Εφαρμογή τεχνολογίας εμποδίων για την παρασκευή προϊόντων με βελτιωμένα χαρακτηριστικά και αυξημένη διατηρησιμότητα

Abstract

Since ancient times, fig fruits have been widely consumed, as they are a commodity of great acceptance by consumers, due to their beneficial properties and distinctive sensory characteristics. However, fresh figs are highly perishable and have a very short shelf life. Thus, it is necessary to find a suitable preservation method to prolong their shelf life. Drying is figs’ traditional preservation method, and is frequently achieved either by sun drying or air-drying in a convective oven. Drying leads to a water activity decrease, resulting in the inhibition of microorganism growth and the delay of deterioration reactions. Nevertheless, drying leads to significant changes of product texture, causing hardening, resulting in decreased consumers acceptability. This can be alleviated by applying a pre-treatment prior to drying, such as osmotic dehydration (OD). OD is a non thermal processing that maintains the nutritional and quality characteristics of food to a large extent. Taking all the above into consideration, the objective of this study concerns the implementation of OD as a pre-treatment of convectional air-drying of figs, in order to create a dried final product of improved quality, compared to that of conventionally dried figs. In this context, fresh “Kymi” figs were submitted to OD and their mass kinetics were studied, with the purpose of finding the optimum conditions where OD should be implemented. Figs were immersed in osmotic solution of different concentrations (80 and 95% glycerol and combination of glycerol-oligofructose in concentration of 40-40%). OD was performed in three different temperatures (25, 35 and 45°C) for a total time of 240 minutes, while stirring. Mass transfer phenomena and changes in water activity values were studied in each case. Results showed that the optimum process conditions are: 45°C temperature and 80% glycerol concentration in the osmotic solution. Due to the non availability of “Kymi” figs, due to their short seasonal harvest, subsequent drying was not applied for this species. Drying was performed using figs of the culture “Black Markopoulo figs”. Since this fig variety is different, OD had to be applied in some conditions, in order to define which is the optimum for this species. The OD process was performed in the same way as “Kymi” figs and the effect of different temperatures (25, 35 and 45°C) and different fig to solution mass ratio (1/5 and 1/7) was studied. In all cases, the osmotic solution consisted of 80% glycerol and total time of the OD process was 300 minutes. Higher water loss, solid gain, and water activity decrease, occurred at the temperature of 45°C, fig/solution mass ratio of 1/5, total time of 90 minutes and osmotic solution of 80% glycerol concentration. These were the optimal processing conditions for “Markopoulo” figs. In order to evaluate the effect of the OD pre-treatment, OD pre-treated and non pre-treated “Markopoulo” figs were submitted air-drying in a convective oven at temperatures of 50, 60 and 70°C. The changes in their water activity values, texture and color parameters were studied. It occurred that drying time of OD pre-treated figs was shortened compared to the non pre-treated samples. Furthermore, softer texture and improved color was achieved due to the pre-treatment. Finally, pre-treated and non pre-treated samples were stored at 25, 35 and 45°C for 45 days in order to examine the texture and color changes that take place during storage. Pre-treated samples showed improved texture during storage, while at 25°C color was also maintained. Therefore, taking into account the results obtained during this research, it can be concluded that osmotic dehydration can be an effective pre-treatment in figs air-drying, since it substantially shortens drying time, resulting in saving energy and cost, while also improves the quality characteristics of the final dried product. This is particularly important, as the figs used were not intended for placing on the market, so the implementation of this processing presents significant advantages for the utilization of figs that would probably be discarded under other circumstances.