Browsing by Publisher "BULGARIAN ACAD SCIENCE"

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    Industrial applications and potential use of ohmic heating for fluid foods
    (BULGARIAN ACAD SCIENCE) Yildiz, H; Guven, E
    Ohmic heating technology is generally used for processing liquids and solid-liquid mixtures (or pumpable foods) in the food industry. In ohmic processing, the product is heated volumetrically by dissipation of electrical current through it. The main advantages of ohmic heating are the rapid processing and relatively uniform heating achieved. In this review, the application and potential of ohmic heating in food industry were examined. Nowadays, the availability of novel ohmic heating systems more advanced than their predecessors makes this technology even more attractive for food processors. Ohmic technology is currently being used commercially throughout the world (USA, Japan, UK, several European countries, etc.) for the pasteurization or sterilization of pumpable foods such as fruit and vegetable products (juices, purees, pulps, etc.), milk, ice-cream mix, egg, whey, soups, stews, heat sensitive liquids, soymilk, etc. and aseptic packaging. Much research is still being carried out to improve the current ohmic systems. In recent years, industrial ohmic heating systems have been developed in different countries by companies. The potential applications of ohmic heating technique in food industry are very wide such as cooking, thawing, blanching, peeling, evaporation, extraction, dehydration and fermentation. Researchers should more investigate the potential applications and its effects on food quality and safety before its industrialization.
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    Changes on rheological properties of pomegranate (Punica granatum L., cv. Hicaznar) juices during concentration process
    (BULGARIAN ACAD SCIENCE) Cevik, M; Sabanci, S; Icier, F; Yildiz, H
    The investigation of the changes on rheological properties during evaporation process could diminish the severe effects of thermal processing at any individual soluble solids content. In this study, the rheological properties of pomegranate juices at different soluble solids content (20, 30, 40 and 50 %) during concentration process applied by using the rotary evaporator were determined. Rheological measurements were conducted in the range of 0-264 s(-1) shear rates by using the concentric cylinder type viscometer. It was found expectedly that apparent viscosity increased as the soluble solids content increased. The apparent viscosity was 0.0024 +/- 0.0001 Pa. s for raw pomegranate juices (15.73 +/- 0.30 % soluble solids) while it increased to 0.01342 +/- 0.0003 Pa. s for the concentrated juice having 50 % soluble solids contents. Four different rheological models were applied to find the suitable model best fitting the experimental data; Newton model, Power Law model, Bingham model and Herschel-Bulkley model. The statistical criteria having highest regression coefficient, lowest root mean square error and lowest chi-square were chosen for selection of best model for fitting. It was determined that the Power law model was best described the experimental shear stress-shear rate relation for pomegranate juices at different concentrations. It was predicted that the consistency coefficient of pomegranate juice increased from 0.005 Pa.s(n) to 0.013 Pa. sn as the soluble solid content was increased from 20 % to 50 %. The rheological data obtained in this study could serve valuable data for calculation of changes in flow behaviors of pomegranate juice in pumping systems depending of their concentration.