مطالعه اثر عصاره آبی آگاو تکیلانا بر خواص آنتی اکسیدانی، آب اندازی و خصوصیات حسی ماست پروبیوتیک

1. Introduction
Agave tequilana is a plant of an angiosperm species that belongs to the family Asparagaceae. It is commonly used to produce Tequila, an alcoholic beverage (López & Urías-Silvas, 2007). Several biological properties of this plant, including antibacterial, antioxidant, and anti-inflammatory properties, have been reported (Sahnoun et al., 2017). Some Agave species demonstrated antioxidant activity (Romero-Lopez et al., 2015). Agave syrup contains phytochemicals comprising flavonoids, polycosanols, and sapogenins, which show anticarcinogen and antioxidant activities (Narvaez-Zapata & Sanchez-Teyer, 2009). Agave juice is used to produce syrup and fructooligosaccharides powder because of its high content of fructans (Salazar-Leyva et al., 2016). Fructans are the principal photosynthetic composition of this plant (Lopez et al., 2003). Fructans are used as food ingredients, including sweeteners, texture modifiers, and fat-replacer in food products (Salazar-Leyva et al., 2016). Several research studies have well supported the prebiotic effect of Agave fructans (López & Urías-Silvas, 2007; Marquez-Aguirre et al., 2013; Ramnani et al., 2015; Urias-Silvas et al., 2008; Zamora-Gasga et al., 2015). 
In recent years, consumers have been concerned about the beneficial value of food and are seeking healthier options (Kowaleski et al., 2020). This growing interest in healthy food has encouraged the industry to search for and develop products that show additional functional/health effects over common nutritional values. Antioxidants such as polyphenols and carotenoids are popular active ingredients representing different health benefits, including anti-cancer, eye-protective, heart-protective, and anti-diabetic properties. Furthermore, probiotic food products are among the most popular functional foods marketed worldwide. The growing consumer interest in probiotic products is because probiotic microorganisms exhibit different health benefits to humans by improving lactose digestion, preventing intestinal infections, preventing cancers, modulating the immune system, and lowering cholesterol (Aryana & Mc Grewa, 2007).
Yogurt is the world’s most popular fermented dairy product market due to its therapeutic, nutritional, and sensory properties. From a nutritional point of view, yogurt is a nutrient-dense food, as it contains protein, riboflavin, vitamins B6 and B12, and calcium. Yogurt and fermented milk products are among the best carrier of beneficial nutrients such as probiotics and antioxidants (O’Sullivan et al., 2016).
In this research, the effect of A. tequilana aqueous extract (ATAE) at 0.5%, 1%, and 1.5% concentrations was investigated on selected physicochemical and sensory properties of probiotic yogurt during the storage.

