FISH(FOOD OF ANIMAL ORIGIN) DETERIORATION & THE PRESERVATION PRINCIPLES

FISH DETERIORATION

Fish tissue is more perishable than animal tissue. This is because the proportion of connective tissue proteins in fish is 3-5% lower than that of meat and 8-10% lower than that of stockfish.

Also, the denaturation temperature of fish connective tissue collagen is much lower than the corresponding beef protein.

The fish myosins also denature much more rapidly than beef or chicken myosins kept under the same conditions.

Besides, fish struggles when caught and use up virtually all the muscle glycogen. Consequently, the lactic acid content of the muscles necessary to exert preservative action becomes depleted.

As soon as fish dies, it begins to deteriorate.

Fish flesh contains between 0.2-2.0% of trimethylamine oxide (TMAO). This compound is an odour precursor and is broken down by spoilage bacteria after death to trimethylamine (TMA), dimethylamine (DMA) and monomethylamine (MMA). TMA is the main contributor to the smell of stale fish.

Four main factors are responsible for fish spoilage. These factors are:

1. Autolysis:  
Autolysis usually precedes bacterial spoilage and involves the breakdown of protein and lipids to amino acids and fat by muscle enzymes.

The amino acids produced are used by microbes for proliferation.

2. Activity of micro-organisms: 
This is the chief cause of decomposition of fresh unprocessed fish muscle.

While the flesh of healthy live fish is generally sterile, large numbers of bacteria are harboured in the surface slime and digestive tracts of living fish.

When the fish is killed, these bacteria attack the constituents of the tissues and grow relatively rapidly, resulting in the production of off-flavours and odours such as TMA.

3. Chemical deterioration: 
The fats of fish are highly unsaturated and become easily oxidized. This results in rancid off-odours and flavours.

Furthermore, the fats of fish contain phospholipids rich in trimethylamine oxide.

TMA is split from the phospholipids by bacteria and natural fish enzymes to produce a strong fishy odour.

4. Attack by insects: 
Flesh flies, blow flies and various beetles attack fish and cause considerable deterioration.

Troublesome scavengers such as mice, rats, hawks, cats, owls, dogs and crows eat up fish and obnoxious vermins like bugs, fleas, lice etc. Feed on fish flesh and contaminate it with bacteria, resulting in a rapid deterioration in the quality of the fish.


THE PRESERVATION PRINCIPLES

As soon as fish dies, it begins to deteriorate. This natural process is irreversible and the preservation principle is to slow down the deterioration, and increase the overall quality and storage life of the fish.

The general principles involved in the preservation include:

1. Scrupulous cleaning and hygiene in handling the fish caught.

2. Rapid and effective processing by:
a). Reducing the moisture content by drying, salting and smoking.

b). Lowering the temperature by rapid freezing to at least -10°c in not more than two hours.

c). Glazing to prevent drying.

3. Good packaging, storage and transport practices: Storage of frozen fish at -18 to -22°c is adequate to preserve the quality for up to 18 months.


REFERENCES

Fox, B. A. and Cameron, A. G. (1989). Food Science, Nutrition and Health. 5th ed. Edward Arnold; A division of Hodder & Stoughton, London.

Ihekoronye, A. I. and Ngoddy, P. O. (1985). Integrated Food Science and Technology for the Tropics. Macmillan Publishers, London.

CASSAVA(FOOD OF PLANT ORIGIN) TOXICOLOGY

Cassava contains the cyanogenic glucoside, linamarin and lotaustralin; linamarin being present in quantity up to 90% of the total.

These are hydrolyzed by the enzyme, linamarase to yield free hydrogen cyanide. In the intact cassava tissue, linamarin is separated from the enzyme linamarase.

Cyanide is exceedinly toxic to man and domestic animals if consumed in amounts in excess of 25-30ppm.

Cassava tubers must therefore be detoxified and the liberated cyanide subsequently eliminated before consumption.

The elimination of cyanide in different cassava-based foods is based on the fact that free cyanide is both water soluble and heat volatilizable while bound cyanide can be converted by enzyme or heat hydrolysis to give water soluble, heat volatilizable hydrogen cyanide.

