Enhancing yogurt products’ ingredients: preservation strategies, processing conditions, analytical detection methods, and therapeutic delivery—an overview

Yogurt development to enhance ingredients and quality

Substantial information regarding the development (as well as manufacture) of yogurt was provided by Yildiz (2009), wherein various areas like manufacturing strategies, (yogurt) microbiology, biochemistry, and technology, followed by the functionality of bioactive dairy ingredients, as well as quality attributes, and other associated nutritional aspects. Indeed, yogurt development has been fueled by advances in biological sciences, which have enabled the yogurt processes to improve, as well as thrive across the various communities around the globe, especially places (where yogurt processes) with cultural/traditional heritage. However, in reviewing the effects that new technology has associated with the modern manufacturing process of yogurt, Das, Choudhary & Thompson-Witrick (2019) opined that in order to improve its marketability quality, it was pertinent that an ideal yogurt possessed an enhanced flavor and texture, and at the same time, has to be produced in such a way that the cost could be reduced through the better application of transit. Besides the increasing global consumption of yogurt, Das, Choudhary & Thompson-Witrick (2019) in their literature synthesis, identified key aspects of yogurt manufacture, namely cultures, fermentation, and styles. To make yogurt development complete, especially from the viewpoint of increasing the overall marketability, Das, Choudhary & Thompson-Witrick (2019) identified key stages, namely: yogurt manufacture, flavor, and texture, functional foods, made in transit, as well as prebiotics. To make the yogurt development process more robust and successful, Soukoulis et al. (2007), believed that the fermentation activities in yogurt manufacture especially at the industrial scale have to be effectively monitored and it is only by this that a consumer attractive and high-quality product output can be assured. To increase the successes in formulating promising innovative yogurt brands, food manufacturers and researchers, even in the recent years, have demonstrated the need to involve non-pathogenic bacterial strains/manufacturing ingredients. The utilisation of these ingredients, and their incorporation has aimed to enhance yogurt product’s physicochemical, nutritional and therapeutic properties, replacing the existing ones in the market with increased consumer safety. By assessing the quality and stability of Opuntia robusta parenchymatous tissue powder in set yogurt, Bernardino-Nicanor et al. (2021) revealed this novel ingredient abridged the vulnerability to syneresis without compromising the yogurt characteristics. Moreover, the formulation prepared using such powder (4.2 g water/g powder) obtained maximum water holding capacity (WHC), anti-oxidant activity with intense yellow-dark colour. By incorporating ground flaxseed (Linum usitatissimum) powder at different levels (1%, 3% and 5%) to yogurt, post-gel-formation, Ardabilchi Marand et al. (2020) revealed the addition of flaxseed powder markedly reduced the ratio of ω-6 to 3 fatty acids although an elevated level of polyunsaturated fatty acid, WHC, pH and viscosity occurred in the fortified yogurt. Mousavi et al. (2019) showed the incorporation of flaxseeds; 4% significantly enhance the viscosity, cohesiveness and the growth of Lactobacillus acidophilus more than 8.82CFU/mL during 13 days of cold storage.

A yogurt developed by Anuyahong, Chusak & Adisakwattana (2020) involved rice-berry (Oryza sativa L-a purple pigmented rice variety of Thailand) extract (RRE) that was utilized at the level of 0.125% to 0.5% w/w. These workers showed the rice-berry extract markedly enhanced the yogurt’s phenolic, peonidin-3-glucoside, cyanidin-3-glucoside, and anthocyanin content without adversely affecting the quality parameters. Almusallam et al. (2021) incorporated date palm spikelet’s extract (Phoenix dactylifera L.) from Khalas and Reziz varieties at different levels (0.5% and 1.0%) to set-type yogurt. The extract would enhance the yogurt texture properties, gel-matrix, WHC while curtailing the microbial count without altering the growth of lactic acid bacteria (LAB). Korkmaz, Bilici & Korkmaz (2021) used the maca (Lepidium meyenii) (@ 5%), propolis extract @ 0.05% and a combination of these additives to prepare yogurt. Such additive provided product with distinct colour and odour with reduced syneresis, which could be altered by varying their concentration. Zhang et al. (2019) showed that yogurt prepared by the incorporation of hot water extract of Moringa oleifera (Drumstick tree) (0.05%) elevated the antioxidant properties and LAB proliferation without affecting the quality parameters over 21 days.