2. Materials and Methods
Preparation of ATAE
A. tequilana was prepared from a plant garden in the Tehran Province of Iran. All the leaves were cut into small pieces and dried for two weeks in the shade at environmental temperature. It was then mashed using a mechanical grinder (Moulinex, Paris, France). For extract preparation, 50 g of the grinded plant was soaked in 450 mL water and shaken for 48 h at 250 rpm, followed by filtration through filter paper of Whatman No. 1, then vaporized at 50°C using a rotary evaporator (Buchi Rotavapor R-114, Switzerland) and further dried at 40°C. The extract powder was refrigerated at 4°C till running the experiments (Dahikar et al., 2010). 
Preparation of probiotic bacteria 
The probiotic bacteria, including Lactobacillus acidophilus (La5) and Bifidobacterium bifidum (Bb-12) were prepared from CHR Hansen (Horsholm, Denmark). Freeze-dried bacteria were added to the sterile MRS Broth medium and incubated for 48 h at 37°C in aerobic conditions and an anaerobic jar for L. acidophilus and B. bifidum, respectively. Bacterial cultures were harvested by centrifugation at 4000×g at 4°C for 10 min, washed twice with sterile saline, and collected by centrifugation. A bacterial suspension with an optical density of 0.1 at 600 nm was prepared. Cell numbers were determined using the surface plate count technique by preparing serial dilutions and plating on MRS (from De Man, Rogosa, and Sharpe) agar. The plates were then incubated at 37°C for 3 days in aerobic and anaerobic conditions for L. acidophilus and B. bifidum, respectively, as mentioned above. The bacterial number was calculated by colony counter. 
Yogurt preparation 
Yogurts (set style) were made from cow’s milk and contained 1.5% (w/w) fat and 12% (w/v) total solids. Raw milk was treated at 85°C for 15 min and then cooled to 42°C (for fermentation). All cultures were used according to the manufacturer’s instructions. Milk was inoculated with yogurt starters, Streptococcus thermophilus, Lactobacillus bulgaricus (Delvo, USA), and probiotic cultures (108 CFU/mL) and mixed thoroughly; immediately ATAE (0%, 0.5%, 1%, and 1.5%) was added to the milk and incubated at 42°C. Plain yogurt without probiotic bacteria and AEAT was prepared as a control. Fermentation continued up to the pH of 4.5±0.02. After fermentation, yogurt samples were cooled to 4°C and stored at this temperature for 21 days.
Physicochemical and sensory analysis
Syneresis was determined using a centrifuge by Najgebauer-Lejko et al. (2014) and Sahan et al. (2008) methods. Syneresis extent was calculated as the weight percentage of whey released after centrifugation.
Total phenolics content (TPC) was estimated using Folin-Ciocalteu reagent and gallic acid as standard as Shori and Baba (2013) described. 
Determination of radical scavenging activity was done by the DPPH method (Brand-Williams et al., 1995). TPC was measured as described by Shori & Baba (2013). Butylated hydroxytoluene (BHT) was used as a standard antioxidant, and the yogurt samples’ antioxidant activity was expressed as mg BHT equivalent/kg yogurt. 
A panel of 5 experienced members evaluated the yogurts’ characteristics for appearance, flavor, texture, and overall acceptability with a point scale from 0 to 5 (0 means unacceptable).
All analyses were performed on storage’s first, seventh, and twenty first days.
Statistical analysis
Statistics on a completely randomized design were performed with the analysis of variance (ANOVA) procedure in SPSS software, version 20 (Chicago, IL, USA). Duncan’s test was used to compare the difference among mean values at the significant level of 0.05 (P<0.05). All experiments were replicated three times.

3. Results 
According to Figure 1, the presence of ATAE significantly increased TPC in the yogurts (P≤0.05); at day 1, the lowest and highest TPC were observed in T3 (389.9 mg gallic acid/kg) and T5 (905.6 mg gallic acid/kg), respectively. The lowest TPCs were observed in control probiotic yogurt (175.2 mg gallic acid/kg) and plain yogurt samples (173.2 mg gallic acid/kg), respectively, without any significant difference from each other (P>0.05). Storage did not cause a significant increase in TPC in the yogurts (P>0.05).

As shown in Figure 2, the antioxidant activity (AA) increases with increasing ATAE concentration (P≤0.05). The AA of plain yogurt was measured at 69 mg BHT eq./kg on day 1, which remained constant during the storage. During 21 days of storage, no statistically significant difference was observed in AA of the control probiotic yogurt compared to plain yogurt (P>0.05). The AA was decreased during the time (P≤0.05).

The results of the syneresis of the yogurt samples during storage are shown in Figure 3. The plain yogurt showed 39.1% syneresis on the first day, which increased to 47% on day 21. No statistically significant difference was found in the syneresis of probiotic yogurt compared to plain yogurt (P>0.05). However, the syneresis was enhanced during that time.

The results of the organoleptic assessment of the yogurt samples are presented in Table 1. The sensory properties of the probiotic yogurt, including appearance, flavor, texture, and overall acceptability, were comparable to the plain yogurt. The addition of AEAT induced significant darkening of the yogurt compared to the control yogurt (P≤0.05), and this effect was concentration dependent. Furthermore, an extract flavor was found by panelists in synbiotic yogurt containing different concentrations of AEAT. The synbiotic yogurt showed less softness and consistency compared to the control yogurt (P≤0.05).

