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Chapter 26: Problem 8

Why do foods high in sugar concentration (jellies, jams, candies, candied fruits) resist microbial contamination? (a) Microbes do not have the necessary enzymes to break down the sugars. (b) High sugar concentrations create sufficient osmotic pressure that inhibits microbial growth. (c) Microbes prefer foods low in sugar. (d) Both a and b. (e) Both \(b\) and \(c\).

Short Answer

Expert verified
(b) High osmotic pressure inhibits growth.

Step by step solution

01

Understanding the Options

First, we read and understand each of the given options to determine which ones explain why high sugar concentration foods resist microbial contamination. Option (a) suggests that microbes lack the enzymes to break down the sugars. Option (b) suggests high sugar concentrations create osmotic pressure that inhibits microbial growth. Option (c) suggests microbes prefer low sugar foods. Option (d) combines the reasons from (a) and (b). Option (e) combines the reasons from (b) and (c).
02

Analyzing Microbial Growth Inhibition

High sugar concentrations cause a high osmotic pressure. This means water is drawn out of microbial cells, which inhibits their growth or kills them. Therefore, option (b) about osmotic pressure is scientifically correct.
03

Evaluating Microbial Preferences

The statement in option (c) that suggests microbes prefer low sugar foods is generally incorrect since microbes can thrive on sugars if osmotic pressure doesn't inhibit them. Thus, option (c) doesn't explain why high sugar foods resist contamination.
04

Confirming the Final Answer

Since option (b) is correct and explains the microbial resistance due to osmotic pressure, and option (c) isn't accurate, we review other combinations. Option (d), which includes (a) and (b), includes both enzymatic issues and osmotic pressure; however, there is no strong evidence that microbe enzymatic breakdown limits significantly. Hence, option (b) alone is the correct choice.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sugar Concentration
Sugar concentration in foods like jellies and jams plays a significant role in food preservation. High levels of sugar create conditions that make it difficult for microorganisms, such as bacteria and fungi, to grow.

This is because sugar attracts water molecules, leading to dehydration of microbial cells. Microbes need water to thrive, and when sugar binds the water molecules, it makes them unavailable to microorganisms. Therefore, the microbes cannot survive in such environments.
  • Sugar creates an environment with low water activity.
  • Microorganisms struggle to grow without accessible water.
  • Preserves the food and extends its shelf life.
Thus, foods high in sugar concentration remain safer from spoilage, extending their longevity effectively.
Osmotic Pressure
Osmotic pressure is another critical concept in understanding food preservation with high sugar concentration. This pressure arises when there's a difference in solute concentration across a semipermeable membrane, such as a microbial cell wall.

In foods with high sugar content, sugar molecules create a hypertonic environment around microbial cells. This means the concentration of sugar outside the cells is higher than inside, causing water to move out of the cells to balance the concentration.
  • Water flows from areas of low solute concentration to high solute concentration.
  • Microbial cells lose water and become dehydrated.
  • Dehydration inhibits microbial growth and activity.
Osmotic pressure effectively acts as a barrier to microbial contamination, preserving the food.
Microbial Growth Inhibition
Inhibition of microbial growth is a key outcome of both high sugar concentration and osmotic pressure. When microbial cells lose water due to the hypertonic environment created by sugars, they become unable to perform essential functions.

Without adequate water, microbes cannot transport nutrients, expel waste, or reproduce. This ultimately leads to the inhibition of growth or death of the microbes.
  • No water, no cellular processes.
  • Microbial reproduction is stalled.
  • Food remains free from spoilage-causing organisms.
This is why high-sugar foods like candies and jams are more resistant to microbial contamination, maintaining their quality for longer periods.

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Most popular questions from this chapter

Match the following microorganisms that can be found in milk to their descriptions: _____Can grow in refrigerated milk _____Causes a fecal flavor in milk _____Causes a viscous slime to form in milk _____Cause milk to sour _____Dairy herds are tested or vaccinated against these human pathogens _____Present in freshly drawn milk (a) Brucella species (b) Staphylococcus epidermidis (c) Pseudomonas species (d) Micrococcus (e) Streptococcus lactis (f) Lactobacillus species (g) Mycobacterium tuberculosis (h) Escherichia coli (i) Acinetobacter johnsoni

Which of the following methods still in use today were developed by early civilizations to preserve food? (a) Canning (b) Drying (c) Acidic conditions (d) Lyophilization (e) \(b\) and \(c\)

What is it about clams that make them especially likely sources of human infection? (a) They have sticky interiors that make microorganism attachments easy. (b) Their ability to glow with Photobacterium phosphoreum attracts pathogenic species of microorganisms. (c) They are best eaten raw. (d) They are filter feeders, obtaining food by filtering water and extracting microbes. (e) Their hard outer shell seals in and concentrates any contaminating microbes.

Which of the following is a protective measure within egg whites that protects the embryo within from microbial contamination? (a) Egg whites are filled with lysozyme that ruptures bacterial cell walls, killing them. (b) Egg whites produce antimicrobial antibodies. (c) Nutrients, vitamins, and minerals are tightly wrapped up by proteins and other substances in the egg white, rendering them unavailable for bacterial use. (d) All of the above. (e) None of the above.

Which of the following is NOT a method of food preservation? (a) Repeated cycles of freezing and thawing. (b) Drying (c) Canning with moist heat under pressure (d) Lyophilization (e) Salting foods
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