The addition of cranberry (Vaccinium subg. Oxycoccus) pomace (0.25–0.75%) to milk before fermentation by Zygmantaitė et al. (2021) led to a marked increase in the size of protein particles, improved gel property and reduced syneresis in the resultant yogurt. The yogurt prepared to incorporate chia (Salvia hispanica) seeds (6%) and strawberries (Fragaria × ananassa) (7.1 ± 0.1 °Brix) (@ 12%) which exhibits good sensory acceptability. Further, the incorporation of chai seeds elevated the concentration of dietary fiber, PUFA, ω-3 fatty acid, crude protein minerals while maintaining the LAB and Bifidobacteria around 10⁷ and 10⁶ CFU g⁻¹ during storage of 35 days (Kowaleski et al., 2020). Hasneen et al. (2020) reported that yogurt was fortified with an aqueous extract of turmeric (Curcuma longa), marjoram (Origanum majorana) or sage (Salvia officinalis) at different levels ranging from 1% to 3% (w/w). Incorporating each herb extract at 1% (w/w) was sensorily acceptable, which enhanced total phenols, flavonoids and antioxidant activity. Moreover, Cais-Sokolińska & Walkowiak-Tomczak (2021) showed that the utilisation of restructured elderberry juice would exhibit good WHC (i.e., 94.4–96.4%) as compared to conventional yogurt.

Para-probiotic yogurt incorporated dead cells of Bifidobacterium lactis BB-12 and Lactobacillus acidophilus ATCCSD 5221 before fermentation was developed by Molaee Parvarei et al. (2021). These workers obtained a product with high WHC, viscosity and reduced syneresis. Such effect depicted the presence of cell components and exopolysaccharides. Huang et al. (2020) incorporated lipase enzyme along with LAB (Streptococcus lactis, Lactobacillus acidophilus, Lactiplantibacillus plantarum, Lacticaseibacillus casei subsp. rhamnosus) that markedly enhanced the free amino acids, with varying volatile compounds, and flavour of food matrix after organic acid production. Ma et al. (2021) isolated (n = 30) Bacillus coagulans strains from vegetable samples-an adjunct culture in preparing the functional yogurt with plenty of genes associated with carbohydrates transference and metabolism, volatile compounds including 2-nonanone, 2-heptanone, 2-hydroxy-3-pentanone and amyl alcohol. Jouki et al. (2021) considered it feasible to produce synbiotic freeze-dried yogurt powder especially by the exploitation of microencapsulation and cryopreservation of Lactiplantibacillus plantarum in alginate-skim milk microcapsules. Such powder would exhibit good solubility, amenable to produce reconstituted yogurt of same colour and viscosity. Cândido de Souza, Souza do Amaral & Lima da Silva Bernardino (2021) revealed that the incorporation of skim milk powder (SMP) markedly affected the fermentation process and physicochemical properties of concentrated Greek yogurt. The addition of 10% SMP in preparing Greek yogurt resulted in an elevated level of protein (6.38–6.61%), lipids, low-fat level (1.37–1.38%), with desirable sensory quality. de Campo et al. (2019) showed that, when zeaxanthin nanoparticles and nano-emulsion (12.5% v/v) were incorporated in the yogurt, the hydrophobic compounds would disperse in the hydrophilic matrix, to further protect the carotenoids during storage.

