Food Safety

Unblanched IQF Vegetables – Can Microbiology be Controlled? Part 2


This is part 2 of a 2-part series on alternatives to blanching.

There are typically 5 common blanching alternatives.  We outlined 2 of them in our May Food Safety section and as promised, this month, we outline the remaining 3 which can be considered microbiological reduction steps:

  1. Peracetic acid treatment

    Peracetic acid, also known as peroxyacetic acid or PAA, can be used to disinfect food surfaces, instruments, packaging, and tanks. Peracetic acid is always sold in solution as a mixture with acetic acid and hydrogen peroxide to maintain its stability. The concentration of peracetic acid in the solution is usually about 10ppm or higher. Ecolab’s TsunamiTM sanitizer is an example of this solution – TsunamiTM is one of the most commonly used sanitizers in the food processing industry. It can be diluted in water and used for fruit washing, packaging washing, and equipment washing. It’s cheap, effective, and dilutes well in water.

    Peracetic acid is a weaker acid than the parent acetic acid, however it is still strong and highly corrosive. Peracetic acid has higher oxidation potential than chlorine sanitizers, but less than ozone. The benefit of peracetic acid is that it has a broad spectrum of activity against microorganisms and is effective even at low temperatures. One of the main downsides is that it is hard to dispose of the chemical.

    Most commonly we see peracetic acid used in the washing step (pre-blanching) as well as the pre-cooling stage (post-blanching) in IQF vegetable production. The maximum concentration allowed for food contact is 80ppm (21 CFR 173.315), and the maximum for a food contact surface is 200ppm (21 CFR 178.1010). Typically, the minimum level for effectiveness is 30ppm. Peracetic acid is very common for raspberry, blackberry, and strawberry raw material disinfection. Processors should be monitoring peracetic acid concentration, ideally hourly, to ensure the correct levels. Peracetic acid sanitizing is approved for use on organic food contact surfaces and equipment by the NOP (National Organic Program).

  2. Chlorine treatment

    In the USA, you likely know that chlorine is a common additive and purifier for swimming pools and public water sources. Virtually all open water systems have problems with microorganisms such as bacteria and algae, and chlorine helps to eliminate these microorganisms. This same principle applies to food processing and fresh-cut produce environments. Chlorine is used as a food grade sanitizing agent for product wash water, transport flumes, equipment rinses, and hand dips. It helps to destroy bacteria, yeasts, molds, spores, and viruses, significantly reducing their levels.

    As a disinfectant, chlorine is typically used in concentrations of 50-200ppm, for instance 50ppm for hand disinfecting, 100ppm for equipment disinfecting, and 100-300ppm for shoes and floors. Similar to peracetic acid, chlorine can be diluted in water and used for fruit washing; a typical concentration would be <30ppm for conventional products, and <3ppm for organic. As another point of reference, according to the Water Drinking Water Act established by the Environmental Protection Agency (EPA), waste water is allowed to have a maximum chlorine level of 4ppm. The US NOP (National Organic Program) approves chlorine’s use (calcium hypochlorite, chlorine dioxide, and sodium hypochlorite) in postharvest management as an algicide, disinfectant, and sanitizer.

    Chlorine is particularly a hot topic in the poultry industry. In the USA, chlorine is often used in concentrations of 20-50ppm to sanitize poultry in processing. In 1997, the EU banned all USA imports of chicken because of this practice. This ban is still in place today, however US exports could open up to the UK post-Brexit. Pro tip: If you are looking for non-chlorinated chicken in the USA, look for the term “air chilled” in the front of the package!

    One of the main downsides of chlorine is that it cannot inactivate every type of microbe (unlike ozone). Chlorine can become bound to organic matter in water, so it is important to clean the water prior to using it as a sanitizing solution. It is also important to continuously monitor chlorination levels – turbidity and organic load impact water clarity, thus affecting the relative level of chlorine. When using chlorinated water, it’s important to monitor the concentration levels on a log sheet, and continuously replace (or circulate) the water. Another main downside of chlorine is that it can leave residual concentrations on the surface of fruits and vegetables. That is one of the reasons why you should always wash fruits + veg when preparing them at home! The main benefit of chlorination is that it provides fairly rapid microbial decontamination at an economical cost.

