Nutritional and functional properties of kefir: review

ABSTRACT

Kefir is a popular and indigenous fermented product that possess various health claims. Kefir grains with varied bacteria are utilized as starters for kefir production of popular genra including Lactobacillus, Leuconostoc, Lactococcus, and Acetobacter species. The complex microbial community in kefir produce various bioactive compounds owing to their metabolic activities. Kefir has various functional and therapeutic properties, which include immune system stimulation, lactose intolerance symptoms, cholesterol reduction, anti-carcinogenic and anti-mutagenic qualities. Several studies have shown anticarcinogenic, anti-microbial and synbiotic potential of kefir. Current review highlights the production technology, nutritional, functional and therapeutic potential of kefir. Furthermore, production strategies, kefir characteristics and probiotic potential are the limelight of the current review.

KEYWORDS:

• Kefir
• production
• probiotic potential
• therapeutic potential

Introduction

Kefir¹ is a fermented beverage made of milk, has been consumed for thousands of decades. It continues as a healthy food^[1,2]. Kefir comes from the Georgia Hills’ northeast corner and is reported to be at least 1000 years old. Kefir grains were initially passed down through the Caucasus tribes from era to era and were thought to be a source of family wealth. The people of this region may have found kefir fortuitously and consumed the healthy beverage for years.^[3] Kefir is a low-alcohol, acidic probiotic beverage made by fermenting milk at ambient temperatures.^[4] It’s decomposed by diverse bacteria and yeasts, including Lactobacillus sp, Lactococcus sp, Leuconostoc sp, and Acetobacter sp.^[2] It is unique fermented food comprises an intricate concerted relationship. These relationships exist among lactose fermenting and non-fermenting yeast and in lactic and acetic acid-producing bacteria and one whose microbiological factors depend on the provenance and agronomic method of the grains.^[2,3,5] The metabolic developments processes make kefir of probiotic strains as these are present in kefir grains.^[6] Kefir grains are tiny, unevenly formed granules that resemble broccoli. Kefir is typically made by injecting kefir grains into milk containing various microbial species such as bacteria and fungi and then fermenting it at 37° or room temperature for around 24 hours.^[7] Kefir comprises more than 50 genera of probiotic bacteria. These probiotic genera formed through lactic-alcoholic fermentation of milk using kefir grains. Kefir grains are inoculated into milk in a specified amount. The fermentation process begins under ideal nutritional and temperature parameters, leading to an increase in the number of microorganisms and numerous metabolites at the end of the cycle.^[8] Lactic acid bacteria (Streptococcus sp, Lactobacillus sp, Lactococcus sp, and Leuconostoc sp,) and yeasts (Candida, Kluyveromyces, Saccharomyces, and Pichia) are the significant components of kefir grains, which are sheathed in a polysaccharide usually known as protein matrix and kefiran.^[5,9] Aside from milk, several nondairy substrates have also been tried to create fermented functional beverages with distinct organoleptic properties, such as molasses and fruit and vegetable juices. These beverages are referred to as sugar or water kefir.^[10] Typically, water kefir grains which are distinct gelatinous particles containing probiotics, are used to make water kefir (WK). Water kefir can be a valuable source of probiotics, prebiotics, and antioxidants for vegans and anyone with dairy allergies or intolerances.^[11] Microorganisms in the fermented foods provide the health benefits along with the improvement of product characteristics. Numerous organic compounds, such as bacteriocins, antibiotics, bacteria, hydrogen peroxide, bioactive peptides, exopolysaccharides, ethanol, carbon dioxide, and other vitamins (B1, B12), and calcium peptides, and amino acids, are produced during the microbial fermentation of kefir beverage.^[12] The probiotic strain percentage varies in milk and water kefir grains, a brief illustration is presented in Table 1.

Table 1. Composition of milk powder kefir.

