Showing posts with label food preservation. Show all posts
Showing posts with label food preservation. Show all posts

Monday, January 24, 2011

THE "FRESH" CONTROVERSY-IS IT LOGICAL?

There is an increasing tendency for people o go for "fresh", "local" "natural" or organic foods and the reason is not far to seek. It is simply the fear factor that is driving millions of consumers away from preserved or processed foods and the food industry is to blame itself for this sorry situation. Historically food technology was evolved over centuries to extend the supply chain so that adequate foods are available all year round. Use of salt or sugar which increases the osmotic pressure in food system to discourage proliferation of pathogens and many spoilage organisms continues even to day though from healthy angle they are shunned by a substantial strata of the society. While uncontrolled salt consumption is known to be linked to hyper tension and cardiovascular disease, high sugar can be responsible for dental decay, diabetes, obesity and other disorders. Organolepticaly too much sugar or salt can create quick satiety. Salt and sugar preserved food products can be farthest from the concept of fresh foods.

Sun drying or the more scientific mechanical drying of perishables which contain high levels of moisture gives products with altered textural features but it still served the purpose of extending the life of the food significantly due to low water activity in such foods after removing bulk of the water content. Besides, the reconstituted final product has drastically different eating quality, not often liked by consumers. Vast improvements in dehydration technology have contributed to better finished products and freeze drying can give a product that can be quite satisfactory though cost wise such products can be very expensive. However dehydrated foods can also never qualify to be called fresh.

One often hears about "Dairy Fresh" milk which is probably taken to mean that the milk is as fresh as the one milked directly from the cow! In reality milk travels over some distance from the point of milking, gets refrigerated, pasteurized and packed before reaching the consumer. In a country like the US raw milk is never allowed to be sold directly and therefore fresh milk in literal sense can never be seen by a US consumer while in India really fresh milk is sold directly to homes within a matter of minutes! Similarly fresh fruits and vegetables which are sold in many markets in India are considered really fresh because not much time elapses between their harvest and bringing to the market. In contrast most fresh produce sold in super markets cannot claim to be fresh because they undergo a series of "processing" involving cleaning, washing, sorting, trimming, cold storage and distribution over considerable distances.

Modern technologies like MAS and MAP in combination with cold storage can extend the life of fresh produce for weeks and months though quality-wise they will always be inferior to farm fresh counterparts. That raises the inevitable question as to what qualifies to be called "fresh"? The current understanding that any food put on sale as early as possible after harvesting is some what vague and there does not appear to be any scientific definition universally accepted. The perishable nature of foods in general calls for preservation, at least till they reach the market and ultimately the bottom line is that the eating quality and nutritive value should not be adversely affected to any significant extent.

As foods, especially the perishable ones are seasonal in nature, their year round availability and supply can be assured only if they are preserved for some time. While some foods like apple, potato, onion etc are amenable to long term storage under MAS and low temperature environment, others can still be stored under such conditions for limited periods. Frozen storage or freeze drying can be the best way of protecting a food from nutrition angle but the consumer will have to compromise on eating quality as there will be deterioration in this respect due to freezing. While under optimum frozen temperature conditions almost all foods can have storage life beyond an year, the sensory quality of products when thawed can never be the same as the fresh material before freezing.

While advances in technology and transportation extends the shelf life of food, there is a price for availability and convenience in terms of nutrition and taste. Probably obsession with the word "fresh" will have to be overcome eventually as it is impossible for the world to meet the demand for such "farm fresh" foods of every consumer in the world. While intense debate goes on regarding even the ability of man to meet the bare food needs of the ever expending population, the protagonists of fresh foods are well advised not to divert the attention of the world from the basic task of increasing food production and making them available to people with maximum nutrient content. The story of organic foods also bears a parallel to fresh foods as it is logistically impossible to raise and supply such foods to meet the needs of entire population! In spite of movements like Local Produce, Slow Foods, Urban Gardening, Roof-top farming, Organic farming etc, it is unlikely that every person on this planet can be provided with "fresh" foods as it is understood commonly.

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

Tuesday, November 30, 2010

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