  3. Ozone treatment

    Ozone is an inorganic molecule with the formula O3, also known as trioxygen. The highest concentration of ozone (typically <10 ppm) can be found in the ozone layer, a region of the Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation.

    Similar to chlorine and hydrogen peroxide, ozone is a powerful oxidizing agent. In fact, studies show ozone is 3000 times faster at killing microorganisms in water than chlorine. Ozone is the 4th most powerful known oxidizing agent; only fluorine, fluorine dioxide, and monatomic oxygen have higher reactivity. With this great power comes some safety risk. For commercial usage, ozone must be used only in low concentrations, as both concentrated gas and liquid ozone may decompose explosively. Furthermore, ozone has also been found to damage respiratory tissues in animals and plants above concentrations of 0.1 ppm.

    In a food processing environment, ozone can be introduced in a “carrier gas” via an ozone generator or other device. Known devices for generating ozone may utilize various forms of energy sources, such as electrochemical, electromagnetic (e.g. UV light, laser light, electron beam), or most commonly electrical (e.g. corona discharge device). In IQF vegetable processing, we most commonly see ozone “spray bars”, where ozone is dissolved into water typically at concentrations of 1.5-2ppm.

    In 2001, the FDA approved ozone usage as a way to sanitize foods and affirmed its GRAS (Generally Recognized as Safe) status. It is also approved for use in organic products by the NOP (7 CFR 205.605). Ozone has been shown to deactivate organisms such as bacteria, fungi, yeast, parasites and viruses, and can also oxidize synthetic substances, such as detergents, herbicides, and pesticides. No known bacterial cells are resistant to ozone. Ozone is used in the food processing industry, both as gaseous ozone and dissolved in water, to reduce bacteria on a wide range of food products and contact surfaces. Processing facilities can use ozonated water to spray onto raw vegetables, and ozone chambers are sometimes used to sterilize raw fruits like apples and oranges.

    The benefits of ozone treatment are that it’s economical (price similar to chlorine), it can be applied instantaneously, and it leaves no chemicals behind as it quickly turns back into oxygen. The downside is the risk to worker safety, and that it has an extremely short life span – ozone has low solubility and its half-life is about 20 minutes in an aqueous solution of 20 degrees C (68˚ F). Although ozone is primarily a disinfectant, it can perform functions such as color reduction, odor and taste removal, algae control, and oxidation of inorganic and organic compounds in water and waste-water. It is also known to extend shelf life in certain products, such as leafy greens or seafood.

We must remember that no single processing step will singlehandedly solve the challenge of providing a low-microbiology and food-safe product. Microbiology is an ongoing effort and focus for all processors, and an extensive list of control points are involved.

We hope you enjoyed and learned a thing or two from this series!



  1. 過酢酸処理

    過酢酸は、PAAとも呼ばれ、食品の表面、設備機器、梱包資材、タンクなどを除菌するのに使うことができます。過酢酸は、安定性を保つため、酢酸と過酸化水素を混ぜた溶液として販売されます。これら溶液の過酢酸の濃度は、通常、10 ppm前後かそれ以上です。例えば、エコラボが販売している除菌剤の「TsunamiTM」は、食品加工の現場で最もよく使われている過酢酸溶液のひとつです。水で薄めて、果物やパッケージ、あるいは設備機器の洗浄に使うことができます。安価で効果が高く、水に溶けやすいのが特徴です。


