Quality of Water and
Ice for Seafood Processing
Water and ice are used for a number of purposes in fish
handling and processing. In fish handling, water is mainly used for washing the
raw material and the containers in which it is packed. In fish processing,
water is used for washing the raw material, utensils, equipments, processing
hall etc. It is used for glazing frozen fish, preparation of brine and ice
manufacture. Water is also used in boilers and in heating /cooling systems. Ice
used for chilling for fish during handling and at different stages of
processing. Thus, fish handling and processing require a copious supply of
potable water. On an average, 10-12 tones of water will be needed to process on
tone of shrimps. The impurities present in the water and ice influence the
quality of the finished product adversely.
Significance of
examination of water
Water is examined mainly for three types of characteristics: Physical,
chemical, and bacteriological.
1.
Physical characteristics
The main Physical characteristics for
which water is examined are colour, turbidity, odour, taste and pH.
a.
Colour and turbidity
Some of the colors encountered in water and
the probable reasons for these colours are presented in Table-1.
Colour
Probable reasons
Yellow and brown organic matter
Yellowish brown tint Traces of iron
Reddish brown Peat
Green Algae
Brown
Colloidal manganese and iron
Various colors industrial waste
Undissolved materials in water
include inorganic substances such, as rock dust, clay, ferric hydroxide,
calcium carbonate etc. and organic substances such as vegetable and animal
matter, oils, fats, grease and microorganisms.
Size of undissolved materials may be
in the colloidal range or as large as grains of sand. The larger granules
settle down rapidly in quiescent water and are seen as sediment while the more
finely divided particles remains suspended and are responsible for turbidity. Water used for fish handling and processing
should have no noticeable colour or turbidity.
b. Odor and taste
Potable water should be of such a quality that it produces neither taste
nor odor. Although the presence of odor is always accompanied by the presence
of taste, it is possible for waters for waters to possess taste without odor.
When this occurs it is usually due to the presence of an excess amount of
certain saline and/or mineral constituents. The tastes due to the constituents
are presented in Table2.
Saline or mineral constituents ` Taste
Common salt Brackish
Sodium sulphate Saline
Iron, Manganese, Aluminum sulphate Bitter
Or excess lime
The Presence of hydrogen sulphide
imparts odor to the water. Contact with painted surface such as bituminous
linings of tanks gives rise to taste and odor to water. Contamination by organic matter from Sewage,
manure, soil and vegetation imparts taste and odor to water. Growth of living
matter such as algae, fungi etc. in water produce taste and odor.
c.
pH
pH of water is an indication of acidity or
alkalinity of water. The pH range is
0-14. Seven is neutral pH. As the pH comes down from seven, the acidity
will increases. Similarly as the pH goes up from seven alkalinity of the water
will increases. Water can be divided
into 3 distinct classes on the basis of the pH value. They are,
1. pH 8 and above. The water in this group contains no free
carbon dioxide but carbonate, with or without bicarbonate.
2. pH above 4.5 but below 8. The water
in this class contains no carbonates, but contains free carbon dioxide and
bicarbonates.
3. pH 4.5 and below . The water in this
class contains some free acids besides carbon dioxide.
Water having pH above 8.5 and below 4.5 are generally corrosive. Sewage
and sewage effluents are generally neutral or faintly alkaline. Factory
effluents are often acidic.
2. Chemical
characteristics
Chemical characteristics may be
divided into four groups; main mineral constituents, constituents relating to
the organic quality of water, metals and toxic substances.
a. Main mineral constituents
Main characteristics under this group
are total dissolved solids, hardness, alkalinity, chlorides and sulphates.
An estimation of total dissolved
solids affords a valuable check on the result of more detailed analysis. Total
dissolved solids also give information with regard to the quality of water.
When large blocks of ice are prepared, the minerals dissolved in the water tend
to concentrate in the central part, which, when solidified, becomes undesirably
cloudy in appearance. Removal of the central part before solidifying and
replacement by fresh water can be resorted to as a means of obtaining uniformly
clear blocks. The total dissolved solid content should not exceed 300ppm for
clear transparent ice.
Hardness of
water is due to the presence of bicarbonates, sulphates and chlorides of
calcium and magnesium. Disadvantages of hard water are soap wastage, the
production of adherent slime or curd in wash basins, baths and on textiles,
being laundered and the formation of scale or fur in boilers, hot water pipes
and household utensils.
Alkalinity above 100 ppm adversely
affects the quality of the frozen prawn products, the defect being bleaching on
cooking.
In most
waters, the whole of the chloride is present in combination with sodium as
sodium chloride. Near the sea the influx of sea water is indicated by an
increase in chlorides and hardness.
b.
Constituents relating to the organic quality of the water
The characteristics in the group are
free and saline ammonia, albuminoid ammonia, nitrite, nitrate etc.
Almost all
the natural water contains traces of ammonium salts. By distillation of such
water the ammonia is carried over in the distillate. This ammonia is free
ammonia (free and saline ammonia). A further quantity of ammonia can be
obtained by adding a strong alkaline solution of potassium permanganate to the
concentrated water and continuing the distillation. This is albumininod ammonia
which is produced by the oxidation and hydrolysis of the nitrogenous organic
matter present in the water.
Some of the sources from where free and saline
ammonia may be derived are the following: Rain water contains traces, the first
fall containing the most. All fertile Soils and all decaying vegetable and
animal matter contain free ammonia. Nitrifying organism convert free ammonia
into nitrates, while ferruginous sands convert nitrates into ammonia. Urine of
man and animals yields large quantities of ammonium carbonate; hence sewage is
rich in free ammonia.
