Lipid oxidation in fillets of herring (Clupea harengus) during frozen storage. Influence of pre-freezing storage.

Fillets of herring (Clupea harengus) were kept on ice for 0, 3, 6, and 9 days prior to storage at −18 \ub0C for 0, 21, 42, 63, and 84 days. At each storage point, peroxide value (PV), absorbance at 268 nm (A268), fluorescent products (FP), α-tocopherol, glutathione peroxidase (GSH-px) activity, and ascorbic acid were measured. As shown by regression analyses, samples held for 6 days on ice formed oxidation products at the highest rate during frozen storage, followed by, for PV and FP, the 9-day samples. These data indicate that severe changes that negatively affect the oxidation process took place in the herring muscle between 3 and 6 days after catch. Both the initial antioxidant levels and the rate of antioxidant loss at −18 \ub0C decreased with increased prefreezing holding time, the latter being most obvious for GSH-px activity and ascorbic acid. α-Tocopherol showed the largest losses and had disappeared entirely from the 6- and 9-day samples at the end of the frozen storage. Partial least-squares regression analysis of the data showed that ice storage had a greater effect than frozen storage on changes in PV, A268, FP, α-tocopherol, and ascorbic acid. For GSH-px activity, frozen storage had the greatest effect

Lipid oxidation in fillets of herring (Clupea harengus) during frozen storage. Influence of pre-freezing storage.

Fillets of herring (Clupea harengus) were kept on ice for 0, 3, 6, and 9 days prior to storage at −18 \ub0C for 0, 21, 42, 63, and 84 days. At each storage point, peroxide value (PV), absorbance at 268 nm (A268), fluorescent products (FP), α-tocopherol, glutathione peroxidase (GSH-px) activity, and ascorbic acid were measured. As shown by regression analyses, samples held for 6 days on ice formed oxidation products at the highest rate during frozen storage, followed by, for PV and FP, the 9-day samples. These data indicate that severe changes that negatively affect the oxidation process took place in the herring muscle between 3 and 6 days after catch. Both the initial antioxidant levels and the rate of antioxidant loss at −18 \ub0C decreased with increased prefreezing holding time, the latter being most obvious for GSH-px activity and ascorbic acid. α-Tocopherol showed the largest losses and had disappeared entirely from the 6- and 9-day samples at the end of the frozen storage. Partial least-squares regression analysis of the data showed that ice storage had a greater effect than frozen storage on changes in PV, A268, FP, α-tocopherol, and ascorbic acid. For GSH-px activity, frozen storage had the greatest effect

Lipid Oxidation in Fillets of Herring (Clupea harengus) during Ice Storage

The influence of ice storage on lipid oxidation, odor, antioxidants, water-soluble catalysts, and microorganisms was investigated in fillets of herring (Clupea harengus) during 15 days. Based on linear regression analyses of the data, significant rises (p ≤ 0.05) in lipid oxidation products were seen after 2−3 days and in “rancid” odor after 2.5 days. Peroxide value (PV), fluorescent product (FP), and ascorbic acid analyses were the chemical measures most strongly correlated to “rancid” odor (r = 0.97). Antioxidants decreased in the following order:  α-tocopherol > ascorbic acid > glutathione peroxidase (GSH-px); however, GSH-px correlated best to the development of lipid oxidation products (rmean = −0.96). The activity of aqueous pro-oxidants, which were enzymatic in nature to a great extent, had decreased by 75% at day 15. No significant increase in total bacteria was seen until after 7 days. There were major local differences in both composition and stability throughout the fillet. Oxidation proceeded most rapidly in the tissue right under the skin, probably explained by its high initial pro-oxidative activity

Influence of skinning on lipid oxidation in different horizontal layers of herring (Clupea harengus) during frozen storage

This study was conducted to evaluate the effect of skinning and of compositional differences on the oxidative stability of various horizontal layers from herring (Clupea harengus) during frozen storage. Herring fillets, with and without skin, were stored at -18°C for 0, 3, 9, 16 and 28 weeks. After each storage period, the fillets were divided horizontally into three layers: ‘under skin’, ‘middle part’ and ‘inner part’. Each layer was then extracted for total lipids, in which peroxide value (PV), absorbance at 234 nm (A234) and 268 nm (A268) as well as lipid-soluble fluorescent oxidation products (FP) were measured. Prior to storage, the fat content, fatty acid pattern and α-tocopherol were also analysed. During storage of skinless fillets, the under skin layer increased most in PV, A234, A268 and FP (P<0·05), followed by the inner and middle parts. In fillets stored with skin, the high oxidation rate of the under skin layer lipids was suppressed, but this layer still gave rise to the highest responses. Firstly, these results point to the protective properties of the skin and, secondly, to the unfavourable composition of the under skin layer: a lot of dark muscle; the silver surface; the highest fat content and the lowest level of α-tocopherol. Concerning the fatty acid pattern in the three layers, the amount of C20: 5, C18:1 and C20:1 in the fat gradually decreased from the under skin layer towards the inner part of the fillet, whereas the opposite was true for C22: 6. © 1998 Society of Chemical Industry

Lipid oxidation in herring (Clupea harengus) light muscle, dark muscle and skin, stored separately or as intact fillets.

