Levels of polychlorinated biphenyls and pesticides in bluefish before and after cooking

Similar levels of polychlorinated biphenyls (PCBs), pesticides, and fat were found in 20 correlated uncooked and cooked (baked) bluefish fillets. Fillets averaged 2.5 ppm PCBs as Aroclor 1254 (whole basis) before cooking; after cooking, with the oil drippings and skin discarded, the average PCB level was 2.7 ppm. Although PCBs, lipophilic pesticides, and fat were lost along with oil drippings and skin that were discarded after cooking, the moisture loss in the fillets during cooking compensated for these weight losses almost completely. After the fillets were cooked and the oil drippings and skin were discarded, the PCB content of the fillets was 27% lower on the average.     

Extracellular production of a functional soy cystatin by Bacillus subtilis

A recombinant Bacillus subtilis producing soy cystatin was developed by subcloning with a soy cystatin gene cloned in Escherichia coli. An active form of cystatin against the cysteine protease from Pacific whiting fillets contaminated with Myxosporidia parasite was constitutively expressed and secreted extracelluarly into the medium. Two gene fragments of signal peptides from kerA and sacB were introduced and compared for secretion efficiency of cystatin. The secretion level of active cystatin improved with the signal peptide of kerA when compared to that of sacB. Inhibitor activity was reduced rapidly after peak expression of the target protein at 36 h of fermentation. The addition of 1% glucose, a suppressor of protease, into the medium sustained the increase of the cystatin activity during fermentation. This study introduced a potential new method for fermentation production of cystatin.     

Optimizing angiotensin I-converting enzyme inhibitory activity of Pacific hake (Merluccius productus) fillet hydrolysate using response surface methodology and ultrafiltration

The in vitro angiotensin I-converting enyzme (ACE) inhibitory activity of Pacific hake hydrolysates was investigated as a function of hydrolysis conditions, starting material variability, and ultrafiltration. Hake fillets were hydrolyzed using Protamex protease under various conditions of pH, hydrolysis time, and enzyme-to-substrate ratio (% E/S) according to a response surface methodology (RSM) central composite design. The hydrolysate produced at pH 6.5, 125 min, and 3.0% E/S had an IC 50 of 165 +/- 9 microg of total solids/mL. ACE-inhibitory activity was not significantly different (P < 0.05) for hydrolysates produced using higher time-enzyme combinations within the model or from fish of different catches. Ultrafiltration (10 kDa molecular mass cutoff) resulted in an IC50 value of 44 +/- 7 microg of peptides/mL, 2.5 times more potent than the commercial product PeptACE Peptides (IC50 = 114 +/- 8 microg of peptides/mL). These results suggest that hydrolysates prepared with minimal fractionation from Pacific hake, an undervalued fish, may be a commercially competitive source of ACE-inhibitory peptides.     

Effect of a low-density polyethylene film containing butylated hydroxytoluene on lipid oxidation and protein quality of Sierra fish (Scomberomorus sierra) muscle during frozen storage

Fresh sierra fish (Scomberomorus sierra) fillets were packed in low-density polyethylene films with butylated hydroxytoluene (BHT-LDPE) added. Fillets packed in LDPE with no BHT were used as controls (LDPE). The packed fillets were stored at -25 degrees C for 120 days in which the film released 66.5% of the antioxidant. The influence of the antioxidant on lipid and protein quality, lipid oxidation, muscle structure changes, and shear-force resistance was recorded. As compared to LDPE films, fillets packed in BHT-LDPE films showed lower lipid oxidation, thiobarbituric acid values (4.20 +/- 0.52 vs 11.95 +/- 1.06 mg malonaldehyde/kg), peroxide values (7.20 +/- 1.38 vs 15.15 +/- 1.48 meq/kg), and free fatty acids (7.98 +/- 0.43 vs 11.83 +/- 1.26% of oleic acid). Fillets packed in BHT-LDPE films showed less tissue damage and lost less firmness than fillets packed in LDPE. A significant relationship between lipid oxidation and texture was detected (R2 adjusted, 0.70-0.73). BHT-LDPE films may be used not only to prevent lipid oxidation but also to minimize protein damage to prolong the shelf life of sierra fish.     

