Preservation Potentials of Essential Oils of Ocimum basilicum and Ocimum gratissimum from Two Agro-Ecological Zones on Freshwater Smoke-Dried Oreochromis niloticus Fish Sold in Some Local Markets in Cameroon

Dried fish are susceptible to bacteria and fungi attack and are liable to chemical changes which cause losses in quality and reduction of shelf-life. It is important therefore to maintain the quality of fish because continuous consumption of contaminated fish and their products may predispose consumers to health hazards. Maintenance of high quality fish therefore calls for adequate and effective preservation techniques. The study examined the effectiveness of essential oils of Ocimum basilicum and Ocimum gratissimum from two Agro-ecological zones of Cameroon in limiting the microbial proliferation and preserving the quality of smoke-dried Oreochromis niloticus fish stored at 25˚C for two months. The plant materials were harvested from the Western Highlands and Monomodal Humid Forest agroecological zones of Cameroon. Extraction of the essential oil from the plants was done by hydro-distillation. The fish species (Oreochromis niloticus) used in this study was chosen based on a survey study on the most consumed species of freshwater smoke-dried fish in the Western Highlands and Monomodal Humid Forest Agro-ecological zones of Cameroon. Heterotrophic bacteria counts, fungi counts and Enterobacteriaceae counts were used to assess the level heterotrophic bacteria, fungi and Enterobacteriaceae respectively in the fish samples during storage and were done by culture techniques using total plate count agar, potato dextrose agar and violet red bile glucose agar respectively. Total volatile basic nitrogen, peroxide value, and thiobarbituric acid reactive substance assays were used as spoilage indices to assess the nutritional quality of the fish during storage. From the survey study, Oreochromis niloticus was the most consumed smoke-dried fish in the Western Highlands (35.45%) and Monomodal Humid Forest (34.55%) agroecological zones. All the EOs caused a significant reduction in the microbial loads, total volatile basic nitrogen, peroxide value, and thiobarbituric acid reactive substance of smoke-dried Oreochromis niloticus as storage progressed. However, the reduction in these values was more pronounced in samples treated with essential oils of O. gratissimum from the Western Highlands, with heterotrophic bacteria, fungi and Enterobacteriaceae counts being 5.89, 6.97 and 4.59 log10 cfu/g respectively at the end of the storage period. This was followed by essential oils of O. gratissimum from the Monomodal Humid Forest with heterotrophic bacteria, fungi and Enterobacteriaceae counts being 6.11, 7.79 and 4.86 log10 cfu/g respectively at the end of the storage period. Also, essential oils of O. gratissimum from the Western Highlands was more effective in preserving the fish quality as lowest total volatile basic nitrogen (12.29 mg/100g), peroxide value (2.79 mEq O2·Kg−1) and thiobabituric reactive substance (1.695 mg MDA/Kg) values were observed for fish samples treated with this extract at the end of the storage period. This was followed by essential oils of O. gratissimum from the Monomodal Humid Forest with total volatile basic nitrogen (14.95 mgN/100g), Peroxide value (3.23 mEq O2·Kg−1) and thiobabituric reactive substance (2.354 mg MDA/Kg) at the end of the storage period. From the results obtained, essential oils from O. gratissimum were more effective than that from O. basilicum in the two agroecological zones and should be considered as natural alternative to chemical preservatives for further application in food preservation.

Dietary fishmeal replacement by Clostridium autoethanogenum protein meal influences the nutritional and sensory quality of turbot(Scophthalmus maximus)via the TOR/AAR/AMPK pathways

Clostridium autoethanogenum protein(CAP)is a promising protein source for aquaculture;however,how CAP influences fish quality is worth extensive research.We randomly allocated 630 turbot with initial body weights of about 180 g into 6 groups,with fishmeal-based control diet or diet with CAP replacing 15%(CAP15),30%(CAP30),45%(CAP45),60%(CAP60),or 75%(CAP75)of fishmeal protein.After a 70-d feeding trial,the fillet yield(P=0.015)and content of protein(P=0.017),collagen(P 0.05).By contrast,the muscle hardness increased linearly with increasing CAP(P=0.004),accompanied by linear reduction of muscle fiber area(P=0.003)and expression of myogenesis-related genes,including cathepsin D(ctsdP<0.001)and muscle ring finger protein 1(murf 1,P<0.001).Phosphorylation of protein kinase B(Akt,P<0.001),target of rapamycin(TOR,P=0.001),eukaryotic initiation factor 4E-binding protein 1(4E-BP1,P<0.001),and ribosomal protein S6(S6,P<0.001)decreased linearly;however,phosphorylation of AMP-activated protein kinase(AMPK,P<0.001),eukaryotic initiation factor 2α(eIF2α,P<0.001),and the abundance of activating transcription factor 4(ATF4,P<0.001)increased with increasing CAP,suggesting that the TOR signaling pathway was inhibited,and the amino acid response(AAR)and AMPK pathways were activated.Additionally,expression of genes related to protein degradation,including myogenic factor 5(myf 5,P<0.001),myogenic differentiation(myod,P<0.001),paired box 7(pax 7,P<0.001),and ctsd(P<0.001),decreased linearly with increasing CAP.In conclusion,CAP could be used to replace up to 15%of fishmeal without negatively impacting turbot quality.However,higher levels of CAP decreased fillet yield,muscle protein content,and muscle fiber diameter while increasing muscle hardness,which could be attributed to the inhibition of the TOR pathway and activation of the AAR and AMPK pathways.

Dietary xanthophyll improved growth,antioxidant,pigmentation and meat quality in the southern catfish(Silurus soldatovi meridionalis Chen)

Xanthophyll has multiple physiological functions to improve the quality of farmed animals.The present study aimed to investigate the effects of xanthophyll on the growth performance,antioxidation,immunity,pigmentation and meat quality of southern catfish(Silurus soldatovi meridionalis Chen).Juvenile southern catfish(18.35±0.04 g)were randomly allocated into 24 cages(30 juveniles per cage),and fed diets with different dietary xanthophyll levels(at 14,42,80,108,126 and 152 mg/kg,dry matter of diet)twice daily for 8 weeks.Results indicated that the diet with 80 mg/kg xanthophyll induced a higher specific growth rate(SGR),feed efficiency ratio and protein productive value.Moreover,the 80 mg/kg xanthophyll diet also increased complement 3,immunoglobulin M(IgM)and lysozyme content more than the other groups.The mRNA expression level of inflammation-related genes and antioxidant enzyme activities further confirmed the effects of 80 mg/kg dietary xanthophyll on improving immune response.The present study also found that the 126 mg/kg xanthophyll diet significantly enhanced the content of total carotenoids and xanthophyll,hydroxyproline,collagen and amino acid in muscle.The diet with 126 mg/kg xanthophylls also induced lower drip loss,thawing loss,centrifugal loss,cooking loss and higher muscle adhesiveness,cohesiveness,springiness,gumminess and chewiness than the other treatments.In conclusion,quadratic regression model analysis based on SGR and IgM revealed that the optimum xanthophyll level in the diet was 86.78 and 84.63 mg/kg,respectively.Moreover,broken line regression analysis based on xanthophyll content in dorsal skin and chewiness in muscle demonstrated that the optimal xanthophyll level was between 89.73 and 108.66 mg/kg in the diet of southern catfish(S.soldatovi meridionalis Chen).