Abstract:
Almonds are often harvested off the ground from around trees which have been fertilized with manure. Potentially hazardous microbes are transferred from the husk to the shells during the dehusking process. During deshelling, shell dust with attached microbes escapes into the atmosphere and can permeate an entire packaging facility, contaminating previously uncontaminated packaging and food products. A sterile barrier is provided around the packaging facility. As the almonds in the shell are passed through the barrier, their shells are sanitized. After the nutmeats are removed from the shells, the nutmeats are sanitized again and packaged in packaging which has been sanitized.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the killing of microorganisms on food items, without degrading the food items. The invention finds particular application in conjunction with almonds and will be described with particular reference thereto. However, it is to be appreciated, the invention will also find application in conjunction with other types of nuts, seeds, dehydrated fruits, and other agricultural products. 
     To promote the growth of agricultural products, fertilizer is typically added to the soil. Manure, a commonly used fertilizer, can carry human pathogens, such as  Salmonella, E - coli,  and  Listeria.  When food items come into contact with the soil during harvesting, or with equipment that has contacted the soil, the food items can pick up the human pathogens on their surface. As the harvested food items are gathered together, the pathogens can be passed from surface to surface by direct contact. 
     When harvesting almonds, for example, it is common to shake the trees dropping the almonds (in their shells and husks) to the ground. The almonds are then collected from the ground. In a first operation, the husks are removed from the almonds, leaving the almonds in their shells. Some almonds are sold in their shells, and others are deshelled prior to packaging. The removed husks would be expected to be the carriers of any human pathogens picked up from the soil. Even after husking, the shell provides a pathogen impermeable package for the nutmeat. Conventional, mechanical shelling operations raise a significant amount of dust, sending dust-sized portions of the shell and any pathogens which might be thereon airborne. 
     Subsequently, the shelled nutmeats undergo various sorting operations. Some of the nutmeats are cooked, which would also be expected to kill any surface pathogens. Other nutmeats are packaged and sold raw. Although the chances of human pathogens being present on the packaged nutmeats might appear relatively remote, there have been recent recalls of almonds for  Salmonella  contamination. 
     One solution to the contamination problem is found in the present assignee&#39;s U.S. Pat. Nos. 5,460,845 and 5,535,667. These patents describe a batch process in which almonds and other food items are exposed to hydrogen peroxide vapor in a vacuum chamber for periods of about a half hour to one hour. These patents also describe limited kill rates at somewhat shorter periods of exposure at atmospheric pressure. 
     Although effective, such batch processing techniques are not readily compatible with modern processing plants in which each processing line processes about 10,000 kilograms of food product per hour or more. 
     The present invention overcomes the above-referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a method of sanitizing human pathogens from surfaces of agricultural food products is provided. The food products are moved continuously on a mesh belt. While the food products are moving along the belt, they are treated with a gaseous oxidizing agent at atmospheric pressure for a sufficient duration to kill human pathogens. 
     In accordance with another aspect of the present invention, an apparatus for sanitizing human pathogens from surfaces of agricultural food products is provided. A mesh belt continuously conveys the food products into, through, and out of a food chamber. A means is provided for supplying a gaseous oxidizing agent at atmospheric pressure to the chamber to treat the food products, the chamber has a length relative to a speed of the mesh belt such that the food products remain in the chamber for a sufficient duration to kill human pathogens. 
     One advantage of the present invention resides in its speed. 
     Another advantage of the present invention is that it provides a flow-through sanitization system which can process food products at the same rate that they are moving along conventional processing assembly lines. 
     Another advantage is that the present invention kills human pathogens in 30 seconds or less. 
     Another advantage of the present invention is that it does not alter the taste of the food products. 
     Another advantage of the present invention is that it does not alter the value of almonds by changing the appearance of the brown skin or pellicle. 
     Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not be construed as limiting the invention. 
