Effects of protein level and fat/oil on emulsion stability,texture, microstructure and color of meat batters

Beef meat batters formulated with increasing protein level (10–15%) and containing 25% beef fat were compared to batters prepared with 25% canola oil. Emulsion stability of the canola oil treatments was higher (less separation during cooking) at the 10–13% protein level compared to the beef fat treatments. However, above 13% protein this was reversed and the canola oil treatments showed high fat and liquid separation, which did not occur at all in the beef fat treatments. This indicates differences in stabilization of fat versus oil in such meat emulsions. Hardness of the cooked meat batters showed significantly (P < 0.05) higher values when the protein level was raised, and was higher in canola oil than in beef fat meat emulsions at similar protein levels. Products’ chewiness were higher in the canola oil treatments compared to the beef fat emulsions. Lightness decreased and redness increased in canola oil batters as the protein level was raised. The micrographs revealed the formation of larger fat globules in the beef fat emulsions compared to the canola oil meat emulsions. The canola oil treatment with 14% protein started to show fat globule coalescence, which could be related to the reduced emulsion stability.     

Feta cheese texture: the effect of caprine and ovine milk concentration

Feta cheese was produced commercially with different caprine to ovine milk ratios. Milk fat concentrations, moisture and salt contents were similar for all the batches. However, the hardness and adhesive characteristics of the cheeses differed in relation to the milk ratio. The hardness of the cheese appeared to be correlated to increased goat milk content. Cryo-scanning electron microscopy (cryo-SEM) of the cheese samples showed that feta cheese with a higher proportion of caprine milk had a more compact and less porous appearance than feta produced from purely ovine milk. This difference in cheese structure helps to explain the difference in hardness between the samples.     

Effects of two types of soy protein isolates,native and preheated whey protein isolates on emulsified meat batters prepared at different protein levels

The effects of substituting 1.5% of the meat proteins with low gelling soy protein isolate (LGS), high gelling soy protein isolate (HGS), native whey protein isolate (NWP), and preheated whey protein isolate (PWP) were compared at varying levels of proteins (12, 13 and 14%), with all meat control batters prepared with canola oil. Cooking losses were lower for all the non-meat protein treatments compared to the all meat controls. When raising the protein level from 12 to 14%, cooking losses increased in all treatments except for the NWP treatments. Using LGS increased emulsification and resulted in a more stable meat batters at the 13 and 14% protein treatments. Textural profile analysis results showed that elevating protein level increased hardness and cohesiveness. The highest hardness values were obtained for the PWP treatments and the lowest for the HGS, indicating a strong non-meat protein effect on texture modification. Non-meat protein addition resulted in lighter and less red products (i.e., lower red meat content) compared to the all meat controls; color affected by non-meat protein type. Light microscopy revealed that non-meat proteins decreased the frequency of fat globules' agglomeration and protein aggregation. The whey protein preparations and HGS formed distinct “islands” within the meat batters' matrices, which appeared to interact with the meat protein matrix.     

Effect of regular and hydrolysed dairy proteins on texture,microstructure and colour of lean poultry meat batters

The use of 2% milk protein isolate (MPI), and some of its fractions which included caseinate, whey protein isolate (WPI), two whey protein hydrolysates (5.2% and 8.5%; WPH‐I and WPH‐II respectively) and β‐lactoglobulin (β‐lac) was evaluated in lean chicken breast meat batters. Adding caseinate and MPI resulted in the highest fracture force values, and caseinate also provided higher yield compared with the control. Both proteins were observed to form distinct protein islands embedded within the meat protein matrix, which appeared to enhance the gel structure. The two hydrolysates provided the highest yield compared with all other treatments. However, adding WPH‐II also resulted in the lowest fracture force and hardness values, while WPH‐I provided similar values to the control. The low hardness value could be explained by the light micrograph which showed WPH‐II interfering with the binding of the meat proteins. The WPI and β‐lac provided similar yield, fracture and hardness values as the control. The colour of the products was most affected by the WHP‐I and WHP‐II; both resulted in lower lightness, yellowness and overall spectra reflectance curves. A cost analysis revealed that caseinate addition was the most economical in this lean meat system.     

Textural properties and microstructure of low-fat and sodium-reduced meat batters formulated with gellan gum and dicationic salts

Instrumental texture characteristics of low-fat, reduced-sodium meat batters formulated with other salts (KCl and MgCl₂ or CaCl₂) with gellan gum were evaluated. Fat and sodium reduction through incorporation of gellan gum and either of the dicationic salts produced less rigid, more ductile structures. Inclusion of magnesium chloride resulted in better performance, whereas addition of calcium chloride resulted in less desirable properties. The dicationic salts level used probably inhibited the gellan gum thermoreversible properties, affecting its water holding properties. Microstructural differences between the dicationic salt treatments were apparently due to the effect of dicationic salt concentration on myofibrillar protein extraction and solubilization, and gellan gum gelation properties. Use of magnesium chloride in tandem with gellan gum in the studied low-fat, reduced-sodium meat batters effectively compensated for the structural differences caused by fat and sodium reduction.     

