EFFECTS OF FUNCTIONAL DAIRY BASED PROTEINS ON NONFAT YOGURT QUALITY

Production of nonfat yogurt demands a careful control of quality parameters. It is common to use skim milk powder (SMP) to increase the total solid content of nonfat yogurt, but some functional dairy-based proteins, such as casein/caseinates and whey proteins, may improve the quality of nonfat yogurt.
The objectives of this study were to use whey protein isolate (WPI), sodium caseinate (NaCn) and yogurt texture improver (TI) in nonfat yogurt manufacture as an alternative for SMP, and to compare their potential influences on the physical, chemical and microbial properties of nonfat yogurts over a 12-day storage. All dry ingredients were added at 1% (w/v) concentration to yogurt milk. Yogurts differed from each other with different hardness values. Acetaldehyde contents of yogurts were in the range of 35–43 ppm. The acetaldehyde content of all yogurt types decreased during storage. The control yogurt had the most tyrosine content, and the WPI-fortified yogurt had the least. Using different dry dairy ingredients did not affect the numbers of starter cultures. In addition, no significant differences were observed among yogurt types regarding their mineral composition.

PRACTICAL APPLICATIONS

Functional dry dairy ingredients can be used to increase the total solid content of nonfat yogurt instead of using skim milk powder (SMP) or evaporation. Their high protein content, water-binding capacity, texture improvement properties and health benefits make these proteins suited for use in nonfat yogurts. This study compares the possible effects of using whey protein isolate (WPI), sodium caseinate (NaCn) and yogurt texture improver (TI) as an alternative for SMP on the physical, chemical and microbial properties of nonfat yogurts. It was found that substitution of SMP for WPI, NaCn and TI at the level of 1% affected the physical, chemical and microbial properties of nonfat yogurt.     

Preliminary observations on the effects of milk fortification and heating on microstructure and physical properties of stirred yogurt

The aim of this work was to study how milk fortification and heating affect yogurt microstructure (micellar characteristics, protein network) and physical properties (viscosity, water-holding capacity (WHC), and graininess). Milk was fortified with skim milk powder (control), whey protein concentrate (WPC), caseinate, or a mixture of caseinate and whey protein. Two heat treatments were applied, giving average whey protein denaturation levels of 58% and 77%. For caseinate-enriched yogurts, the heating effect was negligible. When milk was enriched with WPC, heating led to a high level of cross-linking within the gel network. Heating increased yogurt viscosity and WHC, but also graininess. When milk was fortified with a blend of WPC and caseinate giving a whey protein-to-casein ratio of 0.20, the yogurt viscosity was greatly improved, while graininess was kept low. The results show a relationship between micelle solvation and yogurt microstructure, as well as micelle size in milk base and yogurt graininess.     

Comparison of micellar casein isolate and nonfat dry milk for use in the production of high-protein cultured milk products

High protein levels in yogurt, as well as the presence of denatured whey proteins in the milk, lead to the development of firm gels that can make it difficult to formulate a fluid beverage. We wanted to prepare high-protein yogurts and explore the effects of using micellar casein isolate (MCI), which was significantly depleted in whey protein by microfiltration. Little is known about the use of whey protein-depleted milk protein powders for high-protein yogurt products. Microfiltration also depletes soluble ions, in addition to whey proteins, and so alterations to the ionic strength of rehydrated MCI dispersions were also explored, to understand their effects on a high-protein yogurt gel system. Yogurts were prepared at 8% protein (wt/wt) from MCI or nonfat dry milk (NDM). The NDM was dispersed in water, and MCI powders were dispersed in water (with either low levels of added lactose to allow fermentation to achieve the target pH, or a high level to match the lactose content of the NDM sample) or in ultrafiltered (UF) milk permeate to align its ionic strength with that of the NDM dispersion. Dispersions were then heated at 85°C for 30 min while stirring, cooled to 40°C in an ice bath, and fermented with yogurt cultures to a final pH of 4.3. The stiffness of set-style yogurt gels, as determined by the storage modulus, was lowest in whey protein-depleted milk (i.e., MCI) prepared with a high ionic strength (UF permeate). Confocal laser scanning microscopy and permeability measurements revealed no large differences in the gel microstructure of MCI samples prepared in various dispersants. Stirred yogurt made from MCI that was prepared with low ionic strength showed slow rates of elastic bond reformation after stirring, as well as slower increases in cluster particle size throughout the ambient storage period. Both the presence of denatured whey proteins and the ionic strength of milk dispersions significantly affected the properties of set and stirred-style yogurt gels. Results from this study showed that the ionic strength of the heated milk dispersion before fermentation had a large influence on the gelation pH and strength of acid milk gels, but only when prepared at high (8%) protein levels. Results also showed that depleting milk of whey proteins before fermentation led to the development of weak yogurt gels, which were slow to rebody and may be better suited for preparing cultured milk beverages where low viscosities are desirable.     

