Method and apparatus for antibacterial sanitation treatment of rooms and objects The present invention relates to new methods and apparatus for exploiting the high molecular alkaline cationic polysaccharide chitosan, particularly as an agent for the antibacterial sanitation treatment of food processing rooms and objects therein, as well as other objects. Chitosan has over the last ten years or so proved itself very promising in different aspects, being derived from shellfish like scrimps and crabs by deacetylating naturally present chitin. In this connection it is referred to our international patent application WO 99/64470 having the title:"An integrated plant for producing chitosan".

Chitin is regarded as an insoluble material, while its derivative chitosan is soluble in slightly acidic solutions like diluted acetic or hydrochloric acid and then being regarded as reactive. Chitosan is biodegradable and has anti-microbial activity, is anti- oxidative in nature and has edible film formation properties. By having free amino and hydroxyl groups, chitosan is found to have many potential application areas. In practice the applications of chitosan can be classified in grade categories. In a first group requiring the highest grade should be mentioned biomaterials, a means for anticancer, wound healing and treatment, ointments and dressings, anti-microbial agents, in the immunology field, for the release and distribution of medicaments under full control, surgical sutures, orthopaedics and dental products, as well as column matrices for affinity chromatography, gas-selective membranes, fruit preservation, the cosmetic industry, artificial skin and organs and pharmaceutical activity (Brine, Sandford & Zikatis, 1991).

Other fields of applications of which some are less demanding with respect to purity are anti-cholesterol and fat binding agents, a means for flocculation, clarifying and thickening, the use as a fibre mass, for films, for increasing the resistance against plant disease and as a process supporting and aiding material.

The postulated mechanism of bactericidal action against several pathogens consisting of enzyme inactivation, chelation of essential metal ions and formation of polyelectrolyte complexes with bacterial surface compounds has been investigated thoroughly, see Muzarelle et al;"Chitin in Nature and Technology", Plenum Press, New York, p. 321-323,1986, Muzzarelli et al.:"Antimicrob Agents of N-carboxybutyl chitosan"in Anitmicrob Agents Chemother, 34: p. 2019-2023,1990 and the report: "Chitosan as a compound to extend the shell-life of fish-fillets"by Amrit Paul Singh Tiara, Institute for microbiology, University of Bergen, Norway, spring semester-2001.

Further is referred to the Internet site http ://alimentos-funcionais. com/Yim2. html for a documentation of the antibacterial activity of chitosan for three specific bacteria types.

It has for several years been demonstrated that chitosan in a particular concentration and at a given degree of deacetylation prevents or inhibits the growth of micro-organisms. Several mechanisms for the anti-microbial action have been proposed,

and one suggestion is that chitosan inhibits microbial growth by acting as a chelating agent that hinders metals, trace elements or essential nutrition to be available for the organism to grow at the normal rate (Skjåk-Bræk et al. 1989), and mechanisms influencing the concentration of intracellular Ca2+ and related transport inhibitors (Jackson and Heath, 1993), by making Ca2+ and other essential minerals and nutrition unavailable for growth. A nutrition deprivation alone, however, will not always explain how chitosan rapidly acts as a bactericidal agent, and it is suggested that a more direct attack on the integrity of the outer bacteria cell wall, leading to a lethal lesion is more plausible. It is also possible that the bactericidal effect partly is due to that the metal compositions or residues that remain in a chitosan solution after the reaction therewith, give interaction with non-toxic minerals such as calcium.

Chitosan is available in various forms, such as powder, grains, dissolved, in beans, fibres, flakes, films, and spray solutions, and it can particularly be used as an antibacterial agent due to both its bacteriostatic and bactericidal properties. Applications taking advantage of these properties as well as exploiting the ability of chitosan to maintain a positive electrical charge on particles and small droplets of a solution, are basic to the present invention. The positive charge of chitosan is due to the protonisation of the amino group on carbon number 2 (C2) of the glucosamine monomers at acid conditions.

Although chitosan in several advantageous ways has found its place in various fields of technology, its use as an antibacterial agent gives room for many improvements, and on this background and according to the invention is proposed an extended use for this polysaccharide chitosan, namely for antibacterial sanitation of complete rooms, processing areas and objects.