Effects of batters containing different protein types on the quality of deep-fat-fried chicken nuggets

The effects of soy protein isolate (SPI), whey protein isolate (WPI) and egg albumen (EA) on the quality of deep-fat-fried chicken nuggets were studied. Batter without protein addition was used as a control. Batter pickup and moisture content, oil content, texture, porosity and colour of the nuggets were determined for 3, 6, 9 and 12 min of frying at 180 °C. Additionally, the rheological properties of batters were studied. SPI (3%) provided the highest apparent viscosity and coating pickup. All the batters showed shear-thinning behaviour except EA-added batter. Addition of different proteins to the batter formulation decreased the oil content of the final product. EA reduced the oil content of chicken nuggets significantly but yielded softer products. WPI (3%) was found to be the most effective ingredient on improving quality parameters of deep-fat-fried chicken nuggets. WPI (3%) added batters provided the hardest and crunchiest product with the darkest colour and also significantly reduced the oil content of the fried nuggets.     

Simultaneous application of transglutaminase and high pressure to improve functional properties of chicken meat gels

Low-fat protein gels obtained by pressure are softer than those processed by conventional heat treatment. In this study, microbial transglutaminase (MTGase) (0.3%) was added to chicken batters in order to investigate the combined effect of pressure and enzyme on the functional properties of gels. Batters of meat with egg proteins were treated at 500 MPa for 30 min at 40 °C and then heated at 75 °C for 5 min to inactivate the enzyme. Treated samples showed, under confocal microscopy, a more compact and homogeneous microstructure and exhibited a notable increase in hardness and chewiness as compared to controls that were pressurized but contained no MTGase. They were also harder, more chewy and springy but had a similar cohesiveness and cutting force to those obtained by heat alone.     

Flowability and wetting behaviour of milk protein ingredients as influenced by powder composition,particle size and microstructure

This work aimed to provide a comprehensive characterisation of several physicochemical properties of different milk protein powders frequently used as ingredients in dairy‐based food formulations, in particular flowability and wettability. The flow and wetting properties were influenced mainly by the powder composition, less than by other physicochemical properties, such as particle size and microstructure. Powders with high fat content had poor flow and wetting properties. The wetting properties were also influenced by the protein content (mainly by the casein content) of the powders and were poor for powders having poor release of ionic calcium.     

Effect of ripening with Penicillium roqueforti on texture,microstructure, water distribution and volatiles of chicken breast meat

In this study, the influence of ripening with Penicillium roqueforti on texture, microstructure, protein structure, water mobility and volatile flavour compounds of chicken breast meat was investigated. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that the granule formed and chicken myofibril fractured after ripening. Reduction in α-helix and increases in β-sheet structure content accompanied by decrease in hardness and springiness and increase in gumminess were found in ripened chicken breast meat. Low field nuclear magnetic resonance (LF-NMR) revealed that increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the higher water-holding capacity after ripening with P. roqueforti. In addition, chicken breast meat ripened with P. roqueforti contained more volatile flavour compounds, in particular aldehydes.     

Effects of milk supplementation with skim milk powder, whey protein concentrate and sodium caseinate on acidification kinetics, rheological properties and structure of nonfat stirred yogurt

Milk supplementation with milk proteins in four different levels was used to investigate the effect on acidification and textural properties of yogurt. Commercial skim milk powder was diluted in distilled water, and the supplements were added to give different enriched-milk bases; these were heat treated at 90 °C for 5 min. These mixtures were incubated with the bacterial cultures for fermentation in a water bath, at 42 °C, until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring the pH. Protein concentration measurements, microbial counts of Lactobacillus bulgaricus and Streptococcus thermophilus, and textural properties (G′, G″, yield stress and firmness) were determined after 24 h of storage at 4 °C. Yogurt made with milk supplemented with sodium caseinate resulted in significant properties changes, which were decrease in fermentation time, and increase in yield stress, storage modulus, and firmness, with increases in supplement level. Microstructure also differed from that of yogurt produced with milk supplemented with skim milk powder or sodium caseinate.     

