Volatile compounds of Baltic herring analysed by dynamic headspace sampling–gas chromatography–mass spectrometry

European Food Research and Technology - The effect of storage time at 6&;nbsp;°C on the volatile compounds of Baltic herring was studied using the dynamic headspace–gas...     

Production and frozen storage of minced Baltic herring (Clupea harengus membras)

The production and storage of minced Baltic herring was investigated to develop a convenient semi-finished product which could be manufactured industrially and stored frozen as such or in the form of pre-manufactured convenience foods. Baltic herring has several disadvantages as a raw material for such use, namely small size, dark colour, strong odour, and soft texture. Dark colouring of the mince can be reduced considerably by skinning. The dark pigments of the belly lining are eliminated on filleting. The strong odour which evolves when Baltic herring is heated can be moderated by adding a small amount of suitable protein such as milk protein. This addition also has a positive influence on the water binding capacity and taste of the mince. The texture is improved by adding barley or wheat starch or possibly by pre-texturing part of the mince by heating to give a heterogeneous structure. Fish are skinned prior to mincing and 0.1–0.2% ascorbic acid or sodium erythorbate is added as antioxidant. The mince is vacuum packed in a gas-tight material such as polyethylene/polyamide laminate. In this way it is possible to store frozen minced Baltic herring at ?25 °C for at least one year. Even after such a period the mince is still quite acceptable and no rancidity or peroxides can be detected. Although it appears that certain adverse protein changes cannot be avoided during frozen storage, their effects can be masked in part by adding milk protein, starch and triphosphate to increase the water-binding capacity and generally improve the functional properties of the mince and mince-based products.     

Studies on fish muscle protein. Nutritional consequences of the changes occurring during frozen storage

Samples of cod, whiting, herring, lemon sole and skate muscle were frozen and stored at ? 8°C for up to 20 months. Samples of cod muscle were also stored at ? 30°C. During storage at ?8°C the decrease in the solubility of the muscle proteins in 5% NaCl (denaturation) was most rapid in whiting followed in order by skate, cod, herring and lemon sole. Little change was detected in the NaCl solubility of cod muscle protein stored at ? 30°C. An increase in the pH was found to occur in all the species examined. The relationship between these changes and the toughening that occurs in fish muscle during frozen storage is considered. No nutritionally significant decrease in the lysine availability or the in vitro digestibility of the muscle proteins was found to occur in any of the species examined. In whiting, lemon sole and skate very small, statistically significant, increases in the available lysine content were detected after 7 months of storage at ?8°C and this may indicate that unfolding of the protein chains had occurred.     

Trace metals in herring from the southern Baltic, 1983

The cadmium, lead, copper, zinc, iron, manganese and nickel concentrations have been determined in muscle tissue of 187 herring (Clupea harengus) netted in different regions in the southern part of the Baltic Sea. The method of measurement was atomic-absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for herring muscle tissue were: 0.009 Cd, 0.079 Pb, 0.49 Cu, 9.2 Zn, 9.9 Fe, 0.19 Mn and 0.10 Ni. Some differences in the concentration of particular trace metals between herring stocks sampled have been observed. The mean content of cadmium and lead in muscles of herring examined were below recommended tolerance levels of 0.05-2.0 and 0.5-2.0 mg/kg, respectively. A small number of herring contained cadmium in their muscles at a concentration above 0.05 mg/kg. The results are compared with values reported previously for Baltic herring by other authors.     

Trace metals in muscle tissue of fish taken from the southern Baltic

The determination of Fe, Mn, Ni, Pb, Cu, Co, Zn and Cd was investigated on 123 samples of muscle tissue of cod, herring, sprat and some other species of fish caught in 1981 in the southern Baltic Sea. The ranges and mean levels of metals recorded in this paper are compared with values reported previously by other authors for cod, herring and sprat from different regions of the Baltic Sea. The correlation coefficients between the metal concentrations in cod and herring muscles were calculated. The species-dependent changes of some metals in species analysed were observed.     

Optimisation of conditions for precipitation of collagen from solution using κ-carrageenan. Studies on collagen from the skin of Baltic cod (Gadus morhua)

The effects of the concentration of collagen (0.025–3%), extracted from the skins of Baltic cod (Gadus morhua) and the concentration of κ-carrageenan (0.04–1%), in the presence of NaCl (0–5%), on the yield of precipitated collagen fibrils at 0 °C and at pH 2.2–8 were determined. The yield of precipitated collagen was directly proportional to the ratio, κ-carrageenan to collagen, within the range 0.015–0.4. Collagen dissolved in citric acid could be completely precipitated using κ-carrageenan if the weight ratio of dry reagents was 1:0.4 within a protein concentration of 1.5–0.08%. The maximal yield of precipitated collagen fibrils using κ-carrageenan could be achieved in the pH range 2.2–3. In this range of pH, the presence of NaCl in the system did not affect the efficiency of precipitation of collagen fibrils with κ-carrageenan. The yield of precipitated collagen was lower at 20 °C than at 0 °C.     

