Effect of using dried white sapote fruit (Casimiroa edulis) on the quality characteristics of bio-low-fat goat milk yoghurt drink

Abstract

The white sapote tree is cultivated in Egypt on a limited scale owing to its dietary fruits. For its medical and functional characteristics, different levels of dried white sapote fruit (DWSF) were utilized in the manufacturing of probiotic goat yoghurt drinks as a milk fat replacer, as well as yoghurt cultures of Lactobacillus acidophilus La-5 and Bifidobacterium bifidum Bb-11. The implications of DWSF on the rheological properties (apparent viscosity, flow behavior index, plastic viscosity, consistency coefficient, and yield stress), gross composition, color, sensory, bioactive, and microbiological properties of yoghurt drinks were studied throughout 15 days of storage at 4 °C. The addition of DWSF enhanced the bioactive compounds, water-holding capacity, sensory properties, rheological parameters, color, and bacterial growth. Furthermore, mold, yeast, and coliform were not found in any of the samples until the storage time was over. The total number of viable cells in probiotic treatments was kept at a functional level (>10⁶ CFU/mL) for 15 days. The aggregate results showed that it is possible to generate high-quality bio-yoghurt drinks from goat milk with a delightful flavor, appearance, body & texture, and color by substituting goat milk fat with up to 75 % dried white sapote fruit. The successful creation of high-quality bio-yoghurt drinks from goat milk, enriched with DWSF, not only presents a delightful flavor, and pleasing texture but also signifies a health-conscious innovation. This research paves the way for further investigations into the integration of novel fruit-based ingredients in dairy products, offering new dimensions in the functional foods field.

1. Introduction

Goat milk is high in macronutrients and low in micronutrients. It is a healthy alternative to cow milk that is a good supplier of proteins, antioxidant macromolecules, and vitamins, and is advantageous to individuals in general and infants in particular. For babies with allergies to cow milk, goat milk is preferred since it has a lower allergy rate compared to other kinds of milk (Senaka Ranadheera et al., 2012). Fat composition in goat milk is one of the most important components of the essential physiological, technological, nutritional, and sensory aspects of goat milk. It contributes to flavor, which is the combination of mouthfeel, and taste. Additionally, fat enhances the appearance, texture, creaminess, palatability, and lubricity of food. It also prolongs satiety after meals (Nayik et al., 2022). Foods can be reformulated with specific ingredients that provide some fat-like properties to replace specific fats. These fat alternatives may be based on proteins, lipids, or carbohydrates (Ognean et al., 2006). In developing countries, obesity is a major health concern. It is currently the main cause of adult-type diabetes, colon cancer, and coronary artery disease. Customers have lately expressed a desire to eat fewer high-fat meals and more low-fat ones as a result. Due to the importance of dietary fiber in human nutrition and its effect on fermented dairy products, there is an increase in the need for innovative fiber-based fat alternatives (Aydinol & Ozcan, 2018). Research on the use of fruits and vegetable supplements in various forms, such as fresh, juices, powders, and extracts, has received a lot of interest as a result of the imbalance between the global food supply and the population, especially for low-income groups (Salehi and Aghajanzadeh, 2020, Salehi, 2021, Elkot, 2022, Elkot et al., 2023).The Rutaceae family; is a tiny family composed of cultivated fruiting trees and medicinal herbs, commonly referred to as the citrus family; it is economically significant due to its citrus fruits like lemons and oranges are edible (Pollio et al., 2008). Native Americans named it “Mexican apple, ”Casimiroa“, Sapote Blance, and ”White Sapote“ (Satheesh, 2015). Egypt cultivates the tree for its edible fruits. Fresh White Sapote commercialization has expanded in many countries of the world most recently. White Sapote is a drupe with a thin skin that ranges in color from greenish-yellow to yellow to golden yellow, is 6–11 cm in diameter and weighs between 70 and 700 g. Sweet, smooth, and white to off-white describe the pulp. Some seedling fruit kinds, particularly the pulp next to the peel, may leave a mildly bitter taste in the mouth. The mature fruit's pulp is exceptionally soft, white, cream, or yellowish, and it lacks fiber. The inside of the fruit is sweet with a rough texture and has a flavor similar to that of a banana or peach (Morton, 1987, Khalil et al., 2022). Due to its high nutritional content and importance for human health, the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) recommend that individuals consume dairy products (such as yoghurt, kefir, and cheese) regularly. Nowadays, there is a greater interest in the longevity of probiotic bacteria in yoghurt than ever before. Functional foods in dairy products, such as yoghurt (Elkot, 2017, El-Deeb et al., 2017), ice cream (Abdeldaiem et al., 2023), Labneh (Elkot & Khalil, 2022), and cheese (Khalil & Elkot, 2020), offer a delectable way to enhance our overall health and well-being. Probiotics are living microbes that, when given in appropriate quantities, boost the host's health (Wang et al., 2012). Bio-yoghurt is considered to have a number of health advantages, including better lactose utilization, cancer prevention, preservation of the balance of gut flora, and lowered serum cholesterol levels (Baroutkoub et al., 2010). Additionally, yoghurt containing Lactobacillus acidophilus (L. acidophilus La-5) and Bifidobacterium bifidum Bb-12 (B. bifidum Bb-12) supports healthy cellular performance, stimulates the development of good bacteria in the intestines, and boosts a healthy immune system response. Also, it increases the production of immunoglobulin (A) in the colon, enhancing local immunity against gastroenteritis (Speranza et al., 2018). By creating bacteriocins, deconjugated bile acids, organic acids, hydrogen peroxide, and hydrogen peroxide, probiotic yoghurt also has an inhibiting impact on well-known foodborne pathogens and the capacity to control intestinal infections (Goderska & Czarnecki, 2007). Yoghurt drinks are made by diluting yoghurt in water with juice, sugar or without a pectin dispersion to achieve the desired texture flavor, and color (Tamime & Robinson, 2007). The global marketplace for yoghurt-based drinks is anticipated to expand at a compound 4.8 % annual growth rate from 2020 to 2025 (Mordorintelligence, 2022). Whey separation is regarded as a product issue, and stabilizers are currently added to yoghurt drinks more frequently (Arab et al., 2023). Yoghurt drinks are prepared from stirred yoghurt, which has a low viscosity. Yoghurt drinks must contain at least 8.25 % MSNF, less than 0.5 % fat for free-fat yoghurt drinks, 2 % fat for low-fat yoghurt drinks, and more than 3.25 % fat for full-fat yoghurt drinks, according to the Food and Drug Administration (Chandan & O'Rell, 2013). The current study set out to determine the effects of substituting (0, 0.25, 0.5, 0.75, and 100 %) of milk fat with dried white sapote fruit as a fat replacer on the physicochemical, rheological, color, bioactivity, microbiological, and sensory qualities of a probiotic yoghurt drink.