A summary of studies supplementing ingredients and formulations on yogurt quality is shown in Table 2, which include study aims/property targeted and key findings. For instance, Shori (2020) showed that by incorporating cumin (Cuminum cyminum) and coriander (Coriandrum sativum) into yogurt at different levels, the inhibitory action against α-amylase was possible but with high anti-oxidant activity during storage period. Carmona et al. (2021) using yellow-orange cactus pear pulp, maltodextrin and cladode mucilage ingredients, showed (pulp) pigment “indicaxanthin” with respective high yield and efficiency of 51.2% and 100% via Opuntia ficus-indica pulp (plus maltodextrin). Li et al. (2021a) studied the effect of corn transglutaminase modified Milk Protein Concentrate (MPC) on the texture properties of stirred yogurt, whereas Mohamed Ahmed et al. (2021) studied the effect of argel (Solenostemma argel Hayne) leaf extract on the physicochemical and antioxidant properties of set-yogurt. Tomato (Solanum lycopersicum) and carrot (Daucus carota) have also been used as supplementing ingredients in improving yogurt quality. For instance, Demirci et al. (2020) reported yogurt supplemented with hot break tomato (2.0%) resulted in superior anti-oxidant activity and total phenolic content, whereas Šeregelj et al. (2021) used freeze-dried carrot waste mixed with sunflower (Helianthus annuus) oil, involving prepared beads were homogeneously incorporated into yogurt at levels of 2.5 and 5.0 g/100 g. Carrot waste beads offered satisfactory protection to β-carotene during storage for 28 days at 4 °C. Other works like the utilisation of olive (Olea europaea) pomace derivatives on the bio-accessibility of yogurt (Ribeiro et al., 2021), effect of cheese whey spent and coffee ground powder on the rheological and functional properties of yogurt (Osorio-Arias et al., 2020), effect of bovine colostrum on the acidification rate and rheological properties of yogurt (Bomba et al., 2019), as well as effect of lentil flour on quality of yogurt (Benmeziane et al., 2021) are shown in Table 2. Freeze-dried yogurt with protective agents (Ismail, Aly & Atallah, 2020), impact of dietary fibres on the viscosity of yogurt (Salgado et al., 2021), effect of essential oil and chitosan on the shelf life and sensory quality of yogurt (Zedan, Hosseini & Mohammadi, 2021) are works also shown in Table 2.

Globally, there is elevated production and demand of yogurt with high functional traits and acceptance (Levy et al., 2021). However, non-dairy based yogurts seem restricted due to the limited technological-functional properties. However, Cui, Chang & Nannapaneni (2021) showed soya milk as an alternative to cow milk in preparing yogurt for individuals who suffer cow milk allergy without affecting the starter activity, microstructure, synesis and overall acceptability. Demïr, Simsek & Yıldırım (2021) prepared oat milk-based yogurt following three different strategies namely: (a) untreated raw oat milk, (b) ultra-violet coiled tube type assisted thermally treated oat milk (10-cycles; 77.67 J/ml, at 60 °C), and (c) thermally treated oat milk (63 °C for 30 min). These were employed to develop the oat-milk based yogurt, which were safely produced with the (above-mentioned) treatments (b) and (c). Elsewhere, other non-dairy based ingredients have been successfully exploited to formulate yogurt, e.g., oat protein concentrate (15% w/w), almond (8% w/w), emmer (Triticum dicoccon) flour (30% w/v), cashew milk with tapioca starch, hulled soybeans (7.9% w/v), coconut cream (20% w/v), brown rice (soaked or germinated), quinoa (Chenopodium quinoa) (35% w/v), as well as lupin (Lupinus angustifolius) protein isolate (2% w/v) (Montemurro et al., 2021).

Yogurts’ ingredient preservation strategies

Generally speaking, the essence of food preservation is to ensure there is consumer (food) safety at the top priority, which involves a continuous fight against microorganisms that make (food) unsafe, and cause (food) spoilage. This is what Devlieghere, Vermeiren & Debevere (2004) considered in their work that reviewed the new preservation technologies, in the context of possibilities and limitations. These workers understood that natural compounds, like chitosan, essential oils, nisin, and or lysozyme, could replace chemical preservatives, in order to realize ‘green label’ products. However, these workers also understood that the application of such natural compounds could be hampered given their interaction with food ingredients, as well as changes in the organoleptic properties when such are introduced into the (desired) food products. Also available includes the application of protective cultures, which Devlieghere, Vermeiren & Debevere (2004) considered as either able or unable to produce such antimicrobial compounds like bacteriocins in order to inhibit the growth of unwanted microorganisms.

