CHAPTER I INTRODUCTION
A large proportion, of the w o r ld 's population suffers from undernutrition and m alnutrition including protein deficiency. The reason behind this disturbing fact is lack of knowledge in n u tritio n , low purchasing power, non-
flex ib le food h a b its , inadequate d is t r ib u tio n system and in su ffic ie n t food storage capacity. The Food and Agriculture Organisation (FAO) of the United Nations (Latham, 1984a) has stated that more than 500 m illio n people in the world are underfed. The most important forms of m alnutrition is
protein-energy m alnutrition (PBM) that causes yearly death to about 10 m illio n of children in the age group of 0 - 6
(Latham, 1 9 8 4 b ). The diets of a good proportion of In d ian /
population who belong to low income groups are inadequate according to FA0/WH0 food requirement pattern. The
deficien cies in the diets are both qu alitative and,
quantitative. According to a survey by National In st it u te of N u tritio n , India ( Gopalan et a l , 1 9 8 5 ) , the diets
consumed in India is' cereal based which f a i l to f u l f i l the basic caloric requirements whereas the intake of protein is m arginal. Average diet of an adult In d ia n contain 540 gm cereals, 57 gms proteins in comparison to recommended
dietary allowance of 200 gms and 66 gms, respectively.
Based on a number of surveys by the same In s t it u t e on the
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diets of children of the pre-school age (1 to 5 y e a r s ), it is concluded that diets of more than 90 per cent of the children of poor economic group are d e fic ien t in calories while the deficiency of protein is seen in 30 per cent of the children ( Gopalan et a l , 1 9 8 5 ) .
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O ilseed s, legumes and fis h are the important resources of protein rich foods. Fish is n u tritio n a lly more suitable than vegetable proteins as the former has a good amino acid balance (FAO, 1 9 8 1 a ). Fish not only supply a l l the
essential amino acids but also many of the required minerals and vitam ins. According to FAO Yearbook of Fishery
S t a t is t ic s , V o l .5 7 , 1984, the average daily Indian diet contains low amount of fis h , 3 kg per year, compared to world average of 12 kg per year. So, there is a scope for improving the n u tritio nal status of the people of In d ia by incorporating fis h protein in t h e ir d ie t .
The w o r ld 's landings of fis h have increased from less than 20 m illio n tons in 1945 to about 76 m illio n metric tons in 1983 of which about 67 m illio n metric tons are obtained from the sea (FAO Yearbook of Fishery S t a t is t ic s , Vol 5 6 , 1 9 8 4 ). Available s c ie n t if ic data indicate that world catch of fis h is expected to reach 100 m illio n tons by the end of th is century (E v e re tt, 1981 ; FAO, 1 9 7 9 ).
A ll v a r ie t ie s of marine fis h are not caught for commercial uses. For example, the a d jo in in g oceans of
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north-west Europe alone has roughly 400 species of f i s h , mostly teleosts (bony) but a maximum o f 60 species is
caught. for food (Burgess, 1 9 7 5 ). It is estimated that currently only 60 per cent of the available marine source is harvested (6egenstein, 1 9 8 6 ). The a ccep tability of fis h depend on th eir price and the socio-economic and cultural background of the consumer (Lawson, 1977)- The marine
catches excepting the few commercially important v arieties fetch poor return to the fisherman due to low demand for such items. In some cases, fish are salted and sundried on the open sea-beach but the quality of the dried product makes it unfit for human consumption. Lack of storage
f a c i l i t y , improper handling and problem of d istrib u tio n are responsible for the spoilage of a sig n ifica n t amount of marine catches (Connell et a l , 1982 ; Suzu ki, 1 9 8 1 ).
