Viability of probiotic micro-organisms during storage, postacidification and sensory analysis of fat-free yogurts with added whey protein concentrate

The aim of this research was to evaluate the effect of the addition of whey protein concentrate (WPC) on the viability of Lactobacillus acidophilus and Bifidobacterium longum and on postacidification throughout the shelf life of fat-free yogurts, and also to analyse the sensory characteristics of the products. Postacidification was not significantly changed by the addition of WPC, but was decreased by Lactobacillus bulgaricus inoculation. WPC did not influence the viability of the lactic acid bacteria ( L. bulgaricus and Streptococcus thermophilus ), but it improved the growth and survival of the micro-organisms L. acidophilus and B. longum , especially the former. The panellists did not identify significant differences ( P <  0.05) of the yogurts due to the addition of WPC.     

Effects of standardization of whole milk with dry milk protein concentrate on the yield and ripening of reduced-fat cheddar cheese

Commercial milk protein concentrate (MPC) was used to standardize whole milk for reduced-fat Cheddar cheesemaking. Four replicate cheesemaking trials of three treatments (control, MPC1, and MPC2) were conducted. The control cheese (CC) was made from standardized milk (casein-to-fat ratio, C/F approximately 1.7) obtained by mixing skim milk and whole milk (WM); MPC1 and MPC2 cheeses were made from standardized milk (C/F approximately 1.8) obtained from mixing WM and MPC, except that commercial mesophilic starter was added at the rate of 1% to the CC and MPC1 and 2% to MPC2 vats. The addition of MPC doubled cheese yields and had insignificant effects on fat recoveries (approximately 94% in MPC1 and MPC2 vs. approximately 92% in CC) but increased significantly total solids recoveries (approximately 63% in CC vs. 63% in MPC1 and MPC2). Although minor differences were noted in the gross composition of the cheeses, both MPC1 and MPC2 cheeses had lower lactose contents (0.25 or 0.32%, respectively) than in CC (0.60%) 7 d post manufacture. Cheeses from all three treatments had approximately 10(9) cfu/g initial starter bacteria count. The nonstarter lactic acid bacteria (NSLAB) grew slowly in MPC1 and MPC2 cheeses during ripening compared to CC, and at the end of 6 mo of ripening, numbers of NSLAB in the CC were 1 to 2 log cycles higher than in MPC1 and MPC2 cheeses. Primary proteolysis, as noted by water-soluble N contents, was markedly slower in MPC1 and MPC2 cheeses compared to CC. The concentrations of total free amino acids were in decreasing order CC > MPC2 > MPC1 cheeses, suggesting slower secondary proteolysis in the MPC cheeses than in CC. Sensory analysis showed that MPC cheeses had lower brothy and bitter scores than CC. Increasing the amount of starter bacteria improved maturity in MPC cheese.     

Use of acid whey protein concentrate as an ingredient in nonfat cup set-style yogurt

