UTILIZATION OF INVERSE WATER-IN-OIL EMULSIONS AS FAT REPLACERS IN FRANKFURTER MODEL SAUSAGES: INFLUENCE OF FAT EMULSION CONTENT ON THE ORGANOLEPTIC AND MECHANICAL PROPERTIES

The effect of fat content on the oral perception and the mechanical properties of frankfurter-type sausages was studied by means of absolute and hedonic organoleptic and mechanical tests. Panelists were able to discriminate changes of 5–10% in fat content. A correlation between fat content and organoleptic attributes was found, supporting a perception that the full-fat product is the de facto preferable product, to whose attributes others must conform.
Substituting fat with water-in-fat globules was found to imitate a full-fat sausage adequately in mechanical tests; however, organoleptic tests assessed the true fat content of the sausages. The tests indicate that it might be the absolute amount of fat, not the surface area of fat-covered globules, that correlates to the perception of fattiness. The above should be attributed to the lubrication and flocculation–coalescence of fat droplets with saliva in the mouth.

PRACTICAL APPLICATIONS

The substitution of fat globules by inverse water-in-fat globules in sausages was found to imitate a full-fat sausage adequately in mechanical tests; however, sensory tests confidently assessed the exact, true fat content of the sausages. This observation points out some limitations concerning the use of inverse emulsions as fat substitutes in relevant products.
Correlations between sensory attributes and fat level in sausages could imply that specific norms relating to fat level exist in the consumers, to which low-fat products may have to conform to.
The testers were able to attribute different scores, thus, discriminate sausages different at times by just 5–10% fat content. This could be of importance in the development of new low-fat sausage products.     

Functional and Sensory Properties of Meat Emulsions Produced by using Enzymatically Modified Gelatin

Mettwurst and Bologna sausage were produced from pork using enzymatically modified gelatin (EMG-8), which had been produced with covalent attachment of L-leucine n-octyl ester. EMG-8 improved spreadability, smoothness and softness of the Mettwurst. With the addition of EMG-8, the texture of the Bologna sausage was kept soft over a 1 to 7 day period of storage at 4°C or 2 to 4 weeks of storage at -20°C. Microscopic observation showed that fat globules in the Bologna sausage produced with EMG-8 were more homogeneously distributed than those in a control Bologna sausage.     

Studies on emulsion-type buffalo meat sausages incorporating skeletal and offal meat with different levels of pork fat

Ready-to-eat emulsion-type buffalo meat sausages were developed by using a combination of 80% meat components with 20% pork back fat. The meat components were constituted of 70 parts buffalo skeletal meat and 30 parts offal meat (rumen meat and heart meat in equal proportions). The emulsion stability, cooking losses of emulsions and sausages, composition of cooked sausages, eating quality of sausages and the microscopic characteristics of the raw emulsion and cooked sausages were studied. The light microscope micrograph of the raw emulsion showed uniformly well distributed fat globules embedded in a dense protein gel. The cooked emulsion also showed uniformly sized fat globules well distributed in a fine, compact, coagulated protein gel, which retained their original spherical shape. Good quality emulsion-type sausages could be produced having a high emulsion stability (0·87 ± 0·07 ml fat release/100 g emulsion); a low emulsion cooking loss (9·60 ± 0·60%) and a low sausage cooking loss (8·83 ± 0·48%). The overall acceptability of sausages was also high.     

