Enzymatic modification of selected functional properties of myofibril preparation obtained from mechanically recovered poultry meat

The effect of addition of 3 g/L of commercially available transglutaminase preparation to protein extracts obtained from mechanically recovered poultry meat was studied. The content of free thiol groups (–SH), thermal drip and gel texture were determined. After pre-incubation at 7–8 °C for 1, 3, 5 and 24 h, the samples were subjected to one-step heating at 50, 60, 70 and 80 °C and two-step heating at 50/80, 55/80 and 60/80 °C. The addition of preparation and the extension of pre-incubation time led to decrease of free -SH groups content. After heating, the number of thiol groups decreased, the texture was improved, but thermal drip from gels increased. The amount of –SH groups in gel extracts subjected to one-step heating decreased with simultaneous increase of mechanical strength of gels. Protein gels subjected to two-step heating exhibited higher firmness than gels subjected to one-step heating. Thus, the 3 g/L addition of transglutaminase preparation in combination with one-step thermal processing at 70 °C and pre-incubation for 3 h contributed to improvement of texture properties of model gels and low thermal drip.     

Thermal Gelation of Previously Cooked Minced Meat from Jonah Crab (Cancer borealis)

ABSTRACT:  Crab processing typically involves picking meat from whole cooked product. Remaining meat can be recovered as mince and potentially processed into value-added products. This study focused on gelation of commercially processed crab mince. Objectives of the research were to determine the effects of cryoprotectants, freezing, and various heat treatments on gel formation of washed mince from previously cooked crab. Previously frozen minced meat from thermally processed Jonah crab was washed to remove soluble components. Four different treatments were applied to the washed mince: (1) freezing with cryoprotectants, (2) freezing with no cryoprotectants, (3) no freezing with cryoprotectants, and (4) no freezing with no cryoprotectants. Unwashed mince was used as a control treatment. Sodium chloride (2.5%) was mixed into the mince prior to stuffing into sausage casings and heating at 35 °C/30 min, 90 °C/30 min, or 35 °C/30 min followed by 90 °C/30 min. Gels were tested for proximate composition, color, water-holding capacity, and gel strength. All mince samples formed gels except for the unwashed control. Gels with no cryoprotectants had 10% to 20% greater water holding capacity, lower L* values, and greater gel strength than those with cryoprotectants. Freezing of washed mince resulted in lower water-holding capacity of gels and higher a* values. A 2-stage heating treatment resulted in gels with the greatest gel strength, whereas gels cooked at 35 °C had the greatest distance to fracture. Results indicate that protein gels can be formed using previously cooked crab meat, which may be useful in the development of value-added products.     

FORMATION OF HETEROCYCLIC AMINES IN MEAT EMULSION EXTENDED WITH SOY PROTEIN

Formation of heterocyclic amines (HAs) during heating of meat emulsions at selected temperatures was studied to determine the influence of soy protein and fat contents on yields of HAs. Meat emulsion with two different fat contents, 6% (low) and 19% (high), and with two soy protein contents, 0% (none) and 10%, were used in the study. The emulsions were heated at temperatures of 180 and 200C for times varying from 0 to 40 min. HAs namely IQx (2-amino-3-methylimidazo[4,5-f]quinoxaline), MelQx (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline), and PhIP (2-amino-1-methy-6-phenylimidazo[4,5-b]pyridine) were identified and quantified in the meat emulsions. Concentrations of IQx were from 0 to 8.26 ng/g of emulsion; MeIQx concentrations were from 0 to 14.73 ng/g and PhIP concentrations were from 0 to 2.48 ng/g. Yields of the HAs depended on temperature, time, soy protein and fat contents. Formation of the HAs in the meat emulsions after an initial lag period followed first order kinetics. Increasing soy protein content decreased the maximum concentrations of IQx and MeIQx formed at the different heating condition.     

粤式豉油鸡传统烹煮过程中的质地及风味变化

研究了典型粤式豉油鸡烹煮过程中鸡肉蒸煮损失、离心损失、氯化钠含量、pH 值、质构、嫩度、微观结构和风味物质的变化,结果表明：煮制初期（5 min）,鸡肉蒸煮损失和食盐渗入量迅速增加,分别为4.47%和0.22%,离心损失也达到最大值（32%）;鸡皮、鸡肉色泽品质在热浸10 min后逐渐形成且稳定提升;烹制过程中,鸡肉硬度、弹性和咀嚼性在煮制10 min后明显增加（P<0.05）,至热浸25 min后达到最高,分别为生鸡肉的1.65倍、1.54倍和4.35倍;鸡肉中肌纤维随加热进行不断收缩紧实,纤维结构变化明显;烹煮过程中鸡肉鲜味、甜味及苦味游离氨基酸总量、鸡肉特征香气物质含量逐渐上升,热浸25 min后上述风味物质含量显著增加（P<0.05）;鸡肉的各项感官评分均逐渐上升,总体可接受度不断提高。至热浸25 min后鸡肉中总游离氨基酸含量为328.81 mg/100 g,鸡肉具有一定硬度及韧性,咀嚼感好,风味品质高,满足粤式豉油鸡的口感要求。     