2. Materials and methods

2.1. Materials

Fresh goat milk was collected randomly from Zaraibi goats with small herds. Bulk goat milk samples consisted of 12.40 % total solids (TS), 3.80 % fat, 3.10 % total protein, 4.60 % carbohydrates, 0.90 % ash, 6.70 pH, and 0.17 % acidity (as lactic acid). Milk samples were kept in a refrigerator immediately until they were transferred to the laboratory. High-quality white sapote fruits were procured from a private garden in Egypt, El-Gharbia governorate (season, 2022). The identity of the plant was confirmed according to Khalil et al. (2022). Sugar (sucrose) was obtained through a local marketplace. Pure cultures of Lactobacillus bulgaricus, Streptococcus thermophilus, L. acidophilus La-5, and B. bifidum Bb-11 have been purchased from Chr. Hansen Laboratories, Copenhagen, Denmark. Three repeated transfers in sterilized, 10 % reconstituted skim milk were used to activate each of these strains independently. The analytical grade chemicals utilized in this study were all purchased from Sigma-Aldrich Co. in St. Louis, Missouri, the United States.

2.2. Experimental procedure

2.2.1. Preparing dried white sapote fruits

The peel and seeds were removed from fresh, ripe white sapote fruits after they had been gently cleaned. The pulp was then mixed in a blender. The mixture was dried in a freeze dryer (model: Lyoquest-55 Plus) with a total pressure of 0.13 mbar and a temperature inside the vacuum chamber of − 30 °C, respectively. A heating plate was passed through the tray and the frozen goods to provide sublimation heat. During the secondary drying process, the ultimate product temperature was around 38 °C for 48 hrs (Nowak & Jakubczyk, 2020). The final dried product was stored at − 18 °C until it was used.

2.2.2. Preparing goat milk yoghurt drinks

Fresh goat milk was standardized to 12 % TS, 3.5 % fat, 8.50 % MSNF, 3 % protein, 4.60 % lactose, 0.90 % ash, 6.70 pH, and 0.17 % acidity. The standardized raw milk was pasteurized by heating it in a boiling water bath at 85 °C for 20 min followed by cooling it to 45 °C. Six portions of full-fat pasteurized milk were separated; a 2 % yoghurt starter was used to inoculate the first portion (Streptococcus thermophilus and Lactobacillus bulgaricus) as control natural yoghurt (CN₁). The second portion was inoculated with 2 % of mixed (1:1) yoghurt starter and B. bifidum Bb-11 and L. acidophilus La-5 as control probiotic yoghurt (CN₂). The portions of skimmed goat milk in the ratio of fat substitution with dried white sapote fruit (DWSF) as 75:25, 50:50, 25:75, and 0:100 (T₁, T₂, T₃, and T₄, respectively), and then inoculated with 2 % of mixed (1:1) yoghurt starter, B. bifidum Bb-11, and L. acidophilus La-5, then incubated at 42 °C till pH 4.6, then cooled to 4 °C for 4 hrs. Each treatment received a 6 % sucrose solution (wt of sucrose/wt of water, heated at 90 °C for 5 min, followed by cooling) that was thoroughly combined with yoghurt. Samples were mixed well individually by 0.5 % Carboxy Methyl Cellulose (CMC) for 2 min, using a mixer (T25B, IKA, Labortechnik, Germany) at speed (2400 rpm/min), and then packed in 100 ml sterilized glass bottles which had been sterilized, and kept at 4 °C for 15 days (Fig. 1). The samples were passed to physicochemical, rheological, microbiological, and sensory assessments when fresh (1 day) and after 7, and 15 days, respectively. All experiments were done in triplicate.

Fig. 1.

Methodology for producing bio-goat milk yoghurt drinks.

2.2.3. Physicochemical analyses

Total solids, fat, protein, fiber, ash, acidity, and pH values of DWSF and yoghurt drink samples were evaluated according to AOAC (2016). Difference was used to compute total carbohydrate as follows: [100 – (moisture + protein + fat + ash + fiber) %]. The water holding capacity (WHC) of yoghurt drink treatments was tested according to Yin et al. (2021). Twenty grams of each treatment were centrifuged at 483 × g for 10 min at 20 °C. The supernatant was taken out, and weighted. The following formula was used to calculate the WHC of yoghurt drink samples;

$$WHC\left(\%\right)=\left[\left(\mathit{sample}\mathit{weight}-whey\mathit{weight}\right)/sample\mathit{weight}\right]\times 100$$

2.2.4. Antioxidant activity, phenolic content, vitamins, and minerals analyses

Sample extracts for antioxidants and total phenolic analyses were produced in the manner described by Salehi et al., (2023a). The Folin-Ciocalteu reagent was used to calculate the total phenolic concentration, which was then expressed as milligrams of gallic acid equivalents. (GAE)/100 g, and radical scavenging activity (%) was determined using the DPPH method established by (Wibawanti and Arifin, 2018).

Ascorbic acid was analyzed using the method of AOAC (2016). Thiamine (B1), riboflavin (B2) and niacin (B3) were analyzed by the method of Rudenko & Kartsova (2010). The mineral contents of dried White Sapote fruit and yoghurt drink samples including calcium (Ca), zinc (Zn), and iron (Fe) elements were analyzed using Perkin-Elmer Atomic Absorption Spectrophotometer as indicated by AOAC (2016).

2.2.5. Water holding capacity (WHC) of bio-yoghurt drinks

The WHC of yoghurt drink samples was assessed by the method described by Yin et al. (2021). Twenty grams of each treatment were centrifuged at 483 × g for ten min at 20 °C. After removing the whey layer, the weight reading was taken. WHC of yoghurt drink samples was measured according to the following formula;

$$WHC\left(\%\right)=\left[\left(\mathit{sample}\mathit{weight}-whey\mathit{weight}\right)/sample\mathit{weight}\right]\times 100$$

2.2.6. Rheological properties of goat milk yoghurt drinks

The apparent viscosity, flow behavior index, plastic viscosity, consistency coefficient, and yield stress of yoghurt drink samples were measured utilizing the approach mentioned by Salehi et al., (2023b), using a Brookfield viscometer (Brookfield Engineering Laboratories, USA) at 4 °C equipped with a Sc4-21 spindle running at 10 rpm.

2.2.7. Color attributes determination

A Minolta colorimeter (Model CR-400, Konica Minolta Sensing, Inc., Osaka, Japan, observer angle 10°, measuring head hole 8 mm, calibrated on a white standard L* (100 = white; 0 = black), as well as Minolta color reader (Minolta Camera, Co., Ltd., Osaka, Japan) values, was used to estimate color attributes. Values represent the average of three tests. The color tests were performed in three replications according to Salehi et al. (2023c).

2.2.8. Microbial determinations

In compliance with Standard Methods for the Examination of Dairy Products (Wehr & Frank, 2004), the resulting yoghurt drink samples were microbiologically tested for bacterial, mould, and yeast counts as well as the coliform group. L. acidophilus La-5 on MRS-sorbitol agar (Anaerobic incubation at 37 °C for 72 hrs), Streptococcus thermophilus on ST agar (Aerobic incubation at 37 °C for 24 hrs), and plate counts of B. bifidum Bb-11 were carried out in Bifidobacterium agar under anaerobic incubation at 37 °C for 72 hrs.

