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11 Cards in this Set
- Front
- Back
What makes milk a good growth medium? What doesn't? |
High water content, near-neutral pH, variety of available nutrients High fat (not readily accessible) and low carb source (lactose, microbes prefer glucose) |
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What is the min heating time and temp for milk processing in the US? |
75C for 15 seconds (most processors have increased times and temps) |
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What effect does pasteurization have on psychrotrophs? |
Pasteurization temps inactivate psychrotrophs |
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How do dairy products differ from milk? |
Usually lower pH due to LAB, different water activity, nutrients removed or concentrated, other additives (salt) |
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How many psychrotrophic organisms does it take to result in spoilage? |
One healthy and rapidly growing organism can result in spoilage. Pasteurization kills psychrotrophic bacteria but post pasteurization contamination can occur. |
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Describe psychrotrophic bacteria. Name 4 examples. Which is most common? |
Gram negative rods, generally proteolytic (produce proteases), live in refrigerated conditions Pseudomonadaceae family - most common Neisseriaeceae family Flavobacterium genera Alcaligenes genera |
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Which psychrotrophic bacteria contribute to flavor defects in milk? |
Pseudomonas flourescens, pseudomonas fragi, pseudomonas putida, pseudomonas lundensis
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What is the result of degradation of casein?
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Bitter peptides are formed
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What is the progression of proteases and spoilage?
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Psychrotrophic proteases (enzymes) survive heat process, whey & caseins are degraded (bitter peptides formed), proteolysis continues and causes putrid off flavors |
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Which organisms are responsible for lipase spoilage in milk? What is the result? |
Pseudomonas flourescens result in C4-C8 fatty acid production causing rancid odors and soapy flavor. Oxidation of unsat FA cause cardboard flavor. Pseudomonas fragi cause fruity off flavor in milk Cured cheeses not often affected |
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Describe how psychrotrophs are controlled |
Limit contamination (only 1 cell needed)
Proper cooling (30-37C after milking, 7C within 2 hours, most processors exceed this standard), maintaining cold storage temps |