Udumalebbe Abdul Majeed

ABSTRACT

Tilapia (Oreochromis niloticus) is a freshwater fish species that is widely cultured and frequently consumed in Sri Lanka. It is a good source of proteins and health improving fatty acids.

A study was carried out to investigate the impact of maturity stages (six maturity stages, weight ranging from (97.50 ± 2.12 g to 543.00 ± 12.72 g), geographical distribution, seasonal effects and processing methods on proximate composition and fatty acid profiles of Nile tilapia (O. niloticus) fillets. For maturity variation, six different sized groups of samples were selected. For assessingthe effect of geographical distribution,samples were collected from two different locations, namely, Bandarawela (Wet zone)and Mannar (Dry zone). For studying the seasonal variation, the samples were collected at one month interval over a period of six consecutive months. Smoking, boiling, and frying (in virgin coconut oil) were adopted as processing methods and compared with raw samples.

The proximate composition was assessed as described in the AOAC (1984) and the oil from Tilapia fillets was extracted according to (Bligh and Dyer, 1959). The preparation of fatty acid methyl esters (FAME) and the analysis of GC-MS were done according to (AOCS, 1992).

Proximate values of nutrients namely moisture, ash and fat contents showed a significant variation with maturity stage, geographical location, season and processing method. Significant variation (p<0.05) was observed only in n-6 FAs and n-3/n-6 ratio with respect to maturity stage. Significant variations (p<0.05) were observed in PUFAs, n-3 FAs and EPA+DHA content with respect to time (January, February and March, 2013), whereas no significant variation (p>0.1) was observed with respect to geographical locations. Significant variation (p<0.1) was observed in SFAs with respect to geographical locations, while not (p>0.1) with respect to time (January, February and March, 2013). No significant variations (p>0.1) were observed in MUFAs, n-6 FAs and n-3/n-6 ratio with respect to both geographical location and time as well. Significant variation (p<0.05) was observed in SFAs, MUFAs, PUFAs, n-3 FAs, EPA+DHA and n-3/n-6 ratio with respect to season, whereas, no significant variation was observed in n-6 FAs. Significant variations (p<0.05) were observed in PUFAs, n-3 FAs, EPA+DHA and n-3/n-6 ratio, SFAs (p<0.1) and MUFAs (p<0.1) with respect to processing methods, whereas no significant variation (p>0.1) was observed in n-6 FAs. Marginal variations in FAs were observed in smoking and boiling process, whereas, significant variations in FAs were observed in frying process. Frying in coconut oil significantly reduced the health beneficial n-3 FAs such as EPA and DHA.

Since the study showed significant variations with respect to maturity, geographical location and seasonal variation, it is suggested that Tilapia is reared in ponds under controlled conditions so that the highest benefits with respect to protein content and health beneficial fatty acids are obtained.