2.2.9. Sensory evaluation

Yoghurt drink samples were assessed throughout storage (15 days) for, appearance, acidity, body & texture by a team of a panel of 15 semi-trained evaluators made of laboratory staff and graduate students, aged (25–45 years). The following scores were used to record the results: flavor (20), body & texture (10), appearance and color (10), and the panelists were also asked to list any defects as reported by Clark et al. (2009). A human ethical approval was acquired from the human ethical committee at Faculty of Agriculture &Natural Resources, Aswan University (Egypt) before conducting these tests.

2.2.10. Statistical analyses

The results were statistically examined using two-way analyses of variance (ANOVA) (StatSoft Inc. Statistica ver. 16; Dell, Round Rock, TX, USA). The significance of the variances in the group mean values was evaluated at the level of (p ≤ 0.05) using the Kruskal-Wallis test. Results are represented as averages and standard deviations (SD).

3. Results

3.1. Proximate composition of dried white sapote fruit (DWSF)

The physicochemical characteristics of DWSF, which is utilized to make bio-yoghurt drinks, are displayed in Table 1. Data indicated that the moisture, carbohydrate, protein, fat, fiber, and ash contents were 6.86, 83.26, 2.25, 0.875, 3.13, and 3.43 %, respectively. DWSF contained high amounts of the minerals Ca (641 mg/100 g), Zn (66.43 mg/100 g), and Fe (26.73 mg/100 g). Minerals are incredibly significant chemicals that are required in the diet for the appropriate metabolic activity of human tissues. The findings in Table 1 also show that DWSF contained good contents of total phenolic compounds (PC) (60.21 mg GAE /100 g), antioxidants (AOA) (93.20 %), and 25.12, 0.033, 0.038, 0.453 (mg/100 g) for ascorbic acid, thiamine (B1), riboflavin (B2), and niacin (B3), respectively. The different DWSF color parameter values were 72.10, 3.12, and 15.73 for L*, a*, and b*, respectively.

Table 1.

Chemical composition and color readings, phenolic compounds, and antioxidant scavenging activity characteristics of dried white sapote fruit.

Ingredient	Values
physicochemical properties (mg/100 g)
Moisture	6.86 ± 0.21
Dry matter	93.14 ± 0.27
Total carbohydrates *	83.42 ± 0.16
Crude protein	1.52 ± 0.02
Crude fat (%)	0.875 ± 0.01
Total dietary fiber	3.13 ± 0.05
Ash content	4.20 ± 0.04
Minerals (mg/100 g)
Calcium content (mg/100 g)	641.0 ± 3.12
Zinc content	66.43 ± 0.22
Iron content	26.73 ± 0.04
Antioxidants
Total phenolic compounds (TPC) (mg/100 g)	60.21 ± 0.25
Antioxidant activity (AOA)%	93.20 ± 0.17
Ascorbic acid (mg/100 g)	25.12 ± 0.06
Vitamins (mg/100 g)
Thiamine (B1)	0.033 ± 0.00
Riboflavin (B2)	0.038 ± 0.00
Niacin (B3)	0.453 ± 0.00
Color
L* value	59.10 ± 0.00
a* value	5.90 ± 0.00
b* value	21.50 ± 0.00

*Values are means ± SD of triplicates (n = 3) (p ≤ 0.05).

*Dry weight basis; Total protein = TN × 6.25.

3.2. Impact of supplementing with dried white sapote fruit (DWSF) on the composition of goat milk yoghurt drinks

Table 2 shows the chemical composition of the DWSF-supplemented bio-yoghurt drinks. The total solid, protein, and fat contents in the fresh treatments ranged between 13.58 and 13.82, 3.28–3.43, and 4.07–4.18 g/100 g, respectively. The fresh treatments T₃ and T₄ showed the highest protein values (3.72 and 3.80 g/100 g) and decreased significantly during storage. Also, the effects of supplementing goat milk yoghurt drinks with different concentrations of DWSF on pH values and acidity, described as % lactic acid is represented in Table 2. The pH values of the treated and control goat milk yoghurt drink samples differed significantly (p ≤ 0.05).

Table 2.

Changes in chemical composition (g/100 g), pH values, and acidity% of goat milk yoghurt drinks supplemented with different ratios of dried white sapote fruit (DWSF) during cold storage.

Storage period (days)	Treatments
	Cn1	Cn2	T1	T2	T3	T4
	Total solids (TS) (g/100 g)
Fresh	13.82 ± 0.03bA	13.85 ± 0.00bA	13.92 ± 0.04aA	13.95 ± 0.03aA	13.92 ± 0.00aA	13.95 ± 0.04aA
7	13.65 ± 0.05bB	13.67 ± 0.08bB	13.86 ± 0.01aAB	13.90 ± 0.04aA	13.88 ± 0.05aAB	13.88 ± 0.05aAB
15	13.58 ± 0.03bB	13.55 ± 0.05bC	13.71 ± 0.06aB	13.77 ± 0.02aB	13.78 ± 0.00aB	13.80 ± 0.10aB
Protein (g/100 g)
Fresh	3.43 ± 0.03cA	3.42 ± 0.03cA	3.55 ± 0.05bA	3.60 ± 0.10bA	3.72 ± 0.00aA	3.80 ± 0.08aA
7	3.35 ± 0.00cB	3.35 ± 0.00cB	3.35 ± 0.03cAB	3.50 ± 0.06bB	3.60 ± 0.01abAB	3.65 ± 0.06aB
15	3.28 ± 0.03cC	3.26 ± 0.01cC	3.30 ± 0.05cB	3.37 ± 0.04bC	3.53 ± 0.03aB	3.53 ± 0.00aC
Fat (g/100 g)
Fresh	4.18 ± 0.02aA	4.20 ± 0.08aA	3.30 ± 0.19bA	2.48 ± 0.02cA	1.65 ± 0.10dA	0.60 ± 0.03eA
7	4.12 ± 0.03aAB	4.12 ± 0.00aB	3.25 ± 0.15bB	2.45 ± 0.25cA	1.60 ± 0.00dA	0.58 ± 0.00eA
15	4.07 ± 0.08aB	4.10 ± 0.10aB	3.25 ± 0.05bB	2.40 ± 0.20cB	1.60 ± 0.10dA	0.58 ± 0.02eA
pH values
Fresh	4.95 ± 0.05abA	5.0 ± 0.05aA	4.90 ± 0.00bcA	4.85 ± 0.05cdA	4.85 ± 0.05cdA	4.80 ± 0.00dA
7	4.85 ± 0.05abB	4.90 ± 0.00aB	4.88 ± 0.03abA	4.72 ± 0.03cdB	4.70 ± 0.00 dB	4.70 ± 0.10dA
15	4.75 ± 0.05abC	4.85 ± 0.05aB	4.80 ± 0.00abB	4.71 ± 0.08bcB	4.65 ± 0.03cB	4.70 ± 0.07bcA
Acidity (%)
Fresh	0.81 ± 0.03bcA	0.78 ± 0.01cC	0.82 ± 0.00bcA	0.85 ± 0.05abA	0.85 ± 0.01abB	0.88 ± 0.02aA
7	0.85 ± 0.00bA	0.81 ± 0.01cB	0.85 ± 0.04bA	0.87 ± 0.02abA	0.88 ± 0.00abA	0.89 ± 0.01aA
15	0.87 ± 0.08aA	0.83 ± 0.01aA	0.86 ± 0.00aA	0.88 ± 0.02aA	0.90 ± 0.02aA	0.90 ± 0.00aA

