Marine resources are a highly sought-after source of biologically active compounds used as functional ingredients in foods .
Seaweed is an important marine resource in Ireland.
The Irish seaweed production and processing sector is worth ca.
€30 million per annum and plays an increasing socio-economic role in marine resource utilization.
By 2020, the seaweed sector is projected to move away from a declining wild harvest and fledgling aquaculture production sector to one with sustainable, scientifically based harvesting and downstream processing of value added biopharma and nutraceutical products from Ascophyllum nodosum and other important seaweeds .
A. nodosum (L.) is a brown seaweed, which forms a single bladder centrally in long, strap-like fronds.
It is confined to the North Atlantic basin and is sustainably harvested in various countries including Norway, Ireland and Iceland .
A. nodosum is one of the most researched brown seaweed species and is proving to be very significant in terms of its potential for agricultural and food applications .
A. nodosum has traditionally been used as a fertileizer, a soil conditioning agent, animal feed supplement and also as a human nutritional supplement .
Food products including grains, marine products, meat products, as well as fruits and vegetables are routinely preserved using dryingtechnologies.Raw food products havea widerange of moisture contents, from as low as 18–25% in grains to as high as 90% or more in some fruits, which need to be reduced for long term storage .
Fresh seaweeds collected from the sea are usually dried prior to industrial processing.
Drying significantly affects the nutritional values of seaweed samples.
It has been shown that high temperature drying and cooking significantly affect the nutritional value of the brown seaweed .
In Ireland, drying of seaweeds for the production of different grades of seaweed meal is routinely carried out in rotary dryers.
Different drying methods have varied effects on the nutritional, functional and biological properties of seaweed.
Wong and Chikeung Cheung compared oven drying and freeze drying for extractability and quality of proteins.
They found that oven drying significantly improved the protein extractability and the in vitro protein digestibility of three Sargassum species investigated.
Conventional air drying is a simultaneous heat and mass transfer process, accompanied by phase change which makes it a high-costprocess.
To reduce drying costsand to improve drying efficiency of biomaterials, researchers have investigated various Contents lists available at ScienceDirect
Pre treatment technologies including ultrasonication, microwaves and osmosis
Ultrasonication involves high frequency sound waves above human hearing capacity i.e. above 20 kHz. Unlike electromagnetic waves, they are mechanical waves, which pass through solid, gas and liquid media.
These waves propagate by rarefactions and compression.
These expansions cause negative pressure in the liquid.
If the pressure exceeds the tensile strength of the liquid then formation of vapor bubbles occurs.
These vapor bubbles undergo implosive collapse in strong ultrasound fields which is known as cavitation.
The implosion of cavitation bubbles generates macroturbulence,high-velocity inter particle collisions,and perturbation in micro-porous particles of the biomass. Cavitation near liquid solid interfaces directs a fast moving stream of liquid through the cavity at the surface.
Impingement by these micro jets results in surface peeling, erosion, and particle break down facilitating the release of bioactive compounds from the biological matrix .
Ultrasound can be employed as a pre treatment before drying to improve the drying kinetics and to reduce the energy costs involved in the unit operation.
This study investigated the use of ultrasound as a pre treatment prior to hot air convective drying of seaweed.
The influence of ultrasound power on drying kinetics, water gain, solid loss and changes in color of seaweed were examined.
The combined process of ultrasound and air drying was optimized and various mathematical models were applied to the drying kinetics.