Initial Apparent Viscosity Research Articles

Rheological behaviour of processed avocado pulp emulsions

Shear rate vs. shear stress data were obtained on avocado pulp in water emulsions using a concentric cylinder rheometer and fitted to a power law model. Dilution, as volume fraction of water, had a pronounced effect on the apparent viscosity of the pulp emulsions and the Richardson equation, (ηR= exp.(aϕ) for the emulsion viscosity fitted the data well. A mean slope coefficient, a, of 4.57 can be used as a first approximation. Enzymatic treatment (40°C, 1 h), is slightly more effective than thermal treatment (65°C, 1 h), in reducing the initial apparent viscosity of the pulp‐water emulsions

Rheological properties of gelatinized starch solutions as influenced by thermal processing in an agitating retort

Rheological changes associated with a canned model food (gelatinized starch) were evaluated in relation to factors (retort temperature, rotation speed, can headspace and starch concentration) which influence heating rates of processed foods in an agitating retort. The rheology of gelatinized starch was well described by the power law model. Power law parameters (consistency coefficient and flow behaviour index) were generally influenced by all factors tested with the exception of can headspace in the 8 32 – 16 32 inch range. Even though the starch suspensions were pregelatinized, the rheological characteristics continued to change with processing under all conditions. Heating rates were modeled as a function of retort temperature (110–130 °C), rotation speed (10–20 rpm) and product initial apparent viscosity ( η i ) at a nominal shear rate of 100 s −1, and the apparent viscosity of the processed product was related to η i and the process cook value.

HEAT TRANSFER RATES IN A CANNED FOOD MODEL AS INFLUENCED BY PROCESSING IN an END-OVER-END ROTARY STEAM/AIR RETORT

The effect of various factors on the heat transfer rates of a canned food model (gelatinized starch) were evaluated during thermal processing in an agitating retort. Process variables were retort temperature (110–130C), rotation speed (10–20 rpm), can headspace (6.4–12.8 mm) and starch concentration (3–4%). Thermal process parameters (heating rate index, fh, and heating lag factor, jch) and the resulting process lethality, Fo and cook value, Co were obtained from time-temperature data obtained during processing for three consecutive runs. Rheological properties and color were experimentally evaluated both before and after each run. Overall heat transfer coefficient (Uo) was calculated from the heating rate index using a lumped capacity approach. the study indicated that fh, jch, Fo and Co were influenced (P<0.05) by all process variables except can headspace. Uo was related to retort temperature, rotation speed and initial apparent viscosity. the best dimensionless correlation for Uo was Nusselt number (logarithmic scale) versus specific apparent viscosity and Froude number (R2= 0.65).

Quality of Enzymatically Treated 72° Brix Orange Juice Stored at Refrigerated Temperatures

ABSTRACTFresh Valencia orange juice was treated with 0, 70, and 350 ppm of commercial pectic enzymes, concentrated to 72° Brix and stored at –7°, –1°, 7°, and 13°C for up to 6 months. The 70 ppm enzyme treatment successfully reduced initial apparent viscosity by about 25%. For the 70 ppm enzyme treated samples after 6 months storage at all four temperatures, juice cloud remained acceptable, furfural remained below the significant level, and at −1°C, vitamin C levels were above 32 mg/100 mL. There was no significant difference in taste after 6 months storage at −7°C between control and 70 ppm enzyme treated samples. Product quality of enzymatically treated orange concentrate stored at refrigerated temperatures was of sufficient quality to realize potential savings of 17% in storage and 30% in refrigeration.