Question from a student 201617, 20170501a

Q:

Dear Professor Kwan,

I have some problems regarding the past papers. Thank you for your attention.

‘What are the number of D’s targeted in the standard canning process for each of these microorganisms?’ has been asked in 2013-2014 and 2014-2015 past papers. However, as I check the answers from the blog, I find that 2 different approaches are used to answer the same type of question.

1) 2013-2014: Use ‘time in standard canning process/D value for each microorganisms’ for calculation

2) 2014-2015: Use data of ‘approximate densities of microbial flora in the ham before canning’ and ‘acceptable cell density in canned ham’ for calculation

Which one should we use in the examination? The question is asking about the ‘real target of the canning process that can be achieved’ (1) or the ‘ideal target of the canning process’ (2)?

Can you please also help me check the answer of the question below? Thank you very much.

2013-2014 B5 (d) Cell densities of the microorganisms of the regular lot of ham after canning with the new process

	New D value at 120C	No. of D	Cell densities
Spoilage bacteria	0.0025	3min./0.0025=1200	100*10^(-1200) =10^(-1198)/ml
Bacterial spores	0.25	3min./0.25=12	10*10^(-12) =10^(-11)/ml
Fungal spores	0.05	3min./0.05=60	1*10^(-60) =10^(-60)/ml

Since 10^(-11)/ml < 10^(-8)/ml (acceptable cell density in canned ham), the new process can replace the standard canning process.

A: 

‘What are the number of D’s targeted in the standard canning process for each of these microorganisms?’ has been asked in 2013-2014 and 2014-2015 past papers. However, as I check the answers from the blog, I find that 2 different approaches are used to answer the same type of question.

1) 2013-2014: Use ‘time in standard canning process/D value for each microorganisms’ for calculation

2) 2014-2015: Use data of ‘approximate densities of microbial flora in the ham before canning’ and ‘acceptable cell density in canned ham’ for calculation

The calculation should use 1). 2) was a mistake I made during discussion in review session or email responses this year.  

Which one should we use in the examination? The question is asking about the ‘real target of the canning process that can be achieved’ (1) or the ‘ideal target of the canning process’ (2)?

Should be (1) the ‘real target of the canning process’ (1)

In fact, don't mind whether it is "real or ideal target", as long as the question asked about the standard process, use the standard process to calculate the D value numbers.

Can you please also help me check the answer of the question below? Thank you very much.

2013-2014 B5 (d) Cell densities of the microorganisms of the regular lot of ham after canning with the new process

	New D value at 120C	No. of D	Cell densities
Spoilage bacteria	0.0025	3min./0.0025=1200	100*10^(-1200) =10^(-1198)/ml
Bacterial spores	0.25	3min./0.25=12	10*10^(-12) =10^(-11)/ml
Fungal spores	0.05	3min./0.05=60	1*10^(-60) =10^(-60)/ml

Since 10^(-11)/ml < 10^(-8)/ml (acceptable cell density in canned ham), the new process can replace the standard canning process.

Correct

thank you for pointing out the inconsistency that was a mistake in the review session this year.