    IQF野菜の製造現場における過酢酸の最も一般的な用途は、(ブランチング前の)洗浄段階です。また、(ブランチング後の)冷凍前の段階でもよく使われます。食品との接触が許可される最高濃度は80 ppmで(21 CFR 173.315)、食品と接触する表面に使う場合の最高濃度は200 ppmです(21 CFR 178.1010)。通常、有効性を発揮する最低濃度は30 ppmとされています。過酢酸は、ラズベリー、ブラックベリー、イチゴの原材料の除菌に非常によく使われています。理想的には1時間に1回、過酢酸の濃度が正しいレベルであることを確認すべきです。過酢酸は、米国のオーガニック認定制度(NOP)の下で、オーガニック食品と接触する表面および設備機器への使用が認められています。

  2. 塩素処理


    塩素の除菌液は、通常、50~200 ppmの濃度で使われ、手を除菌する場合は50 ppm、設備機器の場合は100 ppm、靴や床の場合は100~300 ppmです。過酢酸と同様に、塩素も水で薄めて、果物の洗浄に使うことができます。その場合は、オーガニックでなければ30 ppm未満、オーガニックは3 ppm未満です。参考までに、米国では「安全飲料水法」に基づいて環境保護庁(EPA)が、廃水に含まれる塩素の最高レベルを4 ppmと定めています。さらに、NOPでは、オーガニック作物の収穫後の殺藻剤、除菌剤、消毒剤としての塩素(次亜塩素酸カルシウム、二酸化塩素、次亜塩素酸ナトリウム)の使用を認めています。

    塩素は、鶏肉業界で特に熱い論争を呼んでいます。米国では、鶏肉の処理加工の過程で20~50 ppmの濃度の塩素がしばしば消毒に使用されています。しかし、EUは1997年、これを理由として米国産の鶏肉の輸入を全面的に禁止しました。この禁止令は今も有効ですが、イギリスのEU離脱後は、米国の鶏肉に新たな市場が開かれる可能性があります。これはプロからのアドバイスですが、米国で塩素処理されていない鶏肉をお求めになりたい方は、パッケージの前面に「air chilled」(空気冷却)と書かれたものを探してください。


  3. オゾン処理

    オゾンは無機物質で、化学式はO3。3つの酸素原子から成ります。オゾンが最高濃度で存在するのはオゾン層です(一般に10 ppm未満)。成層圏に存在し、太陽からの紫外線のほとんどを吸収しています。

    塩素や過酸化水素と同様に、オゾンは強力な酸化剤です。オゾンは塩素に比べ、水中の微生物を3,000倍速く破壊することが研究の結果分かっています。オゾンは、知られているなかで4番目に強い酸化力を持ち、オゾンを上回るのはフッ素、二フッ化二酸素、単原子酸素だけです。このすばらしい力には、安全性のリスクも伴います。商業的な使用は、低濃度でなければなりません。気体・液体ともに、分解に伴って爆発する可能性があるためです。さらに、0.1 ppmを上回るオゾンは、動物の呼吸器や植物にダメージを及ぼすことも知られています。

    食品加工の現場では、オゾン発生器などの装置を使って、キャリアガスにオゾンを含めて使用することができます。オゾン発生器は、電気化学や電磁気(例:紫外線ライト、レーザーライト、電子ビーム)をエネルギー源を使うこともありますが、最も一般的なのは電気(例:コロナ放電装置)です。IQF野菜の加工では、通常1.5~2 ppmの濃度でオゾンを溶かした水をスプレーで噴霧する工程が最も一般的です。

    2001年、米国の食品医薬品局(FDA)は、食品の消毒法としてのオゾンの使用を認可し、「Generally Recognized As Safe」(一般に安全と認められる)、略してGRASの物質に指定しました。また、NOPによってオーガニック製品での使用も認められています(7 CFR 205.605)。オゾンは、バクテリア、菌類、イースト、寄生虫、ウイルスなどの微生物を失活させるほか、洗剤、除草剤、殺虫剤などの合成物質も酸化させます。オゾンに対して抵抗力のあるバクテリア細胞は見つかっていません。食品加工業界では、オゾンは多岐にわたる製品と接触表面のバクテリアを減らす目的で、気体と液体の両方で使われています。オゾン液を生の野菜に噴霧するほか、リンゴやオレンジなどの生の果物の消毒にオゾン室が使われることもあります。




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