Health Effects of Certain Fermented Foods

Health Effects of Certain Fermented Foods: History

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Fermented foods refer to beverages or foods made by carefully regulated microbial growth and the enzymatic conversion of dietary components. Fermented foods have recently become more popular. Studies on fermented foods suggest the types of bacteria and bioactive peptides involved in this process, revealing linkages that may have impacts on human health. By identifying the bacteria and bioactive peptides involved in this process, studies on fermented foods suggest relationships that may have impressions on human health. Fermented foods have been associated with obesity, cardiovascular disease, and type 2 diabetes.

fermentation
fermented foods
bioactive compounds
health
microorganisms

1. Introduction

Fermentation is a food processing technique, and its origins date back many centuries. The existence of fermented products has been demonstrated to be started in India, Iraq, and Egypt in the years BC [1]. The definition of fermentation according to the International Scientific Probiotic and Prebiotic Association (ISAPP) is “foods made through desired microbial growth and enzymatic conversions of food components”. Fermentation has been used by humans for as long as recorded history to preserve and modify food, resulting in more stable and varied food with distinctive organoleptic, sensory, and functional features [2]. Due to their distinctive flavors, fermented foods are being produced and consumed in greater quantities. There has also been a scientific concentration on the health benefits of fermented foods and their components [3]. In the fermentation procedure, microorganisms, specifically bacteria, yeasts, and mycelial fungus, as well as their enzymes, produce fermented foods. Milk, cereals, vegetables, fruits, legumes, meats, and products are food groups used in fermentation [4].

Food fermentation’s main purposes are to increase food safety and lengthen shelf life; additionally, fermented foods have grown to be known for their positive effects on health [5]. Foods that have undergone fermentation may produce bioactive compounds as byproducts of the process, and fermented foods may contain live microorganisms that have health benefits [6]. The main metabolites and microorganisms involved in food fermentation may be divided into categories: alcohol, carbon dioxide (from yeast), propionic acid (from Propionibacterium freudenreichii), lactic acid (from lactic acid bacteria (LAB) from genera such as Lactobacillus and Streptococcus), acetic acid (from Acetobacter), ammonia, and fatty acids (from Bacillus and molds) [7]. The metabolites produced by the fermenting organisms limit the expansion of spoilage, and pathogenic organisms during food fermentation extend the shelf life of perishable foods [8]. During fermentation, macronutrients are broken down, and digestion is facilitated. Many fermented foods include probiotic-potential bacteria in them [5]. Probiotics are defined in the FAO/WHO report as “Live microorganisms which when administered in adequate amounts confer a health benefit on the host” [9]. According to the ISAPP, these concentrations of probiotics can vary daily from 100 million to over a trillion CFU. The majority have been studied at concentrations of 1 to 10 billion CFU/d [10]. Fermented foods may serve as probiotic carriers, effectively delivering the probiotic to the host and conferring health advantages [11]. Although there may be a fermentation process involved, consumed fermented foods may not contain live bacteria. The term “probiotic” is only used when a product has clearly shown health advantages brought about by the action of well-defined and characterized living microorganisms [2]. The metabolic activity of microorganisms during fermentation results in a number of biochemical alterations that have impacts on the nutritive and bioactive qualities of fermented foods. The bioactive components showing health benefits include exopolysaccharides, bioactive peptides, phenolic compounds, short-chain fatty acids (SCFAs), conjugated linoleic acid (CLA), and γ-aminobutyric acids (GABAs) [12]. Fermented foods and their components can have many health effects such as antioxidant, antidiabetes, anti-inflammatory, anti-hypercholesterolemic, and microbiota modulation effects [13,14,15,16].

2. Fermented Dairy Products

Milk is an important source of macro- and micronutrients. Protein, conjugated linoleic acid, calcium, riboflavin, and phosphorus are macro- and micronutrients that are commonly found in milk. These nutrients have impacts on health and diseases [17]. Milk proteins (whey and casein) have positive effects on satiety and body weight control; have hypotensive, antimicrobial, anti-inflammatory, anticancer, and antioxidant effects; and cause insulin release and glucose regulation [18]. Many fermented products such as yogurt, cheese, and kefir are obtained via the fermentation of milk. In the production of fermented milk products, LAB play a crucial role [19]. Milk fermentation using yeasts, propionibacteria, and LAB may result in the synthesis or increase in the number of bioactive compounds that show some health benefits. These include vitamins, CLA, exopolysaccharides (EPSs), GABAs, bioactive peptides, and oligosaccharides [20]. For example, lactic acid bacteria and propionibacteria can increase the amounts of B₁₂ and folic acid in fermented milk products [21,22,23]. In addition, the fermentation of lactic acid in milk reduces the amount of lactose, which may make fermented dairy products tolerable for people with lactose intolerance [24].

