Sanitising wash water

Transcription

1 Sanitising wash water The issue Wash water sanitisers can prevent cross-contamination but they cannot reversecontamination and fresh produce cannot be entirely decontaminated. Listeria,salmonella and E. coli can remain attached to rough or cut fruit surfaces. No sanitiser or system is the best one; growers should choose the one that works under their individual conditions. All systems should be validated under individual and varying conditions. This verification of a sanitation system involves ongoing measurement and adjustment to assure that the system is being managed as well as possible. Why is this important? Taste, odour and colour of water may be the first indication of a potential food safety hazard, but should not be relied upon when assessing water. Even withsanitisers such as chlorine, ozone, irradiation or peroxyacetic acid, fresh produce cannot be completely decontaminated. Any water in contact with melons should be viewed as having the potential to contaminate fruit. One contaminated item in the wash water can transfer bacteria and viruses to the whole batch. Things to consider It is important to understand the sanitiser chemistry as the performance of the sanitation system can be affected by a number of factors e.g. organic load, ph, temperature. The sanitisers discussed here are: Chlorine-based - Sodium Hypochlorite; Calcium Hypochlorite; Nylate; StabilisedChlorine Dioxide Peroxyacetic acid Oxidising water Ozone

2 Iodine Organic-based Chlorine Chlorine, either as Calcium Hypochlorite or Sodium Hypochlorite, is a very effective way to sanitise fruit and vegetables. The most common Calcium hypochlorite system is tablets that dissolve slowly as water is passed over them. This system can produce huge levels of variability, depending on the flow of the water and on the way the tablets are made. In many cases, this leads to under chlorination, particularly if there is a large organic load (including soil) on the melons. Sodium Hypochlorite is available in a liquid form, making it easy to add the required volume to automated dosing systems. An Oxidation Reduction probe can be used to regulate this addition, however these probes are not very accurate and must be checked by hand on a regular basis. Over chlorination results in chlorine odour that can create WHS issues for workers in the packing shed. In addition to this, over-chlorination can lead to rust formation and corrosion of equipment. Other sanitisers are available that have similar results as Chlorine, these include Nylate and some peroxyacetic acid sanitisers. Although these are slightly more expensive to use all of these can be monitored in solution either by hand (with the use of test strips) or by an automated process including OR probes or PAA probes. Nylate Nylate (bromo-chlorodimethyl hydantoin) forms two biocides in solution; hypochlorous acid (HOCI) and hypobromus acid (HOBr)), which have been shown to be effective against fungal and bacterial organisms, as well as a range of human pathogens, such asstaphylococcus aureus and Salmonella kahla, which pose risks to food safety. It is stable, effective across a broad ph range and at much lower concentrations thanchlorine. Nylate can be used at 5 to 10 ppm. Stabilised Chlorine Dioxide Chlorine Dioxide gas has been used a sanitiser that is dissolved into water. On occasion, the gas can be released from the wash and causes WHS issues.

3 A safer alternative is Stabilised Chlorine Dioxide which differs structurally fromchlorine Dioxide gas and is very safe. Stabilized Chlorine Dioxide is activated when it encounters bacteria. It is very effective as a sanitising agent against all bacteria and viruses and does not corrode metal. However, it is expensive. Peroxyacetic Acid Peroxyacetic Acid (PAA) is made by reacting acetic acid with hydrogen peroxide, resulting in a highly stable PAA solution containing Peracetic acid and hydrogen peroxide. PAA breaks down into acetic acid (vinegar), water and oxygen, making it effective in controlling microbial pathogens and compatible with the environment. Functioning extremely well under cold conditions, PAA does not experience cold temperature failure and sanitization can be carried out on pre-cooled fruit. PAA is registered with FSANZ as a sanitiser for use as a non-rinse washing aid. It is generally used at 50 to 150 ppm and is highly effective against a broad spectrum of bacteria. It has been shown to be particularly effective against Listeria monocytogenes; the mechanism is by direct killing of bacteria but it also leaves a residue of acetic acid behind to slow down potential Listeria growth, effectively creating a lag phase for this bacterium. PAA is more expensive to apply than other sanitation methods and can be difficult to monitor. Monitoring is best done with test strips that show a colour change for PAA as Oxidation Reduction probes (ORP) are not sensitive enough to allow for the precise measurement of this oxidizer in solution. It is available under a number of different trade names including Tsunami, Adoxysan, Summit and Proxitane. Oxidizing water Oxidizing water is produced by passing an electric current through ordinary tap water containing dissolved sodium chloride. The process is called electrolysis and produces a solution of sodium hypochlorite, which is the most common ingredient in household bleach and hypochlorous acid. The resulting water is a cleanser and sanitizer since both sodium hydroxide and hypochlorous acid are efficient disinfecting agents. Oxidizing water has been used for inactivation of a wide variety of pathogens such as E. coli, Salmonella and Listeria.