Hydrolysis of bovine milk fat globules by lipoprotein lipase: inhibition by proteins extracted from milk fat globule membrane

Extraction of membrane proteins from milk fat globules by GuHCl or by MgCl2 made the lipids more accessible to lipolysis by added lipoprotein lipase. The increase in lipolysis paralleled the loss of membrane proteins and was continuous up to 2.5 M GuHCl, which was the highest concentration used. About twice as much protein was extracted with 2.5 M GuHCl as with buffer only. The amount of protein lost was about 50% of total milk fat globule protein. Lipolysis of milk fat globules was inhibited by addition of the extracted protein. The extracted proteins also reduced lipolysis when added to whole milk. More protein was needed to inhibit lipolysis of milk fat globules treated with GuHCl compared with globules treated with buffer only. The inhibition by a given amount of protein decreased if more milk fat globules were used. Protein extracted with MgCl2 had similar effects as those extracted with GuHCl. The major components extracted with MgCl2 migrated in the 40 to 50-kdalton region on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By gel filtration chromatography, two protein fractions were obtained, which inhibited lipolysis more efficiently than the total extract. As has previously been found for inhibition of lipolysis by skim milk, the amount of extracted protein needed to inhibit lipolysis varied between preparations of milk fat globules. Milk with propensity to cold-induced ("spontaneous") lipolysis was normalized by addition of extracted proteins.     

瓜尔豆胶对搅打稀奶油的搅打性能的影响

研究了不同浓度的瓜尔豆胶对搅打稀奶油乳状液的表观黏度、脂肪球粒度、脂肪球界面蛋白浓度、脂肪球部分聚结率、泡沫硬度和搅打起泡率的影响。结果表明，瓜尔豆胶对搅打稀奶油乳状液的表观黏度影响非常显著；瓜尔豆胶浓度过高或过低，都会使得解冻后的乳状液粒径变大；瓜尔豆胶的质量分数越高，脂肪球部分聚结速度越快，泡沫硬度也越大；搅打起泡率随着瓜尔豆胶质量分数增大而降低。     

Microstructure of Whey Protein Isolate Gels Containing Emulsified Butterfat Droplets

The effects of concentration and droplet size of anhydrous butterfat globules on the microstructure of heat-induced whey protein isolate gels (pH 4.60) were studied by scanning and transmission electron microscopy (TEM). All fat globules were emulsified with whey protein isolate and incorporated into the system prior to gelation. Protein aggregates became more closely packed as whey protein concentration was increased from 8 to 15% by weight in gels without added fat. There was no notable change in overall gel microstructure upon addition of fat globules, up to 25% by weight, when viewed by scanning electron microscopy. However, it appeared fat globules were intimately associated with the gel protein matrix. A twofold difference in fat globule size was obvious by TEM. Clusters of droplets became more predominant as butterfat content increased.     

INFLUENCE OF FAT CONTENT AND PRESERVATIVES ON THE BEHAVIOR OF LISTERIA MONOCYTOGENES IN BEAKER SAUSAGE

Behavior of Listeria monocytogenes Scott A in pork liver sausage containing 22–67% fat, and antilisterial activities of sodium lactate, sorbic acid, potassium sorbate and sodium propionate were studied during storage at 4C and 10C. Commercial pork liver sausage batter (22% fat), alone and with additions of lard (15, 30, and 45% by weight) were tested. Concentrations of 1.8% sodium lactate, 0.1% sorbate as the acid or the potassium salt, and 0.2% sodium propionate were tested in heat sterilized sausage inoculated with a 24 h culture of the organism (10⁴ CFU/g). Fat content alone caused small reductions in cell numbers by the end of the storage periods: from log CFU/g of 9.9 to 9.4 after 14 days at 10C, and from 7.3 to 6.5 after 50 days at 4C in the basic sausage formulation and with 45% added fat, respectively. The inhibitory activities of lactate and propionate increased with increase in fat content, and were more pronounced at 4C, where the effects were listericidal. Inhibition by sorbic acid was least influenced by the fat content, and the potassium salt was less antilisterial than the acid.     