2.1. Kefir

Kefir is an acidic alcoholic fermented dairy product with a creamy consistency and a slightly acidic taste, originating from the Balkans, Eastern Europe, and the Caucasus. Traditionally, kefir is produced using cow, sheep, goat, or buffalo milk [25]. Kefir exerts its positive effects on health through whole kefir, kefir grains, lactic acid bacteria, yeasts, organic acids, polysaccharides (kefiran and exopolysaccharides), and various other metabolites [32]. As a result of fermentation, there is an increase in lactic acid and antioxidant activity in kefir compared to normal milk [33]. In addition, Propionibacterium freudenreichii bacteria in kefir grains can cause an increase in B₁₂ and folate levels [22]. Studies on kefir, kefir grains, and kefir components (lactic acid bacteria, organic acids, bioactive peptides, and polysaccharides) have shown that they have antihypertensive [34], anticancer [35], antioxidant [36], anti-inflammatory [37], antidiabetic [38], and hypocholesterolemic effects [39] in addition to effects on bone health [40], cognitive function [41], and microbiota modulation [42].

The bacteria and yeasts identified in kefir can have positive effects on health. Kluyveromyces marxianus is one of the yeasts in kefir. Its strain, obtained from kefir, has been shown to remain alive in the digestive system [43]. Kluyveromyces marxianus B0399 supplementation decreased proinflammatory cytokines (tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, macrophage inflammatory protein-1 (MIP-1) α, IL-12, IL-8, interferon (IFN)-γ) and increased SCFAs (acetate and propionate). Although there was no change in the total bacterial count, the Bifidobacterium genus count increased [44]. Kluyveromyces marxianus A4 and A5 supplementation showed good adhesion in Caco-2 cells. Kluyveromyces marxianus A4 increased Bacteroidetes, Bacteroidales, and Bacteroides, and Kluyveromyces marxianus A5 increased Corynebacteriales and Corynebacterium [45].

2.2. Yogurt

One of the products of the lactic acid fermentation of milk is yogurt. The lactose in its content is converted into lactic acid by bacteria. In this way, it can be tolerated in the case of lactose intolerance. It also has benefits for health due to its protein content, vitamins such as riboflavin, minerals such as calcium, and metabolites that result from fermentation [82]. One of the components in yogurt that may have a positive effect on health is the CLA content. As a result of the increase in fermentation time, the CLA level in yogurt may increase [83].

Studies on the consumption of conventional/probiotic yogurt have evaluated its microbiota modulation [89], hypocholesterolemic [90], antidiabetic, antioxidant [91], and anti-obesity effects [92]. It was found that visceral fat decreased, and the abundances of Streptococcus thermophilus and Bifidobacterium animalis subsp. Lactis species increased in individuals who consumed yogurt. A correlation was observed between Bifidobacterium animalis subsp. Lactis and increased fecal 3-hydroxyoctanoic acid contents [89]. Yogurt supplementation (220 g/day) decreased fasting insulin, insulin resistance, intrahepatic lipid, hepatic fat fraction, serum lipopolysaccharide (LPS), fibroblast growth factor 21, triglycerides, TNF-α, total cholesterol, glutathione peroxidase (GPH-Px), and superoxide dismutase (SOD). In addition, it regulated the microbiota composition [91].

When the effects of probiotic and conventional yogurts were evaluated, the total cholesterol and total cholesterol/high-density lipoprotein cholesterol (HDL-C) ratio decreased as a result of consuming both yogurts. Both yogurts showed hypocholesterolemic effects [90]. In the study by Rezazadeh et al. [94], probiotic yogurt decreased blood glucose, insulin, HOMA-IR, Quantitative Insulin Sensitivity Calculation Index (QUICKI), vascular cell adhesion molecule cell (VCAM)-1, and plasminogen activator inhibitor (PAI)-1 values [94]. Various Lactobacillus and Bifidobacterium species in probiotic yogurts have been shown to lower cholesterol; regulate plasma glucose levels; have antioxidant, anti-inflammatory, and microbiota modulation effects; and have positive effects on cancer and ulcerative colitis [95,96,97,98,99,100].