Physicochemical properties of natural phenolics from grapes and olive oil byproducts and their antioxidant activity in frozen horse mackerel fillets

The reducing and chelating capacities and the affinity for the incorporation into the fish muscle of grape procyanidins, hydroxytyrosol, and propyl gallate were studied together with their antioxidant activity in frozen horse mackerel (Trauchurus trauchurus) fillets. Fillets were supplemented with phenolic antioxidants by (a) spraying an aqueous phenolic solution, (b) glazing with an aqueous phenolic solution, and (c) a previous washing of fillets with water plus spraying an aqueous phenolic solution. The effect of washing on the endogenous pro-oxidant/antioxidant balance of the fillets was also determined. All phenolic compounds were effective delaying lipid oxidation in the fish fillets. The order of antioxidant efficiency in spraying and glazing was propyl gallate > hydroxytyrosol > procyanidins, which was similar to the reducing power of these phenolics, but did not show any correlation with their chelating capacity and their affinity to the fish muscle. Washing the fillets with water prior to spraying phenols increased synergistically the antioxidant activity of grape procyanidins and changed the relative antioxidant efficiency to propyl gallate approximately procyanidins > hydroxytyrosol. This synergism may be a result of a better distribution of the procyanidins onto the fillet surface because of the residual water that remained on the fillets surface after washing.     

Distribution of amylose,nitrogen, and minerals in rice kernels with various characters

The distribution of chemical constituents is known not to be even within a rice kernel. To improve the eating quality of rice or to give it some special traits by adjusting the milling intensity, we investigated the distribution of amylose, nitrogen (N), and specific minerals (P, K, Mg, Ca, and Mn) in rice kernels of 11 cultivars with various characteristics cultivated under similar conditions. The distributions of these constituents were determined using flour samples prepared consecutively by abrasive milling from the outer to the inner portions of hulled rice. In all the cultivars tested, N and the minerals were found to be more abundant in the outer than in the inner portion, but amylose was rich in the inner portion. P, Mg, K, and Mn were extremely rich in the outer portion, while N and Ca were only relatively rich there. Koshihikari, which is the most popular cultivar in Japan because of its excellent eating quality, showed the highest Mg/K ratio in the outermost portion of polished rice. The color of flour samples became pure white going from outside portions toward the center of the kernel, even if the sample was from red rice or purple-black rice because only the surface of hulled rice contains pigments. These findings suggest that the outer portion contains various compounds other than starch and the inner portion contains relatively pure starch. Rice palatability and other characteristics can be improved through controlling the degree of milling using the biased distribution of chemical constituents within a rice kernel.     

喷射蒸煮技术在制备易消化玉米浓缩蛋白中的应用

为了提供一种具有良好消化性的玉米蛋白,该研究以玉米黄粉(corn gluten meal,CGM)为原料,利用亚临界脱脂及酶解超滤技术制备了一种蛋白纯度较高的玉米浓缩蛋白(corn protein concentrates,CPC),并重点考察了制备过程中喷射蒸煮对玉米浓缩蛋白功能性质及消化性的影响。研究结果表明,经喷射蒸煮处理后的玉米浓缩蛋白(jet cooking corn protein concentrates,JC-CPC),普通高温处理的玉米浓缩蛋白(heat treatment corn protein concentrates,HT-CPC)以及未经高温处理的玉米浓缩蛋白(CPC),三者在蛋白质质量分数及氨基酸组成上无明显差异(P0.05)。但JC-CPC的溶解性及功能性质(持水性、起泡性及泡沫稳定性)均显著高于CPC和HT-CPC(P0.05)。体外模拟消化试验结果表明,JC-CPC的水解度(24.02%±0.49%)明显高于CPC和HT-CPC(分别为9.23%±0.45%和14.52%±1.26%)(P0.05),其可溶性氮释放量(62.05%±0.75%)亦高于HT-CPC(40.25%±0.19%)、JC-CPC(21.02%±0.72%)(P0.05)。同时,JC-CPC消化产物的抗氧化试验结果表明,其消化产物具有较高的还原力及1,1-二苯基-2-苦基肼(1,1-Diphenyl-2-picrylhydrazyl,DPPH)自由基的清除能力。因此,利用喷射蒸煮技术,结合亚临界及超滤除杂技术能够为食品工业提供一种具有良好消化性的玉米浓缩蛋白,有望为玉米黄粉的利用提供一条有效途径。     

