STUDY OF RHEOLOGICAL PROPERTIES AND STORAGE LIFE OF RIPE JACKFRUIT PRODUCTS: JAM AND JELLYA. K. TIWARI, A. S. VIDYARTHI, V. K. NIGAM AND M. A. HASSAN
Jams and jellies are used as taste enhancer and commonly applied as spread on breads. It exhibits both viscous and elastic behavior due to its semisolid properties. Measurements of physico-chemical and rheological properties are quite important for the assessment of physical, chemical and mechanical properties and qualities of processed products. Sugar, acid, and high molecular weight polysaccharides are added during the preparation of Jam and Jelly for increasing the viscosity, gel forming structure, improving consistency, textural uniqueness and expansion of shelf life or storage stability by arresting the microbial contaminants through lowering the water activity. The rheological behavior of jackfruit jam and jackfruit jelly was determined using a Brookfield CAP 2000+ at a constant temperature of 30±0.5º C. All measurements were curve fitted into with Bingham and Herschel - Bulkley model to compute yield stress and apparent viscosity. The shear rate typically ranged between 600 s-1 and 2700 s-1for both products. The measurement was started with a low shear rate which slowly ramped to high shear rate. Bingham model gives a yield stress of 9215 D/cm2 and apparent viscosity equal to 567.6 Pa s. While fitted into more realistic Herschel- Bulkley model results yield stress value as 9603 D/cm2, consistency index κ equal to 0.385 Pa sn and R2 value of 0.9972 for jackfruit jam. The experimental data of Jackjelly was also fitted with Bingham Model resulted in the yield stress value of 198.1 Pa with apparent viscosity of 286.7 Pa s. When the same experimental data fitted into Herschel Bulkley model it led to a yield stress τy= 192.4 Pa, τ =0.3344 Pa sn and shear thinning parameter, n=0.9811. The parameters predicts perfectly the behaviour of Jackjelly in the given shear rate range with a regression coefficient, R2=0.9996. The experimental measurements showed that the jackfruit products have a non-newtonian flow behavior.
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