Another useful aspect of consideration in preserving yogurt ingredients is by ensuring that there is an adequate understanding of the fermentation process involved, and this is what Agustinah, Warjoto & Canti (2019) have attempted to do for nonscience participants in their study. These workers employed yogurt making process to engage nonscience participants through an outreach program. The entire activity enabled Agustinah, Warjoto & Canti (2019) to realize the feasibility of equipping the nonscience people with useful tools, which cumulated to their understanding the importance as well as appropriateness of ingredients as well as associated microbiological concepts of yogurt fermentation, through which an improved control/modification of the fermentation process can be achieved. These workers reported that all participants were able to prepare the yogurt ingredients, engaged effectively in the fermentation process, and were able to participate in evaluating the resultant product’s sensory properties. Also among key aspects of preserving yogurt’s ingredients is the proper use of preservatives, which the food industry, according to Ueda et al. (2021), largely rely on additives. These workers understood that, for additives to be used, there must be approved by regulatory institutions, and should not change the food properties beyond the specific target initially/previously designed. However, such additives/preservatives could come with a number of side effects, which has attracted increased research interest towards the use of natural additives, and subsequently evolved to natural-based food additives. Further, it is believed that the use of natural preservatives would capture two important challenges, which include: (a) ensuring there is consumer safety with its usage; and (b) reducing the quantity of waste from degraded foods.

The utilisation of natural products and their derivatives to replace synthetic stabilizers, is growing as a means to curb milk fat and lactose. Development of cost-effective, non-toxic alternative yogurt production to replace synthetic ingredients is needful. A summary of strategies used to replace or reduce sucrose, milk fat and stabilizer in yogurt are presented in Table 3. Added to the diverse formulations, the ingredients that are utilised would also vary, like the instances that have been evidenced with monk fruit (Siraitia grosvenorii) and camel milk (Buchilina & Aryana, 2021), soy milk, sweeteners viz., honey, sucrose, sucralose, strawberry flavour (SF) (Rahmatuzzaman Rana, Babor & Sabuz, 2021), tagatose and sucrose (Torrico et al., 2019), sweeteners and pre-biotics (Costa et al., 2019), corn starch and κ-carrageenan utilised as stabilizers (Skryplonek et al., 2019), as well as aspartame, neotame and lactose (Kumari et al., 2018). A schematic diagram of yogurt preservative strategies, namely sucrose replacer, fat replacer, stabiliser replacer as well as preservatives, is shown in Fig. 3, which would be discussed below, succinctly.

Processing conditions to influence yogurt constituents

In understanding yogurt syneresis, Arab et al. (2022) articulated that the mechanisms of (syneresis) creation, as well as effective factors like additives, were essential to mention prior to even talking about processing conditions. These workers opined this because, from their literature synthesis, the main influencing factors driving yogurt syneresis would include formulation and processing parameters, with the latter dominating with such aspects as thermal processing, homogenization, fermentation, cooling, as well as transportation, which were discussed in detail. Another literature synthesis conducted by Gyawali & Ibrahim (2016) with reference to Greek yogurt, reported that there were aspects of acid whey production that would depend on this specific yogurt’s processing methods. These authors outlined the processing steps in the manufacture of Greek yogurt, which would differ reasonably from that of Arab et al. (2022). Specifically, the processing steps of Greek yogurt, according to Gyawali & Ibrahim (2016), would entail standardized milk subjected to homogenization and pasteurization, thereafter cooling to incubation temperature, the addition of starter culture, and thereafter further incubation. What is key is that, between when the standardized milk is subjected to homogenization and by the time it is to undergo pasteurization, there would be the addition of hydrocolloids, which has helped to fortify the Greek yogurt. These authors were able to articulate the chemical composition, source, as well as characteristics, and applications of selected hydrocolloids, which ranged between animal, and plant sources.

