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This study evaluated the nutritional profile and volatile compounds present in a novel prebiotic (inulin) soursop whey beverage, due to the effects of high-intensity ultrasound (HIUS). The prebiotic soursop whey beverage was produced and processed by non-thermal high-intensity ultrasound varying the power (0, 200, 400 and 600 W) and by high-temperature short time (72 °C for 15 s) thermal treatment. Total acidity, pH, ascorbic acid content, total phenolics compounds content, antioxidant activity, hypertensive activity, fatty acid profile, volatile organic compounds, macro and micro minerals, as well as the heavy metals in these products, were analyzed. Overall, the HIUS technology induced some positive changes in the nutritional profile of the soursop whey beverage including beneficial effects, e.g., increase of phenolic content, improvement of the antioxidant and anti-hypertensive activity and reduction of undesired minerals. Although some negative changes, such as degradation of the ascorbic acid, decrease of some minerals and production of certain volatile compounds were found, the beneficial effects were prominent, thus, opening new opportunities to develop healthy functional beverages.

This study aimed to evaluate the effect of the addition of xylooligosaccharide (XOS, 1.25 g/100 mL) on the pH, physicochemical composition, functional properties, volatile profile, rheological properties, and sensory acceptance of strawberry-flavored whey beverage. The addition of XOS resulted in whey beverages with better functional characteristics (greater antioxidant activity, ACE inhibitory activity, and ⍺-amylase and ⍺-glucosidase inhibition), rheological properties (higher viscosity), volatiles profile, and sensory acceptance (aroma, texture and overall liking), besides providing adequate concentrations of the prebiotic in the product (1.25 g/mL). XOS is an interesting ingredient to improve the functional potential of strawberry-flavored whey beverages.

The objective of this study was to evaluate the effect of the probiotic addition methodology (direct addition of the lyophilized commercial culture, probiotic activated by propagation, or probiotic encapsulated in alginate, 108 CFU/mL) on the physical and chemical characteristics, rheological parameters, volatile compounds profile, probiotic culture survival and sensory acceptance of orange juice during refrigerated storage (7 °C/28 days). The direct addition of the commercial culture was the most suitable methodology, resulting in products with physical and chemical characteristics and sensory acceptance similar to those of the pure product. Furthermore, it improved the volatile compounds profile (presence of octanal, nonanal, decanal, gamma-terpinene, α-phellandrene, o-cymene, alpha-cubebene and 1-hexanol). The addition of the activated probiotic culture resulted in products with higher content of organic acids (acetic, lactic and citric), absence of important volatile compounds and lower sensorial acceptance. The addition of the encapsulated probiotic culture resulted in more consistent products (higher consistency index and lower flow behavior index), decreased organic acid content and lower sensorial acceptance. This is the first study that evaluated the impact of different probiotic addition methodologies on the quality parameters of fruit juices and it indicated that the conventional methodology (by propagation) is not the most appropriate.

The objective of this study was to evaluate the effect of the addition of prebiotics (xylooligosaccharide, galactooligosaccharide, polydextrose, fructooligosaccharide, or inulin) on the quality parameters of Greek yogurt. Composition, rheological parameters, and the volatile compounds profile were evaluated. The effect of prebiotic addition was dependent on the type of the component used. The addition of galactooligosaccharide, polydextrose, and inulin resulted in more consistent (increase in k and decrease in n), elastic (increase in G′), viscous (decrease in tan δ) and firm products (increase in G * and z). In addition, the volatile compounds profile was diverse, with the appearance of isobutyric acid, 5-hydroxy-2,7-dimethyl-4-octanone, 2 (5H) -furanone and/or 2-hydroxy-3-pentanone, which contributes to the sweet aroma, sweet taste, and buttery flavor of the products. The addition of fructooligosaccharides had a negative impact on the rheological parameters, resulting in less consistent, elastic, viscous, and firm products. The addition of xylooligosaccharide resulted in products with intermediate characteristics. Therefore, galactooligosaccharide, polydextrose, and inulin proved to be technological and interesting alternatives for the manufacture of prebiotic Greek yogurts.