2.3. Cheese

Cheese has been produced and consumed for many years. There are 1500 cheese varieties defined in the world. The microorganism content of cheese varies based on the milk used, cheese type, and production [116]. The pH changes that occur during the production and ripening of cheese are heavily influenced by both lactic acid bacteria and yeasts [117]. A meta-analysis study evaluating cheese consumption and its health effects found that cheese consumption (especially 40 g/day) had neutral to moderate benefits for human health, and was moderately inversely connected with all-cause mortality, cardiovascular disease, coronary heart disease, and stroke incidence. It also showed a negative association with the risks of type 2 diabetes and dementia. It is emphasized that these effects are due to the nutrients and bioactive components in cheese [118].

One of the components of cheese that have positive effects on health is bioactive peptides. The type of milk used during cheese ripening, starter culture, and native milk microbiota affect the bioactive peptides formed. Bioactive peptides are composed of certain protein fragments and offer various advantages for regulating bodily processes [121,122,123].

Bioactive peptides in different types of cheese have been shown to have antioxidant, antihypertensive (ACE inhibitory), antimicrobial, and dipeptidyl-peptidase-IV (DPP-IV) inhibitory activity effects [123,124,125,126,127]. In one study, Lactobacillus helveticus A1, which releases the peptide as a key factor in ACE inhibition, was the strain with the strongest ACE inhibitory activity [128]. The number of peptides with angiotensin-converting enzyme (ACE), dipeptidyl peptidase-IV (DPP-IV), and antioxidant activity increased with ripening [129]. The proteolysis of cheese for more than 90 days resulted in increased antioxidant activity. Bioactive peptides derived from αs1-casein and β-CN were detected in cheese. The radical scavenging activity, reducing power, chelate capacity, and ACE inhibition effects of cheese extract derived from these peptides were revealed [124].

The other compound of cheese associated with health is conjugated linoleic acid. The CLA content in cheeses was found to be 0.44 to 1.04 g/100 g of fat in the study by Donmez et al. [134], and 7.5 to 7.9 mg/g of fat in the study by Luna et al. [134]. It was shown that there is an increase in the CLA levels during cheese ripening, but increased storage time decreases the concentration [135]. CLA may have antidiabetic, anticancer, anticarcinogenic, anti-atherosclerotic, antihypertensive, and endothelial function effects [136,137,138].

The development of biogenic amines may occur in cheese as a result of the bioactivities of some microorganisms. Histamine, cadaverine, putrescine, spermine, spermidine, and tyramine biogenic amines have been detected in different cheese types. High levels of biogenic amine consumption have some drawbacks. For example, histamine has effects such as nausea, vomiting, diarrhea, and stomach upset, while tyramine may cause hypertensive effects and may have a negative relationship with monoamine oxidase inhibitors (MAOIs) [139]. It was emphasized that Lacticaseibasillus casei 4a and 5b isolated from cheese reduced tyramine and histamine accumulation, and therefore may be suitable to be used as co-cultures in order to lessen the amount of biogenic amines [140].

3. Fermented Meats

Red meat is any unprocessed mammalian muscle flesh, including frozen or minced meat (such as cattle, veal, pork, or lamb). Meat that has undergone salting, fermenting, smoking, curing, or other methods so as to improve preservation or flavor is well known as processed meat. Pork or beef are typically found as processed meats [145]. The majority of the time, it is agreed that meat and its products provide excellent and high biologic values of proteins, B group vitamins, minerals, trace elements, and some other bioactive components [146]. Figure 1 shows the changes throughout the meat fermentation. Table 2 lists the effects of fermented meat and certain bioactive compounds on health.

Figure 1. Schematic summary of changes throughout meat fermentation.

Table 2. Effects of fermented meat and certain bioactive compounds on health.

