Plant-Based Fermented Foods: Classification, Biochemical Transformations, and Health Benefits

Abstract

In recent years, plant-based fermented foods (PBFs) have become popular all over the world due to their high nutritional value. Compared with traditional foods, PBFs can effectively address dietary issues of high fat content, excessive calories, and elevated cholesterol levels in food formulations, while providing higher nutritional value and enhanced sensory properties (taste and flavor) than conventional plant-based products. These characteristics make PBFs more suitable for people’s yearning for a healthy diet. This review discussed the close relationship between PBFs and human health, elaborating on the definition of PBFs, common types, and the beneficial effects that occur during the fermentation process for human health. Furthermore, we also explored the nutritional value of PBFs. Herein, PBFs are not only rich in probiotics, organic acids, and various bioactive substances that promote gut health and boost immunity but also play a positive role in preventing certain chronic diseases. Finally, this article looks forward to the future development trends of PBFs, predicting their significant potential in healthy eating and sustainability.

1. Introduction

People have found that the significant increase in most chronic non-communicable diseases is related to the global dietary pattern trending towards high fat, high salt, and high sugar [1]. Data from the World Health Organization (WHO) show that the annual incidence of chronic non-communicable diseases causes approximately 43 million deaths globally, which is equivalent to 75% of the global non-pandemic-related deaths [2]. According to the prediction in a research report, by 2050, the number of overweight and obese adults globally may reach 3.8 billion [3], and 15.6% of the global population aged 5–14 suffers from obesity [4], for which the excessive intake of high-calorie processed foods is to blame [5].

Thanks to the view of being “healthier” [6], plant-based foods have come into the public’s view. The concept of plant-based foods is derived from the American Plant Food Association’s “Fruits, vegetables, nuts and whole grains, associated with improved nutrition, but highly processed foods [7].” In a substitution analysis, nuts, whole grains, legumes, and fish appear to be healthier protein sources than eggs, processed meats, unprocessed red meats, and poultry and can also reduce the risk of cardiovascular disease and premature death [8].

Nonetheless, common plant-based foods are deficient in some aspects in terms of appearance, taste, flavor, texture, and nutrition [9]. For example, common plant proteins such as soybeans and peas generally have the problem of lacking essential amino acids (such as methionine) [10,11]. Although plant-based dairy alternatives (PBDA) avoid the problem of lactose intolerance, their protein biological value (BV) is 20–40% lower than that of milk, and it is difficult to match their flavor and texture with those of traditional dairy products [12,13]. These deficiencies directly restrict the application value of plant-based diets in the prevention and control of chronic diseases.

Against this backdrop, fermentation technology, regarded as a “biological enhancer,” demonstrates unique advantages [14]. Actually, there have been numerous studies in recent years proving that fermented foods contain bioactive compounds and have beneficial properties [15,16]. During the fermentation process of food, microorganisms will trigger various biochemical reactions, which are helpful for the release of vitamins, amino acids, short-chain fatty acids (SCFAs), phenolic compounds, extracellular polysaccharides (EPSs), organic acids, and bioactive peptides [17,18,19,20]. These substances are of great benefit to human health: Vitamins, as precursors of many coenzymes, play a key role in the metabolism of nucleic acid precursors, post-synthetic modification of proteins, or control of calcium binding in bones [21]; EPSs have hypocholesterolemia, antioxidant, and immunomodulator properties [22]; SCFAs, such as 4-carbobutyric acid, have an alleviating effect on inflammation [23]; and complex polyphenols and flavonoids are enzymatically hydrolyzed into bioactive and more bioavailable components with strong antioxidant activity [24]. Long-term consumption of PBFs contributes to maintaining the equilibrium of the gut microbiota, boosting immunity, and decreasing the risk of cardiovascular diseases [25,26].

Since PBFs can bring a lot of benefits to human health, they are widely acknowledged as a highly valuable category of health food. Therefore, PBFs are highly popular among those who advocate for a healthy lifestyle and have become an essential element in the modern dietary framework. Given the significance people place on PBFs, this manuscript has described the synergistic effect of their two components on human health from three aspects: the classification of PBFs, the efficacy of fermented foods (Figure 1), and the effect of plant-based foods and the changes of plant-based foods before and after fermentation.

2. Reaction Mechanisms and Common Types of PBFs

Fermented foods are “foods produced through the growth of desired microorganisms and the enzymatic transformation of food ingredients” [21]. There has been extensive research on fermented foods and human health, and researchers now generally believe that fermented foods are good for human health. Fermented foods are also called “functional foods” because the microorganisms contained in them can produce a variety of nutrients and improve human health [27].

2.1. Common Classification of PBFs

Based on the differences in raw food materials, this section introduces the common categories of PBFs on the market and explains the benefits of fermentation (Figure 2).

2.1.1. Fermented Fruits and Vegetables

Fermented fruit and vegetable foods are a category of functional fruit and vegetable products made from fresh fruits and vegetables as raw materials, which undergo a series of preprocessing and processing steps and are inoculated with fermenting microorganisms. Fermented fruit and vegetable drinks contain a variety of nutrients and chemicals that have anti-inflammatory, antibacterial, antioxidant, and anti-cancer benefits [28,29]. Many studies have also shown that fruit and vegetable intake is associated with a lower incidence of chronic diseases such as coronary heart disease, cancer, diabetes, Alzheimer’s disease, and metabolic syndrome, as well as atherosclerosis caused by unhealthy lifestyle habits [30]. Fruits and vegetables have extremely high nutritional value, but compared with other foods, fruits and vegetables are easily affected by various environmental pressures during production and post-harvest processing, handling, and storage, resulting in deterioration of fruits and vegetables [31]. This susceptibility will not only cause huge economic losses but also cause the production of toxins, causing harm to the human body [32]. The use of probiotic fermentation technology to develop fermented fruits and vegetables with special nutritional and health care functions can prolong their shelf life [31,33].

