Advances in Radio Frequency and Ohmic Heating ofFoods

摘要

Interest in both Radio refequency (RF) and Ohmic Heating of Foods has increased inrecent years. In particular, their application to meat products has been investigated. A critical factoris the dielectric constants of the products being heated. These have been measured for meats. Inparticular, dielectric (dielectric constant (ε ') and loss factor (ε?)) and thermal (heat capacity ?,thermal conductivity (k) and thermal diffusivity (α))) properties of two meat batters (pork luncheonroll (PLR) and white pudding (WP)) were measured between 5 and 85 °C. Radio frequency (RF)and microwave (MW) ε? Values varied across 5–85 °C (P<0.05). MW ' and ε? Values for WPtended to peak at 45 °C and decrease thereafter, whereas for PLR, ' and ε? Peaked at 65 °Cwhich appeared to match potato starch gelatinisation within this product. WP and PLR hadsignificantly higher c values at 25 °C, which corresponded to the MP of pork fat. At 85 °C, k valueswere higher (P<0.05) than at 5, 25 and 45 °C but were not higher than values at 65 °C. Αvaluesincreased with temperature (P<0.05).For Ohmic Heating, the electrical conductivity becomes the controlling variable. Efficacy of ohmicprocessing can be influenced by the conductivities of individual components within the food andtheir behaviour and interactions during the heating process. Conductivity measurements on porkcuts indicated that lean is highly conductive compared to fat and addition of fat to lean reduced theoverall conductivity but the addition of fat over the range (I.e. 0–100%) was non-linear. Lightmicroscopy suggested that differences in the conductivities of leg and shoulder lean (entire) (0.76vs. 0.64 S m- 1, respectively) could be due to the denser muscle fibre structure and/or higher intramuscularfat in shoulder vs. leg. This could be of significance for ohmic processing of full muscleproducts.Of course, for both forms of heating, the quality of the heated product becomes the critical factor.The effect of radio frequency (RF) cooking, on the quality (assessed by cook yield, water holdingcapacity (WHC), texture profile analysis (TPA), penetration test (PT), Warner Bratzler shear (WB),colour and sensory evaluation) and cooking time of two types of pork products (leg ham andshoulder ham) were compared to steam (ST) cooked samples. RF cooking of the hams resulted ina shorter cooking time. Instrumental measurements indicated that RF heated samples had a highercook yield (P<0.05), but a lower WHC (P<0.05). TPA indicated that RF cooked samples wereharder (P<0.05), particularly for leg hams. A sensory panel also indicated that panellists coulddistinguish between RF and ST cooked samples (P<0.05).