MECHANICAL AND MICROSTRUCTURAL CHARACTERISTICS OF MEAT DOUGHS, EITHERHEATED BY A CONTINUOUS PROCESS IN A RADIOFREQUENCY FIELD OR CONVENTIONALLY IN A WATERBATH

Meat doughs, all having the same chemical composition, were pasteurise d to a comparable heat intensity (calculated as Cook Values: target le vel of 5 min al 100-degrees-C): (i) while flowing through a glass tube (inner diameter 50 mm) mounted in a special radio-frequency (27 MHz) heating section; (ii) after flowing unheated through the glass tube at the same rate and heated in a waterbath; and (iii) after sampling imm ediately after the pump and heated in a waterbath. The cooked products were sampled in the core and at the rim of the product for rheologica l (oscillation and uniaxial compression tests at small strain), fractu re measurements (uniaxial compression tests at high strain) and micros tructural evaluation (light microscopy and video image analysis). Addi tional core samples were used for a sensory evaluation (triangle tests ) of the texture of the differently processed doughs. The fast heating rate (25-30 K/min) at a mass flow of the dough of 100 kg/h (mean velo city 0.014 m/s) during dielectrical pasteurisation affected the mechan ical character, the microstructure and the triangle test results of co re samples from the sausages, compared to heating in a waterbath. Flow of the unheated dough through the tube of the continuous processing e quipment, followed by heating in a waterbath, had little effect on the results of the mechanical tests, the microscopical evaluation and the triangle tests. The radio-frequency heated products had both higher s torage and loss moduli (were more firm), fractured at higher stress va lues and were considered more firm in the sensory evaluation. The micr ostructure of dielectrically heated versus other samples displayed a m ore open structure of the protein matrix with larger irregularly shape d fat particles that were surrounded by relatively thin and compact pr otein bridges. The effects of flow and heating method on the behaviour of rim samples were very similar to their effects on the core of the products. A comparison of the mechanical behaviour of core and rim sam ples only was significant for radio-frequency heated doughs. The rim s amples had lower storage and loss moduli and fractured at lower stress values than the core samples. Micrographs of the dielectrically heate d rim versus core samples displayed more orientation of connective tis sue particles in the direction of flow and of elongated, larger and ir regularly shaped fat particles. Probably, shear at the wall of the tub e affected the characteristics of the rim samples. All heated doughs d isplayed hardly any cooking losses. The radio-frequency heated product s always displayed a thin layer of moisture on their surface and occas ionally a little fat separation.