Acid whey resulting from the production of soft cheeses is a disposal problem for the dairy industry. Few uses have been found for acid whey because of its high ash content, low pH, and high organic acid content. The objective of this study was to explore the potential of recovery of whey protein from cottage cheese acid whey for use in yogurt. Cottage cheese acid whey and Cheddar cheese whey were produced from standard cottage cheese and Cheddar cheese-making procedures, respectively. The whey was separated and pasteurized by high temperature, short time pasteurization and stored at 4°C. Food-grade ammonium hydroxide was used to neutralize the acid whey to a pH of 6.4. The whey was heated to 50°C and concentrated using ultrafiltration and diafiltration with 11 polyethersulfone cartridge membrane filters (10,000-kDa cutoff) to 25% total solids and 80% protein. Skim milk was concentrated to 6% total protein. Nonfat, unflavored set-style yogurts (6.0 ± 0.1% protein, 15 ± 1.0% solids) were made from skim milk with added acid whey protein concentrate, skim milk with added sweet whey protein concentrate, or skim milk concentrate. Yogurt mixes were standardized to lactose and fat of 6.50% and 0.10%, respectively. Yogurt was fermented at 43°C to pH 4.6 and stored at 4°C. The experiment was replicated in triplicate. Titratable acidity, pH, whey separation, color, and gel strength were measured weekly in yogurts through 8 wk. Trained panel profiling was conducted on 0, 14, 28, and 56 d. Fat-free yogurts produced with added neutralized fresh liquid acid whey protein concentrate had flavor attributes similar those with added fresh liquid sweet whey protein but had lower gel strength attributes, which translated to differences in trained panel texture attributes and lower consumer liking scores for fat-free yogurt made with added acid whey protein ingredient. Difference in pH was the main contributor to texture differences, as higher pH in acid whey protein yogurts changed gel structure formation and water-holding capacity of the yogurt gel. In a second part of the study, the yogurt mix was reformulated to address texture differences. The reformulated yogurt mix at 2% milkfat and using a lower level of sweet and acid whey ingredient performed at parity with control yogurts in consumer sensory trials. Fresh liquid acid whey protein concentrates from cottage cheese manufacture can be used as a liquid protein ingredient source for manufacture of yogurt in the same factory.     

Effect of anthocyanin-absorbed whey protein microgels on physicochemical and textural properties of reduced-fat Cheddar cheese

Reduced-fat foods have become more popular due to their health benefits; however, reducing the fat content of food affects the sensory experience. Therefore, it is necessary to improve the sensory acceptance of reduced-fat foods to that of full-fat equivalents. The aim of this study was to evaluate the effect of adding whey protein microgels (WPM) with an average diameter of 4 μm, or WPM with adsorbed anthocyanins [WPM (Ant)] on the textural and sensory properties of reduced-fat Cheddar cheese (RFC). Reduced-fat Cheddar cheese was prepared in 2 ways: (1) by adding WPM, designated as RFC+M, or (2) by adding WPM (Ant), designated as RFC+M (Ant). For comparison, RFC without fat substitutes and full-fat Cheddar cheese were also prepared. We discovered that the addition of WPM and WPM (Ant) increased the moisture content, fluidity, and meltability of RFC, and reduced its hardness, springiness, and chewiness. The textural and sensory characteristics of RFC were markedly inferior to those of full-fat Cheddar cheese, whereas addition of WPM and WPM (Ant) significantly improved the sensory characteristics of RFC. The WPM and WPM (Ant) showed a high potential as fat substitutes and anthocyanin carriers to effectively improve the acceptance of reduced-fat foods.     

The effect of starter culture and annatto on the flavor and functionality of whey protein concentrate

The flavor of whey protein can carry over into ingredient applications and negatively influence consumer acceptance. Understanding sources of flavors in whey protein is crucial to minimize flavor. The objective of this study was to evaluate the effect of annatto color and starter culture on the flavor and functionality of whey protein concentrate (WPC). Cheddar cheese whey with and without annatto (15 mL of annatto/454 kg of milk, annatto with 3% wt/vol norbixin content) was manufactured using a mesophilic lactic starter culture or by addition of lactic acid and rennet (rennet set). Pasteurized fat-separated whey was then ultrafiltered and spray dried into WPC. The experiment was replicated 4 times. Flavor of liquid wheys and WPC were evaluated by sensory and instrumental volatile analyses. In addition to flavor evaluations on WPC, color analysis (Hunter Lab and norbixin extraction) and functionality tests (solubility and heat stability) also were performed. Both main effects (annatto, starter) and interactions were investigated. No differences in sensory properties or functionality were observed among WPC. Lipid oxidation compounds were higher in WPC manufactured from whey with starter culture compared with WPC from rennet-set whey. The WPC with annatto had higher concentrations of p-xylene, diacetyl, pentanal, and decanal compared with WPC without annatto. Interactions were observed between starter and annatto for hexanal, suggesting that annatto may have an antioxidant effect when present in whey made with starter culture. Results suggest that annatto has a no effect on whey protein flavor, but that the starter culture has a large influence on the oxidative stability of whey.     