According to 'Agriculture Toward 2000* (FAO, 1 9 7 9 ), the loss /
of fis h during processing and d is t r ib u t io n is maximum in developing countries and is equivalent to 3 - 4 m illio n metric tons per year. According to a FAO review in Ceres, Vol 1 7 , N o .l (Anon, 1 9 8 4 ), about 45 per cent of the world marine resource comprise of un d eru tilized v a r ie t ie s . Another potential source of low-cost f i s h , at present wasted, is
'b y catch' f i s h - t h a t is unwanted f is h taken along with a target sp e c ie s, such as shrimp, and la t e r discarded at sea, usually dead. The same FfiO review in Ceres has reported that the s ize of the global 'by catch' is anything between 5 and 16 m illio n metric tons a year, much of it sm all.
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white-fleshed demersal f is h , which are popular for eating and more stable than small p ela g ic v a r ie t ie s . At present however, the shrimp trawlers usually are not equipped to
store and handle 'by catch' f i s h .
1 .1 Marine Fishes and Their U t i l i z a t i o n in In d ia
In d ia ranks seventh in the l is t of top f is h producing countries ( 2 .5 2 m illion metric tons in 1983) of which about 1 .5 m illio n metric tons are obtained from marine resource
(FAO, 1 9 8 4 a ). During traw ling operations for catching shrimps, which support a th riv in g export trade, over 50 per cent of the catch comprises the low-cost f is h (Bose, 1 9 6 9 )• It is d iffic u lt to get exact figures about the u t iliz a t io n of marine fis h landed in In d ia . It is roughly estimated that 30 per cent of the marine f is h are used for drying on sea-beach for human consumption although of very poor quality or for eventual reduction into f is h meal.
The important species of marine fish of India
include elasmobranches, cat f i s h , o il sardines and other sardines, Bombay Duck, sc iaen ids, mackerel, pomfrets, ribbon fis h and the s h e l lf is h (FAO, 1 9 8 4 a ). It is worth mentioning that a l l these v a rie t ie s of fis h are not low- •
cost f i s h , Bombay Duck (Harpodon nehereus) is a typical low-cost v ariety with which the present in v estig atio n was carried out. It is a cheap marine f i s h . The price of fish is Rupees (In d ia n ) 2 to 6 per kg on the coasts of Eastern
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In d ia . The amount of Bombay Duck caught in In d ia in 1983 was 8 3 ,2 3 0 metric tons (FAO, 1 9 8 4 a ). It is a ty p ic a l lean fis h (fat content less than 1 per cent) having a very high moisture,, about 90 per cent. The f i s h is small in s ize
(maximum length 25 cm) and bear, an unattractive white color.
When caught, it has a reddish tinge on the skin but becomes pale as spoilage sets in .
1 . 2 Recent Research for the Processing and U t i l i z a t i o n of Low-Cost Fish
W orld's consumption of f is h and s h e llfis h products was about 50 m illion metric tons in 1978 and this is
expected to reach 100 m illion metric tons before the end of this century (FAO, 1 9 7 9 ). The N atio nal Marine F ish er ies Service of USA (S la v in , 1981) has estimated that the demand of fish in In d i a , P h il ip in e s , Bangladesh, Thailand and
B r a zil w ill more than double in the year 2000. The basis of such estimation was the present rate of population increase in those countries.
I f food production from the sea is to be in creased, there is a need to make better use of the resource already harvested, and must use that part which is currently
unharvested (R egenstein, 1 9 8 6 ). The products from the low- cost marine fis h e s include fermented f i s h , fis h protein concentrate (F P C ), minced fis h products, textured seafood item s, expanded fis h snacks or crackers etc.
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Fermented fis h products are obtained by fermentation of the fis h and the degree of fermentation depends on
factors such a s , whether the fis h are completely or p a rtia lly gutted, proportion of salt used, fat content of f i s h , type of additive an'd temperature at which salted fis h are kept.
Such fermented fis h products are an acceptable food item only in certain countries. In Karnataka and Kerala in In d ia ,
'Colombo Cure* is the fermented fis h product from Mackerel (Tropical Products In s t it u t e , 1 9 8 2 ). .
