Rheological characterization of tomato products is important not only for design of unit operations, but also to optimizeprocesses and guarantee high quality of food products. Time dependence is related with structura...Rheological characterization of tomato products is important not only for design of unit operations, but also to optimizeprocesses and guarantee high quality of food products. Time dependence is related with structural changes due to shear rate. Thus,rheological characterization as a function of time is extremely important to understand the changes that occurred in food productsduring commercial processes. However, these characterizations are rare in the literature for tomato products. Those rheologicalproperties depend of several parameters, such as agronomic, structural and process parameters. In this study, the effect of shear rateon the viscosity at room temperature （22 ~C） of two kinds of tomato sauce （homemade and commercial） is analyzed; using aBrookfield viscometer model 4535, Lab-Line Instruments. Homemade sauce was prepared with fresh saladette tomatoes from a localmarket. Rheological analysis was performed at shear rates from 0.05 to 10.47 sl; using all the spindles available. Statistical analysiswas made using LSD and Duncan tests with a confidence interval of 95% （p-value of 0.05）. It was demonstrated that homemade andcommercial tomato sauce behaved as a thixotropic fluid, due to the typical decrease on viscosity samples observed when testing timewas increased. When tomato sauce is at rest, it has a gelled tridimensional structure; and, as soon as a shear stress is applied, themovement generates an alignment of tomato constituent chains in flow direction, breaking physic entanglements and thus causing adecrease in viscosity as a function of time. Furthermore, it was discovered that the viscosity of homemade sauce was higher than theviscosity of commercial sauce. The latter may be due to the pre-thermal treatment. During this unit operation, polymeric chains oflycopene most likely break into smaller chains of isoprene, causing the observed decrease in viscosity. Besides, commercial saucecontains additives, seasonings, preservatives and thickeners that are not in a homemade sauce.展开更多
Temperature effect was evaluated over the viscosity of commercial carrot puree in the range 30 to 60 ℃, using aBrookfield viscometer, model 4535, Lab-Line instruments. In order to perform the viscosity tests, 28 spec...Temperature effect was evaluated over the viscosity of commercial carrot puree in the range 30 to 60 ℃, using aBrookfield viscometer, model 4535, Lab-Line instruments. In order to perform the viscosity tests, 28 specimens of carrot puree froma local market were used. Totally, 72 tests （each one with a couple replicas） were performed during five minutes, using fourtemperatures （30, 40, 50 and 60 ℃）, six shear rates （0.26, 0.52, 1.05, 2.09, 5.24 and 10.47 s1） and three spindles （4, 5 and 6）.Statistical analysis was performed using LSD and Duncan tests with a confidence interval of 95% （p value of 0.05）. In the currentstudy, it was observed that an increase in the temperature triggers a reduction in the viscosity of the carrot specimens analyzed,although the samples tested at 60℃ were deviated from this trend, which may be due to denaturation of the starch containing carrotsamples at such temperature. Multiple biochemical and micro-structural changes inside the food specimens may begin to occur belowand over the physiological range （20-45 ℃）. Experimental data were analyzed with Power Law model in order to obtain the bestfitted parameters as a function of shear rate： It was observed that the consistent index （k） decreased with an increment in thetemperature; while all the values of parameter ＂n＂ lesser than one, which means that the puree samples behaved as a pseudo-plasticfluid. Besides that, an Arrhenius model was used to fit the parameters as a function of temperature： Parameter A was lower usingtheexperimental data at shear rates of 10.47 s-1. The modeling performed may be helpful for the appropriate selection of some processvariables, as the shear rate and operation temperature, used for the production of carrot puree; all this is in order to obtain the finishedproduct with the desired consistency.展开更多
文摘Rheological characterization of tomato products is important not only for design of unit operations, but also to optimizeprocesses and guarantee high quality of food products. Time dependence is related with structural changes due to shear rate. Thus,rheological characterization as a function of time is extremely important to understand the changes that occurred in food productsduring commercial processes. However, these characterizations are rare in the literature for tomato products. Those rheologicalproperties depend of several parameters, such as agronomic, structural and process parameters. In this study, the effect of shear rateon the viscosity at room temperature （22 ~C） of two kinds of tomato sauce （homemade and commercial） is analyzed; using aBrookfield viscometer model 4535, Lab-Line Instruments. Homemade sauce was prepared with fresh saladette tomatoes from a localmarket. Rheological analysis was performed at shear rates from 0.05 to 10.47 sl; using all the spindles available. Statistical analysiswas made using LSD and Duncan tests with a confidence interval of 95% （p-value of 0.05）. It was demonstrated that homemade andcommercial tomato sauce behaved as a thixotropic fluid, due to the typical decrease on viscosity samples observed when testing timewas increased. When tomato sauce is at rest, it has a gelled tridimensional structure; and, as soon as a shear stress is applied, themovement generates an alignment of tomato constituent chains in flow direction, breaking physic entanglements and thus causing adecrease in viscosity as a function of time. Furthermore, it was discovered that the viscosity of homemade sauce was higher than theviscosity of commercial sauce. The latter may be due to the pre-thermal treatment. During this unit operation, polymeric chains oflycopene most likely break into smaller chains of isoprene, causing the observed decrease in viscosity. Besides, commercial saucecontains additives, seasonings, preservatives and thickeners that are not in a homemade sauce.
文摘Temperature effect was evaluated over the viscosity of commercial carrot puree in the range 30 to 60 ℃, using aBrookfield viscometer, model 4535, Lab-Line instruments. In order to perform the viscosity tests, 28 specimens of carrot puree froma local market were used. Totally, 72 tests （each one with a couple replicas） were performed during five minutes, using fourtemperatures （30, 40, 50 and 60 ℃）, six shear rates （0.26, 0.52, 1.05, 2.09, 5.24 and 10.47 s1） and three spindles （4, 5 and 6）.Statistical analysis was performed using LSD and Duncan tests with a confidence interval of 95% （p value of 0.05）. In the currentstudy, it was observed that an increase in the temperature triggers a reduction in the viscosity of the carrot specimens analyzed,although the samples tested at 60℃ were deviated from this trend, which may be due to denaturation of the starch containing carrotsamples at such temperature. Multiple biochemical and micro-structural changes inside the food specimens may begin to occur belowand over the physiological range （20-45 ℃）. Experimental data were analyzed with Power Law model in order to obtain the bestfitted parameters as a function of shear rate： It was observed that the consistent index （k） decreased with an increment in thetemperature; while all the values of parameter ＂n＂ lesser than one, which means that the puree samples behaved as a pseudo-plasticfluid. Besides that, an Arrhenius model was used to fit the parameters as a function of temperature： Parameter A was lower usingtheexperimental data at shear rates of 10.47 s-1. The modeling performed may be helpful for the appropriate selection of some processvariables, as the shear rate and operation temperature, used for the production of carrot puree; all this is in order to obtain the finishedproduct with the desired consistency.