COMPOSITION OF LIPIDS AND PROTEINS OF DEBONED MINCED AND FILLETED WHITE SUCKER (CATOSTOMUS COMMERSONI)

Total lipids, phospholipids (PL), free fatty acids, TBA, carbonyl values, fatty acids and amino acid composition of filleted sucker (FS) and mechanically deboned minced sucker (MDMS), were determined. Higher PL concentration (534 mg/100 g versus 370 mg/100 g) and higher carbonyl values (0.89 μmoles/g versus 0.61 μmoles/g) were found in MDMS. There were no significant differences between FS and MDMS in fatty acid composition of total lipid and phospholipids. The protein content and amino acid composition of FS and MDMS were similar.     

Effect of nisin and its combination with sodium chloride on the survival of Listeria monocytogenes added to raw buffalo meat mince

Antilisterial activity of nisin (Nisaplin), alone at concentrations of 400 and 800 IU/g and in combination with 2% sodium chloride was incorporated in raw buffalo meat mince. Samples of the raw meat mince were inoculated with 10(3) colony forming units (cfu)/g of L. monocytogenes and stored at 4°C for 16 days and at 37°C for 36 h. Initial estimates of pH, extract release volume, mesophilic and psychrophilic counts were found to be 5.74, 48 ml, 3.5×10(5) and 1.0×10(5) cfu/g of meat, respectively. The growth of L. monocytogenes in the treated groups was significantly (P<0.05) inhibited compared to the control group. The degree of inhibition increased with increasing concentration of nisin and decreasing storage temperature. Addition of 2% sodium chloride in combination with nisin increased the efficacy of nisin at both storage temperatures. The pH in the treated groups remained significantly lower (P<0.01) than in the control groups at both 4 and 37°C.     

The resistance ofListeria monocytogenesto high hydrostatic pressure in foods

Two strains ofListeria monocytogenes(NCTC 11994, Lm1 and a poultry isolate, Lm2) were exposed to high pressure (375MPa) in ultra high temperature (UHT) treated milk, raw chicken mince, raw beef mince, cooked chicken mince and cooked beef mince for up to 30min at ambient temperature. Survival of the two strains in UHT milk was significantly greater than previously observed in non-nutrient phosphate buffered saline (PBS). Survival in cooked chicken mince and cooked beef mince was only marginally greater than survival in PBS, whilst survival in raw chicken and raw beef mince was generally less than observed in PBS. In all food substrates, the proportion of survivors sustaining injury increased with increasing duration of compression.The two strains were also treated at 375MPa in cooked beef mince for up to 30min at 45°C. Inactivation of both strains was greater at 45°C than at ambient temperature. Treatment at 375MPa for 5min at 45°C resulted in approximately 4.5log₈-cycle reduction; however extending the treatment time resulted in only a slight further decrease in cell counts. The effects of temperature (25, 35, 45 and 55°C) on survival at 200 and 375MPa (15min) in UHT milk was also assessed. Increasing the temperature resulted in increasing levels of inactivation.     

Effects of additives and thermal treatment on the content of nitrogen compounds and the nutritive value of hake meat

Heating of minced meat from 40 to 130 degrees C for 10 min and at 120 degrees C from 15 to 60 min with potato starch (3%), soya oil (4%), salt (1.5%), and water (15%) resulted in a decrease in total amino-acid content by 6% on the average, compared to the content in meat without additives. Heating time-dependent changes involved a decrease in the lysine content, while temperature-dependent changes involved a decrease in the valine content. On the other hand, the presence of additives reduced the thermal protein hydrolysis towards the formation of low-molecular nitrogen compounds. Prolonged time of heating of minced hake meat at 120 degrees C produced a more intensive protein hydrolysis than a shorter heating up to 130 degrees C; at the same time with temperatures exceeding 100 degrees C an intensive increase in the ammonia content, decrease in -SH groups content, and a decrease in protein digestibility were observed.     

