Dairy Science and Food Technology Homepage
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
Forum Home Forum Home > Thermal processing > Thermal processing
  New Posts New Posts RSS Feed - Water Activity Effect on D-Value
  FAQ FAQ  Forum Search   Events   Register Register  Login Login


Water Activity Effect on D-Value

 Post Reply Post Reply
Author
Message
cordyceps View Drop Down
Newbie
Newbie
Avatar

Joined: 07 May 2012
Location: California, USA
Status: Offline
Points: 2
Post Options Post Options   Thanks (0) Thanks(0)   Quote cordyceps Quote  Post ReplyReply Direct Link To This Post Topic: Water Activity Effect on D-Value
    Posted: 07 May 2012 at 4:43pm
How does Water Activity affect the lethality curve?
Do we need to consider it in calculation of D-
and F-values?
(Please note that Water Activity is not merely the moisture content of the product.)
Thanks!
Back to Top
Sponsored Links


Back to Top
Admin View Drop Down
Admin Group
Admin Group

Administrator

Joined: 01 Sep 2009
Location: N. Ireland
Status: Offline
Points: 394
Post Options Post Options   Thanks (0) Thanks(0)   Quote Admin Quote  Post ReplyReply Direct Link To This Post Posted: 07 May 2012 at 8:51pm

Welcome to the forum.

In general as the water activity (aw ) decreases (solids increase e.g. sugars and fats) in a food the heat resistance of microorganisms and their D-values increase. As a consequence more heat (and higher F values) is required to obtain a similar log reduction in microbial numbers. The opposite occurs when the water activity increases.

Because the D-value generally increases (sometimes by a large factor) when aw increases, the number of log cycles that a pathogen or spoilage organism is killed will reduce significantly potentially resulting in public health or spoilage problems. I will try to explain this.

Let’s say we have a heat process that has a Fo of 3 and a pathogen that has a D-value of 0.21 minutes. The Fo process will reduce the number of pathogens in the final product by 3/0.21 =14.3 log cycles. A very large reduction.

If the aw is reduced e.g. by the addition of sugars, milk fat and protein the new D-value might  increase to say 0.70 minutes. It might even be higher! Since the Fo remains the same (unless we change it) the number of log cycles the pathogen will be reduced is 3/0.7 = 4.3. This would not be an acceptable process.

Does this explain your query?
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

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