Light muscle, dark muscle, and skin from herring (Clupea harengus) were stored separately or as intact fillets at −18°C. After 0, 2, 8, 12, and 18 wk, all tissues were analyzed for conjugated dienes (A234) and lipid hydroperoxides. In tissues stored separately, total absorbance at 268 nm (A268) and lipid-soluble fluorescent oxidation products (FP) were also monitored. Further, prior to storage these tissues were subjected to measurement of total lipids, lipid classes, fatty acid pattern, α-tocopherol, iron, copper, selenium, and total aqueous pro-oxidative activity. When light muscle, dark muscle, and skin were stored as intact fillets, the following ranking order was seen for A234 and levels of lipid hydroperoxides at the end of the storage period: skin > dark muscle > light muscle. The corresponding ranking order for tissues stored separately was: dark muscle > skin > light muscle, whereas for A268 and FP the orders were: dark muscle > light muscle > skin and light muscle > dark muscle > skin, respectively. The compositional data obtained indicate the highest level of pro-oxidants in dark muscle and the highest level of polar lipids in light muscle. These observations reveal that pro-oxidants, to a greater extent than lipid composition, influence the increase in A234, hydroperoxides, and A268, whereas the reverse seems to be true for the increase in FP. The results also point to the strong influence from oxygen contact and tissue interactions on the progress of lipid oxidation in herring during storage

Lipid Oxidation in Fillets of Herring (Clupea harengus) during Ice Storage

The influence of ice storage on lipid oxidation, odor, antioxidants, water-soluble catalysts, and microorganisms was investigated in fillets of herring (Clupea harengus) during 15 days. Based on linear regression analyses of the data, significant rises (p ≤ 0.05) in lipid oxidation products were seen after 2−3 days and in “rancid” odor after 2.5 days. Peroxide value (PV), fluorescent product (FP), and ascorbic acid analyses were the chemical measures most strongly correlated to “rancid” odor (r = 0.97). Antioxidants decreased in the following order:  α-tocopherol > ascorbic acid > glutathione peroxidase (GSH-px); however, GSH-px correlated best to the development of lipid oxidation products (rmean = −0.96). The activity of aqueous pro-oxidants, which were enzymatic in nature to a great extent, had decreased by 75% at day 15. No significant increase in total bacteria was seen until after 7 days. There were major local differences in both composition and stability throughout the fillet. Oxidation proceeded most rapidly in the tissue right under the skin, probably explained by its high initial pro-oxidative activity

Lipid oxidation in herring (Clupea harengus) light muscle, dark muscle and skin, stored separately or as intact fillets.

Light muscle, dark muscle, and skin from herring (Clupea harengus) were stored separately or as intact fillets at −18\ub0C. After 0, 2, 8, 12, and 18 wk, all tissues were analyzed for conjugated dienes (A234) and lipid hydroperoxides. In tissues stored separately, total absorbance at 268 nm (A268) and lipid-soluble fluorescent oxidation products (FP) were also monitored. Further, prior to storage these tissues were subjected to measurement of total lipids, lipid classes, fatty acid pattern, α-tocopherol, iron, copper, selenium, and total aqueous pro-oxidative activity. When light muscle, dark muscle, and skin were stored as intact fillets, the following ranking order was seen for A234 and levels of lipid hydroperoxides at the end of the storage period: skin > dark muscle > light muscle. The corresponding ranking order for tissues stored separately was: dark muscle > skin > light muscle, whereas for A268 and FP the orders were: dark muscle > light muscle > skin and light muscle > dark muscle > skin, respectively. The compositional data obtained indicate the highest level of pro-oxidants in dark muscle and the highest level of polar lipids in light muscle. These observations reveal that pro-oxidants, to a greater extent than lipid composition, influence the increase in A234, hydroperoxides, and A268, whereas the reverse seems to be true for the increase in FP. The results also point to the strong influence from oxygen contact and tissue interactions on the progress of lipid oxidation in herring during storage