Alpha-Helical Structure of Fish Actomyosin: Changes during Setting

Participation of the α-helix in setting was investigated using circular dichroism. The α-helicity of the actomyosin from eight species of fish decreased during incubation at 30°C or at 40°C. The extent and pattern of decrease differed among species. When rate of decrease was plotted vs rate of increase in strength of gel preincubated at 30°C or at 40°C, the two factors correlated closely. We propose that the unfolding of α-helix initiated setting.     

Antibacterial Effect of Glucose Oxidase on Growth of Pseudomonas fragi as Related to pH

The effect of glucose oxidase (GOX) catalyzed reaction with glucose on Pseudomonas fragi was analyzed in nutrient broth and fish extract media. Growth of P. fiugi in nutrient broth was clearly suppressed by 1.0, 2.0 and 4.0 mg/mL glucose when combined with 0.5–2.0 U/mL GOX. The same GOX/glucose combinations inhibited P. frasi growth in fish extract media. Viable cell numbers in fish media showed clear growth inhibition with combinations of l.0–2.0 U/mL GOX and 8.0–16.0 mg/mL glucose. Higher GOX and glucose rapidly produced 2.0–2.5 unit decreases in pH, but produced enough gluconic acid to precipitate fish proteins. Use of 0.5 U/mL GOX in fish extract media resulted in slow, sustained activity with potential for inhibition of microbial growth in foods without excessive acidity.     

鱼鳞胶原蛋白的酶法提取工艺研究

以草鱼鱼鳞为原料,采用酶解法提取鱼鳞中的胶原蛋白,用正交实验优化提取工艺,并测定了鱼鳞的基本组成成分和鱼鳞胶原蛋白的氨基酸组成。     

淡水鱼皮胶原蛋白提取工艺研究(Ⅰ)

研究了罗非鱼、鳙鱼、草鱼和鲫鱼4种淡水鱼皮胶原蛋白的提取工艺。结果表明,鱼皮用乙醚2次除脂效果显著,除脂率依次为92.4%、95.1%、66.8%和76.7%,除脂后胶原蛋白的提取率和得率都略有增加。除非胶原蛋白的工艺为:先用NaOH浸泡6h,再用NaCl浸泡6h,4种鱼皮胶原蛋白对应的提取率分别为34.4%、28.7%、31.5%和42.5%,得率依次为8.4%、8.0%、8.2%和6.1%,比其他处理相应高出0.4-2.3倍、0.04-1.6倍、0.1-0.9倍和0.07-0.5倍。乙酸的提取效果优于柠檬酸,对应提取率分别为34.8%、23.6%、33.6%、43.0%,得率依次为8.5%、6.6%、8.63%、6.19%,比柠檬酸相应高2.4-4.3倍、1.7-4.0倍。温度对罗非鱼、鳙鱼和草鱼鱼皮胶原蛋白提取影响较大,最佳提取温度都为20℃,其对应提取率依次为34.05%、27.05%、33.38%,得率分别为8.32%、7.54%、8.58%;温度对鲫鱼鱼皮胶原蛋白的提取影响较小,在520℃范围内提取率和得率分别约为42%和6%左右。     

Effect of select parameters on the properties of edible film from water-soluble fish proteins in surimi wash-water

Edible film from water-soluble fish proteins were developed by casting film solution on leveled trays and effects of pH (9.5, 10.0 and 10.5), heating temperature (60, 70 and 80 °C), and heating time (10, 20 and 30 min) of the film solution on various film properties were determined using Response Surface Methodology (RSM). The impact of pH and heating temperature of film solution was more significant, overall, on the film's properties than heating time. Contour plots of tensile strength and elongation at break was highest at pH of 10.0 at 70 °C (2.75-3.02 MPa) but low in elongation at break (6.35-9.16%), while water vapor permeability and oxygen permeability were at their lowest (58.55-65.96 g mm/m² d kPa and 351.33-624.18 cm³ μm/m² d kPa). There was a direct correlation between the films’ and proteins’ solubility on one hand, and heating temperature of film solution on the other, which reversed with change in pH of film solution. Film color was darker and more yellowish with increase in the pH of film solution.     