2.1.2. Fermented Soy

Since ancient times, soy has been an indispensable part of a healthy diet in many Asian countries. Various suitable climates and geographical regions have created a large-scale crop, making soybeans a staple food in Asia. Due to insufficient meat consumption, fermented soy products have played a crucial role as a source of protein in Asian diets [34,35].

Fermented soy products are a category of functional fermented plant proteins made from high-protein plants such as soybeans, walnuts, almonds, etc. by inoculating fermenting bacteria and undergoing food processing treatments.

Compared with ordinary soy products, fermented soy products undergo a series of chemical reactions under the action of enzymes secreted by microorganisms, which leads to an increase in the content of vitamins, essential amino acids, and fatty acids, which greatly enhances the flavor and nutritional value of the product (

Table 1. The origins and nutritional values of various fermented bean products.

Fermented Soy Products	Birthplace	Nutritional Value	References
Soy sauce	China	Contains isoflavones and gamma-aminobutyric acid, which enhance antioxidant activity	[37]
Soy milk	China	As a source of protein and flavoring ingredients, it has antioxidant and antihypertensive properties	[38]
Miso	Japan	Estrogen-like activity, antioxidant and angiotensin converting enzyme inhibitory activity of isoflavones	[39]
Tempeh	Indonesia	It has a variety of biological activities such as antioxidant, antidiabetic, and antihypertensive	[40]
Natto	Japan	Contains many peptides and at least 17 amino acids, making nutrients more accessible	[41]

). Soy protein has the advantages of being low fat, low calorie, and cholesterol-free and is lactose free, making it the best choice for lactose-intolerant patients and vegetarians [36].

2.1.3. Fermented Grains

Fermented cereal foods are a category of functional fermented cereal products made from grains through the process of fermentation. The fermentation process can improve the sensory characteristics and nutritional properties of cereal foods, and it is beneficial to human health [42,43]. Epidemiological studies have shown that grains may help combat various common metabolic disorders, such as diabetes, various cancers, cardiovascular diseases, and obesity [44,45]. In addition, the taste and flavor of fermented grain foods are also better than those of ordinary grain products [46,47]. Cereal fermented beverages are non-dairy products and are considered possible carriers of probiotic strains. Soy-based fermented beverages and fermented cereal foods are the alternative for vegetarians and lactose-intolerant consumers [48].

2.2. Reaction Mechanisms of PBFs

The fermentation mechanism of PBFs is mainly driven by the metabolic activities of microorganisms, involving the transformation of carbohydrates, proteins, and polyphenols, ultimately resulting in unique flavor, texture, and functional characteristics. The manuscript will discuss this from three aspects: the role of microorganisms, metabolic pathways, and substrate transformation.

2.2.1. Synergistic Effects of Microbial Communities

Fermenting microorganisms play a central role in the fermentation of plant-based foods. Through fermentation, microorganisms can transform the nutrients in plant raw materials, making them more easily digestible and absorbed, while also producing new flavors and nutrients. During the fermentation process, lactic acid bacteria can convert the carbohydrates in plant raw materials into lactic acid through the glycolysis pathway, reducing the pH value of the food. This not only plays a certain role in preservation but also endows the food with a unique sour taste and flavor [49]. For example, lactic acid bacteria can produce various enzymes during the fermentation process to hydrolyze proteins into peptides and amino acids and produce flavor precursor substances [50,51,52]. Yeast can produce carbon dioxide gas during the fermentation process, giving food a fluffy texture. It can also produce some volatile compounds to enhance the aroma of the food [53,54]. Molds secrete hydrolytic enzymes such as amylase and protease to decompose plant cell walls and macromolecular substrates, releasing fermentable sugars, amino acids, and other flavor compounds, thereby enhancing the umami taste of fermented products [55,56]. During the production process of some food products, these microorganisms can also interact with each other to produce flavor compounds that enhance the aroma of the products [57] or overcome the deficiencies in single-strain fermentation and improve the quality of the products [58,59].

2.2.2. Generation and Function of Metabolites

During the fermentation process of PBFs, microbial metabolism plays a crucial role and can produce a variety of bioactive substances with important functions:

In terms of antioxidant activity, lactic acid bacteria and yeast exhibit remarkable capabilities. They generate antioxidant substances such as γ-aminobutyric acid (GABA) and glutathione through redox reactions [60,61,62]. GABA, a naturally occurring non-protein amino acid, is mainly formed through an irreversible α-decarboxylation reaction of L-glutamic acid or its salts under the action of glutamic acid decarboxylase [63] (this enzyme is mainly found in bacteria [64,65,66]). It has various physiological functions, among which antioxidant activity is one of its important characteristics [67]. Glutathione is a water-soluble tripeptide composed of glutamic acid, cysteine, and glycine [68]. It can be released from yeast cells through autolysis [69]. It is an important molecule containing sulfhydryl residues, which are the basis for the antioxidant properties of glutathione [70].

The fermentation process also produces prebiotics and probiotics. Prebiotics are selectively fermented ingredients that are beneficial to digestive system health and can stimulate the growth of probiotics [71]. Currently, common carbohydrates have all been used to perform the functions of prebiotics (such as lactulose, fructooligosaccharides, β-glucan, trans-galactooligosaccharides, etc.) [72]. As an exopolysaccharide, β-glucan can effectively stimulate the host’s immune response [73]. It has been proven to exhibit potential anti-cancer activity and is frequently utilized as an adjuvant in clinical applications to enhance drug efficacy [74,75,76].

