Share thisThe commercialization of alkaline hydrolysis technology used in tissue digester systems has led to many new innovations in the process and equipment design — some of which have led consumers to many perceptions and misconceptions regarding the process due to the changing technology.
Making sense of a myriad of new information concerning advances and claims in alkaline hydrolysis technology is an overwhelming task for even the most educated consumer, but a necessary one for anyone considering the science. Features such as “wet” or “dry” processes and “prion” or “non-prion” decontamination cycles require that anyone considering the technology have somewhat of a basic understanding of the process. Past issues regarding pH control, repeatability of the process, and biological oxygen demand (BOD), for example, have clouded the perception of alkaline hydrolysis and have made it even more difficult for the consumer to make educated decisions.
In analyzing all this new information, the main consideration and understanding should be the intent of the process and equipment: ensuring efficacy of the process.
Acquiring a basic knowledge will lead to a better understanding of the methods used to achieve a wet or dry result and its relationship to energy consumption and, since these factors are all inter-related, to cost.
Efficacy
In vivo infectivity studies have validated the effectiveness of the alkaline hydrolysis process for the inactivation of prioninfectivity.1 These studies established baseline parameters for the inactivation of prion infectivity and were adopted by the USDA, European Union, and Canadian Food Inspection Agencies. Potassium hydroxide (KOH) or sodium hydroxide (NaOH) in an amount sufficient to hydrolyze infected animal tissues was used to achieve prion inactivation. Extending this knowledge to whole carcasses, sufficient KOHis needed to allow for its consumption by carcass components such as fat and protein materials. Using a KOH solution of 1 molar is the current accepted working concentration for use in the complete digestion of typical animal carcasses.
In addition to having the correct chemical ratios, water (H2O) is also a key part of the basic hydrolysis reaction. H2O is the key component that breaks chemical bonds by the insertion of its structure between the bonds of the atoms. If there is an inadequate amount of H2O during the hydrolysis process, complete digestion will not occur, leaving behind undigested proteins and possibly viable prions. This concept has been very misunderstood and needs to be made clear—sufficient water is key to the alkaline hydrolysis process. Using less caustic amounts or smaller water volumes in any alkaline hydrolysis process would not meet the recommendations and guidelines of the USDA, European Union, and Canadian Food Inspection Agencies.
The resultant process and its accompanied caustic ratios, based on molar equivalency of the processed tissue, have been reviewed, accepted, and recommended by the USDA, European Union, and Canadian Food Inspection Agency in industry reports published by these agencies.2,3,4 “Approved alkaline hydrolysis processes require processing infectious material in a hydroxide solution calculated on amass per mass basis equal or greater than 9% of the infectious material, which corresponds to 15% sodium hydroxide solution (NaOH) or 19.3% potassium hydroxide solution (KOH)”3of the total processed tissue weight.