Whey protein concentrate and gum tragacanth as fat replacers in nonfat yogurt: chemical, physical, and microstructural properties

The effect of whey protein concentrate (WPC) and gum tragacanth (GT) as fat replacers on the chemical, physical, and microstructural properties of nonfat yogurt was investigated. The WPC (7.5, 15, and 20 g/L) and GT (0.25, 0.5, 0.75, and 1 g/L) were incorporated into the skim milk slowly at 40 to 45°C with agitation. The yogurt mixes were pasteurized at 90°C for 10 min, inoculated with 0.1% starter culture, and incubated at 42°C to pH 4.6, then refrigerated overnight at 5°C. A control nonfat yogurt and control full fat yogurt were prepared as described, but without addition of WPC and GT. Increasing amount of WPC led to the increase in total solids, total protein, acidity, and ash content, whereas GT did not affect chemical parameters. Increasing WPC caused a more compact structure consisting of robust casein particles and large aggregates. Firmness was increased and susceptibility to syneresis was decreased as WPC increased. No significant difference was observed for firmness and syneresis of yogurt fortified with GT up to 0.5 g/L compared with control nonfat yogurt. Increasing the amount of gum above 0.5 g/L produced softer gels with a greater tendency for syneresis than the ones prepared without it. Addition of GT led to the coarser and more open structure compared with control yogurt.     

Production of a high gel strength whey protein concentrate from cheese whey

In order to develop a process for the production of a whey protein concentrate (WPC) with high gel strength and water-holding capacity from cheese whey, we analyzed 10 commercially available WPC with different functional properties. Protein composition and modification were analyzed using electrophoresis, HPLC, and mass spectrometry. The analyses of the WPC revealed that the factors closely associated with gel strength and water-holding capacity were solubility and composition of the protein and the ionic environment. To maintain whey protein solubility, it is necessary to minimize heat exposure of the whey during pretreatment and processing. The presence of the caseinomacropeptide (CMP) in the WPC was found to be detrimental to gel strength and water-holding capacity. All of the commercial WPC that produced high-strength gels exhibited ionic compositions that were consistent with acidic processing to remove divalent cations with subsequent neutralization with sodium hydroxide. We have shown that ultrafiltration/diafiltration of cheese whey, adjusted to pH 2.5, through a membrane with a nominal molecular weight cut-off of 30,000 at 15 degrees C substantially reduced the level of CMP, lactose, and minerals in the whey with retention of the whey proteins. The resulting WPC formed from this process was suitable for the inclusion of sodium polyphosphate to produce superior functional properties in terms of gelation and water-holding capacity.     

乳清浓缩蛋白在酸奶生产中的应用

以鲜奶，奶粉，乳清蛋白等乳成分为主要原料，研究了乳清浓缩蛋白在酸奶生产中的制做方法，对乳清浓缩蛋白代替部分高档脱脂奶粉生产酸奶产品的保水率，粘度，口感及组织状态进行了比较分析。结果表明，在酸奶生产中，添加一定的浓缩乳清蛋白代替高档脱脂奶粉是可行的，产品较为理想。     

The effect of bleaching agent on the flavor of liquid whey and whey protein concentrate