This study aimed to evaluate the effect of the process time (5, 10, and 15 min) and flow rate (10, 20, and 30 mL/min) of cold plasma technology on physio-chemical characteristics (pH), bioactive compounds (DPPD, Total Phenolic Compounds, ACE-inhibitory activity values), fatty acid composition, and volatile compounds profile of chocolate milk drink. The mild (lower flow rate and process time) and more severe (higher flow rate and process time) conditions led to a reduction of the bioactive compounds (total phenolic compounds and ACE-inhibitory activity), changes in fatty acid composition (increased saturated fatty acid and decreased monounsaturated fatty acid and polyunsaturated fatty acid), less favorable health indices (higher atherogenic, thrombogenic and hypercholesterolemic saturated fatty acids and lower desired fatty acids), and lower number of volatile compounds. In contrast, in intermediate cold plasma conditions, an adequate concentration of bioactive compounds, fatty acid composition, and health indices, and increased number of volatile compounds (ketones, esters, and lactones) were observed. Overall, cold plasma technology has proven to be an interesting alternative to chocolate milk drinks, being of paramount importance the study of the cold plasma process parameters.

The present study aimed to evaluate the effect of cold plasma processing parameters (time and flow rate) on the physical (rheological parameters and particle size), microstructure (optical microscopy) and thermal properties (differential scanning calorimetry) of chocolate milk drinks. The beverages treated by cold plasma presented particles with increased size and had higher consistency and altered melting profile (lower temperature and bound water and higher enthalpy) than the pasteurized product, suggesting denaturation processes and formation of protein aggregates. More severe conditions resulted in beverages with particles of larger surface areas ([D 3,2]) and volume diameters ([D4,3]), resulting in higher consistency. Intermediate processing conditions resulted in products with characteristics more similar to the pasteurized beverages. The results indicate that the beverages submitted to cold plasma and pasteurization have different physical characteristics, melting profile and microstructure. Chocolate milk drinks with different characteristics could be obtained varying the cold plasma process parameters.

The effect of microwave heating (MH, 65 and 75 °C for 15, 30, and 60 s) on the bioactive compounds, fatty acid profile, and volatile compounds of orange juice-milk beverage (OJMB) was evaluated during 28 days of refrigerated (4 °C) storage. Conventionally pasteurized (75 °C/15 s) and untreated beverages were used as controls. MH-OJMB presented a lower browning index and higher levels of ascorbic acid, total phenolics, and carotenoids, higher antioxidant activity, and greater α-amylase, α-glucosidase, and ACE inhibitory activity than the pasteurized product, similar to the untreated beverage. No significant differences were observed in the volatile organic compounds and fatty acids levels. Lower temperatures (65 °C) and longer process times (60 s) resulted in higher retention of bioactive compounds. MH can be an alternative to conventional pasteurization for OJMB processing.

This study aimed to evaluate the effect of Lacticaseibacillus casei 01 as a probiotic culture on the production of volatile organic compounds and metabolic profile of Minas Frescal cheese. Lactose (α-lactose and β-lactose), fatty acids (unsaturated and saturated), citric acid, tryptophan, and benzoic acid were the main compounds. Compared with the control cheese, probiotic cheese was characterized by the highest concentration of tryptophan and presented a higher number of volatile acids. The control cheese was characterized by the highest concentration of benzoic acid and fatty acids, resulting in a higher number of volatile alcohols and esters. No differences were observed for α-lactose, β-lactose, and citric acid contents. A clear separation of probiotic and control Minas Frescal cheese was obtained using 1H nuclear magnetic resonance spectra, demonstrating that the addition of probiotic culture altered the metabolic profile of Minas Frescal cheese. Overall, the findings suggested that the addition of probiotic culture promoted the proteolysis in the fresh cheeses, decreased the lipolysis, and altered the volatile compounds. Furthermore, nuclear magnetic resonance spectroscopy coupled to chemometrics tools could be used to differentiate probiotic and conventional cheeses.

This study aimed to develop and characterize mixed beverages (suchás) formulations based on organic apple juice and cardamom tea (F1= 50:50 vv−1, F2 = 60:40 vv−1 and F3 =70:30 vv−1). The formulation (F3) presented the highest total phenolic compounds content (31.79 mg EAG g-1), antioxidant activity (50.04 µg mL-1), total soluble solids (5.1 oBrix), acidity (pH 4.17 and total acidity 0.15 g malic acid 100 mL-1) and sensory acceptance (flavor and overall impression). Furthermore, it presented important volatile compounds (2-methyl-1-butanol, formic acid butyl ester, acetyl pentyl acetate, and α-terpinolene). A synergistic effect of apple juice and cardamom tea was observed for the antioxidant activity and number of volatile compounds, demonstrating the potential of this mixed beverage as a functional food. In conclusion, it was possible to develop a mixed beverage with suitable nutritional, physicochemical and sensory properties using 70% of organic apple juice and 30% of cardamom tea.