Some comments on the usefulness of 2-thiobarbituric acid (TBA) test for the evaluation of rancidity in frozen fish

Rancidity of frozen fish (Baltic cod and herring, mackerel, horse mackerel and hake) was determined by means of TBA value, organoleptical scoring and peroxide value. The correlation between the rancid odour sensory assessment and TBA test results proved insignificant (r = 0.53). Model experiment was undertaken in which promine D with addition of papain was incubated at 50°C over 44 h. It was shown that as accumulation of protein hydrolysis products proceeded the increase of TBA value has taken place without development of rancid odour and with peroxide content below sensibility of sulphocyanide method. With regard to fish, therefore, it seems that the TBA test applied by means of techniques in which the reaction with TBA proceeds in the presence of interfering substances should be treated as a ?freshness test”? rather than a strictly rancidity one.     

Organochlorine pesticides and polychlorinated biphenyls in herring from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC, HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in muscle tissue of 187 herring (Clupea harengus) netted during 1983 in a different regions in the southern part of the Baltic Sea. The mean levels found for herring muscle tissue related to wet weight (microgram/kg) were: 14 HCB, 18 alpha-BHC, 23 beta-BHC, 14 gamma-BHC, delta-BHC remained undetected, 56 sigma BHC, 115 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 84 p,p'-DDD, 51 p,p'-DDT, 250 sigma DDT and 530 PCB. The levels of organochlorine pesticides determined in wet muscles or extractable lipids of herring are nearly 2-3 times as high as those noted in fish sampled in the same area in two years before, whilst for PCBs the wet weight levels were comparable, and when based on a lipid weight are somewhat higher. The results are compared with levels found in herring collected in different regions of the Baltic Sea during 1965-1983, and reported previously by other authors.     

Thermal Denaturation and Aggregation of Proteins in Minced Fish as Studied by a Thermomechanical Method

A thermomechanical method of heating and mixing, was developed to study directly protein denaturation and aggregation in minced fish. It is based on simultaneous and continuous measurement of torque and temperature in a meat sample mixed while being heated. The torque and temperature were continuously recorded. From curves thus obtained, thermal denaturation temperatures of minced samples from 6 marine fish species were determined. The curves showed 4-6 peaks at 32-38°C, 44-46°C, 52-56°C, and 62-75°C, presumably corresponding to denaturation of myosin, actomyosin, sarcoplasmic proteins, and actin, respectively. The temperature range of peak 1 was 4-5°C higher in fatty fish (herring, mackerel) than in lean fish (cod, blue whiting).     

Trace metals in herring from the southern Baltic, 1983

Summary The cadmium, lead, copper, zinc, iron, manganese and nickel concentrations have been determined in muscle tissue of 187 herring (Clupea harengus) netted in different regions in the southern part of the Baltic Sea. The method of measurement was atomic-absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for herring muscle tissue were: 0.009 Cd, 0.079 Pb, 0.49 Cu, 9.2 Zn, 9.9 Fe, 0.19 Mn and 0.10 Ni. Some differences in the concentration of particular trace metals between herring stocks sampled have been observed. The mean content of cadmium and lead in muscles of herring examined were below recommended tolerance levels of 0.05–2.0 and 0.5–2.0 mg/kg, respectively. A small number of herring contained cadmium in their muscles at a concentration above 0.05 mg/kg. The results are compared with values reported previously for Baltic herring by other authors.

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Spurenelemente im Hering aus der südlichen Ostsee, 1983

Zusammenfasung Die Konzentrationen von Cadmium, Blei, Kupfer, Zink, Eisen, Mangan und Nickel wurden in den Geweben von 187 Heringen (Clupea harengus), in verschiedenen Regionen der südlichen Ostsee mit Netz gefangen, bestimmt. Als Meßmethode wurde die Atomabsorptions-Spektrometrie verwendet. Die mittleren Werte, bezogen auf das Frischgewicht, waren: 0,009 mg/kg Cd, 0,079 mg/kg Pb, 0,49 mg/kg Cu, 9,2 mg/kg Zn, 9,9 mg/kg Fe, 0,19 mg/kg Mn und 0,10 mg/kg Ni. Es wurden Differenzen in der Konzentration der Spurenelemente, zu denen aus verschiedener Herkunft gesammelten, beobachtet. Der mittlere Gehalt von Cadmium und Blei lag unter den empfohlenen Toleranzen von 0,05–2,0 mg/kg und 0,5–2,0 mg/kg. Eine kleine Zahl der Heringe enthielt Cadmium in Konzentrationen über 0,05 mg/kg. Die Ergebnisse wurden mit den vorangegangenen und denen anderer Autoren verglichen.

