CHEMICAL COMPOSITION AND RHEOLOGICAL CHARACTERIZATION OF PISTACHIO GREEN HULL'S MARMALADE

Abstract

ABSTRACT This research aimed to study the effect of different levels of pistachio green hull (40–60%) and pectin (0–0.4%) on the flow characteristics of pistachio green hull's marmalade. It was found that pistachio hull's marmalade behaved as a pseudo‐plastic fluid. Seven models were used to describe time‐independent behavior of samples. To evaluate the ability of this models, two statistical parameters namely; R 2 and root mean square error were used and finally power‐law model was found to be the most appropriate to fit the flow curves of pistachio hull's marmalade. Overall, the results showed that increasing the percent of pistachio hull increased the consistency coefficient in the range of 1.9–121 Pa · s n and apparent viscosity in the range of 0.67–7.95 Pa · s, whereas it decreased the flow behavior index in the range of 0.82–0.28. The change of flow behavior index and consistency coefficient with pectin did not follow a descriptive trend. PRACTICAL APPLICATIONS Rheological properties of semisolid foods are important for quality control and process engineering calculations. Pistachio hull's marmalade is a semisolid gel made from puree of pistachio green hull, sugar, acid and pectin, which can be used in different formulations such as cake and cookies. Regarding the rheological data of marmalades in literature, comparisons in absolute terms do not provide useful information, possibly because of two reasons. Due to their complex mathematical geometries, some viscometers might not allow shear rate calculations and, hence, can only produce comparative rather than absolute flow behavior data. Another reason could be the differences in the production method or raw material used. Even very minor changes in composition or processing variables can dramatically influence the rheological properties. The knowledge obtained in this work will enable the pistachio processors to increase the efficiency of the design and quality control throughout the processing of this new product.