Turmeric-Enriched Yogurt: Increased Antioxidant and Phenolic Contents

Abstract

This study investigated the potential of turmeric powder as a functional additive to yogurt, specifically focusing on its effect on the antioxidant capacity and phenolic content. Yogurt samples were prepared with 0.5% and 1.0% turmeric powder, leading to increases in pH, antioxidant capacity (from 10% to 51%), and phenolic content (from 1.39 mg to 30.20 mg per 100 g) compared to plain yogurt. While turmeric showed no antibacterial effects in vitro, its addition resulted in a reduction in yogurt bacteria counts, which remained within the regulatory limits. However, exposure to gastric pH and bile salt conditions led to reductions in the antioxidant activity and total phenolic content of turmeric-enriched yogurt, indicating potential limitations in its stability during digestion. Sensory evaluations revealed a preference for plain yogurt; however, turmeric-enriched yogurts also achieved favorable acceptance scores. These findings indicate that turmeric incorporation can enhance the health benefits of yogurt, offering a promising option for consumers desiring functional dairy products.

1. Introduction

Yogurt is a globally consumed fermented dairy product recognized for its nutritional benefits but also for its functional properties, including digestive health improvement, probiotic effects, and bioactive compound generation during fermentation. The beneficial microorganisms present in yogurt, primarily Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, play a key role in the fermentation process and contribute to digestive health [1]. Additionally, probiotic strains such as Bifidobacterium are sometimes incorporated into yogurt formulations to enhance its health benefits, such as its ability to support digestive health and aid in the prevention and management of digestive disorders [2]. Yogurt consumption has also been linked to various health benefits, including improved blood pressure regulation, cholesterol control, weight management, and enhanced immune function [3]. Consuming 200 g of yogurt per day was associated with suppressing the risk of cardiovascular diseases [4]. The bioactive peptides generated during the yogurt fermentation process have also demonstrated potential antioxidant properties [5]. While the global consumption of yogurt continues to rise, consumers increasingly demand fortified products with added health benefits. This trend has led to the exploration of natural additives, such as bioactive plant components, to enhance yogurt’s nutritional and functional properties [6]. Recent studies have shown that the addition of phenolic-rich components, such as chokeberry fruit [7], Isabel grape [8], and peanut polyphenols [9], to yogurt is effective in enhancing its functional properties and antioxidant capacity.

Turmeric (Curcuma longa), a spice native to Southeast Asia, has gained significant attention due to its well-documented bioactive properties. Despite its long history of medicinal use, the health benefits of turmeric have been increasingly supported by recent research. The primary active compound in turmeric, curcumin, exhibits strong antioxidant, antimicrobial, and anti-inflammatory activities [10]. These properties contribute to its potential in preventing and managing various health conditions, including cancer, cardiovascular disease, and neurodegenerative disorders such as Alzheimer’s [11,12]. For instance, a daily oral dose of 3.6 g of curcumin was recommended for the phase II evaluation in the prevention or treatment of cancers outside of the gastrointestinal tract [13]. A recent study has shown that turmeric bioactive compounds alleviate neuropathic pain by suppressing glial activation and improving mitochondrial function in the spinal cord and amygdala [14]. Due to its anti-inflammatory properties, turmeric has been demonstrated to be beneficial in the management of Crohn’s disease and ulcerative colitis [15,16].

In the literature, the enrichment of yogurt with 0.2% curcumin extract has been reported to exhibit a bitter taste while increasing the water-binding capacity and providing protection against yeasts and molds [17]. In another study, it was found that although turmeric extract enriched the phenolic content of yogurt, it caused a decrease in sensory characteristics [18]. The health benefits of turmeric have been widely documented, as summarized above, and functional food formulations have been studied using the extract. However, it has been shown that the oral absorption of curcumin is relatively low [19]. Although evidence suggests that its effectiveness may be enhanced when incorporated into yogurt or other food products [20], there remains a lack of sufficient research regarding its interactions with various food matrices [21].