4. Discussion
Several studies have reported increased phenolic content in yogurt due to fortification with different plant extracts (Farvin et al., 2010; Mosiyani, 2017; Shori, 2013; Shori & Baba, 2013). In the present study, the polyphenol content of the yogurt samples did not change during storage. It seems that the effect of storage time depends on several factors, such as the bacterial ability to metabolize polyphenols (Shori & Baba, 2013) and the extent of interaction between phenolic compounds and proteins; the more connection between phenolic and proteins, the more decrease in phenolic recovery during the time as reported by Vital et al. (2015). 
It is reported that the AA of yogurt is associated with the release of a large number of peptides and amino acids by lactic acid bacteria during the fermentation of the milk (Farvin et al., 2010; Kudoh et al., 2001; Madhu et al., 2012; Pena-Rasmos et al., 2004). The results revealed a direct relationship between TPC and AA in 0.5%, 1%, and 1.5% ATAE-fortified yogurts. Increases in AA of the plant preparations are related to the TPC content of their composition (Muniandy et al., 2016; Vasco et al., 2008). An increase in the concentration of ATAE induced an increase in AA; the value of DPPH scavenging ability of 0.5%, 1%, and 1.5% ATAE-fortified yogurts was 283, 480, and 617 mg BHT eq./kg yogurt, respectively. This finding is in accordance with other studies, which have shown that the incorporation of different sections of the plant and fruit creates a significant difference between the AA of yogurts fortified with them and that of the control (El-Said et al., 2014; Yadav et al., 2018; Hashemi et al., 2016; de Carvalho et al., 2019; Liu, 2018; Gaglio et al., 2019; Shori & Baba, 2013; Shori, 2013; Mosiyani et al., 2017). However, the antioxidant effects of the synbiotic yogurt samples showed a significant decrease of up to 50% after 21 days of storage. Many studies reported declining yogurts' antioxidant activity during storage (Jozve-zargharabadi et al., 2020; Cho et al., 2020; Bchir et al., 2019; Kim et al., 2019; Mosyani et al., 2017; Oh et al., 2016). This may result from forming a complex between polyphenols and milk proteins (Kim et al., 2019; Bchir et al., 2019; Oksuz et al., 2019; Sánchez-Bravo et al., 2018; Helal et al., 2018; Lamothe et al., 2014).
Adding AEAT to the probiotic yogurt significantly elevated syneresis extent compared to the plain yogurt and probiotic control yogurt (P≤0.05). This result is in agreement with results obtained by Michael et al. (2010), Faraki et al. (2020), Sengul et al (2012), and Ramirez-Santiago et al. (2010), who found that olive, garlic, onion, and citrus extracts, Auricularia auricula aqueous extract, sour cherry pulp, and Pachyrhizus erosus L fibers, respectively, in yogurts led to an increase in syneresis. The rise of whey expulsion from the yogurt may be explained by a weakening casein network due to interaction with active groups of the extract, thermodynamic incompatibility between polysaccharide of the extract and milk proteins, and unbalanced osmotic potential due to depletion flocculation of the casein micelles in the presence of non-adsorbing polymers such as dietary fiber (Michael et al., 2010). The polyphenol-protein interaction, which plays an important role in serum separation, depends on various factors, including proteins and polyphenol nature, temperature, and other bioactive compounds (Vital et al., 2015). However, this observation is not in line with the results of Huang et al., 2020, Guo et al., 2018, Amirdivani et al., 2013, and Narayana and Gupta, 2013, who demonstrated the positive effect of the plant preparations on the decrease of syneresis. Increased syneresis in the yogurt samples over storage time can be explained by protein re-arrangement, which weakens the casein network (Everett & Mcleod, 2005). The increase in syneresis during the storage time was reported earlier (Alighazi et al., 2021; Amirdivani et al., 2013; Zare et al., 2011). 
The studies reported the reduction of organoleptic acceptability of the yogurt incorporated by red ginseng extract (Jung et al., 2016), Hibiscus sabdariffa (Iwalokun & Shittu, 2007), aqueous extract of basil and savory (Mosyani et al., 2017), Chlorella vulgaris and Arthrospira platensis (Beheshtipour & Motazavian, 2012) and green tea extract (Shokery et al., 2017). However, some experiments showed improvement in sensory parameters of yogurt which was fortified with soybean extract (Park & Oh, 2007), agave fructans (Crispín-Isidro et al., 2014), grape and callus extracts (Karaaslan et al., 2011), and cinnamon ethanol extract (Jin et al., 2016). Although the overall acceptability of synbiotic yogurt containing AEAT was lower than that of plain and probiotic control yogurt, they were still acceptable. 