         FIG. 1  is a diagrammatic illustration of a husking and shelling line in accordance with the present invention; 
         FIG. 2  is a diagrammatic illustration of a processing line for shelled nuts or other foods products in accordance with the present invention; 
         FIG. 3  is a detailed illustration of a preferred treatment chamber of  FIGS. 1 and 2 ; 
         FIG. 4  illustrates bacterial concentration reduction in 15 second intervals; 
         FIG. 5  illustrates bacterial concentration reduction relative to a 10 5  control. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     At harvest time, almonds or other shelled food products are received in bulk at a dehusking and deshelling facility  10 . The bulk almonds are emptied into a large hopper or other supply  12  from which almonds or other foods products are supplied to a husk removing machine  14 . The husk removing machine discharges almonds in the shell at one output  16  and outputs the husks through a second output  18 . The husks are removed from the facility and sold for other agricultural uses, such as additives to livestock feed. The almonds in the shell from the outlet  16  are conveyed to a first sanitization chamber  20  on a mesh conveyor belt  22 . 
     The sanitization chamber  20  exposes the almonds in the shell to a gaseous oxidizing agent such as ozone, vaporized liquid oxidants, condensed oxidants, plasma, or the like and combinations thereof. In the preferred embodiment, the gaseous oxidizing agent is in the form of hydrogen peroxide vapor in a concentration of about 1.8 milligrams per liter of air or greater. More specifically to the preferred embodiment, liquid hydrogen peroxide from a liquid hydrogen peroxide source  24  is fed to a vaporizer  26  at a controlled rate. In some cases, it is advantageous if air is dried by a dryer  28  and blown by a blower  30  into the sanitization chamber  20 . 
     An exhaust blower  32  draws peroxide vapor and water vapor from the sanitization chamber and exhausts them to the atmosphere. The exhaust blower  32 , preferably, is operated at a speed relative to the feed blower  30  such that the treatment chamber is maintained at a negative pressure relative to atmosphere so that the vapor hydrogen peroxide does not escape into the working atmosphere. Because the almonds are still in the shell and protected, the treatment chamber  20  can tumble or agitate the almonds, use a stronger concentration of the gaseous oxidizing agent, and can even use oxidizing agents which would leave a residue or adversely affect taste. Preferably, a microbe impermeable barrier wall  34  is maintained across the hulling and shelling facility  10  with one side of the wall being on the input to the treatment chamber  20  and the other side on the output. The chamber  20  has a length, relative to the conveyor belt speed, such that the almonds take 15–30 seconds to traverse the chamber. 
     From the sanitization chamber  20 , the almonds are conveyed to a shelling machine  40  which removes the shells from the almonds. The nutmeats are discharged from a first outlet  42  and the shell fragments are discharged through a second outlet  44 . optionally or alternately, a second sanitizing chamber  20 ′ of the structure described above is disposed after the nutmeat outlet  42 . A packaging machine  46  packages the shelled almonds in relatively large containers, such as 50 lb bags, drums, pallet sized containers, and the like. Preferably, the bulk containers are sealed against airborne pathogens. By sanitizing the portion of the husking and shelling facility  10  which is downstream from the barrier wall prior to the receipt of almonds and by sanitizing all of the almonds in the shell entering the area, all of the packaged nutmeats should be free of human pathogens. Because the husking and shelling operations are commonly performed only around harvest time and the packaging and production lines run year-round, the containers of shelled almonds are typically stored anywhere from a few hours until the next harvest season. 
     With reference to  FIG. 2 , at a packaging facility  50 , the shelled nutmeats are received in a hopper  52  or other supply and fed at a controlled rate onto a mesh conveyer  54  preferably in a layer one nut thick. A barrier wall  56  surrounds the hopper  52  and isolates the area of the hopper from the remainder of the production facility. 
     A sanitization or treatment chamber  60  penetrates the barrier wall  56  such that its inlet receives untreated nuts on the conveyer  54  and its outlet discharges sanitized nuts or other food products on the conveyor  54  which continues downstream. The use of the barrier wall and treatment chamber  60  at the entrance to the processing facility assures that only treated nuts or food products enter the facility. This prevents cross contamination downstream. For example, nuts which are roasted go through a heating process which would normally kill the human pathogens. However, if the roasted nuts should come in contact with a contaminated, not yet roasted nut, or even a worker who had come in contact with a not yet roasted nut, human pathogens can be transferred to the previously sanitized roasted nuts. When every nut in the facility is sanitized, the chances of cross-contamination are minimized. 
