Abstract
The objective of this work was to investigate the potential use of pulsed electric field (PEF) in combination with osmotic dehydration (OD) as a pre-freezing step and to evaluate the effect on quality characteristics and shelf life of frozen kiwifruit. Peeled kiwifruit was subjected to PEF (1.8 kV/cm), sliced and treated in OD-solution [containing glycerol, maltodextrin, trehalose, ascorbic acid, calcium chloride, citric acid, sodium chloride; 1/5 (w fruit /w solution )] for 3 0 and 60 min at 35 °C. Combined, PEF only and OD only treated samples as well as nontreated and blanched (80 °C, 60 s) samples were frozen and stored at constant (- 5 , -10, -15, -25 °C) and dynamic temperature conditions (-18 °C-3 d, -8 °C-2.5 d, -15 °C-3 d). Quality of frozen samples was evaluated by means of drip loss, colour, texture, vitamin C and sensory evaluation (1-9 scale); and shelf life (SL) was calculated. Nontreated and blanched samples presented high drip loss and tissue softening (instrumentally measured as F max decrease). The tissue integrity was well retained in all osmotically pretreated samples. PEF pretreatment caused increase of fruit whiteness (increase of L value) and yellowness (a and/or b value increase); SL calculation was based on colour change. All OD samples had high vitamin content ( 24.6 mg/100 g fresh material compared to 138-154 mg/100 g osmodehydrated material ); PEF led to 93% (of the initial) vitamin retention; blanched samples showed the lowest retention (86.9% of the initial) (criteria for SL calculation). OD and combined PEF-OD treatment increased the shelf life of frozen kiwifruit (up to 3 times; based on sensorial criteria). The developed kinetic models for colour change, vitamin loss, and sensory quality deterioration were validated at dynamic temperature conditions. PEF pretreated OD (at significantly shorter time, 30 min compared to 60 min) kiwifruits retained optimum quality and sensory characteristics. PEF and OD could be used as a preprocessing step of good quality, longer shelf life kiwi sliced frozen products.
Highlights
IntroductionThe antioxidant capacity of the fruit is strongly related to the vitamin C content and the content of phenolic compounds including phenolic acids and flavonoids, and is dependent on the species and cultivar of Actinidia (Leong & Shui, 2002; Du, Li, Ma, & Liang, 2009; Latocha, Krupa, Wolosiak, Worobiej, & Wilczak, 2010; Krupa, Latocha, & Liwinska, 2011)
The objective of this study is to investigate the potential use of pulsed electric field (PEF) in combination with Osmotic dehydration (OD) as a prefreezing step and to evaluate the effect on quality characteristics and shelf life of frozen kiwifruit
The tissue integrity was retained with storage time for all osmotically pretreated, combined with PEF (PEFOD2 and PEFOD1) or not, samples
Summary
The antioxidant capacity of the fruit is strongly related to the vitamin C content and the content of phenolic compounds including phenolic acids and flavonoids, and is dependent on the species and cultivar of Actinidia (Leong & Shui, 2002; Du, Li, Ma, & Liang, 2009; Latocha, Krupa, Wolosiak, Worobiej, & Wilczak, 2010; Krupa, Latocha, & Liwinska, 2011). Main quality characteristics of kiwifruit such as colour, firmness and flavour are negatively affected by conventional processing techniques (drying, canning, and freezing and modified atmosphere packaging) (Stanley, Wegrzyn, & Saleh, 2007). Osmotic dehydration (OD) can be applied as a pretreatment before freezing (dehydrofreezing) to improve and maintain desirable quality characteristics such as colour, flavour and texture, mainly due to the reduction of freezable water ° and properties of functional impregnated solutes
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