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/