The increasing use and demand for whey protein as an ingredient requires a bland-tasting, neutral-colored final product. The bleaching of colored Cheddar whey is necessary to achieve this goal. Currently, hydrogen peroxide (HP) and benzoyl peroxide (BPO) are utilized for bleaching liquid whey before spray drying. There is no current information on the effect of the bleaching process on the flavor of spray-dried whey protein concentrate (WPC). The objective of this study was to characterize the effect of bleaching on the flavor of liquid and spray-dried Cheddar whey. Cheddar cheeses colored with water-soluble annatto were manufactured in duplicate. Four bleaching treatments (HP, 250 and 500 mg/kg and BPO, 10 and 20 mg/kg) were applied to liquid whey for 1.5 h at 60°C followed by cooling to 5°C. A control whey with no bleach was also evaluated. Flavor of the liquid wheys was evaluated by sensory and instrumental volatile analysis. One HP treatment and one BPO treatment were subsequently selected and incorporated into liquid whey along with an unbleached control that was processed into spray-dried WPC. These trials were conducted in triplicate. The WPC were evaluated by sensory and instrumental analyses as well as color and proximate analyses. The HP-bleached liquid whey and WPC contained higher concentrations of oxidation reaction products, including the compounds heptanal, hexanal, octanal, and nonanal, compared with unbleached or BPO-bleached liquid whey or WPC. The HP products were higher in overall oxidation products compared with BPO samples. The HP liquid whey and WPC were higher in fatty and cardboard flavors compared with the control or BPO samples. Hunter CIE Lab color values (L*, a*, b*) of WPC powders were distinct on all 3 color scale parameters, with HP-bleached WPC having the highest L* values. Hydrogen peroxide resulted in a whiter WPC and higher off-flavor intensities; however, there was no difference in norbixin recovery between HP and BPO. These results indicate that the bleaching of liquid whey may affect the flavor of WPC and that the type of bleaching agent used may affect WPC flavor.     

Viability and activity of bifidobacteria in yoghurt containing fructooligosaccharide during refrigerated storage

The viability of yoghurt bacteria and two commercial strains of bifidobacteria was assessed in either yoghurt containing chicory fructooligosaccharide (FOS) or without any prebiotic, during 28 days storage at 4 °C. All the products showed a decrease in the viable count of yoghurt bacteria and bifidobacteria during storage. Numbers of Lactobacillus delbrueckii ssp. bulgaricus decreased faster than those for Streptococcus thermophilus. The viability of bifidobacteria in yoghurt was affected by the strain type and the presence of FOS. Bifidobacterium animalis exhibited better stability in the yoghurt than B. longum. The recommended level of 1 million cells was exceeded for B. animalis throughout storage. The highest viable number of bifidobacteria (3.59–2.25 × 10⁷ CFU g^?1) was obtained in the product containing B. animalis and FOS. Viability of B. longum in yoghurt containing FOS remained above 10⁶ CFU g^?1 for up to 21 days, whereas this level was maintained for only 7 days for that organism in yoghurt without any prebiotic.     

Physical properties of yogurt fortified with various commercial whey protein concentrates

The effects of whey protein concentrates on physical and rheological properties of yogurt were studied. Five commercial whey protein concentrates (340 g kg^?1 protein nominal) were used to fortify milk to 45 g protein kg^?1. Fermentation was performed with two different starters (ropy and non‐ropy). Resulting yogurts were compared with a control yogurt enriched with skim milk powder. The water‐holding capacity of the yogurt fortified with skim milk powder was 500 g kg^?1 and ranged from 600 to 638 g kg^?1 when fortified with whey protein concentrates. Significant rheological differences have been noticed between the yogurts fortified with different whey protein concentrates, independent of the starter used. Three whey protein concentrates generated yogurts with a behavior similar to the control. The two others produced yogurt with lower firmness (15 g compared with 17 g), lower Brookfield viscosity (6 Pa s compared with 9 Pa s), lower yield stress (2 Pa compared with 4 Pa), lower complex viscosity (13 Pa s compared with 26 Pa s), and lower apparent viscosity (0.4 Pa s compared with 1 Pa s) than the control, respectively. The yogurts with the lowest firmness and viscosity were produced with concentrates which contained the highest amount of non‐protein nitrogen fraction (160 g kg^?1 versus 126 g kg^?1 of the total nitrogen), and the highest amount of denaturation of the whey protein (262 versus 200 g kg^?1 of the total nitrogen). Copyright © 2004 Society of Chemical Industry     

The effect of acidification of liquid whey protein concentrate on the flavor of spray-dried powder

