Bacterial cellulose

Bacterial cellulose is an exopolysaccharide produced by different species of bacteria like Acetobacter, Aerobacter, Salmonella, Rhizobium,Sarcina, Achromobacter and Azotobacter; Acetobacter xylinus being most widely studied strain. Structurally, bacterial cellulose comprises of glucose units linked by 1   to     4 beta glycosidic linkages.These nanofibrils then aggregate to form moicrofibrils which crosslink with each other  to form a 3D structure of considerable mechanical strength. 

One of the greatest advantages of bacterial cellulose is that it is purely cellulose and does not contain lignin or hemicelluloses as is the case with plant cellulose. Bacterial cellulose produced by the micro-organism depends upon the culture conditions. Cultures grown under static conditions tend to produce smooth and uniform cellulose while those under agitated conditions usually form spheres and filaments. These differences in structure as well as the water holding and gelling properties of the bacterial cellulose along with its biodegradability and mechanical strength have opened avenues for its use in food, pharmaceutical and other industries.

Nata de pina and Nata de coco are traditional delicacies of the Philippines, and they are nothing but bacterial cellulose! Nata de coco is the cellulose produced when the bacterium grows on coconut milk while the cellulose is called nata de pina when the bacterium grows on pineapple juice or pineapple waste.  It is being used in fruit beverages to provide a mouthfeel and different sensorial experience.

It has shown to act as a stabilizing and suspending agent. 

Addition of bacterial cellulose to icecream helped retain the structure of icecream for an hour once it was out of the freezer. Addition of bacterial cellulose to chocolate drinks has shown to prevent the precipitation of cocoa solids thus giving a homogenous beverage.

Bacterial cellulose in combination with monascus fungi has the potential to form a class of seafood imitators. The monascus fungi imparts color to the combination but no taste while the water holding and gel forming capacities of cellulose give it a texture. It also provides high fiber content, limited calories and healthy nutrients.

Bacterial cellulose has been used as a fat replacer in meatballs and is an approved fat replacer for surimi products. Preliminary studies have shown bacterial cellulose to lower the cholesterol level in vivo and hence it is also being used to produce low cholesterol products. Apart from this, it has also been used in  active packaging in the form of antimicrobial films as well as making edible films.

Apart from food, bacterial cellulose is also widely used in the pharmaceutical industry specially as scaffold for tissue engineering. It is also used in manufacturing drug release systems, and as replacement for skin tissue, cartilage and cornea. Biofill™ and Gengiflex™ are bacterial cellulose products with applications in surgery and dental implants.

Its not just the food and medical fields where bacterial cellulose finds application. It is also employed in cosmetics(as light scatterer in sunscreen), paper-making, optics(as flexible display screens for electronic devices)and acoustics(membranes for loudspeakers).

Reference:

Zhijun Shi et al, Utilization of Bacterial Cellulose in Food, Food Hydrocolloids, 35 (2014) 539-545

Keshk, Bacterial Cellulose production and its Industrial Applications,  J Bioprocess Biotechniq, (2014) 4(2)

Further reading:

http://www.nature.com/nbt/journal/v25/n4/full/nbt0407-389.html

Gellan gum

What is the similarity between Kelcogel, Gelrite, Phytagel and Gel-Gro? All of these are the trade names of the same substance: Gellan gum!

Gellan gum is a microbial exopolysaccharide produced by the bacterium Pseudomonas elodea. Industrial production of gellan gum is carried out using Sphingomonas paucimobilis. Gellan is a high molecular weight polysaccharide composed of repeating units of beta d glucose (60%), L-rhamnose (20%), and glucuronic acid(20%)

There exist three types of gellan gums: Native, deacetylated and clarified. Native gellan gum has two acyl groups in its backbone which are removed by alkaline treatment in deacytylated gellan gum.  Hot deacytylated gellan gum when filtered to remove the protein components yields clarified gellan gum. This is widely used to make agar substitute.

Gellan gum is widely used in the food industry. It is basically used as a substitute for gelatin.  Use of gellan gums in starch jellies helps reduce the setting time of jellies by almost half while maintaining the texture and structure of the end product. It helps prevent moisture fluctuations in sugary foods, icings and toppings. It can also effectively act as a bulking agent for icecreams. Gellan gum when added during cheese making was found to enhance water retention and reduce the losses of protein. Gellan gum also has a probable use in fried foods wherein due to its hydrophilic character, it may reduce the oil-uptake by the food being fried.

The potential of gellan gum in controlled drug release has also been widely studied. Phytagel™ and Gelrite™ are being used as bacterial growth media and medium for plant tissue culture in place of agar. Gellan gum also has potential to replace agarose as the electrophoresis substrate provided it is used in conjunction with a second polymer such as hydroxymethylcellulose to reduce electroosmosis. 

Reference:

Bajaj et al, Gellan Gum: Fermentative production, downstream processing and applications, Food Technol. Biotechnol, 45(4), 341-354, (2007)

Green tea and weight loss

 Green tea is the non-oxidized, non-fermented product made from the leaves of Camellia sinensis. Green tea is being touted as an easy solution to get rid of all the excess fat and slim down. But is it really a miracle worker?

The key to losing weight is increasing the energy expenditure and fat oxidation of the body. Drinking green tea achieves this exact thing: courtesy the catechins present in them. Catechins are the major constituents of green tea and are basically antioxidant molecules.

Energy homeostasis is regulated by the sympathetic nervous system (SNS). Norepinephrine, also known as noradrenaline, is a stimulant of SNS pathway. Norepinephrine can be broken down by the enzyme  catechol O-methyltransferase (COMT) The catechins inhibit the COMT enzyme thereby preventing the breakdown of norepinephrine. Norepinephrine in turn stimulates fat metabolizing enzymes leading to increased fat oxidation. It also upregulates the gene expression of the proteins involved in heat production during ATP generation, thus increasing the energy expenditure.  It also has a negative effect on insulin thereby reducing the glucose uptake in cells.  Also, green tea itself has no calories!

However, drinking green tea does not result in the same outcome for every individual. Research has found that Asians are more likely to be benefited by drinking green tea as compared to the Caucasians. This is because of the inherent genetic variability in the type of COMT enzyme that these 2 populations have. The Asians have a high activity COMT while the Caucasians have a low activity COMT. Therefore, inhibition of the COMT produces a more pronounced effect in the Asian population as compared to the Caucasians.

Reference:

http://www.nature.com/ijo/journal/v34/n4/full/ijo2009299a.html