B. Krol

Radio-Frequency Pasteurization of Sausage Emulsions as a Continuous Process

From different available methods, dielectric heating was chosen as the most promising technique for a continuous and flexible pasteurization process of sausage emulsions.Based on the dielectric properties of sausage emulsions and the required penetration depths, radio frequency heating was then selected.The results of stationary heating tests (27 MHz) and of tests in a specially designed continuous heating line (inner diameter 50 mm) are described. An approximately linear relationship was observed for the temperature increase as a function of the electrode voltage. Temperature increases up to 40°Clmin were realized. Overall energy efficiency was around 30% and probably can be improved.Sausage products heated in the continuous line hada good appearance smooth surface and did not show moisture or fat release.

Mechanical and microstructural characteristics of meat doughs, either heated by a continuous process in a radio-frequency field or conventionally in a waterbath.

Meat doughs, all having the same chemical composition, were pasteurised to a comparable heat intensity (calculated as Cook values: target level of 5 min at 100°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 immediately after the pump and heated in a waterbath. The cooked products were sampled in the core and at the rim of the product for rheological (oscillation and uniaxial compression tests at small strain), fracture measurements (uniaxial compression tests at high strain) and microstructural evaluation (light microscopy and video image analysis). Additional 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 velocity 0.014 m/s) during dielectrical pasteurisation affected the mechanical character, the microstructure and the triangle test results of core samples from the sausages, compared to heating in a waterbath. Flow of the unheated dough through the tube of the continuous processing equipment, 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 storage and loss moduli (were more firm), fractured at higher stress values and were considered more firm in the sensory evaluation. The microstructure of dielectrically heated versus other samples displayed a more open structure of the protein matrix with larger irregularly shaped fat particles that were surrounded by relatively thin and compact protein 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 samples only was significant for radio-frequency heated doughs. The rim samples had lower storage and loss moduli and fractured at lower stress values than the core samples. Micrographs of the dielectrically heated rim versus core samples displayed more orientation of connective tissue particles in the direction of flow and of elongated, larger and irregularly shaped fat particles. Probably, shear at the wall of the tube affected the characteristics of the rim samples. All heated doughs displayed hardly and cooking losses. The radio-frequency heated products always displayed a thin layer of moisture on their surface and occasionally a little fat separation.

Changes in lightness of porcine lean meat batters during processing

The pattern of changes of lightness (L(∗)) for porcine lean meat batters (PLMBs) with time was divided in two phases: chopping process (Phase 1) resulting in a sharp increase of L(∗), and the subsequent storage of the batters for 24 h at 15°C (Phase 2). During Phase 2, L(∗)-values decreased with time approximating a plateau. The subjects of study were effects on the course of L(∗) of: (1) added sodium chloride and phosphate in Phase 2, (2) the fate of air bubbles embedded in the batters in Phases 1 and 2, and (3) changes in light absorption by the pigment myoglobin in Phase 2. (1) Sodium chloride and phosphate appeared to have very little impact on the changes in L(∗) during storage of the PLMBs at 15°C, although microstructural changes were distinct. (2) Continuous entrapment of air during the chopping process had a major effect on the increase of L(∗) in Phase 1, air bubbles being scattering elements in the PLMB. Disproportionation caused a decrease in the number of small air bubbles, resulting in a decrease of L(∗) during the early stage of Phase 2 (about 35 min), immediately after the chopping stage was finished. (3) Strong evidence was obtained that shifts in the absorption traits of pigments (red nitric oxide myoglobin was formed at the cost of grey met-myoglobin) during the period from 1 to 5 h, caused a marked decrease in the pattern of L(∗) during Phase 2.

Effect of citric acid, citrate and slight aw decreases on the bacteriological stability of Hague liver sausage

Combinations of citric acid and citrate, with several carbohydrates and KCl, were tested in a canned Hague liver sausage model for their antimicrobial properties. pH values for the test products ranged from 5·38 to 6·48; a(w) values varied from 0·960 to 0·977. Before pasteurization, the sausage doughs were contaminated with mixtures of bacterial spores. Since the bacteriological stability sometimes appeared to be considerably improved, heated packages were challenged by incubation at 20° and 30°C; some of them for up to 2 years. Incubated packages from the standard formulation spoiled at 30°C within 3 days. Starting from this point, products with a variable, but increased, bacteriological stability were obtained. For the best stabilized batches, first symptoms of spoilage were observed after periods of incubation at 30°C, ranging from 49 to 150 days. Combinations of pH and a(w) values which can be relied upon to yield stable products consistently, cannot be derived from the accumulated data. Citric acid appeared a far more effective stabilizer than its salt. If we regard the undissociated citric acid concentration for these products (a(w) 0·960-0·972) as a significant parameter, values above approximately 13 μmkg(-1), yielded products with remarkable bacteriological stability.

Effect of citric acid and citrate on the shelf stability of canned liver paste processed at reduced F0 values

Citric acid and the combination of citric acid and citrate, in a few cases enriched with potassium sorbate, were tested for their stabilizing effect in a canned liver paste processed at reduced F(0) values. pH values of the rest products ranged from 5·24 to 5·76; a(w) values varied from 0·950 to 0·972. F(0) values of 0·05, 0·30 and 0·85 were applied. Before sterilization, the paste doughs were contaminated with mixtures of bacterial spores. Heated packages were challenged by incubation at 30 and 55°C for up to about 2 years. Incubated packages with the standard formulation at an F(0) of 0·05 showed the first blown cans at 30°C after 24 days. Starting from this point, at this F(0) value products with a variable, but increased, bacteriological stability were observed. At an F(0) of 0·30 a perfectly stable product at 30°C was observed after addition of 0·14% w/w citric acid only (product pH 5·69). Moreover, all tested combinations of additives at F(0) values of 0·30 and 0·85 yielded stable products at this incubation temperature. At the higher F(0) value a clear effect with respect to delaying thermophilic spoilage was observed. The effect of the application of potassium sorbate-in combination with both other additives-at F(0) values of 0·30 and 0·85 proved to be negligible.

A factorial analysis of water-binding properties and firmness of heated, comminuted pork liver and pork loin products as influenced by addition of sodium chloride and pH regulators

Canned, pasteurized, comminuted pork liver and pork loin were used for a factorial study to evaluate the effects of the addition of sodium chloride (0 and 1·8%), acid and alkaline mono- and diphosphates (0 and 0·3% P(2)O(5)), acetic acid (0 and 0·25%), sodium acetate (0 and 0·63%) and glucono-delta-lactone (0 and 0·5%) on their water-binding properties and firmness. The water-binding properties were evaluated by measuring cooking losses (for both types of product) and by moisture release by centrifugation (for the liver products only). The liver products had much better water-binding abilities and were softer than the loin products. The interaction of salt and pH regulators also differed greatly from the interaction for the comminuted loins, resulting in a barely perceptible effect of the pH regulating compounds on the water-binding abilities of the salt-containing comminuted liver. The firmness of the salt-containing liver products was greatly reduced by the addition of acidulants. The loin products were normally affected by the compounds tested, with the exception of Na(4)P(2)O(7). The added amount of this diphosphate caused a considerable rise in the product pH, which resulted in a large reduction in cooking loss, thus leaving no possibility of an extra reduction by the combination of salt and Na(4)P(2)O(7).