Industrial yogurt manufacture: monitoring of fermentation process and improvement of final product quality

Lactic acid fermentation during the production of skim milk and whole fat set-style yogurt was continuously monitored by measuring pH. The modified Gompertz model was successfully applied to describe the pH decline and viscosity development during the fermentation process. The viscosity and incubation time data were also fitted to linear models against ln(pH). The investigation of the yogurt quality improvement practices included 2 different heat treatments (80°C for 30 min and 95°C for 10 min), 3 milk protein fortifying agents (skim milk powder, whey powder, and milk protein concentrate) added at 2.0%, and 4 hydrocolloids (κ-carrageenan, xanthan, guar gum, and pectin) added at 0.01% to whole fat and skim yogurts. Heat treatment significantly affected viscosity and acetaldehyde development without influencing incubation time and acidity. The addition of whey powder shortened the incubation time but had a detrimental effect on consistency, firmness, and overall acceptance of yogurts. On the other hand, addition of skim milk powder improved the textural quality and decreased the vulnerability of yogurts to syneresis. Anionic stabilizers (κ-carrageenan and pectin) had a poor effect on the texture and palatability of yogurts. However, neutral gums (xanthan and guar gum) improved texture and prevented the wheying-off defect. Skim milk yogurts exhibited longer incubation times and higher viscosities, whereas they were rated higher during sensory evaluation than whole fat yogurts.     

Production of a yogurt-like product from plant foodstuffs and whey. Substrate preparation and fermentation

A mixed substrate composed of soya milk, oat flour and dried cheese whey (82, 11 and 7% respectively) had a content of lactose and protein similar to that of milk used for yogurt manufacture. Heat treatment for 20 min at 80°C resulted in a viscosity similar to that of yogurt whilst removing coliform and mesophilic aerobic bacteria, moulds and yeasts. Fermentation with traditional yogurt bacteria did not increase viscosity further, and the final product had similar acidity and texture to yogurt. Acid development, carbohydrate consumption, proteolysis and starters counts were followed during fermentation. The fermentation profile of the mixed substrate was very similar to that of milk.     

Maillard Reaction Products as Encapsulants for Fish Oil Powders

The use of Maillard reaction products for encapsulation of fish oil was investigated. Fish oil was emulsified with heated aqueous mixtures comprising a protein source (Na caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrates (glucose, dried glucose syrup, oligosaccharide) and spray‐dried for the production of 50% oil powders. The extent of the Maillard reaction was monitored using L*, a*, b* values and absorbance at 465 nm. Encapsulation efficiency was gauged by measurement of solvent‐extractable fat and the oxidative stability of the fish oil powder, which was determined by assessment of headspace propanal after storage of powders at 35 °C for 4 wk. Increasing the heat treatment (60 °C to 100 °C for 30 to 90 min) of sodium caseinate‐glucose‐glucose syrup mixtures increased Maillard browning but did not change their encapsulation efficiency. The encapsulation efficiency of all heated sodium caseinate‐glucose‐glucose syrup mixtures was high, as indicated by the low solvent‐extractable fat in powder (<2% powder, w/w). However, increasing the severity of the heat treatment of the sodium caseinate‐glucose‐glucose syrup mixtures reduced the susceptibility of the fish oil powder to oxidation. The increased protection afforded to fish oil in powders by increasing the temperature‐time treatment of protein‐carbohydrate mixtures before emulsification and drying was observed irrespective of the protein (sodium caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrate (glucose, glucose/dried glucose syrup, or oligosaccharide/dried glucose syrup) sources used in the formulation. Maillard reaction products produced by heat treatment of aqueous protein‐carbohydrate mixtures were effective for protecting microencapsulated fish oil and other oils (evening primrose oil, milk fat) from oxidation.     