The effect of partial substitution of NaCl with KCl and the flavor enhancers addition (arginine, yeast and oregano extract) on the bioaccessibility of five minerals (Mg, Ca, K, P and Zn) from potentially Probiotic Prato cheese was evaluated. After 1, 30, and 60 d of refrigerated storage (processing, ripening and refrigerated storage), total concentrations of Mg, Ca, K, P and Zn were determined by flame atomic absorption spectrometry (FAAS). In addition, bioaccessibility assay with a simulated (in vitro) gastrointestinal digestion model was used. Sodium reduction and the addition of flavor enhancers revealed some significant (p

This study presents the emerging high-intensity ultrasound (HIUS) processing as a non-thermal alternative to high-temperature short-time pasteurization (HTST). Chocolate milk beverage (CMB) was subjected to different ultrasound energy densities (0.3–3.0 kJ/cm3), as compared to HTST pasteurization (72 °C/15 s) aimed to verify the effect of the HIUS processing on the microbiological and physicochemical characteristics of the beverage. The application of HIUS at an energy density of 3.0 kJ/cm3 was able to reduce 3.56 ± 0.02 logarithmic cycles in the total aerobic counts. In addition, the ultrasound energy density affected the physical properties of the beverage as the size distribution of fat globule and rheological behavior, as well as the chemical properties such as antioxidant activity, ACE inhibitory activity, fatty acid profile, and volatile profile. In general, the different energetic densities used as a non-thermal method of pasteurization of CMB were more effective when compared to the conventional pasteurization by HTST, since they improved the microbiological and physicochemical quality, besides preserving the bioactive compounds and the nutritional quality of the product.

The addition of organic green banana flour (GBF, 0%, 1%, 3%, or 5% w/v) on the quality parameters of fermented milk was investigated (21 days/5 °C). Suitable viability of lactic and probiotic cultures (>6 log CFU/g) and resistant starch level (3.01–10.29 g/100 g) were observed. 1% and 3% GBF addition increased post acidification, proteolysis and concentration of lactic and acetic acids, but at suitable ranges. Furthermore, it improved the fatty acid (long-chain) and volatile profiles, increasing aroma and flavor acceptance. 3% GBF addition resulted in higher firmness, lower atherogenic and thrombogenic indices and better aromatic profile than 1%, allowing the consumption of lower quantities of the fermented milk (100 g) to provide the minimum daily intake of resistant starch. GBF at 3% is a suitable ingredient in fermented milk formulation, contributing to the development of a synbiotic product with shelf life of at least 21 days.

This study aimed to evaluate the impact in nutritional and rheological parameters on sheep milk ice cream by fat replacement for different prebiotic fibers (inulin, fructo-oligosaccharide, galacto-oligosaccharide, short-chain fructo-oligosaccharide, resistant starch, soluble corn fiber, and polydextrose), also consumer perception (Pivot Profile). Low caloric content, around 98 kcal/100 g, were observed due to prebiotic fibers supplementation; without loss on moisture, carbohydrates or protein values. Sheep milk ice creams presented a pseudoplastic behavior when submitted to flow curve analysis. Moreover, inulin and fructo-oligosaccharide have proven to be a promising alternative as fat substitutes in sheep milk ice cream formulation, due to the similar rheological properties, such as hardness, viscoelasticity and consistency. Sheep milk ice creams containing inulin or fructo-oligosaccharide were also perceived creamier and brighter than control full-fat ice sheep milk ice cream. In addition, most prebiotic ice creams were cited as sweeter than control, meaning those fibers could act as sweeteners. In conclusion, the replacement of sheep milk fat by prebiotics to manufacture sheep milk ice cream can be an effective alternative to improve the nutritional and physiological aspects due to low caloric value and functionality provided by prebiotics.