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Partially with financial support under grant PR-4 (Sea Fisheries Institute)     

Frozen herring as raw material for spice‐salting

One batch of herring (Clupea harengus) was spice‐salted fresh and as thawed after 32 days of frozen storage at −24 °C. After salting, samples of both groups were sent to participating laboratories in Iceland, Denmark, Norway, Germany and England. The herring was kept at 5 ± 1 °C and sampled three times during a 26 week storage period. The development of taste and texture characteristics (determined by sensory evaluation and instrumental texture measurements), formation of low‐molecular‐weight nitrogen compounds and changes in proteolytic activity were followed in both groups. The sensory evaluation results showed that thawed salted herring ripened in a similar manner to herring salted fresh, but at a faster rate. Instrumental texture analysis showed a faster rate of tenderising in thawed salted herring. Proteolytic activity measured as general activity and with specific synthetic substrates was higher in the thawed salted herring. The formation of trichloroacetic acid‐soluble nitrogen and free amino acids was faster in the previously frozen herring. The results show an accelerated but similar rate of ripening in thawed spice‐salted herring in comparison with fresh salted herring. © 2000 Society of Chemical Industry     

Predicting effects of exploitation rate on weight-at-age, population dynamics, and bioaccumulation of PCDD/Fs and PCBs in herring (Clupea harengus L.) in the Northern Baltic Sea

The Baltic Sea ecosystem and fish stocks contain high concentrations of environmental chemicals such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs). This study forecasts how changes in fishing or natural mortality would probably influence concentrations of PCDD/F and PCB in the Bothnian Sea (Northern Baltic) herring (Clupea harengus L.). An age-structured simulation model was developed to forecast herring stock dynamics, catches, and weight-at-age under different assumptions about exploitation and natural mortality. The simulated herring weight-at-age estimates were employed in a bioenergetics model capable of simultaneous estimation of bioaccumulation of 17 PCDD/F and 37 PCB congeners. Although the natural variability in recruitment greatly influences the stock dynamics, considerable changes in weight-at-age would ensue changes in exploitation rate or in natural mortality rate. If exploitation rates increase, growth rates would be higher and herring in the weight categories of commercial fisheries would be younger and contain less PCDD/F and PCB. Hence, the average toxicant concentrations in catches would also decline. However, it is likely that only fairly small changes would occur in toxicant concentrations-at-age. On the other hand, a drastic decrease in herring fishing would substantially increase PCDD/F and PCB concentrations in herring. The study indicated that, in spite of the clear influences of fishing on the toxicant concentrations, fishing alone cannot resolve the problems associated with a high concentration of toxicants in herring; further decreases in loading are still required.     

Lipid Hydrolysis in Frozen Baltic Herring

SUMMARY— The lipid composition of Baltic herring ( Clupea harengus var . membranus) muscle and the hydrolysis during freeze storage was studied with thin-layer chromatography. The concentrations of the various lipid classes were initially 2–5 times as high in dark muscle as in white muscle. Storage for up to 12 weeks at –15°C resulted in an increase of the free fatty acid content from 50 to 1000 mg/100 g in the dark muscle, and from 17 to 280 mg/100 g in white muscle. The increase was due to hydrolysis of lecithin, cephalin and to a varying extent also of triglycerides. According to indirect estimations, roughly 45 and 75% of the free fatty acid formed in dark and white muscle respectively was a result of phospholipid hydrolysis; the remainder of triglyceride hydrolysis. The hydrolysis of lecithin was faster than that of cephalin in both types of muscles. The enzymatic attack showed no preference for anyone of the different fatty acids in the phospholipids.     

Thermal Aggregation of Myosin Subfragments from Cod and Herring

Turbidity of fish myosin subfragment solutions increased with temperature, except cod heavy meromyosin turbidity leveled above 45°C. Extent of aggregation and number of cross-linking sites for cod heavy and light meromyosins were significantly higher than for herring (p<0.05), but only at temperatures above 35°C and 45°C, respectively. Thermal aggregation ability increased linearly with increased surface hydrophobicity (S_o) for the myosin subfragments, except cod heavy meromyosin where the increase in S_o between 45–55°C did not correspond to an increase in cross-linking ability. The lessened aggregation ability of herring myosins may be due to the low cross-linking of the HMM (S-2) region.     

