Effect of red beet cooking water on yoghurt's physico-chemical,textural and antioxidant characteristics

Abstract

This study aimed to evaluate the effect of red beet cooking (Beta vulgaris L.) water on the quality properties of yoghurts prepared with different levels (2, 4, 8, and 10% w/w) compared to the nature sample. Results showed a decrease in pH value and an increase in titratable acidity (TA), fat content, and dry matter with the increasing red beet cooking water concentration. Consumer test revealed that incorporating 4% (w/w) red beet cooking water into yoghurt influences the product's overall acceptability compared to the other formulations. The addition of red beet cooking water at the level of 4% induces significant increase in gel firmness with a decrease in syneresis compared to the control sample. The lightness and yellowing of the product decreased while the redness increased. Furthermore, the effect of red beet cooking water addition was significant (p < 0.05) on total phenolic contents (0.369 ± 0.024) as well as antioxidant activity (0.140 ± 0.008). Beet cooking water may be a potential ingredient in the formulation of functional products.

Graphical Abstract

This is a visual representation of the abstract.

Keywords

formulation syneresis consumer acceptability colour polyphenol compounds

INTRODUCTION

Yoghurt is fermented milk produced by Streptococcus thermophilus and Lactobacillus delbrueckii spp. bulgaricus (Chandan et al., 2017). It's a better source of protein, vitamins and minerals such as calcium, phosphorus, potassium, and zinc than other dairy products (Gahruie et al., 2015). Its intake has been associated with a healthier metabolic profile and a reduced risk of weight gain, obesity, cardiovascular disease, and diabetes mellitus (Yanni et al., 2020).

Colour is one of the crucial external qualities of foods that determines their acceptance by consumers. Consequently, the food industry adds colourants to manufactured products to intensify this feature (Martins et al., 2016). Increasing attention focused on the toxicity of these additives used in food, particularly azo-dyes. The main concern often limiting the use of synthetic colourants concerns their azo-reduction to carcinogenic metabolites by intestinal microbiota (Feng et al., 2012). Currently, synthetic colourants widely used in the food industry are progressively substituted by those from natural sources such as fruits and vegetables. (Caro et al., 2012).

Red beet is grown in many parts of the world, from the Americas to Europe and Asia (Desseva et al., 2020). It is especially rich in bioactive compounds and sugars but has a moderate caloric value (Baiao et al., 2017). It is one of the most potent vegetables concerning antioxidant activity, mainly due to betalains’ presence (Moghaddas Kia et al., 2020). Moreover, the beet extract is approved as a food colourant called red beetroot betalain or betanine (E162). Generally, Red beetroot pigment is obtained from sliced beetroots by pressing or centrifuging blanched ground beets or through an aqueous extraction of shredded beetroots (Directive 95/45/EC). The betanine extract is then concentrated to 60–65% total solids or dehydrated and sold as a powder (Henry, 2012). Furthermore, the high price of natural colourants limits their use by food industries. In this work, the possible use and valorization of water resulting from red beet cooking in the yoghurt preparation both as a bio-colourant and a sucrose substitute represents a great challenge. For this purpose, this work aims to investigate the effect of the addition of different concentrations of red beet cooking water on yoghurt and further evaluate the physico-chemical characteristics, texture, antioxidant activity, microbiological quality of the different formulations as well as yoghurt quality during 28 days of refrigerated storage.

MATERIALS AND METHODS

Materials

Dry whole milk powders (0% and 26% fat) used in this study were supplied by a Djurdjura Danone dairy industry located in the Akbou region of Bejaia province. Freeze-dried starter yoghurt culture (Chris-Hansen SA, USA) consists of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Red beet (Beta vulgaris L.) was purchased from the local market of the Bouira province. All microbial media cultures used were obtained from the Pasteur Institute, Algeria.

Preparation of red beet cooking water

First, the beet with its leaves and stems was washed thoroughly with water containing a few drops of bleach to remove dust and contaminants. The red beet washed was cut and cooked at 90 °C – 100 °C for 15 min, the red beet:water ratio was 0.5:1. The recovered cooking water was filtered, cooled, poured into glass bottles, and stored in the refrigerator at 4 °C until use.

