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11 Cards in this Set

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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)

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)

What effect does pasteurization have on psychrotrophs?

Pasteurization temps inactivate psychrotrophs

How do dairy products differ from milk?

Usually lower pH due to LAB, different water activity, nutrients removed or concentrated, other additives (salt)

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.

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

Which psychrotrophic bacteria contribute to flavor defects in milk?

Pseudomonas flourescens, pseudomonas fragi, pseudomonas putida, pseudomonas lundensis

What is the result of degradation of casein?

Bitter peptides are formed
What is the progression of proteases and spoilage?

Psychrotrophic proteases (enzymes) survive heat process, whey & caseins are degraded (bitter peptides formed), proteolysis continues and causes putrid off flavors

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



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