Polydimethylsiloxane Shows Strong Protective Effects in Continuous Deep-Frying Operations.

Polydimethylsiloxane (PDMS) was previously reported to show no protective effect in continuous deep-frying. In this study, we used canola oil with/without added PDMS to deep-fry shredded potato at 180°C either continuously or with 10-, 20-, or 30-min intervals between frying sessions for 6 h. In continuous deep-frying in canola oil not containing PDMS, far more oil vapor was generated from the oil and the water in the potato compared to frying with 20- and 30-min intervals between sessions and the oil in the fryer accordingly had a lower polar compound content (PC). The longer the oil was used to deep-fry potato, the more steam was generated from potato. Thus, polar compounds evaporated into the air in the steam, resulting in a low PC value of oil in the fryer. In contrast, both thermal deterioration and oil vaporization were remarkably inhibited in canola oil containing PDMS regardless of the frying pattern, and the PC value of the oil in the fryer increased in proportion to the amount of potato deep-fried. Canola oil with/without added PDMS was heated at 180°C for 6 h to confirm the effect of water released from potato on the oxidation of oil. A large increase in PC was observed in canola oil not containing PDMS when heated without water but this increase was inhibited to some extent when water was supplied continuously. On the other hand, the PC of canola oil containing PDMS was far lower than that of oil not containing PDMS, but the addition of water promoted an increase in PC. In conclusion, we observed superior protective effects of PDMS regardless of the deep-frying pattern employed, but the PC value nonetheless increased as the amount of food deep-fried increased. In addition, we confirmed that water in potato strongly correlates to PC increase of oil in the fryer.

Polydimethylsiloxane Droplets Exhibit Extraordinarily High Antioxidative Effects in Deep-Frying.

The addition of more than about 1 ppm polydimethylsiloxane (PDMS) into oil results in PDMS forming both a layer at the oil-air interface and droplets suspended in the oil. It is widely accepted that the extraordinarily strong and stable antioxidative effects of PDMS are due to the PDMS layer. However, the PDMS layer showed no antioxidative effects when canola oil did not contain droplets but rather was covered with a layer of PDMS, then subjected to heating under high agitation to mimic deep-frying. Furthermore, no antioxidative effect was exhibited by oil-soluble methylphenylsiloxane (PMPS) in canola oil or by PDMS in PDMS-soluble canola oil fatty acid ester during heating, suggesting that PDMS must be insoluble and droplets in oil in order for PDMS to exhibit an antioxidative effect during deep-frying. The zeta potential of PDMS droplets suspended in canola oil was very high and thus the negatively charged PDMS droplets should attract nearby low molecular weight compounds. It was suggested that this attraction disturbed the motion of oxygen molecules and prevented their attack against unsaturated fatty acid moiety. This would be the reason in the deep-frying why PDMS suppressed the oxidation reaction of oil. PDMS droplets also attracted volatile compounds (molecular weight below 125 Da) generated by heating canola oil. Thus, adding PDMS to oil after heating the oil resulted in the heated oil smelling less than heated oil without PDMS.

The Antioxidation Mechanism of Polydimethylsiloxane in Oil.

Strong and stable antioxidation effects of polydimethylsiloxane (PDMS) are widely accepted and utilized in commercial frying oil; however, the mechanism is not fully established. On the other hand, canola oil contains about 700 ppm (mg/kg-oil) of the natural antioxidant, tocopherol. Canola oil containing 0, 1 and 10 ppm added PDMS was heated at 180°C for 1 h under stirring, then left for 2-3 days at room temperature; this treatment was repeated 5 times. Compared to pure canola oil, PDMS-containing canola oil exhibited remarkably lower peroxide, p-anisidine and acid values, a lower decrease in tocopherol content but a higher oxygen content during the heating experiments, implicating low oxygen consumption for the oxidation. While PDMS has not been known to exhibit antioxidative effects at ambient temperatures, the present results show that PDMS prevents autoxidation as well as thermal oxidation. In addition, PDMS, not tocopherols, provided the major antioxidative effect during intermittent heating, and the decrease of tocopherols was significantly inhibited by PDMS. Phase contrast microscopy confirmed that PDMS contained in canola oil was suspended as particles. Also, the oxygen content in standing PDMS-containing canola oil decreased as the depth of oil increased, corresponding to the PDMS distribution, which also decreased as the depth of oil increased. Moreover, PDMS had a higher affinity for oxygen than canola oil in a mixture of canola oil/PDMS, 1:1 v/v. Thus, it is suggested that PDMS restricted the behavior of oxygen dissolved in canola oil by attracting oxygen in and around the PDMS particles, which is wholly different from the radical scavenging antioxidation of tocopherol.