*Means (±SD) with small letters (a, b, c, d, e) indicate significant differences among yoghurt drink samples supplemented with different DWSF levels (in rows), p ≤ 0.05.Means (±SD) with capital letters (A,B,C) indicate significant differences among yoghurt drinks samples during storage (in columns), p ≤ 0.05. Means ± SD of triplicates (n = 3). *Fresh (1 day), treatments abbreviations [(Cn₁: control goat milk yoghurt drink); (Cn₂: goat milk yoghurt drink); (T₁: goat milk yoghurt drink substitute 25 % for milk fat DWSF); (T₂: goat milk yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: goat milk yoghurt drink substitute75% for milk fat with DWSF); (T₄: goat milk yoghurt drink substitute100% for milk fat with DWSF).

3.3. Vitamins and minerals content in fresh goat milk yoghurt drinks

The vitamins and mineral content of fresh bio-yoghurt drinks supplemented with DWSF are shown in Table 3. The results disclosed that the averages of thiamine (B1) were 11.35, 11.33, 12.05, 12.10, 12.21, and 12.25 mg/100 g, and for riboflavin (B2) 12.15, 12.15, 13.80, 14.10, 14.15, and 14.33 mg/100 g, while the niacin (B3) contents were 19.20, 19.25, 21.30, 21.80, 21.75, and 21.90 mg/100 g for Cn₁, Cn₂, T₁, T₂, T₃, and T₄, respectively. As seen in the same Table 3, according to the findings, the average calcium readings were 61.35, 61.80, 68.20, 70.50, 71.30, and 72.50 mg/100 g, while zinc recorded 17.20, 17.20, 17.80, 17.90, 18.05, and 18.18 mg/100 g, and iron contents of 12.80, 12.78, 12.90, 12.95, 12.95, and 13.15 mg/100 for Cn₁, Cn₂, T₁, T₂, T₃, and T₄, respectively.

Table 3.

Vitamins and minerals content (mg/100gm) in fresh goat milk yoghurt drinks supplemented with different ratios of DWSF.

Fresh	Treatments
	Cn1	Cn2	T1	T2	T3	T4
	Vitamins content
Thiamine (B1)	11.35 ± 0.81b	11.33 ± 0.27b	12.05 ± 0.00a	12.10 ± 0.00a	12.21 ± 0.00a	21.25 ± 0.35a
Riboflavin (B2)	12.15 ± 0.15b	12.15 ± 0.10b	13.80 ± 0.15a	14.10 ± 0.40a	14.15 ± 0.81a	14.33 ± 0.57a
Niacin (B3)	19.20 ± 0.00c	19.25 ± 0.20c	21.30 ± 0.30b	21.80 ± 0.10a	21.75 ± 0.25a	21.90 ± 0.05a
	Minerals content
Calcium	61.35 ± 3.85c	61.80 ± 0.15c	68.20 ± 0.17b	70.50 ± 1.50ab	71.30 ± 0.60ab	72.50 ± 0.00a
Zinc	17.20 ± 0.20b	17.20 ± 0.40b	17.80 ± 0.00a	17.90 ± 0.40a	18.05 ± 0.05a	18.18 ± 0.21a
Iron	12.80 ± 0.20a	12.78 ± 0.22a	12.90 ± 0.55a	12.95 ± 0.05a	12.95 ± 0.70a	13.15 ± 0.30a

*Means (±SD) with small letters (a, b, c) indicate significant differences among yoghurt drink samples supplemented with different DWSF levels (in rows), p ≤ 0.05. Means ± SD of triplicates (n = 3). *Fresh (1 day), treatments abbreviations [(Cn₁: control goat milk yoghurt drink); (Cn₂: goat milk yoghurt drink); (T₁: goat milk yoghurt drink substitute 25 % for milk fat DWSF); (T₂: goat milk yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: goat milk yoghurt drink substitute75% for milk fat with DWSF); (T₄: goat milk yoghurt drink substitute100% for milk fat with DWSF).

3.4. Phenolic compounds, total antioxidants activity, ascorbic acid of goat milk yoghurt drinks

Yoghurt drink samples supplemented with DWSF had considerably greater levels of ascorbic acid, PC, and AOA than comparable samples, and this difference was expanded by increasing the DWSF level. The results disclosed that T₄ had the highest content of PC (4.90, 4.10, and 3.80 mg/100 g), 11.93, 10.05, and 9.81 %) for AOA, and 3.37, 2.90, and 2.63 mg/100 g for ascorbic acid content in fresh, 7, and 15 days of cold storage.

3.5. Color attributes of goat milk yoghurt drinks

White sapote fruit has a variety of pigments, such as carotenoids, PC, flavonoid compounds, and chlorophyll, which can be used as natural colorants. Table 4 reveals that the control treatment had a much higher overall lightness (76.42) than the other treatments due to the DWSF color. With increasing DWSF addition, L* values declined to 63.15 for yoghurt drinks treated with 100 % DWSF, showing that DWSF-supplemented yoghurt drinks were slightly darker than control yoghurt drinks. When the concentration of DWSF was increased, the yellowness (b*) gradually increased. Furthermore, the whiteness (L value) decreased while “a & b” values increased with the increased DWSF used until the 15th day of storage. It could be explained based on the yellow-orange color of the fruit used. Similar attributes were recorded by Desouky (2018), whose yoghurt drinks were produced from goat milk enriched with different levels of cactus peel fruit pulp, and showed a decline in L values; however, “a“ and” b” values increased by the increasing amount of cactus pear fruit pulp used until the 9th day of storage.

Table 4.

Changes in phenolic compounds and total antioxidant activity of goat milk yoghurt drinks supplemented with different ratios of DWSF during cold storage.