The detoxification mechanism involes: (1) The conversion of bound cyanide to free cyanide by enzyme and heat hydrolysis.
(2). The removal of free cyanide by repeated leaching with water and by heat volatilization.

The various process steps associated with the detoxification of different cassava-based products include:
1. Grating which exposes the glucoside to linamarase for hydrolysis to prusic acid.

2. Fermentation, during which linamarin and lotaustralin are broken down into harmless components.

3. De-watering, which eliminates a substantial quantity of hydrogen cyanide.

4. Cooking and heat toasting, which can also destroys hydrogen cyanide.

Residual cyanide in most cassava products can be neutralized by the enzyme, rhodanase- an organic catalyst found in human cells.

Vitamin B12 from food of animal origin can also neutralize residual cyanide.

With cystine obtained in the diet, the human body is also capable of counteracting hydrogen cyanide.

The consumption of cassava products with high levels of cyanide over a long period has been linked to ailments such as "tropical ataxic neuropathy" and "goitre".


REFERENCES

Adeyemi, I. A. and Balogh, E. (1985). Biotechnology in Food Processing: Prospects in Nigeria. Nigeria Food Journals vol 2, nos 2&3.

Brownsell, V. I., Griffith, C. J. and Eleri, J. (1992). Applied Science Food Studies. Longman Scientific & Technical; UK

DAY 18, 5 ESSENTIAL WISDOM TOOLS FOR A FRUITFUL LIFE

1. Your beliefs don't make you a better

person but your behaviour does.


2. Believe in your dreams and they may come

 true. Believe in yourself and they will come

true.


3. Success is the ability to go from one failure to another with no

loss of enthusiasm.


4. Forget what hurt you but never forget what it tought you.


5. Don't think outside the box but think like there is no box.


GOD BLESS. 

USEFULNESS OF MILK - FOOD OF ANIMAL ORIGIN

Milk is the clean, lacteal secretion of the mammary glands of mammals that is colostrum free. It is a complex mixture of diverse compounds necessary for the nourishment of the young mammal during the period after birth.

Milk and milk products supply almost one-third of the world's intake of animal protein.

COMPOSITION AND NUTRITIVE VALUE OF MILK

The average composition of milk can vary quite considerably between different species of mammals. The factors responsible for this variation include the species of the animal, breed of the animal, stage of lactation, age of the animal, season of the year, feed, time of milking, period of time between milking, and the physiological condition of the animal. These factors also affect the quality of the milk.

Milk composition may also be affected by adulteration with water or other materials, the action of bacteria, lack of agitation during sampling and similar factors.

Nutritionally,  milk is an excellent source of good quality protein and calcium which are necessary for growth and sound bone and teeth development of children.

Milk fat is cherished both as cream and as the main component of butter.

It is palatable, highly digestible and assimilable.

Milk is the only food in which lactose is found naturally.

It is used as a constituent in infant foods and medicinal products.

Milk is rich in various minerals and vitamins including vitamins A and D, thiamin, riboflavin, pyridoxin, biotin, niacin, pantothenic acid, etc.

Fresh milk contains about 87.1% water in which are dispersed milk sugar, lipoprotein, calcium salts and other minor components.

Small amounts of ascorbic acid are also present in raw milk.

PHYSICAL PROPERTIES OF MILK

Physically, milk is both a dilute emulsion, a coloidal dispersion and a true solution. Its physical properties are essentially those of water, modified somewhat by the concentration and state of dispersion of the solid constituents.

Milk has a buffering capacity that maintain its pH at about 6.5 to 6.7 and its titratable acidity at 0.14 to 0.18 percent.

The density which varies between 1.0260 and 1.0320 depends on the fat composition and to a lesser extent on dissolved gases such as Carbon IV oxide and Nitrogen which are present in freshly drawn milk to the extent of 4-5%.

Casein is the major component of milk affecting viscosity. However, fat contributes considerably to viscosity depending on the amount and size of the globules. Lactose, proteins and salt make small contributions to viscosity.

The refractive index, freezing point and boiling point are affected by dissolved substances in the milk. These increase the refractive index and boiling point but depress the freezing point of milk.