Molecular dynamics simulation of cationic complexation with natural organic matter

Molecular computer modelling of natural organic matter (NOM) and its interactions with metal cations in aqueous solution is a highly effective tool for helping to understand and quantitatively predict the molecular mechanisms of metal‐NOM complexation. This paper presents the results of molecular dynamics (MD) computations of the interaction of NOM with dissolved Na⁺, Cs⁺, Mg²⁺ and Ca²⁺. They show that Na⁺ forms only very weak outer‐sphere complexes with NOM, whereas Cs⁺ interacts somewhat more strongly, but also mainly via outer‐sphere association. Mg²⁺ interacts little with NOM due to its strongly held hydration shell. Ca²⁺ has the strongest association with NOM and forms inner‐sphere complexes with NOM carboxylate groups. This last result supports the idea of supramolecular, Ca‐mediated NOM aggregation. Cation‐NOM binding occurs principally with carboxylate groups, and to a lesser extent with phenolic and other –R‐OH groups. The contributions of other NOM functional groups are minimal. The diffusional mobility of NOM‐bound cations is ∼20% (NOM‐Na⁺ outer‐sphere complex) to ∼95% (NOM‐Ca²⁺ inner‐sphere complex) less than in aqueous solutions without NOM. The MD simulation results are in good agreement with NMR spectroscopic measurements for Cs‐NOM solutions.     

Gelation of protein recovered from whole Antarctic krill (Euphausia superba) by isoelectric solubilization/precipitation as affected by functional additives

This study demonstrated that the novel isoelectric solubilization/precipitation can be applied to recover functional muscle protein in a continuous mode from whole Antarctic krill. Protein recovered from whole krill had a much lower ash content than whole krill, suggesting good removal of inedible impurities (shell, appendages, etc.). Lipids were retained to a higher degree with krill protein solubilized at acidic rather than basic pH. The viscoelastic modulus (G') showed that recovered krill protein failed to form heat-induced gel unless beef plasma protein (BPP) was added. Therefore, protease inhibitors are suggested for development of krill-derived products. Even with BPP, the G' decreased between 45 and 55 degrees C. However, krill protein solubilized at acidic pH had a higher decrease of the G' than the protein solubilized at basic pH, likely due to krill endogenous cathepsin L. Krill protein-based gels developed from protein solubilized at basic pH, especially pH 12.0, had better texture (torsion and Kramer tests and texture profile analysis) than acidic counterparts, possibly due to higher proteolysis and denaturation at acidic pH. Gels made from protein solubilized at acidic pH were brighter and whiter likely due to a higher lipid content.     

Rheological and Pasting Properties of Buckwheat (Fagopyrum esculentum Möench) Flours With and Without Jet‐Cooking

Pasting, rheological, and water‐holding properties of buckwheat (Fagopyrum esculentum) flour obtained from whole achenes separated into three particle sizes, and three commercial flours (Fancy, Supreme, and Farinetta) were measured with or without jet‐cooking. Fancy had instantaneous paste viscosity (measured using RVA) after jet‐cooking that was not observed for Supreme or Farinetta, and paste viscosity was lower for the latter two flours. Supreme jet‐cooked flour exhibited higher peak viscosity than flour without jet‐cooking, and paste exhibited high shear‐thinning. Fancy exhibited strongest viscoelastic properties (measured using a rheometer). Jet‐cooking damaged buckwheat flour structure, thereby reducing viscoelasticity. Buckwheat flour pastes experienced shear‐thinning over a wide range of shear rates. Jet‐cooking greatly enhanced water‐holding capacity. Buckwheat flour particle size did not greatly influence paste viscosity. Study showed buckwheat flours have unique pasting and rheological characteristics that have different food applications, which could especially be useful for people with celiac disease as buckwheat is gluten‐free.     