Considering the significant health benefits of turmeric, there is an increasing need to explore its incorporation into everyday foods to enhance their bioactive profiles. Clinical studies have demonstrated that high single oral doses of curcumin (up to 12 g/day) are well tolerated [22,23], suggesting the potential for safely integrating turmeric into various food products. Despite this, studies focusing on the adaptation of turmeric for daily dietary consumption remain limited. A recent study reported that probiotic yogurt made with turmeric extract maintained probiotic bacteria levels while preventing yeast and mold growth [17]. However, to the best of our knowledge, no research has yet examined the bioactive properties of turmeric-enriched yogurt. In this context, the present study aimed to explore the incorporation of turmeric powder at concentrations of 0.5% and 1.0% into yogurt to enhance its bioactive value. Specifically, we evaluated the impact of turmeric on yogurt’s acidity, texture, antioxidant capacity, and total phenolic content and on specific yogurt bacteria. In addition, the stability of turmeric yogurt under gastric pH and bile salt environments has been evaluated in terms of antioxidant and total phenolic contents. The consumer acceptance of the turmeric-enriched yogurts was assessed. The findings of this research will contribute to the literature by presenting turmeric-enhanced yogurt as a functional food alternative, offering a healthier option in the dairy product category.

2. Materials and Methods

2.1. Production of Yogurt

UHT whole cow’s milk (pH 6.5, 3.1% fat, 3.0% protein, and 4.7% lactose) was inoculated with a mixed culture of Streptococcus thermophilus (S. thermophilus) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) (CHR-Hansen, YoFlex^® CH-1, Hørsholm, Denmark) at a concentration of 1:10,000 (w:v). The samples were incubated at 43 °C for approximately 3.5 h in an incubator until the pH dropped below 4.6. After incubation, the plain yogurt was divided into three groups and supplemented with 0%, 0.5%, and 1.0% turmeric powder (TP) supplied from Bagdat Baharat (Ankara, Turkey). The TP concentrations were selected based on preliminary sensory evaluations. After thoroughly mixing them, the yogurt samples were cooled and stored at 4 °C overnight for further analysis. The productions were carried out twice in two independent batches.

2.2. Physicochemical Properties

The pH, titratable acidity (TA), texture, and color of the yogurts were analyzed after 24 h of production. The pH of yogurt was measured using a pH meter (Mettler-Toledo, S220, Greifensee, Switzerland) at 25 °C. The TA was measured using the titrimetric method according to the standard methods and described as the lactic acid percentage (LA%) [24]. The texture of yogurts was measured using a texture analyzer (Brookfield, CT3, Brookfield Engineering Laboratories, Middleboro, MA, USA) equipped with a 4500 g load cell. A compression test was applied using a 25.4 mm diameter cylindrical probe at a 0.5 mm/s test speed and a trigger load of 3.0 g. The sample dimensions were 50 × 50 mm. The texture results were evaluated in terms of hardness (g). The water holding capacity (WHC) of the yogurt samples was evaluated following the method of Gomes et al. [25] with minor modifications. Briefly, 20 g of yogurt was centrifuged at 1250× g for 10 min at 4 °C. The WHC was calculated as the percentage of the yogurt mass retained after serum separation relative to its initial weight. The color parameters were measured with a tintometer (Lovibond RT300, Salisbury, UK) in terms of L*, a*, and b*.

2.3. Extraction of Bioactive Components

Bioactive components on day 1 were analyzed in yogurt extracts prepared using the method suggested by Wojdyło et al. (2007) [26] with some modifications. To prepare the extracts, 3 g of the sample was mixed with 10 mL of a 95% ethanol solution. Subsequently, the test tubes were centrifuged at 5000 rpm for 10 min at 4 °C. The pH of the supernatant was adjusted to pH 7.0–7.2 using 0.1 M NaOH and centrifuged again [27]. The resulting supernatant was used freshly for the analyses of antioxidant and total phenolic contents.

2.4. Antioxidant Activity Assay

Antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Briefly, 200 μL of the extracts (obtained by previously described) was transferred into the test tubes. Then, 3 mL of freshly prepared DPPH solution (0.05 mM in 95% ethanol) was added, and the mixture was vigorously vortexed and kept in the dark at room temperature for 30 min. Subsequently, absorbance was measured at 517 nm using a UV-vis spectrophotometer (Shimadzu UV-1240, Kyoto, Japan) [28]. The antioxidant activity of the samples was calculated using Equation (1):

$$Antioxidant capacity (\%)=\left[{\displaystyle \frac{1-A_s}{A_b}}\right]\times 100$$

(1)

where A_s is the absorbance of the yogurt sample and A_b is the absorbance of the blank prepared with 95% ethanol instead of yogurt sample.