Fermented Foods		Certain Bioactive Compounds	Effects on Health	References
Intestine
	Fermented mutton jerky	x3-2b Lactiplantibacillus plantarum and composite bacteria	Purine content of fermented mutton jerky by x3-2b Lactobacillus plantarum and composite bacteria `↓` In vitro digestion, decreasing purine content by 37x-3 Pediococcus pentosaceus `↑`	[170]
	Cured beef	-	Gastric protein carbonylation `↑` Colonic Ruminococcaceae `↑` Cecal propionate `↑` TBARs and diacetyl in feces `↑` Levels of cecal butyrate, fecal phenol, dimethyl disulfide `↓` Level of fecal carbon disulfide `↑` Colonic Ruminococcaceae `↑`	[171]
	Fermented sausage	Enterococcus faecium CRL 183	Lactobacillus spp. in ascending colon, transverse colon, and descending colon `↓` Bacteroides spp. in descending colon `↓` Enterobacteriaceae in transverse colon and descending colon `↓` Colonic ammonium ions `↑` Butyric acid concentration in transverse colon, ascending colon, and descending colon `↑` Concentration of propionic acids in ascending colon and transverse colon `↑` Concentration of acetic acid in ascending colon, transverse colon, and descending colon `↓`	[172]
	Fermented sausage	-	Release of free iron in digestive system `↑` Concentration of gastric N-nitrosamine `↑`	[173]
	Fermented sausage	Enterococcus faecium S27	Transfer of tetracycline resistance determinant (tet(M)) to E. faecium and Enterococcus faecalis `↑` Transfer of Enterococcus faecium’s streptomycin resistance `↑`	[174]
	Fermented sausage	Bologna sausage (a) Dry fermented sausage (b)	Calcium transporter in Caco-2 cells: in (a) `↑`, in (b) `↓`	[175]
	Fermented salami	Plant extracts	Phenol and p-cresol in colon `↓` Acetate, propionate, butyrate in colon `↑` Enterobacteriaceae `↓` Bifidobacteriaceae `↑`	[176]
	Fermented fish	Staphylococcus sp. DBOCP6	Non-hemolytic and non-pathogenic effects against broad and narrow spectrum antibiotics Ability to adhere to the intestinal wall	[177]
Cardiovascular diseases and ACE-I inhibitory effects
	-	-	Cardiovascular disease risk, stroke risk `↑` Total mortality risk `↑`	[178]
	Salami Sausage		Cardiovascular disease risk `↑`	[179]
		-	Cardiovascular disease risk `↑`	[180]
		-	Total stroke incidence `↑` No association between ischemic stroke and coronary heart disease mortality	[181]
	Bacon Sausage	-	Cardiovascular death risk `↑` Ischemic heart disease risk `↑`	[182]
	Dry-cured pork ham	-	Levels of total cholesterol, LDL, basal glucose `↓`	[183]
	Semi-dry fermented camel sausage	Lactiplantibacillus plantarum KX881772	Inhibition of ACE `↑` Cytotoxicity activity towards Caco-2 cell line `↑` α-amylase inhibition `↑` α-glucosidase inhibition `↑`	[184]
	Fermented pork sausage	Staphylococcus simulans NJ201 Lactiplantibacillus plantarum CD101	ACE inhibition `↑` Superoxide anion scavenging activities `↑` Ferric-reducing antioxidant activity `↑`	[185]
	Dry fermented camel sausage	Staphylococcus xylosus and Lactiplantibacillus plantarum Staphylococcus caarnosus and Latilactobacillus sakei Staphylococcus xylosus and Lactobacillus pentosus	Antioxidant capacity by <3 kDa peptides `↑` Maximum ACE inhibition by <3 kDa peptides Maximum ACE inhibition in sausages with S. xylosus and L. plantarum	[186]
	Dry-cured ham	-	ACE inhibition `↑` Radical scavenging activity `↑` PAF-AH inhibitory effect `↑`	[187]
	Fermented meat	-	Antioxidant activity against OH-radical by GlnTyr-Pro `↑`	[188]
	Dry-fermented sausage	Starter culture (P200S34) and protease (EPg222)	ACE inhibition `↑` Antioxidant activity `↑`	[189]
		-	Risk of cardiovascular mortality, stroke, myocardial infarction via reduction in processed meat `↓`	[190]
		-	Risk of all-mortality cause and cardiometabolic disease via lower consumption `↓`	[191]
		-	Risk of heart failure `↑`	[192]
Cancer
		-	Risk of colon cancer, rectal cancer, breast cancer, lung cancer, and colorectal cancer `↑`	[193]
	Ham Sausage Bacon	-	Breast cancer risk `↑`	[194]
		-	Weak positive association with breast cancer	[195]
		-	Breast cancer risk with diet rich in processed meat `↑`	[196]
	Ham Sausage Bacon	-	Gastric cancer risk `↑`	[197]
	Ham Sausage Bacon	-	Colorectal cancer risk `↑`	[198]
		-	Colorectal cancer risk with lower consumption `↓`	[199]
		-	Colorectal cancer risk with lower consumption `↓`	[200]
		-	Colorectal cancer risk `↑`	[201]
	Ham Sausage Bacon	-	Colorectal cancer risk `↑`	[202]
	Ham Sausage Bacon	-	Colorectal cancer risk `↑`	[203]
		-	Colorectal adenoma risk `↑`	[204]
	Ham	-	Risk of renal cell carcinoma `↑` Risk of bladder cancer `↑`	[205]
	Ham Sausage Bacon	-	Bladder cancer risk `↑`	[206]
	Ham Sausage Bacon	-	Minimal connection to kidney cancer risk	[207]
	Ham Salami Sausage Bacon	-	No association with gliomas	[208]
			Risk of hepatocellular carcinoma `↑`	[209]
Other diseases
		-	Risk of type 2 diabetes `↑`	[210]
	Bacon Salami Sausages	-	Risk of diabetes as well as stroke and coronary heart disease `↑`	[211]
		-	Risk of type 2 diabetes `↑`	[212]
		-	Type 2 diabetes risk `↑`	[213]
		-	Gestational diabetes mellitus risk `↑`	[214]
		-	No change in Crohn’s disease flares	[215]
		-	Risk of mortality via increase in consumption `↑`	[216]
		-	Mortality risk of all causes (except cancer) and cardiovascular-caused mortality `↑`	[217]
		-	Depression risk `↑`	[218]
		N-Nitrosodimethylamine	No change in glioma	[219]
		Diethylnitrosamine	Probability of hepatocarcinogenesis	[220]

