The Impact of Psyllium Mucilage as a Stabilizer on the Physical and Sensory Properties of Vegan Yogurt Ice Cream

Abstract

The present study evaluated the effects of psyllium mucilage (PM) added at levels of 0.25% (PM 0.25), 0.5% (PM 0.5), and 0.75% (PM 0.75), compared to guar gum (GG) and carob gum (CAR), on the rheological properties, overrun, melting, and consumer acceptance of vegan yogurt-based ice (yog-ice) creams. Rheological analysis showed that all formulations exhibited non-Newtonian, shear-thinning behavior (n < 1), although the magnitude varied depending on the hydrocolloid used. PM significantly (p < 0.05) increased viscosity in a concentration-dependent manner, reaching 585.3 mPa·s for PM 0.75, and improved yield stress and structural stability. CAR addition resulted in the lowest apparent viscosity (41.8 mPa·s) but the strongest pseudoplasticity (n = 0.328), whereas GG yielded moderate viscosity. PM ice creams exhibited the lowest extent of melting (1.20 g/g at PM 0.75) and the longest first dripping time (67.2 min). PM addition reduced lightness (L*) and increased redness (a*), with higher levels producing perceptible differences (ΔE > 5). CAR increased hardness (42.2 N), while PM 0.25 and PM 0.5 decreased it (28.9 and 33.9 N). Consumer evaluation confirmed that PM 0.5 achieved the highest overall acceptability (7.58), comparable to GG (7.61), whereas CAR and PM 0.75 reduced scores. Psyllium mucilage thus represents a promising clean-label stabilizer for plant-based yog-ice creams, enhancing melting resistance, textural quality, and sensory appeal at optimal concentrations.

1. Introduction

The demand for plant-based alternatives to traditional dairy products has been steadily increasing in recent years due to growing consumer awareness of health, environmental sustainability, and ethical concerns related to animal-based food production [1,2,3].

One of the most rapidly expanding segments within the plant-based dairy market is vegan yogurt ice cream, which aims to replicate the texture, creaminess, and sensory appeal of conventional dairy-based yogurt ice cream while using entirely plant-derived ingredients [4]. Vegan ice cream, formulated using plant-based milk alternatives such as soy, almond, cashew, coconut, rice, or oat, has gained significant popularity in recent years. This trend is largely driven by its suitability for individuals with milk allergies, lactose intolerance, or those following vegan and plant-based diets [5,6]. Achieving desirable physicochemical and sensory properties in vegan yogurt ice cream presents a significant challenge due to the absence of dairy proteins and fat, which naturally contribute to texture, stability, and mouthfeel in traditional formulations [7,8,9,10].

Yogurt is widely recognized as a nutritious food, rich in probiotics, proteins, and essential nutrients that support gut health and overall well-being. Incorporating yogurt into a frozen dessert format, such as ice cream, provides a palatable and enjoyable way for consumers to benefit from its nutritional properties while enjoying a satisfying treat. This makes yogurt-based ice cream an attractive alternative for individuals seeking both health benefits and sensory pleasure in their diet [11,12]. Plant-based yogurt alternatives have emerged as valuable substitutes for traditional dairy products, aiming to replicate their nutritional and functional properties [13]. Incorporating these vegan yogurts into frozen dessert formats, such as ice cream, represents an innovative approach to combining nutritional benefits with an indulgent sensory appeal [14,15]. Plant-derived ingredients are gaining popularity in the formulation of frozen desserts due to their ability to enhance physicochemical characteristics and provide added nutritional value when compared to conventional dairy-based components. Notable examples include vegetables and fruits such as beetroots, sweet potatoes, carrots, and dates, which contribute both functional and health-promoting properties [16].

Stabilizers play a crucial role in improving the texture, structure, and overall quality of yogurt-based ice cream by enhancing viscosity, controlling ice crystal formation, and preventing phase separation. In conventional dairy yogurt ice cream, stabilizers such as guar gum, xanthan gum, carrageenan, and modified starch are commonly used to achieve the desired rheological and sensory attributes [17,18,19,20,21]. Carob gum (locust bean gum) is a galactomannan extracted from the seeds of the carob tree (Ceratonia siliqua L.), widely used as a thickening and stabilizing agent in various food systems. It exhibits synergistic effects with other hydrocolloids, improves texture and viscosity, and helps control ice crystal growth and water mobility in frozen desserts [22]. However, in vegan formulations, the selection of stabilizers becomes even more critical to compensate for the lack of milk proteins and maintain the integrity of the final product. Due to their low protein content relative to cow’s milk, plant-based alternatives such as almond, rice, and oat milk require the addition of gelling agents, thickeners, or stabilizers to achieve the desired texture and consistency in yogurt or yogurt-like products [4,23,24].