Effect of Fortification with Various Types of Milk Proteins on the Rheological Properties and Permeability of Nonfat Set Yogurt

ABSTRACT: Yogurt base was prepared from reconstituted skim milk powder (SMP) with 2.5% protein and fortified with additional 1% protein (wt/wt) from 4 different milk protein sources: SMP, milk protein isolate (MPI), micellar casein (MC), and sodium caseinate (NaCN). Heat‐treated yogurt mixes were fermented at 40 °C with a commercial yogurt culture until pH 4.6. During fermentation pH was monitored, and storage modulus (G′) and loss tangent (LT) were measured using dynamic oscillatory rheology. Yield stress (σ_yield) and permeability of gels were analyzed at pH 4.6. Addition of NaCN significantly reduced buffering capacity of yogurt mix by apparently solubilizing part of the indigenous colloidal calcium phosphate (CCP) in reconstituted SMP. Use of different types of milk protein did not affect pH development except for MC, which had the slowest fermentation due to its very high buffering. NaCN‐fortified yogurt had the highest G′ and σ_yield values at pH 4.6, as well as maximum LT values. Partial removal of CCP by NaCN before fermentation may have increased rearrangements in yogurt gel. Soluble casein molecules in NaCN‐fortified milks may have helped to increase G′ and LT values of yogurt gels by increasing the number of cross‐links between strands. Use of MC increased the CCP content but resulted in low G′ and σ_yield at pH 4.6, high LT and high permeability. The G′ value at pH 4.6 of yogurts increased in the order: SMP = MC < MPI < NaCN. Type of milk protein used to standardize the protein content had a significant impact on physical properties of yogurt. Practical Application: In yogurt processing, it is common to add additional milk solids to improve viscosity and textural attributes. There are many different types of milk protein powders that could potentially be used for fortification purposes. This study suggests that the type of milk protein used for fortification impacts yogurt properties and sodium caseinate gave the best textural results.     

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.     

How is an ideal satiating yogurt described? A case study with added-protein yogurts

Protein is recognized as the macronutrient with the highest satiating ability. Yogurt can be an excellent basis for designing satiating food as it is protein-based food product. Five different set-type yogurts were formulated by adding extra skim milk powder (MP), whey protein concentrate (WPC), calcium caseinate (CAS) or a blend of whey protein concentrate with calcium caseinate (CAS–WPC). A control yogurt without extra protein content was also prepared. Differences in sensory perceptions (through CATA questions) were related to the consumers' expected satiating ability and liking scores (of several modalities). In addition, an “Ideal satiating yogurt” was included in the CATA question to perform a penalty analysis to show potential directions for yogurt reformulation and to relate sensory and non-sensory yogurt characteristics to satiating capacity.     

Effects of Polymerized Whey Proteins on Consistency and Water-holding Properties of Goat's Milk Yogurt

ABSTRACT The effects of polymerized whey proteins (PWP) on functional properties of goat's milk yogurt were investigated. PWP were prepared by heating whey protein isolate (WPI) dispersion (8.0% protein, pH 7.0) at 90 °C for 30 min. Three reconstituted goat milk (RGM) (12% total solids [TS] as control; RGM with 2.4% unheated WPI; and RGM with 2.4% PWP) and 1 RGM with 16.7% TS were prepared and inoculated with 0.04% yogurt starter culture. Inoculated milk was incubated at 43 °C for 5 h, cooled to 4 °C in an ice‐water bath, and then placed at refrigerator (4 °C) overnight before testing. Incorporation of PWP significantly (P < 0.001) increased the viscosity (by 80%) and decreased the syneresis (by 25%) of the yogurt samples, whereas addition of unheated WPI did not significantly affect the viscosity and syneresis compared with the control. There were no changes in pH, TS, ash, fat, protein, and lactose contents among yogurt samples except the solids fortified control. Yogurt with 16.7% TS had the lowest syneresis but did not improve in viscosity. Transmission electron microscopy micrographs demonstrated that the microstructure of the goat's milk yogurt gel with PWP was denser than the control. Results of this study indicate that polymerized whey proteins may be a novel protein‐based thickening agent for improving the functional properties of goat's milk yogurt and other similar products.     

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.     