↑: increased, ↓: decreased, LDL: low-density lipoprotein, ACE: angiotensin-converting enzyme, kDa: kilodalton, PAF-AH: platelet-activating factor acetulhydrolase, Gln Tyr-Pro: Glycine Tyrosine-Proline.

4. Fermented Vegetables and Fruits

4.1. Fermented Vegetables

Vegetables are a significant part of a healthy diet. Low vegetable consumption leads to negative health effects [227]. One of the ways vegetables are consumed is in their fermented form. Mostly lactic acid and alkaline fermentation occurs when vegetables are fermented [228]. Lactic acid fermentation can occur in vegetables when conditions are suitable (anaerobic conditions, suitable temperature, and humidity and salt concentrations). The products created as a result of vegetable fermentation vary between nations.

A traditional Korean vegetable dish, kimchi (kimchi cabbage), is produced through the fermentation of radish, cucumber, and other vegetables by lactic acid bacteria [230]. Kimchi contains fiber, vitamins (ascorbic acid, etc.), minerals, 3-(4′-Hydroxyl-3′,5′-dimethoxyphenyl) propionic acid (HDMPPA), capsaicin, allyl compounds, isothiocyanate, indole compounds, and thiocyanate [231,232]. In another study using kimchi methanol extract (HDMPPA, quercetin, ascorbic acid, and capsaicin) and kimchi bioactive components, antioxidative (nuclear factor (erythroid-derived 2)-like 2 (Nrf2), SOD1, and GPx increased) and anti-inflammatory (NF-κB, inducible nitric oxide synthase (iNOS), and cyclooxygenase 2 (COX-2) decreased) activities were found to improve cognitive function in mice with amyloid beta (Aβ)25-35-induced Alzheimer’s [233]. The active ingredient of kimchi, HDMPPA, has shown antioxidant, anti-inflammatory, and anti-atherosclerotic effects by lowering cholesterol; reducing cyclooxygenase-2 and ROS levels, lipid peroxidation, and lipid accumulation; and suppressing NF-κB, mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathways and oxidative stress [234,235,236,237].