5. Conclusion
 In this study, we presented a novel, useful yogurt by incorporating ATAE into probiotic yogurt. This study showed a significant increase in TPC and AA of yogurt by adding AEAT. Generally, our results supported using this yogurt formulation as a useful product for improving consumer health. However, as adding the extract increased syneresis and impaired sensory acceptance of the yogurt, investigations on applying encapsulated A. tequilana extract in synbiotic yogurt are recommended.

 
Ethical Considerations

Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.

Funding
The paper was extracted from the MSc thesis of Melika Farzaneh at Department of Food Science and Technology, Shahr-e-Qods Branch, Islamic Azad University.

Authors' contributions
Conceptualization, supervision and writing-review & editing: Vajiheh Fadaei, and Hassan Gandomi; Visualization and writing-original draft: Melika Farzaneh; Resources: Vajiheh Fadaei; Formal analysis and methodology: Hassan Gandomi. Investigation: All authors. 

Conflict of interest
The authors declare no conflict of interest.

Acknowledgments
The authors thank the Mabna Tashkhis Laboratory staff for their hospitality and technical assistance in this program. 

References

Alighazi, N., Noori, N., Gandomi H., & Akhondzadeh Basti A. A. (2021). Effect of ziziphora clinopodioides essential oil stress on viability of Lactobacillus acidophilus and bifidobacterium bifidum microencapsulated with alginate-chitosan and physicochemical and sensory properties of probiotic yoghurt. Iranian Journal of Veterinary Medicine, 15(2), 234-253. [DOI:10.22059/IJVM.2020.303329.1005092]

Amirdivani, S., & Baba, A. S. (2013). Rheological properties and sensory characteristics of green tea yogurt during storage. Life Science Journal, 10, 378-390. [Link]

Aryana, K. J., & Mc Grewa, P. (2007) Quality attributes of yogurt with lactobacillus casei and various prebiotics. LWT - Food Science and Technology, 40(10), 1808-1814. [DOI:10.1016/j.lwt.2007.01.008]

Bchir, B., Bouaziz, M. A.,Blecker, C., & Attia, H. (2019). Physico-chemical, antioxidant activities, textural, and sensory properties of yoghurt fortified with different states and rates of pomegranate seeds (punica granatum L.). Journal of Texture Studies, 6, 1-9. [DOI:10.1111/jtxs.12500][PMID]

Brand-Williams, W., Cuvelier, M. E., & Berset, C. L. W. T. (1995). Use of a free radical method to evaluate antioxidant activity. LWT - Food Science and Technology, 28(1), 25-30. [DOI:10.1016/S0023-6438(95)80008-5]

Beheshtipour, H., Mortazavian, A. M., Haratian, P., & Khosravi Darani, K. (2012). Effects of chlorella vulgaris and arthrospira platensis addition on viability of probiotic bacteria in yogurt and its biochemical properties. European Food Research and Technology, 235, 719-728. [DOI:10.1007/s00217-012-1798-4]

Cho, W. Y., Kim, D. H., Lee, H. J., Yeon, S. J., & Lee, C. H. (2020). Quality characteristic and antioxidant activity of yogurt containing olive leaf hot water extract. CyTA - Journal of Food, 18(1), 43-50. [DOI:10.1080/19476337.2019.1640797]

Crispin-Isidro, G., Lobato-Calleros, C., Espinosa-Andrews, H., Alvarez-Ramirez, J., & Vernon-Carter, E. J. (2014). Effect of inulin and agave fructans addition on the rheological, microstructural and sensory properties of reduced-fat stirred yogurt. LWT - Food Science and Technology, 42, 1-7. [DOI:10.1016/j.lwt.2014.06.042]

Dahikar, S. B., Bhutada, S. A., Vibhute, S. K., Sonvale, V. C., Tambekar, D. H., & Kastur, S. B. (2010). Evaluation of antibacterial potential of trikatu churna and its ingredients: An in vitro study. International Journal of Phytomedicine, 2, 412-417. [DOI:10.5138/ijpm.2010.0975.0185.02058]

de Carvalho, M. W., Arriola, N. D. A., Pinto, S. S., Verruck S., Fritzen-Freire, C. B., & Prudencio, E. S., et al. (2019). Stevia-fortified yoghurt: Stability, antioxidant activity and in vitro digestion behavior. International Journal of Dairy Technology, 72(1), 57-64. [DOI:10.1111/1471-0307.12559]

