EFFECT OF DRYING TEMPERATURE, HUMIDITY AND TIME ON THE PHYSICO-CHEMICAL PROPERTIES OF SUGAR KELP (Saccharina latissima).  

Praveen Kumar Sappati*, Emily Duran-Frontera, Balunkeswar Nayak, Peter VanWalsum
School of Food and Agriculture
University of Maine,
Orono, ME 04469

Sugar kelp (Saccharina latissima) is a marine macro algae and is a rich source of fibers, vitamins, minerals and antioxidants. Due to high amount of moisture (~92%), it is highly susceptible to microbial attack and enzymatic deterioration and is either conventionally sun dried or hot air dried for extending its shelf life. Sun drying is one of the oldest techniques for food preservation, it is very slow, requires clear weather conditions which makes it an unreliable technique for Maine seaweed farmers. Hot air drying induces faster drying rate, but also leads to deterioration of texture and reduction in heat sensitive nutrients including vitamin C, antioxidants, phytochemicals, total flavonoid content and total phenolic content. The aim of this research is to optimize the drying parameters by studying the effect of hot air drying temperature, humidity and time on the physico-chemical properties (water activity, moisture content, pH, color, water holding capacity, oil holding capacity, ash content, fat content, vitamin C, antioxidant capacity and total phenolic content) of sugar kelp.

Fresh sugar kelp samples of approximately 450g were dried at an air temperature of 30°C, 40°C, 50°C, 60°C and 70°C with relative humidity levels of 25% and 50% and air velocity of 10.0 m/s in the convective dryer (Cincinnati sub-zero, CSG, OH, USA). Dried sample were packed in air tight zip lock bags and stored at -80°C for further analyses.

The ash content of the samples were found to be in the range of 23.32% - 33.05% (w.b) and are inversely correlated to the water holding capacity (r = -0.84) and oil holding capacity (r = -0.84), which indicate the textural properties are highly dependent on the ash content irrespective of the drying temperature and humidity conditions. Colorimeter showed the a* values are lower for higher drying temperature indicating higher photosynthetic components, due to low drying time. Heat sensitive nutrients such as vitamin C showed a positive correlation with respect to the drying temperature (30°C to 70°C) indicating drying time have significant effect (p<0.05) and it increases from (0.098 mg to 0.203 mg) and (0.128 mg to 0.211 mg) as the drying temperature increases corresponding to drying humidity of 25% and 50%, respectively (Fig. 1).