Yoghurt preparation

Five recipes that included a control yoghurt sample were prepared as follows: whole milk powders reconstituted with water process were mixed with different levels (2, 4, 8 and 10% w/w) of red beet cooking water heated at 75 °C for 10 min. The mixture homogenized was pasteurized at 95 °C for 5 min and then cooled down to 43 °C. The starter bacteria culture was then added and gently shaken. The mix was poured into glass pots, capped, and incubated at 43 °C for 4 to 5 h. Finally, the yoghurt preparations (BYs) were stored at 4 °C until use. The different formulations of yoghurt were summarized in Table 1.

Table 1.

Yoghurt recipes prepared with or without red beet cooking water for 100g.

Yoghurt recipe	Milk powder (0%)	Milk powder (26%)	Water process	Starter culture	Red beet cooking water
NY	6.750	6.750	86.485	0.015	0.00
BY 2%	6.750	6.750	84.485	0.015	2.00
BY 4%	6.750	6.750	82.485	0.015	4.00
BY 8%	6.750	6.750	78.485	0.015	8.00
BY 10%	6.750	6.750	76.485	0.015	10.00

NY: nature yoghurt; BY: yoghurt prepared with red beet cooking water.

Physico-chemical characterization

The pH, titratable acidity (TA), fat, and total dry extract (TDE) measurements of yoghurt recipes formulated were made respectively, according to AOAC (2000). The TA of BYs was determined using NaOH (0.1 mol L⁻¹) solution. The pH neutralization was achieved at a value of 8.2. In contrast, an indicator of colour (phenolphthalein solution) was used for the nature sample. Results are expressed in degrees Dornic (D), where 1D corresponds to 0.1g L⁻¹ of lactic acid. Fat content (fat %) was also determined for all samples of yoghurt by the Gerber method.

Viscosity

The different yoghurt formulations’ viscosity was measured using a viscosimeter (Anton Paar MCR 301, Anton Paar Gmbh, Graz, Austria) equipped with a Peltier system. The experiments were performed by a parallel plate configuration (diameter 50 mm, gap 0.5 mm) in a controlled stress mode. The prepared samples were sheared in a shear rate range of 0.1–100 s⁻¹ at 25 °C. Measurements were expressed in centipoises (cP).

Microbiological analysis of yoghurts

Microbiological analysis was carried out according to Goldman and Green (2009) methods. Aerobic mesophilic bacteria, coliform, streptococci, lactobacilli, yeasts and moulds were enumerated. The bacterial enumeration was done to ensure that the prepared yoghurt has a higher hygienic and commercial quality.

Consumer acceptance test

A Kramer's rank-Sum test (IS:6273-3-2, 1983) was conducted with ten untrained panelists (five Danone dairy laboratory members aged 26 to 50 and five voluntary university students from 22 to 26). The aim of this test is to study whether rank-sums (or equivalently mean ranks) for various samples differ significantly and which of the samples is significantly superior or inferior to others in preference ranking. The consumers were asked to evaluate the yoghurt samples served in randomly coded opaque pots. Product evaluation was based on the 5-points hedonic scale.

Characterization of the preferred recip

The preferred yoghurt recipe and natural sample were considered to evaluate the kinetic evolution of pH and TA at days 1, 7, 14, 21 and 28 as well as the following characteristics: protein content, Ash content, total phenolic content (TPC), radical scavenging activity (RSA), syneresis, colour, and texture.

Protein content

MilkoScan™ FT120 analyzer (Foss a/S, Hillerod, Sweeden) provides a solid platform for liquid milk analysis. It was used for protein determination. This method employs the FTIR (Fourier Transformed Infrared Spectroscopy) measuring principle, in compliance with IDF (International Dairy Federation) and AOAC (Association of Analytical Chemists) standards. Through this automatic method of high capacity (providing up to 120 reliable measurements per hour), each dairy product parameter was characterized by an infrared wavelength transformed to the mass percentage by Beer-Lambert law. Results expressed are the mean of two sample essays.

Ash content

Ash content of yoghurt samples was determined, according to AOAC (2000).

Total phenolic content

The TPC was determined using the Folin-Ciocalteu's reagent (Singleton et al., 1999).