Storage period (days)	Treatments
	Cn1	Cn2	T1	T2	T3	T4
	Phenolic compounds (mg/100gm)
Fresh	1.95 ± 0.04eA	1.94 ± 0.01eA	2.80 ± 0.15dA	3.53 ± 0.06cA	4.30 ± 0.3bA	4.90 ± 0.00aA
7	1.90 ± 0.02eA	1.88 ± 0.03eA	2.55 ± 0.04 dB	3.11 ± 0.01cB	3.85 ± 0.05bB	4.10 ± 0.10aB
15	1.82 ± 0.00eB	1.80 ± 0.05eB	2.38 ± 0.02 dB	2.95 ± 0.00cC	3.60 ± 0.02bB	3.80 ± 0.04aC
Total Antioxidant activity (%)
Fresh	4.12 ± 0.04eA	4.17 ± 0.01eA	7.55 ± 0.15dA	8.90 ± 0.06cA	9.85 ± 0.3bA	11.93 ± 0.00aA
7	4.03 ± 0.02eAB	4.00 ± 0.03eB	7.25 ± 0.04 dB	8.60 ± 0.01cB	8.80 ± 0.05bB	10.05 ± 0.10aB
15	3.90 ± 0.00eB	3.85 ± 0.05eC	6.80 ± 0.02dC	8.22 ± 0.00cC	8.31 ± 0.02bC	9.81 ± 0.04aC
Ascorbic acid (mg/100gm)
Fresh	0.85 ± 0.00eA	0.86 ± 0.05eA	2.15 ± 0.08dA	2.44 ± 0.04cA	2.90 ± 0.00bA	3.37 ± 0.06aA
7	0.81 ± 0.00eA	0.81 ± 0.01eA	2.00 ± 0.00 dB	2.15 ± 0.02cB	2.60 ± 0.00bB	2.90 ± 0.00aB
15	0.76 ± 0.02eB	0.74 ± 0.01eB	1.90 ± 0.02dC	1.95 ± 0.00cC	2.18 ± 0.03bC	2.63 ± 0.01aC
Color parameters
L*
Fresh	76.42 ± 0.34aA	76.75 ± 0.55aA	74.4 ± 0.1bA	70.13 ± 0.32cA	65.37 ± 0.4dA	63.15 ± 0.15eA
7	72.70 ± 0.35aB	72.9 ± 0.3aB	70.1 ± 0.15bB	65.43 ± 0.06cB	61.3 ± 0.00 dB	59.50 ± 0.5eB
15	68.30 ± 0.2aC	67.25 ± 0.25aC	65.80 ± 0.1bC	62.30 ± 0.00cC	57.80 ± 0.1dC	56.50 ± 0.00eC
a*
Fresh	−2.50 ± 0.05eC	−2.55 ± 0.00dC	−1.62 ± 0.02cB	−1.08 ± 0.01bB	−0.99 ± 0.00aB	−0.75 ± 0.01aB
7	−0.81 ± 0.00aA	−0.81 ± 0.01bA	−2.00 ± 0.00cC	−2.15 ± 0.02dC	−2.60 ± 0.00eC	−2.90 ± 0.00fC
15	−2.20 ± 0.02eB	−2.25 ± 0.00fB	−1.09 ± 0.01da	−0.95 ± 0.00cA	−0.85 ± 0.00bA	−0.70 ± 0.00aA
b*
Fresh	5.63 ± 0.06eA	5.95 ± 0.09dA	6.42 ± 0.06cA	7.09 ± 0.01bA	8.11 ± 0.09aA	8.17 ± 0.03aA
7	5.26 ± 0.02eB	5.68 ± 0.03 dB	6.09 ± 0.06cB	6.75 ± 0.09bB	7.86 ± 0.01aB	7.82 ± 0.10aB
15	4.97 ± 0.06eC	5.15 ± 0.05dC	5.92 ± 0.07cB	6.32 ± 0.08bC	7.42 ± 0.02aC	7.47 ± 0.06aC

*Means (±SD) with small letters (a, b, c, d, e, f) indicate significant differences among yoghurt drink samples supplemented with different DWSF levels (in rows), p ≤ 0.05. Means ± SD with capital letters (A,B,C) indicate significant differences among yoghurt drinks samples during storage (in columns), p ≤ 0.05. Values are means ± standard deviations of triplicates (n = 3). *Fresh (1 day), treatments abbreviations [(Cn₁: control goat milk yoghurt drink); (Cn₂: goat milk yoghurt drink); (T₁: goat milk yoghurt drink substitute 25 % for milk fat DWSF); (T₂: goat milk yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: goat milk yoghurt drink substitute75% for milk fat with DWSF); (T₄: goat milk yoghurt drink substitute100% for milk fat with DWSF).

3.6. Rheological behavior of goat milk yoghurt drinks

Table 5 shows the rheological parameters of the tested bio-yoghurt drink samples. According to the findings, the apparent viscosity, plastic viscosity, consistency coefficient, and yield stress values were higher in the DWSF treatments than in the control samples. In addition, as DWSF levels rose, the values of apparent viscosity, plastic viscosity, consistency coefficient, and yield stress rose as well (p ≤ 0.05). Furthermore, the T₄ treatment values were significantly different (p ≤ 0.05) lower than those of the other treatments and the control, which indicates that the former was more viscous than the latter yoghurt drinks. As a result, dietary fiber and carbohydrate content were 3.13 and 83.42 g/100 g, respectively; these were the main causes of the consistency coefficient's change. The available data revealed that adding DWSF significantly increased the viscosity of yoghurt drinks. Furthermore, except for flow behavior index values, yoghurt drinks created with DWSF tended to exhibit (p ≤ 0.05) higher rheological parameters than those manufactured without it (Table 5). The WHC of DWSF is critical in the production of yoghurt drinks because its decline on the surface stops the whey from separating from the gel and causes texture loss. During storage, all treatments showed significant differences (p ≤ 0.05) in water holding capacity. Entrapping was lost in the control sample (9.0–11.18 %) during the serum phase. The effect of DWSF, with its high carbohydrate and dietary fiber content (83.42 and 3.13 g/100 g, respectively), can explain the increase in whey retention of yoghurt drinks, as indicated in Table 1.

Table 5.

Changes in rheological characteristics of goat milk yoghurt drinks supplemented with different ratios of DWSF during cold storage.

