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

What is Enzyme Modified Cheese?

Enzyme modified cheese or EMC as they are known are a cost effective alternative to natural cheeses. They are produced using enzymes on the cheese curds or immature cheeses to produce a more intense flavor profile as compared to that of natural cheeses. Hence they may be used at a lower level to impart the same flavor. However, EMC although having a strong flavor profile, do not mimic the textural properties of natural cheeses. EMC have approximately a 15-30 fold more intense flavor and are available as pastes or spray-dried powders. EMC find use in processed foods to give a cheesy flavor or to improve the flavor of a comparatively bland cheese product.

The cheese flavor is a result of the proteolytic, glycolytic and lipolytic pathways. While manufacturing EMC these pathways are only followed, the only difference being the use of enzymes rather than the entire culture micro-organism. The culture technique developed when a certain gentleman mixed curd slurry with NaCl in the ratio 2:1 and blended it. He then incorporated enzymes into it and kept the mixtures at 30 C for 4-5 days with constant agitation. A liquid cheese product with characteristic Cheddar, Brick or Romano flavor could be produced from fresh curd in 4-5 days. Nowadays, either of the following two approaches to manufacturing EMC may be taken. Either the hydrolysis of fat and protein occur simultaneously in one step or each of the hydrolysis is carried out separately and then the end products blended together to give the final EMC product.

EMC flavors available include Cheddar, Mozzarella, Romano, Feta, Parmesan, Blue, Gouda, Swiss, Colby and Brick. These cheese flavors find application in cheese analogues, chips, pasta products, salads, ready to eat foods, frozen foods, canned foods and low fat cheese spreads or cheese substitutes.


Reference:

Kieren N. Kilcawley, Martin G. Wilkinson, Patrick F. Fox, Enzyme Modified Cheese, International Dairy Journal, 8, 1998, 1-10.

Wheat Gluten

Gluten is a storage protein found in cereals like triticale, rye, barley; but perhaps the most well known is wheat gluten. Gluten is made up of the monomeric peptide gliadin and the polymeric peptide  glutenin. Some individuals suffer from Celiac disease- an allergic response to gluten. Hence, the advent of “gluten free” claims on many different food products. Wheat gluten is used in many different ways, for both, food and non-food uses.

Bakery: Perhaps the oldest and best known functional use of gluten is in bread making. Although insoluble in water, gluten can bind approximately twice its weight water giving rise to a hydrated viscoelastic mass. This property of gluten helps  hold together the dough used for making bakery products. In addition, owing to its elasticity, gluten can stretch and expand and help trap in the carbon dioxide bubbles generated during fermentation of bread.  

Meat analogues: When subjected to extrusion processing, gluten proteins align to form microfibrils that in turn form a macroscopic fibrous structure. These microfibrils upon hydration swell and give a fleshy appearance to the texturized wheat gluten. The viscoelastic properties of gluten also enable it to be moulded into a desired shape. This property has been harnessed in making meat or sea food replacements. Gluten may be processed and presented as  high value seafood like crab meat. The extrusion process works on gluten to give it the mouth feel and texture of meat.

Condiment: Although gluten is lacking in some essential amino acids like leucine and threonine, it has a high proportion of glutamine. By chemical methods such as deamidation, this glutamine can be converted to glutamic acid. Wheat gluten has thus been used to produce monosodium glutamate or a liquid similar to soy sauce.

Fortification and breakfast cereals: Wheat gluten is used as a low cost additive to fortify flours having low protein content. Even breakfast cereals make use of wheat gluten to increase their protein content and give a characteristic texture to the product. The most notable amongst these is the Kellog’s K cereal which employs wheat gluten as one of its ingredient. Due to its ability to bind water, gluten has been used as a binding agent for fruit purees used as fillings in nutritional fruit bars. It has also been used in producing synthetic cheese and as replacement for sodium caseinate in imitation cheese products.

Non-food uses: Gluten also has many non-food applications such as its use in adhesive bandages, biodegradable materials and edible coatings. Peptides from gluten have also found use in cosmetics. 

