Effect of Carrot Juice on the Texture Properties, Rheology, and Microstructure of Yoghurt

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Introduction
Currently, yoghurt is viewed as one of the most popular fermented dairy products and it has obtained widespread well-being with benefts of energy and nutrition value [1]. Te yoghurt product by microbial fermentation of bovine milk is produced by using probiotic bacteria consisting of a combination of Lactobacillus bulgaricus and Streptococcus thermophilus. During fermentation, these probiotics are responsible for conversion of lactose into lactic that minimizes the pH value. When the pH of fermentable milk attains the isoelectric point of casein in the milk, casein starts to interact with each other, resulting in some poor-quality attributes, such as loss of solubility and the formation of very specifc three-dimensional structure [2,3]. So, improving quality attributes of the yoghurt product is the concern of human research. However, adding food additives including pectin, xanthan gum, starches, and gelatin, among others into yoghurt products is unacceptable for consumers in some countries because humans prefer to natural food products without hydrocolloid stabilizers [4][5][6]. In addition, yoghurt production without additives is also in line with the increasing demand for "green label" products [7]. Tus, it is an inevitable trend to use natural ingredient instead of food additives aiming to improve yoghurt quality and enhance the efectiveness of nutritional values. Apple pomace addition with formulation compensation in yoghurt processing had resulted in an acceptable product and enhanced the extent of yoghurt frmness [2].
Generally, edible carrot portion contains less water, protein, total carbohydrates, and lipids. Moreover, carrot is also classifed as a vitaminized food in that carrot also includes other primary nutritional components; it is rich in dietary fbers (approximately 32 g), vitamins (β-carotene), ascorbic acid, and minerals (e. g. iron, copper, sulfur, magnesium, manganese, and potassium) [8] but lacks in high-quality protein and fat. While yoghurt is rich in protein, lipid, and calcium, it is defcient in vitamin, mineral, and dietary fbers [9]. Terefore, a combination of yoghurt and carrot juice may enhance nutrition [10] and have a frming texture of set-type yoghurt. Yoghurt has been viewed as a carrier of dietary fber and other nutritional components in a variety of studies. From the aspect of nutritional value, dietary fber-rich products such as carrot juice and apple pomace may possess a host of functional characteristics, such as fat adsorption, water hydration, and viscosifying and texturizing properties [11]. Tanje et al. found that dietary fber added into yoghurt by gellingtexturizing and water holding capacity can provide positive contribution to the frm texture and shelf life of yoghurt [12]. Te results from a previous study also proved that the addition of the carrot juice and stabilizer into yoghurt resulted in improved nutritional component and suppressed syneresis but did not specify which ingredient played a leading efect [13].
Te prime purpose of this study was to characterize the functionality of carrot juice as a natural ingredient for dairy products and evaluate the infuence of carrot juice on physicochemical, texture and rheological properties, and functional (total phenolic and ferric reducing power) properties of fermented milk products during cold storage (21 days).

Preparation of Carrot Juice and Yoghurt Samples.
Fresh carrots were cleaned thoroughly, peeled and mixed with deionized water in a ratio of 1 : 1, grounded by a highspeed homogenizer (Hangzhou Joyoung Co Ltd., Hangzhou, China) into juice for 1 min at 20°C, and then centrifuged to collect carrot juice. Te skimmed milk powder and sucrose were dissolved in pure water at contents of 100 g/kg and 60 g/kg, respectively. Afterwards, the carrot juice was added to the skimmed milk at two set concentrations of 1 : 9 and 2 : 8 (w/w) and fully mixed for 10 min with a magnetic stirrer before heating. Te skimmed milk without carrot juice was named as control. Set-type yoghurt was prepared according to the method described by Lucey and Lee with slight modifcations [14]. Carrot-milk mixture was heated at 90°C for 10 min in a water bath and then cooled to approximate 42°C. Tey were inoculated with the DVS starter at a level of 0.06 g/kg milk according to proposal of the supplier, poured into a 50 mL beaker under aseptic conditions, and then fermented at 42°C for about 5 h. Yoghurt samples were stored in a refrigerator at 4°C for 24 h to analyze their chemical composition, microstructure, and textural and rheological properties at day 1 (overnight), 14, and 21.