Study on the effect of polydimethylsiloxane from the viewpoint of oxygen content in oil.

It has been reported that polydimethylsiloxane (PDMS) inhibits oxygen dissolution into oil by forming a monolayer on the surface of the oil, thereby reducing thermal oxidation. In the present study, the distribution of PDMS was determined by the inductively coupled plasma atomic emission spectroscopy in standing PDMS-containing canola oil. PDMS did not disperse in the oil uniformly, but there was a tendency that the PDMS concentration decreased as the depth of oil increased, and the concentration of the bottom part was the lowest. When canola oil was covered with PDMS by dropping it gently on the surface of the oil and kept at 60°C, the oxygen content and oxidation of the oil were lower than those of the control canola oil. PDMS-containing canola oil and canola oil were heated with stirring from room temperature to 180°C, and then allowed to stand while cooling. Oxygen contents of both oils increased up to 120°C then dropped abruptly. While cooling, oxygen contents sharply increased at 100°C and approached the saturation content, although the increase for PDMS-containing canola oil was a little slow. Likewise, the thermal treatment of PDMS-containing canola oil and canola oil at 180°C for 1 h under stirring was repeated 5 times with standing intervals for 2-3 days at room temperature. Oxidation of the former was less than that of the latter in spite of its high oxygen content. In conclusion, the oxygen content of oil with/without PDMS addition increased, but oxidation of PDMS-containing canola oil was inhibited both during heating and standing with intermittent heating. It was suggested that PDMS exerted its antioxidative effect regardless of whether it covered the oil or was dispersed in it.

Oxygen content and oxidation in frying oil.

The relation between oxygen content and oxidation was investigated in frying oils. When canola oil, a canola-soybean oil blend or a trioctanoylglycerol (glycerol tricaprate) sample were heated with stirring, their dissolved oxygen content decreased abruptly at about 120°C and the carbonyl values (CV) increased gradually with heating and reached values of 6-7 at 180°C in the blended and canola oils, while the CV of trioctanoylglycerol was zero up to 150°C. Probably this abrupt decrease in oxygen content above 120°C can be attributed to the solubility of oxygen in oil rather than because of oxidative reactions. The oxygen content of oil that has been stripped of part of its oxygen, increased at temperatures between 25 and 120°C. In oils that have lost their oxygen by being heated to 180°C, standing at room temperature will slowly restore their oxygen content as the oil cools. Intermittent simple heating of oil promoted oxygen absorbance during cooling periods and standing times, and it resulted in an elevated content of polar compounds (PC). Domestic deep-frying conditions also favor the presence of oxygen in oil below 120°C and during the oil's long standing at room temperature. The oxygen content in oil was low during deep-frying, but oxidation was active at the oil/air interface of bubbles generated by foods being fried. Repeated use of oil at temperatures between 25-180°C resulted in oil with low oxygen values.

Oxidation of frying oils during intermittent usage.

We reported previously that in oils used for frying by commercial establishments, a high correlation was observed among their Gardner colors, polar compound contents (PC), carbonyl values (CV) and acid values (AV). However, this was not true for frying oils used in hospitals. In the present study, oils that had been used for deep-frying in hospital kitchens were collected and assayed for PC, CV, AV, and Gardner color value to determine the reason for the differences from oil used in commercial establishments. Hospitals were selected so that variation in the number of inpatients, frying oil fatty acid composition, and frying frequency was obtained. As previously observed, we did not find good correlations between the color of the frying oil and the PC, CV or AV, respectively. The extent of oxidation in batches of oil repeatedly used for deep-frying was in the following order: soybean oil > blended oil > canola oil. After use in deep-frying, where the oxygen content goes effectively to zero, allowing the oil to stand at room temperature resulted in the quick and steady absorption of oxygen until it returned to its initial content. In addition to the effect of thermal treatment of oil, standing time between usages is a significantt cause of oxidation.

Color and chemical properties of oil used for deep frying on a large scale.

Acid value (AV), polar compound content (PC), carbonyl value (CV) and Gardner color of oil used for deep-frying in kitchens at a supermarket, lunch chain store, restaurant, eating house, and hospital were analyzed. All AVs obtained but one (3.38) were within the limit set by the Food Sanitation Act of Japan (AV ≤ 3, peroxide value ≤ 30). However, some oil samples had a PC over 25%, which is beyond the limit legislated by some European countries. When the relation between the Gardner color and the AV, PC, or CV of the oil was investigated, well correlated logarithmic regression curves were obtained from the oil of all kitchens except the hospital kitchen. However, the use of lard-containing canola oil without oil replenishment in the eating house increased color values rapidly. All of the values obtained from pure vegetable oil used almost daily were plotted on a graph. It was found that kitchen-by-kitchen differences in fryer, vegetable oil, frying temperature, heating time, and amounts and kinds of foods fried did not influence the relation between Gardner color value versus AV, PC or CV. In conclusion, frying vegetable oil used in large-scale kitchens without official inspection can be better controlled with Gardner color determination by the operators and administrators. This would improve the quality of the oil ingested by facility patrons.