This study examines the effect of various stabilizers, including natural hydrocolloids such as psyllium (Plantago psyllium L.) mucilage, on the physical and sensory properties of vegan yogurt ice cream. Psyllium mucilage (PM) is rich in dietary fiber. It possesses unique water-binding and gelling properties [25] that may influence the rheological behavior, overrun, hardness, color, meltability, and consumer perception of the yogurt ice cream [14]. Psyllium is regarded as a cost-effective polysaccharide with significant technological potential. As a renewable resource, it exhibits both biodegradable and hydrophobic properties, making it a promising ingredient for hydrogel applications [26].

The incorporation of natural stabilizers aligns with the growing consumer preference for clean-label products that exclude artificial additives and synthetic ingredients. While commercial stabilizers effectively provide structural stability and mouthfeel, there is an increasing interest in exploring plant-derived alternatives that offer additional health benefits and functional properties [27,28]. PM, in particular, has gained attention for its ability to modify texture, retain moisture, and potentially enhance the sensory appeal of plant-based frozen yogurt desserts [29].

This study aims to evaluate the effectiveness of psyllium mucilage as a stabilizer in vegan yogurt ice cream and compare its performance with that of commonly used commercial stabilizers. The investigation will involve analyzing key physical parameters, such as rheological properties, overrun, hardness, melting, and color, alongside a consumer acceptance evaluation. Future research should focus on better understanding the sensory and rheological properties of plant-based frozen desserts to ensure they meet growing consumer expectations.

2. Materials and Methods

2.1. Raw Material

The research material consisted of oat yogurt-based ice cream with psyllium mucilage (PM) applied as a novel stabilizer. Each formulation of oat yogurt-based ice cream included oat yogurt (prepared according to Section 2.2), oat drink (Hafer Natural, Natumi GmbH, Troisdorf, Germany), coconut oil (INTENSON S.A., Całowanie, Poland), sucrose (KGS S.A., Toruń, Poland), corn starch (Naturalnie Zdrowe Sp. z o.o., Wiązowna, Poland), the emulsifier Glice (mono- and diglycerides of fatty acids; Sosa Ingredients, S.L.U., Barcelona, Spain), and hydrocolloids: carob gum (Agnex, Białystok, Poland), guar gum (Agnex, Białystok, Poland), or psyllium mucilage (prepared according to Section 2.3).

2.2. Oat Yogurt Preparation

Oat yogurt was prepared using oat drink and the Vegurt starter culture (000 VIVO-AKTIV, Browary, Ukraine), which consists of maltodextrin and lyophilized strains of lactic acid bacteria: Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus (NCFM^®), Lactobacillus paracasei (Lpc-37), Bifidobacterium lactis (Bi-07), Bifidobacterium lactis (Bl-04), Bifidobacterium bifidum, Bifidobacterium infantis, Lactobacillus gasseri, Lacticaseibacillus rhamnosus, Lactiplantibacillus pentosus, and Lactiplantibacillus plantarum. Fermentation was carried out in an incubator (Heratherm IGS60, Thermo Electron LED GmbH, Langenselbold, Germany) at 39 °C for 15 h, until the pH reached 4.0. The obtained product was cooled and stored at 4 °C, and used for ice cream production after 24 h.

2.3. Extraction of Mucilage from Psyllium Seed

The method of Bukhari et al. [30] was slightly modified for the extraction of psyllium seed mucilage. Mucilage was extracted from psyllium seeds (Agnex, Białystok, Poland) using a water-to-seed ratio of 15:1 (w/w). The mixture of seeds and distilled water (20  ±  2 °C) was mixed at 200 rpm for 5 h using a Spiral Mixer (RM Gastro CZ s.r.o., Prague, Czech), and allowed to swell overnight in refrigerated conditions (3  ±  1 °C). Following this, the cooled aqueous suspension was stirred at 1500 rpm for 5 min using a mechanical stirrer (OS20-Pro, CHEMLAND, Stargard, Poland) in a perforated steel vessel (1.5 mm holes) to separate the mucilage from the seeds. The thin layer of extracted PM was then spread on trays with parchment paper and dried at 50  ±  1 °C for 12 h in a convection drier (FED 115, Binder, Tuttlingen, Germany).

The dried PM was sieved through a 35-mesh sieve to separate the mucilage from the remaining seeds. The extracted mucilage was then vacuum-packed using a Vac-20 SL2A packaging machine (Edesa Hostelera S.A., Barcelona, Spain) and stored at 4  ±  1 °C until needed for the preparation of yog-ice cream. The extraction yield (EY, in %) of PM was calculated using Equation (1), as described by Feizi et al. [29].

$$EY={\displaystyle \frac{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{o}\mathrm{f} \mathrm{e}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{e}\mathrm{d} \mathrm{m}\mathrm{u}\mathrm{c}\mathrm{i}\mathrm{l}\mathrm{a}\mathrm{g}\mathrm{e} \left(\mathrm{g}\right)}{\mathrm{M}\mathrm{a}\mathrm{s}\mathrm{s} \mathrm{o}\mathrm{f} \mathrm{p}\mathrm{s}\mathrm{y}\mathrm{l}\mathrm{l}\mathrm{i}\mathrm{u}\mathrm{m} \mathrm{s}\mathrm{e}\mathrm{e}\mathrm{d}\mathrm{s} \left(\mathrm{g}\right)}}·100\mathrm{\%}$$

(1)

2.4. Ice Cream Making

The experimental formulations of oat yogurt-based ice cream were prepared according to the compositions presented in

Table 1. Recipes for making oat yogurt-based ice cream.