Chemical Composition of Yoghurt and Carrot Juice.
Te fat, protein, and ash contents of yoghurt were detected according to AOAC methods No. 905.02,No. 991.20,and No. 945.46, respectively [15]. Protein contents of yoghurt were estimated by a conversion factor (6.38) of nitrogen to protein.
Te total solids levels of yoghurt and carrot juice were detected as described in AOAC methods No. 990.20 and 920.151 [15].  [16]. Calibration curves were prepared according to the following concentration contents of gallic acid: 25, 50, 75, 100, 125, and 150 μg/mL. Te 100 μL extract and 750 μL of Folin-Ciocalteu solution were mixed, allowed to stand for 5 min, and then gently mixed using 750 μL 6% sodium carbonate (w/v). After standing for 40 min, absorbance was determined at 725 nm with a UV/Visible spectrophotometer (Shimadzu Co. Ltd., Kyoto, Japan) and assayed results were expressed as mg of gallic acid equivalent per 100 g of carrot juice.

Chemical Analysis of Yoghurt and Carrot
Te total phenolic was extracted by the provided method in Wallace and Giusti's literature [17]. Yoghurt samples were blended with 30 mL acidifed methanol (containing 0.1% HCl) for 2 min and then centrifugated for 15 min at 3500 rpm. Te supernatant was mixed with 50 mL of acidifed methanol, and total phenolic was measured as described above.

pH Measurement.
Te pH was determined with a digital pH meter (Mettler, Toledo, FE28 pH, Shanghai, China) at room temperature after a rectifcation using the standard bufer solvents with pH values of 4.01, 6.86, and 9.18, respectively. Total protein content, titratable acidity, and total solids of the yoghurt samples were detected according to the AOAC [18] method using an automatic titration apparatus.

Ferric Reducing Power Measurement.
Te ferric reducing power of carrot juice was detected using the previous method [19]. Te 100 μL carrot juice or yoghurt extracts were blended with 2.5 mL phosphate bufer (0.2 M, pH 6.6) and 2.5 mL 1% potassium ferricyanide and incubated at 50°C for 20 min in a water bath. 2.5 mL 10% trichloroacetic acid was added to the above mixture and centrifuged at 3500 rpm for 10 min. Te upper layer (2.5 mL) and distilled water (2.5 mL) were mixed with freshly prepared ferric chloride reagent (0.1%, 2.5 mL). Absorbance at 700 nm was determined.

Rheological Measurement of Yoghurt.
Viscoelastic and viscosity behaviours of the yoghurt samples were measured by a Bohlin Gemini II Rheometer (Malvern Instruments Limited, Worcestershire, UK) with a cone-plate geometry (cone angle 4°, gap 0.15 mm and diameter 40 mm) at room temperature, according to previous reference methods [20,21]. Te yoghurt samples were allowed to return to room temperature and gently stirred 10 times at 2-3 s per rotation with a tablespoon aiming to achieve a homogeneous state before measurement. Elastic and viscous modulus (G′ and G″) were detected using the cone-plate geometry, frequency sweeps in 0.5% strain and 0.1-10 Hz, and shear rates of 0.1-10/s (within the linear viscoelastic region).
2.6. Texture Analysis of Yoghurt. Te yoghurt texture was determined using a stable Micro Systems Texturometer (Texture Technologies Corp, New York, USA) equipped with a 5 kg load cell as the previous research method [22]. Te samples (50 mm diameter 50 mm height) held in the glass containers were required to equilibrate to room temperature before putting the containers on the console. Te parameters were modifed: head velocity speed of 1.0 mm/s, cylinder probe of 35 mm diameter, surface trigger force of 10 g, and penetration distance of 30 mm. Te samples were replaced in 125 mL containers with 70 mm height and 64 mm diameter. Hardness, cohesiveness, adhesiveness, and springiness were calculated by the XT.RA Dimension ver. 3.7 program.