Thermal gelation properties of surimi-like material made fromsheep meat

Thermal gelation properties of surimi-like material made from sheep meat were investigated. The sheep meat was ground, washed 3 times at a meat to water ratio of 1:5 and dewatered by centrifugation. The effects of washing on the composition, functional properties and colour of the mince, were studied. The washing method resulted in a sharp reduction of the fat content and an increase of the water content and pH of the mince. Lightness (L*) and yellowness (b*) of the mince were improved by washing. A significant reduction (p<0.001) of a* (redness) value and a decrease in the a*/b* ratios and saturation index value of the washed mince were recorded. Gels were prepared from washed and unwashed mince after being blended with 2% NaCl and heated at 75°C for 20 min. The washed mince produced excellent gels as measured by the fold test, elasticity modulus and the percentage recovery. The gels made of washed mince had lower expressible fluid compared to that of unwashed mince. A fibrous protein network structure was evidenced in the gel made from washed mince while observed under a transmission electron microscope.     

FACTORS RESPONSIBLE FOR WHITE FILM FORMATION ON CUT SURFACES OF DRYCURED HAMS

White surface film that forms on cut surfaces of country-style ham was identified as crystalline L-tyrosine. Free L-tyrosine averaged 287.3 μmoles/g (5.2% by weight) in the film and 6.1 μmoles/g in ham tissue from which film had been removed. It is concluded that the film forms because the concentration of free L-tyrosine and certain other free amino acids in ham is greater than solubility levels; therefore, crystals form on the cut surface. The absence of surface film on knuckle muscles and film formation on other muscles of the same slice was attributed to higher NaCl (P < 0.05) of the former which decreased catheptic activity.     

PROTEIN CONCENTRATE FROM CAPELIN (MALLOTUS VILLOSUS) BY SPRAY DRYING PROCESS and ITS PROPERTIES

A process is described for preparing protein powder from washed capelin meat. Whole capelin was subjected to mechanical deboning, and the mince obtained was submitted to a three-step washing procedure using cold aqueous solutions of 0.5% NaCl and 0.5% NaHCO₃ and, finally, cold water. the washed mince was homogenized in an equal quantity of cold water, heated to 70C to reduce viscosity, and centrifuged at 1160 x g for 15 min to remove traces of sediments. the supernatant, containing more than 90% of the washed mince, was spray dried to obtain a powder with a protein content of 85% and having appreciable functional properties.     

不同加热处理发酵酸肉多肽的体外抗氧化活性比较

以酸肉为研究对象,研究酸肉微波、蒸制、油炸、烤制处理后多肽抗氧化活性。比较不同状态下酸肉多肽提取率、巯基(-SH)含量、清除1,1-二苯基-2-三硝基苯肼(DPPH)及羟自由基(-OH)能力、螯合金属离子(Fe2+)、抑制脂质氧化及清除亚硝酸盐能力。结果表明,微波、蒸制、油炸、烤制等热处理后酸肉粗肽液-SH含量分别为25.41 nmol/mg,22.89 nmol/mg,26.62 nmol/mg,24.60nmol/mg,随粗肽液浓度增加,抗氧化能力显著增强,相同浓度不同热处理状态下酸肉粗肽液抗氧化能力不同。在粗肽液质量浓度为5 mg/mL时,微波、蒸制、油炸、烤制、生酸肉等处理粗肽液DPPH自由基清除率及-OH自由基清除率均表现为蒸制>烤制>微波>油炸>生酸肉,Fe2+螯合能力分别为50.61%、52.67%、48.76%、50.58%、57.77%,在与亚油酸反应144h时,粗肽对脂质氧化的抑制率分别为47.33%、57.60%、44.26%、49.03%、51.63%,亚硝酸盐清除率分别为68.81%、75.37%、70.05%、74.86%、76.01%。综合分析,与生酸肉相比,加热处理后酸肉粗肽抗氧化活性提高,且蒸制最好,因此酸肉抗氧化多肽提取适宜的热处理方式为蒸制>烤制>微波>油炸。     

