Milk Quality. Art Hill University of Guelph American Cheese Society

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1 Milk Quality Art Hill University of Guelph American Cheese Society

2 Contents Milk as a growth medium Lactic acid bacteria Spoilage bacteria Major pathogens Introduction to cheese risk analysis Q and A 2

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4 Milk as a growth medium General nutrients: good for microorganisms Milk sugar: lactose tolerance required. Acidity: ph near physiological ph (6.8) Moisture: more than adequate Oxygen levels in milk favor organisms that can grow with or without oxygen. 4

5 H + H + H H+ + Proteins H + H + + Acids/Salts + H + H + H + H + H + H + H + H + H + H + H + H + H + = TA Lower ph = higher acidity = more free H + Higher ph = lower acidity = less free H + ph scale goes from Acid ph < H + > OH - Neutral ph = 7.0. H + = OH - Alkaline ph > H + < OH - ph Protein properties Microbial growth Taste The concept of ph 5

6 Relative sizes of microorganisms Animal cell 10 µm Animal Nucleus Mould cell 10 x 40 µm Yeast cell 5-8 µm Bacterial cell (rod) 2-3 µm Bacterial cell Coccus, 1 µm Virus 0.1 µm 6

7 Growth phases of microorganisms Stationary Logarithmic Death Lag 7

8 What s in the total count? Bactoscan versus TPC Principal spoilage flora Cold tolerant organisms that produce heat stable spoilage enzymes Thermoduric organisms that survive pasteurization: e.g., species of Bacilli and Clostridia (butyric acid formers) Gas formers: yeasts, coliform bacteria, Clostridia Pathogenic bacteria Lactic acid bacteria 8

9 Contents Milk as a growth medium Lactic acid bacteria Spoilage bacteria Major pathogens Introduction to cheese risk analysis Q and A 9

10 Lactic acid bacteria Often referred to as LAB Non spore forming = heat labile Tolerate low levels of oxygen Numbers decrease during cold storage Spherical (1 um) or rod shaped (1 by 2 3 um) Competitive advantages: lactose and acid tolerance 10

11 Natural fermentation of raw milk ph B Yeasts and Moulds C Proteolytic Bacteria A Lactic Bacteria Time - Days D 11

12 Contents Milk as a growth medium Lactic acid bacteria Spoilage bacteria Major pathogens Introduction to cheese risk analysis Q and A 12

13 Cold tolerant organisms Psychrotrophic (some like it cold) Grow at temperatures < 7ºC, but not less than < 2ºC. Milk quality problems associated with: Heat stable spore forming bacteria Elaboration of heat stable enzymes, especially in dirty equipment Mainly species of Pseudomonas 13

14 Coliform bacteria Usually indicate fecal contamination Traditional index of general sanitation; still helpful but not adequate for modern practice Control = good farming and manufacturing practices 14

15 Butyric acid formers Source: any kind of silage; generally in the environment Survive pasteurization: traditional gas test for thermodurics Cause late gas defects Control: environment, bactofugation, microfiltration, nitrate salts, lysozyme, antimicrobial cultures 15

16 Contents Milk as a growth medium Lactic acid bacteria Spoilage bacteria Major pathogens Introduction to cheese risk analysis Q and A 16

17 Dairy pathogens Pathogens: common before 1940 Corynebacterium diptheriae: diptheria Brucella abortus: brucellosis, undulant fever Mycobacterium tuberculosis: TB Coxiella burneti: Q fever 17

18 Dairy pathogens Pathogens that emerged during Staphylococcus aureus: excretes heat stable toxins Salmonella spp: salmonellosis, food infection Enteropathogenic E. Coli: enterotoxins, some heat stable, E. Coli 0157 H7 18

19 Dairy pathogens More Recent Pathogens Yersina enterocolitica: food infection psychrotrophic, heat labile Campylobacter jejuni: food infection, fever and gastroenteritis, heat labile Listeria monocytogenes: psychrotrophic, food infection, heat labile Bacillus cereus: important spoilage agent, some strains are mildly pathogenic; heat stable spores; cold tolerant 19

20 Raw Milk Quality Tests 1. Organoleptic 2. Total plate counts good < 3,000/ml; maximum 100,000/ml 3. Coliforms: good < 10/ml; concern > 25; max 100/ml 4. Psychrotrophes (grow at T < 7 o C) good < 1,000/ml 5. Somatic cell counts: good <100,000/ml; concern >300,000/ml; ON penalty >499, Rapid test for inhibitors 7. Disk assay (official inhibitor test) 8. Composition: fat, protein, casein if possible 20

21 Contents Milk as a growth medium Lactic acid bacteria Spoilage bacteria Major pathogens Introduction to cheese risk analysis Q and A 21

22 Risk Assessment: a science based process to identify and characterize hazards, assess exposure, and characterize risk. Adapted from the WHO risk analysis model Risk Communication: the interactive exchange of information and opinions about risk. Risk Management: a policy based process to evaluate risk, and to select, implement, and validate mitigation strategies.