Bacteria and yeast	State or territory			Reference
Milk kefir grains
Kazachstania aerobia	Italy			Garofalo et al. (2015)
Kazachstania solicola	Italy			Garofalo et al. (2015)
Pichia fermentas	Taiwan			Wang et al. (2008)
Saccharomyces unisporus	Portugal, Taiwan			Wang et al.,2008
Saccharomyces cerevisiae	Brazil, South			Garofalo et al., 2015;
Lactococci Population (log(CFU/mL))	8.8 ± 0.0
Water kefir grains
Zymomonas mobilis	China			Cao et al. (2019)
Pseudomonas fragi	China			Azi et al. (2019)
Lactobacillus harbinensis	Romania			Angelescu et al. (2019)
Bifidobacterium tibiigranuli sp. Nov	Germany			Eckel et al. (2020)
Kefir Samples with the Addition of Milk Powder(Control)
	Kefir A	Kefir B	Kefir C	Reference
Protein Content (%)	3.1 ± 0.1	3.1 ± 0.1	3.1 ± 0.1	(Ziarno, M., et al., 2021) ^[Citation13]
WHC (%)	63.9 ± 0.4	66.1 ± 0.4	60.6 ± 0.3
Hardness (N)	1.35 ± 0.04	0.65 ± 0.02	0.96 ± 0.03
Adhesiveness (mJ)	7.60 ± 0.38	1.60 ± 0.08	3.00 ± 0.15

Table 2. Nutritional profile of the kefir.

Nutritional attributes	Nutritional components	Concentration	References
Vitamin mg/kg	Vitamin B1 Vitamin B5 Vitamin B2 Vitamin A Vitamin K	<10 3 <5.5 <1 <1	^[Citation35] ^[Citation41]
Amino acid mg/100 g	Threonine Valine lysine Isoleucine Methionine Phenylalanine Tryptophan	182 220 376 262 137 231 70	^[Citation42]
Mineral Macro-element (%)	Potassium Calcium Phosphorus Magnesium	1.65 0.84 0.30 1.46	^[Citation41,Citation42]
Micro-element (mg/kg)	Copper Cobalt Iron Molybdenum Manganese Zinc	7.32 14.6 92.4 0.33 23.3 3.10	^[Citation41,Citation42]
Ash	Ash contents	0.55%-0.66%	^[Citation43]

Kefirs constitute vitamins, essential amino acids that aid the body with healing and maintaining function. It also includes adequate proteins that are easily digested. There are various advantages of kefir consumption. Kefir has long been regarded as a drug to treat multiple ailments and disorders.^[14] A marketable mixed culture of kefir was appointed for fermentation of germinated barley flour. The results of phenolic extraction and high antioxidant and anti-diabetic properties in soymilk fermentation were mainly induced by Kefir culture.^[15,16] Hence, the kefir mediates fermentation and sprouting combined as a methodology for biocatalysis to enhance concentration and biocompatibility of phenol-related compounds and related gastrointestinal health, antioxidants, and anti-hyperglycemia. Therefore, the benefits of eating kefir barley are helpful for persistent oxidative stress and hyperglycemia management. Various microorganisms isolated from kefir represent bile salts in the gut and high survival against the low pH, as a result, it adheres to intestinal secretions. Furthermore, these microbes can produce antagonistic compounds such as antimicrobial peptides and organic acids, which can prevent pathogenic bacteria from adhering to the intestinal secretions.^[17]

The various bioactive components of kefir including polysaccharides and peptides have considerable capability for resisting the escalation and enhancing the death of tumor cells. This review paper explained production and fermentation strategies of milk kefir, which have microbiological and probiotic potential. Moreover, kefir is used in value added food products and this improve the nutritional and therapeutic potential of food product. Kefir grain has been linked to a variety of biological functions, including better digestion and antibacterial, hypocholesterolaemia, and antiheamorrhagic potential.

Production strategies

Kefir grains or mother cultures are the solitary means to make it (Figure 1). Kefir is made by a starter culture of kefir grain, which are little slimy white balls. A stable coalition of 40 to 50 prokaryotes and eukaryotes lives there.^[18] Lactic acid bacteria and acetic acid bacteria, which include participants of genera Leuconostoc, Lactococcus, and Lactobacillus are the utmost bacterial species and play a vital role in milk fermentation and kefir flavor.^[7]

Figure 1. Kefir grains.