Sauerkraut is another fermented vegetable product that has been studied. Similar to kimchi, the bacteria isolated from sauerkraut, exopolysaccharides, and the bioactive compounds formed as a result of fermentation have shown antioxidant, antibacterial, and immunomodulatory effects [248]. It was also revealed that the Lactiplantibacillus plantarum strain isolated from sauerkraut may have a probiotic effect. Lactiplantibacillus plantarum S4-1 decreased the total cholesterol, triglyceride, and LDL-C contents [251]. The fermentation of sauerkraut resulted in the formation of ascorbigen, indole-3-carbinol, and the degradation of glucosinolates [258]. Ascorbigen may show antioxidant properties [259], while indole-3-carbinol can show antioxidant, anti-inflammatory, anti-obesity, antidiabetic, anti-atherosclerotic, anticancer, antihypertensive, and neuroprotective effects [260].

4.2. Fermented Fruits

Fruits show positive effects on health due to their fiber, low energy density, vitamin/mineral (potassium, vitamin C, etc.), and phytochemical (polyphenols and carotenoids) contents [270]. There are studies evaluating the health effects of the fermentation of many fruits. Studies on fermentation in fruits such as apples, mangoes, papayas, lemons, and citrus have been carried out [271,272,273,274,275]. Fermented fruits can be made from fruits mainly based on lactic acid and acetic acid fermentation [276,277]. The use of lemon-fermented products resulting from the fermentation of lemon with Lactobacillus OPC1 decreased the total triglycerides and total cholesterol in the liver and regulated the lipid metabolism and gut microbiota in rats [275]. It was revealed that fermented papaya products may exhibit immunomodulatory, antioxidant, anticancer, anti-inflammatory, antidiabetic, and antidyslipidemic properties. Fermented papaya decreased pro-inflammatory cytokines and pro-oxidant components [271]. Lactobacillus acidophilus (BCRC14079)-fermented mango peel decreased Aβ accumulation, a neuronal protective product, by inhibiting oxidative stress and increasing BDNF expression in neural cells [273].

The fermentation of fruits using selected probiotic strains resulted in beneficial sensory and health effects. Yang et al. [276] found that the fermentation of apple juice with Lactobacillus acidophilus, Lacticaseibacillus casei, and Lactiplantibacillus plantarum bacteria increased the antioxidant and antibacterial capacities of apple juice. The total amino acid content and lactic acid content increased, while the total phenolic acid content decreased. The gallic acid, protocatechuic acid, and catechin concentrations increased with fermentation, but the total phenolic acid content decreased with the effect of storage [276]. As a result of the fermentation of cherry juice using nine Lactobacillus strains, Lactobacillus acidophilus 150 and Limosilactobacillus fermentum DT41 fermentations increased the polyphenol contents compared to the baseline [278]. Dragon fruit fermentation (Lactiplantibacillus plantarum FBS05) increased antibacterial and antioxidant activities [279]. Cirlini et al. [280] evaluated the organic acid content in elderberry fruit and found lactic acid as the main organic acid. Malic acid found in the fruit before fermentation decreased with fermentation, the amount of citric acid varied according to the bacteria, and tartaric acid was also found in fermented juices [280]. Kiwifruit juice fermentation (Lactobacillus acidophilus 85 (La85), Lactobacillus helveticus 76 (Lh76), and Lactiplantibacillus plantarum 90 (Lp90)) resulted in the formation of protocatechuic acid and catechins. Protocatechuic acid was the highest in Lh76 fermentation. These compounds have antioxidant effects. Caffeic acid was not detected as a result of fermentation [281].

