Module 5 Flashcards
1
Q
How much of all agricultural commodities are lost each year and why?
A
- 10 - 20 %
- Weeds, insects, microbes, rodents, birds
2
Q
What does food deterioration involve?
A
- Heat, cold, light, oxygen, moisture, dryness, food enzymes, microorganisms, and macroorganisms.
3
Q
What are the 3 general categories of microorganisms?
A
- The good, the bad, and the ugly
4
Q
Which microorganisms grow fastest in foods?
A
Bacteria
5
Q
Bacteria may exist in two forms, which are:
A
- Vegetative cells - actively metabolizing cells
- Spores - dormant form
6
Q
Yeasts grow more slowly than bacteria but […].
A
- can tolerate more severe environmental conditions, for instance:
- not inhibited by pH to the same extent
- can grow in low water activity foods
7
Q
Describe moulds.
A
- Filamentous, produce spores
- Can grow on foods that have low pH and lower water activities
8
Q
Describe oxygen requirements of microbes.
A
- Aerobic - grow only in presence of oxygen
- Anaerobic - grow only in the absence of oxygen
- Facultative anaerobic - can grow in the presence or absence of oxygen
9
Q
What are psychrophiles or psychrotrophs?
A
- Grow well in cold temperatures
- Psychrotrophs are the major cause of spoilage in refrigerated foods.
10
Q
What are mesophiles?
A
- Grow well in moderate temperatures.
- Most spoilage and disease-causing organisms are mesophiles.
- Most have optimum growth temperature of 37C.
11
Q
What are thermophiles?
A
- Grow best at high temperatures
- Most are spoilage causing
12
Q
Pests are major contributors to post-harvest losses. Rodents alone ruin […].
A
> 30,000,000 tonnes of food each year worldwide
13
Q
Give examples of enzymes endogenous to foods.
A
- 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 textural change.
- You also no doubt have experienced the browning of apples, potatoes and peaches after they have been sliced and exposed to oxygen in the atmosphere. 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:
14
Q
How can enzymes be inactivated? [3]
A
- Heat
- Chemicals (e.g., antioxidants)
- Controlling the gaseous environment
15
Q
Describe the temperature effects on microbial growth and enzymatic activity.
A
- Rates of reactions generally increase as the temperature increases until an optimum is achieved, after which any further increase in temperature, causes the rates of reaction to decrease because of the inactivation of microorganisms or enzymes or because of inhibitory effects on chemical reactions.
- Excessive heat also denatures proteins, breaks emulsions, removes moisture from foods (drying out), and destroys vitamins.
- Cold temperatures can also deteriorate food. A well-known example is “chill injury”, the change in texture and discolouration of fruits and vegetables when they are exposed to freezing temperatures.
- Freezing temperatures can deteriorate liquid foods such as milk, causing emulsions to break and fat to separate, and denaturing protein causing it to curdle or coagulate. “Freezer burn” due to loss of moisture can occur in solid and liquid foods.
16
Q
Describe the effects of moisture on microbial and enzymatic activity.
A
- Water loss during storage (e.g., wilting of lettuce in the refrigerator), or water uptake (e.g., by dehydrated foods) can lead to deterioration.
- Retrogradation of starch, resulting in staling of bread, is caused by packing of linear starch molecules leading to the exclusion of water that was previously absorbed during gelatinization. The bread becomes tough and develops a dry texture.
- Changes in water activity (free versus bound water) can influence chemical and enzymatic reactions and microbial growth.
17
Q
Describe the effects of oxygen food quality.
A
- Oxygen is an important factor in food quality since many oxidative reactions lead to deterioration in the quality of food and, in some cases, to losses in nutritive value. Oxidative deterioration is often accelerated by light.
- For example, deterioration frequently occurs because of lipid oxidation in food products. The development of rancidity in breakfast cereals, vegetable oils and oil-based products, and deep-fried foods is due to the reaction of oxygen with fats, particularly those with high unsaturated fatty acid content. This type of rancidity is known as oxidative rancidity. This is in contrast to rancidity induced in foods upon the release of free fatty acids by very high temperatures or by the action of lipase enzymes, either endogenous or produced by spoilage-causing microorganisms. The latter rancidity is known as hydrolytic or lipolytic rancidity.
- Oxidation of vitamins and colour pigments can lead to the deterioration of nutritive quality and aesthetic appeal of foods.
18
Q
Describe the effects of physical deterioration on microbial and enzymatic activity.
A
- Physical abuse causes tissue disruption and release of enzymes into tissues which can lead to changes such as enzymatic browning mentioned earlier.
- Furthermore, improper packaging, for example, can cause crushing and tissue damage, making foods such as fruits and vegetables particularly susceptible to microbial invasion as well as enzymatic and chemical reactions.
19
Q
Describe the effect of time on food quality.
A
- For the majority of foods, quality will decrease with time.
- Food preservation, packaging and storage practices are aimed to maintain this quality for as long as possible (shelf life); however, eventually the quality of any food will decrease with time.
20
Q
What are perishable foods?
A
- Foods that are not processed or are only minimally processed and have a shelf-life of 60 days or less
- Spoilage is usually caused by microbial growth or senescence
- E.g., meat, leafy vegetables, soft fruits, milk
21
Q
What are semi-perishable foods?
A
- Last between 2 to 6 months as a result of some form of preservation
- E.g., ice cream, cheeses, dry snack foods
