SIGNIFICANCE OF ANALYSIS OF LIPIDS
LOW L .K . & NG C .S .
Fish lip id s e x is t as p h o s p h o lip id s (tissu e fat) a n d trig ly c e rid e s (d e p o t fa ts o r n e u tra l lip id s).
D u rin g s to ra g e , fis h lip id s d e te rio ra te b y h y d ro ly s is a n d o x id a tio n .
B o th p h o s p h o lip id s a n d trig ly c e rid e s a re h y d ro ly z e d b y e n z y m e s in to fre e fa tty a c id s . T h e in d ic e s u se d fo r m e a s u rin g th e d e g re e o f h y d ro ly s is are:
i) th e p h o s p h o lip id c o n te n t ii) th e a c id v a lu e (AV)
iii) th e fre e fa tty a c id v a lu e (FFA) iv) th e s a p o n ific a tio n v a lu e (SV)
D u rin g o x id a tio n , th e h ig h ly u n s a tu ra te d fa tty a c id s o f fis h fa ts re a c t w ith a tm o s p h e ric o x y g e n to y ie ld a c o m p le x s e rie s o f c o m p o u n d s in c lu d in g a ld e h y d e s , k e to n e s , a n d a c id s o f lo w e r m o le c u la r w e ig h t. T h e s e b y -p ro d u c ts c o n trib u te to th e u n p le a s a n t ta s te a n d ra n c id o d o u r o f s p o ilt fish . E x p o s u re o f th e fis h to h e a t a n d lig h t, to m o is tu re , a n d to th e p re s e n c e o f tra c e s o f c e rta in m e ta ls (eg. c o p p e r, n ic k e l a n d iron) a c c e le ra te s th is o x id a tio n re a c tio n . T h e re a c tio n in v o lv e d m a y b e s u m m a riz e d as fo llo w s :-
C h e m ic a l p a ra m e te rs w h ic h a re u se d fo r d e te rm in in g th e e x te n t o f s p o ila g e d u e to o x id a tio n o f fish lip id s a re :-
i) th e p e ro x id e v a lu e (POV)
ii) th e th io b a rb itu ric a c id n u m b e r (TBA) iii) th e o x id a tio n in d e x
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