A Study on Management of the Clean Air in Aseotic Filling and Packaging (Development of Microorganisms Management Technology by means of Optical Particle Measurement)

Aseptic filling and packaging is a method to distribute food products at ambient temperature for a long term. Nowadays, various foods such as beverages, soup, boiled rice, noodles are produced with this method. It is indispensable to prepare a highly clean environment without microbial decomposition in the process of filling and packaging besides sterilization of contents and containers so as to distribute less acid and perishable foods at ambient temperature. As a management method of maintaining clean rooms, periodical inspections on environmental microorganisms are carried out. The test results however cannot directly apply to the production process, because it takes time to culture and analyze microorganisms. As countermeasures for this issue, with the common idea that microorganisms are airborne by sticking to particles such as dust, there is another method to avoid microbial pollution secondarily by indirect measurement of particle concentration in the environment to manage the clean air. By aseptic filling and packaging in production process, it is popular that washing and sterilization by spraying chemical solutions in a clean booth where production devices are installed, prevent microbial pollution of foods. However, a normal optical particle counter (OPC) cannot work high humidity such as food prodution process. Therefore, even under such environment, I developed a method to measure concentration of airborne particles continuously. Furthermore, I examined management of the clean air by measuring concentration of particles is based on the NASA reports that concentration of airborne particles and microorganisms in the environment has a good correlation. Now, in the first chapter of "Introduction", I sorted out the kinds and their features of currently available method of both measuring environmental microorganisms and prevailing method of masuring concentration of airbone particles. In addition, form the viewpoint of microbial contamination control, I explained fundamental composition of aseptic filling and packaging in this study, taking into account the comparison with the conventional production method of food packaging. In the second chapter of "The Development of New Type of Optical Particle Counter System to Control Biological Clean Room for Aseptic Filling and Packaging", I proposed an idea about the system to measure particles continuously under high humidity atmosphere of the aseptic filling and packaing environment. Commercially available OPCs are susceptible to the contamination of the inside of the device or broken by decay because of highly concentrated the droplets of water and the droplets of chemical solutions at the time of washing and sterilization in the process caused by structural and optical features of device designing. It follows that in most cases, management by measuring dust is never implemented or if implemented, it limits to intermittent sampling, which could prolong device lifetime as much as it could.Continuous environment monitor could affect the productivity by shortening production time because measuring could not start until the atmosphere of droplets in the environment is well lowered after sterilization. If measuring just after sterilization is possible continuously, it can be judged whether the atmosphere of droplets is lowered below the level on the spot. Subsequently, to decrease loss time of actual working time could make the productivity improve. In order to solve these issues, I designed, manufactured and verified a particle concentration measuring system that in application of inertia impact could selectively segment and weed out droplets, which could damage particle concentration measurement. As a result, it was revealed that it would be always possible for the system to measure it continuously, and that particles of 1.0 micron or larger in diameter could not be necessary to be evaluated. Next, though it differs from the original purpose, it was also identified that particles not only on micron level but also on smaller than micron level would generate in