Microstructure Observation and Syneresis Analysis of
Yoghurt. Te microstructure of the samples was evaluated using the S-3400N Scanning Electron Microscope (Hitachi High-Technologies Co., Tokyo, Japan) following a previous method performed with some changes [22]. A cube (4 mm × 4 mm × 3 mm) was segregated from about 1 cm under the surface and fxed using 0.1 mol/L phosphate bufer (pH 6.8) including 25 g/kg glutaraldehyde for 24 h. Te specimens were washed with 0.1 mol/L phosphate bufer (pH 6.8) three times for 10 min each time and dehydrated with diferent concentrations of ethanol (50-90%, 15 min each time). Afterwards, the specimens were dipped in tertbutyl alcohol, absolute ethanol solutions (1 : 1, v/v), and tertbutyl alcohol (15 min) and then lyophilized in liquid nitrogen (48 h). Te treated specimens were placed on the holders in a Hummer VI sputtering system (Matsushita Electric Industrial Co., Osaka, Japan) with an adhesive carbon flm bonding and with gold spraying and then observed and photographed with a magnifcation of ×2000 under the scanning electron microscope.
Syneresis of the samples was detected according to the method described by Keogh and O'Kennedy [23]. Syneresis was counted as the supernatant (whey) produced after lower speed centrifugation (at 222 ×g for 10 min) of 20 g yoghurt samples. Te supernatant was dumped and weighed right away. Te syneresis parameter of these samples was expressed as weight %.

Statistical
Analysis. All data derived from analyses were obtained from at least three independent experiments and reported as means ± standard deviations. Diferences between the multiple groups were carried out using one-way analysis of variance (ANOVA) and two-way analysis of Spearman. All analyses and the reported data were carried out with Duncan's analysis and Spearman's analysis SPSS 16.0 software (SPSS Inc., Chicago, IL, USA) and MS Excel 2003 (Microsoft Corporation, Redmond, WA, USA).

Chemical Composition of Carrot Juice and Milk Used.
Te freshly prepared carrot juice's total carbohydrates, moisture, total solids, and total phenolic contents assayed on weight basis were 6.0, 91.7, 7.6%, and 46.3%, respectively, and similar to previously reported values on carrot juice by Negri Rodríguez Livia et al. [8]. Te milk water, total solids, fat, protein, and ash contents were 86.8, 13.2, 3.2, 3.0, and 0.8, respectively, and consistent with those reported for cow milk [24].

Chemical Composition of Yoghurt.
In this study, crude protein, total solids, fat, and ash contents (%, w/w) of these samples were in the range of 2.7-3.1%, 15.4-16.6%, 2.8-3.3%, and 0.70-0.73%, respectively (Table 1). Tis meant that chemical composition of these yoghurt samples was signifcantly (P < 0.01) afected by carrot juice addition. Being accompanied by carrot juice increase, fat content decreased while the moisture level of yoghurt increased. With carrot juice doses increased, crude protein content signifcantly lowered, but the diference was insignifcant (P > 0.05) between yoghurt samples containing 15% and 20% carrot juice. Te ash level of yoghurt samples also reduced as carrot juice addition levels increased even though ash values of yoghurt samples including 10% and 20% carrot juice were similar.
Changes of proximate composition in yoghurt samples were responsible for composition diference between used carrot juice and milk. Carrot juice addition had a certain dilution infuence on composition of yoghurt, and this was dependent on high moisture levels of carrot juice. Information on yoghurt composition is mandatory from quality inspection department. According to the description in Codex for yoghurt standard, in the present study, yoghurt samples are satisfed with these requirements [25].

Total Phenolic and Ferric Reducing
Power. Some factors e.g., sanitizing reagent contamination, protein metabolized by bacteria, specifc fodder fed by cattle, and deliberate addition as particular functional constituents result in phenolic compound occurrence in dairy products [26]. Total phenolic level increase and correspondingly ferric reducing power increase could be expected to be present in yoghurt Journal of Food Quality 3 samples with higher contents of carrot juice. Because of the phenolic level in carrot juice used being relatively low, total phenolic content and ferric reducing power are enhanced though carrot juice fortifcation was slight. Tis is partly due to the binding of phenolic compound with milk casein before gel formation during fermentation. Te present phenomenon is consistent with the previous study. When adding the grape seed extract into milk before fermentation, total phenolic content and ferric reducing power had no signifcant change [26,27]. Te total phenolic content in carrot should be related to cultivar, postharvest handling, and processing methods [8]. Hence, there is possible potential to improve yoghurt quality with antioxidant, dietary fbers, and provitamin A supplementation for other possible phytonutrients (e.g., ascorbic acid, tocopherols, phenolic, and fbers) derived from carrot juice.

