Juice viscosity, determination

Once the constant-temperature water bath has reached 30°C, measuring the viscosities of pure solutions like standard oils requires 15 min per sample. The most time-consuming part of the measurement is cleaning and drying the viscometer between samples. Preparing fruit pastes and juices for viscosity determination will take 1 hr for two to four different samples and then an additional -15 min/sample for the viscosity measurements. 

USING CAPILLARY VISCOMETRY TO DETERMINE THE VISCOSITY OF SERUMS, FRUIT JUICES, OR PASTES... 

Control. Factory control is based on temperature, pH, and polarization. Cane is tested by various means as it comes to the mill to determine its characteristics and to determine the amount to pay the farmer. Control of microbial infection, discussed above, is important. The starch content of juice from immature cane can be significant (e.g., in Louisiana and South Africa), and amylase enzyme may be added continuously to the clarified juice to reduce it. Starch will cause severe viscosity problems if not removed. If there is a problem with dextran, dextranase enzyme can be added, but it is expensive and not as effective as desired.40... 

Unlike biopolymer dispersions where the intrinsic viscosity is known and the polymer concentration can be chosen a priori, often for fluid foods the concentration of soluble (e.g., pectins in fruit juices) and insoluble solids can be determined only posteriori, and the determination of their zero-shear viscosities is also difficult due to instrument limitation and due to the existence of yield stress. However, in many foods, it may be possible to identify the components, called key components, that play an important role in the rheological properties. 

The Arrhenius equation did not describe very well the influence of temperature on viscosity data of concentrated apple and grape juices in the range 60-68 °Brix (Rao et al., 1984, 1986). From non-linear regression analysis, it was determined that the empirical Fulcher equation (see Ferry, 1980 p. 289, Soesanto and Williams, 1981) described the viscosity versus temperature data on those juice samples better than the Arrhenius model (Rao et al., 1986) ... 

The capacity can be increased further by reducing the viscosity of the liquid to be filtered. This can be achieved by treating fruit juices enzymatically and also by increasing the filtration temperature. The ideal temperature is determined by the temperature resistance of the membrane material and on the other hand by the fact that it must not impair the quality of the product. 

The rheological properties of fluid tomato sauce products are important quality parameters. The flow properties of the juice, i.e viscosity and consistency, are determined primarily by the insoluble components [180-186]. The viscosity of the serum, the soluble fraction of the tomato juice after removal of insoluble material, is mainly determined by the polymeric substances, mostly pectin, i.e., the flow... 

Pectolytic preparations lower white must viscosity and thus accelerate sedimentation (Figure 11.15). In less than an hour, the colloidal equilibrium is destabilized, resulting in a rapid sedimentation and increased must limpidity. A more compact must deposit, facilitating static settling, is rare. This treatment can lead to excessive juice clarification. Its use should be determined according to must... 

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