Earlier workers like Seth, Mishra & Deka (2017) reported that the functional and reconstitution properties of spray-dried sweetened yogurt powder could be influenced by processing conditions. In their study, these workers showed that the solubility of powder could be significantly (p < 0.05) affected by feed rate, whereas the wetting time of powder would increase significantly (p < 0.001) with spray-drying temperature. More so, these workers showed that bulk, tapped, and particle densities obtained various ranges. Overall, their work provided credible evidence that processing conditions specifically inlet air temperature and atomization pressure would cause some decreases in water activity as well as flow properties of the sweetened yogurt powder, with a positive effect on the feed rate. Previously, Koc et al. (2010) investigated optimum process conditions of plain yogurt to improve the viability and other quality attributes by way of spray drying. These workers employed a pilot-scale spray dryer to perform their drying experiments, and because optimization was sought, the process conditions employed a central composite rotatable design (CCRD). The resultant yogurt powder measured some physical properties (water activity, titratable acidity [lactic acid, %], and pH), and this approach helped to determine how spray-drying conditions affected the outcomes. These workers studied the morphological structure of the powder by scanning electron microscopy (SEM) analysis, alongside ensuring optimization settings like air inlet temperature of 171 °C, the air outlet temperature of 60.5 °C, and feed temperature of 15 °C. Spray drying of yogurt particularly at the optimum process condition was found to improve the survival of lactic acid bacteria, overall sensory acceptability, and with minimal color change with acceptable moisture content for the lengthened storage period.

Given the nature of yogurt constituents, Clark, Michael & Schmidt (2019) believed that to better understand the processing conditions, the rheological properties are key and should be given strong consideration. Besides the rudiments of rheology underscored by key facets like body, texture, mouthfeel, and microstructure, there are a number of associated styles that are marketed across various communities, enhanced by each having variations brought about by different fat contents, sugar-free, and flavor options. Clark, Michael & Schmidt (2019) further asserted that in yogurt, there are rheological changes arising from the ingredients, emerging from the use of milk from different species, optional additional dairy ingredients, the addition of hydrocolloids, use of exopolysaccharide-producing cultures, the addition of fruit, vegetables or herbs, alongside other functional ingredients. These workers further demonstrated that in yogurt, the rheological changes arising from processing, (as well as storage and handling) would be underpinned by such facets as base processing, fermentation, storage, sensory evaluation, as well as handling.

A summary of strategies used in the processing and their effects on yogurt constituents are compiled in Table 4. Recent published evidence show processing techniques like high-pressure processing, pulse electric field, extrusion, micro fluidization, sonication and others. Processing techniques contribute to enhance, for example, colloidal stability, microstructure, texture, particle size, and maintain stability of yogurt during storage (Lopes et al., 2019; Körzendörfer & Hinrichs, 2019; Demirci et al., 2020; Chanos et al., 2020; Levy et al., 2021). During the pre-processing of milk (pasteurization, homogenisation) and further transformation into yogurt, the milk undergoes physicochemical changes significantly affecting both nutritional and sensory parameters. Yamamoto et al. (2021) showed the fumaric acid produced by the S. thermophilus can function as a symbiotic element during the fermentation of yogurt to stimulate the growth of L. bulgaricus. Tribst et al. (2020) investigated the impact of homogenisation and stirring process on the sensory and physicochemical properties of stirred-type yogurt prepared from refrigerated, frozen and thawed sheep milk. The cold preservation (freezing or thawing) negatively affects the characteristic of yogurt, besides homogenisation and stirring not sufficient to evade poor sensory attributes. Advances in scientific knowledge, upgraded analytical instruments and novel methodologies make achieving the desired or improved nutritional and sensory parameters of yogurt possible.

