Chemical and near-infrared determination of moisture, fat and protein in tuna fishes

Moisture, protein, free fat and total fat were determined in Tuna Fishes (38) skipjack (Katsuwonus pelamis) (20) and yellow fin (Thunnus albacares) (18) by chemical methods. Moisture was determined by freeze-drying or lyophilization, oven-dry methods and by using electronic moisture analyzer. Protein content was determined using Gerhardt semi-micro Kjeldahl and combustion methods. Total fat was determined using acid-hydrolysis method and free fat was determined by Soxhlet method. Near-infrared spectra of the fishes (28) and partial least square regression with the reference methods namely lyophilization method for moisture, combustion method for proteins, acid-hydrolysis method for total fat and Soxhlet method for free fat were used to set a calibration model. This regression model was then used for quantifying the named components of the fishes (5), considered as unknowns, from their near-infrared spectra. There is a good comparison between the results from the different chemical methods and the components quantified using the near-infrared spectroscopy method. An outcome of this work is that near-infrared spectroscopy can serve as an accurate and fast method for quantifying the components of fishes.