Solids Extraction of Cod Frame and Effects on Ultrafiltration of the Aqueous Extract

Grinding, pH adjustment, heat treatment and centrifugation were studied to recover solids from ground cod frames and to apply ultrafiltration (UF) to the resulting aqueous phase. Early heat treatment (90°C/20 min) dissolved collagen into aqueous phase resulting in a very low UF flux. A pH adjustment to 4.5 after grinding (～0.32 cm die), with no heat resulted in efficient separation after centrifuging. UF of the aqueous phase showed an increase in initial flux (23 L/hr m²). However, when the same aqueous material was heated and then centrifuged (1–2% solids removed), UF flux was further increased to 46 L/hr m²and this process gave highest solids recovery (90%).     

Effects of storage time and chemical preservatives on the total volatile basic nitrogen content in chilean mackerel (Trachurus murphy) prior to fish meal production

Total volatile basic nitrogen (TVB-N) as a measure of protein degradation and total microbial counts or stored raw mackerel (Trachurus murphy), which had been treated with chemical preservatives, were compared with the TVB-N and microbial counts of untreated fish. In unpreserved fish, decomposition of fish protein was rapid. Treatment of mackerel with acetic (1000-5000 μg kg^?1), which was the most effective of the parameters studied, approximately halved the rate of increase in TVB-N compared with the untreated samples. Changes in the total microbial counts presented a similar trend.     

The effect of selenium on antioxidant system in erythrocytes and liver of the carp (Cyprinus carpio L.)

The effect of selenium‐supplemented diet (sodium selenate and selenium yeast) on antioxidant in erthrocytes and liver of the carp (Cyprinus carpio L.) fingerlings was studied. With this goal, the activities of glutathione peroxidase (GSH‐Px), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and glutathione‐S‐transferase (GST), as well as glutathione (GSH + GSSG) level, were determined. In the group supplemented with sodium selenate, no significant changes in the activity of the above enzymes were recorded in both the erythrocytes and in the liver, with the exception of GST activity that was significantly reduced in the plasma compared with the controls. Glutathione content was at the control level. In the group supplemented with selenium‐yeast, the activities of GSH‐Px, CAT, and SOD were significantly increased in erythrocytes, whereas GST activity and plasma content of GSH + GSSG were reduced compared with the controls. At the same time, the activities of hepatic SOD and GST were increased compared with the controls. These results demonstrate that organically bound selenium (selenium‐yeast) acts more efficiently on antioxidant system of the carp fingerlings than inorganic selenium salts.     

Use of immunological techniques for detecting species substitution in raw and smoked fish

 Immunological techniques based on double immunodiffusion and immunodotting have been designed to detect the substitution of halibut (Hippoglossus hippoglossus) for sole (Solea solea) fillets. An immunodotting technique has been also developed to differentiate between smoked cod (Gadus morhua) and smoked eel (Anguilla anguilla) fillets. Antisera raised against water-soluble extracts of raw halibut and smoked cod were employed. Antiserum to cod proteins did not show cross-reaction with eel proteins, whereas antiserum to halibut proteins cross-reacted with sole proteins. Species-specific antiserum to halibut proteins was achieved by adsorption on a polymer of sole proteins. These methods are very easy to perform and provide the basis for the development of rapid tests for detecting species substitution in fish products. Received: 18 April 1996/Revised version: 5 July 1996     

Use of cysteine to remove mercury from shark muscle

The efficiency of cysteine to remove mercury from sliced and minced shark was evaluated. Treatment with 0.5% cysteine at pH 2.0–2.5 and subsequent washing with sodium chloride (5%) failed to remove the mercury from the sliced shark. The efficiency of 0.5% cysteine at pH 7.0 in removing mercury from minced shark was 40–45% (dry material), obtained by two of the three methods studied. This removal rate was considered relatively low for it failed to attend to the practical proposal of decontaminating species of fish highly contaminated by mercury. The need for fuller understanding of the mechanisms involved in the removal of mercury by cysteine was also considered.