Nondestructive determination of fat content in frozen skipjack by near infrared (NIR) spectroscopy with fiber optics in interactance mode

Abstract

Nondestractive determination of fat content in frozen skipjack by near infrared (NIR) spectroscopy with fiber optics using the interactance method (400-1100 nm) was investigated. As a result of multiple linear regression based on actual fat (range 1-55%) and second derivative value of the absorbance (d2 log (1/R)), good results could be obtained when fat content analyzed using flesh from skin surface to 5 mm depth of skipjack was used as a chemical value. The highest multiple correlation coefficient of 0.91 with a standard error of calibration (SEC) of 5.8% was obtained in case of calibration equation with four optical terms including 926 nm as the first wavelength. The standard error of prediction (SEP) was 6.4% with a bias of -0.1%. This prediction accuracy was affected by thawing process, because spectrum was changed by melting of ice into water on the skin of fish. However, the fat measuring system mentioned above is still useful for a frozen skipjack.