Shelf-life of pasteurised chilled foods

Transcription

1 Shelf-life of pasteurised chilled foods MSFR Project jointly steered by the Chilled & Frozen Foods MIG and the Microbiology MIG January 2013 December 2015 Third update for the Micro MIG, 12th January 2016 Linda Everis, Microbiology Department Tel +44 (0)

2 Why? - need for the project Historically chilled foods have been processed for 90/10 (long life) or 70/2 (short life) Aimed at 2 specific food pathogens L.monocytogenes and C.botulinum Limited advice available on the effects of other surviving organisms on product shelflife

3 What? objectives of the work Determine range of organisms of concern to this food group Investigate the effects of ph, aw, heat process and storage conditions on growth of surviving non-target microorganisms

4 How? the approaches Literature review to identify organisms capable of surviving 90 C for 10mins and 70 C for 2mins and growing at refrigeration temperatures <8 C. Collect microbial isolates from chilled foods Determine effects of process temperature on microbial survival and subsequent ability of organisms to grow under conditions of ph, aw, and MAP in model systems : dairy, vegetable protein based

5 Project Milestones - Number Milestone Description Resp. Due Date (DD/MM/YY) Date Completed (DD/MM/YY) M1 Completion of Literature review GDB 31/04/ /09/2013 M2 M3 M4 M5 Completion of screening studies of UK and EU foods for key spoilage organisms Completion of experimental matrix on effect of 70/2 and 90/10 (and equivalent lethality processes) on survival of key spoilage organisms Obtaining data on effect of different chill storage temperatures on survival/growth of heat treated spoilage organisms Completion of trials on effects of ph/aw/map on survival/growth characteristics LKE 31/10/ /09/2013 LKE 31/03/ /05/14 LKE 31/07/ /05/14 LKE 31/03/2015 March 2015 M6 Completion of trials in model foods and real foods LKE 31/09/2015 July 2015 M7 Completion of RD GDB 31/12/2015 Dec 2015 M8 Completion of peer reviewed article GDB 31/12/2015 Dec 2105

6 Project Deliverables Deliverable Description Resp. Due Date (DD/MM/YY) Date Completed (DD/MM/YY) Guidance document on completion of project GDB/LKE 31/12/2015 Completed Presentations to Microbiology Panel and Chilled Foods Panel annually and on completion of project Peer reviewed article in final quarter of the project LKE/GDB Autumn 2013 Autumn 2014 Autumn 2015 Winter 2016 Completed GDB/LKE 31/10/2015 Completed

7 Literature review: RD 366: Microbiological quality of chilled pasteurised food products: A review

8 Aim of main study To assess the potential for spoilage Bacilli to survive a 90 C for 10 mins process or a range of equivalent heat processes and to subsequently grow under conditions of reduced ph and water activity at chill temperatures.

9 Equivalent processes:90 C/10min Temp Time

10 Heating studies- ph 3 crops B.weihenstephanesis (crop no 1), B.pumilis (milk) (crop no 2), B.cereus 1761 A (crop no 6) ph: 5.0, 5.5,6.0,6.5,7.0 Heat treatments: Non heated, 95/2.8 mins, 90/10 min,85/36 min,80/130min Storage :5,8 C Check turbidity daily Plate out day 0,weeks 1,2,3,4,6,8,10

11 Conclusions ph study The results of the ph study have shown that : B.Weihestephanesis,B.pumilus and B.cereus are able to grow at chill temperatures and at a ph of 5.0 when subjected to heat processes of 90 C/10min or equivalent. Under conditions of lowered ph there are differences in the initial log reduction observed and time to growth (1 log cfu/g) between seemingly equivalent heat processes.

12 Heating studies- aw 3 crops B.weihenstephanesis (crop no 1), B.pumilis (milk) (crop no 2), B.cereus 1761 A (crop no 6) Aw : 0.99,0.98,0.97,0.96 Heat treatments: Non heated, 95oC/2.8 mins 90 o C/10 min,85 o C/36 min,80 o C/130min, Storage :5,8 o C Check turbidity daily Plate out day 0,weeks 1,2,3,4,6,8,10

13 Conclusions : aw study The results of the aw study have shown that : B.Weihestephanesis,B.pumilus and B.cereus are able to grow at chill temperatures and at aw 0.96 when subjected to heat processes of 90 C/10min or equivalent. Under conditions of lowered aw there are differences in the initial log reduction observed and time to growth (1 log cfu/g) between seemingly equivalent heat processes.

14 Food studies Foods : Chicken puree, Rice pudding, Carrot puree Organisms: B.weihenstephanesis, B.pumilis, B.cereus Heating conditions: Non heated, 95 o C/2.8 mins 90 o C/10 min,85 o C/36 min,80 o C/130min, Storage temperature: 8 C Packaging : Air, VP Enumerated for APC weekly intervals

15 Conclusions: food study The results of the food validation study have shown that : Growth of all strains was limited in carrot compared with the chicken and rice pudding. This is probably due to the carrot having a lower ph (4.9). Growth was also observed for both air packed and VP packed products. Growth was observed throughout the heat treatments.

16 Further information Project websites: campdenbri.co.uk/research/shelf-life-chilled-foods.php Research summary pages: campdenbri.co.uk/research/summary.php R&D report on Microbiological quality of chilled pasteurised food products: A review RD 366 R&D report Effect of heat process, ph, aw and storage temperature on the growth of spoilage Bacilli and peer reviewed paper in approval system Heat resistance of spoilage Bacilli at 90 C/10min and equivalents- Technical note in production

17 Shelf-life of pasteurised chilled foods MSFR Project jointly steered by the Chilled & Frozen Foods MIG and the Microbiology MIG January 2013 December 2015 Heat Resistance & Decontamination group input Rob Limburn, Microbiology Department Tel +44 (0)

18 Background New heat resistance data generated for Bacillus spp. Comparison of effect of reduced A w and ph on heat resistance of 3 psychrotrophic Bacillus spp. Bacillus cereus Bacillus weihenstephanensis Bacillus pumilus D-values carried out in modified nutrient broth

19 Methodology Spores of each Bacillus spp. prepared and suspended in: Nutrient broth (ph, A w 1.00) Adjusted nutrient broth (ph 5.0) Adjusted nutrient broth (Aw 0.96) Filled into thin-walled glass spheres and heated within an oil bath at a range of temperatures to determine D- and z-values.

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21 Results - Effect of reduced ph Organism Temperature ( C) NB D-value (minutes) ph5.0 B.cereus B.pumilus B.weihenstephanensis z-value (C ) z-value (C ) z-value (C ) Expected decrease in the D-value of organisms. D-values were reduced by 52-92% compared with unadjusted NB

22 Results Effect of A w Organism Temperature ( C) D-value (minutes) NB Aw 0.96 B.cereus B.pumilus B.weihenstephanensis z-value (C ) z-value (C ) z-value (C ) Expected increase in the D-value of organisms. In all but 1 case, D-values were increased by % compared with unadjusted NB

23 Conclusions Z-values determined ranged from C Spores of psychrotrophic Bacillus species may present problems in pasteurised chilled foods. In situations where psychrotrophic bacilli are causing issues, these specific D- and z-values may be used to accurately calculate the required increase in process times and temperatures to sufficiently reduce levels of these organisms.