Greek Yogurt Research Articles

Quantitative Descriptive Analysis and Acceptance Testing of Yogurt with no Added Sugar

This study aimed to evaluate the effect of sucralose added in Greek Yogurt flavored with araticum (Annona crassiflora) and mangaba (Hancornia speciosa) through sensory characterization. The Greek yogurt was prepared with skimmed milk, inoculated starter cultures, filtered and it was supplemented with the appropriate amount of sucralose, added sweetened and pasteurized fruit pulp (araticum or mangaba). The total phenolic compounds and texture were performed and sensory analyses were carried out by Quantitative descriptive analysis (QDA) and acceptance test in storage for 7 and 28 days. The QDA results showed that the main attributes were color, lightness, creaminess, presence of particles, fullness, and aroma. Eighty percent and 85% of the panelists were said they would buy the araticum Greek yogurt and the mangaba Greek yogurt after 7 days of storage, respectively. Additionally, 71% and 77% were said they would buy the araticum Greek yogurt and the mangaba Greek yogurt after storage for 28 days at 4ºC, respectively. The sensory profile and acceptance test results of the Greek yogurts developed indicated no perceptions caused by adding sucralose to the yogurt after storage for different times. The highest concentration of phenolic compounds in the araticum Greek yogurt was perceived by the panelists in aroma and flavor attributes. Changing sucrose to sucralose was not imperceptible under the storage and consumption conditions.

Catalytic Production of Glucose-Galactose Syrup from Greek Yogurt Acid Whey in a Continuous-Flow Reactor.

The hydrolysis of lactose in aqueous solutions and dairy waste streams was studied using Amberlyst 70 as a heterogeneous acid catalyst in a continuous-flow packed-bed reactor. The catalyst was stable during hydrolysis of an aqueous lactose feed but deactivated owing to mineral poisoning when the dairy waste Greek yogurt acid whey (GAW) was used as the feedstock. A catalyst deactivation model was developed and showed that the deactivation of the Amberlyst 70 catalyst was proportional to the amounts of cations, urea and amino acids flowing through the catalyst bed. The Amberlyst 70 catalyst was regenerable with an aqueous acid regeneration treatment. Based on the experimental data, a rigorous technoeconomic analysis was performed for the production of glucose-galactose syrup (GGS) via lactose hydrolysis of GAW using three different catalysts. This approach shows that the GGS produced from GAW could become a valuable revenue stream for Greek yogurt manufacturers.

Functional, textural, and sensory properties of milk protein concentrate-based supercritical fluid extrudates made with acid whey

ABSTRACT The worldwide Greek yogurt market is a growing multi-billion-dollar industry in need of a solution for its environmentally problematic acid whey byproduct. This study evaluated the effects of concentrated Greek acid whey (GAW) substituted in lieu of water during extrusion of milk protein concentrate-based snacks. Water, unhydrolyzed GAW, and hydrolyzed GAW were used as the three liquid sources during extrusion and physicochemical, textural, and sensory properties of the extrudates were evaluated. Addition of GAW significantly (P < .05) increased extrudate radial expansion ratio (RER) and porosity and decreased piece density. GAW generally improved textural characteristics of hardness, crispness, and crunchiness or produced extrudates comparable to commercial products. A consumer sensory acceptance test showed that GAW significantly improved hedonic and Just About Right (JAR) scores in all four attribute categories. The results indicate GAW’s potential to replace water during extrusion, simultaneously utilizing an environmentally undesirable byproduct while improving extruded snack foods.

Yogurt Acid Whey Utilization for Production of Baked Goods: Pancakes and Pizza Crust.

