Fp628 nitrogen analyzer

Proximate analysis was performed on the frozen fillet samples. Moisture and ash content of catfish fillets were determined using AOAC (1990) methods #950.46, modified with lyophilization, and #923.03 [27 ], respectively. Chopped fillets were lyophilized in a VirTis Genesis 35EL freeze-dryer (SP Industries, Warminster, PA, USA), using a 7-day program and moisture content determined gravimetrically. Dried samples were placed in ceramic crucibles and incinerated in a muffle oven at 500 °C, followed by weighing to determine ash content. Nitrogen content was determined by pyrolysis with an FP628 nitrogen analyzer (Leco Co., St. Joseph, MI, USA). Protein content was calculated as 6.25 times the percent nitrogen. Total lipid content was determined gravimetrically by a modification of the Folch procedure [28 (link)] using a Dionex ASE 350 accelerated solvent extractor (Thermo Fisher Scientific, Waltham, MA, USA) where the lyophilized samples were transferred to 34 mL ASE cells and extracted with methylene chloride at 100 °C and 1500 psi into pre-weighed 60 mL vials. The solvent was removed in vacuo at 35 °C using a RapidVap Vacuum Evaporation System (Labconco Co., Kansas City, MO, USA). Moisture, ash, and lipid contents were determined in duplicate, and protein content was determined in triplicate for each replicate sample.

Proximate analysis was performed on ground samples. Moisture content was determined gravimetrically, in triplicate, after drying the sample in a 103°C oven for 24 hr. The sample was then collected and used to analyze ash and protein content. Ash content was obtained gravimetrically by heating the dried sample in a muffle furnace (Thermal Scientific Lindberg Blue M) at 550°C for 5 hr. Protein analysis was performed in triplicate using a FP628 nitrogen analyzer (LECO Co., St. Joseph, MI), and protein content was determined by multiplying the results by 6.25. EDTA was employed as the calibration standard. Pseudo lipid content was obtained by subtracting percent moisture, ash, and protein from 100. All data presented in this article were based on wet weight unless otherwise specified.