[Survey of Total Mercury Content in Fishery Products].

The total mercury content in 112 fishery products, purchased from Osaka city during 2013-2018, was measured using a heating vaporization mercury analyzer. The average total mercury content in all tuna processed products was found out to be 0.115 µg/g (median=0.070 µg/g). Notably, albacore tuna exhibited the highest mercury content with an average concentration of 0.301 µg/g (median=0.296 µg/g). The total mercury concentration of the fishery products, except processed tuna and Kezuribushi (comprising shavings of dried and smoked mackerel, sardine, as well as horse mackerel), was generally low (<0.1 µg/g).The provisional tolerable weekly intake (PTWI) for mercury as set by the Joint FAO/WHO Expert Committee on Food Additives is 4.0 µg/kg body weight/week. On an average, for Japanese diet, the total weekly mercury intake from fishery products for a person weighing 50 kg was estimated to be 0.13 µg/kg body weight/week, which was 3.3% of the PTWI. These values indicate that it was not a problem to consume fishery products normally. However, albacore tuna cans have a relatively high total mercury concentration; thus, pregnant women consuming them daily may exceed the tolerable weekly intake of methylmercury (2 µg/kg body weight/week) as set by the Food Safety Commission of Japan.

Effects of popping on nutrient contents of amaranth seed.

Amaranth seeds can be popped by heating. The traditional method of popping in a skillet is simple, but it is difficult to control the heating time and temperature. To overcome these disadvantages, we developed a fluidized bed continuous processing system based on hot air heating for producing popped amaranth seeds in bulk. Using this system, we evaluated the effects of heat treatment at 260 °C for 15 s on the contents of B-group vitamins and essential and trace elements in amaranth seeds. The results showed that the treatment did not affect the content of B-group vitamins, and the recovery for essential and trace elements was 97-196%. This popping system is useful for processing amaranth seeds in terms of the product quality and nutrition.

Development and Validation of Simultaneous Analysis of Minerals and Toxic Elements in Foods by ICP-MS.

We have developed and validated an inductively coupled plasma-mass spectrometry (ICP-MS) method for the simultaneous analysis of minerals and toxic elements in foods. Food samples were digested by microwave irradiation to prepare solutions for measurement by ICP-MS. Optimal gas mode and internal standard for each element were selected as appropriate. The method was validated for eighteen elements in total using three certified standard reference materials, namely, Typical Japanese Diet, Rice Flour-Unpolished and Infant/Adult Nutritional Formula, according to the guidelines of the Ministry of Health, Labour and Welfare of Japan. The trueness and precision of the method were all within the acceptable limits, except for Na in Rice Flour-Unpolished.

[Determination of uranium in spinach].

After the severe accident at the Fukushima-1 Nuclear Power Plant in March 2011, radioactive contamination of food has become a matter of serious concern in Japan. There is considerable information about radioactive iodine and cesium, but little is known about uranium contamination. We determined uranium content in spinach by the Japanese official method (Manual on Radiation Measurement of Food in Emergency Situations). In the preliminary study, we confirmed that the use of a microwave digestion system for preparing the test solution of spinach could shorten the testing time and give acceptable results. The manual recommends the use of two elements (Tl and Bi) as internal standards for measurement of uranium by ICP-MS. We found that Tl was more suitable than Bi to quantify trace amounts of uranium in spinach. However, it was necessary to determine Tl or Bi concentrations in the sample before analysis, since some samples of spinach contained significant amounts of these elements. The uranium contents of 9 spinach samples bought in April and May 2011 were less than 10 µg/kg, which are very low compared to the provisional regulatory limit in Japan.