	GG	CAR	PM 0.25	PM 0.5	PM 0.75
Oat yogurt (g)	500	500	500	500	500
Oat drink (g)	200	200	200	200	200
Coconut oil (g)	100	100	100	100	100
Sucrose (g)	170	170	170	170	170
Emulsifier Glice (g)	0.3	0.3	0.3	0.3	0.3
Corn starch (g)	25	25	25	25	25
Guar gum (g)	2.5	-	-	-	-
Carob (g)	-	2.5	-	-	-
PM powder (g)			2.5	5	7.5

. The control sample and the experimental variants differed in the type and concentration of hydrocolloids applied.

Psyllium mucilage (powder) was added at three levels: 0.25% (PM 0.25), 0.5% (PM 0.5), and 0.75% (PM 0.75). For comparative purposes, formulations with guar gum (GG) and locust bean gum (carob, CAR) were prepared, as these hydrocolloids are commonly used stabilizers in ice cream production [31].

The oat drink, coconut oil, sucrose, corn starch, hydrocolloid, and emulsifier were heated with continuous stirring on an induction plate to 75 °C and maintained at this temperature for 5 min. The mixture was then rapidly cooled to 4 °C using a blast chiller (KTC110, Küppersbusch Hausgeräte GmbH, Gelsenkirchen, Germany). After the addition of oat yogurt, the mixture was homogenized at 8000 rpm for 5 min using a MagicLAB homogenizer (IKA, Staufen, Germany). Before freezing, the mixture was aged for 4 h at 4 °C, and subsequently frozen using an ice cream freezer (RCHI-01, expondo Polska Sp. z o.o., Zielona Góra, Poland) to −15 °C. The obtained ice cream was then packed in polypropylene (PP) containers, sealed with foil using a heat sealer, and stored at −25 °C for at least 5 days before analysis.

2.5. Overrun

Overrun was measured triplicate using a 50-mL plastic cup by comparing the weights of the mix and ice cream in the same-volume container [32]. Overrun was determined according to the following Equation (2):

$$Ov\left(\%\right)={\displaystyle \frac{M_M-M_{IC}}{M_{IC}}}·100$$

(2)

where Ov (%) is the overrun percentage, M_M (g) is the weight of a given volume of mix, and M_IC (g) is the weight of the same volume of ice cream.

2.6. Phase Separation

The ice cream samples were melted, and then 10 mL of each sample was transferred into individual tubes. The tubes were stored at 4 °C for 7 days. An equation was used to calculate the phase separation (PS in %) (syneresis rate) [32] (3):

$$PS(\%)={\displaystyle \frac{V_{SL}}{V_S}}·100$$

(3)

where V_SL (g) is the total volume of separated liquid (mL), and V_S is the total volume of the sample (mL).

2.7. Melting Characteristics

The determination of the melting rate of the ice creams was performed in accordance with Javidi et al. [33], with minor adaptations. To better characterize the melting behavior of the ice cream mixes, two parameters were determined: the first dripping time (FDT, min), defined as the time elapsed until the first drop of melted ice cream appeared, and the extent of melting (EM), expressed as in (4):

$$EM={\displaystyle \frac{M_0}{M_{120}}}$$

(4)

where M₀ represents the initial mass of the sample and M₁₂₀ the mass remaining after 120 min of melting. The ice cream samples were tempered at −18 °C for 24 h and removed successively from the freezer immediately before measurement, ensuring minimal temperature change prior to the testing. Approximately 30 g of ice cream was scooped and placed on a wire mesh (1 mm mesh size) positioned above a beaker, and allowed to melt at ambient temperature (25 ± 1 °C). All measurements were carried out in triplicate for each formulation.

2.8. Rheological Properties

The flow behavior of the aged ice cream mixes was analyzed using a Mars III rheometer (Haake Thermo Fisher Scientific Inc., Waltham, MA, USA) equipped with a concentric cylinder geometry (CC 25 DIN) with a 5.3 mm gap. Samples (15 mL) were measured at 4 °C. Upward and downward shear rates (from 1 to 200 s⁻¹ and from 200 to 1 s⁻¹, respectively) were applied to obtain the flow curves. All measurements were performed in triplicate.

The upward shear stress–shear rate data were fitted to the Herschel–Bulkley model as follows (5):

$$\tau ={\tau }_0+k{\dot{\gamma }}^n$$

(5)

where τ is the shear stress (Pa), τ₀ the yield stress (Pa), k the consistency coefficient (Pa·sⁿ), n the flow behavior index (–), and $\dot{\gamma }$ the shear rate (s⁻¹).