The increased production of Greek-style yogurt in the past decade has induced the need for the reintroduction of the nutrients of its byproduct, yogurt acid whey (YAW), into the food system to combat food waste and aid sustainability. However, the processing and treatment of acid whey, which can be environmentally damaging if disposed of incorrectly, can be costly and complex. Upscaling YAW as an ingredient in food products with minimal re-processing is a cost-effective way to bypass the need for further abatement. To span a broad spectrum of baked products (sweet and savory, biologically and chemically leavened, dairy or water based, oven or surface baked, batter or dough, etc.), pilot commercial pizza crust and pancake formulations incorporating acid whey as a functional ingredient were developed. Dimensions and physico-chemical properties of samples were measured at production and over shelf life at room temperature (23 °C). Consumer sensory testing (n = 120 and n = 108, respectively, Just About Right (JAR), nine-point hedonic, purchase intent, and demographics) were conducted for both products. All instrumental trials and analyses (°Brix, aw, color attributes, viscosity, dimension measurements, and texture analysis) were conducted in triplicate for statistical analysis. Cochran’s Q and post-hoc tests on sensory data showed that liking for at least one experimental YAW sample for each of the pizza and pancake formulations were on par with their respective commercial product, despite the reduction of buttermilk, salt and sugar from the YAW formulations. Adding sustainability claims brought the purchase intent on par with the controls. Replacement of water by weight of YAW was more appropriate than by water content of the YAW. Sourness was the main undesirable trait of YAW samples based on penalty analysis. The use of YAW improved the shelf life of baked goods based on their respective failure mechanisms (textural properties and mold growth). YAW is a suitable ingredient in the formulation of sustainable, healthy, safe, and commercially successful baked products that have a tolerance or can benefit from a sour flavor profile.

Efficiency assessment of water reclamation processes in milk protein concentrate manufacturing plants: A predictive analysis

Milk protein concentrates (MPC) are increasingly used as protein fortifiers in food formulations, as a means to increase cheese yield, and in the manufacture of Greek-style yogurt. However, manufacturing of MPC requires significant volumes of input water and generates polluting by-products such as permeates and/or diafiltrates. Reverse osmosis was suggested to reduce the impact of both issues by reclaiming water from dairy fluids, thereby reducing the volumes of by-products to be treated. Filtration performance data was obtained from the reverse osmosis of dairy fluids, namely skim milk and ultrafiltration permeate, and from the polishing process of their respective permeates. It allowed the comparison of various water reclamation scenarios through a predictive analysis, which revealed that, without increasing operational costs, preconcentrating the skim milk prior the MPC manufacture would reduce the use of water and electricity by 35% and 10%, respectively, compared to a traditional process that consists in the concentration of skim milk by ultrafiltration, followed by the concentration of the resulting retentate by reverse osmosis.

Consumption of Greek yogurt during 12 weeks of high-impact loading exercise increases bone formation in young, adult males – a secondary analysis from a randomized trial

Exercise combined with protein and calcium has been shown to benefit bone turnover and bone metabolism. Greek yogurt (GY) contains important nutrients that support bone but has yet to be studied with exercise for this purpose. Thirty untrained, university-aged, males were randomized to 2 groups (n = 15/group): GY (20 g protein, 208 mg calcium/dose) or placebo pudding (PP; 0 g protein, 0 g calcium/dose) consumed 3×/day on training days and 2×/day on nontraining days. Both groups underwent a resistance/plyometric training program for 12 weeks. Blood was obtained at weeks 0, 1, and 12 to measure procollagen-type-I-N-terminal-propeptide (P1NP) and C-terminal-telopeptide (CTX). After outlier treatment, P1NP increased more over time in GY versus PP (p = 0.002; interaction). Both groups decreased CTX over time (p = 0.046; time effect). Following 1 week of training, there was a trend towards a significant increase in CTX in PP with no change in GY (p = 0.062; interaction). P1NP changed more in GY than PP (baseline to week 12; p = 0.029) as did the P1NP/CTX ratio (p = 0.015) indicating a greater increase in formation with GY. Thus, GY added to a high-load, high-impact exercise program positively shifted bone turnover towards increased formation while attenuating resorption. GY could be a plausible postexercise food to support bone health in young adult males. Novelty Greek yogurt, with exercise, increased bone formation in young adult males over 12 weeks. After 1 week of an osteogenic exercise program, Greek yogurt tended to blunt a rise in bone resorption seen with the placebo. Greek yogurt is a plausible postexercise food that supports bone.