Radical scavenging activity assay

Free RSA of samples was measured using Brand-Williams et al. (1995) method. Antioxidant activity was expressed as percentage inhibition of the DPPH radical and was determined by the following equation:

RSA % = [(A_{control} - A_{sample}) ╱ A_{control}] \times 100

Colour measurements

The colour of yoghurt samples was measured by Minolta Chroma Meter CR10 (Cielab Korica Minolta, Japan) according to Abbasi and Azari (2009) method. The colour was expressed in lightness (L), redness (RG) ( + /− red-green), and yellowing (YB) ( + /− yellow-blue).

Texture analysis

Texture measurements were carried out as described by Fiszman et al. (1999). The penetration test was performed with a TA plus texture analyzer (LLYOD Instruments) connected to a computer programmed with texture analysis software. A 12.7 mm diameter cylinder probe was introduced into the samples at a speed of 1 mm.s⁻¹. The yoghurt samples’ gel firmness was measured through the probe moving at different distances (1 mm to 22 mm) without sample stirring. Triplicate measures were performed for each yoghurt. The parameters assessed were the firmness as the force required to resist or break the gel yoghurt and the force at a distance penetration of 15 mm (F_max).

Syneresis

The syneresis rate (%) expressed as the volume of separated whey per 100mL of yoghurt was determined after 15 days of storage at 4°C (Koksoy and Kilic, 2004).

Statistical analysis

All analysis were carried out in triplicate. Results were reported as mean values ± standard deviations. One-way ANOVA and Tukey tests were employed to determine the significant differences between treatments (p < 0.05). The statistical analysis was performed on the software Statistica 6.

RESULTS AND DISCUSSION

Physicochemical characteristics of the different formulations of yoghurt

As shown in Figure 1, the addition of beet cooking water in yoghurt induced significant pH value variation (p ˂ 0.05). The pH ranged from 4.106 ± 0.042 (BY4%) to 4.250 ± 0.034 (BY2%) compared to the control one (4.456 ± 0018). Similar results were observed by Subhashini et al. (2018) for drinkable yoghurt fortified with grape pomace powder at different levels (0.5, 1.0 and 1.5%). In the same way, lower initial pH values of yoghurts fortified with encapsulated carrot waste extract (2.5 and 5 g 100 g⁻¹) or with different concentrations (0.0, 0.1, and 0.2 g 100 mL⁻¹) of Argel leaf extract (ALE) (Solenostemma argel Hayne) were observed in comparison to the control sample (Seregelj et al., 2021; Mohamed Ahmed et al., 2021). Zhang et al. (2019) concluded from their study on yoghurt supplemented with moringa extract that phytochemical component might be responsible for the enhanced fermentation activity of lactic acid bacteria and thus the rapid drop in pH. In our study, the red beetroot composition (high content of vitamins, antioxidants, and other biologically active compounds) could cause the recorded pH decrease.

Figure 1.

pH and titratable acidity changes. Values are Mean ± SD of three replicates. BY: yoghurts prepared with red beet water cooking, NY: natural yoghourt. ^a,b,c Different superscripts letters indicate statistical differences (p < 0.05).

For TA, samples formulated with beet cooking water showed a significant increase (p ˂ 0.05) compared to the NY sample (Figure 1) comforted by the findings of Cordova-Ramos et al. (2018), Brahmi et al. (2021) and Mohamed Ahmed et al. (2021). Similar results were also recorded by El-Messery et al. (2019) and Ahmad et al. (2020) investigations on yoghurts’ fortification by encapsulated and apple peel extract, respectively.

Total dry extract

According to Figure 2, the TDE content of the yoghourt increased significantly with beet cooking water compared to the value obtained for natural yoghurt. The difference is significant for the beet cooking water level ranging from 4% to 10%, while the difference is insignificant for 2%. Similarly, a recent study by Benmeziane et al. (2020) indicated that the inclusion of lentil flour in the yoghurts significantly increased the dry extract compared to the control yoghurt.

Figure 2.

Total dry extract and fat content changes. Values are Mean ± SD of three replicates. BY: yoghurts prepared with red beet water cooking, NY: natural yoghourt. ^a,b,c Different superscripts letters indicate statistical differences (p < 0.05).

