EXTRACTION OF AGAROSE AND ITS APPLICATIONS

BY- PALASH D GUJARATHI

In addition to edible and other direct uses, marine algae provide a rich and diverse source of raw material for the manufacture of seaweed gums, a group of natural compounds characterized by their thickening and gelling properties. Such compounds find wide application in the food, pharmaceutical and industrial sectors.

INTRODUCTION

Agar is polysaccharides derived from algae. They are hydrocolloid sources, with many applications in the food, pharmaceutical, cosmetic, biotechnology industries as gelling agents, thickeners or stabilizing and emulsifying agents. Agar constitute two well defined families of polysaccharide, derived from different genera in Rhodophyta, collectively known as agarophytes . The basic structure of agar is a regularly alternating sequence of 3-1-galactose and 4-linked 3,6-anhydro-L-galactose

LOCAL METHODS OF EXTRACTION

GENERAL PRINCIPLEThe steps required to obtain agar from seaweed are -1. Cleaning of seaweed2. Chemical pre-treatment3. Extraction of seaweed4. Filtration and gelation of extract5. Bleaching and dewatering of gel

Agar is insoluble in cold water and the seaweed may safely be washed with water to remove solubleimpurities, such as salt, as well as to assist in the separation of foreign matter, such as other weeds,sand, stone.

CLEANING OF SEAWEED

CHEMICAL PRE-TREATMENTAlkali pre-treatment has been found to be the most useful for a product of higher gel strength being obtained.

The purpose of alkali treatment is that increased gel strength results from production of 3, 6-anhydrogalactose units induced by alkaline hydrolysis of galactose-6-sulphate groups within the agar molecule also to soften the weed and prepare it for extraction.

EXTRACTIONAgar is extracted from seaweed using hot water. Although adjustment of the pH is sometimes beneficial, and the use of certain additives, such as phosphates, is claimed to improve yields or colour.

The seaweed is usually added to boiling water in the extraction vessel, which is heated either by live steam introduced through pipes at the bottom of the vessel.

After addition of the seaweed, boiling is continued for between 1 and half to 3 hours.

Samples of extract and weed at intervals and tests them with fingers; good gel formation and the right ‘feel’ when the weed is pressed between the fingers indicate that extraction is complete.

FILTRATION AND GELATION OF THE EXTRACT

On completion of the extraction, the hot aqueous extract is allowed to drain through a metal screen at the bottom of the holding vessel. The screen retains the bulk of the seaweed residue and allows the liquid extraction to pass through several layers of filter cloth. These remove finer, particulate matter.

the long established method of freezing and thawing the gel is universally used. The freeze-thaw cycle is critical not only to the successful dewatering of the gel but to the attainment of a good quality product as well, the cold thaw water, in which the agar is insoluble, removing low molecular weight polysaccharides, salts and pigments.

Within a few hours of forming a gel (no more than 24 hours, otherwise the gel deteriorates) the trays of agar are placed in a freezer, where they are stored for periods of at least 20—24 hours (and sometimes as long as 72 hours) at temperatures ranging from — 10 to — 20°C. The process of freezing should be slow rather than rapid so that a uniformly frozen gel matrix is obtained. To help achieve this, the agar gel is ‘combed’ with a metal ‘comb’ before placing it in the freezer; this also makes the subsequent washing and drying more efficient and gives the finished product its characteristic mat-like appearance.

After removing the trays from the freezer, the agar is allowed to thaw, then washed with waterand bleached, usually by immersing in tank containing hypochlorite solution. Treatment is generally not more than 10— 15 minutes. The agar is washed again several times, before finally being laid put on mesh screens to dry in the sun.

BLEACHING AND DEWATERING OF THE GEL

AGAR

OVERVIEW

APPLICATIONS OF AGAROSE

APPLICATION IN FOOD INDUSTRY Gelagar is a complete range of tailored food grade agar agar powders especially developed to be used in all different confectionery,  jam and glazing applications. Different Gelagar  types have been developed for the following applications : fruit jellies , Jams ,soft candies , gelatines . bakery fillings ,ice creams , puddings and marshmallows

APPLICATION IN DENTAL Dentagars are technical agar powders to be used in dental impression applications.

Dentagars are offered with different gel strengths and different meshes.

APPLICATION IN PHARMA Pharmaceutical Agar is used in the pharmaceutical industry for many applications such as suspending agent for Barium Sulphate Radiology, intestine regulation, surgical lubricants and in preparations of emulsions, suspensions, capsules, etc.

APPLICATION IN LABSBactagars are very pure bacteriological grade agar powders extracted only from very selected seaweed Gelidium.

Bactagar system is the perfect media for bacteria growth and can be used in all bacteriological applications. Bactagars are offered with low, medium and high gel strengths. NA

Unbleachagar  system offers very special unbleached agar powders for health food applications extracted from very selected seaweeds Gelidium and Gracilaria of different origins.

Unbleachagar offers agar agar powders having different properties but the common characteristic is the extremely low content of chlorophorm and chlorine.

APPLICATIONS IN HEALTH

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