El-Said, M. M., Haggag, H. F., El-Dina, H. M. F., Gad, A. S., & Farahat, A. M. (2014). Antioxidant activities and physical properties of stirred yoghurt fortified with pomegranate peel extracts. Annals of Agricultural Sciences, 59(2), 207-212. [DOI:10.1016/j.aoas.2014.11.007]

Everett, D. W., & McLeod, R. E. (2005). Interactions of polysaccharide stabilizers with casein aggregates in stirred skim-milk yoghurt. International Dairy Journal, 15(11), 1175-1183. [DOI:10.1016/j.idairyj.2004.12.004]

Faraki, A., Noori, N., Gandomi, H., Banuree, S. A. H., & Rahmani F. (2020). Effect of auricularia auricula aqueous extract on survival of lactobacillus acidophilus la-5 and bifidobacterium bifidum bb-12 and on sensorial and functional properties of synbiotic yogurt. Food Science and Nutrition, 8(2), 1254-1263. [DOI:10.1002/fsn3.1414][PMID][PMCID]

Farvin, S., Baron, C., Skall N., & Jacobsen C. (2010). Antioxidant activity of yoghurt peptides: Part 1-in vitro assays and evaluation in omega-3 enriched milk. Food Chemistry, 123(4), 1081-1089. [DOI:10.1016/j.foodchem.2010.05.067]

Gaglio, R., Gentile, C., Bonanno, A., Vintaloro, L., Perrone, A., & Mazza, F., et al. (2019). Effect of saffron addition on the microbiological, physicochemical, antioxidant and sensory characteristics of yoghurt. International Journal of Dairy Technology, 72(2), 208-217. [DOI:10.1111/1471-0307.12569]

Guo, X., Xie, Z., Wang, G., Zou, Q., & Tang R. (2018). Effect on nutritional, sensory, textural and microbiological properties of low-fat yoghurt supplemented with Jerusalem artichoke powder. International Journal of Dairy Technology, 71(S1), 167-174. [DOI:10.1111/1471-0307.12404]

Hashemi, S. M. B., Amininezhad R., Shirzadinezhad E., Farahani M., & Yousefabad S. H. A. (2016). The antimicrobial and antioxidant effects of citrus aurantium l. flowers (bahar narang) extract in traditional yoghurt stew during refrigerated storage. Journal of Food Safety, 36(2), 153-161. [DOI:10.1111/jfs.12222]

Helal, A., & Tagliazucchi, D. (2018). Impact of in-vitro gastro-pancreatic digestion on polyphenols and cinnamaldehyde bioaccessibility and antioxidant activity in stirred cinnamon-fortified yogurt. LWT-Food Science and Technology, 89, 164-170. [DOI:10.1016/j.lwt.2017.10.047]

Huang, Y., Zhao, S., Yao, K., Liu, D., Peng, X., & Huang, J., et al. (2020). Physicochemical, microbiological, rheological, and sensory properties of yoghurts with new polysaccharide extracts from lactarius volemus fr. using three probiotics. International Journal of Dairy Technology, 73(1), 168-181. [DOI:10.1111/1471-0307.12653]

Iwalokun, B. A., & Shittu, M. O. (2007). Effect of hibiscus sabdariffa (calyce) extract on biochemical and organoleptic properties of yogurt. Pakistan Journal of Nutrition, 6(2), 172-182. [DOI:10.3923/pjn.2007.172.182]

Jin, H. J., Yang, H. S., Lee, S. C., & Huh, C. K. (2016). Quality and storage characteristics of yogurt containing lacobacillus sakei ALI033 and cinnamon ethanol extract. Journal of Animal Science and Technology, 58(16), 2-7. [DOI:10.1186/s40781-016-0098-0][PMID][PMCID]

Jozve-Zargarabadi, E., Fadaei-Noghani, V., & Fallah Huseini, H. (2020). Viability of starter bacteria and anti-oxidative activity of a functional yogurt containing silybum marianum seed extract. Applied Food Biotechnology, 7(3), 135-142. [DOI:10.22037/afb.v7i3.26998]