A mutation in the methionine aminopeptidase gene provides phage resistance in Streptococcus thermophilus

Streptococcus thermophilus is a lactic acid bacterium widely used by the dairy industry for the manufacture of yogurt and specialty cheeses. It is also a Gram-positive bacterial model to study phage-host interactions. CRISPR-Cas systems are one of the most prevalent phage resistance mechanisms in S. thermophilus. Little information is available about other host factors involved in phage replication in this food-grade streptococcal species. We used the model strain S. thermophilus SMQ-301 and its virulent phage DT1, harboring the anti-CRISPR protein AcrIIA6, to show that a host gene coding for a methionine aminopeptidase (metAP) is necessary for phage DT1 to complete its lytic cycle. A single mutation in metAP provides S. thermophilus SMQ-301 with strong resistance against phage DT1. The mutation impedes a late step of the lytic cycle since phage adsorption, DNA replication, and protein expression were not affected. When the mutated strain was complemented with the wild-type version of the gene, the phage sensitivity phenotype was restored. When this mutation was introduced into other S. thermophilus strains it provided resistance against cos-type (Sfi21dt1virus genus) phages but replication of pac-type (Sfi11virus genus) phages was not affected. The mutation in the gene coding for the MetAP induces amino acid change in a catalytic domain conserved across many bacterial species. Introducing the same mutation in Streptococcus mutans also provided a phage resistance phenotype, suggesting the wide-ranging importance of the host methionine aminopeptidase in phage replication.

Assessing the Acceptability of Non-fat Greek Yogurt as a Fat Replacer to Produce a Low Saturated Fat Cookie

Assessing the Acceptability of Non-fat Greek Yogurt as a Fat Replacer to Produce a Low Saturated Fat Cookie

Commentary: Greek Yogurt and 12 Weeks of Exercise Training on Strength, Muscle Thickness and Body Composition in Lean, Untrained, University-Aged Males.

Commentary: Greek Yogurt and 12 Weeks of Exercise Training on Strength, Muscle Thickness and Body Composition in Lean, Untrained, University-Aged Males

Manufacture of high-protein yogurt without generating acid whey – Impact of the final pH and the application of power ultrasound on texture properties

The fermentation of preconcentrated milk is a challenging method to avoid acid whey during the manufacture of high-protein fermented milks like Greek yogurt. Milk concentrates (10% protein) were fermented to a final pH of 5.0, 4.8, or 4.6 and processed into stirred yogurt. Additionally, the potential of power ultrasound (US) as a post-processing tool was examined by sonicating the stirred yogurt with a sonotrode at 20 kHz. Set gels fermented to pH 4.8 and 5.0 were considerably softer than gels fermented to pH 4.6. Stirred yogurts fermented to pH 4.8 or 5.0 were less grainy and exhibited a reduced apparent viscosity and water-holding capacity. The application of US further decreased the visual graininess and product viscosity whereas the particle size was only slightly affected. The final pH and sonication are two powerful approaches to control the rheological properties of high-protein fermented milks, offering the potential for innovative processes and products.