Micro-particulate extrusion was used by Hossain et al. (2020) when investigating the effect of (micro-particulated) whey proteins on properties of reduced-fat plain-type stirred yogurt formulations. A strong correlation between particle size of whey protein and firmness/creaminess in yogurt was found. Micro-fluidization process was used by Demirkesen, Vilgis & Mert (2018) when investigating how it influenced different properties of yogurt formulation. The optimization of enzymatically (α-amylase; 0.015 g/100 ml) hydrolyzed potato (Solunum tubersum) powder with whole milk powder was utilised by Ahmad et al. (2019) to produce a high-quality yogurt. Whereas Lopes et al. (2019) investigated the effect of pressure (10–100 MPa) and temperature (25–50 °C) on fermentation kinetics of yogurt, Körzendörfer & Hinrichs (2019) sought to understand the effect of vibrations on the structural properties of yogurt by constructing a cylindrical tank of height 600 mm and placed a shaker in the bottom that resulted in the generation of the vertical vibration, which during processing at an industrial scale, would structurally disturb the (yogurt’s) gelation. Vieira et al. (2019) mentioned that, despite LAB with potential to produced yogurt under pressure (10–40 MPa at 43 °C), increased pressure significantly affected the fermentation process. Levy et al. (2021) prepared non-dairy yogurt-like product by the incorporation of potato protein isolate with high-pressure homogenisation (HPH). Besides the 200 MPa level to reduce the downstream potato protein isolate sedimentation, the stability against the phase-separation of yogurt increased with homogenisation pressure.

Elsewhere, Olarte Mantilla et al. (2020) conducted a systematic trial on consumers (n = 117) to understand the effect of particles addition on the sensory acceptability of yogurt. For that study, fabricate agar microgels were incorporated into nine yogurt samples at varying modules between 210 and 550 kPa; fabricated with 5% and 10% agar; particle size 30 and 100 μm; 2% and 5% particle concentration w/w. Sensory analysis indicated that yogurt comprising of 5% w/w particles were better accepted than those containing 2% w/w particles. Zhao, Fu & Li (2020) showed that adding alkali pre-treated curdlan (curdlan (1 g in 40 ml of 0.1 mol/L sodium hydroxide)) offered unique advantages to set-yogurt without adversely affecting the performance of the starter culture kinetics. Curdlan also enhanced the resistance of the yogurt against oscillation deformation and high shear stress (5–50 s⁻¹). Curdlan-a water-insoluble linear β-(1,3)-glucan, with a high molecular weight polymer of glucose, forms elastic gels when subjected to heating (65–80 °C).

Analytical methods to detect challenges affecting yogurt constituents

The development rapid and reliable analytical methods with sophisticated analytical techniques help the identification of novel components, adulterants, and storage-related changes in yogurt (Temizkan et al., 2020; Teixeira et al., 2021). High-tech analytical methods of interest specifically in the context of detecting the diversity of changes in yogurt products include gas chromatography–mass spectrometry (GC-MS), fourier-transform near-infrared (FT-NIR), fourier-transform mid-infrared (FT-MIR) spectroscopy, direct competitive fluorescence-linked immunosorbent assay (dcFLISA), sensitive fluorescence polarization immunoassay (FPIA), as well as reversed-phase high-performance liquid chromatography-diode array detection (RP-HPLC-DAD) (Griffiths, 2010; Zhou et al., 2019a; Chen et al., 2019; Paulo Vieira et al., 2020; Sharma & Ramanathan, 2021; Teixeira et al., 2021). Given the nature of adulterants and adulteration in food products of bioactive importance, Okpala (2019) understood that detecting them could technically pose challenges/difficulties. This is primarily because the adulterant may hold approximately same/similar chemical composition with the food product. The above-mentioned high-tech analytical methods are among those Okpala (2019) considered to operate at microscopic levels with specialist facilities able to detect (adulterants and adulteration) challenges, which in the context of this current work, could emanate with the likes of yogurt constituents.

Flavor profiling by GC-MS and sensory analysis of yogurt derived from ultrasonicated and homogenised milk (Sfakianakis & Tzia, 2017), determination of phthalate residues in different yogurt types using GCMS and associated related-intake estimations (Sireli et al., 2017), GCMS-based metabolomic investigation into changes in goat milk yogurt during storage (Sharma & Ramanathan, 2021), as well as simple and rapid quantitation of the key volatile flavor compounds in yogurt by headspace GCMS (Alonso & Fraga, 2001) are among the several works that have employed GCMS techniques in various yogurt products. Elaborating for instance on the work of Sharma & Ramanathan (2021), from the storage-related metabolic changes in goat milk yogurt during 28 days, GC-MS helped in the identification of 129 metabolites. Indeed, the metabolic data revealed that tyrosine, phenylalanine, aminoacyl-tRNA and tryptophan bio-synthesis metabolism were markedly altered during 14 days of storage, whereas, the propanoate metabolism and fatty acid bio-synthesis were affected during 14–28 days interval of storage.