pH and Titratable Acidity of Yoghurt.
Whether the added carrot juice had a certain efect on the yoghurt product was important to dairy production, taking into account that the fermentation time is prime to actual production for dairy enterprises. Terefore, the pH and titratable acidity were detected in yoghurt fermentation processing. Te results exhibited that the pH value and titratable acidity showed corresponding decreasing and increasing trend during fermentation processing, respectively, being accompanied by the extended fermentation time (  [27,28]. Carrot juice included soluble dietary fbers such as viscous polysaccharides, which might be used as facilitating factors to promote LAB proliferation during fermentation processing and human digestive tract. Another study had also found that dietary fbers could increase probiotic growth by adding dietary fber in vegetables in yoghurt products [29]. Tese mentioned results provided strong scientifc support for our present study. Moreover, the pH value of all samples minimized from 4.4 to 4.2 during the 21-day storage period (P < 0.01) ( Table 3), but the largest pH dr op occurred in the first 7-day cold storage stage. Te samples fortifed with carrot juice exhibited lower pH compared to the control samples during most of the cold storage period. At the same time, the titratable acidity of the yoghurt samples increased in similar tendency with the decrease in the pH value. Te pH and the titratable acidi ty had slight changes for all samples at theendofthe 21-day cold storage period (P > 0.05). Te obvious drop of pH in the first 7-day cold storage stage has similar results with the previous study of adding vegetables and fruit byproducts into yoghurts [30]. Consequent rise of lactic acid introduced by highly active starters led to this decrease at the initial stage of cold storage. Ingredient acids found in carrot juice can cause a positive efect on the pH and acidity of yoghurt.

Postacidifcation of Yoghurt with Carrot Juice.
During yoghurt storage, pH reduction or titratable acidity enhancement adequately took on the postacidifcation phenomenon. Te results displayed in Table 3 showed that all detected samples had postacidifcation phenomenon because of observing pH reduction and titratable acidity increase at diferent times of yoghurt storage. According to the analysis method described in two previous literatures [31,32], a 2-way ANOVA was carried out. Based on the results of the study listed in Table 3, the correlation of storage time and the amount of carrot juice signifcantly (P < 0.05) afected variation of pH and titratable acidity value. In the situation of the same storage time, carrot juice addition obviously brought about the changes of the pH value and the titratable acidity value. Te results showed that yoghurt samples with 10% and 20% carrot juice supplemented always manifested a lower pH level and a higher titratable acidity level, as compared to control samples without carrot juice. In general, after the 21-day storage period, yoghurt samples with carrot juice had a proximate titratable acidity value, which increased more obviously than the control sample. Te carrot juice level was a signifcant infuencing factor for titratable acidity and postacidifcation of yoghurt samples. It is well known that lactic acid is prime organic acid produced in yoghurt products. Te obtained results also verifed that during storage both carrot juice concentration and storage time had an efect on the amount of lactic acid of these samples. When prolonging storage time, lactic acid contents of these yoghurt samples also enhanced signifcantly. Similarly, addition of carrot juice was responsible for an increased lactic acid level in yoghurt samples with carrot juice. What is more special is that titratable acidity ranged from 0.70 for the control sample to 0.96 titratable acidity for samples with 20% carrot juice. Tese data confrmed that carrot juice addition resulted from lactic acid production during the 21-day storage period. Te lactic acid values observed in our study were lower than previously reported [33]. From favor development perspective, titratable acidity should be controlled within certain limits because of consumer preferences. Titratable acidity of this study was above the minimum limit of 0.60 recommended by Codex [25]. During yoghurt storage, further proliferation of S. thermophilus and L. bulgaricus also infuenced lactic acid formation due to lactose fermentation that is considered as the prime reason of yoghurt products postacidifcation [15]. Terefore, postacidifcation is an inevitable event in the storage period of yoghurt, including viable LAB. In the current study, these yoghurt samples showed a further increase in titratable acidity during storage. In a previous study of Patel and coauthors, high-amylose maize starch and inulin could enhance lactic acid production of a set-type yoghurt fermented only with one stain (L. casei or L. acidophilus) [34]. Another study found that starches and yam mucopolysaccharides were mixed to be able to promote the metabolism and proliferation of LAB, which resulted from the fermentation and hydrolysis of lactose [35]. Our study found that carrot juice endued with the stored yoghurt samples with carrot juice owning higher lactic acid levels (Table 4), indicating the phenomenon being consistent with these above studies. It was suggested that carrot juice could be used to enhance the postacidifcation of yoghurt samples.

