Effects of sulfated polysaccharides from green alga Ulva intestinalis on physicochemical properties and microstructure of silver carp surimi

The aim of this study was to isolate sulfated polysaccharides from green alga Ulva intestinalis (UIP) and evaluate its potential application as a new hydrocolloid in surimi formulation. Compositional analysis showed that UIP comprised carbohydrate (65.3%), protein (8.4%), sulfate (18%) and uronic acid (5.6%) with the average molecular weight of 64.2 × 103 g mol−1. FT-IR revealed the presence of sulfate esters as indicated by the peaks at 826 (C–O–S) and 1257 (S–O) cm−1. In order to examine the effects of UIP on the characteristics of silver carp surimi, it was added into surimi paste in four levels (0.25–1.0 g/100 g) while protein/water contents were kept constant. The UIP addition reduced the pH of surimi gel from 6.6 to 6.4. Emulsifying stability of surimi pastes were notably improved by UIP addition while emulsification capacity showed no changes. The addition of UIP up to 0.25 g/100 g maintained the textural characteristics and water holding capacity of surimi gels. The gel whiteness was not adversely changed by UIP addition up to 0.75 g/100 g. The SEM images revealed the presence of compact microstructures with dense surfaces due to UIP addition. All products formulated with different UIP levels were judged acceptable by the sensory panel. Based on the present study, the incorporation of seaweed sulfated polysaccharides at low concentrations into surimi are not likely to compromise quality and therefore could be suggested as a functional ingredient in surimi and surimi-based products with beneficial health effects.