Effects of osmotic dehydration on the quality of semi-refined carrageenan

The study investigated the effects of osmotic dehydration (OD) as pre-treatment to the quality of mechanically air-dried semi-refined carrageenan (SRC). It aimed to evaluate some physical and textural properties of SRC as influenced by osmotic temperature. Dried seaweeds of the specie Kappaphycus alvarezii were used as raw material. After cooking and washing, the seaweed samples were subjected to osmotic dehydration in a saturated sugar solution at temperatures of 30O, 40O, and 50OC. The samples were then subjected to mechanical air-drying and milling to create powdered products. For property evaluation, both powder and gel samples were used. The osmotically air-dried products (OAD) were compared to conventionally-produced air-dried (AD) samples. Osmotic dehydration both induced moisture loss and solute uptake in the products. Due to sucrose gain, OD produced lighter powders and clearer gels from semi-refined carrageenan. Indeed, sugar was able to improve product clarity. OAD gels also had lower pH values, more viscous, and with greater strength than AD gels. In effect, this enhanced product qualities implied greater versatility and range of application for the semi-refined carrageenan, making it more competitive with its refined counterpart. However, osmotically air-dried (OAD) powders had higher water activity than purely air-dried (AD) samples. This is a challenge to the storability and shelf-life of the product, implying the need to develop appropriate packaging system for it.

Keywords – osmotic dehydration; semi-refined carrageenan; mass transfer; diffusion; empirical models