Apparent viscosity was obtained from the flow curve as the mean value at a shear rate of 100 s⁻¹ during the increasing shear rate phase. The thixotropic index (TI) of the samples was calculated as the hysteresis loop area between the upward flow curve (A_up) at increasing shear rate and the downward flow curve (A_down) at decreasing shear rate, according to Equation (6) [34]:

$$TI(\%)={\displaystyle \frac{A_{up}-A_{down}}{A_{up}}}·100$$

(6)

2.9. Color

The color properties of the ice cream were assessed using a chromometer (Model CR-400, Konica Minolta Inc., Tokyo, Japan) in the L*a*b* system. The measurements were performed with an 8 mm diameter measuring head, a D65 illuminant (6500 K color temperature), and a standard 2° observer. This device was calibrated with a white standard (L* = 98.45, a* = −0.10, b* = −0.13). Color coordinates, including L* (lightness), a* (ranging from green −a* to red +a*), and b* (ranging from blue −b* to yellow +b*), were recorded on the ice cream surface within one minute after removal from the freezer, in six repetitions. The color difference coefficient (ΔE) between the control sample with (GG) and the other formulations was calculated using Equation (7) as follows:

$$∆E=\sqrt{{\left(L_x^{*}-L_0^{*}\right)}^2+{\left(a_x^{*}-a_0^{*}\right)}^2{+\left(b_x^{*}-b_0^{*}\right)}^2}$$

(7)

where L*₀, a*₀, and b*₀ are the color coordinates of the ice cream with GG, and L*_x, a*_x, and b*_x are the color coordinates of the ice cream with PM or carob gum (CAR).

2.10. Texture

Mechanical properties were evaluated on tempered ice cream samples (−18 °C for 24 h) according to Javidi et al. [33], with slight modifications. Ice cream samples were removed successively from the freezer (−18 °C) immediately before measurement and were not held at room temperature prior to the test, ensuring that all measurements were performed on samples with minimal temperature changes from storage. A penetration test was performed at room temperature using a texture analyzer (Model 5965, Instron, Norwood, MA, USA) equipped with a stainless-steel cylindrical probe (8 mm diameter). The penetration depth was set at 15 mm, with a test speed of 2 mm·s⁻¹. From the force–deformation curves, two parameters were determined: hardness, defined as the peak compression force (N) during penetration, and adhesiveness, defined as the negative area (N·s) under the curve during probe withdrawal. All measurements were carried out in six repetitions.

2.11. Consumer Acceptance

The consumer acceptance of ice cream was evaluated according to Devalekar and Udachan [35], with some adaptations, to assess the influence of PM addition. The attributes of taste, color and appearance, body and texture, flavor, and overall acceptability were scored using a 10 cm unstructured hedonic scale with defined endpoints (0 = dislike extremely; 10 = like extremely), in accordance with the Polish Norm PN-ISO 11136:2017-08 [36] and PN-ISO 5492:2009 [37]. The test was conducted with 38 semi-trained consumers (21 females and 17 males), aged between 22 and 43 years. The participants were mostly research professionals who work with food products on a daily basis and students in food technology and human nutrition, all of whom declared themselves as regular ice cream consumers. Ice cream samples were frozen at −20 °C overnight and evaluated in 20 g portions after 5 min of equilibration at room temperature. Each scoop was served in a disposable plastic cup coded with a three-digit random number. Panelists were provided with a glass of water to cleanse their palate between samples.

2.12. Statistical Analysis

The effect of PM addition on the examined parameters was analyzed using Statistica 13.3 (StatSoft Inc., Tulsa, OK, USA). Verification of the difference significance of investigated parameters was studied using LSD Fisher’s test with a significance level of α = 0.05. Before ANOVA, data were tested for normality (Shapiro–Wilk test) and homogeneity of variance (Levene’s test) to ensure the assumptions for parametric analysis were met.

3. Results

3.1. Extraction Yield

In this study, an extraction yield of 10.63 ± 0.5% (w/w) was obtained during psyllium mucilage production. This represents a relatively high yield for a method based solely on mechanical separation of mucilage, achieved without the use of lyophilization. Higher yields can be achieved through freeze-drying or combined extraction methods, depending on the extraction conditions and the characteristics of the raw material. In the case of chia seeds, even with the use of lyophilization, an extraction yield (EY) < 9% was obtained [38,39].

3.2. Rheological Analysis of Ice Cream Mixes

Investigating the rheological properties of ice cream is crucial for designing innovative formulations that align with consumer acceptance [40]. The type and concentration of stabilizer significantly influenced the rheological behavior of the vegan yogurt-based ice cream mixes (

Table 2. Rheological parameters of ice cream mixes of vegan yogurt-based ice creams as affected by the addition of guar gum (GG), carob gum (CAR), and psyllium mucilage (PM).