Jung, J., Paik, H. D., Yoon, H. J., Jang, H. J., Jeewanthi, R. K. C., & Jee, H. S., et al. (2016). Physicochemical characteristics and antioxidant capacity in yogurt fortified with red ginseng extract. Korean Journal for Food Science of Animal Resources, 36(3), 412-420. [DOI:10.5851/kosfa.2016.36.3.412][PMID][PMCID]

Karaaslan, M., Mustafa, M., Vardin, H., & Turkoglu, H. (2011). Phenolic fortification of yogurt using grape and callus extracts. LWT - Food Science and Technology, 44, 1065-1072. [DOI:10.1016/j.lwt.2010.12.009]

Kim, D. H., Cho, W. Y. ,Yeon, S. J., Choi, S. H., & Lee, C. H. (2019). Effects of lotus (nelumbo nucifera) leaf on quality and antioxidant activity of yogurt during refrigerated storage. Food Science of Animal Resources, 39 (5), 792-803. [DOI:10.5851/kosfa.2019.e69][PMID][PMCID]

Kowaleski, J., Quast, L. B., Steffens, J., Lovato, F., dos Santos, L. R., & da Silva, S. Z., et al. (2020). Functional yogurt with strawberries and chia seeds. Food Bioscience, 37, 100726. [DOI:10.1016/j.fbio.2020.100726]

Kudoh, Y., Matsuda, S., Igoshi K., & Oki, T. (2001). [Antioxidative peptide from milk fermented with Lactobacillus delbrueckii subsp. bulgaricus IFO13953 (Japanese)]. Journal of the Japanese Society for Food Science and Technology, 48(1), 44-50. [DOI:10.3136/nskkk.48.44]

Lamothe, S., Azimy, N., Bazinet, L., Couillard, C., & Britten, M. (2014). Interaction of green tea polyphenols with dairy matrices in a simulated gastrointestinal environment. Food and Function, 5(10), 2621-2631. [DOI:10.1039/C4FO00203B][PMID]

Liu, D. (2018). Effect of fuzhuan brick-tea addition on the quality and antioxidant activity of skimmed set-type yoghurt. International Journal of Dairy Technology, 71, 22-33. [DOI:10.1111/1471-0307.12395]

Lopez, M. G., Mancilla-Margalli, N. A., & Mendoza-Dıaz, G. (2003). Molecular structures of fructans from agave tequilana weber var. azul. Journal of Agricultural and Food Chemistry, 51, 7835-7840. [DOI:10.1021/jf030383v][PMID]

López, M. G., & Urías-Silvas, J. E. (2007). Agave fructans as prebiotics In: N. Shiomi, N. Benkeblia, & S. Onodera (Eds.),  Recent advances in fructooligosaccharides research ( pp 645-662).Kerala:Trivandrum. [Link]

Madhu, A. N., Amrutha, N., & Prapulla S. G. (2012). Characterization and antioxidant property of probiotic and synbiotic yogurts. Probiotics and Antimicrobial Proteins, 4(2), 90-97. [DOI:10.1007/ -012-9099-6][PMID]

Márquez-Aguirre, A. L., Camacho-Ruiz, R. M., Arriaga-Alba, M., Padilla-Camberos, E., Kirchmayr, M. R., & Blasco, J. L., et al. (2013). Effects of agave tequilana fructans with different degree of polymerization profiles on the body weight, blood lipids and count of fecal lactobacilli/bifidobacteria in obese mice. Food & Function, 4(8), 1237–1244. [DOI:10.1039/c3fo60083a][PMID]

Michael, M., Phebus, R. K., & Schmidt, K. A. (2010). Impact of a plant extract on the viability of lactobacillus delbrueckii ssp. bulgaricus and streptococcus thermophilus in nonfat yogurt. International Dairy Journal, 20, 665-672. [DOI:10.1016/j.idairyj.2010.03.005]

Mosiyani, Z. G., Pourahmad, R., & Eshaghi, M. R. (2017). Investigating the effect of aqueous extracts of basil and savory on antioxidant activity, microbial and sensory properties of probiotic yogurt. Acta Scientiarum Polonorum Technologia Alimentaria, 16(3), 311-320. [DOI:10.17306/J.AFS.2017.0509][PMID]

