White-flesh guava juice clarification by a fixed-angle conical rotor centrifuge laboratory and characterization of continuous disk stack centrifuges.

The two objectives of this paper were to determine the effect of centrifugation parameters on guava juice physicochemical characteristics and to identify operational characteristics of continuous disc-stack centrifuges based on the performance of a laboratory centrifuge. Effects of g-force (149 g-3731 g) and centrifugation time (10-40 min) on juice physicochemical characteristics (protein, pectin, galacturonic acid, dry matter, total soluble sugars contents; pH; electrical conductivity, clarity and particle size distribution) were assessed. Laboratory centrifuge performance was evaluated for 1343 g, 2388 g and 3731 g. At 1343 g, separation limits (x max ), feed flow-rates of disc-stack centrifuges and cut-off sizes (x 50 ) were determined for corresponding laboratory centrifuge operation times. Significant decrease in average particle size, protein and pectin contents was observed, contrary to juice clarity. Similar clarification efficiency was obtained for g-forces ≥ 1343 g. x max were 2669 nm, 2200 nm and 1783 nm, with corresponding x 50 for continuous centrifuges, 1887 nm, 1556 nm, 1261 nm, for 20 min, 30 min and 40 min, respectively.

Pectinase hydrolysis of guava pulp: effect on the physicochemical characteristics of its juice.

The objective of this research is to assess the effect of enzymatic treatment of guava puree on the physicochemical parameters of the juice. Pectinases from Aspergillus niger were applied to the puree at 43 ± 3 °C under constant stirring. Enzyme concentrations used were: 0.033 % (w/w), 0.055% (w/w), 0.078 % (w/w) and 0.1 % (w/w). For each enzyme concentration, the treatment times were varied from 3 - 90 min. Physicochemical parameters of raw puree and enzymatically treated juice were determined. These were: viscosity, pH, electric conductivity, protein and polyphenol content, galacturonic acid content, color, TSS, and antioxidant capacity. Particle distribution, homogeneity of raw puree and juice samples dried extracts were assessed using a Field Emission Scanning Electron Microscopy (FESEM). A 91% viscosity decrease was recorded for each enzyme concentration after 3 min of enzyme reaction. That drecrase was accompanied by an increase in galacturonic acid content with increasing depectinization factors. Enzyme treatment of guava puree led to a decrease in pH, protein and polyphenol contents and an increase in conductivity and color. Analysis of FESEM images of guava samples bestowed a decrease in particle size, a scattering of particles in the medium, an increase in continuous phase proportion and an improvement of sample homogeneity with increasing values of processing parameters, due to the breaking-down of bigger particles and the solubilization during depectinization.