Hydrocolloid Type	AV * (mPa·s) at 100 s−1	k (Pa sn)	n (-)	τ0 (Pa)	R2	TI (%)
GG	208.7 ± 4.8 c	2.905 ± 0.386 d	0.479 ± 0.091 b	1.415 ± 0.497 a	0.998	3.82 ± 0.24 b
CAR	41.8 ± 4.6 a	0.198 ± 0.011 a	0.328 ± 0.087 a	1.923 ± 0.098 b	0.994	2.12 ± 0.32 a
PM 0.25	181.5 ± 16.1 b	0.252 ± 0.027 b	0.523 ± 0.037 c	2.261 ± 0.154 c	0.995	39.20 ± 0.85 d
PM 0.5	494.8 ± 69.5 d	0.420 ± 0.074 c	0.853 ± 0.049 d	5.005 ± 0.474 d	0.998	30.15 ± 7.42 c
PM 0.75	585.3 ± 52.3 e	0.509 ± 0.153 c	0.875 ± 0.049 d	8.055 ± 0.662 e	0.993	56.56 ± 4.46 e

(^a–e) show the significant differences in a column (p ≤ 0.05).; * AV—apparent viscosity; τ₀—the yield stress (Pa); k—the consistency coefficient (Pa·sⁿ), n—the flow behavior index (–).

). All mixtures with guar gum (GG), carob gum (CAR), and psyllium mucilage exhibited non-Newtonian, shear-thinning behavior (n < 1), a characteristic typical of hydrocolloid-stabilized systems [41]. The addition of CAR had a limited impact on apparent viscosity (41.8 mPa·s; p ≤ 0.05), yielding the lowest AV among the tested stabilizers. However, it exhibited the most pronounced pseudoplastic behavior, as reflected by the lowest flow behavior index (n = 0.328). In contrast, the addition of psyllium mucilage (PM) significantly modified the rheological characteristics, as evidenced by the highest AV, consistency index (k), and yield stress (τ₀) values, especially at concentrations of 0.5% and 0.75%. At the lowest PM addition level (0.25%), a moderate viscosity (181.5 mPa·s; p ≤ 0.05) was observed, but the mix already displayed higher shear-thinning (n = 0.523; p ≤ 0.05) compared to GG. This suggests that even small amounts of PM can create a continuous network of hydrated soluble fiber, capable of retaining water and limiting phase mobility. Similar trends were described by Erem et al. [42], who observed that fiber-rich hydrocolloids in vegan ice cream-type frozen desserts promoted higher viscosity and structural stability due to their water-binding capacity. Increasing the concentration of PM to 0.5% and 0.75% not only markedly enhanced viscosity (494.8 and 585.3 mPa·s, respectively; p ≤ 0.05), but also shifted the flow behavior index (n) towards near-Newtonian values (0.853 and 0.875, respectively). This phenomenon may be explained by the formation of structured mucilage networks rich in arabinoxylans and heteroxylans [43], which substantially increase viscosity while diminishing shear-thinning due to their resistance to molecular alignment under shear. At higher concentrations, the mucilage appears to form a dense, gel-like matrix in which shear-thinning effects become less pronounced. Comparable results were reported by Henden et al. [14] for oat-based vegan frozen desserts, where increasing hydrocolloid concentration (xanthan gum) elevated viscosity while reducing the extent of pseudoplasticity. Similarly, Narala et al. [44] demonstrated that fiber incorporation (inulin) in vegan ice creams increased viscosity and stabilized the mix, although the degree of shear-thinning remained strongly concentration-dependent. The high yield stress (τ₀) values observed for PM samples (2.26–8.05 Pa) further confirm its strong structuring capacity, which is desirable for preventing ice crystal growth and improving body and texture during storage. Comparable findings were noted by Devalekar and Udachan [35] in prebiotic vegan ice cream, where the addition of soluble fiber-based stabilizers enhanced mix consistency and melting resistance.

The significantly higher thixotropy index (TI) in PM samples (30–57%) compared to GG and CAR (<4%) suggests a pronounced structural breakdown under shear, followed by incomplete recovery. This behavior can be attributed to the gel-like network formed by psyllium polysaccharides, which is more sensitive to shear stress. Similar observations were made in aquafaba- and fruit-based vegan ice creams by Erem et al. [42], where fiber-rich stabilizers displayed high thixotropy due to their fragile network structures.

3.3. Overrun and Melting Parameters of Ice Cream Mixes

The results in

Table 3. Overrun (Ov), phase separation (PS), first dropping time (FDT), and extent of melting (EM) of vegan yogurt-based ice creams as affected by the addition of guar gum (GG), carob gum (CAR), and psyllium mucilage (PM).