2.5. Total Phenolic Content Analysis

The total phenolic content was determined using the Folin–Ciocalteu colorimetric method. Briefly, 100 μL of the extract was transferred into test tube and mixed with 200 μL of Folin–Ciocalteu reagent. After 3 min, 1 mL of sodium carbonate solution (20% w/v in water) and 2 mL of distilled water were added to the test tubes, and the mixture was allowed to stand in the dark at room temperature for 1 h [28]. Subsequently, the absorbance values of the samples were measured against a blank at 760 nm using a spectrophotometer (Shimadzu UV-1240, Japan). The total phenolic content was determined using the standard curve equation of gallic acid, y = 0.0032x + 0.0622 (R² = 0.9983). The results are expressed as mg of gallic acid equivalent (GAE) per 100 g of sample.

2.6. Evaluation of Gastric pH and Bile Salt Tolerance

The stability of phenolic compounds in yogurt samples was assessed under simulated gastric pH and bile salt conditions using the method of Izzo et al. [29] with slight modifications. For the gastric pH environment, each sample was adjusted to pH 3.0 using 0.5 M HCl. For the bile salt tolerance test, 0.5% (w/w) bile salt (Merck, Darmstadt, Denmark) was added to the yogurt media. The samples were incubated in a water bath at 37 °C for 3 h. As a blank test, yogurt samples without any added acid or bile salt were incubated at the same conditions. After incubation, samples were weighed according to the extraction procedure described in Section 2.3. The supernatants were collected as extracts for further analysis. The antioxidant activity and total phenolic content of the treated samples were measured using a UV-vis spectrophotometer according to the procedures described in Section 2.4 and Section 2.5. The tolerance of bioactive materials was calculated using Equation (2):

$$Tolerance (\%)=\left[{\displaystyle \frac{Bioactive material in treated yogurt\ast }{Bioactive material in untreated yogurt\ast }}\right]\times 100$$

(2)

* All yogurts were incubated at 37 °C for 3 h before the measurements, as indicated in the methods.

2.7. Antibacterial Activity

The antibacterial activity of the fresh yogurts was determined by the agar well diffusion method [30]. Standard strains of Salmonella enterica serovar Typhimurium (ATCC 51812), Escherichia coli (ATCC 25922), and Staphylococcus aureus (ATCC 25923) were cultured separately in tryptic soy broth (Merck, Darmstadt, Germany) at 37 °C for 24 h. The bacteria strains were spread on tryptic soy agar (Merck, Darmstadt, Germany) at a concentration of 7 log CFU/mL. The plates were then left to dry, and wells with a diameter of 8 mm were made using a sterile agar drill. Aliquots (100 μL) of yogurt samples were transferred into the wells. The plates were then incubated aerobically at 37 °C for 24 h to allow bacterial growth and the diffusion of antimicrobial compounds from the yogurt into the agar medium. After the incubation period, the plates were examined for the presence of clear zones around the wells, indicating the inhibition of bacterial growth.

2.8. Enumeration of Yogurt Bacteria

The enumeration of yogurt bacteria was performed on storage days 1 and 15. Yogurt samples (10 g) were homogenized, and serial dilutions were prepared using sterile Ringer’s solution. The viable cell counts of S. thermophilus were determined by pour-plating on M17 agar (pH 6.8) (Biokar, Adana, Turkey) and incubating aerobically at 37 °C for 48 h. The viability of L. bulgaricus was assessed using MRS agar (pH 5.4) (Biokar, Adana, Turkey) through pour-plating and anaerobic incubation at 37 °C for 72 h [31]. The results were expressed as the logarithm of total counts of colony-forming units (CFUs) per gram.

2.9. Sensory Evaluation

Yogurts were evaluated for appearance, texture, flavor attributes, and overall acceptance. The panel consisted of 95 pre-trained females and males aged 18–50, comprising students and staff from the Food Engineering Department of Sakarya University. Each yogurt sample group was served in 25 g portions at 15 °C. Panelists assessed the sensory attributes of yogurts using a hedonic scale, where 1 represents dislike, 5 represents average, and 9 represents very good [32].