Off-flavors in whey protein negatively influence consumer acceptance of whey protein ingredient applications. Clear acidic beverages are a common application of whey protein, and recent studies have demonstrated that beverage processing steps, including acidification, enhance off-flavor production from whey protein. The objective of this study was to determine the effect of preacidification of liquid ultrafiltered whey protein concentrate (WPC) before spray drying on flavor of dried WPC. Two experiments were performed to achieve the objective. In both experiments, Cheddar cheese whey was manufactured, fat-separated, pasteurized, bleached (250 mg/kg of hydrogen peroxide), and ultrafiltered (UF) to obtain liquid WPC that was 13% solids (wt/wt) and 80% protein on a solids basis. In experiment 1, the liquid retentate was then acidified using a blend of phosphoric and citric acids to the following pH values: no acidification (control; pH 6.5), pH 5.5, or pH 3.5. The UF permeate was used to normalize the protein concentration of each treatment. The retentates were then spray dried. In experiment 2, 150 μg/kg of deuterated hexanal (D₁₂-hexanal) was added to each treatment, followed by acidification and spray drying. Both experiments were replicated 3 times. Flavor properties of the spray-dried WPC were evaluated by sensory and instrumental analyses in experiment 1 and by instrumental analysis in experiment 2. Preacidification to pH 3.5 resulted in decreased cardboard flavor and aroma intensities and an increase in soapy flavor, with decreased concentrations of hexanal, heptanal, nonanal, decanal, dimethyl disulfide, and dimethyl trisulfide compared with spray drying at pH 6.5 or 5.5. Adjustment to pH 5.5 before spray drying increased cabbage flavor and increased concentrations of nonanal at evaluation pH values of 3.5 and 5.5 and dimethyl trisulfide at all evaluation pH values. In general, the flavor effects of preacidification were consistent regardless of the pH to which the solutions were adjusted after spray drying. Preacidification to pH 3.5 increased recovery of D₁₂-hexanal in liquid WPC and decreased recovery of D₁₂-hexanal in the resulting powder when evaluated at pH 6.5 or 5.5. These results demonstrate that acidification of liquid WPC80 to pH 3.5 before spray drying decreases off-flavors in spray-dried WPC and suggest that the mechanism for off-flavor reduction is the decreased protein interactions with volatile compounds at low pH in liquid WPC or the increased interactions between protein and volatile compounds in the resulting powder.     

Effects of polymerized goat milk whey protein on physicochemical properties and microstructure of recombined goat milk yogurt

Goat milk whey protein concentrates were manufactured by microfiltration (MF) and ultrafiltration (UF). When MF retentate blended with cream, which could be used as a starting material in yogurt making. The objective of this study was to prepare goat milk whey protein concentrates by membrane separation technology and to investigate the effects of polymerized goat milk whey protein (PGWP) on the physicochemical properties and microstructure of recombined goat milk yogurt. A 3-stage MF study was conducted to separate whey protein from casein in skim milk with 0.1-µm ceramic membrane. The MF permeate was ultrafiltered using a 10 kDa cut-off membrane to 10-fold, followed by 3 step diafiltration. The ultrafiltration-diafiltration-treated whey was electrodialyzed to remove 85% of salt, and to obtain goat milk whey protein concentrates with 80.99% protein content (wt/wt, dry basis). Recombined goat milk yogurt was prepared by mixing cream and MF retentate, and PGWP was used as main thickening agent. Compared with the recombined goat milk yogurt without PGWP, the yogurt with 0.50% PGWP had desirable viscosity and low level of syneresis. There was no significant difference in chemical composition and pH between the recombined goat milk yogurt with PGWP and control (without PGWP). Viscosity of all the yogurt samples decreased during the study. There was a slight but not significant decrease in pH during storage. Bifidobacterium and Lactobacillus acidophilus in yogurt samples remained above 10⁶ cfu/g during 8-wk storage. Scanning electron microscopy of the recombined goat milk yogurt with PGWP displayed a compact protein network. Results indicated that PGWP prepared directly from raw milk may be a novel protein-based thickening agent for authentic goat milk yogurt making.     

