Investigation of effects of different thickeners on rheological properties of pomegranate jam

Fruits and vegetables can be processed into different products. These consistent products include, but not limited to jam, marmalade, jelly, spreads, preserve and preparations. Jam is a thick product made by mixing one or more kinds of fruit, fruit pulp, or their combination and water and sugar.Jams or jam-like products can be produced based on product properties using fresh fruit or cut fruit, fruit pulp, or fruit juice with sugar, glucose syrup, acid, color pigments, thickeners, and water. Thickeners such as pectin, xanthan gum, guar gum, locust bean gum and carrageenan can be used in jams and jam-like products to get desirable consistency.In this study, the effects of using different thickeners on rheological properties of pomegranate jam were investigated. In jam production, frozen pomegranate arils, sugar, and water and three different concentrations (0,2; 0,4; 0,6% of fruit weight) of three different thickeners such as pectin, guar gum, carrageenan were used. Citric acid was also used at one of the three different concentrations (0,4; 0,6; 0,8% of fruit weight) in jam formulations. Jam production was made by the technique of cooking at open caldron. The mixture were cooked until water soluble solid content reached 74%±1,45 and the jam produced was filled to glass jars when the jam temperature was between 85 and 88°C. The samples were analyzed after storing for two weeks at room temperature. Rheological behavior, color, pH, titratable acidity, water soluble solid content, and total solid content analyses were performed in the syrup of samples. Moreover, pectin analysis was done in the samples made by using pectin. Color, pH, titratable acidity, pectin, water soluble solid content, and total solid content analyses were carried out in raw material.In this study, three-way interaction among type of thickener, concentration of thickener, and quantity of acid existed for apparent viscosity. The highest appearance viscosity value was found as 334041 cp in the samples having %0,6 pectin and %0,4 acid; and the lowest apparent viscosity value was found as 475,92 cp in the samples having %0,6 guar gum ve %0,6 acid. There were no differences between apparent viscosity of jam samples made by guar gum and carrageenan. However, apparent viscosity of jam samples made by pectin was higher than that of others. Although the jam samples made by pectin exhibited non-newtonian flow and showed pseudoplastic properties, samples made by guar gum and carrageenan exhibited newtonian flow.The highest titratable acidity was found in the samples made by using the highest acid addition (%0,8), and 0,4 or 0,6% of pectin. On the other hand the lowest titratable acidity was determined in samples made by using the lowest acid (0,4%) and carrageenan (0,2%) concentrations. It was found that titratable acidity of jam samples made by using pectin was higher than that of jam samples made by guar gum or carrageenan. Although the highest pH value was found in the samples made by adding the lowest acid value (%0,4) and 0,6% guar gum, the lowest pH value was found in the samples made by adding the highest acid (0,8%) and %0,6 of guar gum. It was also found that increasing concentration of all thickeners, increased pH value of jam samples. The highest pectin concentration was found in samples made using the highest rate of pectin (0,6%) and acid (0,8%). On the other hand the lowest pectin content was found in samples made by using the lowest amount of pectin (0,2%) and acid (0,4%).The highest L* value was found in samples having 0,6% guar gum and %0,4 acid whereas the lowest L* value was found in samples having %0,6 pectin and %0,4 acid. L* value of jam samples made by pectin were lower than that of jam samples made by guar gum or carrageenan. It was found that increased used of pectin reduced L* value of jam samples. The highest a* value was found in the samples containing 0,4% of pectin and 0,6% of acid, and the lowest a* value was found in samples containing %0,6 guar gum and 0,4% acid. It was found that a* value of jam samples made by using pectin was found higher than that of samples made by guar gum or carrageenan. The highest b* value was found in the samples containing 0,2% of pectin and 0,8% of acid, the lowest b* value was found in samples containing 0,4% of carrageenan and 0,4% of acid. The b* value of jam samples made by using pectin were found higher than that of samples made by guar gum or carrageenan. The highest hue value was found in the samples containing 0,6% of guar gum and 0,4% of acid, the lowest hue value was found in the samples containing 0,6% of guar gum and 0,8% of acid. Three-way interaction among type of thickener, concentration of thickener, and quantity of acid was effective on hue value. The highest a/b value was found in the samples containing 0,4% pectin and 0,6% acid, the lowest a/b value was found in samples containing 0,6% of guar gum and 0,4% of acid. It was found that a/b value of jam samples made by using pectin was higher than that of samples made by using guar gum. Power-law, Herschel-Bulkley and Casson models gave high confidence of fit (R2) values (between 0,941 and 1,00) for the rheolojical properties of pomegranate jam. Generally, higher confidence of fit values was obtained with Herschel-Bulkley. ?K? values of jam samples containing pectin fit by Herschel-Bulkley were higher than those having guar gum and carrageenan. Increasing pectin quantity, increased ?K? value of jam samples. According to this model, ?n? values of jam samples made by pectin were lower than those made by guar gum or carrageenan. According to this model, ??0? values of jam samples made by pectin were lower than those made by guar gum or carrageenan.