Fat content

The fat content of yoghurt significantly increased with increasing beet cooking water concentration compared to the control sample (NY) (p ˂ 0.05) (Figure 2). Moreover, there were no significant differences in fat content for BY4% and BY10% samples. In agreement with our study, Yadav et al. (2016) and Subhashini et al. (2018) reported an increase of fat content. Also, Curti et al. (2017) observed significant differences in fat contents between the control sample and supplemented yoghurts with quinoa flour at 1, 3 and 5 g 100 mL⁻¹.

Yoghourt viscosity

The viscosity values of beetroot yoghourt varied from 215298 ± 18771 cP (BY4%) to 239220 ± 9805 cP (BY10%) (Figure 3). The addition of red beet cooking water at 2% and 4% led to lower viscosity, while a slight tendency of the increase was observed for samples fortified with 8% and 10% compared to the nature sample. Overall, the difference between the different formulated yoghurt samples’ viscosity values is statistically insignificant (p˃0.05). Our results are in agreement with those obtained by Sani et al. (2013) and Dabija et al. (2018) for yoghurt enriched with respectively Spinacia oleracea extract and different types of fibres (inulin, pea, oat and wheat).

Figure 3.

Viscosity of the different formulations of yoghurt. Values are Mean ± SD of three replicates. BY: yoghurts prepared with red beet water cooking, NY: natural yoghourt. ^a,b,c Different superscripts letters indicate statistical differences (p < 0.05).

Microbiological analysis

The microbiological parameters obtained for the yoghurts are summarized in Table 2. In our case, they were not detected in all yoghurt samples analyzed. These results are less than 10 cfu g⁻¹ as recommended by Mostert and Jooste (2002) and Codex Alimentarius (2011).

Table 2.

Effect of red beet cooking water addition on the total viable count.

Yoghurt sample	Germ (cfu/g)
Yoghurt sample	Streptococcus thermophilus	Lactobacillus bulgaricus	Faecal coliforms	Total coliforms	Yeast and moulds	Aerobic mesophilic bacteria
NY	1.63 × 10⁸	1.61 × 10⁷	0	0	0	0
BY 2%	1.65 × 10⁸	1.64 × 10⁷	0	0	0	0
BY 4%	1.72 × 10⁸	1.68 × 10⁷	0	0	0	0
BY 8%	1.76 × 10⁸	1.73 × 10⁷	0	0	0	0
BY 10%	1.82 × 10⁸	1.79 × 10⁷	0	0	0	0

cfu: colony forming unit.

Viable lactic flora is a critical factor in the finished product in acidification and nutritional health (Zare et al., 2011). Lactic acid bacteria's viability showed a slight increase in red beet cooking water incorporated in the yoghurt (Table 2). It is recommended that fermented milk contain at least 10⁷cfu g⁻¹ (Codex Alimentarius, 2011). The current results have shown that the incorporation of red beet cooking water has no negative impact on starter bacteria activity.

Consumer acceptance test

Comparing rank-sums values obtained for the different yoghurt samples showed that the BY2% sample was significantly inferior to others in preference ranking at a 5% level of significance. So, BY4% was the most accepted and appreciated by all the tasters. The four samples’ ranking is as follows: BY4%, BY10%, BY8%, BY2%. Only the sample for which consumers expressed greater acceptability was retained for further analysis, namely the BY4%.

CHARACTERIZATION OF THE PREFERRED RECIPE BY THE CONSUMER

Evolution of pH and titratable acidity during storage

Results of Table 3 mentioned that both pH and TA were significantly (p < 0.05) affected by the beet cooking water incorporated in the yoghurt throughout storage days. The pH was lower while the acidity increased compared to the control sample during all storage days. Besides, there was no significant difference in the pH values for all formulations between day 1 and 28 days of storage. On the other hand, the samples’ TA values with red beet cooking water increased during the storage time with a significant difference (p < 0.05) after 14, 21 and 28 days. We observed a slight increase in acidity during the control sample storage, but the difference was not statistically significant (p˃0.05). A recent study by Mohamed Ahmed et al. (2021) reported that at all storage intervals, the pH of ALE fortified yoghurts was lower than the control (p < 0.05), and no difference was perceived between 0.1 and 0.2 g.100 mL⁻¹ of ALE-fortified yoghurt in agreement with our results. In the same tendency, they indicated significant higher acidity values (p < 0.05) compared to the control sample throughout the whole storage period. In other previous studies, yoghurt supplemented with orange fibre (Erkaya-Kotan, 2020) and concentrated strawberry pulp (Jaster et al., 2018) showed similar pH, and TA changes trend the storage period. Wang et al. (2019) indicated that samples fortified with apple pomace at 0.1, 0.5 and 1% concentrations showed lower pH than the control during most of the storage period, comforting our results (Table 3). Still, they reported a drop in pH values from 4.6 to 4.3 for all samples during the first 21 days within the 28-day storage period (p < 0.05).