Storage period (days)	Treatments
	Cn1	Cn2	T1	T2	T3	T4
	Apparent Viscosity (mPas)
Fresh	32.4 ± 0.7eC	33.29 ± 0.8eC	40.11 ± 1.31dC	45.31 ± 0.25cC	51.28 ± 0.72bC	55.60 ± 0.6aC
7	37.5 ± 0.5 dB	36.80 ± 1.0 dB	47.23 ± 0.00cB	48.80 ± 0.2cB	55.50 ± 1.0bB	59.40 ± 0.8aB
15	41.4 ± 0.6dA	40.80 ± 0.2dA	51.50 ± 1.7cA	51.90 ± 1.4cA	60.30 ± 0.2bA	65.50 ± 0.5aA
Flow behavior index
Fresh	0.92 ± 0.00aA	0.91 ± 0.01bA	0.88 ± 0.01cA	0.84 ± 0.00dA	0.80 ± 0.01eA	0.78 ± 0.03eA
7	0.90 ± 0.02aA	0.90 ± 0.00aA	0.85 ± 0.05bB	0.81 ± 0.01bcB	0.78 ± 0.00cdB	0.74 ± 0.03dA
15	0.88 ± 0.01aA	0.87 ± 0.05aB	0.84 ± 0.04aB	0.75 ± 0.00bC	0.77 ± 0.00bB	0.69 ± 0.01cB
Plastic viscosity (mPas)
Fresh	25.80 ± 0.65eC	25.90 ± 1.1eC	28.30 ± 0.3dC	33.50 ± 1.0cC	38.50 ± 0.6bC	46.30 ± 0.2aC
7	28.30 ± 0.3eB	28.30 ± 0.3eB	31.20 ± 0.3 dB	36.10 ± 0.9cB	41.20 ± 0.1bB	48.50 ± 0.06aB
15	30.20 ± 0.8eA	30.10 ± 0.4eA	33.15 ± 0.15dA	37.00 ± 0.9cA	43.10 ± 0.1bA	49.60 ± 0.1aA
Consistency coeffcient (N/ m2)
Fresh	21.30 ± 0.6eC	21.10 ± 0.5eB	25.60 ± 0.2dC	28.10 ± 0.4cC	30.30 ± 0.1bC	35.10 ± 0.4aC
7	22.80 ± 0.8 dB	22.75 ± 1.3 dB	28.00 ± 0.00cB	31.30 ± 0.00bB	32.40 ± 0.00bB	37.20 ± 0.5aB
15	24.15 ± 0.3eA	24.10 ± 0.00eA	30.00 ± 0.00dA	34.00 ± 0.00cA	35.00 ± 0.00bA	39.40 ± 0.00aA
Yield stress (N/ m2)
Fresh	0.80 ± 0.00eB	0.81 ± 0.00eB	0.85 ± 0.05 dB	0.89 ± 0.01cB	0.95 ± 0.00bB	1.02 ± 0.02aC
7	0.84 ± 0.03dA	0.85 ± 0.01dA	0.87 ± 0.01dAB	0.92 ± 0.02cB	0.99 ± 0.02bA	1.12 ± 0.01aB
15	0.87 ± 0.00eA	0.86 ± 0.00eA	0.90 ± 0.00dA	0.96 ± 0.00cA	1.03 ± 0.03bA	1.18 ± 0.00aA
WHC (%)
Fresh	11.12 ± 0.06eA	11.18 ± 0.00eA	18.20 ± 0.30dA	25.30 ± 0.17cA	30.30 ± 0.00bA	36.40 ± 0.40aA
7	9.11 ± 0.01eB	9.23 ± 0.00eB	16.10 ± 0.06 dB	22.20 ± 0.12cB	28.80 ± 0.06bB	32.80 ± 0.17aB
15	9.00 ± 0.00eB	9.00 ± 0.05eC	14.80 ± 0.30dC	20.00 ± 0.00cC	27.50 ± 0.50bC	30.25 ± 0.07aC

*Means (±SD) with small letters (a, b, c, d, e) indicate significant differences among yoghurt drink samples supplemented with different DWSF levels (in rows), p ≤ 0.05. Means ± SD with capital letters (A,B,C) indicate significant differences among yoghurt drinks samples during storage (in columns), p ≤ 0.05. Means ± SD of triplicates (n = 3). *Fresh (1 day), treatments abbreviations [(Cn₁: control goat milk yoghurt drink); (Cn₂: goat milk yoghurt drink); (T₁: goat milk yoghurt drink substitute 25 % for milk fat DWSF); (T₂: goat milk yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: goat milk yoghurt drink substitute75% for milk fat with DWSF); (T₄: goat milk yoghurt drink substitute100% for milk fat with DWSF).

3.7. Microbiological properties of goat milk yoghurt drinks

Table 6 shows viable counts of Streptococcus thermophilus, Lactobacillus bulgaricus, L. acidophilus La-5, and B. bifidum Bb-11 in yoghurt drink samples during storage periods. The results obtained indicate that the T₄ had the highest count of Streptococcus thermophilus; it was 7.71, 7.60, and 7.26 for fresh, 7, and 15 days of storage, respectively. However, the results indicate that T₂ and T₃ had the highest counts of Lactobacillus bulgaricus. Also, T₄ had the highest count of L. acidophilus La-5 and B. bifidum Bb-11 whether in fresh or stored samples. Until the end of the storage period, the total number of bacteria generally decreased gradually in all samples.

Table 6.

Viable cell counts (log CFU / ml) of bacterial starter strains of yoghurt drinks supplemented with different ratios of DWSF during cold storage.

Storage period (days)	Treatments
	Cn1	Cn2	T1	T2	T3	T4
	Streptococcus thermophilus
Fresh	7.33 ± 0.01bA	7.35 ± 0.03bA	7.35 ± 0.26bA	7.52 ± 0.01abA	7.55 ± 0.05abA	7.71 ± 0.18aA
7	7.20 ± 0.00cAB	7.19 ± 0.06cB	7.26 ± 0.11bcA	7.40 ± 0.10bA	7.44 ± 0.06abB	7.60 ± 0.17aA
15	7.10 ± 0.15aB	7.04 ± 0.07aC	7.12 ± 0.03aB	7.24 ± 0.03aB	7.29 ± 0.04aC	7.26 ± 0.08aB
Lactobacillus bulgaricus
Fresh	7.21 ± 0.02abA	7.24 ± 0.00abA	7.19 ± 0.00bA	7.34 ± 0.10aA	7.33 ± 0.14abA	7.27 ± 0.03abA
7	7.12 ± 0.01aB	7.11 ± 0.04aB	7.11 ± 0.16aA	7.22 ± 0.04aA	7.23 ± 0.00aA	7.15 ± 0.25aB
15	7.03 ± 0.04abC	6.91 ± 0.09bC	7.02 ± 0.07abA	7.11 ± 0.22abA	7.08 ± 0.07abB	7.08 ± 0.99abB
L. acidophilus La-5
Fresh	ND	6.64 ± 0.06dA	7.39 ± 0.00cA	7.84 ± 0.30bA	8.33 ± 0.02aA	8.44 ± 0.11aA
7	ND	6.40 ± 0.00cB	7.27 ± 0.00bB	7.54 ± 0.60bA	8.11 ± 0.11aB	8.24 ± 0.01aB
15	ND	6.09 ± 0.02cC	7.08 ± 0.00bC	7.12 ± 0.01bB	7.87 ± 0.03aC	8.00 ± 0.25aB
B. bifidum Bb-11
Fresh	ND	7.80 ± 0.10cA	8.12 ± 0.00bA	8.23 ± 0.07bA	8.43 ± 0.02aA	8.43 ± 0.12aA
7	ND	7.50 ± 0.00eB	7.77 ± 0.03 dB	8.11 ± 0.00cB	8.21 ± 0.01bB	8.34 ± 0.05aA
15	ND	7.23 ± 0.20bC	7.54 ± 0.30bC	8.00 ± 0.00aC	8.07 ± 0.03aC	8.09 ± 0.20aB

*Means (±SD) with small letters (a, b, c, d, e) indicate significant differences among yoghurt drink samples supplemented with different DWSF levels (in rows), p ≤ 0.05.Means (±SD) with capital letters (A,B,C,D) indicate significant differences among yoghurt drinks samples during storage (in columns), p ≤ 0.05. Means ± SD of triplicates (n = 3). *Fresh (1 day), treatments abbreviations [(Cn₁: control goat milk yoghurt drink); (Cn₂: goat milk yoghurt drink); (T₁: goat milk yoghurt drink substitute 25 % for milk fat DWSF); (T₂: goat milk yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: goat milk yoghurt drink substitute75% for milk fat with DWSF); (T₄: goat milk yoghurt drink substitute100% for milk fat with DWSF).