2.2.3. Dynamic Regulation of Substrate Conversion

During the substrate conversion process of PBFs, the dynamic regulation mechanism is achieved through the specific enzyme system secreted by microorganisms, which significantly improves the bioavailability of anti-nutritional factors (phytic acid, tannins, enzyme inhibitors, etc.) in the raw materials. Anti-nutritional factors are usually associated with reduced protein digestibility and mineral absorption rate. Therefore, foods with high contents of such substances are always considered to be low-nutritional-value foods [77]. However, fermentation seems to reduce the content of anti-nutritional factors in foods and increase the in vitro protein digestibility [78,79].

Taking soybeans, grains, and vegetables as examples, the naturally occurring phytic acid (inositol hexaphosphate) in them forms stable chelates with divalent minerals (such as iron, zinc, and calcium) through phosphate groups [80,81]. These chelates are difficult to be digested and absorbed by humans, which will reduce the nutritional value of foods [82,83]. Some common LABs can catalyze and hydrolyze phytic acid into inositol and free phosphate groups by synthesizing microbial phytase, reducing the concentration of phytic acid and thus improving the bioavailability of mineral ions [84,85]. For example, in grains fermented by Lactobacillus plantarum subsp. plantarum, Lactobacillus fermentum, and Lactobacillus casei subspecies, the percentages of phytate reduction at the end of fermentation were 52.58%, 46.39%, and 37.11% respectively [86]. Research has proven that phytic acid is the main inhibitor of iron absorption. When the phytic acid consumed by the testers decreased from its natural amount of 4.9–8.4 to less than 0.01 mg/g isolated, the absorption of iron increased by four to five times [87]. This has important clinical significance for the prevention of nutrition-related chronic diseases such as iron deficiency anemia.

Tannins are a group of phenolic compounds present in the secondary metabolism of plants. They can form stable complexes with proteins, other polymers (such as cellulose, hemicellulose, pectin), and minerals, reducing the catalytic effect of digestive enzymes on proteins [88,89,90]. In an experiment investigating the nutritional characteristics of sorghum flour, the phytic acid, tannins, and oxalates in sorghum flour fermented by Lactobacillus plantarum decreased by 77%, 96.7%, and 67.85%, respectively [91]. Lactobacillus plantarum hydrolyzes tannins into gallic acid and glucose by secreting tannase. The formed gallic acid is decarboxylated to pyrogallol by gallic acid decarboxylase, which improves protein absorption [92].

3. Benefits of PBFs

3.1. Beneficial Substance Produced by Metabolic Processes

PBFs are inherently rich in a variety of nutrients, such as protein, dietary fiber, vitamins, minerals, and beneficial microbial metabolizers [32]. After the fermentation process, the content of these nutrients is retained, and their bioavailability may increase due to chemical changes during the fermentation process [15,93]. For example, some of the active substances, such as bacteriocins in milk during fermentation, are increased [94], which have been shown to prevent infection by some pathogenic microorganisms [95].

3.1.1. Organic Acids

Organic acids refer to organic compounds that are acidic and contain one or more carboxyl groups, which play an important role in maintaining the nutritional value and sensory quality of food [96]. At the same time, organic acids can also improve human health: pyruvic acid provides energy for the human body through the tricarboxylic acid cycle; citric acid is an important intermediate product in various metabolic pathways in animals and plants, and sodium citrate is a common anticoagulant in clinical practice; and malic acid can quickly provide energy for the human body, achieving the goals of resisting fatigue and protecting the liver, kidneys, and heart [97].

Citric acid, malic acid, and tartaric acid are used as acidity regulators, which can maintain or change the pH value of food [98]. However, for some fruits like kiwifruit and citrus fruits, their juices are not suitable for direct consumption due to the high content of citric acid. Fermentation can effectively reduce the content of citric acid and other substances in food [99,100], thereby enhancing the taste of the juice. Take the fermentation of papaya as an example. Lactic acid bacteria decompose metabolic sugars (free sucrose, fructose, and glucose) through fermentation to form organic acids such as lactic acid and acetic acid [101,102]. The total organic acid content of fermented papaya increases significantly [103] (Table 2). Pyruvic acid can be used as a preservative to prevent food from spoiling and effectively extend the shelf life. Therefore, the fermented papaya is less prone to spoilage and can be preserved for a long time.

3.1.2. Active Substances

Bioactive compounds are found in small amounts in plant-based foods as secondary metabolites and are additional nutrients with positive health effects [104]. These bioactive substances beneficial to the human body show relatively obvious changes before and after fermentation. (Table 3). For example, the lowest total flavonoid content in raw soybeans was 2.36 mg GAE/g, while the total flavonoid content in fermented soybean products varied from 3.67 mg GAE/g in spicy fermented bean curd to 12.37 mg GAE/g in black bean and pig knuckle. Probably affected by soybean raw materials, the total phenol content varied. Generally speaking, significant changes in the total phenol content values were found among various fermented soybean products and raw soybeans (p < 0.05) [105].

There is growing evidence that the consumption of bioactive compounds can improve health and reduce the risk of chronic disease [106]. Flavan-3-ols have a positive impact on cardiometabolic outcomes, including reducing the risk of diabetes and cardiovascular-related outcomes [107,108]. Some polysaccharides can stimulate the proliferation and activation of immune cells and enhance the defensive ability of the immune system [109,110,111].

