Influence of osmotic dehydration pre-treatment and combined drying method on physico-chemical and sensory properties of pomegranate arils, cultivar Mollar de Elche
Introduction
Epidemiological studies concluded that high consumption of fruits and vegetables reduces the risk of chronic diseases (EUFIC, 2012). Among fruits, pomegranate (Punica granatum L.) and pomegranate-based products have been specifically associated with inhibition of prostate, breast, and lung cancer (Orgil, Spector, Holland, Mahajna, & Amir, 2016), reduction of dyslipidaemia, and cardiovascular issues (Haghighian et al., 2016), antioxidant stress effect (Orgil et al., 2016), and anti-diabetic properties. Pomegranate owns its health-related properties to the unique composition of biologically active components, mainly polyphenols from the fruit peel (exterior rind) (Calín-Sánchez et al., 2015).
Pomegranates are usually available on the market as fresh fruits or as beverages, basically juices, concentrates or wine (Jaiswal, DerMarderosian, & Porter, 2010). In smaller amounts, they are available as an additive to jams, jellies, and are used for candy production (Tezcan, Gültekin-Özgüven, Diken, Özçelik, & Erim, 2009). To prolong the arils shelf-life, different drying processes have been applied; however, they had a significant impact on the final products quality (Kingsly & Singh, 2007). Dried pomegranate arils are a great source of vitamins and minerals and are rich in biologically active components (Alaei & Amiri Chayjan, 2015). The main purpose for production of dried pomegranate arils is consumption of the arils as a nibbling snack.
Among Spanish pomegranates, the most popular cultivar is “Mollar de Elche”, which production is safeguarded by a Protected Designation of Origin (DOP) since 2016 [R (UE) 2016/83]. This cultivar is recognized worldwide, due to its high sweetness intensity and arils with soft woody portion. It has also disadvantages, such as pale pink colour that significantly decreases the quality of pomegranate-based products, especially the juice after the heat treatment. Besides, its sensory profile is too flat with a predominating sweetness and with very weak fruity notes (Vázquez-Araújo et al., 2014).
There are agronomic practices that can be used to improve the flavour of some fruits. Regulated deficit irrigation led to pomegranate fruits, cv. “Mollar de Elche” with a more complex sensory profile and enriched chemical composition (high punicalagin content); these fruits are called “hydroSOStainable” (Galindo et al., 2014).
The appearance of commercial dried arils is mostly not acceptable for consumers, due to intense browning. A previous study (Calín-Sánchez et al., 2013) showed that high quality dried arils could be prepared using appropriate drying methods. It was indicated that the application of fruit or berry juices (e.g. chokeberry) during the osmotic dehydration (OD) step could improve the functionality, and colour of the dried products, by transferring bioactive and organoleptic-active compounds from the osmotic solution into the dehydrated pomegranate arils (Calín-Sánchez et al., 2013).
Considering all the above, the aim of this study was to evaluate the physico-chemical and sensory properties of the dried arils prepared using first osmotic dehydration (OD), with selected fruit juice concentrates, and later a combined drying technique [convective pre-drying (CPD) and vacuum-microwave finish drying (VMFD)] for dehydration of pomegranate arils cultivar “Mollar de Elche”. The drying kinetics, quality parameters (anthocyanin content, antioxidant capacity, colour, rehydration ratio), and descriptive sensory profile were studied.
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Material
Pomegranates [cultivars “Mollar de Elche” (used for preparation of dried arils) and “Wonderful” (used for preparation of osmotic solution)] were cultivated in a farm located in Murcia (Spain) under regulated deficit irrigation (RDI) (Galindo et al., 2014). Pomegranate fruits (∼100 kg) were hand-harvested in mid-September 2015 at a commercial maturity stage (∼15 °Brix), and immediately posted to Poland. The pomegranate fruits were submitted to short term storage (less than 2 weeks) at 5 °C at an
Moisture content (MC), water loss (WL), solid gain (SG), and drying kinetics
The osmotic dehydration in different fruit solutions reduced MC of “Mollar de Elche” arils from an initial 81.5 ± 0.7% down to an average value of 72.1 ± 0.4% (Table 1). The WL was not affected by the nature of the osmotic solution; it reached a mean of 30.2 ± 0.6%, and ranged from 28.9% and 30.7% (Table 1). Similarly to previous studies (Lech et al., 2015), a mean increase of 19.2 ± 1.6% in SG was observed after osmotic pre-treatment, with the OD treatment using pomegranate juice cultivar “Wonderful”
Conclusions
Osmotic dehydration using “Wonderful” pomegranate and chokeberry concentrated juices improved the quality of dried “Mollar de Elche” pomegranate arils in terms of rehydration rate, antioxidant capacity, colour, and sensory profile; however still further research is needed to fully optimize this combined drying treatment because the freeze-dried sample still had higher anthocyanin content and better instrumental colour parameters. On the basis of the results obtained connected with colour,
Acknowledgments
The authors are grateful to the projects AGL2013-45922-C2-1-R y AGL2013-45922-C2-2-R (Ministerio de Economía y Competitividad, Spain). Author Marina Cano-Lamadrid was funded by a FPU grant from the Spanish Ministry of Education. This study was supported by a grant of the KNOW Consortium “Healthy Animal – Safe Food”, MS&HE Decision No. 05-1/KNOW2/2015.
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