large quantity in washing and sterilization process in the experiment. This is different from the phenomenon conceived so far. We also made some study on the mechanism. In the third chapter of "A Correlation Study between Airborne Microorganisms and Airborne Particles", I examined whether the management method of the airborne particle concentration would be appropriate or not as management technique of airborne microbial cocentration. We have understood that relationship of concentration between airborne microorganisms and particles has correlation as NASA data say. This understanding, therefore, has been applied how to manage the clean air in the environment. Moreover, easy and real-time measurement is available with this notion. However, comparing the concentration relation between airborne microorganisms and particles with NASA definition in the similar method, it doesn't necessarily come to the same result. It can be said that Japan is far different from USA in terms of the environment brought about by four seasons. Taking into account these circumstances, I conducted a survey in view of features of particle distribution in diameter. In case I used concentration of airborne particles as a monitor for concentration of microorganisms, the distribution features of concentration of airborne microorganisms, far different from Junge distribution which is well recognized as concentration distribution of airborne particles, turns out to be a similar distribution with normal distribution around a certain range of particles diameter. At the same time, the relation of concentration between airborne microorganisms and particles could have a high correlation at measured site and management on airborne microorganisms by concentration of airborne particles could be effective. In the fourth chapter, by both studies of chapter 2 and chapter 3, I demonstrated that even in the environment with high humidity like food production factory, measurement of concentration of airborne particles in application of the system in question could be a feasible method to manage airborne microorganisms. ,無菌充填包装は常温で長期間食品を流通可能にする方法であり,現在は,飲料,スープ,米飯,麺類など様々な食品が製造されている.このような製造工程において,特に食品の酸性度が低く微生物変敗を生じやすい食品を常温流通化するためには,内容物,容器の殺菌だけでなく,充填・包装する工程での微生物汚染のない高清浄環境が不可欠である.清浄空間の維持管理方法として,環境微生物の定期的な検査を実施しているが,微生物はその培養・分析には長時間を要するため,製造に直接反映できない.その欠点を補う手段として,微生物は塵埃等の微粒子に付着し浮遊しているという従来からの考えに従い,環境中の微粒子濃度を間接的に測定し,空気の清浄度を維持・管理することにより,2次的に微生物汚染の回避を図る方法がある.無菌充填包装では製造工程上,食品の微生物汚染を防止する目的で殺菌剤等を製造装置が配置されたクリーンブース内に噴霧し,洗浄・殺菌を行うのが一般的である.また,多くの場合,製造工程中も高湿度環境が発生する.しかし,通常の微粒子濃度測定器(以下OPCに略)は,食品製造のような高湿度環境下では利用できない.そこでこのような製造環境下でも,連続的に浮遊微粒子濃度を測定することが可能な方法の開発を目的とした.さらに従来からNASA資料で提示されている,環境中に浮遊する微粒子と微生物の濃度相関において,微粒子濃度測定による清浄度管理が適正な手法であるかどうかを検証するため,以下の研究を行った.1章「緒論」では,現在使用されている環境微生物の測定法の種類とその特徴を整理した.また現在使用されている微粒子測定法についても同様に整理した.さらに微生物管理の観点から,従来の包装食品製造法と無菌充填包装を考察し,今回目的の対象とする無菌充填包装の基本的な構成について説明を行った.2章「無菌充填包装環境管理のための光学的微粒子測定法の開発」では,高湿度環境下で連続的な微粒子測定可能なシステムの提案を行った.浮遊微粒子濃度管理に使用する市販の微粒子計測器は,機器設計の構造的・光学的特性上,洗浄・殺菌工程時の高濃度液滴粒子や薬剤液滴粒子等により,機器内部が汚染する,あるいは腐食等により破損するケースが多い.従って,通常これらの塵埃計測による管理は全く実施しないか,実施しても間欠的なサンプリングに限定して,機器寿命を極力延長する方法で対応している.環境監視を連続化した場合は,殺菌終了後の測定環境内液滴粒子の雰囲気が十分に低下するまで計測を開始できないため,製造時間が短くなり,生産性に影響するという問題がある.従って殺菌工程終了直後から連続計測できれば,規定値以下に到達したことを即座に判断でき,実質稼働時間ロスを限定できるため,生産性向上が可能になる.これらの問題対策として,微粒子の慣性衝突を応用し,微粒子濃度測定に障害を生じる液滴粒子を選択的に分離・除去する微粒子濃度測定システムを設計・製作し検証を行った.その結果,作成システムによる常時連続測定が可能であることが判明した.また,1.0μm以上の粒径は,実際の評価対象粒径にならないことが明らかになった.次に,実験において洗浄・殺菌工程でミクロンオーダーの粒子だけでなく,多量のサブミクロン粒子が発生するという事象も確認された.これは従来考えられてきた事象と異なる事象であり,今後の液滴微粒子をより制御する上で重要であると考え,そのメカニズムについても若干の考察を行った.第3章「浮遊微生物と浮遊微粒子の濃度相関関係に関する考察」では,浮遊微生物の管理方法として,浮遊微粒子濃度の管理方法が適切な手法であるか検討を行った.従来,浮遊微粒子と浮遊微生物の濃度関係は,NASA規格に記載されたデータから,相関関係があるとの認識により,環境の清浄度管理に適用できると考えられてきたことによって利用されてきた.それ以外にも,測定が簡便なこと,リアルタイムの測定が可能なことなどが主な理由である.しかし,浮遊微粒子と浮遊微生物の濃度をNASA規格と同様の方法で比較して見ると,必ずしもNASA規格と同じ結果になるとは限らない.これは四季等で,環境条件が大きく異なる日本国内においては,その傾向が顕著になるとも言われている.こうした状況を踏まえ,今回,特に測定環境の人,空調等を考慮した条件で調査を行った.また,浮遊微粒子濃度を浮遊微生物濃度のモニターとして利用する場合,浮遊微生物の粒径分布特性上の観点から調査を行い,浮遊微生物の濃度分布特性が,気中に浮遊する一般的な微粒子濃度分布として認知されているJunge分布とは大きく異なり,ある粒径域を中心に正規分布に近似した分布であることが分がった.さらに浮遊微生物と浮遊微粒子の濃度関係は,測定個所域で考えれば,高い相関関係が得られると推測され,浮遊微粒子濃度により浮遊微生物濃度を管理する有効性を示唆できた.第4章では,第2章および第3章において得られた研究成果により,食品製造工場等,高湿度環境でも,考案したシステムを利用して浮遊する微粒子濃度を計測することにより,浮遊微生物を管理できることを示し,全体の研究の総括とした