LANTIBIOTICS-A SUPER PRESERVATIVE FOR FOODS?

A recent news item appearing in many media across the world proclaims the discovery of a natural antibiotic, isolated from bacteria and further claims that it can fight against "infamous' food pathogens like Salmonella, E.coli and Listeria. But is it a new discovery? Of course the scientists from Minnesota University who "discovered" the new antibiotic do not claim that the concept of natural antibiotics, different from the conventional ones, is not new as there are a few such well established antibiotics, coming under the category of "Lantibiotics", produced by gram positive bacteria belonging to Streptococcus and Streptomyces groups, effective against other gram positive bacteria with pathogenic potential.

Lantibiotic group of anti microbials are different from conventional antibiotics in that they are polycyclic thioether amino acids containing unusual amino acids like Lanthionine, Methyl Lanthionine, Dehydroalanine and 2-Aminoisobutyric acid. They are chemically dipeptides containing these amino acids. One of the most effective Lantibiotics is Nisin which has been in use for many years, especially by the Dairy Industry and there are others like Epidermin, Duramycin, Mersacidin, Actagardin, Lacticin, Nukacin among 30 such bacterial metabolites already identified by scientists. They are called Lantibiotics to denote that they contain Lanthionine amino acid having antibiotic properties.

How Lantibiotics are different from conventional antibiotics which are several in number, serving humanity ever since Penicillin was discovered by Alexander Fleming in 1948? Unlike normal antibiotics this new class of anti microbial substances do not have the ability to enter the blood stream through the GI tract, limiting their use in internal treatment. They are not stable under the conditions prevalent in the GI tract and are degraded fast losing their activity. Use of Lantibiotics is currently limited to topical applications for fighting skin infections and fast healing of wounds. Coming under the category of Bacteriocins, Lantibiotics work against other gram positive bacterial species either by disrupting cell wall production or interfering with several physiological functions of the host cells, seriously affecting cell multiplication leading to death. Most pathogenic bacteria are fortunately gram positive in nature and there lies the secret of success of Lantibiotics.

A sterling advantage of using Lantibiotics as preservatives for food is their relative safety in terms of development of resistance which is a critical area of concern currently in the meat industry which uses same front line antibiotics made by pharma companies to treat human ailments. According to one estimate more than 80% of antibiotics produced in the US goes to meat industry which uses them liberally to sanitize the meat before marketing. Incorporation of antibiotics in poultry feed is also reported to be in practice, mainly to accelerate the growth of birds and increased meat yield. As meat consumption in the world is growing significantly, human exposure to these antibiotics can lead to development of resistant pathogen strains which will be difficult to treat, calling for newer antibiotics continuously. Many strains of virulent E.coli are known to be unresponsive to treatment with any known antibiotics raising serious questions regarding the advisability of their indiscriminate and uncontrolled use.

The claim by some scientists that Lantibiotics can bring about dramatic changes in the food processing field is somewhat far fetched as of now because of many practical constraints. As these new class of natural preservatives are relatively unstable under a wide range of pH conditions, there is a serious question regarding their reliability under real field conditions. Under basic conditions they are known to undergo oxidation losing their antibacterial property. There appears to be some efforts for evolving analogs of these substances with better stability under different processing conditions and lot needs to be done to identify the type of foods which can be preserved with Lantibiotics. Once the stability issue is resolved, Lantibiotics may become an industry standard. As these are chemically peptide group of compounds, whether there could be allergic complications in some consumers is not known. The safety issues, though not believed to be of any serious nature at present, will gain focus once Lantibiotics become acceptable for wide range use in food products. The technology for producing Lantibiotics in pure condition without artifacts and contaminants, is not considered perfect at present and this is an area requiring further work.

V.H.POTTY
http://vhpotty.blogspot.com/
http://foodtechupdates.blogspot.com

NISIN AS A FOOD PRESERVATIVE

Nisin is one of the most effective natural antibacterials chanced upon by man and it was originally isolated in 1928 becoming a popular food preservative extensively used by the food industry. Nisin belongs to the broad group of antibiotics commonly known as Lantibiotics because they contain the unique special amino acid Lanthionine. There are about 30 members in Lantibiotics group, the most famous being Nisin A. Some of the other well known members of this group include mersacidin, actagardin, subtilin and epidermin. Nisin itself has variants designated as Nisin Types A, Z, F, Q derived from the bacteria Lactococci lactis while types U and U2 are obtained from Streptococci species. Generally Lanthionine antibiotics are effective against Gram positive bacterial pathogenes but in combination with the chelation agent, EDTA they can be equally effective against Gram negative bacteria also.