Cooking process: a new source of unintentionally produced dioxins?

To improve understanding of human background exposure to dioxins, the influence of cooking on dioxin concentrations in food has received much attention. Studies have focused on changes in the distribution of dioxins that originate from raw foods. However, the possibility of dioxin formation during cooking has been neglected. In this study, cooking experiments were designed to investigate the generation of dioxins during cooking at high temperature and with flavorings containing organic chlorine. Solid, liquid, and gas phase samples were collected during cooking. The results indicate that dioxins can be generated during some cooking processes, such as burning, or when cooking with reactive organic chlorides, and the dioxins are more likely to be present in the smoke (gas phase) than the edible portion (solid and liquid phases). Thus, more attention should be given to cooking of raw foods and organic chlorine-containing flavorings at high temperature. Maintaining good ventilation during cooking is also necessary to reduce human exposure risk to dioxins.     

Inhibition of the pathogenicity of Magnaporthe grisea by bromophenols, isocitrate lyase inhibitors, from the red alga Odonthalia corymbifera

Magnaporthe grisea is a fungal pathogen of rice that forms appressoria that penetrate the outer cuticle of the rice plant. Data from recent studies indicate that M. grisea isocitrate lyase (ICL), a key enzyme in the glyoxylate cycle, is highly expressed during appressorium-mediated plant infection. Bromophenols isolated from the red alga Odonthalia corymbifera exhibited potent ICL inhibitory activity and blocked appressoria formation by M. grisea in a concentration-dependent manner. In addition, these compounds protected the rice plants from infection by M. grisea. Rice plants infected with wild-type M. grisea Guy 11 exhibited significantly lower disease severity with bromophenol treatment than without, and the treatment effect was comparable to the behavior of the Deltaicl knockout mutant I-10. The protective effect of bromophenols and their strong inhibition of appressorium formation on rice plants suggest that ICL inhibitors may be promising candidates for crop protection, particularly to protect rice plants against M. grisea.     

Purification and identification of a protease inhibitor from glassfish (Liparis tanakai) eggs

Two protease inhibitors of 67 and 18 kDa, respectively, were purified from glassfish, Liparis tanakai, eggs by affinity chromatography. The smaller protein was purified with a yield and purity of 0.25% and 49.69-fold, respectively, and was characterized for further study. The glassfish egg protease inhibitor exhibited stability between 50 and 65 degrees C in an alkaline environment (pH 8). It was shown to be a noncompetitive inhibitor against papain, with an inhibitor constant (Ki) of 4.44 nM. Potent glassfish protease inhibitor with N-Val-Gly Ser-Met-Thr-Gly-Gly-Phe-Thr-Asp-C amino acid residues was synthesized and its inhibitory activity was compared. Moreover, the 18-kDa protein inhibited cathepsin, a cysteine protease, more effectively than did egg white protease inhibitor, whereas the reverse was true for papain. Glassfish egg protease inhibitor is classified as a member of the family I cystatins.     

Mercury contamination of fish in the Ojibwa diet: I. Walleye fillets and skin-on versus skin-off sampling