1. On commercial level, kefir is prepared by following ways: (i) By the application of pure freeze-dried industrial kefir cultures to ferment milk, and (ii) Using the back slopping which is the “Russian method,” a series of fermentations that starts with kefir prepared with grains and later that the cultures were used as organic starter cultures for milk fermentation.^[19,20]

2. The procedure of making water (sugary) kefir is the same as milk kefir. It is based on fermentation of sugar solutions or sugary substrates rather than milk using appropriate kefir grains made of polysaccharides and bacteria. Based on existing research, water kefir grains (WKG) and traditional milk kefir grains (MKG) share comparable microbial properties, particularly for lactic acid bacteria and yeast species such as Lactobacillus, Leuconostoc, Kluyveromyces, Pichia, and Saccharomyces^[21]

Microbiological character of kefir

The actual microbial makeup of kefir grains is still a matter of debate. Grain-based milk kefirs have been shown to include more than 50 different yeast and bacterial species, which have been thoroughly examined elsewhere.^[17] On the basis of percentage of kefir grains to milk the microbiota of kefir grain can fluctuate, the temperature and time of fermentation (Both are inextricably tied to the botanical origin of kefir grains and, as a result, to climatic shifts.) and the most common substrate for fermentation is bovine milk, but supplementary choices include soy drinks, rice coconut, buffalo, sheep and goat.^[17,22] As a result of the various microbial consortiums that may form within kefir grain, it is possible to create a variety of kefir products with different microbiological, thermodynamic, physiochemical, nutritional, and sensory qualities.^[23]

The kind and frequency of microbial species in milk and water kefir, however, might differ based on the carbon and energy sources that are available for fermentation.^[10] It is reported that kefir grains can adjust to new carbon sources, which can impact their granulation, microbial development, and the microbiological characteristics of the finished beverage. Generally speaking, selective pressure is seen at the species level. For example, the metabolism of the Saccharomyces species is stimulated, which raises the alcohol content in water kefir beverages.^[24]

Fermentation process

The inoculation of grain directly to liquid is a traditional method. Before being inoculation with 2.5–10.5% (typically 5%) kefir grain, raw milk is heated and cooled until 19–25°C. After fermentation of 18–24 hours at 20–25°C milk is sieved to separate the grains and the sieved grains can be dried at 37°C or room temperature and hoarded at low temperature for use in the next inoculation operation. Before being drunk, kefir is stored at 4°C for a short period while.^[25] The traditional process for kefir production has been presented in the Figure 2.

Figure 2. Traditional process for kefir production.

Throughout the world, people drink sugary kefir, a traditional homemade beverage. Brown sugar, which is used to make sugary kefir, is Pasteurised and then homogenized with water. The product that has been pasteurized is combined with kefir grains, cooled, and allowed to ferment for about 24 hours at a temperature of 25 to 30 degrees Celsius. After that, the kefir is packaged after being filtered to remove the grain content. The product is transported and stored to the final customer without disrupting the cold chain.^[21]

Probiotic potential

The word ‘’probiotics” originated from Greek word “probios,” which means “for life,” but according to FAO/WHO latest definition’’ they are living organism, when supplied in suitable proportion deliver well-being advantages to the consumer.” Probiotics include assortment of microorganism such as bacteria, molds and yeast strains. The most customary strains of probiotic are Lactobacillus sp. and Bifidobacterium. Nonbacterial organisms such as Saccharomyces cerevisiae and Saccharomyces boulardii are widely accessible as probiotic supplements. A successful probiotic bacteria meet specific characteristics, including being safe, alive, and able to survive in the gastrointestinal tract.^[26] Potential probiotic yeasts can be extant in various fermented foods and beverages, through kefir existence among the most common. It’s formulated by fermenting milk exploitating yeast and bacterial strains as a starter culture that adheres to the polysaccharide matrix (106–108 cfu/g). Kefir has gained acceptance in Russia and the former Soviet states over the last era. Its popularity continues to expand, and nations such as Malaysia are opening to commercialize kefir production.

Fermentation of water kefir

Water kefir grains are often used as an inoculum in water kefir fermentation. Several issues related to specific nature of grains and significance of grains during water kefir fermentation remained unanswered.^[27] Determination of density and microbial colonizing, as well as their role during fermentation of water kefir, the researcher was able to be better described the features of the grains of water kefir. The latter was achieved by using a modeling method to characterize the generation of wet mass (expressed as EPS generated) in water kefir grains as a time function during the fermentation process. Fermentation of Water kefir is often done anaerobically, but it can also be done aerobically.^[28] The presence of oxygen in an aerobic process causes acetic acid bacteria to proliferate after many back slopping processes, resulting in the formation of significant quantities of acetic acid. The short-term impacts, on the other hand, have yet to be examined. In fermentation of water kefir, the most usual substrate is sucrose and it is converted to acetic acid, mannitol, lactic acid, glycerol, ethanol and a range of fragrance components by the microbes.^[29,30] The major microorganisms of water kefir are yeasts, acetic acid bacteria (AAB), bifidobacterial and lactic acid bacteria (LAB).^[31,32] From all these, selected microorganisms possess probiotic qualities (Romero-Luna et al., 2020). The important microorganisms are Lacticaseibacillus paracasei (earlier known as Lactobacillus paracasei), Lentilactobacillus hilgardii (earlier known as Lactobacillus hilgardii), Saccharomyces cerevisiae and Liquorilactobacillus nagelii (earlier known as Lactobacillus nagelii).