2.10. Statistical Analysis

The results were analyzed using analysis of variance (ANOVA) with Tukey’s Honestly Significant Difference (HSD) test to determine significant differences at a 95% confidence level between yogurt samples, employing Minitab 16.0 software (Minitab Inc., State College, PA, USA). Principal component analysis (PCA) was performed to evaluate the relationships and variations among the physicochemical, antioxidant, and other bioactive properties of the yogurt samples.

3. Results and Discussion

3.1. Physicochemical Properties of Yogurt Samples

The physicochemical properties of the yogurt samples are given in

Table 1. Physicochemical properties of yogurts.

	C	TP_05	TP_1
pH	4.10 ± 0.02 b	4.19 ± 0.01 a	4.17 ± 0.01 a
TA (LA%)	1.25 ± 0.04 a	1.06 ± 0.02 b	1.09 ± 0.02 b
Hardness (g)	18.4 ± 0.3 a	18.0 ± 0.7 a	18.0 ± 0.8 a
WHC (%)	60.2 ± 0.6 c	62.0 ± 0.3 b	63.4 ± 0.6 a
L*	84.8 ± 1.6 a	78.6 ± 0.7 b	76.9 ± 0.4 c
a*	−1.4 ± 0.0 b	−1.2 ± 0.3 b	−0.8 ± 0.2 a
b*	5.9 ± 0.0 c	57.9 ± 1.9 b	67.8 ± 0.9 a

TA: Titratable acidity expressed as lactic acid percentage; WHC: water holding capacity; L*, a*, and b*: color values; C: control (plain yogurt); TP_05: yogurt with 0.5% turmeric; TP_1: yogurt with 1% turmeric. Lowercase letters indicate differences between sample groups (p < 0.05).

. The pH value in the control group (C) was measured to be 4.10. The addition of TP (in yogurts TP_05 and TP_1) resulted in a significant increase in pH, ranging from 4.17 to 4.19. These results indicate that TP might have decreased the acidity level of the yogurt. The titratable acidity in the control (C) was 1.25 (LA%), and it decreased to 1.06–1.09% with the addition of TP. The decrease in acidity was independent from the concentration of TP. Shalaby and Amin [18] also observed an increase in pH and a decrease in acidity in the yogurts produced by preparing aqueous extracts from TP. Similarly, Rahmatalla et al. [33] reported that the addition of 0.25–0.75% TP to yogurt resulted in an increase in pH and a decrease in acidity compared to plain yogurt. In another study, it was reported that the addition of 0.5–3.0% TP during the fermentation of soybean paste (Doenjang) resulted in an increase in pH [34]. The observed increase in pH and decrease in acidity in the yogurts supplemented with TP could be attributed primarily to the chemical composition of turmeric, which has a pH of about 5.90 in powdered form [35].

In terms of texture, no significant differences were observed in the hardness values among the samples. However, the WHC and color properties of the yogurt were significantly influenced by the addition of turmeric. The WHC of the control yogurt was measured as 60.2%, while the WHC of the TP_05 and TP_1 yogurts increased significantly with turmeric addition, reaching 62.0% and 63.4%, respectively. In comparison, the WHC of the TP_05 and TP_1 yogurts increased significantly with the addition of turmeric, reaching 62.0% and 63.4%, respectively, corresponding to the turmeric concentration. The WHC is a critical quality parameter in yogurt as it directly reflects its structural integrity during storage. A higher WHC indicates reduced syneresis, which is essential for maintaining the desired texture and consistency. Wang et al. [36] reported that the addition of 1% apple pomace to yogurt had no significant effect on syneresis, yielding values similar to those of plain yogurt. However, in line with our study, many studies on fortified yogurts have reported that powdered additives tend to enhance the WHC of plain yogurt. Studies have demonstrated that the addition of mulberry powder [37], carrot fiber [38], and maca powder [39] improved the structure of the yogurts and enhanced their WHC levels.