The mechanism of weight-loss promoting effects of oil heated with vegetable protein.

We have previously reported that a soy oil-containing experimental diet (fat-free AIN93G containing oil thermally processed with soybean protein followed by filtration), inhibited body weight increases without any adverse effects when given ad libitum to male Wistar rats for 12 weeks. In the present paper, the mechanism of weight-loss promoting effects was investigated. Fasted 10-week-old rats were fed a slurry composed of AIN93G (fat-free), Cr(2)O(3) (marker), water, and 7 wt% soy oil or fresh oil (control) and sacrificed at 20, 60, 90, 120, 150, 210, 270 or 360 min. The stomach, small intestine, cecum, colon and feces were then collected to determine the distribution of the slurry in the digestive tract. The results indicated that the content was transferred faster from stomach to small intestine in the soy oil group than in the control group. Fecal excretion (derived from a commercial standard diet ingested before slurry administration) in the soy oil group was significantly higher than in the control group. Digestive enzyme activities, lipase, sucrose, and maltose, were not inhibited by soy oil. In addition, feces collected in the 12-week feeding experiment were more in the dry weight and contained higher levels of nitrogen and water in the soy oil group than in the control group, revealing that an increased amount of nutrition was continuously excreted in the former group. The above-described findings suggest that soy oil stimulated peristalsis of the gastrointestinal tract and that colon contents are actively excreted, resulting in safe and steady body weight decreases.

Effects of docosahexaenoic acid in an experimental rat model of nonalcoholic steatohepatitis.

Docosahexaenoic acid (DHA) regulates the lipid metabolism and inflammation that is closely associated with oxidative stress. The present study investigated the effects of DHA on the development of nonalcoholic steatohepatitis (NASH). To induce fatty liver, rats were fed choline-deficient high-fat diets (CDHF). The rats were then divided into 4 groups treated over the subsequent 6 weeks as follows: control, CDHF, CDHF+oxidative stress (NASH), and NASH+DHA (1.0 g/kg, p.o.). Rats of the control group were fed MF chow diet only. NASH rats showed severe steatohepatitis and liver fibrosis. Treatment with DHA significantly decreased the n-6/n-3 ratio in the livers and increased plasma SOD like activity compared with NASH rats. In addition, DHA attenuated the liver fibrosis during NASH development. Therefore, a higher DHA ratio in the liver of NASH rats might regulate the inflammatory response through a low n-6 ratio and diminished oxidative stress, effectively inhibiting liver fibrosis during NASH progression. These results suggested that DHA is a novel functional food for the prevention of NASH.

Effects of oil thermally processed with vegetable protein on gastrointestinal tract content transfer.

It has been reported that oil heated with vegetable protein under reduced pressure, followed by filtration (soy oil), decreased body, liver and retroperitoneal fat tissue weights and serum triacylglycerol levels in Wistar rats. In order to clarify the mechanism of these weight-loss promoting effects, gastrointestinal tract content transfer was traced. Fasted 10-week-old rats were fed a slurry containing AIN93G without fat, Cr(2)O(3) (marker), and 7 wt% soy oil or fresh oil (control) and sacrificed at 20, 60, 120, or 360 min; then, blood, stomach, small intestine, cecum, colon and feces were collected. The results indicated that the content transferred faster from stomach to small intestine in the soy oil group than in the control group. At 60 min after the ingestion of diet, an increased serum triacylglycerol level was found in the soy oil group. In addition, fecal excretion in the soy oil group was significantly higher 120 min after the administration than in the control group, suggesting that soy oil stimulated peristalsis of the colon and that colon contents (food ingested before administration) were actively excreted.

A novel body weight-loss promoting oil prepared with vegetable protein.