     The treatment chamber  60 , like the treatment chamber  20 , includes a source  62  of a gaseous oxidizing agent, such as an ozone source, other vapor sterilant source, or a plasma source. Again, a source of liquid hydrogen peroxide of about 35% concentration and a vaporizer are preferred. A blower  64  supplies the gaseous oxidizing agent into the treatment chamber  60 . The gaseous oxidizing agent, after moving among the food product, passes to an exhaust where a blower  66  exits the gas to atmosphere. Again, the relative speed of blowers  64  and  66  are preferably such that a slight negative pressure is maintained in the treatment chamber. More preferably, air curtains  68  are provided at the inlet and the outlet. The air curtains prevent the gaseous sanitizing agent from escaping from the chamber into the surrounding processing facilities and prevent contaminants from the surrounding facilities which could alter the sanitization process from entering the chamber. For example, if excess humidity from the production facility entered the treatment chamber, the water vapor could dilute the treatment gas or could alter the vapor pressure in the chamber, permitting condensation to occur. 
     The treatment chamber  60  has a length which is calculated such that at the normal movement speed of the conveyor belt  54 , the food products dwell in the chamber for a prescribed treatment time, preferably 15–30 seconds. The flow of the gaseous oxidizing vapor through the chamber is sufficiently vigorous that the food products vibrate on the mesh conveyor belt, changing their points of contact and permitting all portions of the surface to be treated with the oxidizing vapor. Yet, the gaseous oxidizing agent flow is preferably not so vigorous that the food products are agitated to the point that they can become scarred or otherwise loose cosmetic appeal, hence value. 
     The sanitized almonds or other food products are passed to downstream processing equipment  70 . This equipment includes sorting stations for sorting the food products by quality, e.g., broken versus unbroken nuts, nuts with whole unscarred pellicles versus nuts without, and the like. The sorted nuts are conveyed to various processing lines. For example, some pass to roasting stations where they are roasted, salting stations where salt or other spices are added, and the like as is conventional in the food processing arts. Finally, a packaging machine  72  packages metered amounts of the processed food product into appropriate consumer packages. 
     With reference to  FIG. 3 , the sanitizing systems  20  and  60  preferably include an inlet duct  80  which supplies air to a housing  82  which houses an appropriate dryer for the incoming air, liquid peroxide supply, vaporizer, and blower. Vapor output tubes  84  supply the generated vapor to distributed portions of a lower manifold  86 . The vapor is moved upward through the mesh conveyor belt  54  into an upper manifold  88 . Vapor from the upper manifold  88  is pulled by a blower through a catalytic destroyer which converts hydrogen peroxide vapor to water vapor and discharges the water vapor through a discharge duct  92 . 
     With reference to  FIG. 4 , sample almonds were inoculated with 3.7×10 8  inoculum of salmonella bacteria to achieve an initial bacterial concentration of about 10 6 . These almonds were treated with 1.8 milligram/liter concentration of hydrogen peroxide vapor at 33–34° C.  FIG. 4  illustrates the log reduction at 15 second intervals. It will be seen that 15 seconds produces about a 3 log reduction. Similarly,  FIG. 5  shows the relative reduction of a test sample  100  at 5 second intervals from a 10 5  initial bacterial concentration, relative to a control  102  that was not subject to the hydrogen peroxide vapor. Again, a 3 log reduction was achieved in 15 seconds. Although tests were conducted at 5 logs, naturally infected almonds are more apt to have an initial bacterial count in the order of 10 2 –10 3    Salmonella.    
     The oxidizing agent treatment is preferably conducted at temperatures below 40° C. Higher temperatures tend to cause cooking of oil in the nuts and other food products, altering flavor. Hydrogen peroxide vapor is also preferred. Exposure to concentrations of 1.8 mg/liter for periods of many minutes have been shown to have no adverse organoleptic effect on the treated product. Further, hydrogen peroxide vapor does not require an aeration zone. Although 15 seconds provides sanitization of human pathogens, longer exposure times can also be used to kill spores and achieve a higher level of kill. Such higher levels of kill would improve not only safety, but also the safe shelf time for the products. 
     Although described with particular reference to almonds in the preferred embodiment, it is to be appreciated that similar concerns and treatment parameters are also effective on a wide variety of nuts and grains, seeds, and spices. The processes are also amenable to dehydrated and dried vegetables and fruits. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.