Production of enriched pomegranate leather with functional compounds using refractance window and microwave assisted hot air drying

In this study, formulation optimization, determination of drying conditions and enrichment activities were carried out for the production of pomegranate pestil with increased functionality. In the formulation optimization studies, triple combinations of cold gelling hydrocolloids (locust bean gum, pregelatinized starch and xanthan gum) according to the mixture design were tested in pestil production and the optimum ratios of the hydrocolloids were calculated to provide pestil with the best physicochemical properties. Optimized formulation was dried using hot air drying (50, 60 and 70ºC), microwave assisted hot air drying (50, 60 and 70ºC) at two different microwave power (90 or 180W) and refractance window drying (90, 95 and 98ºC) in drying experiments and their effect on drying kinetics and physicochemical properties of the pestils were investigated. Enrichment of pestils was done using either pomegranate peel phenolics or pomegranate seed oil at three different ratios (1%, 3% and 5%) and effects of these ingredients on colour, texture and sensorial properties of pestils were determined. In the last stage of the study, four different products were stored at three different temperatures and the changes in the physicochemical properties of the product were monitored.According to the mixture design results, it was determined that the mixture providing the best pestil production in terms of physicochemical properties was 7.5% locust bean gum and 2.5% pregelatinized starch on dry matter basis. The results showed that, pestils produced using optimum formulation without heat treatment were superior in bioactive compounds and textural properties but they had similar sensorial properties compared to the pestil produced in traditional technique from pomegranate concentrate.It has been determined that the drying model, which expresses the best of drying of the pestils, is the Midilli model, regardless to the drying conditions. While the best drying method for phenolic compounds is determined as microwave assisted hot air drying, hot air drying and refractance window drying were determined to be superior according to the anthocyanin content, ascorbic acid content, HMF content, volatile compounds and the texture.Enrichment of pestils with pomegranate seed oil decreased sensory acceptability of pestil while enriched pestil with pomegranate peel phenolics had similar sensory properties to control pestils regardless of concentration. It was determined that the total phenolic and total flavonoid contents of the enriched pellets were 1.5 times higher than the control samples.All chemical components except HMF and ellagic acid gradually decreased during storage. It has been determined that the degradation of total monomeric anthocyanins and individual anthocyanins is in accordance with the second order kinetics and the loss of ascorbic acid is in accordance with the zero order kinetics. Especially, HMF content of the samples stored at 35 and 22ºC incrased according to the zero order kinetics. The amounts of ellagic acid in the pestils increased probably due to formation of the free ellagic acid by degradation of ellagitannins during storage. It has been determined that the volatile components of nonenzymatic browning reactions were formed during storage. Statistical analyzes applied to volatile compounds showed that short-term storage at 35°C was equivalent to long-term storage at low temperatures. Sensory analysis of the stored samples revealed that control and enriched pellets had similar sensory properties. Additionally, hot air dried samples and refractance window dried pesptils had similar sensorial properties expect textural properties. Decrease in all sensorials properties occurred during storage of pestils.When the results obtained within the scope of the thesis are evaluated in general, hydrocolloids can be used to produce pestils which is rich in functional components but does not contain toxic compounds. Furthermore, the results of the study shown refractance window is an important alternative production process for continuous pestil production. Enrichment with pomegranate peel phenolics enhances the functional properties of pomegranate pestil without changing its sensory properties. In order to maintain the functional properties of the pestil longer, it should be stored at low temperature.