The L* value (lightness) was highest in the control group (84.8 ± 1.6) and decreased proportionally with increasing TP concentrations. The a* and b* values, representing color tones, were also significantly affected by TP addition. The highest b* value (67.8 ± 0.9) was observed in the TP_1 group, indicating a notable increase in the yellowish hue of the yogurt due to TP incorporation. The a* values, which reflect the green-to-red spectrum, indicated a slight greenish tone across all samples, with negative values shifting towards green. The control yogurt (C) exhibited an a* value of −1.4, which was similar to that of TP_05. However, the TP_1 sample (−0.8) showed a slight shift toward red with higher turmeric concentrations. Turmeric pigment is known for its stability under acidic conditions compared to alkaline pH [40]. Therefore, the observed color variations were solely attributed to the increasing concentration of turmeric powder.

3.2. Antioxidant Activity of Yogurt Samples

The antioxidant activities of the yogurt samples were evaluated in terms of the DPPH radical scavenging activity, presented as percentages in Figure 1. The results demonstrate a significant increase in antioxidant activity with TP addition compared to the control. Briefly, the TP_1 group exhibited the highest activity (51.11%), followed by TP_05 (35.04%), whereas the control yogurt revealed the lowest activity (10.22%). The compounds in TP that have been reported to contribute to its antioxidant activity include curcumin, which is the main bioactive phenolic compound in turmeric. Curcumin has been shown to exhibit antioxidant activity by preventing lipid peroxidation in various cells, such as erythrocytes and liposomes [41]. Additionally, ar-turmerone, another compound in turmeric, has been identified as possessing antioxidant properties [42]. In the literature, DPPH scavenging activity values ranging from 53% to 65% have been reported for different varieties of turmeric extracts [43].

There are many studies in the literature examining the use of bioactive plants to enhance the antioxidant properties of yogurt. For instance, Cho et al. [44] reported that using 0.5% omija fruit extract increased the DPPH scavenging activity of yogurt from 57% to 65%. Another study found that adding 1% aronia fruit to plain yogurt increased its antioxidant activity, in terms of the DPPH scavenging activity, from 59% to 69% [45]. However, the antioxidant capacity in these studies appears to be higher than that in our research, likely due to differences in pH adjustment during the extraction process. Nonetheless, the increase in antioxidant activity from fruit addition in these studies was lower compared to the results observed in our study. In a study investigating the phenolic properties of green tea yogurt, the DPPH scavenging activity of plain yogurt was reported to be around 10–15%, similar to the findings of our study. Furthermore, the samples produced by extracting green tea in milk demonstrated antioxidant activity levels of 30–40% [46].

3.3. Total Phenolic Content of Yogurt Samples

The total phenolic content (TPC) results are presented in Figure 2. The highest TPC was observed in the TP_1 group, with a value of 30.20 mg GAE per 100 g of yogurt, followed by TP_05, exhibiting a TPC of 17.51 mg GAE/100 g. The control group (C) had the lowest TPC, with a value of 1.39 mg GAE/100 g. The results suggest that incorporating TP into a yogurt formulation significantly enhances the phenolic content, which is associated with health-promoting properties.

Plain yogurt contains a limited amount of phenolic compounds, primarily derived from the breakdown of milk proteins during the fermentation process. These phenolic compounds inherently originate from the milk rather than from plant-based ingredients, which typically contribute a significantly higher phenolic content in flavored or fortified yogurt varieties [46,47]. Turmeric powder is rich in phenolic compounds. The main polyphenolic compound, which is also responsible for the yellow color of turmeric, is curcumin. The other phenolic compounds found in turmeric include demethoxycurcumin, bisdemethoxycurcumin, and calebin A. These compounds are known for their various health-promoting properties, including antioxidant, anti-inflammatory, and anti-cancer activities [48].

There are studies in the literature that have demonstrated the potential to enrich the phenolic content of yogurt by adding bioactive components. For instance, Karaaslan et al. [49] added grape extract to yogurt, increasing the total phenolic content from 1.5–2 to 7–8 mg per 100 g of product, which is lower than the results in our study. Similarly, another study examined the effects of adding various plant powders to yogurt at a 1% concentration, finding that the total phenolic content increased from 13 mg to 26 mg in 100 g of plain yogurt with beetroot and to up to 49 mg with rosehip fruit powder, which is even higher than the values we observed in our research [50]. The total phenolic content of turmeric has been determined to range between 38 and 157 mg/g in studies depending on the species and varieties [51]. The value observed in the yogurt containing 1% TP (TP_1) in our study was slightly below this range. This phenomenon has been reported to be influenced by the variety, climatic conditions, as well as the particle size of turmeric powder [52].