As a bland , dry powder fis h protein concentrate
(FPC) may be incorporated into various human foods such as flo urs, cereals, baby foods, soft drinks etc (Novak et a l , 1977 ; G il l i e s , 1 9 75)* According to a patent literatu re (Whaley et a l , 1 9 6 5 ) , the protein content of the FPC may go as high as 97 per cent with a very long shelf l i f e . But the lim itation of the use of FPC is it s poor functional
property and are regarded as protein supplements rather than as food in it s own rig h ts. Early attempts has produced
something called FPC-A, now recognized as dismal fa ilu r e whereas its successor FPC-B has generated a l it t l e more enthusiasm from the point of acceptance among the under
nourished (FAO, 1 9 8 4 ) .
Minced fis h technology o ffers a hig hly promising alternative in the economic u t il iz a t io n of low-cost marine fis h (Gopaiumar, 1987 ; Grantham, 1 9 8 1 ) . Frozen minced fis h is an acceptable commodity in in te rn a tio n a l f is h .t r a d e
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(L a n ie r, 1986 ; Mandigo, 1 9 8 6 ) . Minced fish is also used for products lik e Surimi, Kamaboko etc that can serve as a base m aterial for fabricated foods like fish fin g e r s , sticks and other texturized products (L e e , 1986 ; Su zu k i, 1 9 8 1 ). The fibrous nature of the mince can be considerably improved by the process of extrusion cooking (Krishtensen et a l , 1984 ; Connell et a l , 1982) or by adding other chemical agents like starches, g e la tin and even by pre
cooking. The product of such tex tu riza tio n process are crab-stick, shrimp analogue and marine beef (S u zu k i, 1 9 8 1 ).
Minced fish is also used in several parts of the world where cereal-based t r a d itio n a l f is h products are
consumed, mainly after deep o il fry in g . Such a product is a f is h cracker or 'keropok1 in M alaysia and neighbouring
states. Sim ilar products are generally named as 'h a l f p ro d u c ts ', 'interm ediates' or expanded fish snacks in
Europe or North America (Maga et a l , 1985 ; Yu et a l , 1981) In recent y ears, a number of investig ations has been in it ia ted (Stanley et a l , 1978 ; Murray et a l , 1980 ; Das, 1981 ; Yu et a l , 1981 and Maga et a l , 1985) to develop acceptable
expanded products through extrusion of blends of minced fis h (from marine or freshwater) and cereal flours (r ic e or tapioca) or defatted soy f lo u r . The products are of good quality and are acceptable to the taste panels. Incorpora
t io n of even 25 - 35 per cent of minced fish did not impart any objectionable flavor- in those products.
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1 ,3 Extrusion Cooking
An extruder is b asica lly a screw pump which consists of a flighted Archimedes screw that rotates in a t ig h t ly f i t t i n g statio n ary s l e e v e or b a r r e l (M iddlem an, 1977) .and
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form a continuous plastic or soft m aterial through a d ie . An extruder is a machine which shapes materials by the process of extrusion (Harper, 1 9 7 9 ) . It is a v e r s a tile machine capable of performing operations like m ixing,
h eating, shaping etc in concert with' the pumping function.
Several designs are possible for extruders. The commonly used extruder contains a flig h te d screw(s) or worm(s) and the action of the f l ig h t s on the screw pushes the p lastic ized m aterial forward and creates the pressure behind the discharge end so that it extrudes through the opening.
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Extrusion cooking combines the heating of food
products with the act of extrusion to create a cooked and shaped food product. Extrusion cooking call also be d e s c r i
bed as a process whereby moistened, starchy, and/or
proteinaceous foods are cooked and worked into a v is c o u s, p la stic lik e dough. Cooking is accomplished through the application of heat, either direc tly by steam in je c t io n or in d ire ctly through jackets, and by d issip atio n of the
mechanical energy through shearing occuring w ithin the dough. The resu lts of cooking the food ingredients during
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extrusion are g e latin izatio n of sta rc h , the denaturation of protein, the inactivation o f many raw food enzymes which can cause deterioration during storage, the destruc
tion of naturally occuring toxic substances such as trypsin in hibito rs in soybean, and the diminishing of m icrobial counts in the fin a l product (Smith, 1 9 8 0 ) . The temperatures reached by the food during cooking extrusion can be quite high (200°C ) but the residence time at these elevated temperatures is very short (5 to 10 sec) such that extrusion processes are often called HTST (high
temperature/short time) process. They tend to maximize the b e n efic ial effects of heating foods while m inimizing the detrimental effects (Harper, 1 9 8 1 a ) .