23 Cheese borne hazards: prevalence in raw milk Food Borne Pathogen Campylobacter jejuni Number of Studies Prevalence : average % Prevalence: range Shiga-toxin E. coli Listeria monocytogenes Salmonella spp Staphylococcus aureus Yersinia enterocolitica Note: Several studies found much higher levels by PCR

24 Cheese borne hazards: environmental Listeria: 7 28% of noncontact surfaces in cheese plants. Examples: 17% of 243 noncontact surfaces (Menendez); 11% of noncontact surfaces in eight NJ artisan cheese factories; 4% niche sites; D Amico, Brazil, two cheese plants, 13 & 10%, Barancelli, 2011) Chilli, 22%, Garces-Aviles, , NJ Oaxaca plant, Listeria in seven contact and noncontact sites, matched PAGE for isolates in the product Survival demonstrated in cheese brine (5 days) and rennet extract (Ryser 1989)

25 Some Cheese Borne Illnesses in North America Year Location Details 2010 Nevada 1 ill; homemade queso fresco; raw milk; Campylobacter 2010 New Mex 38 ill; 1 HUS; Gouda; new strain of E. coli 0157:H Washington Several illnesses suspected; raw milk cheese; Listeria 2007 Kansas 67 ill; fresh cheese; raw milk; Campylobacter; community fair 2008 Quebec 1 death; 90 ill; fresh Cheddar curd; Salmonella 2007 Ontario 12 ill; raw milk cheese; mobile cheese-maker; Campylobacter 2007 Ontario 1 infant HUS; mother ate raw milk cheese 2006 Ontario 2 children hospitalized; raw milk and cheese; E. coli; 2002 Edmonton 13 ill (5 hospitalized, 2 HUS); raw milk Gouda cheese

26 Some properties of some pathogens associated with cheese Organism Listeria monocytogenes Campylobacter jejuni Salmonella spp Enteropathogenic E. Coli (e.g., 0157 H7) Yersina enterocolitica Staphylococci aureus Properties Infectious dose high; mortality high Cold, acid and salt tolerant Requires full pasteurization Ubiquitous in food environments Infectious, low doses Infectious, low doses Infectious, low doses Cold and acid tolerant In cheese usually from milk Psychrotrophic In cheese, usually from people contact

27 Pathogenic Hurdles in Cheese Making Cold storage of milk Cultures Water activity (a w ) Temperature history Exposure history Ripening time Slows or stops growth of both pathogens and competitors Antimicrobials, time versus ph profile a w, salt in moisture E.g., Pathogenic survival dramatically reduced in thermophilic cheeses ( E.g., parm versus Cheddar; especially critical for fresh including heat-acid cheeses. Pathogens decline due to low ph, decreasing a w, antimicrobials, and low oxygen

28 Listeria presence and survival in cheese 329 red-smear cheeses from five European countries: 15.8% Listeria spp; 6.4% L monocytogenes; 10.6% with L. innocua, 1.2% with L. seeligeri; No change from 1985 to 2000 (Rudolf & Scherer, 2001). Marth 1991 review of LM survival: Parm, 10 mo; Cheddar > 14 mo; Feta >2 mo; smear Brick, Blue, Camembert supported growth. Genigeorgis 1991; inoculated 24 types and 28 brands; counts declined for all ripened cheese with cultures and surface ph <5.5. Incidence on cheese appears independent of milk heat treatment (Data and citations in Rudolf, 2001)

31 Risk Characterization Risk associated with cheese considering all varieties and current practices of manufacturing, distribution and use is low, but there is opportunity for substantial improvement, especially for certain higher risk varieties and sectors.

32 Cheese Risk Management priorities While emphasizing the need for validation our perception of cheese safety mitigation priorities are: Varieties with minimum or ripened ph > 5.5 Intelligent inclusion of heat treatments in risk assessment and mitigation strategies Cross contamination in food service and retail stores Artisan manufacturers in new world countries Some traditional practices in old world countries. E.g. AOC Comté: spruce planks; washing 3x per wk with salty morge derived from older Comté; microcci and yeast dominate. Temperature sequence: C, C and 4-9 C.

33 Risk Communication Inclusive of all stake holders at all levels Active and transparent exchange of knowledge, opinions, and values Goals: listen, learn, educate, train, inform, motivate Governments, educators, trade associations, managers have key roles and obligations.

Food Microbiology 101

Food Microbiology 101 Nina G. Parkinson NGP Consulting November 6, 2018 Food Safety and Sanitation Conference Summary Microbiological contamination of food Routes of contamination by pathogens Overview