Key findings:

The study found that adding black cumin oil to yogurt significantly affected pH and water holding capacity but not viscosity. Higher concentrations of black cumin oil decreased the pH, viscosity, and water holding capacity of the yogurt. Optimal concentrations should be carefully considered to balance these effects.

What is known and what is new?

Yogurt is traditionally made through bacterial fermentation, and black cumin oil has anti-allergic, anti-tumor, antibacterial, and anti-inflammatory properties. This study reveals that adding black cumin oil to yogurt significantly impacts pH and water holding capacity, with higher concentrations decreasing these parameters, while viscosity remains unaffected.

What is the implication, and what should change now?

Incorporating black cumin oil into yogurt can alter its pH and water holding capacity, potentially affecting its texture and shelf life. Producers should optimize the concentration of black cumin oil in yogurt to achieve desired health benefits without compromising product quality, possibly focusing on lower concentrations to maintain optimal pH and water holding capacity.

Fresh Cow's Milk is a liquid derived from the udderof a healthy and clean cow, obtained through the milking process, without any addition or reduction of content, and having undergone no treatment except cooling [1]. Milk is one of the essential nutritional sources for humans, primarily fulfilling nutritional requirements and maintaining bone and dental health. Fresh milk needs to undergo processing before consumption to reduce the potential presence of pathogenic bacteria dissolved during the milking process. Milk can be processed through paste urization or transformed into a dairyproduct. The quality of the result ing milk depends on its nutritional content, such as water, fat, lactose, non-fat dry matter, and protein.

Yogurtis a dairy product made through the fermentation of Lactobacillusacidophilus, Lacto bacillus bulgaricus, and Streptococcusthermophilus bacteria. The fermentationprocessofyogurtaims to break down the sugar content in milk and producelacticacidcompounds. Lactobacillus bacteriaplay a significant role in aroma formation, while Strep to coccus bacteria are moreinvolved in taste development [2].

According to Hasruddin and Prativi (2015), yogurt is a product resulting from milk fermentation using lactic acid bacteria, having a semi-solid form and a distinct texture and flavor. Additionally, yogurt contains superior nutritional value compared to fresh milk. The fermentation process in yogurt results in a decrease in milk pH to 3.8 - 4.5, which is one of the reasons for the acidic taste in yogurt [3].

Black cumin oil has numerous benefits for the body, such as preventing allergic reactions in asthma, acting as an anti-tumor agent, having antibacterial and anti-inflammatory properties [4]. The benefits of black cumin oil stem from its active ingredients, including thymoquinone, thymohydroquinone, dithymoquinone, thymol, carvacrol, nigellicine, nigellidine, nigellimine-N-oxide, and alpha-hederin (Hutapea, 1994). Besides its active ingredients, black cumin contains valuable nutritional content: Water 6.4%, Fat 32%, Crude fiber 6.6%, Protein 20.2%, Ash 4%, and Carbohydrates 30.8% [5].

Yogurt with the addition of black cuminoilis expected to provide benefits in the physical quality of the resulting yogurt. Some aspects of this physical quality include pH level, viscosity, and water holding capacity in yogurtwithadded black cuminoil during the yogurt fermentation process. This study aims to determine the influence of adding black cuminoilat concentrations of 1%, 2%, 3%, 4%, and 5% in the yogurt-making processon the pH, viscosity, and water holding capacity of the produced yogurt.

Fresh cow's milk is obtained from a dairy farm located in Tanjungsari, Sumedang, Indonesia. Black cuminoilisacquiredfroman herbal medicine store also located in Tanjungsari, Sumedang, Indonesia. The yogurt starter is obtained from Yogour met, a division of the Lallem and Group, based in Montreal, Canada.

Preparation of Mother Starter Yogurt

The preparationofthe starter yogurt involves dissolving 15% skim milk in 50 ml ofwater, followedby a pasteurizationprocessat 80°C for 10 minutes. The milkisthencooledto a temperatureof 43°C to 45°C and inoculated with 0.5% (0.25g) starter yogurt, afterwhichitisincubatedat 43°C for 6 hours [6].