4 Oxidizing water (OW) does not need special approvals in Australia for direct and indirect food contact applications and can be used as food washing aid without rinsing. Any chemical formed during the electrolysis step reverts back to the same chemicals that existed prior to electrolysis in due time. This type of system is automated and easy to operate with monitoring based on measurement of residual free chlorine which is easy to record for QA purposes. OW has relatively low power consumption, depending on the quality of the water and the level of disinfection required. Maintenance is low cost and simple, regular electrode cleaning by reverse electrolysis is automated and does not require any chemicals or service water. The short cleaning cycle minimises loss of capacity. Titanium electrodes and PVC cells provide long life and easy maintenance. Australian manufacturers of oxidizing water units seem to be uncommon, however Unipolar do promote a patented electro-chemical technology to generate disinfectants for food (including fruit) washing. Ozone Ozone is a gas that has to be generated on site as it is very unstable. It is even more unstable in water and over very short periods of time it decomposes into oxygen. When there is a large amount of dirt and organic matter present, the activity of ozone decreases significantly. It is also very corrosive. It is a colourless gas and has a pungent smell which creates a WHS risk. Iodine Iodine has strong anti-microbial activity. The iodine concentration used depends on contact time and the microbial load on the product to be treated. Iodine is less corrosive than chlorine and works at a wider ph. It is effective at ph 8 and above. Due to iodine s lack of reaction to organic matter, it has been shown to be effective at killing pathogens in higher water turbidity levels. The Iodoclean System is a fully automated and enclosed post harvest sanitising system which uses iodine as the active ingredient. The system does not require ph adjustment as iodine operates in a very wide ph range. It has little or no adverse effect on ph, eliminating all of the ph monitoring problems encountered with chlorine.

5 Handling and mixing chemicals is eliminated as the iodine is supplied in a sealed canister and the system constantly monitors the active iodine disinfectant available and adjusts dosage levels to meet any increase in the organic load. Organic sanitisers There are a number of sanitisers that are used, mainly in the organic industry. Testing by Robert Premier [1] has shown that organic sanitisers did not perform as well as other tested sanitisers. To achieve maximum killing of bacteria, organic sanitisers must be left in contact with the fruit for up to 45 minutes. This group of sanitisers includes: Citrox, a formulation of soluble citrus bioflavonoids Aussan is derived from fruit and vegetables CitroFresh is composed of citric acid, malic acid, bitter orange extract and vegetable glycerine. Acetic acid best results with 4% acetic acid For more information refer to Comparison of sanitisers factsheet What can I do? When choosing the type of sanitising system that suits the individual farm situation, there are a number of factors to consider, however the best sanitizer is the one that works for your product under your conditions. 1. Validation Validation is the process of demonstrating that the system designed can adequately control identified hazards to produce a safe, unadulterated product. That is, validation demonstrates that your process is capable of accomplishing what you expect from it. The two elements of validation are the technical support for the system design and the practical on-farm demonstration proving the system can perform as expected. The sanitising system can effectively prevent cross contamination by microorganisms under farm conditions. 2. Verification

6 Verification involves ongoing monitoring and recording to assure that the system is being managed according to the food safety plan. 3. Operational Set Point The Operational Set Point is the margin above or below the specified critical limits in a HACCP or food safety plan. For example, with a critical limit of 10ppm free chlorine, the Operational Set Point could be to always operate above 12ppm. Further information [1] Information has been adapted from Evaluation of vegetable washing chemicals (2013) R Premier Global F.S. Pty Ltd, a report funded through Horticulture Australia Ltd. The full report can be downloaded athttp://vgavic.org.au/pdf/r&d_vg09086_vegetable_wash_water_extract.pdf