Report 1 (Microbiology and Engineering)

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1. INTRODUCTION

Because human food sources are of plant and animal origin, it is important

to understand the biological principles of the microbial biota associated with

plants and animals in their natural habitats and respective roles. Although it

sometimes appears that microorganisms are trying to ruin our food sources

by infecting and destroying plants and animals, including humans, this is by

no means their primary role in nature. In our present view-of life on this

planet, the primary function of microorganisms in nature is self-

perpetuation. During this process, the heterotrophs and autotrophs carry

out the following general reaction:

All organic matter

(carbohydrates, proteins, lipids, etc.)

Energy + Inorganic compounds

(nitrates, sulfates, etc.)

It is essentially nothing more than the operation of the nitrogen cycle and

the cycle of other elements. The microbial spoilage of foods may be viewed

simply as an attempt by the food biota to carry out what appears to be their

primary role in nature.

Microbiology fall into four categories; bacteria, yeasts, molds1, viruses.

MICROBIOLOGY

BACTERIA

YEAST

MOLD

VIRUS

Bacteria is the most common food-borne pathogens. Bacteria growth rates,

under optimum condition, are generally faster than those of the yeasts and

molds. Below is a few list of important microorganisms the makes food-

borne occurs.

1 A large group of fungi (like penicillium) that cause mold (as on bread or cheese). A common trigger for

allergies (http://www.biology-online.org/dictionary/Molds)

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2. MICROORGANISMS SOURCE IN THE FOOD

The microorganisms live in many medium such as air, water, soil, plant

materials, and the skin J expected to persist in soils. The bacterial biota of

seawater is essentially Gram-negative, and Gram-positive bacteria exist

there essentially only as transients. Contaminated water has been

implicated in Cyclospora contamination of fresh raspberries.,

Plants and Plant Products. It may be assumed that many or most soil and

water organisms contaminate plants. However, only a relatively smallnumber find the plant environment suitable to their overall well-being.

Those that persist on plant products do so by virtue of a capacity to adhere

to plant surfaces so that they are not easily washed away and because they

are able to obtain their nutritional requirements. Notable among these are

the lactic acid bacteria and some yeasts. Among others that are commonly

associated with plants are bacterial plant pathogens in the genera

Corynebacterium, Curtobacterium, Pectobacterium, Pseudomonas, and

Xanthomonas; and fungal pathogens among several genera of molds.

Food Utensils. When vegetables are harvested in containers and utensils,

one would expect to find

some or all of the surface organisms on the products to contaminate contact

surfaces. As more and more vegetables are placed in the same containers, a

normalization of the microbiota would be expected to occur. In a similar

way, the cutting block in a meat market along with cutting knives and

grinders are contaminated from initial samples, and this process leads to a

buildup of organisms, thus ensuring a fairly constant level of contamination

of meat-borne organisms.

Gastrointestinal Tract. This biota becomes a water source when polluted

water is used to wash raw food products. The intestinal biota consists of

many organisms that do not persist as long in waters as do others, and

notable among these are pathogens such as salmonellae. Any or all of the

Enterobacteriaceae may be expected in fecal wastes, along with intestinal

pathogens, including the five protozoal species already listed.

Food Handlers. The microbiota on the hands and outer garments of handlers

generally reflect the

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environment and habits of individuals, and the organisms in question may

be those from soil, water, dust, and other environmental sources. Additional

important sources are those that are common in nasal cavities, the mouth,

and on the skin, and those from the gastrointestinal tract that may enter

foods through poor personal hygiene practices.

Animal Feeds. This is a source of salmonellae to poultry and other farm

animals. In the case of some silage, it is a known source of Listeria

monocytogenes to dairy and meat animals. The organisms in dry animal feed

are spread throughout the animal environment and may be expected to

occur on animal hides.

Animal Hides. In the case of milk cows, the types of organisms found in rawmilk can be a reflection of the biota of the udder when proper procedures

are not followed in milking and of the general environment of such animals.

From both the udder and the hide, organisms can contaminate the general

environment, milk containers, and the hands of handlers.

Air and Dust. Although most of the organisms listed in Table 22 may at

times be found in air and dust in a food-processing operation, the ones that

can persist include most of the Gram-positive organisms listed. Among fungi,

a number of molds may be expected to occur in air and dust, along

with some yeasts. In general, the types of organisms in air and dust would

be those that are constantly reseeded to the environment. Air ducts are not

unimportant sources see the table below;

Molds are filamentous fungi that grow in the form of a tangled mass that

spreads rapidly and may

cover several inches of area in 2 to 3 days. The total of the mass or any large

portion of it is referred to as mycelium. Mycelium is composed of branches

or filaments referred to as hyphae. Those of greatest importance in foodsmultiply by ascospores, zygospores, or conidia. The ascospores of some

genera are notable for their extreme degrees of heat resistance. One group

forms pycnidia or acervuli (small, flask-shaped, fruiting bodies lined with

conidiophores). Arthrospores result from the fragmentation of hyphae in

some groups

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Table 1. eight important source of bacteria

Note: XX indicates a very importance sourcea

Primary waterb

Primary soilc

Nontuberculous

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Picture 1. Moldy bread2

Yeasts may be viewed as being unicellular fungi in contrast to the molds,

which are multicellular; however, this is not a precise definition, as many of

what are commonly regarded as yeasts actually produce mycelia to varying

degrees.