红心火龙果替代部分脂肪对香肠蛋白质理化特性和脂质氧化的影响

传统香肠的脂肪含量通常较高，不符合低脂健康的消费发展需求，研究脂肪替代物，创制新型低脂香肠制品具有重要意义。本研究以猪后腿肉为原料，并以火龙果果肉替代香肠原始配比中10%、30%、50%的脂肪，分析其对香肠蛋白质溶解度、色差、感官品质、巯基含量、表面疏水性、荧光强度、酸价及硫代巴比妥酸反应物值（TBARs）等的影响。结果表明，随火龙果比例的增加，总蛋白、肌浆蛋白和肌原纤维蛋白溶解度均显著增加（P<0.05），与对照组相比，30%组分别增加12.1%、8.4%和18.6%。感官评价结果表明，30%组各方面都高于其他组。与对照组相比，10%组巯基含量显著增加，表面疏水性显著减少（P<0.05）。综上，红心火龙果替代部分脂肪加入至香肠中能够增加蛋白质溶解度、提升感官品质、抑制脂质氧化，且当添加量为30%时，香肠品质最佳。     

Effects of skipjack roe protein hydrolysate on properties and oxidative stability of fish emulsion sausage

Effects of skipjack roe protein hydrolysate (SRPH) at various levels (0–3 g/100 g) on properties and oxidative stability of emulsion sausage from broadhead catfish (Clarias macrocephalus) fortified with skipjack tuna roe lipids were investigated. The addition of SRPH increased hardness, cohesiveness and resilience of sausage (p < 0.05). Finer fat globules were visualised in the sample added with SRPH at higher amounts. Nevertheless, the incorporation of SRPH at all levels had no impact on likeness of sausages. SRPH was shown to retard lipid oxidation of sausage during extended storage of 12 days as evidenced by the lower peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS), in comparison with the control. After 12 days, the sausage with 3 g/100 g SRPH had the retained docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), accounting more than 80%. Addition of SRPH had no effect on the organoleptic properties but could prevent the development of rancidity. Nevertheless, it showed no pronounced impact on microbial growth. SRPH could therefore be used as a natural antioxidative emulsifier in cooked fish emulsion sausage.     

Microstructural Comparisons of Meat Emulsions Prepared with Corn Protein Emulsified and Unemulsified Fat

The microstructures of comminuted meat products containing 0, 1 and 2% of corn germ protein as a powder additive and as a stabilizer for pre-emulsified fat (PEF) were studied. A modified fixation technique and protein contrasting ingredient were used to improve the resolution of the microstructure. Meat products containing 2% protein additive exhibited a uniform distribution of fat globules and increased water and fat binding capacity. Corn germ protein used as a stabilizer in PEF preparation formed a more uniform distribution of fat globules than of additive product. These protein micellar structures may stabilize the larger size fat globules, resulting in less coalescence of the fat component during heat treatment.     

Confocal Scanning Optical Microscopy of Meat Products

Confocal scanning optical microscopy (CSOM) was used to observe the internal structure of frankfurters and summer sausage. This new method allows optical sectioning of thick specimens and thus avoids the potential problem of smearing encountered when fat globules and bacteria are at the surface of sections.     

Development of the milk fat microstructure during the manufacture and ripening of Emmental cheese observed by confocal laser scanning microscopy

Changes in the physico-chemical properties and microstructure of milk fat globules were investigated during the manufacture and ripening of Emmental cheese. The measurement of fat globule size and apparent zeta-potential showed that they were slightly affected during cheese milk preparation, i.e. storage of cheese milk overnight at 4 °C and pasteurisation. After rennet-induced coagulation and heating of curd grains, coalescence caused the formation of large fat globules (i.e.>10 μm). The structure of fat in Emmental cheese was characterised in situ using confocal laser scanning microscopy (CLSM). The rennet-induced coagulation lead to the formation of a continuous network of casein strands in which fat globules of various sizes were entrapped. Heating of curd grains induced the formation of fat globule aggregates. Pressing of the curd grains resulted in the greatest disruption of milk fat globules, their coalescence, the formation of non-globular fat (free fat) and the release of the milk fat globule membrane (MFGM) material. This study showed that milk fat exists in three main forms in ripened Emmental cheese: (i) small fat globules enveloped by the MFGM; (ii) aggregates of partially disrupted fat globules and (iii) free fat, resulting from the disruption of the MFGM and allowing free triacylglycerols to fill voids in the protein matrix. The curd grain junctions formed in Emmental cheese were also characterised using CLSM: they are compact structures, rich in protein and devoid of fat globules.     