It has been reported that oil thermally processed with wheat gluten (gluten oil) exhibited safe weight-loss promoting effects in animal experiments. However, as the oil has a high color index, and its chemical properties and smell differ from those of fresh oil, it is uncertain if the oil will find market acceptance. In order to resolve the issue, frying oil was heated with soybean protein under reduced pressure (soybean protein oil), resulting in a product with an appearance, chemical properties and smell comparable to those of fresh oil. This improved oil was mixed (7 wt%) with powdered AIN93G no fat, defined standard diet and fed to 10-week-old Wistar rats ad libitum. The experimental rats grew normally, ingesting the same amount as that of the control rats; however, there was a negative correlation between body weight increases and fecal weight increases. After the 12-week feeding period, all the rats were sacrificed to obtain blood and organs. In the experimental group, liver weight, retroperitoneal fat tissue weight and serum triacylglycerol (TG) levels decreased significantly. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and histological analysis supported the safety of the improved oil. In conclusion, it was found that soybean protein oil inhibited body weight increases without any adverse effects in animal experiments. The oil holds promise as a novel dieting oil that steadily decreases body weight at an appropriate rate.

Cytotoxic compounds generated in heated oil and assimilation of oil in Wistar rats.

We have previously suggested that gluten binds with decomposition products from thermally oxidized oil during frying, and that low-molecular-weight compounds bound to browned gluten damage the liver in rats. Ten-week-old male Wistar rats were fed for 11 weeks ad libitum a diet containing 7 wt% fresh frying oil and 0.1 wt% gluten heated in/without oil at 180 degrees C for 10 h. Feces collected weekly and serum were subjected to lipid and hematological analyses, respectively. Values obtained in the analyses did not differ from those of the control group. The results show that thermally processed gluten does not influence the digestion, absorption, metabolism, and growth of rats, regardless of the cytotoxic low-molecular-weight compounds, and that ingested fresh oil was assimilated normally. Together with the previous results, the odor of thermally processed gluten stimulated the rats' appetite, and completely assimilable fresh oil and cytotoxic low-molecular-weight compounds bound to gluten were ingested, and thus organ damage and rapid body weight increase were observed. As commercial deep-fried products are often made with repeatedly used oil with periodically added fresh oil, similar to the present experimental diet, obesity and organ damage may also occur in humans.

Effects of thermally processed oil on weight loss in rats.

We have previously proposed that thermally processed oil holds promise as a dietary supplement intended for weight loss. We employed a thermal process whereby oil was heated to 180 degrees C for 10 h in the absence and presence of gluten. We compared the effects of three diets, untreated oil, heated oil, heated oil and gluten on body weight, retroperitoneal weight and lipid composition and fecal lipid contents. Ten week-old male Wistar rats were fed ad libitum a diet containing 7 wt% of the oil for 12 weeks. The oil heated with gluten showed low levels of food efficiency and oil absorption ratios, and high levels of fecal oil excretion, oil content and bile acid content. Diets containing thermally treated oils resulted in significantly lower retroperitoneal tissue weights and lipid contents as compared to the control group; the groups fed the heated oil and gluten diets showed a general decrease in the fatty acid (especially linoleic acid) amount. In conclusion, oil heated with gluten was not fully digested and thus excreted without showing any detrimental effects on either the organs or feces. This resulted in safe and effective weight loss in growing adult rats.

Chemical properties and cytotoxicity of thermally oxidized oil.

Heated frying oils with different chemical properties in terms of AV (acid value), POV (peroxide value), COV (carbonyl value), and contents of polar compounds (PC) and triacylglycerol (TG), as well as color and odor, were obtained. Male Wistar rats were fed ad libitum for 12 weeks a powdered diet (AIN93G; no fat) containing 7 wt% of fresh oil (control) or one of the frying oils described above. The rats were subjected to anthropometric measurements, hematological analyses, and observations of the liver and kidneys. All of the rats grew well, and no gross symptoms attributable to the experimental oils were observed. However, the rats fed a diet containing the heated oil developed apparent liver damage to different degrees regardless of the chemical properties of the ingested oils. Thus, it was suggested that the chemical properties evaluated here had little to do with the cytotoxicity of heated oil, although the properties express quality of oil. Volatile compounds seem to be major candidates for the toxic agents in heated oil because oils with rancid and deteriorated odor show strong toxicity.

Acrylamide content of commercial frying oil.

After Swedish researchers reported that heated foods such as potato chips and French fries contain acrylamide, the potential for health damage resulting from the consumption of these foods became a widespread concern. Used frying oils collected from food manufacturing companies were subjected to acrylamide determination using GC/MS-SIM, but the compound was not detected. Thus, we conclude that frying oil used in deep frying would not contaminate foodstuffs with acrylamide and that the recovered oil, much of which is used as a component of animal feeds, would be safe for livestock. Model experiments heating oil at 180 degrees C suggested that no acrylamide was formed either from a mixture of major amino acids exuded from frying foodstuffs and carbonyl compounds generated from oxidized oil, or from oil and ammonia generated from amino acids.