Hydrocolloid Type	Ov (%)	PS (%)	FDT (min)	EM (g/g)
GG	39.32 ± 1.87 d	19.54 ± 2.28 b	42.22 ± 3.12 c	2.22 ± 0.08 c
CAR	25.48 ± 2.14 b	32.22 ± 1.52 c	28.31 ± 2.42 a	3.09 ± 0.15 d
PM 0.25	34.27 ± 1.86 c	15.49 ± 2.11 a	35.27 ± 3.31 b	1.71 ± 0.11 b
PM 0.5	32.73 ± 1.53 c	21.16 ± 2.24 b	52.13 ± 2.74 d	1.39 ± 0.21 a
PM 0.75	19.38 ± 0.98 a	35.02 ± 3.38 c	67.22 ± 3.48 e	1.20 ± 0.07 a

(^a–e) show the significant differences in a column (p ≤ 0.05).

indicate that the type and concentration of hydrocolloids influenced overrun (Ov), phase separation (PS), first dropping time (FDT), and extent of melting (EM) of vegan yogurt-based ice creams.

Overrun is a dependent parameter affected by the freezing and aeration process, which involves multiple physical changes, including the action of proteins and surfactants in the formation and stabilization of foam, partial coalescence of the fat emulsion, and solution concentration due to the freezing of liquid water [45]. The significantly highest Ov was observed in samples with GG (39.32%; p ≤ 0.05). Relatively high Ov values were also recorded for PM 0.25 and PM 0.5 samples (34.27% and 32.73%, respectively), whereas the PM 0.75 sample exhibited the lowest overrun (19.38%, p ≤ 0.05). The CAR sample showed a moderate overrun (25.48%). These results suggest that GG is more efficient at incorporating air into the ice cream matrix, while higher PM concentrations likely increase mix viscosity, limiting air incorporation. Air is a crucial component in the development of ice cream structure, as the quantity of air incorporated during freezing affects the size of ice crystals; larger crystals are typically observed in ice creams with lower overrun [46,47].

Phase separation (PS) is a critical indicator of the stability of frozen dessert systems. The lowest PS was observed in samples PM 0.25 (15.49%, p ≤ 0.05) and GG (19.54%, p ≤ 0.05), while the significantly highest PS values (p ≤ 0.05) were noted for the CAR sample (32.22%) and PM 0.75 (35.02%). These findings confirm that the efficiency of stabilizers in maintaining matrix integrity is concentration- and hydrocolloid-type dependent. Comparable tendencies have been reported in vegan ice cream formulations based on almond drink, where the addition of hydrocolloids significantly enhanced stability and reduced visible separation, while control samples without stabilizers showed rapid phase separation during storage [48]. Similarly, psyllium husk powder has been described as an effective stabilizer in ice cream systems, reducing serum separation and improving structural cohesion, which is consistent with the low PS observed in PM 0.25 [49]. The high water-binding capacity and the presence of arabinoxylans and heteropolysaccharides in psyllium mucilage contribute to enhanced water immobilization, thereby decreasing phase separation at moderate concentrations. Conversely, the high PS values observed for PM 0.75 suggest that excessive psyllium addition may disrupt matrix homogeneity, likely due to over-gelation and reduced miscibility of hydrocolloids within the protein–polysaccharide system.

The samples PM 0.5 and PM 0.75 showed FDTs of 52.13 min and 67.22 min, respectively—these are prominently higher than GG (42.22 min) and CAR (28.31 min), exhibiting statistically significant differences (p ≤ 0.05). This suggests that PM, at sufficient concentration, improves melt resistance in vegan yogurt-based ice creams more than guar gum or carob gum.

The observed increase in first dripping time (FDT) with increasing concentrations of psyllium mucilage (PM) is consistent with findings in vegan frozen dessert literature. Akalın et al. [15] showed that the addition of stabilizers and higher total solids in plant-based milk frozen desserts delayed FDT, i.e., the time taken for the first droplet to appear, indicating improved structural resistance to melting. Similarly, Erem et al. [42] observed that vegan fruit-based frozen desserts supplemented with fibers or stabilizers had significantly longer first drop times during storage compared to control formulations without stabilizers. The mechanisms here are likely similar to those discussed in the cited studies: increased viscosity, better water immobilization, and a more stable network (protein-polysaccharide interactions) that resists drip formation. As found by Henden et al. [14], higher viscosity in mixes correlates with longer FDT—the highest PM concentration likely creates a denser matrix, delaying melt onset.

For the extent of melting (EM), all samples stabilized with PM exhibited significantly lower values compared to GG and CAR (p ≤ 0.05). The ice cream PM 0.75 has the lowest EM (1.20; p < 0.05), showing resistance to melting. The significantly higher EM for CAR (3.09; p < 0.05) suggests that this formulation is much less stable under melting conditions. Notably, even at the lowest inclusion level (0.25%), PM reduced EM more effectively than GG (1.71 vs. 2.22), highlighting its superior ability to bind water and create a stable gel-like network within the frozen matrix. This confirms that PM, even at minimal concentrations, enhances the meltdown resistance of vegan yogurt-based ice cream formulations. This can be linked to higher total solids, increased viscosity, stronger gel network formation, and better capacity of hydrocolloids + polysaccharides (like psyllium mucilage) to immobilize free water and limit ice crystal growth, all of which slow down melting. Henden et al. [14] noted that oat-based vegan ice creams with xanthan gum (a hydrocolloid) had improved melting stability when the mix viscosity was higher. In Aydemir et al. [50], vegan ice creams enriched with stabilizers exhibited reduced melting rate over 120 min. Similarly, Erem et al. [42] found that the addition of fiber or stabilizing agents in vegan frozen desserts led to slower meltdown behavior.

