Rational for Food Preservation Flashcards
What causes about 10-20% of all agricultural commodities lost each year (pre-harvest deterioration)?
Weeds, insects, microorganisms, rodents and birds.
All foods (agricultural & aquatic products) undergo varying degrees of deterioration after harvest (post-harvest) and during storage.
True or false?
True
What kinds of deterioration happens to food?
Losses occur in the nutritional value, safety, and aesthetic appeal (colour, texture, flavour).
Food is subject to physical, chemical and biological deterioration.
Food deterioration involves: heat, cold, light, oxygen, moisture, dryness, food enzymes, microorganisms and macroorganism.
What is the objective of food preservation technologies?
To delay the onset of spoilage and to enable the creation of new food products from the resource commodities.
What are the good, the bad, and the ugly microorganisms?
Which microorganisms contribute to producction of fermented foods?
Microorganisms can be put to good use for the production of fermented foods, but that they can also be the causes of spoilage and food borne diseases.
Bacteria, yeasts and moulds may contribute to production of fermented foods, as well as food spoilage and food borne disease.
Viruses although not considered true microorganism they can be agents of food borne disease but do not cause food spoilage, nor are they used to produce fermented foods.
What microorganism grow fastest in food?
Bacteria
What two forms do bacteria exist in?
- vegetative cells, which are actively metabolizing cells, consume nutrients and produce waste products.
- spores, which are the dormant form of the bacterial cell. The spore is analogous to the seed of a green plant. All of the genetic material is contained within the spore. When favourable conditions are encountered, the spore germinates and produces an actively metabolizing bacterial cell capable of cell division).
How do yeasts reproduce?
Budding
Compare yeast to bacteria.
They generally grow more slowly than bacteria but can tolerate more severe environmental conditions than bacteria.
For example yeasts are not inhibited by pH to the same extent as bacteria
Yeasts can grow in many foods with low water activity that would normally inhibit growth of bacteria
Some yeasts are used to produce fermented foods and beverages.
Compare mould to yeast.
Moulds are filamentous and are also found on most foods of agricultural and aquatic origin. Most moulds produce spores.
Like yeasts, moulds can grow on foods that have a low pH and also in foods with low water activities that would inhibit growth of bacteria and yeasts.
Some moulds are used in the production of mould-fermented foods (e.g. mould ripened cheeses), but most moulds are agents of food spoilage and many also produce toxins (mycotoxins) under favourable conditions.
What is clostridium botulinum?
In food preservation and processing, the spores of Clostridium botulinum, an anaerobic bacterium, are of great concern because the spores are very heat resistant.
Clostridium botulinum is also the group of bacteria that produces the toxin that causes the very serious illness, botulism.
How are microorganisms characterized?
On the basis of temperature ranges and oxygen requirements over which growth occurs.
What is a thermophile?
Thermophiles grow best at high temperatures.
Most thermophilic organisms are spoilage-causing.
What is a mesophile?
Mesophiles grow well in moderate temperatures.
Many mesophiles have an optimum growth temperature of 37°C.
Most spoilage and disease-causing organisms are mesophiles.
What are psychrophiles and psychrotrophs?
Psychrophiles grow well in cold temperatures, while Psychrotrophs have adapted to living and multiplying in cold environments.
Psychrotrophs are the major cause of spoilage in refrigerated foods
What type of microorganism grows only in the presence of dissolved oxygen?
AEROBIC
grow only in the presence of dissolved oxygen
(Bacteria, yeast, mould)
What kind of microorganism grow only in the absence of dissolved oxygen?
ANAEROBIC
grow only in the absence of dissolved oxygen
(Bacteria)
Which microorganism can grown in the presence or absence of oxygen?
FACULTATIVE ANAEROBE
can grow in the presence or absence of oxygen
(Bacteria, yeast)
What are pests?
Pests are major contributors to post-harvest losses
Rodents alone ruin >30,000,000 tonnes of food each year worldwide
Insects are believed to destroy 5-10% of the U.S. grain crop annually, and in some parts of the world this figure can be as high as 50%
Pests will damage the food and open it to microbial contamination
Rodent, insect and bird control are important factors in the agriculture and food industries.
What are parasites?
Parasites can cause damage to food quality.
An example is the visible appearance of parasitic cysts in fish flesh which lowers the quality and market value of infested products.
Parasites such as Trichinella spiralis in pork and Anisakis species in some types of fish can also cause health problems in humans if they are ingested through inadequately cooked or improperly processed foods, infested with those parasites.
Give an example of deterioration of food quality by enzymes.
The softening of fruit tissue and the changes in flavour and colour during storage after picking are examples of deterioration of food quality by enzymes.
It is enzymatic action that causes the softening of apple tissue during storage, with texture changing from that of a crisp apple to a somewhat soft and mealy apple with a concomitant loss of sweetness.
Enzymes in the apple tissue degrade pectins that cement the cells together, leading to the textural change.
What causes the browning of apples?
This browning phenomenon is known as enzymatic browning and is catalyzed by an enzyme known as polyphenol oxidase which catalyzes the oxidation of colorless phenols in the tissues to brown colored compounds, as shown in the following equation:
How can enzymes be inactivated?
Enzymes can be inactivated by means of heat, chemicals (e.g. antioxidants), and by controlling the gaseous environment.