Effects of replacing buttermilk with yogurt acid whey in ranch dressing

Greek-style yogurt has expanded from 5 to 50% of the US yogurt market in the past decade, accompanied by a corresponding increase in production of its by-product: yogurt acid whey (YAW). Yogurt acid whey qualities (e.g., low pH, mineral content, astringency, and saltiness) present challenges for processing, disposal, and ingredient use. A shelf-stable ranch dressing was formulated by replacing buttermilk in the control with YAW and concentrated YAW (6.3 to 25.2 °Brix). Added salt, gums, and acids were adjusted. The effects of buttermilk substitution on stability were studied on pasteurized samples (8 mo at room temperature). A consumer sensory study (n = 96) was conducted utilizing hedonic and just-about-right scales. Purchase intent and demographic data were also collected. A focus group (n = 7) evaluated the sensorial attributes of the samples after 6 mo. The experiment was performed in triplicate and all instrumental analyses (pH, soluble solids as °Brix, water activity, refraction index, and color) were conducted in triplicate for statistical analysis. Increasing the gum content in YAW samples resulted in equivalent texture liking compared with the control. Matching the control's NaCl concentration resulted in undesirable higher saltiness. The pH of the 18.9 °Brix YAW ranch sample without lactic acid added was under 4.6, with no effect on flavor liking. Increasing concentrations of YAW decreased L* and water activity, and increased the refractive index and hue. The YAW samples presented minimum changes over 8 mo of storage and had better water retention than the control. We conclude that 15 to 17 °Brix YAW is the optimal replacement for buttermilk in a dressing. The formulation of dressings may be accomplished successfully, sustainably, and cost effectively, with minor processing adjustment, by substituting buttermilk with YAW.

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.

Impact of purslane (Portulaca oleracea L.) extract as antioxidant and antimicrobial agent on overall quality and shelf life of Greek-style yoghurt

This study investigated the effect of purslane (Portulaca oleracea L.) leaves extract on Greek-style yogurt. Purslane extract showed higher antioxidant values and antimicrobial activity against Escherichia coli ATCC25922; Salmonella typhimurium ATCC14028. The fortified of Geek-style yogurt with lyophilized purslane extract 2.2g/L (S1) and 4.4g/L (S2) significantly increased the antioxidant capacity. Greek-style yogurt made with 4.4g/L lyophilized purslane extract received the highest antioxidant capacity and lowest sensory acceptability comparing with control and low dosage of lyophilized purslane extract. DPPH scavenging activity % of S1 and S2 samples had no obvious change during storage period, while, FRAP values were decreased in all treatments after 14 days of storage.The treatment of Geek-style yogurt fortified with 2.2 g/L lyophilized purslane extract was the most preference in sensory acceptability. This study recommended that the increasing of shelf life and antioxidant capacity and stability of all-natural Greek-style yogurt, a dosage of lyophilized purslane extract 2.2g/L should be incorporated. Moreover, the P. oleracea could be used in functional foods as it has some bioactive components.

A potential technological application of probiotic microcapsules in lactose-free Greek-style yoghurt

The potential of lactose-free Greek-style yoghurt as a new matrix for incorporation of spray-dried microcapsules containing the probiotic Bifidobacterium lactis BB-12 was evaluated. Three different microcapsule formulations were produced using gum arabic, inulin and maltodextrin as wall materials. All formulations showed encapsulation yield above 96% and good probiotic viability (>8 log cfu g−1) throughout 30 days of storage (4 °C). Microcapsules produced with gum arabic and inulin showed the best physical properties (lowest moisture, solubility and hygroscopicity values, and highest bulk and tapped densities), and thus were selected to be added to the yoghurt. Addition of the microcapsules increased the product's pH, firmness and adhesiveness; however, it did not affect the viability of the starter cultures. After 30 days of storage, probiotic viability was above 6.5 log cfu g−1, indicating that lactose-free Greek-style yoghurt may be an appropriate matrix for B. lactis BB-12.

Greek Yogurt and 12 Weeks of Exercise Training on Strength, Muscle Thickness and Body Composition in Lean, Untrained, University-Aged Males.