FTIR together with chemometric analysis enables rapid detection of milk-fat or oil adulteration in yogurt, without any sample preparation (Temizkan et al., 2020). FT-NIR spectroscopy combined with multivariate analysis, is what (Grassi et al., 2013) used to monitor the lactic acid fermentation process to delineate possible deviations in quality parameters. Teixeira et al. (2021) showed how vibrational FT-NIR coupled with chemometric tools helped to detect goat’s yogurt and cheese adulterated with cow milk. Principal component analysis (PCA), Q-control chart and partial least squares-discriminant analysis (PLS-DA) helped to distinguish goat’s cheese and yogurt adulterated with 10%, 15% and 20% of cow milk. Specifically, the use of FT-NIR was robust in evaluating the authenticity of goat products. Comparison between the NIR spectra of authentic and adulterated samples of goat yogurt and cheese revealed spectra of yogurt and cheese with resembling behaviour yet with no visual difference. Specific to the yogurt spectra, two main bands, one at 5,171 cm⁻¹ and the other 6,881 cm⁻¹, were considered as associative with the O-H bonds.

Elsewhere, Paulo Vieira et al. (2020) used the RP-HPLC-DAD to study the biogenic amines in pro-biotic yogurt. The method appeared precise, and effective to rapidly detect biogenic amines (tyramine, spermine, putrescine, spermidine and cadaverine) even at a low concentration. Time of analysis and losses of biogenic amines were reduced the during sample preparation, which enhanced precision, recovery, and sensibility, especially in the lower concentration levels. Purification step by precipitation eliminated interferences present in the yogurt samples, with increased detecting sensitivity of biogenic amines. Elsewhere, the direct competitive fluorescence-linked immunosorbent assay (dcFLISA) was used by Zhou et al. (2019b) for ultrasensitive detection of aflatoxin M1 (AFM1) in pasteurized yogurt, which employed 150-nm quantum dot beads (QB) as the carrier of competing antigen. The proposed dcFLISA methodology was considered a novel strategy with ultrahigh sensitivity for AFM₁ detection, with very low detection limitation of 0.6 pg/mL for real pasteurized yogurt, considerably below the maximum permissible level of the European Commission standard. Chen et al. (2019) used sensitive fluorescence polarization immunoassay (FPIA) for the identification of di-isobutyl phthalate (DIBP) in yogurt. The tracers of different lengths of bridges were synthesised with hapten molecule (a) fluorescein isothiocyanate (FITC); (b) fluoresceinthiocarbamyl ethylenediamine (EDF); and (c), fluoresceinthiocarbamyl hexylenediamine (HDF). The tracer synthesized with a short bridge with hapten and fluorescein showed good fluorescence polarization immunoassay performance for Di-isobutyl phthalate. The FITC-labelled DIBP conjugate (DIBP-FITC) as the optimal tracer for FPIA of Diisobutyl phthalate. There was a good reproducibility for FPIA given by 77.80–115.60% average recovery from spiked yogurt samples.

Therapeutic role of yogurt—a modern drug delivery system

A summary of yogurt’s function/role as a modern drug delivery system are presented in Table 5. The various studies shown targeted ailment to include bowel movement or constipation (Khuropakhonphong et al., 2021), diabetes (Patil et al., 2021), oxidative stress (Rezazadeh et al., 2021), anthropometric and biochemical indices (Razmpoosh et al., 2020), endothelial dysfunction and glycemic indexes (Rezazadeh et al., 2021), hyperlipidaemia in pre-diabetic patients (Mostafai et al., 2019), as well as cardiometabolic and inflammation (Rezazadeh et al., 2020). As a target to prevent gastrointestinal disorders, yogurt continues to serve as a carrier of nutritional bioactive products or pharmaceuticals. Consumption of sugar-based yogurt can result in enamel demineralization, especially in individuals with poor oral hygiene. Shen et al. (2020) suggested the incorporation of food additives with anti-cariogenic properties, including casein phosphopeptide (CAP), amorphous calcium phosphate (ACP) or their combination (CPP-ACP) at a 0.5% level in yogurt that can assist in preventing enamel de-mineralization, and restore enamel subsurface lesion re-mineralization.

