When frying oil is used for a long time, secondary products of lipid thermal oxidation, such as polar polymers, carbonyl compounds, etc., accumulate in the oil, accompanied by an increase in acid value. So far, the increase in acid value has been thought to be based on the hydrolysis of triglycerides by water transferred from frying materials. However, the acid value of oil heated while spraying water was not increased in the low oxygen atmosphere where thermal oxidation does not progress. The addition of long chain free fatty acids, short chain free fatty acids or hydroperoxides into heated oil did not potentiate the increase in acid value under the low oxygen atmosphere. These results suggest that the increase in acid value of frying oil is not simple hydrolysis of triglycerides but the result of ester decomposition mediated by initial oxidation intermediates or oxygen molecules themselves.

Polydimethylsiloxane (PDMS) is utilized in commercial oil for frying food. It has been reported that PDMS shows extraordinarily strong antioxidative effects under thermal treatment, despite being designated as antifoamer. There are many interpretations of the theories regarding of the antioxidative effects of PDMS, such as “formation of a monolayer of PDMS at the air-oil interface” and “a decrease in the convection current of frying oil”. However, the mechanisms are still not completely understood. This report elucidates the status of PDMS and oxygen in oil and describes an examination of the antioxidative mechanism of PDMS that was performed by measuring the chemical characteristics and tocopherol content of heated oil. The addition of more than about 0.06 μg/cm² PDMS at the air-oil interface results in PDMS forming both a layer at the oil-air interface and droplets suspended in the oil. PDMS-containing canola oil was allowed to stand at room temperature with the upper void volume replaced with nitrogen gas. The PDMS concentration and oxygen content tended to decrease as the depth of the oil increased. The oxygen content of the oil with added PDMS was higher than that without PDMS addition, but oxidation of PDMS-containing canola oil was inhibited both during heating and standing with intermittent heating. In addition, oxygen-saturated canola oil with added PDMS was placed in a vial that was hermetically sealed such that there was no air at the top. When the oil was subsequently incubated at 60°C, oxidation was markedly inhibited. These results demonstrate that the PDMS droplets exhibit an antioxidative effect separate from that of the PDMS monolayer. No antioxidative effect was observed when using either silicone oil, such as polymethylphenylsiloxane dissolved in canola oil, or PDMS in PDMS-soluble fatty acid isopropyl ester, suggesting that PDMS must be insoluble and droplets in oil for PDMS to exhibit an antioxidative effect during deep frying. The zeta potential of PDMS was –74±10.6 mV, indicating that countless PDMS droplets are stably scattered in oil. This attractive force is believed to disturb the motion of oxygen clusters and prevent their attack against unsaturated fatty acid moieties, thus suppressing oxidation by PDMS.

Human can distinguish food whether should intake or evade for body by taste perception. Sweetness and Umami prompt to consume carbohydrates and proteins each for energy intake and to compose body. From a nutritional point of view, it is reasonable that taste of oil and fats has existed as well as sugar and amino acid, whereas mainly has been considered oil and fats have no tastes other than texture stimulus. We showed that arachidonic acid contribute to make foods better, especially umami was increased by arachidonic acid. Besides, rodent studies elucidated that composed materials of arachidonic acid affected taste perception.

Compound diversity in agricultural and food products is affected by environmental factors during food production. This diversity strongly impacts food quality and human health. Nuclear mag netic resonance (NMR) is a spectroscopic technique which has been used to analyze molecular structure and dynamics. NMR spectra are applicable to metabolomic studies and can be used to identify the characteristics of a given sample, providing structural information on the various compounds contained therein. Magnetic resonance imaging (MRI) uses a magnetic field gradient to encode spatial information into an NMR signal. MRI provides information on the morphology, distribution, and mobility of water molecules in a sample. We have been developing NMR-based methods for evaluating and predicting the quality of agricultural and food products. This report focuses on the various applications of NMR in agricultural and food sciences.