Characteristics of kefir

Water kefir is a naturally carbonated, mildly acidic fermented beverage. It is commonly made by fermenting a sugar solution, often including fresh or dried fruits (and occasionally a lemon slice), using water kefir grains.^[33] Milk kefir is made by inoculating kefir grain into whole milk, partially skimmed milk, or skimmed milk, that are made up of gelatinous as well as casein colonies of microorganisms (yeast and bacteria) that coexist in a synergistic relationship. The following are some of the kefir’s characteristics.

Nutritional characteristics

The main bacterial species in the complex Water kefir grain community are lactic acid bacteria, especially those belonging to the Lactobacillus species. Acetic acid bacteria play a supporting role in the presence of oxygen. Among the dominating members are yeast, including both Saccharomyces and non-Saccharomyces species. Apart from using distinct substrates, the bacterial communities in sugar water kefir and milk kefir are similar (LAB predominates), however the yeast communities might differ greatly (milk kefir mostly contains non-Saccharomyces yeasts).^[34] Water kefir (Sugary) has been demonstrated to be helpful as a substitute probiotic source for vegans or people who are lactose intolerant. Numerous bacteria found in sugary kefir have been shown to exhibit probiotic qualities, including adherence to the mucosa through intestinal lumen penetration, colonization, and pathogen inhibition.^[21] Milk kefir is usually made by fermenting milk by inoculation of kefir grains and mainly contain fat <10%, protein 2.7% and lactic acid 0.6%. This nutrition status depends upon milk.^[20] Kefir beverages is manufactured from semi-skimmed, nonfat milk, and full-fat, with low-fat kefir supplements becoming increasingly popular. Kefir was traditionally made by microbial fermentation of milk of cows, now recent findings claim that it can be made with milk from, camels, goats, sheep, and buffalo.^[3,5] The kefir beverage made from different cattle may have minor nutritional differences. Kefir is high in vitamins such as vitamin B1, B5, C and B5, as well as vital amino acids and minerals, all of these provide advantages to healing, fitness, and homeostasis. The source of milk and microbial flora added in kefir preparation have great effect on the vitamin content. Propionibacterium pituitosum and Propionibacterium peterssoni generate vitamin B12, while Propionibacterium Shermanii and Freudenreichii subsp. aided in the creation of greater amount of vitamin B6.^[35] Kefir is great source of amino acids valine, isoleucine, methionine, serine, threonine phenylalanine, tryptophan, alanine and lysine that play an important role in the CNS (central nervous system). Proteins that have been partly digested such as casein is also present in kefir that helps in its absorption and digestion by the body^[36] Protein, carbohydrate, and lipid metabolism are all affected by the necessary amino acids found in considerable levels in kefir, as well as immune response maintenance, body weight regulation, and energy balance. Amino acids protect elderly people from impairment and help them live longer and healthier lives.^[37,38] Patients with severe traumatic brain injury benefited from the branched-chain amino acids contained in kefir^[38] For people who have trouble digesting large amounts of lactose, the main sugar found in milk, kefir is an excellent choice. Kefir’s fermentation process results in a decrease in lactose concentration and an increase in β-galactosidase.^[39] It was determined that LAB activity was the cause of the biogenic amines found in kefir samples. Tyramine was discovered to be a prevalent biogenic amine, while putrescine, cadaverine, and spermidine were detected in every sample.^[40] The nutritional portrayal of the kefir has been presented in Table 2.

Table 3. Therapeutic potential of kefir.

