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Loss of redness (a*) as a method to measure hemoglobin-mediated lipid oxidation in washed cod mince

Artikel i vetenskaplig tidskrift
Författare Daniel Wetterskog
Ingrid Undeland
Publicerad i Journal of Agricultural and Food Chemistry
Volym 52
Nummer/häfte 24
Sidor 7214-7221
ISSN 0021-8561
Publiceringsår 2004
Publicerad vid Institutionen för anatomi och cellbiologi
Sidor 7214-7221
Språk en
Länkar dx.doi.org/10.1021/jf0307907
Ämnesord Redness; a*; lipid oxidation; cod; hemoglobin; TBARS; Hb
Ämneskategorier Biologiska vetenskaper, Lantbruksvetenskap, skogsbruk och fiske

Sammanfattning

Instrumental measurement of redness loss (decrease in a* value) was evaluated as a tool to follow hemoglobin (Hb)-mediated lipid oxidation in fish muscle. Two washed cod mince model systems were used (prepared at pH 6.5 and 5.5), both fortified with 15 μmol/kg of trout Hb and adjusted to pH 6.5 and 81% moisture. The rate of oxidation was varied through pH alterations (pH 6.1 and 6.9) and addition of an antioxidative cod muscle press juice. During ice storage, TBARS, painty odor, and a* values were followed. In all “oxidizing” samples, a* values correlated well with TBARS and painty odor development; r = −0.95 and −0.77, respectively. In press juice containing samples, the correlation was lower (0.55 for a* vs TBARS) because there was a slight a* value decrease even in the absence of measurable lipid oxidation. a* values distinguished between “oxidizing” and stable samples within 1 day, before any lipid oxidation products could be chemically detected. It was confirmed in an aqueous phosphate buffer model system that the redness loss corresponded to a buildup of brownish met-Hb at the expense of oxy- and deoxy-Hb. The a* value data were best used as a lipid oxidation index by calculating the rate of decrease (k value) in the “initial phase” of the redness loss (before accumulation of lipid oxidation products) or in the “differentiation phase” (during the exponential raise in TBARS/painty odor). Calibration to lipid oxidation products must, however, be made for each specific sample type. Washing method, pH, Hb-type, etc., all affected both k values and absolute a* readings. Small yellowness (b*) increases also occurred along with a* value losses, possibly the result of polymerized Schiff bases.

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