Reference:

Day et al, Wheat-gluten uses and Industry needs, Trends in Food Science & Technology, 17 (2006) 82–90

Randomly Amplified Polymorphic DNA

Randomly amplified polymorphic dna (RAPD) as the name suggests are the products of a PCR  reaction primed by arbitrarily selected primers.

How is it different from conventional PCR?

In conventional PCR, one designs the forward and reverse primers with the aim that they will anneal to the gene of interest. In order to accomplish this, it is necessary that one knows the sequence of the gene of interest. The next few steps follow a cycle wherein the primers first anneal, then a polymerase extends them and again the extended products are denatured making them ready for the next cycle of primer annealing.

In case of RAPD, the knowledge of the gene sequence is not a pre-requisite. One selects random primers which at low temperature display lower fidelity and hence anneal to many arbitrary sites on the DNA template with a variety of mismatches. After a few initial steps of annealing at lower temperature the amplification may then be carried out according to the conventional PCR or may also be continued even at the same temperature. When these amplified products are run on a gel, a pattern of bands is obtained which is unique for a particular species and is dependent upon the primers used.

Selection of primers

A single random primer will seldom be informative. When we use many such primers and then score them; will the RAPD profile make some sense in terms of polymorphism. Polymorphism maybe detected when the fingerprint of one sample shows an amplified band while the other sample does not even when the same primer is used with both the samples.

RAPD may be generated due to mutation in template (insertions/deletions) or presence of alleles in heterozygous individuals. However, these cannot be pinpointed as such because RAPD markers are dominant i.e they amplify many loci in a single go with a single primer.     

Some of the amplified bands are easily recognizable while some others may be difficult to interpret. The ambiguity arises due to the fact that every primer will possess different power to distinguish between different sites of amplification. Also there will exist competition between primers and different sites. Certain amplified fragments may interfere in the amplification or separation of other segments. Reproducibility of the RAPD pattern becomes problematic below a certain concentration of genomic DNA and may produce smears. On the other hand, there maybe poor resolution if the genomic concentration is very high                   

Reference:

Molecular Biomethods Handbook, second edition, John M Walker, Ralph Rapley,  chpt 10, pg 132-147                                                                                                                                               

What is Sitosterolemia?

Cholesterol synthesized by the human body plays an important role as part of the cell membrane. It is a type of sterol. However, plants do not synthesize cholesterol. Instead they have phytosterols of which sitosterol is a comparatively abundant phytosterol. When we eat plant derived foods, phytosterols are ingested into the body but they are not absorbed into the blood. Sitosterolemia is a rare recessive autosomal disease in which individuals absorb large quantities of plant sterols and this is stored in their blood and tissues. It is also referred to as phytosterolemia or plant sterol storage disease.

The clinical signs may include small yellowish outgrowths on various parts of the body, called xanthomas. These may also occur within the body such as in the tendons.  These are made up of accumulated lipids.  Joint stiffness and haemolytic anaemia may also be present.

The underlying cause of this genetic disorder is mutations in the genes ABCG5 or ABCG8. These genes code for a transport protein sterolin (sterolin 1 and sterolin 2 respectively) The sterolin 1 and sterolin 2 then form a heterodimer which acts as a transporter protein. Sterolin is the protein involved in transport of sterols out of the apical cells of the intestines. When there exists a mutation in any one of these genes, this transport protein malfunctions resulting in sitosterolemia. An interesting observation is that, mutations have always been seen in both the alleles of any 1 of the genes never in both of them together.

People diagnosed with sitosterolemia need to consume foods lower in plant and shellfish sterols. Patients may be given ezitimibe which acts as a sterol absorbtion inhibitor. If the individual is not responding to this therapy then use of cholestryramine and/or partial ileal bypass surgery may be recommended.

References:

http://ghr.nlm.nih.gov/condition/sitosterolemia

http://www.ncbi.nlm.nih.gov/books/NBK131810/