Table 3.

pH and titratable acidity of yogurt during 28 days of storage at 4°C.

Storage time (days)	pH		TA (°D)
Storage time (days)	NY	BY4%	NY	BY4%
1	4.46 ± 0.018^aA	4.11 ± 0.042^aB	75.30 ± 0.351^aB	83.00 ± 1.154^aA
7	4.47 ± 0.017^aA	4.12 ± 0.020^aB	76.50 ± 0.763^aB	85.00 ± 1.527^acA
14	4.41 ± 0.006^aA	4.11 ± 0.029^aB	78.60 ± 0.702^aB	89.10 ± 0.305^bcA
21	4.46 ± 0.030^aA	4.13 ± 0.020^aB	78.00 ± 1.00^aB	89.75 ± 0.250^bA
28	4.47 ± 0.008^aA	4.10 ± 0.020^aB	78.25 ± 0.629^aB	89.83 ± 0.600^bA

^a,b,c

Different superscripts letters within same column indicate statistical differences (p < 0.05).

^A,B

Different superscripts letters within same line indicate statistical differences (p < 0.05).

Protein content, ash, total phenolic content and antioxidant activity of beetroot preferred yoghurt

As shown in Figure 4, supplementation of yoghurt with beetroot cooking water induced an increase in protein and ash content (p ˂ 0.05) according to with Yadav et al. (2016) results for sample yoghurts enriched with beetroot powder at 0, 6, 8 and 10%.

Figure 4.

Ash, protein content, polyphenol content and antioxidant activity of the natural yoghurt (NY) and yoghurt formulated with red beet cooking water at 4%. Values are Mean ± SD of three replicates. ^a,b Different superscripts letters within the same column indicate statistical differences (p ˂ 0.05).

Our results revealed that the addition of beet cooking water led to a statistically significant increase (p ˂ 0.05, Figure 4) in the polyphenol content (TPC) and antioxidant activity of the sample BY4% compared to the control yoghurt (NY). Yoghurt fortified with ALE (Solenostemma argel Hayne) gave the same results (Mohamed Ahmed et al., 2021). Likewise, the study on the effect of steviol glycosides as a sugar substitute on the probiotic fermentation in milk gels enriched with red beetroot (Beta vulgaris L.) bioactive compound (Ozdemir and Ozcan, 2020). Numerous reports demonstrated that supplementing yoghurts with moringa leaf extract (Zhang et al., 2019), chia seed extract (Kwon et al., 2019), and pomegranate juice powder (Pan et al., 2019) improved the TPC and antioxidant activity of yoghurt compared to plain yoghurt. Several studies have shown that beetroots (Beta vulgaris L.) possess strong antioxidant power attributed to their high amounts of biologically active compounds (Chhikara et al., 2018; Babarykin et al., 2019).

Colour measurements

Colour measurements of lightness (L*), redness (a*), and yellowness (b*) of the preferred yoghourt are shown in Table 4. The statistical analysis indicated a significant difference in colour attributes among samples. Addition of beet cooking water induced a decrease of colour factors (L* and b*) while a* increase compared to the control yoghurt consistent to the findings of Demirkol and Tarakci (2018) as well as those of Ozdemir and Ozcan (2020). The maximum (a*) value thus obtained may be due to red and blue-purple colours of red beetroot attributed to anthocyanins’ concentration (Patras et al., 2010; S’cibisz et al., 2019).

Table 4.

Colour attribute of the control (NY) and preferred yoghurt (BY4%).