Influence of freezing and of frozen storage on the specific heat capacity of trout and herring fillet

Effects of freezing and frozen storage on the specific heat capacity difference of native (not heat denatured) and heat denatured fillet () of trout and herring have been studied for the first time. Single and double freezing of fillet induced a clear reduction of the of up to 15 mJ g⁻¹ K⁻¹ at each freezing step. Frozen storage at −20 °C reduced the of herring fillet but not of trout fillet. This is in agreement with the earlier detected instability of myosin transition temperature of herring and the stability of myosin transition temperature of trout [1]. The is suggested as a new parameter for the evaluation of protein stability at freezing and frozen storage of fish. It has been shown, that a reversible endothermic effect between 2 and 22 °C in herring fillet is accompanied by a decrease of the storage modulus in the chopped fillet, which characterises the flexibility of the proteins. This mechanical change and the endothermic signal are missed in the chopped trout fillet at heating from 2 to 22 °C. This cold, reversible relaxation of fish proteins can be understood as a requirement for subsequent protein denaturation at frozen storage.     

Isolation and some properties of collagen from the backbone of Baltic cod (Gadus morhua)

Ossein from Baltic cod backbone was obtained after extraction of non-collagenous protein with 0.1 M NaOH solution and demineralization with 1.0 M HCl solution. The extractions were performed at 4 °C for 24, 48 and 72 h using a solid/solution ratio from 1:4 to 1:8 (w/v). After 48 h of extraction in 0.5 M acetic acid only about 25% of collagen was dissolved. After 48 h of extraction at optimal concentration of pepsin (4 mg/g ossein) the collagen was dissolved almost completely. Collagen solubilized in acetic acid could be almost completely precipitated with κ-carrageenan, at protein/polysaccharide ratio 1:1 (w:w). The denaturation temperature of Baltic cod backbone collagen was 14.4 °C and the conversion factor of hydroxyproline to collagen was 15.7.     

Tissue distribution of perfluorinated surfactants in common guillemot (Uria aalge) from the Baltic Sea

Perfluorinated alkyl surfactants (PFAS) were investigated in tissues and organs of the common guillemot (Uria aalge) from the Baltic Sea. Concentrations of 11 perfluorinated carboxylates, four perfluorinated sulfonates, and perfluorooctane sulfonamide were determined in egg, liver, kidney, and muscle of adult guillemot, as well as in liver from chicks, all sampled in 1989. Additionally, whole herring homogenates from 2005 were analyzed, herring comprising a large part of guillemot's diet. Quantifiable concentrations of PFAS were found in all samples. Perfluorooctane sulfonate (PFOS) was predominant, followed by perfluorotridecanoate (PFTriDA) and perfluoroundecanoate (PFUnDA). The median concentration of PFOS was highest in eggs (325 ng/g wet weight (w wt)) followed by chick liver (309 ng/g w wt), kidney (127 ng/g w wt), adult liver (121 ng/g w wt), and muscle (14 ng/g w wt). Comparatively low levels of PFOS were found in herring, leaving a blurred picture of uptake routes. PFAS concentrations in livers of male and female guillemots did not differ significantly. Some PFAS showed higher concentrations in eggs than in female livers. The ratio of levels in egg/female liver, indicating mother-to-egg transfer capacity, increased with increasing PFAS chain length. PFOS showed a higher tendency for transfer than carboxylates of carbon chain lengths C9-C13.     

Fish, fishing, and pollutant reduction in the Baltic Sea

The Baltic Sea is heavily polluted yet supports major commercial fisheries for cod (Gadus morhua), herring (Clupea harengus), and sprat (Sprattus sprattus). Emissions of persistent organic pollutants, such as polychlorinated biphenyls (PCBs) and DDT, were high during the 1960s and 1970s, and concentrations in fish and other fauna are still significant. Several models of the fluxes of these pollutants among the water, sediment, and atmosphere have been developed, but these generally omit the roles of fish and fisheries. We show that the standing stock of the most abundant fish species in the Baltic Sea was a sink for 260 kg of PCBs in the late 1980s to early 1990s and that the fishery removed as much or more PCB (31 kg yr(-1))than other budget components (e.g., degradation in the water column). Accounting for fish and fisheries could increase our understanding of the fluxes of pollutants, and banning the discard of highly contaminated organs such as cod liver could be part of the pollution management.