Fruit vinegars are among other fermented products obtained from fruits. Two different fermentations can occur in vinegar: alcoholic and acetic acid fermentation. The microbiota leading to vinegar production varies. Acetic acid can be produced in large quantities by the Acetobacter and Komagataeibacter species [277]. Vinegar is obtained from many fruits such as grapes, apples, pomegranates, and blueberries. Polyphenols and organic acids, especially acetic acid, can show beneficial effects in fruit vinegar [284]. Bioactive components such as catechins, p-hydroxybenzoic acid, gallic acid, syringic acid, caffeic acid, p-coumaric acid, and chlorogenic acid have been provided in different kinds of vinegar [285,286]. Apple cider vinegar has been found to have hypocholesterolemic, antidiabetic [287,288,289], antioxidant [288,290], antimicrobial, anti-inflammatory [291], and anti-obesity effects [290] and improve cognitive function [292] reproductive function, and liver function [293]. Apple cider vinegar may exert antidiabetic effects by decreasing HOMA-IR, fasting blood glucose, HOMAβ, and OUICKI levels [287,288,289,293]. It may be effective in hypercholesterolemia by improving the total cholesterol, triglyceride, LDL cholesterol, total cholesterol/HDL-C, and LDL-C/HDL-C levels [287,289,290,293], and in non-alcoholic fatty liver disease by improving hepatic enzymes and reducing steatosis and inflammation in the liver [289,293]. It also has effects on neurodegeneration, ovulation, and obesity.

5. Fermented Legumes

Plants of the Leguminosae family make up legumes. Peas, chickpeas, lentils, soybeans, and peas are examples of edible legumes [334]. Because of the important and nourishing bioactive compounds that legumes contain, they are essential for human nutrition [335]. They are all rich in protein, fat, carbohydrate, and minerals [334,336].

Due to the inclusion of non-nutrient components, legumes have a limited potential to be digested and bioavailable. It is suggested to use soaking, boiling, or fermentation to improve digestion and bioavailability. Thus, especially with fermentation, non-nutritious foods are changed into substances with nutritional value [339]. Antioxidant chemicals produced by the fermentation of soybeans include furanones, peptides, 3-hydroxyanthranilic acid, and melanoidins. Additionally, bioactive substances with anti-inflammatory effects include isoflavone, butyric acid, 2S albumin, α-linolenic acid, soy sauce polysaccharides, and glycones [340]. The fermentation process uses microorganisms to catalyze metabolic reactions and produce bioactive chemicals [341]. A traditional Korean dish, cheonggukjang, is produced in the wake of the fermentation of soybeans. Bioactive compounds not found in raw soybeans are produced during fermentation as a result of isoflavones such as phenolic acids, genistein, phytic acids, saponins, daidzein, and trypsin inhibitors [342,343].

Fermentation improves digestibility and produces new bioactive chemicals that are helpful to health. It has links to cancer, diabetes, inflammation, antioxidants, and diabetes [353]. The health-protective molecule, GABA, which rises with fermentation, is a substance [354]. It has an impact on enhancing cell viability and preventing oxidative damage [355]. One of the legumes that receives a lot of attention globally is soybean, which, along with its fermentation, has a regulating effect on the stool microbiota [356]. Increases in the catalase, superoxide dismutase, and glutathione peroxidase levels, along with a decrease in reactive oxygen species and pro-inflammatory cytokines (NF-κB, IL-β, COX-2, and TNF-α), give fermented soy products anti-inflammatory effects [357]. Additionally, it affects vital enzymes that are part of the hypoglycemic processes, including α-amylase and α-glucosidase [358]. The primary bioactive ingredient in fermented soybeans, daizein, has been linked to diseases such insulin resistance, obesity, and dyslipidemia [359].

6. Fermented Cereals

Cereals are also best processed through fermentation, a time-honored technique [401]. The fermenting method is becoming more and more popular due to the growing interest in dietary consumption and nutrition [402]. In Africa, foods made from fermented grains are used as staple foods [403]. Among the most common grains utilized in fermentation are wheat, corn, teff, sorghum, and millet [404]. It is possible to give examples of regionally fermented grain-based dishes like Mawè and Ogi [405]. Utilizing Streptococcus thermophilus during fermentation enhances texture and flavor while also increasing volatile chemicals (diacetyl and acetoin) [406]. The fermentation process decreases the moisture and carbohydrate contents while increasing the total protein and ash contents in corn beverages fermented with Lactobacillus bulgaricus and Streptococcus thermophilus [407]. The traditional Peruvian drink, “Chicha de siete semillas”, is fermented using Streptococcus macedonicus and Leuconoctoc lactis. This fermented cuisine contains a lot of GABAs and is made from grains, pseudograins, and legumes. Streptococcus macedonicus is typically chosen for maize preparation if corn is to be used as a grain source [408]. Amahewu is another type of fermented grain. Amahewu is a fermented oatmeal or beverage made from corn that is mostly enjoyed in South Africa. Depending on the graft type, the type of maize, and the present fermentation circumstances, Amahewu’s nutritional and sensory qualities may change [409]. Bacillus, Arthrobacter, Lactobacillus, Ilyobacter, Clostridium, and Lactococcus are only a few of the numerous and distinct microbial species that are abundant in the fermented rice-based beverage, Chokot, made in India [410]. A popular fermented beverage made from grains called boza is enjoyed in many Balkan nations. Boza is rich in lactic acid bacteria, including Pediococcus parvulus, Lactobacillus parabuchneri, Limosilolactobacillus fermentum, Lactobacillus coryniformis, and Lactobacillus buchneri. Other types of microbiota found in boza, however, include yeasts such Pichia fermentans, Pichia norvegensis, Pichia guilliermondii, and Torulaspora spp. [411]. Boza, a grain-based food, is likewise high in putrescine, spermidine, and tyramine [412]. It has health impacts in addition to enhancing the functional and nutritive value of fermented grain products and satisfying the demands of contemporary consumers for health-promoting products [413].