Preparation of Black CuminYogurt

The production of black cumin yogurt begins with paste urizing 50ml of freshmilk at 80°C for 10 minutes. Subsequently, the milk is cooled to a temperature of 43°C to 45°C, after which black cuminoilis added in concentrations of 1-5% ofthe total milk volume. It is then in oculated with 5% starter yogurt and incubated at 43°C for 24 hours.

pH value

Proses The pH value analysis for yogurt with added black cuminoilis performed using anelectronicpH meter. Before,measuring the pH values, it's essential to clean the pH meter byrinsingthecathode end of the pH meter indicator with distilled water solution. Then, dry the cathode using a tissue. The cleaned cathodeend should be calibrated by dipping it intobuffersolutions with pH values of 4 and 7 [7]. After the calibration process, thecalibratedpH meter is then used to measure the pH of a 25 ml sampleofyogurtthat has beenmixedwithblackcuminoil. The measurement results can be read directly from the pH meter. This process ensures accurate measurement of the acidity or alkalinity (pHvalue) oftheyogurtsampleswithvaryingconcentrationsofblackcuminoil.

Viscosity

The viscosity of yogurt with added black cuminoilis measured using a viscometer based on the method described by (Suliasih et al., 2019) [8]. Yogurt with added black cuminoili splaced in a jarandstirred slowly using a stirringrod for 30 seconds before pouring it into the visco meter container. A cylindrical-shaped spindle is used at a speed of 3000 rpm for 60 seconds. Viscosityisexpressed in centipoiseunits (dPa's).

Water Holding Capacity (WHC)

Regarding the determination of Water Holding Capacity (WHC), theprocedure, initiallypresented by (Setyawardani et al., 2020) [9] and further adapted, involves several steps. A 10 ml yogurt sample is weighed, followed by centrifugation at 3000 rpmfor 10 minutesatroomtemperature. The whey separated during this process is then weighed. The WHC iscalculatedusingthe formula :

This measurement approach assesses the yogurt's ability, with added black cumin oil, to retain water after centrifugation, providing insights into its water-holding capacity.

Statistical Analysis

The study utilized the Completely Randomized Design (CRD) method, consisting of 5 treatments involving the addition of black cumin oil at levels of 1% (P1), 2% (P2), 3% (P3), 4% (P4), and 5% (P5). Each treatment was replicated four times, resulting in a total of 20 experimental units. The collected data on pH values, Water Holding Capacity, and Viscosity were subsequently analyzed using Analysis of Variance (ANOVA) and further assessed through the Duncan Multiple Range Test [10]. This rigorous statistical analysis was conducted to scrutinize the impact of different concentrations of black cumin oil on the mentioned parameters, providing a comprehensive understanding of their effects on the yogurt. 

pHValue

The research results regarding the effect of the addition black cuminoil on the pH value of yoghurt are presented in Table 1.

Table 1. pH Values of Yoghurt under Various Treatments

Based onthe data presented in Table 1, it is evident that yogurt with the addition of black cuminoil exhibits an average pH value ranging from 3.94 to 4.05. The pH values in yogurt supplemented with black cuminoiltend to elevate the result in gyogurt's pH level. Statistical analysis using analysis of variance (ANOVA) demonstrates a significant effect (P<0.05) of adding black cuminoil during the yogurt-making process on the resulting yogurt's pH values. Further examination was conducted utilizing the Duncan multiple range test to identify differences among the various treatments involving the addition of black cuminoil during the yogurt-making process.

Table 2. Mean pH Values of  Yoghurt under Various Treatments

Note: Mean values followed by different lower case letters (subscripts) in the same row indicate statistically significant differences.

Berdasarkan According to Table 2, the pH values of yogurt with the addition of black cuminoil significantly impact each treatment administered during the yogurt-making process. The pH values of yogurt with added black cuminoil remain within the range considered ideal foryogurt, as indicated by (Solikhah et al., n.d.) [3], which suggests that good yogurt falls within the pH range of 3.8 – 4.5. This study reveals that the addition of black cuminoil substantially influences the increase in theresultingyogurt'spHvalue. The rise in pH in yogurt may beat tributed to the addition of black cuminoil during they ogurt fermentation process, affecting the activity of lactic acid bacteria. This alteration can result in the production of acetic acid and citric acid during fermentation, leading to an increase in theresulting pH value [11]. The elevation in the resulting yogurt'spH value could be due to black cuminoil, which has a pHrangeof 5, potentially raising the yogurt'spH as its concentration increases [12].