Removal of milk fat globules from whey protein concentrate 34% to prepare clear and heat-stable protein dispersions

Whey protein concentrates (WPC) are low-cost protein ingredients, but their application in transparent ready-to-drink beverages is limited due to turbidity caused by fat globules and heat instability. In this work, fat globules were removed from WPC 34% (WPC-34) to prepare heat-stable ingredients via the Maillard reaction. The removal of fat globules by acid precipitation and centrifugation was observed to be the most complete at pH 4.0, and the loss of protein was caused by micrometer-sized fat globules and protein aggregates. Spray-dried powder prepared from the transparent supernatant was glycated at 130°C for 20 and 30 min or 60°C for 24 and 48 h. The 2 groups of samples had comparable heat stability and degree of glycation, evaluated by free amino content and analytical ultracentrifugation, but high-temperature, short-time treatment reduced the color formation during glycation. Therefore, WPC-34 can be processed for application in transparent beverages.     

Effect of homogenization and heat treatment on the behavior of protein and fat globules during gastric digestion of milk

The effects of homogenization and heat treatment on the formation and the breakdown of clots during gastric digestion of whole milk were investigated using a human gastric simulator. Homogenization and heat treatment led to formation of coagula with fragmented and crumbled structures compared with the coagulum formed from raw whole milk, but a larger fraction of the protein and more fat globules were incorporated into the coagula induced by action of the milk-clotting enzyme pepsin. The fat globules in the whole milk appeared to be embedded in the clots as they formed. After formation of the clot, the greater numbers of pores in the structures of the clots formed with homogenized milk and heated whole milk led to greater rates of protein hydrolysis by pepsin, which resulted in faster release of fat globules from the clots into the digesta. Coalescence of fat globules occurred both in the digesta and within the protein clots no matter whether they were in homogenized or heated milk samples. The formation of clots with different structures and hence the changes in the rates of protein hydrolysis and the release of milk fat into the digesta in the stomach provide important information for understanding the gastric emptying of milk and the potential to use this knowledge to manipulate the bioavailability of fat and other fat-soluble nutrients in dairy products.     

Extrusion for Producing Low-fat Pork and its Use in Sausage as Affected by Soy Protein Isolate

Low-fat pork was produced at extrusion temperatures (ET) of 25, 32.2,43.3,54.4, or 65.6°C with addition of soy protein isolate (SPI) at 0,1.5, or 3% and evaluated by measuring chemical and physical properties of low-fat pork sausage links. ET and SPI addition influenced moisture retention and fat reduction. The highest ET(65.5°C) gave the highest fat reduction in extrudates. TBARS decreased as ET and SPI increased. Extrudates at higher ET made darker and redder sausages. The hardness value of the control was not different from that of sausages from 65.6°C ET extrudates. The fat-reduced sausages were more springy and cohesive than the control. Depending on fat reduction, twin-screw extrusion influenced sausage color, texture, and lipid oxidation. The sausage links from 65.6°C ET extrudates with 1.5% SPI had the lowest fat, lowest TBARS, least cooking loss and were not different in hardness from control high-fat sausages.     

Disruption of fat globules during concentration of whole milk in a pilot scale multiple-effect evaporator

The effects of heat treatment by direct steam injection (DSI) and concentration of whole milk using a pilot scale multiple-effect evaporator on fat globule size and the total milk fat globule membrane (MFGM) proteins were examined. In both nonpreheated and preheated whole milk, the size of milk fat globules decreased while the surface protein concentration of the fat globules increased as the milk passed through each effect of the evaporator. These results indicate that the fat globules were disrupted during DSI heating and evaporation and the proteins from the skim milk were adsorbed onto the fat globule surface.     