克氏原螯虾不同可食部位风味成分分析

以克氏原螯虾为研究对象,分别测定克氏原螯虾熟制前后基本营养成分、可食组织得率的变化,运用电子鼻、固相微萃取-气相色谱-质谱联用、气相色谱-离子迁移谱（gas chromatography ion mobility spectrometry,GC-IMS）等技术结合游离氨基酸含量研究克氏原螯虾不同可食部位风味成分的变化。结果表明：克氏原螯虾的重要可食部位是尾肉与肝胰腺,且含有大量蛋白质与脂肪;其中克氏原螯虾肝胰腺熟制前后气味差异远大于尾肉熟制前后气味差异;熟制前后克氏原螯虾尾肉和肝胰腺中共检出59 种挥发性物质,结合GC-IMS分析可知,虾肉熟制后出现新的风味物质,并且一些原有物质（乙酸乙酯、丁酸甲酯和3-辛酮等）含量升高,肝胰腺熟制后挥发性有机物种类（醛类、酮类以及少量醇类和呋喃等物质）减少,含量大部分降低,也有少量物质（乙醇、丙醛、丁醛和戊醛等）含量升高;克氏原螯虾肝胰腺熟制后游离氨基酸总量明显升高,达119.63 mg/g,而尾肉熟制前后游离氨基酸总量相比肝胰腺熟制前后变化较小,但含量很高,达237.51 mg/g。     

EFFECT OF SODIUM NITRITE CONCENTRATION ON N-NITROSODIMETHYLAMINE FORMATION IN FRANKFURTERS

The effect of nitrite concentration on N-nitrosodimethylamine (DMNA) formation using frankfurter emulsion was investigated. Sodium nitrite was usually added to the emulsion to give levels of 150, 750, 1050, 1500 and 2500 mg/kg of meat. The frankfurters were cooked with light smoke for either 2 or 4 hr. DMNA was determined in all samples by GLC with an alkali flame ionization detector and confirmed by GLC-MS when sufficient amounts were present. Residual nitrite analysis indicated that about one-half of the sodium nitrite added was still present after processing. 19 μg DMNA per kg meat was found in frankfurters that contained 2500 mg sodium nitrite per kg of meat and processed for 2 hr. Indications of DMNA in levels of 3–14 μg/kg meat were obtained with frankfurters containing 750–1500 mg sodium nitrite per kg meat and processed for either 2 or 4 hr depending on the nitrite level. There appeared to be some tendency for an increase in DMNA formation on increasing processing time.     

Gelation of reconstituted whey powders by heat

Whey protein preparations isolated from cheese whey form stable gels when their aqueous solutions are heated at 80°C. The gels consist of polypeptide chains crosslinked by disulphide bonds. They dissolve if a sulphydryl (-SH) reagent is added after heating; their formation is retarded if compounds that react with -SH groups are added before heating. Opaque gels are formed from powders containing relatively large amounts of total -SH; clear gels form from those with low total -SH. Gels form faster on heating in N₂ instead of air. Gels form more slowly at alkaline pH; it is suggested that this effect is caused by electrostatic repulsion between protein molecules with like charges.     

鱼鱼肉与白鲢鱼鱼糜混合热聚集行为分析

为了研究不同混合比例下鳀鱼鱼肉与白鲢鱼鱼糜的热聚集行为,本文以凝胶强度、动态流变、热稳定性、粒径、内源荧光、拉曼光谱和扫描电子显微镜作为测定指标。当鳀鱼鱼肉与白鲢鱼鱼糜的质量比例为1:9和2:8时,混合体系的凝胶强度可达到7568.01和6804.22 g·mm。当鳀鱼鱼肉与白鲢鱼鱼糜的质量比例为0:10、1:9和2:8时,混合体系的热稳定性和储能模量最高。随着加热的进行,混合体系的最大荧光强度逐渐降低,与未加热时相比,第一段加热后(40 ℃,30 min)和第二段加热后(40 ℃,30 min;90 ℃,20 min)分别降低了38.8%和44.4%。当鳀鱼鱼肉与白鲢鱼鱼糜的质量比例为1:9时,二段式加热后混合体系中的α-螺旋相对含量最低,β-折叠相对含量最高;微观结构最为致密。结果表明,当鳀鱼鱼肉与白鲢鱼鱼糜的质量比例为1:9时,混合体系的热聚集效果最佳。     

CHANGES IN PROXIMATE COMPOSITION OF THORNBACK RAY (RAJA CLAVATA, L. 1758) SURIMI DURING WASHING AND FROZEN STORAGE

The effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. The crude ash content which was initially found as 1.38% in raw thornback ray decreased approximately 12 and 80% after the first and second washing, respectively. After the third washing, crude ash content increased to 207% of the amount in the second washing because of addition of salt to the last washing water. The crude protein content of mince also decreased approximately to 28 and 20% after the first and second washing, respectively. After the third washing, the decrease in the lipid levels was approximately 30%. At the end of 6 months of frozen storage at − 23.8  ±  2C, dry matter, crude ash and crude protein contents increased in a greater ratio in surimi containing 4% sorbitol, 4% sucrose and 0.3% Na-tripolyphosphate than surimi prepared with 8% sorbitol and 0.3% Na-tripolyphosphate.

