Supporting document 3 Scientific information for the assessment of raw milk products – Cheeses (at 2nd call for submissions) – P1022 Primary Production & Processing Requirements for Raw Milk Products Executive summary Standard 4.2.4 of the Food Standards Code contains requirements for the production of raw milk products where it can be demonstrated that processing ensures that pathogenic microorganisms that may be present in the raw milk are reduced to safe levels. The food safety outcomes can achieved through: 1) Controls on production, collection and transport that ensure the initial level of an identified hazard in the raw milk at the start of processing will not impact on the safety of the final product. 2) The intrinsic physico-chemical characteristics of the raw milk product do not support growth. 3) Controls during processing that result in no net increase in hazard levels during manufacture. Food safety outcome 1 deals with the production, collection and transportation of raw milk and is dealt with in the document Guide to the requirements for raw milk products in Standard 4.2.4 -– Primary Production and Processing Standard for Dairy Products. This document examines the range of scientific information that may be required to demonstrate food safety outcomes 2 and 3. Examples of the application of existing tools such as default criteria and predictive equations are presented to aid decision making. A focus is on the type of pathogen challenge studies available to meet the food safety outcomes. This includes demonstrating that the physico-chemical characteristics of the cheese do not support the growth of pathogens through to determining the time required for no net increase in pathogen concentration. The document is to be considered in conjunction with the Guide to the validation of raw milk products. Demonstration of the food safety outcome 2 requires evidence that the physico-chemical characteristics of the cheese (e.g. pH, moisture, salt, water activity, lactic acid etc.) do not support the growth of pathogens. Methods available to assess the likelihood of pathogen growth in cheeses can include default physico-chemical parameters, predictive equations using growth rates or probability of growth and cheese challenge studies. Predictive equations were evaluated to determine their utility for determining the growth rate or probability of growth based on a limited number of characteristics (pH, salt and moisture) against published cheese challenge studies for Listeria monocytogenes. i The probability of growth equation developed by Augustin et al. (2005) has been selected as an appropriate screening tool. This equation was found to accurately predict (greater than 90% probability of growth) those cheeses where growth was found to occur in challenge studies. However, predictions where growth was not observed in challenge study cheeses were less clear. Use of predictive equations such as this could allow cheese makers to consider changes in the manufacturing processes, selection of starter/adjunct cultures or ingredients (such as salt) to re-formulate cheeses which are less likely to support the growth of pathogens. Pilot scale production of raw milk cheeses could be used to determine the variability in the characteristics of raw milk cheese. Demonstration of the food safety outcome 3 requires evidence of no net increase in pathogen concentration through the entire cheese making process. This is likely to require evidence from cheese challenge studies, where pathogens are deliberately added to milk and their concentration measured over time (at key stages of the cheesemaking process). The growth rate of pathogens during the early stages of cheese making (e.g. milk warming prior to addition of starter cultures) is much faster than the inactivation rate during maturation. This highlights the importance of rapid acidification at the start of the cheese making process to limit the growth of pathogens during this stage in an effort to minimise the time required to achieve no net increase (taking account reductions during ripening/maturation). Quantitative analysis of milk challenge studies, where pathogens are grown with lactic acid bacteria showed that there was a strong negative correlation between the maximum rate of acidification and the total amount of growth of pathogens; faster acidification rates results in less growth. The applicability of published challenge studies in the scientific literature was analysed. The cheese making process involves many different processing steps, temperatures and times, ingredients (salt, coagulating agents) etc. Challenge studies are almost exclusively observational and based on recipes rather than replicating commercial practice. Subtle variations between a published challenge study and a proposed process may lead to different outcomes. This is especially true as very few published challenge studies are conducted using raw milk as a starting ingredient. For the purposes of demonstrating no net growth, it is likely that challenge studies will need to be conducted using the same processes, starter cultures and ingredients as proposed for the commercially produced product. ii Table of Contents EXECUTIVE SUMMARY ............................................................................................................................... I LIST OF FIGURES ...................................................................................................................................... IV LIST OF TABLES........................................................................................................................................ VI 1 BACKGROUND .................................................................................................................................... 7 2 ESTABLISHING NO GROWTH IN CHEESE ..................................................................................... 9 2.1 CHEESE CLASSIFICATION ...................................................................................................................... 9 2.2 CHEESE PHYSICO-CHEMICAL CHARACTERISTICS ............................................................................... 11 2.3 AVAILABLE TOOLS TO ESTABLISH NO GROWTH ................................................................................... 13 Default criteria ............................................................................................................................................ 14 Predictive equations ................................................................................................................................. 15 2.4 VALIDATION OF TOOLS TO ESTABLISH NO GROWTH............................................................................ 16 2.5 DISCUSSION ........................................................................................................................................ 21 3 ESTABLISHING NO NET INCREASE .............................................................................................. 23 3.1 CHEESE PRODUCTION STEPS ............................................................................................................. 23 3.2 STARTER CULTURE BEHAVIOUR .......................................................................................................... 23 3.3 MILK CHALLENGE STUDIES .................................................................................................................. 25 Effect of starter cultures on pathogen growth ....................................................................................... 25 Variability in pathogen response to a starter culture ............................................................................ 29 3.4 CHEESE CHALLENGE STUDIES ............................................................................................................ 30 Cheese formation ...................................................................................................................................... 32 Maturation and ripening............................................................................................................................ 35 3.5 ESTABLISHING NO NET INCREASE ....................................................................................................... 38 3.6 DEMONSTRATING THROUGH CHALLENGE STUDIES ............................................................................ 43 3.7 DISCUSSION ........................................................................................................................................ 44 4 CONCLUSION .................................................................................................................................... 46 5 REFERENCES .................................................................................................................................... 47 APPENDIX 1 STARTER AND ADJUNCT CULTURES USED IN PATHOGEN CHALLENGE STUDY CHEESES .................................................................................................................................................... 51 APPENDIX 2 SUMMARY OF PHYSICO-CHEMICAL TESTS PERFORMED IN CHEESE CHALLENGE STUDIES ............................................................................................................................. 53 APPENDIX 3 PREDICTION OF WATER ACTIVITY FOR CHALLENGE STUDY CHEESES ............. 57 APPENDIX 4 QUANTIFYING ACIDIFICATION KINETICS ..................................................................... 63 iii List