Structural properties of stirred yoghurt as influenced by whey proteins

The effect of whey protein addition on structural properties of stirred yoghurt systems at different protein and fat content was studied using laser diffraction spectroscopy, rheology and confocal laser scanning microscopy (CLSM). The composition of heated milk systems affected micro- and macroscopic properties of yoghurt gels. Particle size increased as a function of increasing whey protein content and decreased as a function of increased fat level. Firmness (elastic modulus) and apparent viscosity of manufactured yoghurt samples increased as a function of increased interparticle interactions, mainly caused by self-aggregation of whey proteins or aggregated whey protein-coated fat globules, respectively. The resistance towards shear-induced disruption of yoghurt gels increased with an increasing proportion of casein protein in the protein mixture, whereas products with high whey protein level revealed lower resistance behaviour towards shear-forces. CLSM images illustrated that the presence of large whey protein aggregates and lower number of fat globules lead to the formation of an interrupted and coarse gel microstructure characterised by large interstitial spaces. The higher the casein fraction and/or the fat level, the less interspaced voids in the network were observed. However, it is evident that the addition of whey proteins reinforces firmness properties of low-fat yoghurts comparable to characteristics of full-fat yoghurt.     

响应面法优化鸡肝肠加工工艺的研究

本研究以鸡肝为主要原料,利用响应面分析法优化其加工工艺。采用物性仪对鸡肝肠硬度、弹性、胶粘性、咀嚼性等分析,得出斩拌时间、水分添加量、大豆分离蛋白添加量对鸡肝肠质地的影响。进而采用Box-Behnken响应面设计试验,得到鸡肝肠的最优工艺条件。最佳鸡肝肠的加工工艺为斩拌时间8.3 min、大豆分离蛋白添加量为1.99%、水分添加量39.98 mL。采用上述方法,以感官分值和弹性为指标,鸡肝肠的综合品质较好,感官分值可达到92.90,弹性0.85,工艺优化结果具有良好的生产前景。     

蛋清蛋白乳化香肠的研制

主要研究了原料肉肥瘦比、蛋清添加量和卡拉胶添加量对乳化香肠品质的影响。实验结果表明,原料肉肥瘦比、蛋清添加量和卡拉胶添加量对乳化香肠品质有不同程度的影响,通过L9(34)正交实验得到最佳配比为:原料肉肥瘦比2∶8,蛋清蛋白添加量6%,卡拉胶添加量0.3%。在此最佳配比下,乳化香肠的感官评分为8.0,系水力为79.41%,剪切力为1.588kg.f。     

Rheological properties and microstructure of Cheddar cheese made with different fat contents

Reduced- and low-fat cheeses are desired based on composition but often fall short on overall quality. One of the major problems with fat reduction in cheese is the development of a firm texture that does not break down during mastication, unlike that observed in full-fat cheeses. The objective of this investigation was to determine how the amount of fat affects the structure of Cheddar cheese from initial formation (2 wk) through 24 wk of aging. Cheeses were made with target fat contents of 3 to 33% (wt/wt) and moisture to protein ratios of 1.5:1. This allowed for comparisons based on relative amounts of fat and protein gel phases. Cheese microstructure was determined by confocal scanning laser microscopy combined with quantitative image analysis. Rheological analysis was used to determine changes in mechanical properties. Increasing fat content caused an increase in size of fat globules and a higher percentage of nonspherical globules. However, no changes in fat globules were observed with aging. Cheese rigidity (storage modulus) increased with fat content at 10°C, but differences attributable to fat were not apparent at 25°C. This was attributable to the storage modulus of fat approaching that of the protein gel; therefore, the amount of fat or gel phase did not have an effect on the cheese storage modulus. The rigidity of cheese decreased with storage and, because changes in the fat phase were not detected, it appeared to be attributable to changes in the gel network. It appeared that the diminished textural quality in low-fat Cheddar cheese is attributed to changes in the breakdown pattern during chewing, as altered by fat disrupting the cheese network.