Levent Bayindirli

Mathematical analysis of freeze concentration of apple juice

Abstract Apple juice concentrate was produced by freeze concentration. A double-strength juice was produced in a single-stage process, whereas with a multi-stage process higher concentration levels were achieved. Lowering the refrigeration temperature shortened the time required to achieve a certain concentration level. To account for the distribution of the apple juice solids between the juice and ice, a distribution coefficient was found. A sigmoidal curve was fitted to describe the freeze concentration process and simulated the experimental data with correlation coefficients of approximately 0·99.

The effect of depectinization and clarification on the filtration of sour cherry juice

Abstract Filtration rate and resistance are affected by the operations prior to filtration in fruit juice production lines. In this research, the effects of depectinization and clarification on filtration resistance and rate were evaluated. Filtration studies on raw juice, depectinized juice and depectinized plus clarified juice were compared. It was observed that pretreatments reduce the resistance considerably. In addition, the effects of the amount of precoating and the filter medium type on filtration rate were also studied. Decreasing the amount of precoating increased the filtration rate. Fabric filter medium had a lower resistance than commercial asbestos filter pads.

Mathematical analysis of lye peeling of tomatoes

Abstract Time-temperature-concentration relations for lye peeling of tomatoes were investigated and a mathematical model was developed and tested. The time-temperature correlation was linear, while the time-concentration correlation was exponential. Two sets of treatments were used in the experiments: (a) treatment with sodium hydroxide alone; and (b) pretreatment with sorbic acid followed by immersion in sodium hydroxide. Treatment with 9% sodium hydroxide at 90°C for 60 s was sufficient to peel the tomatoes. The model developed predicted the results with a correlation coefficient of approximately 0·99.

Frequency factor-activation energy compensation relations for viscosity of the fruit juices

Abstract Activation energy-frequency factor compensation was studied for the viscosity of sour cherry, apple and grape juices. According to Eyrings theory, which relates liquid viscosity to a chemical reaction, liquid molecules are activated to escape from a cage formed by their nearest neighbours in order to slide over each other. Activation entropies of this process were positive. This result implied that the activated complex had higher vibrational and rotational freedom than the other liquid molecules and verified Eyrings viscosity model for fruit juices. Sour cherry juice had an apparent isokinetic temperature (460 K) showing that activation occurred via formation of structurally similar complexes at all concentrations.

Effective thermal conductivity of potato during frying: Measurement and modeling

Abstract The effective thermal conductivities of potato were measured at various stages of the frying process. Samples were taken at 30 s intervals during frying, and two different methods (line heat source and modified Fitch method) were used to measure the effective thermal conductivity. An iterative Kopelman model was used for the prediction of thermal properties. The effective thermal conductivity decreased as frying time increased. The variation of experimental measurements by both methods and modeling were within 10% over most of the range studied. The probe method yielded values that were not significantly different than the modified Fitch method. Lower standard deviations were obtained with the modified Fitch method.