Muniandy P., Shori A. B., & Baba A. S. (2016). Influence of green, white and black tea addition on the antioxidant activity of probiotic yogurt during refrigerated storage. Food Packaging and Shelf Life, 8, 1-8. [DOI:10.1016/j.fpsl.2016.02.002]

Najgebauer-Lejko, D., Żmudziński, D., Ptaszek, A., & Socha, R. (2014). Textural properties of yogurts with green tea and pu-erh tea additive. International Journal of Food Science and Technology, 49(5), 1149-1158. [DOI:10.1111/ijfs.12411]

Narayana, N. M., & Gupta, V. K. (2013). Effect of total milk solid content adjusted by adding ultrafiltered milk retentate on quality of set mango yoghurt. International Journal of Dairy Technology, 66(4), 570-575. [DOI:10.1111/1471-0307.12081]

Narváez-Zapata, J. A., & Sánchez-Teyer, L. F. (2009). Agaves as a raw material: Recent technologies and applications. Recent Patents on Biotechnology, 3, 185-191. [DOI:10.2174/187220809789389144][PMID]

Oh, N. S., Lee, J. Y., Joung, J. Y., Kim, K. S., Shin, Y. K., & Lee, K. W., et al. (2016). Microbiological characterization and functionality of set-type yogurt fermented with potential prebiotic substrates cudrania tricuspidata and moru alba l. leaf extracts. Journal of Dairy Science, 99, 1-12. [DOI:10.3168/jds.2015-10814][PMID]

Oksuz, T., Tacer-Caba, Z., Nilufer-Erdil, D., & Boyacioglu, D. (2019). Changes in bioavailability of sour cherry (prunus cerasus l.) phenolics and anthocyanins when consumed with dairy food matrices. Journal of Food Science and Technology, 56 (9), 4177-4188. [DOI:10.1007/s13197-019-03888-2][PMID][PMCID]

O’Sullivan, A. M., O’Grady, M. N., O’Callaghan, Y. C., Smyth, T. J., O’Briena, N. M., & Kerry, J. P. (2016). Seaweed extracts as potential functional ingredients in yogurt. Innovative Food Science and Emerging Technologies, 37, 293-299. [DOI:10.1016/j.ifset.2016.07.031]

Park, K. B., & Oh, S. H. (2007). Production of yogurt with enhanced levels of gamma-aminobutyric acid and valuable nutrients using lactic acid bacteria and germinated soybean extract. Bioresource Technology, 98, 1675-1679. [DOI:10.1016/j.biortech.2006.06.006][PMID]

Pena-Rasmos, E. A., Xiong, Y. L., & Arteaga, G. E. (2004). Fractionation and characterization for antioxidant activity of hydrolyzed whey protein. Journal of the Science of Food and Agriculture, 84, 1908-1918. [DOI:10.1002/jsfa.1886]

Ramirez-Santiago, C., Ramos-Solis, L., Lobato-Calleros, C., Peña-Valdivia, C., Vernon-Carter, E. J., & Alvarez-Ramirez, J. (2010). Enrichment of stirred yogurt with soluble dietary fiber from pachyrhizus erosus l. urban: Effect on syneresis, microstructure and rheological properties. Journal of Food Engineering, 101(3), 229-235. [DOI:10.1016/j.jfoodeng.2010.06.023]

Ramnani, P., Costabile, A., Bustillo, A. G. R., & Gibson, G. R. (2015). A randomized, double-blind, cross-over study investigating the prebiotic effect of agave fructans in healthy human subjects. Journal of Nutritional Science, 4, 1 -10. [DOI:10.1017/jns.2014.68][PMID][PMCID]

Romero-Lopez, M. R., Osorio-Diaz, P., Flores-Morales, A., Robledo, N., & Mora Escobedo, R. (2015). Chemical composition, antioxidant capacity and prebiotic effect of aguamiel (agave atrovirens) during in vitro fermentation. Revista Mexicana de Ingeniería Quimica, 14(2), 281-292. [Link]

Sahan, N., Yasar, K., & Hayaloglu, A. A. (2008). Physical, chemical and flavour quality of non-fat yogurt as affected by a β-glucan hydrocolloidal composite during storage. Food Hydrocolloids, 22(7), 1291-1297. [DOI:10.1016/j.foodhyd.2007.06.010]

