Non-Thermal Effects of Microwave Oven Heating on Ground Beef Meat Studied in the Mid-Infrared Region by Fourier Transform Infrared Spectroscopy

Abstract

ABSTRACT The effects of cooking by microwave oven on the secondary structure of lipid and protein contents in bovine ground beef were investigated in the midinfrared region by Fourier transform infrared (FTIR) spectroscopy to highlight the nonthermal effects of microwave oven heating. Samples of bovine ground beef were cooked in a conventional electric oven at the temperature of 175°C for 15 min and in a microwave oven at 800 W for 1½ min. Spectra analyses of bovine meat after cooking in the conventional oven evidenced a relevant increase in intensity of the carbonyl band at 1742 cm−1 and of the methylene group at 2921 and 2853 cm−1 that can be attributed to the Maillard reaction. In contrast, the increase in intensity of these bands after microwave oven heating was less than that which occurred after conventional cooking, showing that the temperature in ground beef meat samples during microwave heating was less than that induced by conventional heating. Spectral analysis in the amide I, II, and III regions showed that a significant increase in intensity occurred in the region from 1660 to 1675 cm−1 and around 1695, 1635, 1575, and 988 cm−1 after cooking by means of a microwave oven. These features, which can be attributed to β-turns and β-sheet structures, are characteristic of disorder processes in meat protein contents and increasing transition dipole coupling due to higher contents in aggregated β-sheet structures. This result highlighted nonthermal effects of microwave oven heating in the protein's secondary structure.