Texture and Rheological Properties of Yoghurt Containing
Carrot Juice. Te textural characteristics of these samples are shown in Table 5. From a perspective of these obtained data, a combination of carrot juice and stored time mainly had a signifcant efect on hardness, cohesiveness, and adhesiveness values. But springiness values were not afected by carrot juice and stored time. In terms of detail, extended storage time was responsible for enhanced hardness, cohesiveness, and adhesiveness values, whereas carrot juice (especially for the yoghurt sample with 20% carrot juice) also brought about value increases for these indices. One of the most key parameters of yoghurt products is hardness. Te hardness value of mixtures of yoghurt with 10% and 20% carrot juice all increased by 105 g, showing these samples  Journal of Food Quality with the carrot juice indeed formed a frm texture. Moreover, the hardness of yoghurt samples with carrot juice was higher than that of the control sample with the same storage time. Terefore, it can be concluded that carrot juice played a positive efect on the hardness of milk mixtures. Te two past studies also showed that some contribution of food stabilisers resulted in the increased hardness and adhesiveness of yoghurt [36,37]. Normally, the hardness of yoghurt is related to the content of total solids [38]. However, yoghurt samples adding carrot juice only slightly increased total solids content (Table 3). Adding carrot juice caused an obvious efect on textural quality of mixtures of milk fortifed with 10% and 20% carrot juice. Tis is an implication that the current strategy adding carrot juice into the yoghurt product (not for the purpose of enhancing total solid content) in this way can indeed make yoghurt capable of a stable and rigid texture. Tree rheological parameters such as elastic, viscous moduli, and apparent viscosity were determined and compared for all samples stored for 1, 14, and 21 days of cold storage, in order to analyze the relationship between the addition level of carrot juice and value changes of these indices. Te present study only provided the data for all samples with cold storage of 14 days (Figure 1). Te results demonstrated that yoghurt samples containing 20% carrot juice were capable of higher viscosity values than that of the control and 10% carrot juice samples. Simultaneously, the same phenomenon was observed in fortifed yoghurt samples when G'/G″ values of these samples were compared. In general, the control and yoghurt with 20% carrot juice exhibited the lowest and highest parameter values, respectively, implying that the addition dose level of carrot juice resulted in enhanced rheological properties for these prepared yoghurt samples. In addition, G' values of yoghurt fortifed with 10% and 20% carrot juice were much greater than G″ values at the evaluated frequencies, revealing that they behaved like solid properties [39]. Yoghurt with 10% carrot juice had the proximate viscous modulus but higher elastic modulus compared to control. Yoghurt samples fortifed with 20% carrot juice displayed the highest elastic and viscous modulus. Tis took on the efect of the carrot juice on yoghurt quality. Te TPA results exhibited that all yoghurt samples had diferent textural features. Mixtures of milk containing 10% carrot juice and the control had similar texture index values (P > 0.05). Yoghurt with 20% carrot juice showed lower cohesiveness, higher hardness, and adhesiveness (P < 0.05) but proximate springiness (P > 0.05) compared to control without carrot juice and yoghurt with 10% carrot juice.
Various types of food additives are found in yoghurt products in order to improve rheological properties of yoghurt. Te two previous studies reported that casein in milk was cross-linked with transglutaminase to form protein polymers, resulting in enhanced rheological texture [40,41]. When enzymatic cross-linking treated milk protein, increased G′/G″ values were found in yoghurt samples [42]. A past study also showed that adding gelatin into camel milk could increase G″ values of acidifed camel milk [43]. At the same time, the other study demonstrated that the G′ value was enhanced by mixing gelatin with sodium caseinate [44]. Additionally, some researchers found that the values of three evaluated indices (viscosity and G′/G″ moduli) increased when cross-linked gelation was introduced into set-type skimmed yoghurt [45]. In this study, adding carrot juice to yoghurt samples meant that soluble polysaccharides were present in yoghurt. It is reasonable that carrot juice-fortifed yoghurt samples had the trend of increasing index values.

