Answer to the question from a student 20141029

Dear Professor Kwan,

Sorry to bother you.I am a student of MSc NFST.

Can you post the model answer for the following question? 

I think that we don't have tutorial in our lecture and don't know the correct answer. Thank you so much!

9. You are the senior technical manager of an apple cider bottling factory.  You are responsible for food safety management system ISO22000 based on HACCP.  The following happened last week: i.          On Tuesday, your technician rushed into your office and informed you that the quality control laboratory have made a mistake in measuring the pH of the apple cider  delivered yesterday for bottling.  The actual pH of the food was 4.5 and the laboratory used a malfunctioning pH meter and reported a pH value of 4.0.  ii.         Some of the apple cider was bottled and pasteurized already, using the pasteurization process designed for apple cider of pH4.0. iii.        The technician thought that the pasteurization process was not sufficient and suggested a corrective action that the bottled apple cider should be processed one more time for 10 minutes at 105°C. iv.        He provided you with the information from the quality control laboratory as described below.  v.         You had to judge whether the technician’s decision was correct or not and answer the questions below.
			Approximate microbial flora in apple cider (Number/ml)				Acceptable cell density in bottled apple cider(Number/ml)
Spoilage bacteria			1000				less than		0.0000001
Bacterial spores			100				less than		0.000001
Fungal spores			100				less than		0.000001

The problematic pasteurization process:     10 minutes at 105°C.

For apple cider:                                                                                                     

D values and Z values of the microbes at pH4.0:
	D value at 105°C(minute)	Z value(°C)
Spoilage bacteria	0.001	2
Bacterial spores	0.1	10
Fungal spores	0.002	5

D values and Z values of the microbes at pH4.5:
	D value at 105°C(minute)	Z value(°C)
Spoilage bacteria	0.01	5
Bacterial spores	2	15
Fungal spores	0.02	10

Answer the following questions.  Show your calculations :

a.            Calculate the F values set in the pasteurization for these target microorganisms?                                                                                 (1 marks)   At 105°C Spoilage bacteria: from 1000/ml to 0.0000001/ml -->10D=0.01min Bacterial spores: 100/ml to 0.000001/ml -->8D=0.8 min Fungal spores: 100/ml to 0.000001/ml -->8D=0.016min

b.            Calculate the number of D’s that actually occurred in the problematic pasteurization process for these target microorganisms?                                                            (2 marks)   Spoilage bacteria: 10min/0.01min=1000D Bacterial spores: 10min/2 min=5D Fungal spores: 10min/0.02min=500D

c.             Calculate the cell densities of the microorganisms in the processed apple cider with actual pH of 4.5 after they were processed for 10 minutes at 105°C?                                                                                                                                (2 marks) Spoilage bacteria: 1000/101000=10-997 (per ml) Bacterial spores: 100/105=10-3(per ml) Fungal spores: 100/10500=10-498 (per ml)

d.            Was the proposed additional pasteurization process needed and if needed, was it sufficient for the processing of the one-time processed apple cider with wrong pH measurement?  Explain briefly.                                                                                       (1 mark) Needed. Reason: Bacterial spores-->10-3/ml, larger than the acceptable level of 10-6/ml.       sufficient or not: additional 10 minutes at 105°C Bacterial spores at 10-3/ml for additional 5D reduction --> 10-3/ml x 10-5 =10-8/ml Sufficient

e.             Was the technician correct in his suggestion of the additional remedial processing?  If he was wrong, fire him and suggest alternative pasteurization time to treat the problematic bottled apple cider at 105°C.  Explain briefly.                                (1 marks) According to above calculation. The remedial processing should be sufficient. The technician was correct.

f.              Suggest a new process with a combination of pasteurization temperature and time for the remaining batches of apple cider (pH4.5).  These data may be useful for your consideration: heating for 10 minutes at 105°C for ten bottles of apple cider costs HK$1 and heating for 1 minute at 120°C for ten bottles of apple cider costs HK$5. Explain briefly your process with justification.   The current cost: HK$1 per 10 bottles=HK$0.1/bottle if 10 min at 105°C. Need to do it twice. So cost for the remaining batches would be HK$0.2/bottle. If we adjust the If increased to 120°C, time for pasteurization will need to be: D value for bacterial spores: one log decrease-->2 min to 0.2 min For 8D reduction target, the time needed will be 0.2min x 8=1.6min The cost at 120°C for 1.6 min for 10 bottles would be around HK$8  -->HK$0.8/bottle The process should be maintained at 20 min at 105°C for a lower cost.

I look forward to hearing from you.