Controlling the Unseen
By measuring and controlling this intrinsic property, food technologists can simultaneously minimize enzymatic browning, inhibit mold growth, and ensure a product's texture remains stable over its intended shelf life.
A. Total Moisture Content
B. Water activity
C. Refrigeration temperature
D. Packaging Atmosphere
B. Water activity
I. For quantification of yeast, plate count agar is used.
II. For quantification of molds, potato dextrose agar that is adjusted to basic pH is used.
Which of the following is correct?
A. Only I is true
B. Only II is true
C. Both I and II are true
D. Both I and II are false.
A. Only I is true
"I. For quantification of yeast, plate count agar is used."
A chef wants to create a new reduced-sugar jam. Which change is most likely to happen if the sugar content is lowered without adding another humectant (like pectin or sorbitol)?
A. Water activity will decrease, improving shelf stability.
B. Water activity will increase, making microbial growth more likely.
C. Total moisture will decrease, but water activity will remain the same.
D. Sugar type determines taste only, not water activity.
B. Water activity will increase, making microbial growth more likely.
Which of the following is NOT TRUE about water activity?
A. It is the measure of the amount of available water.
B. It is a direct measure of the total water content present in a food product.
C. It is the ratio of partial pressure of water in solution over partial pressure of pure H2O at the same temperature.
D. It is practically equal to the surrounding RH of the immediate air surrounding the product.
B. It is a direct measure of the total water content present in a food product.
A food manufacturer creates a new shelf-stable snack with a water activity of 0.87. This formulation effectively prevents spoilage from most bacteria, but the product must still be protected from contamination by this other microbial group, which can thrive at this lower water activity level. What is this microbial group?
A. Yeasts
B. Molds
C. Bacteria
D. Osmophiles
A. Yeasts
Why is a 0.85% NaCl solution specifically used when preparing a cell suspension of microbial cultures? (Sa procedure to)
A. To provide nutrients that stimulate rapid microbial growth during suspension.
B. To create a hypertonic solution that dehydrates cells for easier counting.
C. To maintain an isotonic environment that prevents cell lysis or plasmolysis.
D. To sterilize the cells by exposing them to mild salt stress.
A. To provide nutrients that stimulate rapid microbial growth during suspension.
How does the lowering of the water activity of the substrate affect the normal metabolic activities of microorganisms
A. It directly denatures all microbial proteins, causing immediate cell death.
B. It primarily encourages microbes to switch to a more efficient mode of spore formation.
C. It provides more free water, accelerating enzymatic reactions and growth.
D. It triggers osmotic stress, prolongs the lag phase, and reduces the growth rate and final cell count.
D. It triggers osmotic stress, prolongs the lag phase, and reduces the growth rate and final cell count.
What is the effect of water activity of food on microbial stability of the food products?
A. It has no significant effect, as pH and temperature are the primary controlling factors.
B. It directly denatures microbial proteins, providing a sterilizing effect.
C. It determines microbial stability by controlling free water availability, creating osmotic stress that restricts growth, with lower water activity generally increasing stability.
D. It primarily affects the color and texture of food, with any impact on microbes being incidental.
C. It determines microbial stability by controlling free water availability, creating osmotic stress that restricts growth, with lower water activity generally increasing stability.
Mingyu, a food scientist from SVT Food Inc., prepares three sweetened condensed milk samples with varying dilution levels:
1x (undiluted - full concentration) - water activity (aw) = 0.67
2× half strength:(50% H2O, 50% Condensed) aw = 0.74
4× (quarter-strength) (75% H2O, 25% Condensed) aw = 0.82
Although all samples have similar total moisture content, the 4× diluted sample exhibits the fastest yeast growth. Which explanation best accounts for this observation?
A. Dilution lowers solute concentration, reducing osmotic pressure and increasing the amount of free water available for microbial metabolism.
B. Dilution increases total moisture content, but water activity remains constant because solutes have no effect on vapor pressure.
C. Dilution strengthens hydrogen bonding between water and sugar, creating more bound water and raising water activity.
D. Dilution increases solute concentration gradients, drawing water out of cells and suppressing microbial growth.
A. Dilution lowers solute concentration, reducing osmotic pressure and increasing the amount of free water available for microbial metabolism.