Improved Acid, Flavor and Volatile Compound Production in a High Protein and Fiber Soymilk Yogurt-like Product

The effects of added caseinate (CAS), casein hydrolyzate (CASHY) and whey protein hydrolyzate (WPHY) on acid, flavor and volatile compound production in a high protein and fiber soymilk yogurt-like product were studied. High protein and fiber soymilk, produced by blending soaked, boiled and dehulled soybeans with Swiss cheese whey ultrafiltration permeate, was fermented with a mixed S. thermophilus and L. bulgaricus yogurt culture. The concentrations of lactic acid, key volatile compounds, i.e., acetaldehyde, acetone, and diacetyl, and the flavor and texture of the resulting soymilk based yogurt formulated with added CAS or CASHY were comparable to those in a milk yogurt control.     

Freezing Qualities of Raw Ovine Milk for Further Processing

Raw whole ovine (sheep) milk was frozen at −15°C and −27°C and microbiological and physico-chemical properties were evaluated periodically. Total bacteria decreased at a faster rate in milk stored at −15 than at −27°C. Acid degree values for milk stored at −15°C were significantly higher than that stored at _27°C. Samples stored at −15°C exhibited protein destabilization after 6 mo of storage, while those stored at −27°C were stable throughout the 12-mo storage period.Frozen ovine milk was evaluated in several products including cheese, yogurt, and whey protein concentrates. Products produced from milk frozen at −27°C exhibited good sensory and functional characteristics. Ovine whey showed a higher proportion of β-lactoglobulin, about the same proportion of α-lactalbumin and lower proportions of serum albumin and immunoglobulin than bovine whey. Ovine whey protein concentrate showed significantly better foam overrun, foam stability, and gel strength than bovine or caprine whey protein concentrates.     

Power ultrasound as a tool to improve the processability of protein-enriched fermented milk gels for Greek yogurt manufacture

One approach to avoid production of acid whey during the manufacture of high-protein yogurt and related products is to concentrate the milk before fermentation. However, the resultant gels are firm so that stirring in the tank and further processing are difficult on an industrial scale. We hypothesize that power ultrasound (US) during fermentation softens the gel because sound waves cause cavitation and strong shear forces in the fluid. Skim milk was standardized to different protein contents up to 12%, heated (85°C, 30 min), and acidified with thermophilic or mesophilic starter cultures. An excessive increase in gel firmness as a function of protein content was detected. In the next series of experiments, US was applied during fermentation. Milks (10% protein) were acidified at 43.5°C and sonicated from pH 5.8 to 5.1 with a sonotrode (20 kHz, 20 W). Immediately after fermentation, gels were agitated using a rheometer with a vane geometry. The maximum torque required to break the gel was reduced by 75% following US, and gel firmness was reduced by 80%. Gels were then processed into stirred yogurt and analyzed. Sonicated samples were smoother with fewer large aggregates. Confocal laser scanning microscopy images suggested a less cohesive structure and more compact microgel particles, resulting in reduced viscosity. We concluded that US is a promising tool to weaken the gel and facilitate further processing. This enables new approaches for the manufacture of Greek yogurt, particularly in regard to avoiding production of acid whey and developing products with novel textures.     

Production and Evaluation of Yogurt with Concentrated Grape Juice

Fruit yogurt was prepared by adding concentrated grape juice (pekmez) CGJ, to milk. Optimum CGJ concentration and its influence on quality and fermentation process of yogurt were evaluated. The pH, titratable acidity, protein content, viscosity, whey syneresis, starter bacteria, mold and yeast counts were determined weekly at 4°C for 1 month. Addition of 10% CGJ provided desired sweetness. After 4h incubation of 5–10–15% CGJ-added yogurts the pH was 4.44, 4.98 and 5.90, respectively, and the control was pH 4.26. CGJ addition increased fermentation time and decreased viscosity. During storage, acidity of 10% CGJ-added yogurt remained lower (P<0.05) than controls. CGJ did not affect (P>0.05) protein content and molds or yeasts were not detected.     

The effect of substitution of fat by microparticulate whey protein on the quality of set-type, natural yogurt

Low calorie yogurts were manufactured from reconstituted skimmed milk powder using microparticulate whey protein (Simplesse 100® in wet and dry form) as a fat substitute. They were compared with yogurt containing anhydrous milk fat (AMF 1·5%). The quality of whey protein based yogurts (at a 1·5% level of addition) was high and similar to that of the control samples containing AMF. However, serum separation was higher and firmness was lower for yogurts containing microparticulate whey protein than for those containing AMF. This difference between yogurt containing AMF and microparticulate whey protein was most marked when microparticulate whey protein (ie, wet type) was incorporated on an equivalent dry matter basis to AMF. The sensory panel identified significant differences (p<0·05) between products containing AMF and microparticulate whey protein only in terms of sour odour and perceived serum separation.     