Yeasts can be differentiated from bacteria by their larger cell size and their

oval, elongate, elliptical, or spherical cell shapes. Typical yeast cells range

from 5 to 8 m in diameter, with some being even larger. Older yeast

cultures tend to have smaller cells. Most of those of importance in foods

divide by budding or fission.

Yeasts can grow over wide ranges of acid pH and in up to 18% ethanol.

Many grow in the presence

of 5560% sucrose. Many colors are produced by yeasts, ranging from

creamy, to pink, to red. The

asco- and arthrospores of some are quite heat resistant. (Arthrospores are

produced by some yeast-like fungi.)

2 http://en.wikipedia.org/wiki/File:Verschimmeltes_Brot_2008-12-07.JPG

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Picture 2. Dried yeasts3

3. MICROBIAL GROWTH

The growth of microbial population can be generalize by using the curve

below (see pic.3). an initial lag phase occurs as organism start to grow and

adapt to new environmental condition. The lag phase is very important

because the maximum extensions of shelf life and length of production run

are directly related to the length of the lag phase. Once adaption has

occurred, the culture enters into the maximum (logarithmic) growth rate,

and control the microbial growth is not possible without major sanitation or

other drastic measures. Numbers can double as fast as 20 to 30 min under

optimum conditions. Toxin production and spore maturation, if possible,

usually occur at the end at the end exponential phase as the culture enters

the stationary phase. At this time, essential nutrients are depleted and/or

inhibitory by-products are accumulated. Eventually the culture dies, the rate

depending on the organism, the medium, and the other environmental

characteristics.

3 http://en.wikipedia.org/wiki/File:Dry_yeast.jpg

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Numberofcelllogarithmic

scale

time

lag

log

stationary

death

picture 3. Typical microbial growth curve4

The growth of microorganism has their own factors which are divided into

two categories, first is intrinsic factor that are function of the food itself and

second is the extrinsic factor that are the function of environmental in which

the food is held.

4. INTRINSIC FACTOR

The parameters of plant and animal tissues that are an inherent part of the

tissues are referred to as intrinsic parameter. These parameters are as

follows:

1. Nutrient content2. Inhibitor3. pH4. Competing organism5. water activity6. Biological structuresEach of these substrate-limiting factors is discussed below, with emphasis

placed on their effects on microorganisms in foods.

4.1. Nutrient

4 1994 ASHRAE Refrigeration Handbook, p.9.1

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Like other living organism, microorganisms require food to grow. Carbon

and energy source are usually supplied in the form of sugars and starches.

Nitrogen requirements are met by the presence of protein. Vitamins and

minerals are also necessary. Lactic acid bacteria have rather exacting

nutritional requirements, while may aerobic spore formers have

tremendous enzymatic capabilities and are capable of growth on the wide

variety of substrates. Cleanable system facilitate the removal of residual

food material and deprive microorganisms of the nutrients required for

growth, thus preventing a buildup of organisms in the environment

4.2. Inhibitors

Inhibitor may be present in the food by naturally or addicted withpreservatives. Preservatives are not substitute for hygienic practices and,

with time, microorganisms may develop resistance. A cleanable system is

still essential in preventing the development of resistance population.

4.3. Competing Microorganisms

The presence of other microorganisms also affect the organisms in foods.

Some organisms produce inhibiting compounds or has fast generation times,

other are better able to use the available nutrients in a food matrix.

4.4. Water Activity

One of the oldest methods of preserving foods is drying or desiccation;

precisely how this method came to be used is not known. The preservation

of foods by drying is a direct consequence of removal or binding of moisture,

without which microorganisms do not grow. It is now generally accepted

that the water requirements of microorganisms should be described in

terms of the water activity (aw) in the environment. This parameter is

defined by the ratio of the water vapor pressure of food substrate to thevapor pressure of pure water at the same temperature: aw = p/po, wherep

is the vapor pressure of the solution and po is the vapor pressure of the

solvent (usually water). This concept is related to relative humidity (RH) in

the following way: RH = 100 aw.13 Pure water has an aw of 1.00, a 22%

NaCl solution (w/v) has an aw of 0.86, and a saturated solution of NaCl has

an aw of 0.75 (Table 2).

