7 replies to this topic

[SUJIT_KGPIAN]

Dear All

Can anybody help me in determining the Fo Value of Sterilisation.
Please give an example, say our sterilisation temperature is 110 Deg. C & time is 2 Minutes.
Is there any ideal Fo value or so for sterilisation

[Simon]

Can anybody help Sujit with his sterilisation query?

[Bawdy]

Hi Sujit,

I can help you with your enquiry, as it so happens i have a lot of experience and qualifications in thermal processing, but i would need to know a lot more information then you have already provided.

Ideally for hermetically sealed low acid products (pH>4.6, and water activity >0.85), you want to achieve a F0 of 2.8 minimum, your example of 110 degrees for 2 minutes does not even begin to register any meaningful F0, about 0.018. In practice however most thermal processors shoot for F0s of over 5, some even as high as
18-20.

That said,


1) What is the product?
2) pH?
3) Briefly outline the process, i.e heated then aseptically filled, put into a can/glass jar/plastic bowl then retorted etc.

Look forward to your reply.

Paul.

[SUJIT_KGPIAN]

Dear Paul

Thanks for your reply.

coming to the queries.

The product is tropical fruit puree (Mango, Papaya & Guava)
pH Below 4.0
Puree is mechanically extracted from fruits, preheated to around 60Deg C, Decanted, Sterilised (105 - 110 Deg C) for 60 to 200 Seconds 7 packed in pre-sterile aseptic bags.

Hopefully now you can solve it. Kindly let me know the formula you are employing to determine the Fo Value.

Thanking You Again.
Sujit

Hi Sujit,

I can help you with your enquiry, as it so happens i have a lot of experience and qualifications in thermal processing, but i would need to know a lot more information then you have already provided.

Ideally for hermetically sealed low acid products (pH>4.6, and water activity >0.85), you want to achieve a F0 of 2.8 minimum, your example of 110 degrees for 2 minutes does not even begin to register any meaningful F0, about 0.018. In practice however most thermal processors shoot for F0s of over 5, some even as high as
18-20.

That said,


1) What is the product?
2) pH?
3) Briefly outline the process, i.e heated then aseptically filled, put into a can/glass jar/plastic bowl then retorted etc.

Look forward to your reply.

Paul.

[Charles.C]

Dear SUJIT_KGPIAN,

I am also interested in seeing any further input from Bawdy.

Thermal sterilisation is not really my area however I can offer a few thoughts / references relating yr post.

I am guessing that flexible packaging may not hv such a detailed database as typical canned products (?).

Since other people may be interested in this topic, I should mention that there are several other threads here on Fo, eg -

http://www.ifsqn.com...dpost__p__35127

http://www.ifsqn.com...dpost__p__30234

http://www.ifsqn.com...dpost__p__42776

http://www.ifsqn.com...dpost__p__45085

As you probably know, it is relevant to consider both safety / commercial sterility as far as the heat treatment is concerned. IMEX, it is relatively easy to find explicit comments / equations on processing for safety. It seems to be far difficult to find the same for commercial sterility which will obviously relate to the specific product.

Hv attached two document giving a readable introduction to the relevance of F values and a convenient (Excel) method of numerical calculation respectively.

 thermal process calculations.pdf   2.02MB   509 downloads
 Process Lethality Spreadsheet.xls   122KB   490 downloads

I noted some general comments (attachment below) about low pH items / F values however I guessed the most common problems with yr product type (if any) are spoilage from yeasts / moulds ?

 low pH.png   174.9KB   35 downloads

Subsequently I found this document relating to process data for purees from which this extract seemed possibly interesting –

Thermal process calculations for apricot and papaya purees and nectar’s
The reviewed heat resistance parameters of pectin methylstrase were used in the required calculations (assuming?) that this enzyme is more heat resistant than the non sporulating bacteria like Lactobacilli and Leuconostoc, yeast and moulds which are responsible for the spoilage of high acid food (Dastur et al. (1968), Nath and Ranganna (1983) and Magalhaes, et al. (1999).

(The associated data is given in some detail here) –

 thermal process time some canned fruit products.pdf   243.77KB   227 downloads

I can post a few more documents on the interpretation / formulae for calculation of F0 if you are interested.

Hopefully Bawdy will know more than I could find.

Rgds / Charles.C

PS Slightly OT from a high acid POV but this collection of Fo values in use is maybe of some general interest -

 Fo values used commercially on UK marker 2000.pdf   82.25KB   288 downloads

[Bawdy]

Hi Sujit,


Because of the acidity of your product, to talk about F0s is almost irrelevant, FOs are only used for products with pH >4.6 because at thse pHs C. botulinum is a problem. At the pH of your product C.bot is not an issue, so your thermal process need not be anywhere near as severe. Certainly not severe enough to generate any F0s to calculate. You dont really start to accumulate any real significant F0s until the PRODUCT reaches temps greater than 111.1 degrees. I stress the product, because it is the product temp that is important, not the temp of the apparatus/kettle,/retort/steam you are using to heat the product.

Also there is a general (always exceptions to the rule) relationship between the pH and the lethal temperatures, as the lower the pH the bug can survive the easier it can be killed by heat. You can hot fill and invert most acidifed products and get a shelf stable product. Think about jam and fruit preserves - For centuries people have been making fruit/acidified preserves in exactly this manner, simply hot fill and seal. Tomato based pasta sauces are another example of this. Quite often the only reason whole/portioned fruit is cooked once sealed inside cans/jars is for textural purposes, or to blanch them to de-activate enzymes etc, not safety reasons, or because the fill temps are not high enough. in the fruit puree examples given in the above attachements, the initial temps at the start of the thermal process were in the 38-42 degree range. Nowhere near hot enough.


To further assist you, what is the temperature of the product when you close the bag/pouch? Then, is the product cooled in some way, if so how? I am also assuming your sterilising step is running the product through a heat exchanger? Is the 110 degree figure you quote the temp of the product or the steam going into the heat exchanger?


Look forward to your reply.


Paul.

[pablo coronel]

Due to the acidity of your product the presence of spores is not veyr common.
Thus your target is killing vegetative microorganisms and probably moulds and yeasts.

These are more sensitive to heat than spores by several orders of magnitude.

I think you need to hire someone with experience to better asses the safety of your product as the information provided in good faith in this forum can not be used for any legal defense.

[Charles.C]

Dear SUJIT_KGPIAN,

A little feedback to the previous posts might be helpful (eg Bawdy's queries).

I hv added a few more, possibly useful, attachments below.
The high-acid scenario is compared to low-acid in (hh1). Yr original query regarding the calculation of Fo is discussed/illustrated in detail in (hh2) (for example see the low acid eq.21 [also highlighted in my previously posted attach.]). Some tabulated values of "D" as could be related to eq.21 are given in (hh3).

It would perhaps be interesting to inform as to the basis for yr current thermal process, eg (1) what was the intended target micro-organism / enzyme / whatever ? and (2) what was the basis for the utilised heating time ?

 hh1 - Food technology thermal fact sheet.pdf   640.83KB   283 downloads
 hh2 - equations for safety, commercial sterility, sterilizations.pdf   58KB   272 downloads
 hh3 - various D values, spore-vegetative pathogens.pdf   106.07KB   265 downloads

Rgds / Charles.C