Table 2. Changes in the organic acid content of different PBF products before and after fermentation.

Raw Material	Fermentation Strain	Organic Acid Content g/L		References
		Before Fermentation	After Fermentation
Papaya	Lactobacillus	0.55 ± 0.05 (pyruvate)	1.13 ± 0.15 (pyruvate)	[103]
		53.2 ± 2.8 (malic acid)	77.6 ± 3.5 (malic acid)
	Lactiplantibacillus plantarum	0.55 ± 0.05 (pyruvate)	1.20 ± 0.11 (pyruvate)
		53.2 ± 2.8 (malic acid)	74.2 ± 2.0 (malic acid)
Blueberry	LacidophilusSaccharomyces cerevisiae RV002, Pichia fermentans JT-1-3, Saccharomyces cerevisiae NP-7-5	1.73±0.08 (citric acid	0.98 ± 0.02 (citric acid)	[112]
		1.53 ± 0.10 (malic acid)	0.99 ± 0.03 (malic acid)
		0.9 ± 0.04 (tartaric acid)	0.52 ± 0.06 (tartaric acid)
Grape	Saccharomyces cerevisiae	5.07 ± 0.02 (tartaric acid)	3.97 ± 0.04 (tartaric acid)	[113]
		1.87 ± 0.02 (malic acid)	1.43 ± 0.00 (malic acid)

Table 2. Changes in the organic acid content of different PBF products before and after fermentation.

Raw Material	Fermentation Strain	Organic Acid Content g/L		References
		Before Fermentation	After Fermentation
Papaya	Lactobacillus	0.55 ± 0.05 (pyruvate)	1.13 ± 0.15 (pyruvate)	[103]
		53.2 ± 2.8 (malic acid)	77.6 ± 3.5 (malic acid)
	Lactiplantibacillus plantarum	0.55 ± 0.05 (pyruvate)	1.20 ± 0.11 (pyruvate)
		53.2 ± 2.8 (malic acid)	74.2 ± 2.0 (malic acid)
Blueberry	LacidophilusSaccharomyces cerevisiae RV002, Pichia fermentans JT-1-3, Saccharomyces cerevisiae NP-7-5	1.73±0.08 (citric acid	0.98 ± 0.02 (citric acid)	[112]
		1.53 ± 0.10 (malic acid)	0.99 ± 0.03 (malic acid)
		0.9 ± 0.04 (tartaric acid)	0.52 ± 0.06 (tartaric acid)
Grape	Saccharomyces cerevisiae	5.07 ± 0.02 (tartaric acid)	3.97 ± 0.04 (tartaric acid)	[113]
		1.87 ± 0.02 (malic acid)	1.43 ± 0.00 (malic acid)

Table 3. Changes in the total phenol content and total flavonoid content of different PBF products before and after fermentation.

Raw Material	Fermentation Strain	Biologically Active Ingredient mg/g				References
		Before Fermentation		After Fermentation
		Total Phenol Content	Total Flavonoid Content	Total Phenol Content	Total Flavonoid Content
Papaya	Lactobacillus acidophilus	0.032 ± 0.006	0.50 ± 0.06	0.027 ± 0.009	1.11 ± 0.17	[103]
	Lactiplantibacillus plantarum	0.032 ± 0.008		0.029 ± 0.006	1.45 ± 0.13
Wheat bran	Lactobacillus acidophilus KCTC 3164	1.61 ± 0.62	0.88 ± 0.11	2.80 ± 0.27	1.01 ± 0.08	[114]
	Lactobacillus helveticus KCTC 3545			1.98 ± 0.21	0.71 ± 0.07
	Enterococcus faecalis KCTC 3206			2.33 ± 0.09	0.71 ± 0.08
Saccharin japonica	Monascus purpureus	1.658	0.227	8.443	0.463	[115]
White quinoa	Lactiplantibacillus plantarum 299v	4.68 ± 0.05	-	7.78 ± 0.07	-	[116]
Rice	Lactobacillus fermentum KKL1	11.8	0.04	63.42	45.36	[117]

Table 3. Changes in the total phenol content and total flavonoid content of different PBF products before and after fermentation.

Raw Material	Fermentation Strain	Biologically Active Ingredient mg/g				References
		Before Fermentation		After Fermentation
		Total Phenol Content	Total Flavonoid Content	Total Phenol Content	Total Flavonoid Content
Papaya	Lactobacillus acidophilus	0.032 ± 0.006	0.50 ± 0.06	0.027 ± 0.009	1.11 ± 0.17	[103]
	Lactiplantibacillus plantarum	0.032 ± 0.008		0.029 ± 0.006	1.45 ± 0.13
Wheat bran	Lactobacillus acidophilus KCTC 3164	1.61 ± 0.62	0.88 ± 0.11	2.80 ± 0.27	1.01 ± 0.08	[114]
	Lactobacillus helveticus KCTC 3545			1.98 ± 0.21	0.71 ± 0.07
	Enterococcus faecalis KCTC 3206			2.33 ± 0.09	0.71 ± 0.08
Saccharin japonica	Monascus purpureus	1.658	0.227	8.443	0.463	[115]
White quinoa	Lactiplantibacillus plantarum 299v	4.68 ± 0.05	-	7.78 ± 0.07	-	[116]
Rice	Lactobacillus fermentum KKL1	11.8	0.04	63.42	45.36	[117]

3.2. Improve Food Sensory Properties

With the improvement in living standards, people’s pursuit of flavor is also becoming more and more intense. The sense of taste affects the selection, intake, absorption, and digestion of food [118]. The final sensory quality of fermented food and the overall product acceptance largely depend on the content and composition of flavor substances [119]. The smell of food is also closely related to volatile aroma compounds. There are many aroma precursors in fruits, such as sugars, glycosidic bonds, and amino acids [120], which usually lack unique aroma characteristics. However, after a series of biochemical reactions such as fermentation, these precursors can be converted into complex aroma compounds, which contribute to the development of rich and diverse flavors [121].

