Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 20, 2006
Publication Date: N/A
Determinations of the total volatile base nitrogen (TVB-N) are routinely used to evaluate fish quality. TVB-N consists of ammonia, monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA), the levels of which are altered during spoilage by bacterial or enzymic degradation of trimethylamine oxide (TMAO). The levels of TVB-N and TMAO are different for each fish species and further differentiated within the various fish parts. In addition, TVB-N and TMAO are altered by the type of processing and time of storage. TVB-N levels have been routinely measured in fish muscles during ice storage; however, little is known about the distribution of the individual constituents in other fish parts. As the utilization of fish processing by-products increases and higher value products are produced, levels of TVB-N and TMAO become of increasing importance as a quality characteristic.
A quick and sensitive capillary electrophoretic method slightly modified from Timm and Jørgensen (2002) was used to simultaneously determine the levels of ammonia, MMA, DMA, TMA and TMAO in aqueous extracts from a variety of materials made from fish processing by-products. The instrument used was an Agilent capillary electrophoresis system equipped with a buffer replenishment system, UV/VIS diode array detector, Chem Station software, auto sampler and Agilent fused silica capillary with extended light path. Detection was made in the indirect mode by measuring the difference in absorbance at 310 nm and 215 nm for the separated compounds. Aqueous extracts were analyzed from fish by-products of several cold water fish species and included heads, viscera frames, whole fish, milt and roe. In addition, bone meal, liver meal, fish meal and freeze dried stickwater were analyzed.
TVB-N ranged from 1.46±0.45 mg/kg (n=3) in black cod heads to 157.75±23.47 mg/kg (n=3) in freeze-dried stickwater from red salmon. Ammonia was present in 100% of the samples, ranging from 1.46±0.45 mg/kg (n=3) in black cod heads to 128.10±13.65 mg/kg (n=3) in freeze-dried stickwater from red salmon. MMA was not detected in any of the samples. DMA and TMA were detected in 39% and 32% of the samples and TMAO was detected in 79% of the samples. The results suggested there is a wide distribution on the levels of TVB-N and TMAO in the materials tested. Lower levels of TMAO were detected in viscera samples in comparison to the other fish by-products; which suggested that the bacterial or enzyme make-up within viscera is degrading TMAO. Lower levels of TMAO in fish meal may indicate decomposition of TMAO or fractionation into the stickwater during processing.