This study was aimed at developing a new functional fermented beverage manufactured with semi-skimmed sheep milk and strawberry pulp (Fragaria × ananassa Duch.) and commercial prebiotic ingredients. We also compared the performance of the yogurt starter cultures and a Lactobacillus plantarum strain (CECT_8328) with potential probiotic properties. We assessed the nutritional profile, bioactivity compounds, viability of lactic acid bacteria during storage, and survival of L. plantarum after in vitro simulated digestion during the storage period. The lactic acid bacteria were viable throughout the storage period, but only L. plantarum maintained good viability after simulated digestion. Nevertheless, neither inulin nor potato starch increased bacterial viability. The fermented semi-skimmed sheep milk strawberry beverages we developed are good sources of minerals and proteins.

The present study aimed to evaluate the physicochemical parameters of sheep milk yogurt smoothies (SMY) containing inulin at different levels (0, 2, 4, and 6%). Titratable acidity and pH, yogurt bacteria counts, fatty acids profile, and healthy lipid indices were evaluated during 28 d of refrigerated storage. As expected for yogurts, Streptococcus thermophilus counts decreased 1 to 3 log cycles and Lactobacillus delbrueckii ssp. bulgaricus counts decreased 1 to 2 cycles from d 1 to 28. The protective effect of inulin on bacteria survival and viability in the food matrix was not verified in the prebiotic SMY during storage, regardless of inulin level. Although lower post-acidification was observed in prebiotic SMY due to inulin addition, no changes were verified in short-chain fatty acids (SCFA) or polyunsaturated fatty acids (PUFA). In contrast, an increase in medium- and long-chain fatty acids (MCFA and LCFA) and monounsaturated fatty acids (MUFA) was observed during storage in all SMY. The most significant levels of fatty acids in SMY were oleic acid, followed by palmitic and myristic acids. A high positive correlation between conjugated linoleic acid (CLA) and oleic acid (r=0.978) was observed. The cis-9,trans-11 CLA isomer represented approximately 78% of total PUFA and 2% of total fatty acids, whereas α-linoleic acid comprised about 22% PUFA and 1% of total fatty acids in SMY. The fatty acid changes during storage were associated with the metabolic activity of the starter bacteria, especially for oleic acid and cis-9,trans-11 CLA isomer. Thus, the SMY represented a great source of these compounds. We observed that inulin levels did not affect fatty acids. A nonsignificant decrease in atherogenic index was observed during storage in all SMY, and a positive correlation (r=0.973) was found between atherogenic index and thrombogenic index of SMY. High correlations were observed between lauric and myristic acids and saturated fatty acids (r=0.907 and r=0.894, respectively), providing evidence of their atherogenic and thrombogenic potential. A negative correlation was observed between stearic acid and atherogenic index (r=-0.612) and between oleic acid and atherogenic index. Sheep milk yogurt could be characterized as a food with low atherogenic and thrombogenic risk because of its healthy lipid composition. Therefore, addition of inulin to SMY could be a good option to improve functionality of this food matrix for dairy companies wishing to enter the functional food market.

This study aimed to evaluate the effect of the addition of prebiotic components (long-chain inulin, medium-chain inulin, oligofructose and polydextrose, 5 g/100 g) on the characteristics of ice cream processed with water-soluble extract of rice by-product. The products were evaluated for the technological parameters (overrun, melting rate, texture parameters, and color parameters), bioactive compounds (antioxidant, anti-hypertensive and anti-diabetic activities), fatty acid profile, and volatile compounds profile. The addition of prebiotic components resulted in ice creams with greater functionality, due to the increase in antioxidant activity (1.3–1.4 times), ACE inhibitory activity (2.80–3.6 times), α-amylase inhibitory activity (2.5–2.93 times), and α-glucosidase inhibitory activity (2.56–3.42 times). The addition of polydextrose and oligofructose resulted in products with higher melting rate and altered texture and color parameters, but greater functionality (bioactive compounds) and health indices (decreased hypercholesterolemic saturated fatty acid index and increased desired fatty acid index). Ice cream with long-chain inulin presented lower consistency, while ice cream with medium-chain inulin had improved volatile profile (appearance of 2-butanone, 3-methyl, fruity aroma). This is the first study involving a prebiotic ice cream processed with water-soluble extract of rice by-product, and the results indicate the potential of the product, which presented adequate physical-chemical, technological and functional characteristics.