* ND: means Not Detected.

3.8. Sensory evacuation of goat milk yoghurt drinks

Fig. 2 depicts the sensory assessment of fresh and preserved yoghurt drink samples. The levels of DWSF and the extent of storage time were the main elements bearing on the organoleptic qualities scores, and all goat milk yoghurt drinks with significant variations were acceptable among each other (Fig. 2). The color and appearance did not alter significantly, whether in fresh or stored treatments. Furthermore, all DWSF-treated treatments are characteristic of a specific and better taste compared to the control; this is because of the high concentration of dried fruit used. The finished products had a nice overall appearance, a nice body and texture (soft and silky), and a nice, creamy flavor. T₃ (consisting of 75 % DWSF) was distinguished by ideal flavor, body, and texture and achieved the highest liking in organoleptic characteristics when fresh or following storage. Figure 2 results show that the T₄ recorded the lowest rankings for appearance and color. On the other hand, the organoleptic scores of the control treatments were the lowest. In general, the data gathered revealed that, when compared to controls, higher acceptability scores were obtained by using probiotic strains and supplementing with DWSF at a 75 % ratio. Yoghurt culture outperformed all other treatments in terms of look, body & texture, and flavor. Others think that the addition of DWSF influenced consumer approval. In general, studies showed that probiotic yoghurt drinks prepared with L. acidophilus La-5 and B. bifidum Bb-11 bacteria and/or fortified with DWSF had higher acceptability scores.

Fig. 2.

Hedonic for the sensory evaluation of goat milk yoghurt drinks supplemented with different ratios of dried white sapote fruit during cold storage. *Fresh (1 day), treatments abbreviations [(Cn₁: control yoghurt drink); (Cn₂: bio-yoghurt drink); (T₁: bio-yoghurt drink substitute 25 % for milk fat DWSF); (T₂: bio-yoghurt drink substitute 50 % for milk fat with DWSF); (T₃: bio-yoghurt drink substitute75% for milk fat with DWSF); (T₄: bio-yoghurt drink substitute100% for milk fat with DWSF). *Values are means ± standard deviations of triplicates (n = 3), P ≤ 0.05.