The advantages of extrusion cooking lie in continu
ous processing fa c ilit y using numerous ingredients and processing conditions in an energy e ffic ie n t way (Harper, 1979 i Smith, 1 9 8 0 ) . The labor and flo o r space requirements per unit of pro duction are less than for other cooking/
forming systems enhancing cost effectiven ess (Harper, 1981a) The current variety of extruded products is impressive Examples of extrusion cooked products are precooked and
m odified starches, ready-to-eat c e re a ls, snack foods, breading su b stitu te s, beverage bases, soft-moist and dry pet foods, textured plant pro tein s, confectionary products etc (C la rk , 1986 ; Smith, 1980 ; Harper, 1 9 7 9 ).
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Some of the lim it a t io n s w ith the e x t r u s io n o f f i s h mince are
a) D esig n o f an extruder for h a n d l in g f i s h mince or fish- cereal b len d s is not a v a il a b le as most o f the food extruders in p r a c t ic e at p r e s e n t , are developed for the extrusio n o f pla*it products l ik e so y b e an , corn e t c .
M oreover, these extruders do not have the f l e x i b i l i t y to change the le n g th o f e x t r u s io n .
b) Literature for processing of blends of cereal and vegetable proteins from legumes or oilseeds is available whereas the same for cereal and f i s h protein rich food dough is lim ited . The previous researchers on extrusion of fish-cereal blends were aimed at product development only whereas basic engineering data like productivity or flow rate of extruder, power consumption and v is c o sity during extrusion are not a v a ila b le . /
The problem of extrusion of fish- cereal blends is that the effect of the process variab les ^uch as their ratio in the feed m ix, length of extruder, temperature of extrusion, ro tatio nal speed of extruder screw etc on the productivity of extruder, energy consumption and product characteristics such as rheological and textural behaviour are s t i l l largely unknown. This is also true for extrusion of plant products such as corn, wheat, r i c e , soybean etc.
The nutritio n al status such as in-vitro d i g e s t i b il i t y of the extrudate from fis h is also unknown at p r e s e n t ..
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1 .4 Scope of the Present Work
Keeping in mind of the problems o f extrusion of fish- cereal blends, the present in v estig atio n has been aimed to develop a suitable extruder for u t il iz a t io n of low-cost marine fish in production of acceptable food item s. Scope of research exists in enumerating the relationships between the process variables of extrusion and fin a l product
characteristics. These findings should help in the control of fin ish ed product accep tability with particular reference to texture. The present research may indicate a good option for the better use of marine resources.
1«5 S p ecific Objectives of the Present Research
The present research has been in it ia t e d with the broad objective of using the low-cost marine fishes lik e Bombay Duck in generating a protein r ic h food. The sp ecific objectives are
a) development of a food extruder fo;c production of fish-cereal blended food for human consumption b) mathematical modelling of the output of the
extruder
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c) effect of process v ariab les (length to diameter
ratio of screw i . e . length of extrusion, blend ratio temperature o f.e x t r u s io n and ro tational speed of screw) on
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i) expansion, bulk density and breaking strength of the dry extrudate
i i ) energy consumption
i i i ) rheological properties of extrudate dough such as apparent v is c o s it y , flow behaviour index and consistency coefficient
iv) textural properties such as hardness,
cohesiveness, springiness and chewiness of the product when it is wetted/rehydrated , A
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d) changes in the microstructure of extrudate by processing
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e) n u t ritio n a l status of the developed product.
f) determination of the s u it a b ilit y of the extruded products as fish cracker and f is h analogue.
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Emphasis has been made on process engineering of extrusion and on the textural and physical properties of the developed food whereas lesser attentio n is paid to technological d e tails of product development and n u t r i
tio n a l status of the extrudate.