3.4. Principle Component Analysis (PCA) of Some Physicochemical and Bioactive Properties of Yogurt

The first component (PC1) accounted for 92.8% of the total variance, while the second component (PC2) explained 7.2%; together, they represent the entire dataset, as shown in Figure 3. The addition of turmeric led to increases in the pH, antioxidant activity, TPC, and WHC of the yogurt samples. The b* value also increased with turmeric addition. In terms of the hardness, lightness (L*), and acidity, the control yogurts displayed dominant characteristics. Considering the position of TP_1 in the PCA graph, it was demonstrated that the incorporation of turmeric into yogurt led to a significant increase in bioactive compounds and the WHC.

3.5. Gastric pH and Bile Salt Tolerance of Bioactive Compounds

The gastric pH (pH 3.0) and 0.5% bile salt tolerance values of the yogurt samples were determined after 3 h of incubation at 37 °C, and the obtained results were calculated as a percentage relative to the untreated blank sample incubated under the same temperature and time. The tolerance values of the bioactive materials are given in

Table 2. Gastric pH and bile salt tolerance of bioactive compounds in yogurt samples.

	Gastric pH Tolerance (%)	Bile Salt Tolerance (%)
Antioxidant capacity
C	100 ± 1.4 a	109.0 ± 1.4 a
TP_05	92.2 ± 3.2 a	104.5 ± 1.0 a
TP_1	74.4 ± 0.2 b	97.5 ± 2.1 b
Total phenolic compounds
C	98.1 ± 2.0 a	97.0 ± 4.1 a
TP_05	95.8 ± 1.9 ab	95.5 ± 5.0 a
TP_1	88.9 ± 0.4 b	87.5 ± 3.0 b

C: control (plain yogurt); TP_05: yogurt with 0.5% turmeric; TP_1: yogurt with 1% turmeric. The lowercase letters indicate differences between sample groups (p < 0.05).

.

The control yogurt (C) exhibited stability in the antioxidant capacity and total phenolic content under both gastric pH and bile salt conditions, suggesting that it was the least affected by the treatments. The sample with 0.5% TP (TP_05) remained relatively stable under the tested conditions, with a slight reduction in the total phenolic content observed only in the acidic environment. The increase in antioxidant measurements observed in C and TP_05 after incubation, compared to their initial values, may be attributed to changes in the redox potential during incubation [27]. The sample containing 1% TP (TP_1) exhibited a decline in both the antioxidant capacity and total phenolic content under both acidic and bile salt conditions. Specifically, the antioxidant activity decreased by 25.6% in the gastric pH environment compared to its initial value, while a loss of 11.5% was observed in the bile salt medium. In terms of the total phenolic content, TP_1 showed an 11.1% reduction after incubation in the acidic environment compared to its initial value and a 9.2% decrease relative to the control. In the bile salt medium, the total phenolic content decreased by 12.5% from the initial value and by 9.5% compared to the control yogurt.

In the literature, the addition of black pepper was reported to enhance the bioavailability of curcuminoids by 2000% [53]. In a study where curcuminoid powder was added to buttermilk yogurt, an 11% loss in the curcuminoid content was observed in the yogurt matrix; however, their bioaccessibility was reported to be 15 times higher than that in the water medium [54]. In another study, the incorporation of encapsulated turmeric oleoresins into the yogurt matrix resulted in an increase in bioaccessibility, suggesting the potential for further enhancement in different matrices [20].

3.6. Antibacterial Activity and Yogurt Bacteria Counts of Samples

The antibacterial activity of the yogurts was investigated using the well diffusion method. However, no significant activity against the test bacteria was observed, as illustrated in Figure 4. The absence of an antimicrobial effect of plain yogurt on the test bacteria (S. Typhimurium, E. coli, and S. aureus) was an expected result and has also been confirmed in previous studies reported in the literature [55].