	Effects	Dose	Reference
Therapeutic character of Kefir
Hypocholesterolemic	Lessened fat storage in adipose Reduced obese Reduce total cholesterol Low-density lipoprotein (LDL) Low serum triacylglycerol (TG)	140–141 mg/kg BW/day	^[Citation51]
Antimicrobial	Stifled aflatoxin B1 Exhibit anti-biofilm formation to prevent tooth decay	7–10% (v/v)	^[Citation53,Citation54]
Antiheamorrhagic	Diminution in ulcer size Lactic and acetic acid production Production of granulation tissue and re-epithelialization Fibroblast growth	12 weeks treatment	^[Citation55–57]
Anti-Diabetic	Lower plasma glycemic levels, Higher glutathione peroxidase Essnhanced insulin discharge		^[Citation58,Citation59]

Table 4. Enrichment of kefir grains with different extracts.

Extract	Enrichment	Effect	Reference
Kefir + Linum usitatissimum (flaxseed)	1.0% (w/v)	↑ Viability and Growth	^[Citation45]
Kefir + hazelnut milk	25.0–50–75% (w/v)	↑ Viability and Growth	^[Citation46]
Kefir + black and green tea	2.0–4.0% (w/v)	↑ Antioxidant activities ↑ sensory characteristics	^[Citation71]
Kefir + vegetable juices	4% (w/v)	↑ Alcohols ↑ Antioxidant activities ↑ Volatile compounds	^[Citation47]
Kefir + pomegranate juice	15% (w/w)	↓ pH values ↑ Acidity ↓ Colorimetric parameters	^[Citation72]
Kefir + honey	3% (w/w)	↓ Acidity ↓ Colorimetric parameters ↑ Viscosity ↑ Sweetness	^[Citation73]

Enrichment and fortification in kefir

Due to their GRAS (Generally Recognized as Safe) status, medicinal herbs as extracts or essential oils are safe for use in food, including dairy products.^[44] The pharmacological constituents in these plant-derived substances are usually a complex matrix of phytochemical substances. Several studies have shown that adding phytoconstituents to kefir can boost its health benefits. These are the following fortified and enriched food products. Table 4 showed enrichment of kefir grains with different extract.

Linum usitatissimum (flaxseed)

Linum usitatissimum (flaxseed) extract that are rich in fiber,-linolenic acid and lignans had an in vitro impact on the expansion and survival of kefir-isolated lactic acid bacteria. The growth of Lactobacillus plantarum (KCTC3105) Lactobacillus bulgaricus (KCTC 3635), Lactobacillus brevis (KCTC 3102), and Lactobacillus kefiranofaciens (DN1) was significantly higher after treatment with crude flaxseed extract as compared to the control.^[45]

Hazelnut milk

The infusion of hazelnut milk to kefir drink (25%, 50%, and 75%) enhanced its nutritional qualities, organic acids composition, and kefir microbe survival during storage. In kefir samples, hazelnut milk (50–75%) had a boosting impact on the improvement of lactobacilli and lactococci. In addition, there was a spike phenolic compounds and antioxidant capacity.

In terms of organic acids, fortification with hazelnut milk resulted in a decrease in lactic and citric acid content while dramatically boosting malic and acetic acid levels.^[46]

Fruit juices

The antioxidant properties of kiwi and pomegranate juices is high. After fermentation, esters compounds were found in increased concentrations, particularly in grape, pomegranate, and apricot. The findings also suggest that kefir-like fruit-based drinks (KLB) having high nutritional and functional qualities could be developed.^[47] Fermented beverages based on melon, onion, strawberry, carrot, fennel, and tomato juices have similar results as the back slopping fermentations were performed by water kefir bacteria. The most microbes were found in melon juice. Lactic fermentation took place in almost all of the juices. Alcohol concentration rises, whereas aldehyde concentrations diminished. The use of papaya juice as the main substrate for fermentation by two lactic acid bacteria yielded positive results; both strains produced a considerable amount of volatiles with roughly similar modifications. The reduction in pH was 0.05 units. L. acidophilus was observed to be lower than L. plantarum because the L. plantarum function is highly dependent on the presence of organic acids, especially lactic acid.^[48]

Therapeutic potential of kefir

Kefir has a wide variety of therapeutic benefits due to the existence of several components of the Antibacterial spectrum as presented in the Table 3. The presence of antibacterial compounds and metabolic finished products formed by starter cultures are allied to the antibacterial effect of fermented milk products. Kefir has a great bacteriostatic effect on gram negative bacteria than it does on Gram-positive bacteria, but it has a weaker bactericidal effect.^[49]