Estimation
of albuminoid ammonia is the most sensitive chemical test for organic
pollution, when taken in conjunction with the free and saline ammonia, nitrate
and nitrite contents. The free ammonia and albuminoid ammonia contents should
be considered together, since their relative proportion is more important than
the actual quantities. The reasons are discussed below. In all sewages and many
sewage effluents, the amount of free ammonia greatly exceeds that of the albuminoid
ammonia. In the crude sewage, the free ammonia is 2.5 times more than albuminoid ammonia. Hence,
in many cases, sewage, pollution is indicated when a natural or untreated water
yields more free ammonia than albuminoid ammonia. Decaying vegetable matter in water yields
more albuminoid ammonia than free ammonia. During chlorination, if organic
matter is present in water, its demand must be satisfied before any chlorine is
available for germicidal action. Presence of free and saline ammonia in amounts
more than traces cause considerable retardation of sterilization.
Nitrates are
present in most waters. Their only concern with purity and wholesomeness
relates to considerations of pollution by sewage or manure, since they may be
derived from the oxidation of nitrogenous organic matter of animal origin. The
more efficient the progress of sewage purification, the less is the amount of
nitrogen as free ammonia and the greater the amount of nitrogen as nitrites and
nitrates.
c. Metals
The characteristics under this group are iron,
manganese, zinc and copper. Iron in excess of 0.3 ppm can cause water to appear
as rusty. Poisoning due to manganese in water is rare. Zinc salts are poisonous
only in very large doses. Copper salts in natural surface waters occur in trace
amounts. Their presence beyond this level is an indication of pollution.
d. Toxic substances
The main characteristics in the group are fluoride, cyanide, lead,
arsenic, chromium, silver, selenium, cadmium and barium. As these substances
are toxic, they should not be present in more than permitted levels in water
and ice used for fish handling and processing.
3 .Bacteriological
examination of water
Contamination by sewage or faecal
matter is the greatest danger associated with drinking water. If such
contamination has occurred and if, among the contributors there are carriers of
infectious diseases; the water can cause diseases such as typhoid and
dysentery. Sewage-polluted water may also contain the viruses of poliomyelitis
other viruses of the enterovirus group, or the virus of infectious hepatitis.
Animals and birds may carry intestinal organisms pathogenic to man. The use of
contaminated water for the preparation of food may allow the multiplication of
intestinal pathogens and hence is harmful.
The direct search for the presence
of specific pathogenic bacteria or viruses in water is impracticable for
routine control purposes. Pathogens present in water are usually outnumbered by
the normal intestinal organisms. These pathogens tend to die out more rapidly.
It is possible to isolate pathogens from water but their isolation and
identification are comparatively time consuming. The isolation of viruses is
more difficult and requires lengthily procedures. Bacteriologists have
therefore evolved simple and rapid tests for the detection of normal intestinal
organisms such as Coliforms, faecal streptococci and clostridium perfringens (clostridium welchii). These organisms are
easier to be isolated and identified. The presence of normal faecal organisms
in a water sample indicates that pathogens could be present.
The organism most commonly used as
indicators of faecal contamination are the Coliform group as a whole, and
particularly Escherichia coli which
is the most frequent type of Coliform organism present in human and animal
intestine, numbering more than 100 million per gram of fresh feaces. The distribution of Coliform organisms in
nature suggests that they may all be primarily faecal organisms but that
outside the body, types other than E. coli have greater chance of survival and
can multiply in certain circumstances.
The greatest value of the test for
faecal streptococci lies in assessing the significance of doubtful results from
the test for Coliforms, particularly the occurrence of large numbers of Coliforms,
in the absence of E. coli. The presence of streptococci would confirm
the faecal origin.
The test for Clostridium perfringens has uses similar to that for faecal
streptococci. Clostridium perfringens forms spores which survive for a much
longer time than the vegetative organisms of the Coliform group. The presence
of clostridium perfringens in natural
water indicates that faecal contamination has occurred. In the absence of E. coli the occurrence of clostridium perfringens in water
together with other Coliform organisms suggests that faecal pollution has not
been recent.
Standards
Most of the uses of water in food industry
necessitate certain standards of quality.
In many cases, water of the standard of public supplies is quite
satisfactory. But for certain industries, water of more specialized nature is
required. A comparison of the India
Characteristic Tolerance
Food
industry Ice manufacture
1.
Colour
(Hazen units), Max. 20 5
2.
Turbidity
(Units), Max. 10 5
3.
Odor None None
4.
pH 6.5
to 9.2 6.5
to 9.2
5.
Total
dissolved Solids 1000 1000
Mg/L,
Max.
6.
Alkalinity
(as CaCO3) - 100
Mg/L, Max.
7.
Total
Hardness (as CaCO3) 600 600
Mg/L, Max.
8.
Sulphate
(as SO4), 200 200
Mg/L, Max.
9.
Fluoride
(as F), Mg/L, Max. 1.5 1.5
10. Chloride (as CI), Mg/L, Max. 250 250
11. Cyanide (as CN), Mg/L, Max. 0.01 0.01
12. Selenium (as Se), Mg/L, Max. 0.05 0.05
13. Iron (as Fe), Mg/L, Max. 0.3 0.3
14. Magnesium (as Mg), Mg/L, Max. 75.0 125
15. Manganese (as Mn), Mg/L, Max. 0.2 0.2
16. Copper (as Cu), Mg/L, Max. 1.0 1.0
17. Lead (as Pb), Mg/L, Max. 0.1 0.1
18. Chromium (as C+6), Mg/L,
Max. 0.05 0.05
19. Zinc (as Zn), Mg/L, Max. 15.0 15.0
20. Arsenic (as As), Mg/L, Max. 0.2 0.2
21. Nitrate (as N), Mg/L, Max. 20 -
22. Phenolic substances 0.001 0.001
(As C6H5OH),
Mg/L, Max.)
No comments:
Post a Comment