PRACTICAL APPLICATIONS

In the present study, the effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. Washing procedure significantly decreased crude ash, crude protein and crude fat content of mince. There were significant differences in moisture, crude ash, and crude protein contents during the 6 months storage period of frozen surimi obtained by using different cryoprotectant mixtures. The folding test scores were highest in fresh surimi and during the first two months of storage. Thornback ray can be used for the production of surimi.     

CONTENTS OF CYTOCHROMES IN YEAST

The contents of cytochromes in yeast were determined quantitatively from the absorption spectra, using a solid cell paste of intact yeast. During the industrial production of baker's yeast, the contents of the cytochromes, particularly of cytochrome aa₃ at successive stages, increased gradually with increasing aeration. In semi-aerobically grown baker's yeast, the contents of cytochromes aa₃, b and c were 0·9, 2·9 and 2·9 × 10^?5 moles/litre of fresh yeast (total amount 6·7 × 10^?5 moles/litre), while in vigorously aerated commercial baker's yeast the respective values were 2·3, 4·8 and 5·2 × 10^?5 moles/litre (total amount 12·3 × 10^?5 moles/litre). In brewer's yeasts separated after the brewing process, the contents of cytochromes were markedly lower than in baker's yeast grown with limited aeration, whereas in top-fermenting yeast the total cytochrome content, aa₃ + b + c, was in some samples markedly higher, 7·1 × 10^?5 moles/litre, than in bottom-fermenting brewer's yeast, 2·4 × 10^?5 moles/litre. When brewer's bottom yeast was grown on a laboratory scale under increasing aeration, a maximum appeared in the cytochrome contents when aeration was moderate, and increased aeration inhibited the formation of cytochromes. The cytochrome contents in brewer's bottom yeast may exceed the amounts found in commercial baker's yeast. In addition to aeration, the type of metabolism influences the amounts of cytochromes in yeast.     

Effect of different cooking methods on some lipid and protein components of hamburgers

The effects of different cooking methods on the lipid and protein fractions of hamburger were evaluated. The lipid component was subjected to the following analyses: peroxide value; p-anisidine; total and free fatty acids; cholesterol and its oxidation products (quantified as 7-ketocholesterol). Lysinoalanine (LAL), free amino acids and D-amino acids (D-AA) were also determined in the protein fraction. All results were compared with a raw control. No significant differences were found among the cooking treatments with respect to D-AA and LAL. The degree of proteolysis, lipolysis and lipid oxidation varied depending on the treatment conditions. Regarding cholesterol oxidation, the combination of roasting and microwave heating caused more oxidation than the other treatments. The raw meat, however, showed an advanced degree of oxidation (25.2 ppm of total 7-ketocholesterol/120 g ground meat).     

发酵剂及猕猴桃蛋白酶促进马肉发酵香肠蛋白质的降解

为了提高马肉发酵香肠的品质,添加发酵剂和猕猴桃蛋白酶,促进其发酵成熟和肌肉蛋白质的降解。以新鲜马肉和马脂肪为原料,分别设计三个试验组,一组为对照组,另两组为处理组;对照组不采取处理,而两个处理组添加2%的发酵剂和0.05%的猕猴桃蛋白酶,并在相应条件下进行发酵,检测其总氮、非蛋白氮等指标,并通过SDS-PAGE电泳分析其肌肉蛋白质的降解情况。结果表明,灌肠后(0 d)各组总氮含量为3.09 g/100 g左右,而加工结束后(28 d),对照组(CK组)、发酵组(A组)、猕猴桃蛋白酶组(B组)总氮含量分别是3.41 g/100 g、3.85 g/100 g及4.15 g/100 g,说明总氮含量明显上升,并且发酵剂和猕猴桃蛋白酶的影响显著;28 d CK组、A组、B组非蛋白氮含量分别为0.42 g/100 g、0.52 g/100 g、0.65 g/100 g,与0 d非蛋白氮含量0.22 g/100 g相比,CK组上升1.9倍,A组上升2.4倍,B组上升2.9倍;SDS-PAGE电泳结果表明,在整个加工过程中A组与B组肌浆蛋白逐渐发生降解,大分子条带发生了明显的变化,发酵剂对马肉发酵香肠肌浆蛋白和肌原纤维蛋白的降解有显著的促进作用,猕猴桃蛋白酶对肌浆蛋白的影响显著,并比发酵剂大,但对肌原纤维蛋白的作用不大。