Nisin is a unique short chain poly cyclic peptide containing 34 amino acids and it can boast of some special uncommon amino acids like lanthionine, methyl lanthionine, didehydro alanine and didehydro amino butyric acid. The variants of Nisin differ basically in terms of the number of amino acids contained in the polypeptide varying between 24 and 34 amino acid moieties per molecule. Their excellent solubility in water, proven safety for humans and high effectiveness at low concentrations make them ideal for preservation of many foods. More important they are digested in the GI like any other peptides and proteins leaving no traces that can cause problem. Added to this it has high resistance against acidic environment and commonly encounterd processing temperatures. It is used in a variety of foods that include milk and milk products, meat and derived products, poultry meat, fish products, canned foods, fruit juices, plant proteins, fast food preparations and health care products. Unlike conventional chemical preservatives, Nisin action is independent of pH and there for are excellently suited for extending the life of many traditional food products of India.

Lantionine antibiotics are classified under two broad groups, A and B based on their mode of action against pathogens. Type A antibiotics containing flexible polypeptides cause pores or holes on the cell wall of the contaminating bacteria causing the cell content to leak out leading to their eventual death and Nisin & Epidermin are important members belonging to this type. In contrast Type B products inhibit some of the vital enzymes required for survival and growth of the pathogenic bacteria and prominent ones include Mersacidin and Actagardin. Generally a concentration of 1-25 ppm would be sufficient to get 100% kill of the infection. With an ADI value of 0.13 mg per kg body weight, Nisin is considered safe as the use dosage rarely exceeds 2-3 mg per serving. An international unit (IU) of Nisin is the dose required to inhibit one cell of Streptococcus agalatiae in 1 ml broth and a standard Nisin preparation should have 900 IU per mg. Recent toxicological evidence using nisin preparations containing low Sodium Chloride, usually used for adjusting the potency has further raised the ADI values several fold confirming the innocuous nature of this preservative.

Attempts are being made to increase the potency of Nisin as a broad spectrum antibiotics against major disease vectors through genetic engineering techniques and possibly such efforts may succeed eventually. Bioengineered Nisin, still in an experimental stage, is reported to be effective against difficult to eradicate bacteria such as MRSA, Vancomycin resistant Enterococci VRE, Listeria etc. The antibacterial characteristics of Nisin A, Z, F and Q which are more effective some bacterial species and those of Nisin U and U2 against others are combined through gene transfer to evolve new Nisin variant for use against a wide range of bacteria. It is a question of time before world comes to recognize the potential of Nisin antibiotics for ensuring safety of most of the foods which are facing serious infection problems from many pathogenic bacteria forcing the industry to recall tainted products from the market and incur heavy financial set back.

Food industry world over is going through a difficult period because of increasing cost of processing and higher expectation of the consumer regarding lower prices, better quality and absolute safety. Energy inputs required to get products with impeccable safety credentials are very high while over heated food products tend to lose its quality in terms of taste, texture and flavor. A priority goal for the industry is cutting down on energy cost in day to day operations and Nisin can achieve significant energy saving because of its synergistic effect with temperature calling for lower heating schedule to obtain complete sterilization. Same is true while using chemical preservatives which are under critical scanner regarding their safety and use of Nisin in conjunction with chemical preservatives at lower levels can achieve same results. One of the advantages of Lanthionine antibiotics is that they are never used to fight infectious diseases in man and there fore the much feared antibiotic resistance is a non-issue.

While all look rosy there can be hiccups for using Nisin as a universal preservative because, being a peptide there can be a few who may develop allergy against this preservative. Though there are no major allergic episode so far, presence of milk proteins in Nisin preparation derived from milk substrate can pose problems to consumers vulnerable to lactose allergy. How ever there is technology to produce Nisin using plant derived materials as substrate for fermentation and this problem is unlikely to pose any major challenge to this unique preservative in the near future.

V.H.POTTY
http://vhpotty.blogspot.com/
http://foodtechupdates.blogspot.com