According to a first aspect of the invention it is therefore proposed a method for the antibacterial sanitation treatment of a room and objects by means of an inherently cationic antibacterial agent, by using the agent in a liquid solution having a specified formula so as to present a predetermined solution strength and intrinsic viscosity, supplying said agent solution to an agent container, feeding the agent solution from the container to a pressure generating means to increase the solution pressure, and distributing the pressurised agent solution through a distribution means for protonising said solution into particles and spraying them into the room to cover the surfaces thereof and objects therein, said distribution means being configured to maintain the cationic property of the agent in the solution during the protonisation so that each particle thereof is carrying a positive electrical charge.

The distribution means can comprise a nozzle network having several distribution nozzles, and the pressure generating means can be a remotely controlled pump for continuous or periodically interrupted distribution of the antibacterial agent solution.

According to a second aspect of the invention the agent is used in at least one liquid solution having specified formulas so as to present corresponding predetermined solution strengths and intrinsic viscosities, supplying said at least one agent solution to a corresponding number of vessels, and feeding said objects through each vessel during a submerging so as to receive a coating of the antibacterial agent.

The objects can be fresh food units fed forward through a process system, said system comprising a first vessel containing a first solution of said antibacterial agent, a second vessel containing a second solution of same antibacterial agent, and in case additional vessels also containing specific solutions of same antibacterial agent, of which the submerging in each vessel is pre-programmed to last given time periods.

The antibacterial agent comprises preferably the polysaccharide chitosan, and in a typical example said agent uses low density chitosan in a solution having a viscosity of 8-100 ml/g, mixed with 2-5 % alcohol containing ascorbic acid. In another example the agent is made as follows: 1. Dissolving the chitosan in a volume (V) of water containing 1 % acetic acid, so as to give around 5 % by weight and a viscosity of 20-30 ml/g, II. mixing the solution from I. above with a volume (3V) of water having pH 12-13 due to a lye additive, III. stirring the solution from II. above to obtain a reaction and a depositing of solid material, filtering the liquid out, IV. dissolving the solid material from III. above in a solution as in I. above, thereby providing an oligomeric chitosan solution, and V. diluting the solution from IV. above to approximately 0. 5 %.

According to the invention there is also provided an apparatus for the antibacterial sanitation treatment of a room and objects by means of an inherently cationic antibacterial agent, by using an agent container for the agent in a liquid solution having a specified formula so as to present a predetermined solution strength and intrinsic viscosity, a pressure generating means to increase the solution pressure, and a distribution means for atomising said solution into small particles and spraying them into the room to cover the surfaces thereof and objects therein, said distribution being configured to maintain the cationic property of the agent in the solution during the protonisation so that each particle thereof is carrying a positive electrical charge.

In order to spray the chitosan agent conveniently into a production room or facility it is preferred to use a number of nozzles to ensure a sufficiently fine distribution in the form of a thin protonised film. A thin and near invisible covering layer of anti- bacterial material thereby is deposited and maintained active by a continuous supply of fresh chitosan or from one treatment interval to the next.

The strength and thereby the viscosity of the chitosan agent to be chosen will depend upon the application, and an intrinsic or dynamic viscosity (n) from very low to

fairly high will fall within the scope of the invention, that is from between 8 and 100 ml/g (very low to low) and up to 600-1500 ml/g (medium to high). In a typical example is used a chitosan solution containing ascorbic acid and to which 2-5 % pure alcohol is added.

This mixture is found suited for a distribution through nozzles of the preferred and specified types, at an intrinsic mixture viscosity of 8-100 ml/g. The nozzles can be arranged in an array or network in the ceiling of a room.

The use of chitosan in this way as an antibacterial agent is offering a long-time effect, but anyhow a program for following-up should be established. In order to maintain an effective action of the spray distributed chitosan agent also in a room where surfaces and objects for example are frequently displaced it can therefore be necessary to supply the agent continuously or over fairly long intervals. However, due to the non-toxic property of chitosan this is fully acceptable from the point of view of personal health, although there can be some practical inconveniencies. A solution can be to carry out the sanitation over periodically shifted areas. In more static room conditions the spraying can be done when the room is unoccupied, for example during the night or after working hours. Typical rooms or areas to be treated or sanitised in this way are production sites for nutrients and food processing, namely sites under rigid regulations regarding bacterial activity.

