardness, and improved the organoleptic acceptability of the product; therefore, it is recommended to use this new method before frying various products. As future research, it is suggested that more research be done regarding the use of magnetized water in the processing of various foods.