Viscosity

The research results regarding the effect of the addition of black cuminoilon the viscosity of yoghurt are presented in Table 3.

Table3. Viscosity of  Yoghurt u nder Various Treatments

Based on the data presented in Table 3, it's observed that yogurt with added black cuminoil exhibits an average viscosity ranging from 0.40 to 0.60 dPa's. The viscosity values of yogurt supplemented with black cuminoiltend to decrease. Statistical analysis using analysis of variance (ANOVA) indicates that adding black cuminoil in yogurt production does not have a significant effect (P>0.05) on the viscosity values of the yogurt. 

Table 2. Meanviscosity Values of Yoghurt under Various Treatments

Note: Mean values followed by different lower case letters (subscripts) in the same row indicate statistically significant differences.

Based on Table 4, the average viscosity values of yogurt supplemented with various concentrations of black cuminoil (1%, 2%, 3%, 4%, and 5%) do not exhibit a significant impact on the yogurt's viscosity. Viscosity measures the consistency of a food product. The decrease in yogurt viscosity is attributed to the addition of liquid black cuminoil, which decreases the resulting yogurt's viscosity. The viscosity of yogurt can be in fluenced by the protein contentpresent in milk. Milk protein shave the ability to bind water, leading to an increase in viscosity [13]. The reduction in viscosity in yogurt with added black cuminoil might be due to the decrease in water-holding capacity (whey off) by the casein gel at the isoelectricpH, resulting in decreasedviscosity[14].

Water Holding Capacity (WHC)

The research results regarding the effect of the addition of black cuminoilon the Water Holding Capacityofyoghurt are presented in Table5.

Table5. Water holding Capacity of  Yoghurt under Various Treatments

Basedonthe data presented in Table 5, it is apparent that yogurt supplemented with black cuminoil demonstrates an average water holding capacity ranging from 75.74% to 83.53%. The waterholdingcapacity in yogurt with added black cuminoiltends to decrease as the concentration of the oil increases. Statistical analysis using analysis of variance (ANOVA) suggests a significant effect (P<0.05) of adding black cuminoil during yogurt productionon the yogurt's water holding capacity. Further analysis using the Duncan multiple range test aimed to identify differ ences among the various treatments in volving the addition of black cuminoil in the yogurt production process.

Tabel 6. Mean Water Holding Capacity Values for Various Treatments

Note: Mean values followed by different lower case letters (subscripts) in the same row indicate statistically significant differences.

Based on Table 6, the Duncan multiple range test results indicate that the water holding capacity of yogurt with added black cuminoil at concentrations of 1%, 2%, 3%, and 4% significantly differs when compared to the 5% concentration. However, the 1% and 2% concentrationsdo not significantly differ from the 3% and 4% concentrations. The waterholding capacity reflects the yogurt's ability to retain water during centrifugation treatment. The decrease in the water holding capacity of the result in gyogurt is attributed to the addition of liquid black cuminoil, which can reduce the yogurt's water holding capacity.

The water holding capacity of the resulting yogurt indicates its quality. The highertheyogurtquality, the great eritsability to retain free water [15]. The water holding capacity of yogurt can be influenced by the fat content in milk. The fatcontent in milk has the ability to bind water, resulting in an increased water holding capacity in yogurt [16].

The addition of black cuminoil in yogurt production at concentrations of 1%, 2%, 3%, 4%, and 5% significantly affects the pH and water holding capacity but does not significantlyimpact yogurt viscosity. With theincrease in the concentration of added black cuminoil during yogurt production, there is a tendency for a decrease in the pH, viscosity, and water holding capacity of the yogurt.

Conflict of Interest: The authors declare that they have no conflict of interest

Funding: No funding sources

Ethical approval: The study was approved by the Institutional Ethics Committee of Universitas Negeri Makassar

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