The influence of temperature, frequency, composition and physicochemical characteristics of sheep milk on its dielectric properties was evaluated as well as the performance of different chemometric methods to predict the dielectric properties and classify the type of sheep milk (whole, semi-skimmed and skimmed). Of the chemometric methods evaluated, artificial neural network exhibited the best performance for prediction of the dielectric properties, while sensitivity analysis showed temperature, electrical conductivity, and fat and calcium content as variables with the most impact. All pattern recognition techniques showed 100% for recognition and prediction ability to classify correctly the type of milk. Although the approach used in this study is limited to the specific operating conditions and sheep milk studied, chemometric methods have proven to be promising tools because of accuracy and suitability for both prediction of the dielectric properties of sheep milk and monitoring quality control parameters of milk and dairy products.

The effect of cold plasma processing time and gas flow on bioactive compounds such as vitamin C, carotenoids and phenolic compounds, DPPH, angiotensin-converting-enzyme (ACE) inhibitory activity, fatty acids profile, and volatile compounds of guava-flavored whey beverage was investigated. For comparative purposes, a pasteurized beverage was also manufactured. Cold plasma increased the concentration of bioactive and volatile compounds, and proportionated changes in the fatty acids profile. The milder conditions like lower flow rate and processing time, resulted in higher vitamin C and volatile compounds levels, and higher antioxidant activity, but with a lower carotenoids content and a less favorable fatty acids profile. More drastic conditions like higher flow rate and processing time resulted in products with lower vitamin C and volatile compounds levels, but with higher carotenoids content and ACE inhibitory activity. It can be concluded that the cold plasma processing can improve the properties of the guava-flavored whey beverages (increased concentration of bioactive and volatile compounds), while the effect on the fatty acid profile and ACE inhibitory activity is dependent on the process parameters (processing time and flow rate).

The objective of this study was to determine polycyclic aromatic hydrocarbons (PAH) in Coalho cheese samples (CC, n = 30) barbecued in charcoal at different distances (5, 15, or 20 cm). PAH were determined using liquid-liquid extraction (LLE) followed by gas chromatography-mass spectrometry (GC-MS). The CC samples presented all the 16 PAH monitored by the health agencies, including 8PAH considered as the most toxic. The benzo [a]anthracene (BaA) and dibenz [a,h]anthracene (DBA) levels were determined, which ranged from 140.7 to 149.4 μg kg−1 to 135.0–139.5 μg kg−1, respectively. The toxicity values showed that the human exposure to PAH in the preparation and consumption of CC is classified as a serious risk or potential risk to cause cancer in humans, with levels higher than 83% and 69% for BaA and DBA, respectively, which are the compounds with the highest carcinogenicity index. The distance to the heat source had no effect on the parameters evaluated. Thus, CC presented high concentrations of PAH and potential risk for the health of Brazilian consumers. Therefore, consumers should be aware of the type of preparation and consider the condition of lightly toasted CC as a food-safe and appropriate consumption profile.

The objective of this study was to evaluate the effect of ultrasound treatment on the microbiological quality, protein and free amino acid profile of fresh and frozen stored semi-skimmed sheep milk. Milk was treated as fresh or frozen and stored up to one, three and six months. Output power time and pulse time were the parameters combined to design four different ultrasound (US) treatments: power 78 W and duration 6 min (US1); power 78 W and duration 8 min (US2); power 104 W and duration 4 min (US3) power 104 W and duration 6 min (US4). Pulse duration was of 4 s for each treatment. Sample US1 was discarded due to non effectiveness of US treatment, while other samples showed interesting results. Also, it was verified a frost effect on microorganisms in all samples which were frozen before treatment. No relevant change was reported on amino acid profile. The study showed promising results: the ultrasound treatment inactivated or eliminated the studied contaminant bacteria in semi-skimmed sheep milk, while maintained acceptable amount of lactic bacteria, which could be advantageous for dairy products processing.