Sahnoun, M., Bejar, S., Daoud, L., Ayadi, L., Brini, F., & Saibi, W. (2019). Effect of agave americana l. on the human, and aspergillus oryzae S2 α-amylase inhibitions. Natural Product Research, 33(5), 755–758. [DOI:10.1080/14786419.2017.1408094][PMID]

Salazar-Leyva, J. A., Osuna-Ruizi, I., Rodriguez-Tirado, V. A., Zazueta-Patron, I. E., & Brito-Rojas H. D. (2016). Optimization study of fructans extraction from agave tequilana weber azul variety. Food Science and Technology Campinas, 36(4), 631-637. [DOI:10.1590/1678-457x.11216]

Sánchez-Bravo, P., Zapata, P., Martínez-Esplá, A., Carbonell-Barrachina, A., & Sendra, E. (2018). Antioxidant and anthocyanin content in fermented milks with sweet cherry is affected by the starter culture and the ripening stage of the cherry. Beverages, 4 (3), 57-69. [DOI:10.3390/beverages4030057]

Sengul, M., Erkaya, T., Sengul, M., & Yildiz, H. (2012). The effect of adding sour cherry pulp into yoghurt on the physicochemical properties, phenolic content and antioxidant activity during storage. International Journal of Dairy Technology, 65(3), 429-436. [DOI:10.1111/j.1471-0307.2012.00838.x]

Shokery, E. S., El-Ziney, M. G., Yossef, A. H., & Mashaly, R. I. (2017). Effect of green tea and moringa leave extracts fortification on the physicochemical, rheological, sensory and antioxidant properties of set-type yoghurt. Journal of Advances Dairy Research, 5(179), 2-10. [DOI:10.4172/2329-888X.1000179]

Shori, A. B., & Baba, A. S. (2013). Antioxidant activity and inhibition of key enzymes linked to type-2 diabetes and hypertension by azadirachta indica-yogurt. Journal of Saudi Chemical Society, 17(3), 295-301. [DOI:10.1016/j.jscs.2011.04.006]

Shori, A. B. (2013). Nutritional and therapeutical values of chickpea water extract enriched yogurt made from cow and camel milk. American Journal of Drug Discovery and Development, 3(2), 47-59. [DOI:10.3923/ajdd.2013.47.59]

Urías-Silvas, J. E., Cani, P. D., Delmée, E., Neyrinck, A., López, M. G., & Delzenne, N. M. (2008). Physiological effects of dietary fructans extracted from agave tequilana gto. and dasylirion spp. The British Journal of Nutrition, 99(2), 254–261.[DOI:10.1017/S0007114507795338][PMID]

Vasco, C., Ruales, J., & Kamal-Eldin, A. (2008). Total phenolic compounds and antioxidant capacities of major fruits from Ecuador. Food Chemistry, 111(4), 816-823. [DOI:10.1016/j.foodchem.2008.04.054]

Vital, A. C. P., Goto, P. A., Hanai, L. N., Costa, S. M. G., Filho B. A. A., & Verata, C. (2015). Microbiological, functional and rheological properties of low fat yogurt supplemented with pleurotus ostreatus aqueous extract. LWT - Food Science and Technology, 64, 1028-1035. [DOI:10.1016/j.lwt.2015.07.003]

Yadav, K., Bajaj, R. K., Mandal, S., Saha, P., & Mann, B. (2018). Evaluation of total phenol content and antioxidant properties of encapsulated grape seed extract in yoghurt. International Journal of Dairy Technology, 71(1), 96-104. [DOI:10.1111/1471-0307.12464]

Zamora-Gasga, V. M., Loarca-Pina, G., Vazquez-Landaverde, P. A., Ortiz-Basurto, R. I., Tovar, J., & Sayago-Ayerdi, S. G. (2015). In vitro colonic fermentation of food ingredients isolated from agave tequilana weber var. azul applied on granola bars. LWT - Food Science and Technology, 60, 766-772. [DOI:10.1016/j.lwt.2014.10.032] 

Zare, F., Boye, J. I., Orsat, V., Champagne, C., & Simpson, B. K. (2011). Microbial, physical and sensory properties of yogurt supplemented with lentil flour. Food Research International, 44, 2482-2488. [DOI:10.1016/j.foodres.2011.01.002]