By using chitosan in the methods according to the invention an environment friendly nature product is obtained, replacing synthetic products and further providing effects that previously have not been achieved. In this manner the use of chitosan can replace some of the antibacterial methods of today, also giving the benefit of completely avoiding the development of bacterial agent immunity, which is not the case with other similar agents of the synthetic type.

In addition to the antibacterial effects the polysaccharide chitosan also has many other documented properties to be regarded as positive regarding environment effects.

According to the invention chitosan in specific solutions and mixtures is mainly used for sanitation purposes, either by spraying a chitosan agent of given specifications into a room or process area, or by bringing objects into the agent, in order to cover the surfaces of interest completely.

Tests carried out in the fish processing industry are relevant to a typical example of the latter method, as it has been demonstrated that a submerging of fish fillets in chitosan to a certain degree reduces and delays the natural bacterial activity that finally spoils, degrades and starts decomposition of such fresh food.

A typical process plant for the processing of fresh food objects of this kind comprises several stages and a conveyor to feed the objects from an intake and onwards to the packing of the processed objects. At one stage, usually one of the latest ones, the objects are completely submerged in a solution, in the following referred to as an agent and including chitosan as an active antibacterial ingredient. The agent will primarily be

active at the surface of each object, functioning as an effective barrier against microbial putrification, thereby offering a longer first class or fresh lifetime. This method has been worked out to replace complicated antibacterial actions used till now but has so far not come into wide use, partly due to practical problems and partly due to a suboptimal chitosan solution.

The invention will now be described further, and it is referred to the drawings, wherein: Fig. 1 is a principal illustration for the antibacterial sanitising treatment of a room by means of nozzles in the room ceiling, and fig. 2 illustrates a corresponding treatment of fresh food by submerging in a chitosan solution.

Fig. 1 illustrates the use of a chitosan agent for the antibacterial sanitation of a room suited for food processing. A pump 205 is arranged between a chitosan agent container 206 and a nozzle network 207 having several nozzles 208. The nozzles 208 are arranged in the room ceiling and positioned so as to provide an even distribution of the agent over the room surfaces and the objects therein. The chitosan agent can preferably contain low density chitosan and be of a viscosity of 8-100 ml/g, mixed with 2-5 % alcohol containing ascorbic acid, or be made according to the following method : 1. Chitosan is dissolved in a volume V of water containing 1 % acetic acid, so as to give around 5 % by weight and an intrinsic viscosity of 8-100 ml/g.

II. The solution from 1. above is mixed with a volume 3V of water having pH 12- 13 due to a lye additive.

III. The solution from II. above is stirred to obtain a reaction and a depositing of solid material. The liquid is filtered out.

IV. The solid material from III. above is dissolved in a solution as in I. above, thereby providing an oligomeric chitosan solution.

V. The solution from IV. above is diluted to approximately 0.5 % to become the requested antibacterial agent suitable for a spray distribution as small droplets.

Fig. 2 shows an antibacterial treatment of fresh food units 132 fed through a process system 130, in the illustrated version in a simple form having only one treating step. The units are however generally and according to the invention submerged in a number of recipients-of which one vessel 134 using one of a corresponding number of chitosan mixtures or formulas is shown. A typical and preferred choice for an effective treatment in a single vessel 134 as shown is by using a chitosan agent having the following formula:

25 g animal gelatine dissolved in 1 litre of water, chitosan 1-3 % by weight and of medium molecular weight Mw is added and the pH reduced to between 4.5 and 5.5 by the adding of acetic or ascorbic acid, and 2-18 % by weight of the commercial available preservative Bactomin is added, possibly also together with 2-5 % pure alcohol so as to achieve a total average intrinsic viscosity between 300-600 ml/g.

The units 134 can be submerged for about 1-2 minutes in each subsequent vessel, whereby an antibacterial protection is provided in the form of a deposited sealing film over the entire fresh food surface, said film maintaining its efficiency over several days, dependent of the type of items or units and the number of treatment steps during the process. In this way the natural degradation is reduced accordingly so that the treated units are maintaining their freshness.

A typical treatment chain could have three vessels, each containing a different chitosan solution.