Physical properties of yoghurt manufactured with milk whey and transglutaminase

The effect of milk protein polymerization prior to the yoghurt fermentation process was evaluated by enzymatic reaction with microbial transglutaminase (Streptoverticillium mobaraense). Yoghurt samples were manufactured with 100% milk or by substituting milk with 20 or 30% of liquid milk whey, aimed at determining the use of natural milk whey in dairy products. Transglutaminase was added at a protein ratio of 0.5 U g⁻¹ to all samples and evaluated regarding rheological behavior, syneresis index and texture profile. The addition of enzyme transglutaminase contributed to syneresis prevention and increased the consistency index in yoghurt samples manufactured with milk whey. Yoghurt manufactured from 70% milk plus 20% milk whey, followed by enzymatic treatment, presented similar characteristics to traditionally manufactured yoghurt (C 100), with no alteration in the syneresis of the samples (p > 0.05) and presented texture parameters similar to the control yoghurt (C 100).     

Effect of laccase and transglutaminase on the textural and water-binding properties of cooked chicken breast meat gels

The effects of laccase and transglutaminase (TG) on the firmness and weight loss of cooked chicken meat homogenate gels were investigated at laboratory scale. The salt, trisodium pyrophosphate and meat contents were also used as variables. Laccase decreased firmness and increased weight loss of phosphate-free, low-meat (65%) and low-salt (1%) gels, although it modified myosin and troponin T and reacted with isolated myofibrils. By applying both low-salt (1%) and low-phosphate (0.17%) amounts, gel firmness decreased and weight loss increased (p<0.05) greatly. A high dosage of TG significantly improved (p<0.05) the strength of phosphate-free, low-meat and low-salt homogenate gels compared to the corresponding no-enzyme controls. TG improved gel firmness of the low-meat homogenate to the level of the homogenate containing 75% meat. Weight loss was increased significantly (p<0.05) in all cases when the high-TG dosage was used. Enzymes were not capable of improving either texture or water-holding capacity in the low-salt–low-phosphate system. The firmness and cooking loss of the chicken meat products containing different amounts of meat, salt and TG were investigated at pilot scale. Under the conditions and dosages used, TG was capable of improving (p<0.05) firmness of the products without a significant reduction in water-holding capacity.     

高静压对添加酪朊酸钠鸡肉糜制品特性及其微观结构的影响

在肉制品加工中运用高静压技术对其改性将得到发展。研究侧重在50～600MPa和5～40min范围内单因素考察添加1.5%酪朊酸钠鸡肉糜制品保水性、质构、凝胶强度、色泽特性的影响,并从微观结构上分析其作用机理。结果表明:与未受压的对照样比较,200～500MPa和10～30min都能显著增强其保水特性(p<0.01),过低压力50MPa和过高压力600MPa有明显降低保水性现象(p<0.01);制品质构特性(硬度、咀嚼性)随着压力增大而增大;凝胶强度也同样随着压力增加而增加,但在600MPa出现明显劣化(p<0.01),从侧面反映了保水性变化特点;制品色泽(白度、彩度)基本上随着压力增大和时间延续均分别逐渐增大和下降;而保压时间对鸡肉糜制品的保水性、质构与凝胶强度的影响相对有限。综合分析,300MPa、20min的高静压条件处理可获得较高出品率、较好质构特性和色泽的添加酪朊酸钠鸡肉糜制品。     

Effects of ultrafiltration of whole milk on some properties of spray-dried milk powders

The objective was to produce spray-dried milk powders for assessment subsequently in chocolate. Milks were ultrafiltered to increase their protein content (3.08–5.33 g 100 g⁻¹), concentrated to different solids levels (42.8–52.3 g 100 g⁻¹) and spray-dried to produce powders (26–59 g 100 g⁻¹ fat). The relationships between the milk protein content, concentrate viscosity and some powder properties were quantified. The free-fat content of the powders increased linearly to 74 g 100 g⁻¹ fat with milk protein content for 26 and 40 g 100 g⁻¹ fat powders. The particle size and moisture content of the powders increased linearly with concentrate viscosity for 26 g 100 g⁻¹ fat powders. Differences between the control and ultrafiltration-treated milk powders were explained. The free-fat content and the particle size increased with the fat content of the control powders. The vacuole volume of the powders was inversely more related to the free-fat content than to the fat content of the control powders.     