In the experiment, the soybean co-cultured by the two strains of Bacillus velezensis SDL1 and Lactiplantibacillus plantarum Ly8 enhanced the synthesis of branched-chain amino acids and threonine by reducing the acid content and increased the content of some esters, acetyl urea and pyrazine, achieving its superior flavor characteristics [122]. In another experiment, no strong beany odor associated with the presence in the unfermented protein mixture was detected in the fermented pea and rice protein mixture. In addition, the unpleasant odor compounds egg thronal, methyl mercaptan, and bergamot-like compounds in the unfermented protein blend were significantly reduced by 40%, 78%, and 99%, respectively, in the fermented protein blend, demonstrating that the sensory properties of the fermented pea and rice protein concentration blend were improved compared to the unfermented protein mixture [123].

For reducing the unpleasant odors in the raw materials, there is also a method by which yeast can produce pleasant odor-active compounds during the fermentation process [124]. It has a very wide range of applications in the food field. Research has found that for foods fermented with aroma-producing yeasts, the contents of esters and other substances are increased. For example, three types of aroma-producing yeasts can biosynthesize ethyl acetate and isoamyl acetate through esterification and alcoholysis pathways, greatly increasing the concentrations of esters and alcohol flavor compounds in high-salt liquid fermentation soy sauce during the fermentation process [54]. Moreover, fig wines fermented with non-Saccharomyces contain more odorant active substances than fig wines fermented with Saccharomyces cerevisiae, achieving the purpose of enhancing the aroma [125]. While organic acids play an important role in the sensory properties and stability of alcoholic beverages [126], volatile and non-volatile organic acids are particularly noteworthy factors. These organic acids play a crucial role in shaping the sour aroma through the positive and postnasal sense of smell in the nasal passage [127]. Non-volatile organic acids can also produce drinks with sour taste or mouthfeel [128].

4. PBFs’s Potential Benefits to Human Health

There is increasing focus on the potential mechanisms of PBFs in the prevention of chronic non-communicable diseases (diseases that exist for a long time and usually progress slowly, including cardiovascular diseases, cancers, chronic respiratory diseases, and diabetes). Studies have shown that after microbial fermentation, the physicochemical properties of plant-based foods undergo significant changes. Bioactive components are significantly enriched through microbial transformation pathways, while antinutritional factors and potential harmful metabolites are degraded or transformed; in addition, the fermentation process can enhance the bioavailability of functional components and limit the intake of some pathogenic factors by regulating intestinal absorption efficiency. In this section, we reviewed using PBFs as a new intervention strategy for the prevention of chronic diseases (Figure 3).

4.1. Regulate Blood Sugar and Improve Insulin Resistance

Diabetes mellitus (DM) is a non-communicable chronic metabolic disease characterized by hyperglycemia, deficient insulin secretion, and insulin action. It has become a major public health problem worldwide, with significant economic and social repercussions [129].

Insulin and glucagon are synthesized by beta cells and alpha cells, respectively, and are key factors in regulating blood sugar stability. Many studies have found that fermented soy products can potentially improve pancreatic damage and promote insulin secretion, thereby minimizing hyperglycemia conditions [130,131]. Kwon et al.’s study also found that giving fermented soy products to 90% of rats with pancreatic excision diabetes had a significant increase in the number of beta cells, that is, insulin secretion was improved, while unfermented soy did not have this effect [132]. In animal determination experiments, the blood glucose levels of mice fed fermented pomegranate juice were significantly reduced compared with mice in the HFD group. Another study found that CD-1 mice with drug-induced diabetes had a significant decrease in blood glucose levels after taking pomegranate juice for four months [133]. The research results of fermented soybean products in improving pancreatic injury and promoting insulin secretion and of pomegranate juice in lowering blood glucose levels provide new research directions and intervention ideas for the prevention and treatment of diabetes.

Diabetes is a major global public health issue. PBFs show potential in alleviating T2DM [134]. Among the 3,833 participants in the study by Díaz-López et al., individuals with higher intakes of total dairy products, fermented dairy products, low-fat dairy products, and yogurt had a 32% to 41% reduced risk of developing T2DM [135]. Similar conclusions can be found in several other human experiments: The fasting blood glucose and glycated hemoglobin levels of individuals who consumed fermented dairy products were significantly reduced at the end of the experiment, indicating that fermented dairy products may prevent T2DM and related complications [136,137,138,139].

Regrettably, most of these studies are still at the stage of animal experiments. In the future, more high-quality clinical studies are urgently needed to further verify the efficacy and safety of PBFs in the human body and clarify their mechanism of action and effective dose, thereby providing more scientific and reliable strategies for the prevention and treatment of diabetes and helping to solve the economic and social burden caused by diabetes.

4.2. Reduce Cholesterol and Triglyceride Absorption

Cholesterol levels have long been considered the most important risk factor for the development of cardiovascular disease. As early as 1961, studies showed that saturated fatty acids increase cholesterol levels, which in turn increases the risk of developing cardiovascular disease [140]. Many animal and clinical experiments have shown that some probiotics can lower blood lipids. Probiotics can reduce total cholesterol levels by lowering density lipoprotein (LDL) cholesterol [26,45].

