Home Cheese starters Donate support Site Probiotics Cheese yield Cheese quality Cheese science Italian cheese Anti-microbial  proteins Phages Primary production Ice cream Wine Calculators Harvard referencing Packaging Jobs
 FAQ   Search   Events   Register   Login

# Calculate D value

 Author Topic Search   Topic Options Admin Admin Group Administrator Joined: 01 Sep 2009 Location: N. Ireland Status: Offline Points: 394 Post Options    Thanks(0)    Quote  Reply Topic: Calculate D value    Posted: 11 Feb 2012 at 11:37pm Welcome back. I am going to explain how to do this by calculating the slope of the thermal death curve for the organism you have studied using an Excel function called "slope". The D-value is then obtained by obtaining the negative reciprocal of the slope. 1. I presume that you have these values in an Excel spreadsheet? If not create a workbook with 3 columns, Time (minutes), Colony forming units/ml, and Log10 colony forming units/ml. 2. Convert your colony forming units (CFU)/ml values to their log10 equivalents. 3. Excel 2010 has a useful slope function to calculate the slope of the linear regression line for x and y values and I will explain how to use this function. 4. Lets assume that your time values (x values) are in column A and range from A2 to say A15 and the corresponding log10 colony forming units/ml are in column C and range from C2 to C15. The slope can then be calculated using =slope(C2:C15, A2:A15). 5. The D-value is obtained by obtaining the reciprocal of the slope and multpling this value by -1. 6. I suggest that you produce a figure showing the relationship between time and the reduction in Log10 CFU/ml. Show the experimental values and add a trendline. Use Excel to calculate the linear regression equation and show the r2 value. If this is less than 0.9 consider your error sources and look for "tailing" of your data points. Sponsored Links mstrange Newbie Joined: 30 Nov 2010 Status: Offline Points: 4 Post Options    Thanks(0)    Quote  Reply Posted: 11 Feb 2012 at 5:09pm Hi again!  Got table of time (mins) and nos of survivors at 200F. Pl can you tell how to calculate D at 200F? Thanks.
 Post Reply Tweet

 Forum Jump -- Select Forum --  Announcements and forum news  Ice cream  Spreadsheet and site calculators  Cheese yield  Thermal processing  Harvard referencing  Cheese quality  LP containing milk replacers  Pro and prebiotics  Starter cultures  Wine science and technology  Employment and food careers  Food infections and intoxications  Food Science  Nutrition and health  General dairy  Cheese manufacture and varieties  Bacteriophages for lactic acid bacteria  Modeling  Cheesemaking equipment for small dairies  Preservation of raw milk using the LP system Forum Permissions You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot delete your posts in this forumYou cannot edit your posts in this forumYou cannot create polls in this forumYou cannot vote in polls in this forum

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.