3.4. Color of Ice Cream

As shown in

Table 4. Changes in color coordinates (L*, a*, b*) on the surface of vegan yogurt-based ice creams as affected by the addition of guar gum (GG), carob gum (CAR), and psyllium mucilage (PM).

Hydrocolloid Type	L*	a*	b*	ΔE
GG	84.58 ± 3.39 c	3.73 ± 0.19 a	6.94 ± 0.87 b	-
CAR	74.85 ± 1.84 a	7.87 ± 0.12 e	8.22 ± 0.38 c	10.24 ± 0.85 c
PM 0.25	81.60 ± 1.96 b	4.16 ± 0.10 b	5.21 ± 0.64 a	3.48 ± 0.49 a
PM 0.5	79.33 ± 1.27 b	4.71 ± 0.05 c	5.41 ± 0.46 a	5.56 ± 0.71 b
PM 0.75	75.27 ± 3.00 a	5.40 ± 0.09 d	5.32 ± 0.53 a	9.59 ± 0.89 c

(^a–e) show the significant differences in a column (p ≤ 0.05).

, the addition of different stabilizers significantly affected the color coordinates (L*, a*, b*) of oat yogurt-based ice creams (p ≤ 0.05). The control sample with guar gum (GG) was significantly the lightest (L* = 84.58; p ≤ 0.05), while the incorporation of carob gum (CAR) and the highest level of psyllium mucilage (PM 0.75) resulted in a significant reduction in lightness (74.85 and 75.27, respectively, p ≤ 0.05). This darkening effect of CAR is consistent with its intrinsic brownish pigment, which has been previously reported to decrease the lightness of ice creams and other frozen desserts [51,52]. The dried psyllium mucilage used in yog-ice cream in our study exhibited relatively low lightness (L* = 54.65) and higher redness (a* = 7.42, b* = 8.98), which explains its contribution to the observed decrease in L* values and the increase in a* coordinates of the ice cream samples with increasing PM addition.

The redness a* values increased significantly with CAR and with increasing PM addition (p ≤ 0.05), resulting in a more saturated red color. In the study by Souza et al. [53], ice cream formulations enriched with psyllium mucilage showed statistically significant differences in the a* coordinate compared to the control. This confirms that the incorporation of psyllium mucilage can change the color of frozen desserts to a redder color. This effect may be attributed to the natural coloration of the hydrocolloids and potential interactions between plant-derived polysaccharides and oat proteins during freezing and storage. Similar tendencies of increased redness in hydrocolloid-stabilized frozen desserts have been observed in earlier studies [31].

For b* values, the sample (CAR) showed the highest yellowness (b* = 8.22), while the addition of PM at all tested levels significantly reduced b* to a constant level (5.21–5.41), causing less yellowness (p ≤ 0.05), compared to the control sample (GG) (b* = 6.94). This trend suggests that PM contributes to a visually paler and more neutral product.

PM at the lowest concentration (0.25%) induced the smallest changes in total color difference (ΔE = 3.48), while PM 0.5, PM 0.75, and CAR produced noticeable changes (ΔE = 5.56, ΔE = 9.59, and ΔE = 10.24, respectively). According to the CIE (International Commission on Illumination) classification, ΔE values above 3 are considered perceptible to the human eye. The observed color difference between the PM and control samples was primarily attributed to variations in lightness (L*) and redness (a*).

3.5. Textural Properties

The hardness of the vegan yog-ice cream is represented in Figure 1. The hardness of the ice cream samples varied markedly depending on the type and level of stabilizer applied. The control sample with GG exhibited a hardness of 38.34 N, while the use of CAR increased hardness to 42.17 N (p ≤ 0.05), indicating that carob gum produced a firmer structure. This observation is consistent with previous studies reporting that carob gum can enhance the gel matrix and reduce ice crystal mobility in frozen desserts [54,55].

The incorporation of PM at 0.25% and 0.5% resulted in a significant (p ≤ 0.05) softening effect on ice cream compared to the GG sample, with hardness values of 33.85 N and 28.90 N, respectively. These results suggest that low levels of PM interfered with the development of a rigid ice cream structure, likely due to its water-binding capacity and its ability to increase serum phase viscosity [56]. Similar softening effects were reported for fiber-enriched ice creams, where polysaccharides increased water retention but weakened the overall gel network [57]. In contrast, the highest hardness was observed for PM 0.75 (49.13 N; p ≤ 0.05), suggesting that at elevated concentrations, psyllium mucilage forms a more rigid network. This can be attributed to its high water-binding ability and gel-forming capacity, which are facilitated by the presence of arabinoxylans and other soluble polysaccharides [58]. This suggests that at higher levels, PM not only immobilized free water but also contributed to the formation of a more viscous and compact matrix.