7. The Other Side of Fermented Foods

Dairy products, vegetables and fruits, legumes, meats, and grains are among the fermentable food groups. Microorganisms that play roles in fermentation and the bioactive compounds released during fermentation have antioxidant, anti-fungal, and antidiabetes effects; are involved in the protection of cognitive function and the regulation of intestinal microbiota; and have anti-inflammatory, antihypertension, anticancer, and anti-obesity effects (Figure 3).

Figure 3. Schematic summary of the effects of fermented foods on health.

Although fermentation has positive impacts on health, another aspect of it needs to be examined. One of the aspects that should be emphasized is the biogenic amines contained in some fermented products. Biogenic amines are compounds that exist especially in fermented meat products and increase with fermentation [430]. Biogenic amines such as spermidine and cadaverine cause an increase in N-nitrosodimethylamine and N-nitrosopiperidine levels [431]. The nitrosamines belong to the carcinogen group. While the most prevalent forms of nitrosamines in meat are N-nitrosodimethylamine and N-nitrosopiperidine [432], the International Agency for Research on Cancer categorizes N-nitrosopiperidine as group 2B, while N-nitrosodimethylamine is classified as group 2A [433].

Another component found in fermented foods that has been linked to health is biogenic amines. Histamine, tyramine, putrescine, and cadaverine are the biogenic amines that are most frequently observed [434]. The bacterial decarboxylation of the appropriate amino acids using substrate-specific decarboxylase enzymes is the primary method used to create biogenic amines in food. For example, histamine is formed from the amino acid histidine via histidine decarboxylase, while cadaverine is formed from lysine [435]. They can occur in many fermented foods such as cheese, sauerkraut and another vegetables, soybean, meat, fish, beer, wine, etc. [434,435]. Biogenic amines have many roles in the body such as protein, hormone, and nucleic acid syntheses, blood pressure control, and the promotion of cell growth. However, excessive intake may have toxic effects. Many symptoms such as food poisoning, headache, and sweating can be seen [436]. Biogenic amine formation and an increase in the amount can be prevented by paying attention to the storage temperature of foods, packaging processes, natural components, and appropriate starter culture selection [437].

Another unhealthy compound that can be found in some fermented foods is salt. High salt consumption has negative health effects. It is therefore important to reduce salt consumption. However, reducing salt in fermented foods may pose a problem with regard to food safety, texture, and flavor [440]. While ensuring that this reduces salt intake, it may cause the development of pathogenic microorganisms. Reducing the salts used may result in increased yeast, Enterobacteriaceae, and microbial growths [441]. Microbial growth can occur due to the decrease in water activity. As a result of the increase in some microorganisms, the formation of biogenic amines and nitrosamines may increase [430,442,443,444,445,446].

The future growth of the fermented food sector is made possible by the lowering of sodium and nitrosamines in traditional fermented foods. Studies on fermented foods show heterogeneous characteristics. This makes it difficult to compile the studies on a fermented food and to make a general evaluation of the positive and negative properties of that fermented food. In addition, studies on the amounts of fermented foods consumed by people need to be increased. In this way, responses to the effects of the amounts of fermented foods consumed on humans can be evaluated.

This entry is adapted from the peer-reviewed paper 10.3390/fermentation9110923

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