In this study, the addition of Lactobacillus casei Zhang in the manufacture of Minas Frescal cheese was investigated. Minas Frescal cheeses supplemented with probiotic bacteria (Lactobacillus casei Zhang) were produced by enzymatic coagulation and direct acidification and were subjected to physicochemical (pH, proteolysis, lactic acid, and acetic acid), microbiological (probiotic and lactic bacteria counts), and rheological analyses (uniaxial compression and creep test), instrumental color determination (luminosity, yellow intensity, and red intensity) and sensory acceptance test. The addition of L. casei Zhang resulted in low pH values and high proteolysis indexes during storage (from 5.38 to 4.94 and 0.470 to 0.702, respectively). Additionally, the cheese protocol was not a hurdle for growth of L. casei Zhang, as the population reached 8.16 and 9.02 log cfu/g by means of the direct acidification and enzymatic coagulation protocol, respectively, after 21 d of refrigerated storage. The rheology data showed that all samples presented a more viscous-like behavior, which rigidity tended to decrease during storage and lower luminosity values were also observed. Increased consumer acceptance was observed for the control sample produced by direct acidification (7.8), whereas the cheeses containing L. casei Zhang presented lower values for all sensory attributes, especially flavor and overall liking (5.37 and 4.61 for enzymatic coagulation and 5.57 and 4.72 for direct acidification, respectively). Overall, the addition of L. casei Zhang led to changes in all parameters and affected negatively the sensory acceptance. The optimization of L. casei Zhang dosage during the manufacturing of probiotic Minas Frescal cheese should be performed.

The effect of the Lactobacillus casei 01 and inulin addition on sheep milk ice cream during storage (-18 °C, 150 days) was investigated. Control, probiotic and synbiotic ice cream (10% w/w sheep milk cream; 10% w/w sheep milk cream, L. casei 01, 6 log CFU/mL; 10% w/w inulin, L. casei 01, 6 log CFU/mL, respectively) were manufactured. Microbiological counts (probiotic count, survival after in vitro gastrointestinal resistance, Caco-2 cell adhesion), bioactivity and microstructure were analysed. Physical and textural characteristics, colour parameters, thermal analysis and organic acids/volatile compounds were also evaluated. All formulations supported L. casei 01 viability and maintained above the minimum therapeutic level (>6 log CFU/mL) during storage. Inulin did not affect L. casei 01 survival after the passage through simulated gastrointestinal tract and adhesion to Caco-2 cells while improved the ACE-inhibitory and antioxidant activity. L. casei 01 addition produced several volatile compounds, such as carboxylic acids, alcohols, aldehydes and ketones. Also, scanning electron microscopy showed an interaction between probiotic bacteria and inulin fibre on synbiotic ice cream and the adhesion of L. casei to Caco-2 cells was observed.

The effects of the concentration of watermelon juice at different temperatures (45, 55, or 65 °C) on the physicochemical and sensory characteristics, antioxidant capacity, and volatile organic compounds (VOCs) of whey-based popsicles were investigated. Total phenolic content, lycopene, citrulline, VOCs, melting rate, instrumental colour, antioxidant capacity, and the sensory characteristics (hedonic test and free listing) were determined. The temperature led to a significant decrease in bioactive compounds (total phenolics, lycopene, and citrulline). The popsicle manufactured with reconstituted watermelon juice concentrated to 60 °Brix at 65 °C presented higher antioxidant capacity and was characterized by the presence of alcohols, aldehydes and ketones and presented a similar acceptance to the untreated popsicle (except for flavour). It is possible to combine whey and concentrated watermelon juice for the manufacture of bioactive-rich popsicles, using the concentration temperature of 65 °C as a suitable processing condition for potential industrial applications.

The stability of probiotic yogurts added with glucose oxidase and packaged in different plastic packaging systems that present different oxygen permeability transfer rates (0.09, 0.2, 0.39 and 0.75 mL O2/day) was evaluated during 28 days of refrigerated storage. Probiotic stirred yogurts were submitted to physicochemical (pH, proteolytic activity, dissolved oxygen) and microbiological analyses (yogurt bacteria, Lactobacillus acidophilus and Bifidobacterium longum) as well as the content of organic acids (lactic and acetic acid) and aroma compound (diacetyl and acetaldehyde) were assessed. Overall, yogurts packaged in plastic containers with lower oxygen permeability rates showed a higher extent of post-acidification, proteolysis and organic acid production. Additionally, these samples also presented a lower content of dissolved oxygen and a lower decrease of the probiotic bacteria count. No influence on the production of aroma compounds was observed. Our results suggest that the use of packaging systems with different oxygen permeability rates coupled with the addition of glucose oxidase presented an interesting technological option to minimize the oxidative stress in probiotic yogurts.