陶瓷膜超滤技术浓缩乳清的工艺参数研究

采用孔径为20nm的无机陶瓷膜超滤干酪副产物乳清,浓缩乳清蛋白。通过对膜过滤压力、温度以及乳清pH三个因素进行单因素分析以及正交实验优化,得到最佳工艺条件:操作压力0.25MPa,温度51℃,pH6.1,此条件下超滤膜渗透通量达到169.37L/m2.h,乳清蛋白可浓缩至5.4%,经喷雾干燥制得WPC蛋白质含量为38.2%。     

乳清浓缩蛋白对搅拌型酸奶品质特性影响的研究

研究了以全脂奶粉和乳清浓缩蛋白（WPC-3503）为原料，按照全脂奶粉：乳清浓缩蛋白为100：0，90：10，80：20，70：30的质量配比生产乳固形物含量为12％的酸奶，对含有不同乳清蛋白比例的酸奶在贮藏过程中理化特性、乳酸菌总数的变化以及感官特性进行了比较分析。结果表明，WPC-3503代替10％-20％全脂奶粉生产酸奶时，在贮藏过程中可减缓pH值及酸度的变化速度，提高酸奶的黏度和保水率，改善感官特性，但对乳酸菌总数无明显的影响。     

Effect of double homogenization and whey protein concentrate on the texture of ice cream

Ice cream samples were made with a mix composition of 11% milk fat, 11% milk solids-not-fat, 13% sucrose, 3% corn syrup solids (36 dextrose equivalent), 0.28% stabilizer blend, or 0.10% emulsifier and vanilla extract. Mixes were high temperature short time pasteurized at 80 degrees C for 25 s, homogenized at 141 kg/cm2 pressure on the first stage and 35 kg/cm2 pressure on the second, and cooled to 3 degrees C. The study included six treatments from four batches of mix. Mix from batch one contained 0.10% emulsifier. Half of this batch (treatment 1), was subsequently frozen and the other half (upon exiting the pasteurizer) was reheated to 60 degrees C, rehomogenized at 141 kg/cm2 pressure on the first stage and 35 kg/cm2 pressure on the second (treatment 2), and cooled to 3 degrees C. Mix from batch two contained 0.28% stabilizer blend. Half of this batch was used as the control (treatment 3), the other half upon exiting the pasteurizer was reheated to 60 degrees C, rehomogenized at 141 kg/cm2 pressure on the first stage and 35 kg/cm2 pressure on the second (treatment 4), and cooled to 3 degrees C. Batch three, containing 0.10% emulsifier and 1% whey protein concentrate substituted for 1% nonfat dry milk, upon exiting the pasteurizer was reheated to 60 degrees C, rehomogenized at 141 kg/cm2 pressure on the first stage and 35 kg/cm2 pressure on the second (treatment 5), and cooled to 3 degrees C. Batch four, containing 0.28% stabilizer blend and 1% whey protein concentrate substituted for 1% nonfat dry milk, upon exiting the pasteurizer was reheated to 60 degrees C, rehomogenized at 141 kg/ cm2 pressure on the first stage and 35 kg/cm2 pressure on the second (treatment 6), and cooled to 3 degrees C. Consistency was measured by flow time through a pipette. Flow time of treatment 3 was greater than all treatments, and the flow times of treatments 4 and 6 were greater than treatments 1, 2, and 5. Flow time was increased in ice cream mix by the addition of stabilizer. Double homogenization lowered ice cream mix flow time in the presence of stabilizer, but no difference in flow time was observed without stabilizer addition. Treatment 4 had a lower mean ice crystal size at 10 d postmanufacture compared with treatment 3; however, overall texture acceptability between treatments 3 and 4 was similar. Mean ice crystal size of treatment 6 was less at 18 wk postmanufacture compared with treatment 3; however, overall texture acceptability for treatments 3, 4, and 6 was similar. Mean ice crystal sizes of treatments 1, 2, and 5 were greater at 10 d and 18 wk compared with treatment 3. Sensory evaluation indicated that treatments 3, 4, and 6 had higher mean scores for icy, coldness intensity, and creaminess than treatments 1, 2, and 5 at 10 d and 18 wk postmanufacture.