Milk and/or whey protein plus resistance exercise (RT) increase strength and muscle size, and optimize body composition in adult males and females. Greek yogurt (GY) contains similar muscle-supporting nutrients as milk yet it is different in several ways including being a semi-solid food, containing bacterial cultures and having a higher protein content (mostly casein) per serving. GY has yet to be investigated in the context of a RT program. The purpose of this study was to assess the effects of GY consumption plus RT on strength, muscle thickness and body composition in lean, untrained, university-aged males. Thirty untrained, university-aged (20.6 ± 2.2 years) males were randomized to 2 groups (n = 15/group): fat-free, plain GY or a Placebo Pudding (PP; isoenergetic carbohydrate-based pudding) and underwent a combined RT/plyometric training program 3 days/week for 12 weeks. They consumed either GY (20 g protein/dose) or PP (0 g protein/dose) daily, 3 times on training days and 2 times on non-training days. After 12 weeks, both groups significantly increased strength, muscle thickness and fat-free mass (FFM) (p < 0.05). The GY group gained more total strength (GY; 98 ± 37 kg, PP; 57 ± 15 kg), more biceps brachii muscular thickness (GY; 0.46 ± 0.3 cm, PP; 0.12 ± 0.2 cm), more FFM (GY; 2.4 ± 1.5 kg, PP; 1.3 ± 1.3 kg), and reduced % body fat (GY; −1.1 ± 2.2%, PP; 0.1 ± 2.6%) than PP group (p < 0.05 expressed as absolute change). Thus, consumption of GY during a training program resulted in improved strength, muscle thickness and body composition over a carbohydrate-based placebo. Given the results of our study, the general benefits of consuming GY and its distinctiveness from milk, GY can be a plausible, post-exercise, nutrient-rich alternative for positive strength, muscle, and body composition adaptations.

Role of single serving form of dairy on satiety and postprandial glycaemia in young and older healthy adults.

Dairy proteins reduce appetite and improve postprandial glycaemic response in adults. However, there are no reports of dairy in amounts usually consumed on satiety and postprandial glycaemia in either young or older adults. In a randomized crossover design, 30 healthy young adults (age: 23.5 ± 0.5 years; body mass index (BMI): 21.8 ± 0.4 kg/m2) and 30 healthy/overweight older adults (age: 65.2 ± 0.5 years; BMI: 24.7 ± 0.6 kg/m2) consumed 1 serving (according to manufacturers' labels) of skim milk (0.1% milk fat (MF)), whole milk (3.25% MF), plain Greek yogurt (2% MF), cheddar cheese (31% MF), and water (energy-free control) after a 12-h fast. Subjective appetite was measured every 15-30 min over 3 h. Blood glucose and insulin were measured at baseline and every 15-30 min over 2 h. All dairy treatments reduced post-treatment subjective appetite area under the curve (AUC) over 3 h by 8%-17% more than water. Greek yogurt reduced appetite 3-h AUC more than skim and whole milk by 9% and 7%, respectively (p < 0.0001). Post-treatment blood glucose 2-h AUC was 42% lower in young compared with older adults (p = 0.003). It was also 52%-78% lower after cheese compared with milks and yogurt (p < 0.0001). Post-treatment insulin AUC after cheese was only 10%-15% of that after milks and Greek yogurt (p < 0.0001). We conclude that single servings of dairy differ in effect on postprandial satiety and glycaemia and merit consideration in management of metabolic syndrome.

Short communication: Composition of coproduct streams from dairy processing: Acid whey and milk permeate

This article provides composition information for 3 abundantly available but little characterized dairy coproduct streams: acid whey from Greek yogurt (GAW), acid whey from cottage cheese (CAW), and milk permeate (MP). Three replicate samples obtained on different dates from several dairy processors were analyzed. The main component in all streams was lactose, with up to 3.5, 2.1, and 11.9% in GAW, CAW, and MP, respectively. Crude protein content ranged from 1.71 to 3.71 mg/g in GAW, 1.65 to 5.05 mg/g in CAW, and 3.2 to 4.35 mg/g in MP, and pH ranged from 4.21 to 4.48, 4.35 to 4.51, and 5.4 to 6.37, respectively. Chemical oxygen demand varied from 52,400 to 62,400 mg/L for GAW, 31,900 to 40,000 mg/L for CAW, and 127000 to 142,000 mg/L for MP; biochemical oxygen demand ranged from 45,800 to 50,500 mg/L (GAW), 32,700 to 40,000 mg/L (CAW), and 110,000 to 182,000 mg/L (MP). The GAW had the lowest pH (4.21-4.48) and highest mineral content of all streams. These data will assist processors and researchers in developing value-added uses of these dairy coproducts.