In another experiment, researchers found that the serum TG, TC, and LDL-C of hypercholesterolemic mice were significantly elevated, while the serum HDL-C level decreased. Notably, mice fed with fermented fruit juice containing Lactiplantibacillus plantarum EM and a high-fat/high-cholesterol diet showed a significant reduction in serum TG, TC, and LDL-C levels, which suggested that taking EM juice can improve hypercholesterolemia caused by a high-fat/high-cholesterol diet. Additionally, the fecal excretion of TL, TG, and TC after consuming EM juice was more than 1.33 × 10⁹ L. plantarum EM cells/mL, which was significantly higher than that of other groups. This proves that the juice fermented by Lp. plantarum EM is effective in preventing hypercholesterolemia [141].

The same conclusion was also drawn in human experiments. The researchers recruited 30 subjects who had no other diseases except hyperlipidemia. They were asked to consume a fixed amount of fermented red chili sauce for each meal. After 12 weeks, the total cholesterol level decreased from 215.5 ± 16.1 mg/dL to 194.5 ± 25.4 mg/dL [142]. In another two-parallel, double-blind, placebo-controlled intervention, the total cholesterol, low-density lipoprotein cholesterol (LDL-c), and non-high-density cholesterol of participants who received the tested Lactobacillus-fermented yogurt daily also decreased significantly [143].

These research findings have provided rich theoretical basis and research directions for in-depth exploration of the application of fermented foods in the prevention of cardiovascular diseases and regulation of blood lipids. However, more large-scale and multi-center human clinical trials are still needed to further clarify the mechanism of action, the optimal dosage, and the applicable population of probiotic fermented foods in the human body, to promote their practical application in cardiovascular health maintenance.

4.3. Enhances Antioxidant Capacity

Proteins, flavonoids, phenolic compounds, and carotenoids in plants are generally considered natural antioxidants and have attracted attention because of their special nutritional value. Multiple studies have proven that carotenoids have potential health-protective effects against many degenerative diseases, including cardiovascular diseases, age-related macular degeneration, and certain types of cancer [144,145,146,147]. (Flavonoids and phenolic compounds are mentioned in Section 3.1.2).

However, these substances in food may be destroyed by processing, reducing the already low bioavailability. Fermentation can convert conjugated phenols into free phenols by using microbial enzymes and can also change the composition by changing the protein composition, so as to achieve the purpose of improving the antioxidant capacity of food [148].(

Table 4. Changes in anti-oxidative effects of different PBFs products before and after fermentation.

Raw Materials	Fermentation Strains	Anti-Oxidative Effects	References
Papaya	Lactobacillus acidophilus	The free radical scavenging activity of DPPH and ABTS decreased, indicating that the growth of Lactobacillus acidophilus requires the scavenging of free radicals [154].	[103]
	Lactiplantibacillus plantarum	The free radical scavenging activity of DPPH and ABTS was improved, and the antioxidant capacity was enhanced.
Wheat bran	Lactiplantibacillus plantarum KCTC 3104	The free radical scavenging activity was higher than that of raw wheat bran, and the equivalent antioxidant capacity of Trolox was enhanced.	[114]
	Enterococcus faecalis KCTC 3206
Saccharin japonica	Monascus purpureus	The free radical scavenging activity of ABTS increased by 1.8 times.	[115]
Chickpea	Cordyceps militaris SN-18	The antioxidant activity was enhanced with the increase of total phenol content.	[155]
Cocoa Beans	Pichia kudriavzevii	The content of total phenol and total flavonoids was increased, and it has strong antioxidant potential.	[156]

).Plant-based foods are an important source of natural antioxidants in the human diet. During the fermentation process, microorganisms can enhance the antioxidant properties of plant-based foods by releasing active components bound to the cell wall [149]. Similarly, in the fermentation experiment of amaranth, it was also concluded that the fermentation process has a positive impact on antioxidant capacity by increasing phenolic and/or flavonoid compounds (induced by microbial hydrolysis reactions) and through their microbial synthesis [150,151,152]. Similarly, in a clinical study, researchers were pleasantly surprised to find that the simultaneous intake of β-carotene and milk fermented by lactic acid bacteria significantly increased the absorption rate of dietary β-carotene in humans and rats [153].

These research achievements have wide applications: In the food sector, they provide a theoretical basis for developing functional foods with high antioxidant activity. Future research can further optimize the combination of strains and fermentation processes to precisely control the functional properties of plant-based foods.

4.4. Regulation of Intestinal Microbiota

The human gut microbiome is a large and diverse community that contains many types of life: bacteria, archaea, eukaryotic viruses, viruses, and parasites [157,158]. These microbial florae provide a venue for PBFs to participate in the physiological activities of their hosts. Consuming fermented foods can improve intestinal barrier integrity and intestinal immunity through different mechanisms and maintain intestinal homeostasis.

PBFs can influence gut health by virtue of the probiotics they contain. PBFs are rich in probiotics such as lactic acid bacteria and Bifidobacterium. After these probiotics enter the gut, they affect the gut barrier function by regulating the expression of genes and proteins involved in tight junction signal transduction in intestinal epithelial cells [159,160]. Meanwhile, beneficial bacteria can secrete some antibacterial substances or compete with pathogens for nutrients and space, preventing the attachment and colonization of harmful bacteria. In this way, the proportion of beneficial bacteria in the gut microbiota can be increased, and the balance of the gut microecosystem can be maintained [161,162,163,164]. In an experiment evaluating the effects of PBF intake on the gut microbiota of consumers and non-consumers, researchers examined the presence of various beneficial bacteria in the intestines of 115 subjects. They found that several microorganisms associated with fermented food consumers originated from the microorganisms in fermented foods and confirmed that the abundance of gut microbiota in consumers was significantly higher than that in non-consumers [165]. In another 17-week experiment on the effects of a fermented diet on the human microbiome and immune system of adults, researchers also found that a diet high in fermented foods increased the diversity of the human microbiota and reduced inflammatory markers [166].