荧光定量免疫层析法测定鸡肉和牛奶中的氯霉素

目的建立一种荧光定量免疫层析法测定动物源性食品鸡肉与牛奶中氯霉素残留的分析方法。方法将氯霉素鼠单克隆抗体与羧基化铕微球进行偶联标记。经过荧光微球活化、探针偶联等一系列条件优化确定最佳反应体系条件,根据纸条测试线(T线)信号值与质控线(C线)信号值的比值(T/C)和样本中氯霉素浓度建立定量标准曲线。针对鸡肉和牛奶样品,对荧光免疫层析检测方法的灵敏度、准确度和精密度等进行评价,并与液相色谱-串联质谱法(liquid chromatography-tandem mass spectrometry,LC-MS/MS)标准仪器分析方法进行比较。结果本研究建立的荧光免疫层析检测方法对鸡肉和牛奶中氯霉素残留的检出限分别为0.041μg/kg和0.040μg/kg,定量限分别为0.079和0.100μg/kg,添加回收率在76.26%～112.92%之间,变异系数均小于15%。结论本研究建立的荧光定量免疫层析方法灵敏度高、稳定性好,且与使用仪器方法得到的检测结果一致性较高,适用于鸡肉和牛奶中氯霉素残留的现场快速检测。     

DSC study on the influence of meat source, salt and fat levels, and processing parameters on batters pressurisation

 Hydrostatic high-pressure/temperature treatments were conducted at low (10 °C) and high temperatures (60, 70, and 80°C) on different types of meat batters. Pressure-induced effects on proteins were intensified by sodium chloride molarity at low and high temperatures. Treatments at 10°C under pressurisation yielded net thermal destabilisation effects on meat proteins pertaining either to muscle or batter systems. Heating at usual cooking temperature of 70°C under pressure yielded net stabilising effects on meat batter proteins. Overheating at 80°C was needed for entire protein denaturation. Pork and chicken meats were very similar in behaviour but chicken batters exhibited relatively higher thermal- and pressure-induced protein denaturation. Both kinds of physical destabilisation/stabilisation of proteins by pressure-induced effects increased with pressure level. Received: 30 December 1999 / Revised version: 14 February 2000     

Effect of addition of gelatin on microstructure of acidic milk gels and yoghurt and on their rheological properties

A study was made of the effect of the addition of gelatin on the microstructure of acid-heat-induced milk gels (90°C, pH=5.3) and yoghurt with and without the addition of 5% of milk solids, and a comparison was made with the microstructure of acidic milk gelatin gels obtained without heating (pH=5.3). It was seen that in the acid-heat-induced gels and in yoghurt the gelatin interacted with the network of milk proteins as a connection between the clusters formed, whereas it was the gelatin alone that was the basis of the formation of the gel when the milk did not reach the casein coagulation point (pH=5.3, unheated). The results of firmness tests indicated that the addition of 1.5% of gelatin developed fairly firm, deformable systems in all the cases studied, with a definite break point and almost total absence of syneresis. Dynamic rheology showed that the yoghurts with added gelatin exhibited more solid-like behaviour than the ones prepared without it.     

Effect of gamma irradiation on the texture and microstructure of chicken breast meat

This study investigated the textural and microstructural properties of chicken breast meat exposed to gamma irradiation ((60)Cobalt) and stored at 4?°C. Textural properties of the irradiated (n=27) and unirradiated chicken breasts (control) were determined by measuring shear force and cooking loss at day 0 and at 2-day intervals for a 14-day refrigerated storage period. In addition, microstructural changes of the irradiated and unirradiated chicken breasts were compared. Irradiated chicken breasts had more cooking loss and higher (P<0.0001) shear force than unirradiated chicken breasts. Transmission electron microscopy showed significant differences (P<0.0001) in size of myofibril units (sarcomeres) between irradiated and unirradiated breast. Shrinkage in sarcomere width (myofibril diameter) and disruption of myofibrils in irradiated breast meat were also noticed when compared with unirradiated breast meat.     

Effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken meat

This study examined the effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken leg and breast meat. The meat was frozen at three different temperatures (−7, −12 and −18 °C) and then stored at −18 °C for up to 6 months. A significant effect of frozen storage duration on lipid oxidation was detected in leg and breast meat, whereas freezing temperature had no significant effect. In leg meat, freezing at −7 °C had a significant impact on protein oxidation, measured as the increase in carbonyl groups and the decrease in total sulphydryl groups, after 3 months of frozen storage. Lipid and protein oxidation appeared to occur simultaneously in chicken meat during frozen storage and was more intense in leg meat than in breast meat.     

Milking and milk processing: traditional technologies in the yak farming system of the Qinghai-Tibetan Plateau, China

Yak milk and its products are widely consumed by local herders and are regarded as the resources of economic income by the households on the Qinghai-Tibetan Plateau. Yak raisers have developed their own milking skills and milk-processing technologies through a long history of yak keeping. All of these traditional skills and technologies have their own characteristics. In this paper, the methods and procedures of milking and milk processing in yak farming systems are reviewed.