Effect of dairy and nondairy snacks on postprandial blood glucose regulation in 9-14-year-old children.

In adults, dairy consumption improves short-term blood glucose regulation. It is unknown if these short-term benefits extend to children of different weight statuses. The objective of this study was to investigate the effect of a dairy and nondairy snack in both normal-weight (NW) and overweight/obese (OW/OB) children on blood glucose regulation and food intake (FI). In a repeated-measures crossover design, 11 NW and 7 OW/OB children (age: 9-14 years), consumed, in random order, a dairy (Greek yogurt, 198.9 g, 171 kcal, 0 g fat, 17 g protein) or nondairy (mini sandwich-type cookies, 37.5 g, 175 kcal, 7.5 g fat, 1.3 g protein) snack containing 25 g of available carbohydrates. Ad libitum FI was measured 120 min after snack consumption. Blood glucose, insulin, C-peptide, and glucagon-like peptide-1 (GLP-1) were measured at 0 min (before the snack), and at 30, 60, 90, and 120 min after snack consumption. Insulin secretion was calculated from deconvolution of C-peptide. Hepatic insulin extraction was calculated as C-peptide divided by insulin. FI did not differ between snacks (P = 0.55). Mean blood glucose was lower (P < 0.001) and insulin higher (P < 0.0001) in the 120 min after consuming the dairy snack. C-Peptide concentrations (P = 0.75) and insulin secretion (P = 0.37) were not different between snacks. The increase in insulin was explained by reduced hepatic insulin extraction (P < 0.01). Consumption of the dairy snack also increased mean GLP-1 concentrations (P < 0.001). In conclusion, consumption of a dairy snack by NW and OW/OB children results in reduced postprandial blood glucose concentrations and elevated circulating insulin compared with a nondairy snack possibly because of delayed hepatic insulin extraction.

Nonthermal concentration of liquid foods by a combination of reverse osmosis and forward osmosis. Acid whey: A case study

Acid whey from Greek-style yogurt (GAW) has become abundantly available in recent years. Due to its low solids content, low pH, high lactose and mineral content, GAW is challenging to transport and process. In this study, a combination of reverse osmosis (RO) and forward osmosis (FO) was developed for the nonthermal concentration of GAW. Permeate flux, retentate concentration, and specific energy were evaluated for the individual and combination processes. GAW (6.6°Brix) was concentrated to 19.6°Brix by RO (3 × ), then to 40.2°Brix (6 × ) by FO. During the concentration, permeate fluxes dropped from 33.2 L/m2h to 2.6 L/m2h for RO and from 3.6 L/m2h to 1.6 L/m2h for FO. The specific energy consumption was 0.29 kWh/kg water for RO and 0.65 kWh/kg water for FO, from which half pertains to the osmotic agent regeneration. This combination process can become an efficient nonthermal method for concentrating challenging or sensitive liquid foods and beverages.

Effect of Greek-style yoghurt manufacturing processes on starter and probiotic bacteria populations during storage

This study compared viable counts of Streptococcus thermophilus (starter) and Lactobacillus helveticus R0052 (probiotic), as a function of two manufacturing processes of Greek-style (GS) yoghurt: centrifugation of a curd (GS-CF process) or ultrafiltration of milk prior to fermentation (GS-UF process). Fresh GS-UF and GS-CF yoghurts had between 3 and 7 times higher counts of Lb. helveticus R0052 and S. thermophilus than the regular stirred yoghurt (Control). Strain R0052 was three times more stable in the GS-CF yoghurt than in the Control over the 44 d storage period. The highest lactose content (44 g L−1) was obtained in the Control, while 60% less was obtained in the GS-UF yoghurt; the opposite trend was observed for lactic acid and galactose. Free amino acid levels were 33% higher in the GS products. GS yoghurt can be 10 times better than traditional yoghurt to deliver probiotic bacteria, as a function of the process used.