Abstract
In the present study, Fourier‐transform infrared spectroscopy (FTIR) is investigated as a method to measure connective tissue components that are important for the quality of Atlantic cod filets (Gadus morhua L.). The Atlantic cod used in this study originated from a feeding trial, which found that fish fed a high starch diet contained relative more collagen type I, while fish fed a low starch (LS) diet contained relative more glycosaminoglycans (GAGs) in the connective tissue. FTIR spectra of pure commercial collagen type I and GAGs were acquired to identify spectral markers and compare them with FTIR spectra and images from connective tissue. Using principal component analysis, high and LS diets were separated due to collagen type I in the spectral region 1800 to 800 cm−1. The spatial distribution of collagen type I and GAGs were further investigated by FTIR imaging in combination with immunohistochemistry. Pixel‐wise correlation images were calculated between preprocessed connective tissue images and preprocessed pure components spectra of collagen type I and GAGs, respectively. For collagen, the FTIR images reveal a collagen distribution that closely resembles the collagen distribution as imaged by immunohistochemistry. For GAGs, the concentration is very low. Still, the FTIR images detect the most GAGs rich regions.
Highlights
Fish filet quality is an important factor for consumer acceptance
The current study investigates the potential of Fourier-transform infrared spectroscopy (FTIR) spectroscopy to measure connective tissue components, collagen and GAGs in Atlantic cod filets
As connective tissue distribution differs within a sample, the spatial distribution of collagen type I and GAGs was further investigated by FTIR imaging in combination with immunohistochemistry
Summary
Fish filet quality is an important factor for consumer acceptance. Gaps, tears and splits in filets are major problems for the fish industry today. Connective tissue consists of a complex threedimensional structural network of collagens, proteoglycans (PGs) and glycoproteins and has a major role in the attachment of muscle fibers and regulating tissue strength [2]. PGs are complex and multifunctional molecules consisting of a protein core with a variable number of covalently attached carbohydrate side chains, the glycosaminoglycans (GAGs) [7] They are important for the spatial organization of collagen fibers, regulating collagen fiber diameter [8, 9] and collagen crosslinking [10], and thereby indirectly the strength of the connective tissue. The current study investigates the potential of FTIR spectroscopy to measure connective tissue components, collagen and GAGs in Atlantic cod filets. As connective tissue distribution differs within a sample, the spatial distribution of collagen type I and GAGs was further investigated by FTIR imaging in combination with immunohistochemistry
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