During the past two years, walleye (Stizostedion vitreum) have been collected and prepared into skin-off fillets and submitted for total mercury analysis. The survey included 105 fish from 18 lakes in 10 counties in northern Wisconsin and the upper peninsula of Michigan. Fourteen lakes yielded walleye fillets with greater than 0.5 ppm mercury, and six lakes yielded samples in excess of 1.0 ppm mercury. Fourteen fish were collected in the spring and prepared as fillets ground up as either skin-on or skin-off samples. The difference in Hg was significant (T₁₄=?3.26,p=0.006) with skin-on fillets, resulting in an approximately 10% decrease in mercury concentrations. Results of this study suggest that by leaving the skin on the sample, mercury concentrations will be reported 10% lower than if the skin is removed. Obviously, consumption advisories based on skin-off samples could provide more protection for Ojibwa people eating the spring harvest of walleye. In the fall, the difference in Hg samples between skin-on versus skin-off, was less and not statistically significant. However, removal of the skin would be expected to underestimate lipophilic organochlorine burdens and may not be appropriate for fish species where PCBs, DDT, and chlordanes are the major concern. Fall data for 67 fish from 26 lakes in 9 counties are also reported.     

Effects of cooking and storage on residues of cyadox in chicken muscle

The aim of this study was to investigate the depletion of residues of cyadox in chicken muscle over time. The heat stabilities of cyadox (CYX) and its two metabolites, 1,4-bisdesoxycyadox (BDCYX) and quinoxaline-2-carboxylic acid (QCA), in water, cooking oil, and as incurred residues in chicken muscle were investigated. CYX was shown to be unstable with a half-life of about 37.7 min in 100 degrees C water. In hot cooking oil at 180 degrees C, all three compounds were unstable. CYX decreased quickly and was not able to be detected after heating for 2 min. Diode-array analysis of CYX standard solution in cooking oil indicated that a portion of BDCYX was formed. The residues of CYX and BDCYX deteriorated rapidly in frozen storage, while that of QCA changed slowly. Muscles containing CYX residues were boiled, microwaved, or fried for the specified times. During boiling, CYX and BDCYX were reduced 94% and 81% in 10 min, respectively. During microwave cooking, CYX and BDCYX were reduced 54% and 47% in 2.5 min, respectively. During frying, CYX and BDCYX were reduced 86% and 76%, respectively. No significant reduction of QCA was found for the three cooking methods. The half-lives of CYX residues in cooked chicken muscles were estimated as follows: 2.22 min for CYX and 4.44 min for BDCYX by boiling; 6.66 min for CYX and 9.36 min for BDCYX by microwaving.     

Structural carbohydrate differences and potential source of dietary fiber of onion (Allium cepa L.) tissues.

Onion tissues of three varieties were evaluated for dietary fiber (DF) composition. Insoluble (IDF) and soluble (SDF) dietary fibers were subjected to acid hydrolysis, and the resultant neutral sugars, uronic acids, and Klason lignin were quantified. Brown skin exhibited the highest total dietary fiber (TDF) content (65.8%) on a dry matter basis, followed by top (48.5%) and bottom (38.6%), IDF being the main fraction found. The SDF:IDF ratio decreased from inner to outer tissues. Brown skin and outer leaves byproducts appear to be the most suitable sources of DF that might be used in food product supplementation. The chemical composition reveals that cellulose and pectic polysaccharides were the main components of onion DF in all tissues, although differences between them were noticed. An increase in the uronic acids/neutral sugars ratio from inner to outer tissues was found, suggesting that the galactan side chain shows a DF solubilization role.     

Inhibitory effect of mimosine on polyphenoloxidase from cephalothoraxes of Pacific white shrimp (Litopenaeus vannamei)

The inhibitory effect of mimosine on polyphenoloxidase (PPO) from the cephalothorax of Pacific white shrimp (Litopenaeus vannamei) was studied. Mimosine showed inhibitory activity toward PPO from white shrimp with an apparent molecular weight of 210 kDa as evidenced by the decrease in the activity staining band, as compared to the control. An inhibition kinetic study revealed that mimosine exhibited the mixed type reversible inhibition on PPO from white shrimp with a Ki value of 3.7 mM. Mimosine showed copper (Cu2+) reduction and chelating capacity in a dose dependent manner. Mimosine could react with the intermediate browning product, thereby rendering lower red-brown color formation. Therefore, mimosine could inhibit PPO by different modes of inhibition and could be used to prevent melanosis formation in Pacific white shrimp.     