Turmeric is a plant known for its antibacterial potential, attributed to its volatile oil-containing turmerones as active compounds [56]. Turmerones represent a group of components known for their anti-inflammatory properties. However, turmerones could be damaged by heat during the drying process [57] or exposed to oxidation in light-permeable packaging [58]. In the study by Uthman et al. [59], 17% of active compounds (Curcuma longa extract) were isolated from turmeric, and the minimum inhibitory concentration of the extract was reported as 25 mg/mL for E. coli and S. aureus. In our study, the amount of active compounds present in 1 g of turmeric added to 100 g of yogurt likely remained below this threshold, which may explain the absence of antibacterial activity.

Yogurt bacteria, as they are Gram-positive, are recognized to be more susceptible to antimicrobial agents due to their structural differences from Gram-negative bacteria. According to the regulations, the total count of yogurt bacteria (L. bulgaricus and S. thermophilus) must be a minimum of 6 log CFU/g during storage [60]. Consequently, the inhibitory effect of TP incorporation in yogurts on the specific yogurt bacteria was determined through bacterial enumeration, and the results are given in Figure 5. The enumeration of yogurt bacteria exhibited a reduction both with the incorporation of TP and the progression of storage. A loss in viability concurrent with a decrease in pH during storage was expected, as also observed in the findings of Glušac et al. [61]. On the 15th day of storage, while the control products revealed a 1.9% decrease in viability, the samples including TP exhibited a reduction of 3.4–3.5% in yogurt bacteria viability. During storage, no difference was observed between the two concentrations—0.5 and 1.0%—of TP. Rahmatalla et al. [62] also reported that the incorporation of 0.5% TP into plain yogurt led to a reduction in lactobacilli counts from 6.35 to 5.59 log cfu/g. These counts, measured on the first storage day, correspond to a 12% decrease in viability, which is significantly higher than the viability loss observed in our results. Buniowska-Olejnik et al. [17] reported that in probiotic yogurt enriched with 0.2% curcumin extract, the Bifidobacterium strain remained at the recommended level (at least 7 log CFU/g) throughout 28 d of storage.

3.7. Sensory Attributes

Based on the sensory attributes, differences were observed in terms of the appearance, texture, flavor, and overall acceptance (Figure 6). The control group (C) received higher scores for appearance, flavor, and overall acceptance compared to the groups with TP (p < 0.05). The texture of the samples was not affected by TP addition, in accordance with the analytical texture results given in Table 1. Regardless of the concentration, TP_05 and TP_1 received lower appearance, flavor, and overall acceptance scores in contrast to the plain yogurts. However, all yogurts received high scores (ranging between 6.6 and 8.5) in terms of the analyzed parameters, thus indicating favorable sensory acceptance. In the study of Lučan Čolić et al. [63], similar results were obtained; ice creams prepared with 0.5% and 1% TP received lower scores compared to plain ice cream. While in our study, products containing 0%, 0.5%, and 1% TP received overall acceptance scores of 7.8, 7.0, and 6.7, respectively, in the ice cream study [63], the products were scored as 7.4, 6.9, and 6.3, respectively.

4. Conclusions

This study demonstrated that turmeric powder is a promising functional additive for enhancing the bioactive properties of yogurt, particularly by significantly improving the antioxidant activity and phenolic content. These findings highlight the potential of turmeric-enriched yogurt as a functional food product that aligns with the growing demand for natural, health-promoting ingredients in the food industry. Beyond its immediate effects on the antioxidant and phenolic profiles, turmeric’s known bioactive compounds, such as curcumin, may offer additional health benefits when incorporated into fermented dairy products. However, it should be noted that the addition of turmeric at a 1% concentration led to a decrease in both the antioxidant capacity and total phenolic content under gastric pH and bile salt conditions, suggesting a potential loss of bioactive properties during digestion. Although turmeric exhibited a slight inhibitory effect on specific yogurt bacteria, the bacterial count remained within regulatory limits even on the 15th day of storage. Additionally, while the yogurt remained within sensorially acceptable limits, it is recommended that future studies incorporate flavoring agents to improve the sensory attributes, taste, and overall acceptance of turmeric-enriched yogurt. Furthermore, studies on its long-term impact on the gut microbiota composition and metabolic health could provide deeper insights into its potential role in supporting digestive and overall health.