Open-focused microwave-assisted Kjeldahl digestion for determination of nitrogen in food materials
1997
Suzuki, T. (National Food Research Inst., Tsukuba, Ibaraki (Japan)) | Yasui, A.
Microwave-assisted Kjeldahl digestion of food materials were successfully accomplished within 35 min at atmospheric pressure using an open-focused system. It was compared with the conventional improved Kjeldahl method using gas heating for determination of nitrogen in roasted and ground soybeans, miso, wheat flour, highly milled rice, loin ham, shiba-shrimp and powdered cream. Samples (0.3-1g), 20 ml of cone. H2SO4, 15g of K2SO4, 0.5g of TiO2, 0.5g of CuSO4 and boiling stone were taken in 250 ml digestion tubeand treated by using a programmed seven to eight-step digestion, which consisted of power (140-332.5W), time (1-10 min) and with/without the addition of hydrogen peroxide. It was necessary to continue microwave heating for 10 min after digestive solution became clear. The Kjeldahl digestions by the conventional method were accomplished in 90-100 min. The results by microwave-assisted method agreed well with those by the conventional one
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