柑橘黄龙病蒸汽快速热处理升温特性及田间防治效果

为了深入了解柑橘黄龙病湿热蒸汽快速热处理时韧皮部的升温特性,针对柑橘黄龙病细菌位于韧皮部的特点,构建了室内和田间试验装置,主要包含加热罩、湿热蒸汽发生装置、树体表面和韧皮部温度采集装置。通过比较热处理前后韧皮部温度变化,作物恢复程度差异和黄龙病病菌浓度变化,分析获取湿热蒸汽快速热处理合理参数组合。室内试验选用1 a生柑橘树,研究了树体表面温度为55~65℃,蒸汽输送压力为0.015和0.03 MPa,不保温和保温处理30 s对于韧皮部升温和作物恢复的影响。试验结果:树体表面温度为65℃及以上时,作物都因热损而死亡,采用60℃作为热处理温度阈值,有利于韧皮部温度提高。较高的蒸汽输送压力(如0.03 MPa),虽有利于作物所在环境温度的快速升高,但其作用于韧皮部的传热时间短,韧皮部温度并没有得到有效提高,而加热后的30 s保温处理普遍有利于韧皮部温度提高。田间试验选用9 a生柑橘树,研究了树体表面温度为60℃,蒸汽输送压力为0.03 MPa,保温时间30 s的组合参数对于黄龙病病菌浓度和作物恢复的影响。试验结果:4棵染病柑橘树经过热处理,其中2棵恢复到未染病状态,2棵病菌浓度降低。2棵未经过热处理的染病柑橘树,其病菌浓度没有变化。室内和田间试验结果表明:湿热蒸汽快速热处理能有效促进染病柑橘树的生命力恢复,明显降低病菌浓度;对于柑橘黄龙病田间湿热蒸汽快速热处理,不能只关注树体表面温度的快速提高,而应关注韧皮部温度的有效提高;热处理应考虑直接蒸汽加热和关闭蒸汽后保温的综合影响,为了增加韧皮部传热,应尽量选取较高升温上限和较低输送压力。研究结果为柑橘黄龙病田间热处理防治提供参考。     

Effect of meat cooking on physicochemical state and in vitro digestibility of myofibrillar proteins

The effect of meat cooking was measured on myofibrillar proteins from bovine M. Rectus abdominis. The heating treatment involved two temperatures (100 degrees C during 5, 15, 30, and 45 min and 270 degrees C during 1 min). Protein oxidation induced by cooking was evaluated by the level of carbonyl and free thiol groups. Structural modifications of proteins were assessed by the measurement of their surface hydrophobicity and by their aggregation state. With the aim of evaluating the impact of heat treatment on the digestive process, myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin) in conditions of pH and temperature that simulate stomach and duodenal digestion. Meat cooking affected myofibrillar protein susceptibility to proteases, with increased or decreased rates, depending on the nature of the protease and the time/temperature parameters. Results showed a direct and quantitative relationship between protein carbonylation (p<0.01) and aggregation (p<0.05) induced by cooking and proteolytic susceptibility to pepsin. However, no such correlations have been observed with trypsin and alpha-chymotrypsin.     

Effect of industrial processing on the distribution of aflatoxins and zearalenone in corn-milling fractions

The aim of this study was to investigate the distribution of aflatoxins and zearalenone levels in various corn-milling fractions. Corn kernels and six derived milling fractions (germ, bran, large and small grits, flour, and animal feed flour) were sampled in an industrial plant; both conventional and organic corns were sampled. To evaluate the effect of cooking, samples of polenta were prepared starting from naturally contaminated flour. Conventional and organic lots showed mycotoxin contamination. For both lots, germ, bran, and animal feed flour showed a marked concentration factor from 239 to 911% accounting for both the low yields of the derived products and the distribution of aflatoxins and zearalenone contamination in the outer parts of the kernels. Conversely, a reduction factor of at least four times from raw material to finished products was observed. Polenta samples were unaffected by the cooking process, with levels of contamination similar to those of starting flour.