Hypocholesterolemic

Hypercholesterolemia is a hazard for heart disease and can result in mortality.^[50] Kefir powder at 0.1% to 0.2% lessened fat storage in adipose and hepatic tissues of obese mice fed a high-fat diet (HFD). In mice, kefir reduced obese or body weight while also lowering total cholesterol (TC), low-density lipoprotein (LDL) and serum triacylglycerol (TG). In mice, four weeks of kefir (140–141 mg/kg BW/day) treatment reduced fatty liver condition by lowering TG and TC levels^[51]

Antimicrobial

Kefir has a sturdier antibacterial impact than traditional antibiotics like ampicillin against various pathogens, including Salmonella enteritidis, Escherichia coli, and Staphlococcus aureus.^[52] Its carbohydrate content is accountable for this impact. The antibacterial activity of kefiran, Suspension of kefir, and kefir grains, a polysaccharide that are soluble in water are found in the grains of kefir, was investigated against several bacterial and fungal infections. Streptococcus faecalis KR6 and Fusarium graminearum CZ1 showed the highest activity. Aflatoxin is a dangerous chemical that is created in grains stored for longer period and causes liver cancer, thus it must be monitored to ensure that it is safe. At 7–10% (v/v), kefir stifled aflatoxin B1 production and Aspergillus spore development.^[53] Tooth decay is caused by the microorganisms Streptococcus sobrinus and Streptococcus mutans. Lactobacillus strains derived from kefir (Lactobacillus kefiranofaciens DD2) exhibit anti-biofilm formation and growth restriction against these microorganisms.^[54]

Antiheamorrhagic

A wound is caused by the skin being opened, cut or broken by physical harm. The insertion of bioactive substances, such as lactic and acetic acid produced by bacteria, was found to elucidate the efficacy. The relationship between active ingredient content and probiotic therapeutic efficacy was deemed to be shaky, and more research is needed. Wounds treated with L. acidophilus cured faster after being burned in the rat than treatment of wound with Eucerin ointment. L. acidophilus is thought to work by speeding the production of granulation tissue and re-epithelialization through its anti-inflammatory properties.^[55] In diabetic foot ulcer (DFU) patients, 12 weeks of kefir treatment resulted in a considerable diminution in ulcer size.^[56] In tandem with activation fibroblast growth (BGF) that is a basic mesenchymal potent stimulus, kefir increased migration and proliferation of human dermal fibroblast (HDF) cells, transforming growth factor-1 (TGF-1), and reduced IL-1 expression (bFGF). Kefir’s bacteriostatic action reduces the growth of Pseudomonas aeruginosa and Staphylococcus aureus, resulting in speedier burn wound healing.^[57]

Anti-Diabetic

Kefir undoubtedly illustrates potential for the obesity handling and accompanying disorders of metabolic.^[58] Infusion of goat milk kefir as well as black rice extract has an anti-diabetic effect equivalent to that of glibenclamide. Furthermore, Diabetic rats given soy milk and goat milk kefir showed anti-diabetic properties, as seen by lower plasma glycemic levels, higher glutathione peroxidase (GPx) action, and enhanced insulin discharge.^[59]

Intestinal flora modulation

It has until now to be determined that athletes use kefir as a supplement. The ability of kefiran to modify the intestinal and gastrointestinal microbiota of BALB/c rodents by escalating Bifidobacteria colonies while changing Lactobacillus populations offers more signal for kefir’s gut microbiota modification impact.^[60] Shigella flexneri was prevented from rationalizing into the inflammatory response and human intestinal epithelial cells was reduced by following a pre-treatment with a microbiological combination made up of yeast and bacteria extracted from kefir.^[61]

