| 1. |
- Undeland, Ingrid, 1968, et al.
(författare)
-
Comparison between methods using low-toxicity solvents for the extraction of lipids from herring (Clupea harengus)
- 1998
-
Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072 .- 0346-718X. ; 61:3, s. 355-365
-
Tidskriftsartikel (refereegranskat)abstract
- Three alkane/alcohol/water-based lipid extraction systems were evaluated to determine which would be the best replacement for the frequently used chloroform/methanol/water system, nowadays known to be very toxic. All the methods were applied to samples of minced herring (Clupea harengus) differing in quality and composition. In addition to comparisons of total lipid yield, the extracted lipids were compared with respect to content of triglycerides, phospholipids, free fatty acids, ?-tocopherol, lipid hydroperoxides and conjugated dienes. The content of phospholipids was found to differ most between the lipids extracted by the four methods. Here, the chloroform/methanol/water system was the most efficient, followed by heptane/ethanol/water/sodium dodecyl sulphate (SDS) and then iso-propanol/hexane. However, by decreasing the level of SDS, the efficiency of the heptane/ethanol/water/SDS system in extracting phospholipids was increased to the same level as that of the chloroform/methanol/water system. This decrease in SDS also resulted in a higher recovery of free fatty acids. The lack of correlation between yields of phospholipids and yields of lipid oxidation products throughout this study was surprising because of the often-described susceptibility of phospholipids to oxidation.
|
|
| 2. |
- Undeland, Ingrid, 1968, et al.
(författare)
-
Lipid Oxidation in Minced Herring (Clupea harengus) during Frozen Storage. Effect of Washing and Precooking
- 1998
-
Ingår i: Journal of Agricultural and Food Chemistry. - 0021-8561 .- 1520-5118. ; 46, s. 2319-2328
-
Tidskriftsartikel (refereegranskat)abstract
- A 23 factorial experimental design was used to investigate the effect of washing in combination with precooking on the oxidative stability of lipids in minced herring (Clupea harengus) at −18 °C. The following variables were studied: washing (no, yes), cooking time (38, 54 min), and cooking temperature (55, 100 °C).The responses monitored were peroxide value (PV), absorbance at 234 nm (A234), absorbance at 268 nm (A268), and lipid soluble fluorescent products (FP). A partial least-squares regression analysis (PLS) revealed that the best lipid stability was obtained at minimum cooking time and at lower temperature. On the basis of compositional analyses and in vitro experiments, this finding was proposed to be due to heat inactivation of catalytic enzymes, without simultaneous activation, for example, of hemoproteins. Washing reduced these benefits from precooking by removal of pro-oxidative enzymes and also through a reduction in the amount of antioxidants as well as a relative increase in phospholipids and free fatty acids in the fat.
|
|
| 3. |
- Undeland, Ingrid, 1968, et al.
(författare)
-
Lipid oxidation in fillets of herring (Clupea harengus) during frozen storage. Influence of pre-freezing storage.
- 1999
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 47:5, s. 2075-2081
-
Tidskriftsartikel (refereegranskat)abstract
- Fillets of herring (Clupea harengus) were kept on ice for 0, 3, 6, and 9 days prior to storage at −18 °C 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 °C 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.
|
|
| 4. |
- Undeland, Ingrid, 1968, et al.
(författare)
-
Lipid Oxidation in Fillets of Herring (Clupea harengus) during Ice Storage
- 1999
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 47:2, s. 524-532
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