Microstructure and Syneresis of Yoghurt with Carrot Juice.
Microstructure analysis can be used to better explain the results from textural and rheological analysis [46]. Microstructural features of these samples were also identifed. Te micrograph of a continuous focculent protein structure was observed ( Figure 2 1 d). Te results indicated that when carrot juice was added to fermented milk, the particles from carrot juice mixed into the three-dimensional network structure; moreover, a network of thickening protein strands was founded in the fortifed fermented milk samples. Te yoghurt including 20% carrot juice exhibited a consistent network of protein resulting from the embedded carrot juice particles (Figure 2 14 d). As the levels of carrot juice increased to 20%, the network showed less compact. Te micrographs of the yoghurt samples without carrot juice are consistent with the control in past studies [47,48]. Te yoghurt with carrot juice made about diferent structure from that of yoghurt containing inulin and pectin. Te protein network of the yoghurt with carrot juice showed more pores compared with the network of fermented milk with exopolysaccharides produced lactic acid bacteria [49]. A relatively stable protein network with carrot juice particles trapped in the yoghurt sample with 10% carrot juice has not been found in other studies. Such kind of microstructure can correlate greatly with results of texture analysis, and the highest similarity that this sample showed is compared with the yoghurt samples containing other levels of carrot juice.
Syneresis is a main defect in fermented dairy products that may afect acceptability and the shelf life due to undesirable appearances. Carrot juice addition obviously   infuenced syneresis of yoghurt ( Figure 3). In this study, all yoghurt samples demonstrated an increased syneresis extent (P < 0.05) with their storage period prolonged, showing the storage period resulted in enhanced yoghurt syneresis. However, from data comparation perspective, the results showed that the control sample at each time point made about the highest syneresis, whereas the yoghurt sample with 10% carrot had the lowest one. Tus, it is concluded that carrot juice had an obviously positive efect on yoghurt productions in reducing syneresis. A previous study concluded that syneresis extent of yoghurt might be increased with extension of the storage period [49]. Under normal circumstances, dietary fbers or other macromolecules found in yoghurt can reduce syneresis extent of yoghurt; for example, the concentration of inulin in 30-150 g/kg could obviously reduce syneresis [50]. In another past study, yam mucilage increased viscosity of yoghurt and depressed yoghurt syneresis [51,52]. In this study, carrot juice included polysaccharides that could enhance yoghurt viscosity. Terefore, the yoghurt samples with 10% carrot juice demonstrated less syneresis than the control samples. However, it is also observed that the yoghurt samples containing 20% carrot juice possessed higher syneresis than the control and the yoghurt with 10% carrot juice. It could be proposed that the higher viscosity obtained from a higher content of carrot juice addition might inhibit acid-caused aggregation of casein particles Syneresis (%) Figure 3: Syneresis values of carrot juice-fortifed yoghurt during the cold storage period at 4°C. Values are showed as mean-± standard deviation. a−c Means followed in the same row by different lowercase letters are signifcantly diferent for the same parameter (P < 0.05). A−C Means followed in the same column by diferent capital letters are signifcantly diferent for the same parameter (P < 0.05).
during fermentation and have a negative efect on the microstructure of yoghurt. Te yoghurt sample with 10% carrot juice might make about a fner microstructure and have less syneresis than the yoghurt sample containing 20% carrot juice. Syneresis was found in yoghurt when gels spontaneously trend to shrink, leading to expelling liquid [53]. In the present study, there is a decreasing tendency of syneresis extent in the presence of 10% carrot juice compared to the control, whereas syneresis extent increased with the carrot juice level increased to 20% (Figure 3). Carrot juice is expected to include abundant pectin [6], which can dissolve during heating processing of CJ-milk mixture before fermentation as the ambient viscosity increase. Other soluble dietary fbers in carrot juice had similar infuence. In addition, CJ contains prime various insoluble dietary fbre, which can interfere with gel structure continuity and result in an increase of syneresis extent, whereas the soluble composition would reduce syneresis extent by binding water and reinforcing the viscosity of gel continuous phase. Tereby, although increasing the CJ level to 20% provides very good water binding ability and viscosity increase, at the same time it also provides a higher vast of insoluble particles, which may interfere with the gel and enhance syneresis extent.

Conclusion
Addition of carrot juice enhanced the pH, reduced fermentation time (especially for the 10% carrot juice), and fnally developed a frming and more homogeneous yoghurt gel during the storage period. Te micrograph of microstructure was correlated with the rheological and texture analysis. Compared with other samples, the yoghurt with 10% carrot juice showed the frmest structure over 21-day storage time among the three levels of carrot juice determined. Tus, carrot juice has a potential advantage to be incorporated as a nature texturizer and stabilizer during yoghurt fermentation processing. In the future, we need to perform some sensory experiments to verify consumer recognition of supplemented yoghurt products, and colour or favour regulations should also meet consumer needs.

Data Availability
Te data that support the fndings of this study are available on request from the corresponding author upon reasonable and uncommercial request.