Optimization of Yogurt Production Using Demineralized Whey

The effect of three independent fermentation variables: demineralized whey powder (0.0; 1.5 and 3.0%), lactic culture concentration (1.0; 2.0 and 3.0%) and mix treatment temperature (85; 90 and 95°C) was studied. Fermentation time to reach pH 4.3, instrumental consistency and appearance, visual consistency and taste of the product were evaluated. Product consistency increased as mix treatment temperature increased and demineralized whey powder decreased. The powder had a stronger influence on instrumental consistency than did temperature. Appearance was better when whey powder was used at 1.4 to 1.6%. Visual consistency decreased as whey powder increased but addition of demineralized whey powder did not negatively affect yogurt flavor.     

Why semicarbazide (SEM) is not an appropriate marker for the usage of nitrofurazone on agricultural animals

A comprehensive global database on semicarbazide (SEM) in foodstuffs and food ingredients is presented, with over 4000 data collected in foods such as seafood (crustaceans, fish powders), meat (beef, chicken powders), dairy products (e.g. raw milk, milk powders, whey, sweet buttermilk powder, caseinate, yoghurt, cheese), honey and other ingredients. The results provide evidence that the presence of SEM in certain dairy ingredients (whey, milk protein concentrates) is a by-product of chemical reactions taking place during the manufacturing process. Of the dairy ingredients tested (c. 2000 samples), 5.3% showed traces of SEM > 0.5 µg/kg. The highest incidence of SEM-positive samples in the dairy category were whey (powders, liquid) and milk protein concentrates (35% positive), with up to 13 µg/kg measured in a whey powder. Sweet buttermilk powder and caseinate followed, with 27% and 9.3% positives, respectively. SEM was not detected in raw milk, or in yoghurt or cheese. Of the crustacean products (shrimp and prawn powders) tested, 44% were positive for SEM, the highest value measured at 284 µg/kg. Fish powders revealed an unexpectedly high incidence of positive samples (25%); in this case, fraudulent addition of shellfish shells or carry-over during processing cannot be excluded. Overall, the data provide new insights into the occurrence of SEM (for dairy products and fish powders), substantially strengthening the arguments that SEM in certain food categories is not a conclusive marker of the use of the illegal antibiotic nitrofurazone.     

Influence of Wall Material and Inlet Drying Air Temperature on the Microencapsulation of Fish Oil by Spray Drying

Several single and composite milk-originated wall materials were used to microencapsulate fish oil via spray drying at various inlet drying air temperatures. Skim milk powder (SMP), whey protein concentrate, whey protein isolate (WPI), 80% WPI?+?20% milk protein concentrate, and 80% WPI?+?20% sodium caseinate (NaCas) were applied as the wall for capsules generated at drying air temperatures of 140, 160, and 180 °C. The higher the drying air temperature, the higher was the particle size, encapsulation efficiency, and peroxide value and the lower was the moisture content and bulk density. The microcapsules prepared with SMP showed the highest encapsulation efficiency and lowest peroxide value for the oil due to the presence of lactose in its chemical composition. Differential scanning calorimetry and Fourier transform infrared analyses indicated the absence of any significant interaction between SMP and fish oil.     

Small and large deformation rheology and microstructure of κ-carrageenan gels containing commercial milk protein products

The rheological behaviour of commercial milk protein/κ-carrageenan mixtures in aqueous solutions was studied at neutral pH. Four milk protein ingredients; skim milk powder, milk protein concentrate, sodium caseinate, and whey protein isolate were considered. As seen by confocal laser microscopy, mixtures of κ-carrageenan with skim milk powder, milk protein concentrate, and sodium caseinate showed phase separation, but no phase separation was observed in mixtures containing whey protein isolate. For κ-carrageenan concentrations up to 0.5 wt%, the viscosity of the mixtures at low shear rates increased markedly in the case of skim milk powder and milk protein concentrate addition, but did not change by the addition of sodium caseinate or whey protein isolate. For κ-carrageenan concentrations from 1 to 2.5 wt%, small and large deformation rheological measurements, performed on the milk protein/κ-carrageenan gels, showed that skim milk powder, milk protein concentrate or sodium caseinate markedly improved the strength of the resulting gels, but whey protein isolate had no effect on the gel stength.