Metabolites produced during food fermentation, such as polyphenols and short-chain fatty acids, can regulate the intestinal environment and inhibit inflammation through chemical signals. Many studies have shown that polyphenols can stimulate the growth of symbiotic bacteria and beneficial microbial communities while inhibiting the growth of pathogenic bacteria by altering the gut microbiota [167,168,169]. However, polyphenols are easily recognized by the body as exogenous substances, so their bioavailability is relatively low. Researchers measured the plasma concentration and urinary excretion of adults after a single-dose intake of polyphenols and found that a small portion of dietary polyphenols (5–10% of the total intake) can be absorbed and utilized by the small intestine after deglycosylation. Still, the bioavailability of most polyphenols remains low [170]. Fermentation can decompose complex fibers (such as cellulose and pectin) into fermented foods into soluble dietary fibers through various hydrolases (such as amylase and β-glucosidase) secreted by microorganisms and release bioactive compounds (such as polyphenols and flavonoids) originally wrapped by the fibers, thereby improving the bioavailability of polyphenols [171,172]. Taking the fermentation of beans as an example, enzymatic hydrolysis can significantly release the bound polyphenols (such as anthocyanins and protocatechuic acid) originally wrapped by fibers, converting them into free polyphenols and increasing their bioavailability by approximately 80% [173]. Short-chain fatty acids (SCFAs) can also balance the gut microbiota by inducing a more favorable environment for the growth of beneficial gut microorganisms or influencing mucus concentration [174,175]. In addition, SCFAs activate the mitogen kinase signaling pathway through G protein-coupled receptors on intestinal epithelial cells, promote the production of immune factors, improve the intestinal immune function of mice, and enhance the intestinal barrier function [176,177]. In a mouse model of inflammatory bowel disease fed with fermented barley and soybeans, the intestinal morphology was restored, and the levels of tight junction proteins were increased, which was beneficial to intestinal integrity [178].

In summary, PBFs can regulate the gut microbiota, enhance the gut barrier function, and inhibit the inflammatory response. Their characteristic of improving gut health through multiple pathways provides a scientific basis for targeted nutritional interventions in gut-related diseases such as inflammatory bowel disease and metabolic syndrome. Currently, there are still very few clinical studies on diseases. In the future, it is necessary to further explore their molecular mechanisms and clinical translation pathways.

5. Industrialization Challenges of PBFs

The first four chapters of this paper systematically expound the remarkable advantages of PBFs in improving the sensory characteristics of food and enhancing nutritional functions. These advantages are strongly promoting PBFs to gradually enter the market, showing certain market potential. However, to achieve large-scale industrialization, it is still necessary to break through multi-dimensional bottlenecks:

5.1. Potential Safety Risks

Microbial contamination is considered an important factor leading to frequent food safety accidents and foodborne diseases [179]. To ensure the nutritional value and safety of food during fermentation, storage, transportation, and marketing, we must take effective measures to prevent possible contamination at each stage.

5.1.1. Exogenous Pollution

The open fermentation environment makes it easy for microorganisms (such as molds and bacteria) in water, air, the human body, or mechanical equipment to enter the fermentation system [180,181,182]. These microorganisms will compete with the target fermenting microorganisms for nutrients during the fermentation process, affecting the fermentation effect and even producing toxins [183]. They may also change the metabolic pathway of fermentation, producing undesirable metabolic products, which in turn affect the quality and safety of fermented foods. Researchers attempted to design LAB to express specific enzymes capable of degrading mycotoxins or producing antibacterial peptides with enhanced efficacy, but the efficiency was limited [184].

We hope that by adopting the laminar flow clean system, steam sterilization device, and air filtration technology, we can prevent foreign microorganisms from competing for nutrients and interfering with the target fermentation metabolism and avoid the formation of toxins (such as aflatoxin) and abnormal metabolic products. By optimizing fermentation parameters (pH, temperature, dissolved oxygen) and real-time monitoring of the fermentation process, we can ensure the reproducibility of beneficial metabolic pathways (such as phenolic conversion and SCFAs production) and prevent the formation of undesirable metabolic products. Simultaneously implementing the whole-process HACCP system and setting up microbial and toxin detection controls at critical control points (raw material acceptance, pre-treatment, main fermentation, sterilization, and packaging) is of crucial practical significance in reducing potential hazards and improving food quality [185,186].

5.1.2. Endogenous Contamination

Under normal circumstances, microorganisms in food are generally harmless. However, under certain specific conditions, they may secrete some risk substances harmful to the human body (such as biogenic amines and nitrosamines). During the fermentation process, some microorganisms will decompose proteins and amino acids in food to produce biogenic amines (such as histamine and tyramine) [187,188]. Research shows that excessive intake of biogenic amines can cause headaches, palpitations, or allergic reactions, posing a safety risk to special populations (such as those taking monoamine oxidase inhibitors) [189,190]. Meanwhile, due to the non-standard use of chemical nitrogen fertilizers, there is often a phenomenon of excessively high nitrite residues in plant raw materials [191]. Under low pH conditions, nitrites react with amines or amides naturally present in plants to form carcinogenic nitrosamines [192,193,194].