As shown in Figure 2, the control sample with GG showed low adhesiveness (2.59 mJ), while CAR significantly increased adhesiveness (3.84 mJ; p ≤ 0.05), consistent with its stronger gel-forming capacity. Samples with PM showed variable adhesiveness, with PM 0.5% and 0.75% exhibiting higher values than the GG sample (3.46 and 4.41 mJ, respectively; p ≤ 0.05), suggesting stickier textures that could negatively influence mouthfeel at elevated concentrations. The lowest adhesiveness was observed in PM 0.25% (1.44 mJ; p ≤ 0.05), corresponding with the softest texture. These results indicate that psyllium mucilage can modulate not only the firmness but also the adhesiveness of ice cream, depending on its concentration.

3.6. Consumer Acceptance Results

Consumer acceptance evaluation represents a key quality indicator that reflects potential consumer preferences. The scores obtained for vegan yogurt-based ice creams with different hydrocolloids are presented in Figure 3. Samples GG, PM 0.25, and PM 0.5 received higher flavor scores (6.38, 6.46, and 6.72, respectively) compared to CAR and PM 0.75. The relatively low flavor acceptance of CAR (5.51) can be attributed to its intrinsic brownish notes and slight aftertaste, as also reported by Henden et al. [14] in plant-based frozen desserts stabilized with carob gum. Conversely, psyllium mucilage at 0.5% yielded the best flavor (6.72), suggesting that moderate fiber addition can enhance the sensory perception of vegan ice creams without imparting off-flavors, consistent with findings by Narala et al. [44] for inulin-enriched vegan ice creams.

Taste was rated highest in GG (7.83), outperforming all PM levels and CAR. Guar gum’s neutral taste and ability to stabilize ice cream likely explain this preference, as previously noted by Javidi et al. [33]. PM at 0.25% (7.68) maintained good taste acceptance, but higher PM (0.75%) reduced taste to 6.12, indicating that excessive mucilage can negatively affect sensory perception, possibly due to a specific psyllium mouthfeel.

The best scores were observed in GG (8.9) and PM 0.25 (8.5), both significantly higher than CAR (6.85) and PM 0.75 (6.4). This trend aligns with colorimetric findings, where carob gum increased redness and darkened the mix, reducing visual appeal. Psyllium mucilage at 0.25% supported a favorable appearance due to stable color and smooth surface, similar to reports by Henden et al. [14], who observed higher consumer scores for xanthan-containing vegan ice creams with bright and uniform surfaces.

Texture was the most discriminating parameter. PM 0.5 (8.1) and GG (7.9) reached the highest scores, indicating superior creaminess and mouthfeel. CAR (5.2) received the lowest rating, confirming its weaker textural contribution when used alone. Importantly, PM at 0.75% showed reduced texture acceptance (6.44), consistent with Narala et al. [44], who reported that excessive fiber addition can lead to undesired gumminess and lower creaminess perception.

Overall acceptance reflected the combined effect of individual attributes. GG (7.61) and PM 0.5 (7.58) were very similar, suggesting that psyllium mucilage at moderate addition can match the consumer preference level of guar gum. PM 0.25 also showed good acceptability (7.14), whereas CAR (6.22) and PM 0.75 (6.9) were less preferred. These findings reinforce earlier conclusions by Javidi et al. [33] and Henden et al. [14] that hydrocolloid type and dosage critically determine consumer acceptance of vegan ice cream.

4. Conclusions

This study demonstrated that the type and concentration of hydrocolloids significantly affect the rheological properties and consumer acceptance of vegan yogurt-based ice creams. Guar gum (GG) and carob gum (CAR) produced typical pseudoplastic systems, with CAR showing the lowest apparent viscosity and the strongest shear-thinning behavior. GG, on the other hand, provided a more stable structure with moderate viscosity, contributing to favorable sensory attributes.

The most interesting effects were observed for psyllium mucilage (PM). Even at a low concentration, PM enhanced apparent viscosity and improved consumer acceptance in terms of color, appearance, and texture. The optimal PM level was 0.5%, which received the highest scores for texture and overall acceptability, comparable to GG. However, higher doses of PM negatively affected sensory attributes, suggesting that excessive gel structuring affects product palatability.

Overall, psyllium mucilage showed strong potential as a functional ingredient in vegan frozen desserts, including formulations based on vegan yogurt. When applied at the optimal concentration, it improves viscosity, structural stability, and consumer acceptance. These findings are consistent with previous reports on plant-based hydrocolloids and highlight the potential of psyllium as a clean-label, fiber-rich stabilizer for the development of innovative vegan ice creams with desirable textural and sensory qualities. A limitation of this study is that long-term storage effects were not evaluated and may be addressed in future research.