4. Discussion

Chemical analysis of DWSF showed that it had a high nutritional and composition value. Similar findings were recorded by Workineh (2021), who found that the moisture, carbohydrate, protein, fat, fiber, and ash levels of DWSF were (from 5.39 to 8.18); (from 80.42 to 83.17); (from 2.40 to 2.46); (from 1.13 to 1.14); (from 3.63 to 3.69); and (from 3.17 to 3.21), respectively, affected by the method of drying. The high carbohydrate content of DWSF fruits suggests that they are a potent source of overall energy. According to Satheesh (2015), white sapote fruits provide more energy than bananas, mango, apple, or guava. Furthermore, white sapote fruits contained more ash than apples. Because of its high ash content, the fruit might be an excellent supplier of nutrients that are necessary for metabolism.The obtained results showed that DWSF is high in B-complex vitamins such as B1, B2, and B3 and minerals such as Ca, Zn, and Fe. These findings were comparable to those of (Workineh, 2021, Khalil et al., 2022). Color is regarded as a significant property of dried products and a general quality control indicator due to the caramelization and browning processes that occur during processing. On the other hand, Freeze-drying causes a slight change in color due to the low temperature required for the process and the absence of liquid water. Supplementing bio-yoghurt drinks made from goat milk with DWSF had a significant impact on the content of the drinks. The obtained results demonstrated that chemical composition analysis demonstrated significant (p ≤ 0.05) variations between the performed treatments and the control samples. The results indicate an increase in total solid content (TS) with increasing substitution ratios. This may be due to the ability of DWSF and its high content of fibers and carbohydrates to participate in hydrophobic bonds formed among protein molecules as a final product of yoghurt gel and thus increase the concentration of TS. Yoghurt drink samples added with DWSF exhibited considerably higher amounts of ascorbic acid, PC, and AOA in comparison to other samples, and this difference increased when the DWSF dosage was increased. This could be due to the presence of phenolic compounds in protein interaction samples (Ozdal et al., 2013). At the protein's isoelectric point, specifically during the production of yoghurt, these interactions are at their peak. However, as milk fat was gradually replaced with DWSF, the amount of fat in the mixture dropped. Microorganisms' lipolytic activity has been blamed for the decrease in fat content (Yin et al., 2021). According to (Canon et al., 2022), the interaction of lactose and basic amino groups during storage may be responsible for a reduction in protein and total solids content. As a result, this occurrence exposed the drop in protein content after 15 days of storage. The supplementation with DWSF to goat milk decreased the pH levels of the treated yoghurt drink samples, which were lower compared to the control samples. The T₄ treatment had the lowest pH, while the control sample had the highest pH value. It was also clear that the pH changes among yoghurt drink samples were limited, which could be related to enzymatic reactions that transform lactose into resulting organic acids as well as the stimulated development and bacterial strain activity in the yoghurt drink matrix. This is consistent with previous findings (Ranathunga & Rathnayaka, 2013 & Khalil et al., 2022), indicating that white sapote fruit promoted the development and activity of bacterial strains isolated from yoghurt drink samples. In the probiotic yoghurt drink samples, lactic acid and acetic acid are generated by L. acidophilus and B. bifidum, respectively. As a result, probiotic yoghurt drink samples had a higher rate of post-acidification compared to the control (Cn₁). Additionally, all samples of yoghurt drinks had a progressive rise in acidity throughout the cold storage period, which may have been brought on by the development and activity of bacterial strains. However, as a result, probiotic yoghurt had a higher rate of post-acidification as the amount of added DWSF increased, with the greatest values found in the yoghurt drink supplemented with 100 % DWSF and the lowest values recorded in the control yoghurt drink. Throughout the duration of storage, the pH value of all yoghurt samples reduced while the acidity (%) rose. These results were consistent with Hossain et al. (2012), who proved that lactose to lactic acid conversion during storage may be the cause of the increase in titratable acidity. Briefly, the acidity values of yoghurt samples were generally constant because of the low storage temperature (4 °C) and the high growth rates of microorganisms, which limited the growth of microbes. Minerals content (Ca and Zn) and vitamins B (B1, B2, and B3) in all yoghurt drink samples varied significantly (p ≤ 0.05), but iron content was insignificant. The contents of vitamins and minerals in yoghurt drink samples increased when the amount of DWSF was increased. Furthermore, our findings are consistent with those of Khalil et al. (2022), who discovered that adding fresh white sapote fruit to yoghurt raises the vitamins and mineral content. Previous data indicated that Casimiroa edulis fruits are high in ascorbic acid, PC, and AOA, which is consistent with the finding by Khalil et al. (2022). As storage time increased, all treatments' phenolic components and AOA decreased considerably (p ≤ 0.05), which can be explained by a decrease in PC stability as well as interactions between enzymes and chemicals. Also, the breakdown of polymeric phenolic compounds increased the development of lactic acid bacteria with storage (Qu et al., 2021). Yoghurt's antioxidant activity was also reported to decline while being stored (Dimitrellou et al., 2020). The earlier findings are in agreement with (Abd-Eltawab & Ebid, 2019; Khalil et al., 2022). They found similar increases in AOA and total phenol levels when fresh white sapote and fig fruit were added to set yoghurt. For all yoghurt treatments, ascorbic acid, total phenols, and AOA gradually decreased after storage. Additionally, they found that AOA levels in yoghurt samples decreased throughout storage. This could be explained by how some PC in LAB decomposes into aromatic acids like phenylacetic, phenyl propionic, and benzoic acid. Subgroups of PC include phenolic acids, flavonoids, and tannins. Color is an essential indicator of food quality since it concerns product desirability, safety, maturity, and freshness, and it has an impact on the final acceptability and quality of the product (Pereira et al., 2021). It could be explained based on the yellow-orange color of the fruit used. Similar attributes were recorded by Desouky (2018), whose yoghurt drinks were produced from goat milk enriched with different levels of cactus peel fruit pulp, and showed a decline in L values, while the values “a“ and ” b” increased as the amount grew of cactus pear fruit pulp used until the 9th day of storage. The rheological properties play an influential role in the food properties; the control treatments had a considerably (p ≤ 0.05) greater flow behavior index than the other DWSF-containing treatments. The trend of the observed findings agrees with those reported by (Desouky, 2018, El-Samahy et al., 2006). The decrease in the flow behavior index is an indicator of the increasing pseudo-plasticity of yoghurt drinks. In contrast to the control, the apparent viscosities of the yoghurt drink samples enhanced with DWSF were considerably (p ≤ 0.05) greater. The above results may occur as a response; the viscosity of yoghurt is commonly attributed primarily to hydrocolloids, its fat and protein content, heat treatment, the acidification rate, the blend of lactic acid bacteria used, and the storage term all have an impact on the texture of food products. (Sodini et al., 2004). The rheological properties of the resulting bio-yoghurt drinks were also greatly improved by the total solids of the yoghurt that were added to the mixture. It is easy to see that adding DWSF to yoghurt drinks has a significant impact on their total solids and dietary fiber contents. Because only goat milk was used in its preparation (control), no dietary fiber present would have affected the rheological metrics (Ismail et al., 2016). From the previous results, it can be inferred that replacing milk fat with DWSF improves yoghurt texture. A rise in yoghurt viscosity was previously had earlier documented by Abdeldaiem et al. (2023), who reported that the substituteof milk fat with roasted barley has improved yoghurt drink texture. The treatment samples treated with DWSF showed high water holding capacity (WHC). This is usually caused by improper storage of the yoghurt, an imbalanced whey protein to casein ratio, and a high incubation temperature. Fortunately, DWSF affected yoghurt WHC (Abdeldaiem et al., 2023). The highest WHC values were seen in T4 treatments, either fresh or after storage intervals. These findings correspond with those of Khalil et al. (2022), who discovered that supplementing flavored yoghurt with white sapote fruit increased WHC values in both fresh and stored samples for up to 21 days. The WHC trend for all samples dropped throughout the time of storage. The total bacterial counts of the control yoghurt drink (Cn₁) sample was lower than those of the probiotic control yoghurt drink (Cn₂) in both fresh and stored conditions. This could be because post-acidification was greater in Cn₂ samples compared to Cn₁ samples, which affects bacterial survival. Furthermore, the microbial growth of the T₁ sample was significantly greater than that of the Cn₁ and Cn₂ samples. The addition of DWSF influenced the proliferation of bacteria, which increased with the addition of fruit. The initial numbers of B. bifidum Bb-11 were higher than those of Lactobacillus. bulgaricus. The counts of Lactobacillus bulgaricus, Streptococcus thermophilus, L. acidophilus La-5, and B. bifidum Bb-11 decreased gradually during storage, and this decline is probably due to increased acidity in yoghurt drinks. These results correspond with those of Buriti et al. (2014), who used guava and sour pulps to prepare dairy beverages. These results lead us to the conclusion that WSF acts as prebiotics for bifidobacteria and L. acidophilus and thereby increases the activity of probiotics in yoghurt drinks. These findings agree with those of Khalil et al. (2022); they acquired an interest in the addition of white sapote fruit pulp prompted the yoghurt aggregate viable LAB count to increase. Also, according to Jin et al. (2018), fruits and vegetables contain bioactive substances that can be employed as substrates for probiotic bacteria development. All yoghurt drink samples were free of coliforms, mold, and yeasts when fresh and throughout storage. This could be related to the effectiveness of milk heat treatment, which prevents contamination of vegetative cells, as well as sanitation and hygienic conditions during product preparation. Sensory qualities such as texture, flavor, color, and taste have a significant impact on food preferences and customer acceptability. As a result, the success of yoghurt as an ingredient in the food is mostly determined by its sensory features, and adding flavors to yoghurt has been proven to enhance options for customers and aid in marketing. The smoothness of the yoghurt may be improved by additional ingredients such as milk carbohydrates and total solids (Abdeldaiem et al., 2023). However, the T₄ recorded the lowest rankings for appearance and color. This may be because of the darker hue seen when the DWSF was increased. On the other hand, the organoleptic scores of the control treatments were the lowest. In general, the data gathered revealed that when compared to controls, probiotic strains and supplementation with DWSF at a ratio of 75 % produced higher acceptance scores. The findings were in line with those made by Baraka et al. (2011), who concluded the safe conclusion that the bifidobacteria-added yoghurt sample. Yoghurt culture outperformed all other treatments in terms of look, body & texture, and flavor. Others think that the addition of DWSF influenced consumer approval.

5. Conclusion

Dried white sapote fruit (DWSF) can be used to create a novel low-fat bio-yoghurt drink made from goat milk. According to the data presented above, the physicochemical and rheological properties of goat milk yoghurt drinks are improved by substituting various levels of DWSF (0, 25, 50, 75, and 100 %) for milk fat. As the amount of DWSF added to the yoghurt drink treatments improved, so did the PC, antioxidant activity, and WHC. The high content of fibers and carbohydrates may play a role in the hydrophobic interactions between protein molecules. The sensory evaluation of DWSF-based goat yoghurt drinks was deemed desirable by the panelists due to the volatile phenols and phenolic compounds produced by the yoghurt cultures. With the addition of DWSF, which promoted the development of probiotic bacteria, the total number of viable cells in probiotic treatments was kept at a functional level (>10⁶ CFU/mL) for 15 days. In any case, the use of sapote fruit in the production of a variety of healthy, low-fat dairy products seems to have a promising future.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.