Probiotics can ferment non-digestible carbohydrates, which can produce short-chain fatty acids (SCFA) including butyrate, acetate and propionate in the colon. Chang et al. (2021) estimated the concentration of SCFA in yogurt fermented with combinations of probiotics strains including Lactobacillus acidophilus, Lactobacillus gasseri and Bifidobacterium bifidum. Yogurt prepared with the combination of (a) S. thermophilus + L. bulgaricus + L. acidophilus (b) S. thermophilus + L. bulgaricus + B. bifidum and (c) S. thermophilus + L. bulgaricus + L. gasseri obtained elevated levels of acetate in probiotic yogurt. Lim et al. (2020) isolated Limosilactobacillus fermentum KU200060 from the watery kimchi and the potential of probiotic yogurt was assessed for antibiotic susceptibility, aptitude to adhere to HT-29 cells, hazardous enzyme production, and gastric acid tolerance. The isolated L. fermentum strain appeared safe and stable in the gastric conditions, able to inhibit the biofilm formation by Lacticaseibacillus rhamnosus and S. mutans via restricting the formation of water-insoluble glucans.

Buchilina & Aryana (2021) supplemented monk-fruit extract in yogurt base (low dose, medium dose, high dose, metformin) to Wistar rats (n = 70) and assessed the blood glucose, oral glucose tolerance, insulin, HbA1c Levels and organ coefficient (liver, thymus, spleen, kidney) at stipulated intervals up to 42 days. The synbiotic yogurt fortified with monk fruit extract showed positive effects in rats induced with type-2 diabetes mellitus-the mechanism attributed to the reduced insulin resistance, defence function of β-cell, glucose control and improved intestinal microbiota homeostasis. Ban et al. (2020) observed the anti-diabetic effect on feeding synbiotic yogurt fortified with monk fruit extract in streptozotocin and a high-fat diet-induced type-2 diabetes Wistar rats model. Li et al. (2020) fed yogurt (0.5, 1, or 2 g/L) fortified with γ-aminobutyric acid (GABA) to induced type-2 diabetes mellitus mice for 12 weeks. Supplementation of yogurt with GABA @ 2 g/L could ameliorate insulin sensitivity. Elsewhere, Li et al. (2021b) showed the consumption of synbiotic yogurt prepared by the Bifidobacterium animalis species BB12 and konjac mannan oligosaccharides positively facilitated the faecal excretion and alleviated constipation in animal model.

The rutin is a dietary flavonoid obtained from fruits and vegetables that exhibits different clinical applications viz removal of toxin from the body. Acevedo-Fani et al. (2021) exploit rutin extracted form Japanese pagoda tree (Sophora japonica) with, ≥95%, and determine the gastrointestinal behaviour of yogurt enriched with casein-rutin co-precipitate (RuYO) and yogurt (unfortified) combined with rutin powder in a vegetable-based capsule (CtYO +Ru) in a semi-dynamic in-vitro digestion protocol. The RuYO obtained good rutin bio-accessibility as compared to CtYO + Ru in-vitro. The supplementation of high-fat diet; protein (26.2%); fat (34.9%); raw fibre (6.4%); carbohydrates (26.3%) and vitamin and minerals (5.8%) with yogurt to mice (5–6 old-week male/female rats) resulted in the reduction of the triglycerides and cholesterol in blood serum and liver. A marked reduction in the pro-inflammatory cytokines was observed in rats fed on a high-fat diet supplemented with yogurt (Siroli et al., 2021). Moreover, the consumption of yogurt, rich in acetate, enhanced the defensive function of intestinal epithelium (Chang et al., 2021).