To reduce the occurrence of the above situations, we believe that strict strain screening and functional regulation should be carried out. According to the characteristics of raw materials (such as protein/phenol content) and different metabolic goals, non-pathogenic strains with specific functions (such as lactic acid bacteria and yeasts) should be selected. For example, strains carrying amino acid decarboxylase genes (hdc, tdc) should be excluded through whole-genome sequencing to inhibit the synthesis of biogenic amines [35,195,196]. Alternatively, strains with nitrate reductase activity (such as Lactobacillus plantarum) can be screened to degrade nitrite [197,198]. Online biosensors can be used to regulate temperature, dissolved oxygen content, and pH value in real time (for example, the activity of decarboxylase is the lowest when the pH is between 4.2 and 4.8) and limit the conditions that are favorable for microorganisms to undergo chemical reactions and produce undesirable metabolic products. At the same time, techniques such as gas chromatography can be used to monitor their content and block pollution occurrence at any time [199].

Through effective control of risk substances such as biogenic amines, nitrites, and nitrosamines, the safety of PBFs can be maximally ensured, allowing consumers to consume them with greater peace of mind.

5.2. Inconsistency of Product Efficacy

5.2.1. Fluctuation of Bioactive Components in Raw Materials

The bioactive components of plant raw materials show significant fluctuations due to differences in origin, variety, and harvest season, which directly affect the stability of the content and composition of functional components in the final product.

For example, catechins are the compounds responsible for the bitterness and astringency in tea. The total catechin content in the fresh buds and young leaves of green tea picked during the summer and monsoon crop seasons is significantly high [200]. In the subsequent tea processing, more methods need to be adopted to reduce the bitterness and astringency of tea and tea products [201].

To address the issue of fluctuations in the bioactive components of raw materials and enhance the stability and quality of products, it is necessary to establish a global raw material database. This database should integrate information on plant raw materials from different origins, varieties, and harvest seasons. Meanwhile, combined with geographical indication certification, it can accurately identify the specific origins and production characteristics of high-quality raw materials. With quality control standards for active ingredients, quantitative analysis can be conducted along with maintaining strict control of the key active ingredients in raw materials. Through data mining and intelligent algorithms, raw material combinations with stronger mutual compatibility can be screened out from the massive information in the database to ensure the stability of the fermentation process and the consistency of product efficacy, providing a solid raw material foundation for the industrial production of high-quality PBFs.

5.2.2. Process Sensitivity and Standardization Challenges

All microorganisms have their optimal growth environments, and different target products also require changes in the fermentation environment. Therefore, PBFs have very strict requirements for fermentation conditions. A slight deviation can lead to a slowdown in the growth and metabolic rate of microorganisms or even their death, and the production rates of key metabolites (such as phenols and short-chain fatty acids) will also fluctuate. It is urgent to develop an intelligent fermentation system. This system will be centered around an AI-driven sensor network, which can analyze metabolic dynamics in real time and achieve automatic feedback adjustment of process parameters such as strain ratio and fermentation duration.

Once fluctuations in the production rate of key metabolites are detected, the system will immediately adjust the corresponding parameters to ensure that the fermentation process is always in the optimal state, thereby stabilizing the production rate of key metabolites and guaranteeing the stability and reliability of the PBFs product quality.

6. Summary and Prospect

In conclusion, the raw materials of PBFs are mainly divided into three categories: fruits and vegetables, soy products, and grains. PBFs significantly enhance nutritional value and health functions through microbial transformation. All of them can balance organic acids through fermentation, achieving natural preservation and palatability synergy. Fermentation also promotes the transformation of antioxidant substances such as phenols and carotenoids, driving the innovation of functional foods. On the sensory level, aroma-producing yeasts and organic acids work together to build a multi-level flavor system. In terms of health benefits, the metabolic products of PBFs can regulate the balance of intestinal flora and enhance the immune barrier, and their bioactive peptides and antioxidant substances also have protective effects such as lowering blood pressure and blood lipids.

Although certain achievements have been made in the research of PBFs, the development of PBFs still faces multiple challenges. Currently, the raw materials and forms of PBFs on the market are relatively monotonous. The raw materials mainly consist of soybeans and grains, while the potential of nuts, seeds, and materials of both medicinal and edible origin (such as wolfberry and polygonatum) has not been fully exploited. The product forms are mostly concentrated in beverages or foods, but innovative forms such as fermented seasonings and medicines (such as fermented Chinese herbal preparations) are worthy of exploration. For instance, in response to the low content of active ingredients or toxicity issues of Chinese herbal medicines, microbial fermentation technology can effectively enhance their efficacy, reduce toxicity, and improve flavor, providing a new path for the modernization of Chinese medicine. The existing achievements are mostly based on in vitro experiments or animal models; however, the potential mechanism between PBFs and immune regulation, as well as metabolic regulation, in the complex physiological environment of the human body are still unclear.

In the future, large-scale multi-center randomized controlled trials combined with multi-omics technologies are needed to precisely analyze the actual effects of PBFs in the prevention and treatment of chronic diseases. Technological innovation is the key bottleneck for the industry to make breakthroughs. The biological utilization rate and product texture of plant proteins still need to be improved through strain selection and process optimization. Meanwhile, controlling production costs and standardizing production processes are essential for large-scale application. Only by promoting the diversification of raw materials, in-depth understanding of mechanisms, and intensive technology in a coordinated manner can we expect to achieve the industrial transformation of PBFs from “experience-driven” to “data-driven,” making them truly a new generation of healthy foods with controllable safety and clear efficacy.