Yoghurt sample	Colour attribute
Yoghurt sample	L*	a*	b*
NY	67.233 ± 1.230^a	−2.560 ± 0.088^a	15.100 ± 0.264^a
BY 4%	59.166 ± 0.338^b	7.900 ± 0.100^b	11.760 ± 0.120^b

^a,b

Different superscripts letters within the same column indicate

statistical differences (p ˂ 0.05). L*: lightness, a*: redness, b*: yellowness.

Texture and syneresis analysis

In the current study, BY4% has significantly (p ˂ 0.05) higher Fmax value (0.345 ± 0.024 N) than nature yoghurt (0.204 ± 0.017 N) (Figure 5) in contrast to the results of Trigueros et al. (2016) on yoghurt with quince (Cydonia oblonga Mill.) scalding water. Furthermore, red beet water cooking addition resulted in higher firmness of yoghurt (p ˂ 0.05) reflecting gel strength (Figure 5) compared to the control, a compatible finding of the low pH of BY4% and NY sample as shown in Figure 1. According to our data, Wang et al. (2019) observed that the set type yoghurts with 0.5 and 1% apple pomace were significantly firmer than the control sample in agreement with data indicated by Ozdemir and Ozcan (2020) for a fermented gel with red beetroot milk gel.

Figure 5.

Syneresis and textural characteristics (firmness and Fmax) of the natural yoghurt (NY) and yoghurt formulated with red beet cooking water at 4%. Values are Mean ± SD of three replicates. ^a,b Different superscripts letters within the same column indicate statistical differences (p ˂ 0.05).

In this study, the addition of beetroot cooking water significantly affected syneresis (p < 0.05) (Figure 5). The value of control yoghurt (NY) was 0.8 ± 0.0115. Simultaneously, it decreased to 0.23 ± 0.132 in the yoghurt fortified (BY4%) comforted by the findings of Cordova-Ramos et al. (2018) for yoghurts formulated with jumbo squid powder.

Similar to our data, Ozturk et al. (2018) showed that whey separation was significantly decreased with peeled oleaster (Elaeagnus angustifolia L.) flour (PO) and unpeeled oleaster flour (UPO) fortifications (1% and 2%). Ozdemir and Ozcan (2020) have recently registered a lower syneresis value in milk gel with red beetroot pulp. In the same trend, the incorporation of ALE (ALE) reduced the syneresis of yoghurt compared to the control with the least values recorded in 0.1 g 100 mL⁻¹ ALE-fortified yoghurt (Mohamed Ahmed et al., 2021). In our study, the low value of syneresis of the BY4% sample compared to the nature yoghurt may be explained by either the high protein and lipid content of red beet cooking water (Figures 2 and 4) polyphenols content and casein network in the yoghurt or a combination (Ranadheera et al., 2012; Oliveira et al., 2015).

CONCLUSION

Overall, our results showed that the addition of the different concentrations (2, 4, 8, or 10% w/w) of red beet cooking water affect significantly the pH, TA, TDE, and fat content (p ˂ 0.05), but there was no significant effect on viscosity (p˃0.05). However, yoghurt enriched at 4% level improves colour perception (red colour) of the final product and induces a significant decrease in syneresis compared to the control sample. Furthermore, supplementation of red beet cooking water had a potential effect on firmness, polyphenol, and antioxidant activity. These results could be of commercial interest for the industrial production of functional foods containing active ingredients with natural low-calorie sweeteners and colourants.

Supplemental Material

sj-docx-1-fst-10.1177_10820132221137386 - Supplemental material for Effect of red beet cooking water on yoghurt's physico-chemical, textural and antioxidant characteristics

Supplemental material, sj-docx-1-fst-10.1177_10820132221137386 for Effect of red beet cooking water on yoghurt's physico-chemical, textural and antioxidant characteristics by Fatima Halladj, Hayat Amellal-Chibane, Radhia Aitfella-Lahlou, Mohamed Amokrane Bourai and Amazigh Tigrine in Food Science and Technology International

Footnotes

DECLARATION OF CONFLICTING INTERESTS

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

FUNDING

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Fatima Halladj

Radhia Aitfella-Lahlou

SUPPLEMENTAL MATERIAL

Supplemental material for this article is available online.

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