Surface tension and interfacial tension are affected by protein, phospholipids, fat, free fatty acids and treatment that change the concentration of these substances.

CHEMICAL CONSTITUENTS OF MILK

The principal constituents of milk are protein(mainly casein), fat, milk sugar(lactose), minerals and other miscellaneous factors. These vary in amounts for different animal species.

PROTEIN: 

The main protein in milk is casein, representing about 80% of the total milk protein in coloidal suspension.

It also contains small quantities of lactalbumin (0.5%) and lactoglobulin (0.06%).

In fresh milk, casein exists as calcium caseinate - a complex calcium: calcium phosphate suspension of casein miscelles.

Casein may be precipitated out in form of calcium paracaseinate from milk by treating with dilute acid or by heating under pressure.

Casein is used to improve the whipping property of cream topping from vegetable fat to improve the body of yogurt and sour cream.

LIPIDS: 

The lipid fraction of milk is composed primarily of fat although there are also small amounts of sterols, phospholipids, the fat soluble vitamins A and D, carotenes and xanthophyll.

The main sterol found in milk is cholestrol which occurs to the extent of about 0.015%.

Lipids are significant in milk system because:
(i) they are active emulsifying agents and (ii) they are rich in unsaturated fatty acids and easily oxidized giving rise to the "oxidized" flavour of milk and the "richness" flavour of milk products.

MILK SUGAR(LACTOSE): 

Lactose is the principal carbohydrate in milk. It has a solubility of only about 20% at room temperature.

Lactose is readily assimilated as food, being hydrolysed into glucose by the enzyme lactase.

In souring of milk(fermentation), lactic acid bacteria convert lactose to lactic acid, thus giving the soured milk its characteristics flavour.

Some individuals lose the ability to digest lactose and become lactose-intolerant due to a deficiency of the enzyme lactase in the intestinal mucosa as they grow older.

The phenomenon is more common among adult Africans, American Indians and Asians.

MINERALS:  

Milk is noted for its abundant supply of minerals. The major minerals contained in milk are calcium, phosphorus, potassium, sodium, magnesium, chlorine and sulphur.

Traces of other minerals such as aluminium, boron, zinc, manganese and silicon are also present.

It is however deficient in copper and iron as the presence of these minerals would catalyse oxidation thereby producing a metallic or oxidized flavour.

Calcium is the chief mineral in milk. As calcium phosphate, it forms a part of the casein particle and influences its behaviour towards precipitation with rennin, heat and acids.

VITAMINS AND ENZYMES:

Milk is a fairly good source of the water soluble vitamins B and C, the fat soluble vitamins A, D, E, K.

Also present in milk are the enzymes: phosphatase, lipase, catalase, peroxidase, protease, diastase, amylase and lactase.

Phosphatase and peroxidase are useful as indices of heat of treatment.


REFERENCES

Campbell, J. R. and Marshall, R. T. (1975). The Science of Providing Milk for Man. McGraw-Hill Book Co. NY.

Egbekun, M. K. (1997). Food Biotechnology in Sustenable Food Production and Food Security in Nigeria. Proc 28th Annual Conf. Nutri. Soc. Nigeria.

Fox, B. A. and Cameron, A. G. (1989). Food Science, Nutrition and Health. 5th ed. Edward Amold; A division of Hodder & Stoughton, London.

Passmore R. and Eastwood M. A. (1987). Human Nutrition and Dietetics. 8th Ed. Churchill Livingstone, London.

Pyke M. (1981). Food Science and Technology. 4th Ed. John Murray, London.

DAY 17, 5 ESSENTIAL WISDOM TOOLS FOR A FRUITFUL LIFE

1. Your  significance is not in

your similarity to another, but

in your point of difference from

another.

- MIKE MURDOCK


2. A merry heart does good like

 a medicine.

- HOLY BIBLE


3. People are always blaming their circumstances for what they

are. The people who get on in this world are the people who get

up and look for the circumstances they want and, if they can't

find them, make them.

- GEORGE BERNARD SHAW


4. Resolving a problem will relieve your stress more quickly and

effectively than just complaining about it.

- KEITH HARRELL


5. The broken become masters at mending.

- MIKE MURDOCK


DO HAVE A BLESSED DAY.