Lecture 3: Nutrients, pH, and Redox Flashcards
From the standpoint of nutrients, why are some food products a better medium for growth than others?
Review slides -9 and pay close attention to the differences between milk and tea. This will help you determine why bacteria are more apt to grow in milk.
What inorganic ions are important for bacterial growth/nutrition? Why?
See slide 6. HINT- One of them is important to maintain cell membranes. Which was important for DNA/RNA synthesis? Which is so crucial for bacterial growth that your body tries to sequester it during an infection?
What is the difference between total acid present and pH?
pH is the amount of ionizable hydrogens present (varies with pKa) while total acidity is the amount of all present acid regardless of ionizable hydrogens.
See Slide 12.
What are the major components of the bacterial cell and what elements do bacteria need to gather from their environment in order to synthesize these de novo (from scratch, in other words)?
Protein: Carbon, nitrogen, sulfur for cysteine and methionine
DNA/RNA: Carbon, nitrogen, phosphate (for the backbone)
What is the FDA Food Code?
A handbook providing guidance for government, food manufacturers, merchants, etc, concerning the safe preparation of food for consumers. See first paragraph: http://www.fda.gov/Food/GuidanceRegulation/RetailFoodProtection/FoodCode/
What are arguments for and against the use of gloves when preparing foods, as made by the state of California?
See link to the short article on the class website, under the links for lecture 3
What must an organism be able to do if it wants to utilize large proteins (such as caseins), carbohydrates (such as starches), or fat molecular for growth or energy?
Remember that a point I keep coming back to, is that bacteria (at least the ones we talk about in food microbiology) are unable to take up large molecules from their environment. They need to digest large molecules such as proteins, carbohydrates, and fats using enzymes such as proteases, amylases, and lipases into smaller molecules such as amino acids, glucose, and short chain fatty acids respectively, before they can transport them efficiently.
Milk is a great source of nutrients, but most are in the form of large proteins, fats, etc. How does Pseudomonas deal with this and grow in milk?
See the Pseudomonas slide, number 9, from the lecture.
What is the general pH of eggs, fish and other meats, milk, vegetables, citrus fruit, and soft drinks?
See slide 10; I’m not expecting you to know exact values, but you should appreciate for example which have neutral to slightly acidic pH’s (pH around 6-7), which are acidic (pH 2-6), and which have pH’s higher than 7.
In general, what are the pH ranges for minimal, optimal, and maximal growth for bacteria, yeasts, and molds?
See slide 11
Explain why organic acids become more antimicrobial at lower pH’s.
See slide 12. Also, there is a good explanation on page 406 (Figure 25.1) of your textbook.
How can 2 foods with the same composition have different redox potentials?
The preparation of the food can impact it’s contact with oxygen. The same food, if prepared differently, can have massively different redox values. See slide 16 for an example with steak.
What are the 6 factors that determine the redox potential of a food?
See Slide 15.
What are the preferred redox potentials for strict aerobes, fungi, facultative anaerobes, and anaerobes?
See slide 17