Kefir beverages as a dietary supplement

In current situation of COVID-19 epidemic, which is mainly happen due to SARS-CoV-2, has impaired billions of people all over the world, and humanity is still working to find a remedy.^[62] Kefir is well known for protective the liveliness of microbial strains while also offering probiotic properties.^[2] Probiotic strains found in satisfactory concentrations in kefir have been postulated as useful agents for advancing immunity and used as a biological shield to help normalize the pandemic of COVID-19 hype^[63] because they contain immunomodulating compounds like peptidoglycans, nucleic acids and lipoteichoic acid, also promoting the development of antiviral agents like hydrogen peroxide, lactic acid, and bacteriocins. Probiotic strains have been suggested as useful nutraceuticals for preventing viral infections.^[64] Kefir bacteria create initial components and secondary metabolites such as antimicrobial peptides, polysaccharides, CO2, organic acids and bacteriocins, during the milk fermentation bioprocess. Plentiful therapeutic metabolites have been demonstrated to conquer the growth of spoilage bacteria and harmful microbes in food storage, acting as natural preservatives.^[65] Especially, in viral activity bioactive peptides are conveyed to sort out the situation, boosting the immune system of consumer by causing viral attachment to be disturbed.^[64,66] Similarly, probiotic bacteria’s bacteriocins can be explored as inhibitors of main targets revealed during metabolite profiling for anti-COVID-19 treatments^[64,67]

Limitations and safety of milk and water (sugar) kefir

Kefir is a well-defined due to its foremost health benefits as a good preparatory point of microorganisms, there are numerous limitations to kefir usage. These negatives are largely attributable to its high cholesterol level and the potential for allergic reactions. Adapting to nondairy sources of energy, as demonstrated by sweet kefir, could be another approach to receive the favorable health effects of kefir. Solution of brown sugar is the most common alternate foundation for kefir nowadays, and sugar kefir is the result. Yeast species such as Kluyveromyces pichia, Leuconostoc, Saccharomyces and Lactobacillus are found in sugary kefir, which has a microbial association that is comparable to that of conventional milk kefir fermentation. Sugary kefir was discovered to be more beneficial than milk kefir in changing the mice lipid profile. Microorganisms presented the optimum development on melon extract. Compound that is highly volatile in strawberry, onion juices, melon and terpenoids is esters, this is in large amount in carrot. Apart from enhancing the aroma of kefir, strawberry tomatoes, onion extracts were contributed to its ample effect regarding antioxidant.^[47] The dairy business has always been concerned about safety and quality control of kefir material. However, the safe use of kefir has received little attention. Pathogens use hemolysis as a virulence factor, and the first safety metric to be investigated in vitro was bacterial hemolytic activity. Antibiotic sensitivity is crucial factor for safety.^[68] Microorganism that is beneficial in technology of dairy are Lactobacilli (yogurt, fermented milk, cheese). Streptomycin, clindamycin, erythromycin, tetracycline, gentamicin and ampicillin were known to be vulnerable to L. kefir strains that did not produce α or β hemolysis. Both gram-positive and gram-negative bacteria were inhibited by L. kefir strains. Aflatoxin G1 (AFG1) is the most hazardous pollutants found in nuts, and it can be harmful to your health. As a result, AFG1 reduction is most important in safety for food concerns. The use of kefir grain has a substantial impact on pistachio nut AFG1 decontamination. The enhanced biological detoxification approach utilizing 70°C treated kefir grains might be used to remove AFG1 on a regular basis.^[69] Enterococcus durans strains were found to inhibit gram-negative and gram-positive bacterial infections. Such bacteria demonstrated similar adhesion strength to mucins and were able to tolerate gastrointestinal circumstances that were simulated. E. Duran’s strains were shown to have great effect regarding anti-inflammation, as evidenced by substantial flagellin-induced Caco-2 cell response suppression. The findings demonstrated that Consumers are not at risk from E. Duran’s, and it has the competence to be a part of a balanced diet and a font of probiotics.^[70]

Conclusion

Lactic acid bacteria and acetic acid bacteria, which include participants of genera Leuconostoc, Lactococcus, and Lactobacillus are the most common bacterial species and play an important role in milk fermentation and kefir flavor. Kefir mainly contain fat <10%, protein 2.7% and lactic acid 0.6%. Kefir has a wide variety of therapeutic benefits due to the presence of several components of the Antibacterial spectrum. Adapting to nondairy sources of energy, as demonstrated by sweet kefir, could be another approach to receive the favorable health effects of kefir. Solution of brown sugar is the most common alternate foundation for kefir nowadays, and water or sugar kefir is the result but still more research is required in this field for understanding the detailed therapeutic mechanism of kefir. Some researchers are exploring the potential therapeutic applications of kefir and its probiotic content in the prevention and management of certain health conditions. Future applications may involve kefir being used as an adjunct therapy in clinical settings.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. University Centre for Research & Development, University School of Business, Chandigarh University, Gharuan, Mohali, Punjab, 140413, India.