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Table 2. relationship between water activity and concentration salt solution

The water activity (aw) of most fresh foods is above 0.99. The minimum

values reported for the growth of some microorganisms in foods are

presented in Table 3. In general, bacteria require higher values of aw for

growth than fungi, with Gram-negative bacteria having higher requirements

than Gram positives. Most spoilage bacteria do not grow below aw = 0.91,

whereas spoilage molds can grow as low as 0.80

Table 3. Approximate Minimum awValues for Growth of Microorganisms

Important in Foods5

5 James M Jay,2005; Modern food microbiology 7 th edition,

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4.5. PH

It has been well established that most microorganisms grow best at pH

values around 7.0 (6.67.5), whereas few grow below 4.0 . Bacteria tend to

be more fastidious in their relationshipsto pH than molds and yeasts, with

the pathogenic bacteria being the most fastidious. With respect to pH

minima and maxima of microorganisms, those represented in picture 4,

should not be taken to be precise boundaries, as the actual values are

known to be dependent on other growth parameters. For example, the pH

minima of certain lactobacilli have been shown to be dependent on the type

of acid used, with citric, hydrochloric, phosphoric, and tartaric acids

permitting growth at a lower pH value than acetic or lactic acids

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Picture 4. Approximate pH growth ranges for some food-borne organisms

5. EXTRINSIC FACTORS

The extrinsic factor of that influence the growth of microorganisms are

temperature, environmental relative humidity, and oxygen levels.

Refrigeration and ventilation system play a major role in controlling these

factors.

5.1. Temperature.

Microorganisms are capable of growth over a wide range of temperature.

Minimum growth temperatures for a variety of spoilage and pathogenic

bacteria of significance in food are summarize in table 4.

Table 4. minimum growth temperature for some bacteria in foods

Organism Possible significant Approximate

min growth

temp,oC.

Staphylococcus aureus Food-born disease 10

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Salmonella spp. Food-born disease 5.5

Clostridium botulinum Food-born disease

proteolic 10

nonproteolic 3

Lactobacillus and

leuconostoc

Spoilage of cooked sausage 3

Listeria monocytogenes Food-borne disease 1

Acinetobacter spp Spoilage of precooked

food

-1

Pseudomonads Spoilage of raw fish, meats,

poultry, and dairy products

-1

The lowest temperature at which a microorganism has been reported to

grow is 34C; the highest is somewhere in excess of 100C. It is customary

to place microorganisms into three groups based on their temperature

requirements for growth. Those organisms that grow well at or below 7C

and have their optimum between 20C and 30C are referred to as

psychrotrophs. Those that grow well between 20C and 45C with optima

between 30C and 40C are referred to as mesophiles, whereas those that

grow well at and above 45C with optima between 55C and 65C are

referred to as thermophiles.

5.2. Environmental relative humidity

As previously discussed as an essential intrinsic growth factor, is also major

extrinsic factor. Environmental water acts as a vector for transmission of

microorganisms from one location to another through foot traffic or

aerosols.

5.3. Oxigen

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Microorganisms

classified by oxygenrequirement

AEROBIC

ANAEROBIC

By controlling the oxygen level to prolong storage life by retarding growth of

spoilage organisms in addition to influencing ripening processes. Vacuum

packing of food also uses this extrinsic growth factor by inhibiting the

growth of strict aerobes.

6. DESIGN FOR CONTROL OF MICROORGANISMS

DESIGN

Prevention ofContamination

Prevention ofGrowth

Destruction ofOrganisms

Prevention ofGrowth

Water control

sanitation

Humidity control

freezing

Picture 5. Food temperature chart6

High temperatures destroy most bacteria. The higher the temperature,

6 Taken fromhttp://www.doh.state.fl.us/Environment/community/food/temp.htm

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the quicker and more effective the kill. Low temperatures prevent bacteria

from reproducing.

Bacteria thrive in a temperature range from 5 degrees C to 60oC. This

range includes room temperature and body temperature. In this range

bacteria reproduce wildly and have the greatest potential for

contamination spread and infection.

Hot foods are generally cooked between 62.7 and 100oC. It is important

that center of grilled meat reaches at least 62.7oC. Verify this with a

meat thermometer. The minimum storage temperature for hot food is

160 degrees C. Cold foods should be kept at a range of -17.7 to 5oC. The

maximum storage temperature for cold food is 5 oC. Frozen foods should

be kept frozen between -17.7 and - 34oC.

In the ASHRAE standard 52.1-1992, dust has to be suppressed to prevent

the contamination of food, food is expose with air, the filtration of air is

important by using 95% filters that dust would be sufficiently removed

from the contamination. HEPA (high-efficiency particulate air) filters

provide sterile air and are used for cleanrooms.

Picture 6. HEPA filter7

7 Taken fromhttp://en.wikipedia.org/wiki/File:HEPA_Filter_diagram_en.svg