Plant-Derived Extracts in Tofu Production and Functionalization: Current Status and Future Perspectives

1. Introduction

Tofu is a protein-rich food obtained through the coagulation of soymilk proteins, followed by pressing the resulting curds into molds to eliminate excess whey. In concept, the manufacturing process of tofu shares significant similarities with traditional cheese making.

1.1. Soymilk and Tofu Characteristics

The main characteristics of soymilk are reported in Table 1. Compared to cow’s milk, soymilk exhibits a comparable protein content, whereas its fat and carbohydrate (sugar) levels are approximately half as high. The composition of soymilk directly dictates the nutritional profile of tofu, which is characterized by a high protein concentration, low saturated fat levels, a complete absence of cholesterol, and a rich content of essential minerals such as iron, calcium, and magnesium [1] (Table 1).

Worldwide tofu production reaches an estimated 10 million tons per year. China is the world’s leading producer and consumer, followed by Japan, South Korea, Vietnam, and Indonesia, while European and North American markets are experiencing rapid growth.

1.2. Tofu Benefits

Soybean-based foods, particularly tofu, represent a cornerstone of global human nutrition, serving as an accessible and highly digestible source of high-quality proteins, essential minerals, and bioactive isoflavones such as genistein, daidzein, and glycitein [2,3,4,5,6]. These phytochemicals, recognized for their phytoestrogenic properties, are widely associated with significant health-promoting benefits, such as mitigating cardiovascular risks, reducing blood cholesterol levels, and helping prevent chronic conditions like osteoporosis and specific types of cancer [2,3,4,5,6,7].

1.3. Tofu Making

The traditional manufacturing process is based on the thermal denaturation of soymilk proteins, primarily glycinin (11S) and β-conglycinin (7S), which constitute approximately 80% of the total protein content [3,4]. Heating represents a critical technological step required to expose inner hydrophobic groups and negatively charged disulfides, while simultaneously inactivating anti-nutritional factors such as the Kunitz Trypsin Inhibitor (KTI) and lipoxygenase enzymes responsible for undesirable beany flavours [2,6,8].

Coagulation, the most decisive phase for tofu quality, is traditionally achieved by using salts as coagulant agents, namely magnesium chloride (nigari) or calcium sulphate (gypsum) [9], whereas alternative methods employ organic acids such as lemon juice and vinegar. Nigari is obtained from seawater after the selective removal of sodium chloride, serving essentially as a by-product of salt production. The use of nigari yields a smooth, tender tofu with a slightly sweet taste, while enriching the product with trace minerals, particularly magnesium [9]. Alternatively, soy protein coagulation can be induced using organic acids like glucono-δ-lactone (GDL) [4,6,7]. These agents drive protein aggregation through isoelectric point reduction, salt bridging, and no-covalent interactions such as hydrogen bonding [2,3,6]. Despite their efficacy, traditional coagulants present several operational drawbacks; for instance, certain salt coagulants have limited solubility and demand precise handling to prevent batch inconsistencies, whereas rapid-acting acid coagulants frequently lead to hard, non-uniform, or gritty textures [4,6,8].

1.4. Plant-Derived Coagulants

Driven by the contemporary shift toward clean-label products and the increasing demand for sustainable functional foods, recent research has pivoted toward plant-derived coagulants [6,10]. These vegetable alternatives, ranging from fruit juices to floral extracts, not only serve as effective protein-aggregating agents but also act as multifunctional ingredients capable of enriching tofu with polyphenols and antioxidants, thereby aligning production with modern nutritional requirements and sustainability goals [2,3].

Recent studies have validated the efficacy of various botanical extracts in inducing protein aggregation while simultaneously enhancing the nutritional and functional profile of the final product. For instance, extracts from cardoon flowers (Cynara cardunculus) and Hibiscus (Hibiscus sabdariffa) have demonstrated effective coagulating properties [10], with cardoon-based coagulation yielding superior results compared to magnesium chloride [8]. Furthermore, the valorisation of agro-industrial by-products, such as grape pomace, has emerged as a promising strategy to enrich tofu with high concentrations of polyphenols and robust radical-scavenging activity, effectively transforming it into a multifunctional food item [6]. Other natural agents, including lemon juice, tamarind, kiwi, and Moringa oleifera, have been investigated for their ability to influence yield, moisture retention, and mineral content [4,11,12,13].

In addition to their role in coagulation, plant extracts can act as natural preservatives, addressing the inherently short shelf-life of protein-rich soy products [2]. Aqueous extracts of tulsi (Ocimum sanctum), for instance, have been shown to extend tofu’s shelf-life up to 7–8 days without refrigeration by inhibiting lipid peroxidation and proteolytic activity [2]. Similarly, essential oils from galanga and ginger exhibit potent antimicrobial properties, while preserving textural integrity during storage [14].

The choice of plant-based coagulants significantly modifies the textural and sensory characteristics of tofu [3]. While traditional salt coagulation often produces a firm, granular structure, acid-driven plant coagulants tend to yield a softer, more porous matrix [2,4,8,10]. This versatility enables the development of a diverse range of products, varying from traditional solid blocks to creamy soy puddings such as douhua [2].

Although soybean remain the primary vegetable source of protein for tofu manufacturing, alternative oilseeds and legume sources have also been explored, including kenaf (Hibiscus cannabinus), sesame and peanut seed [15].

Herein, we provide a comprehensive review of the latest research regarding the development and application of plant-based coagulants for tofu making. The potential benefits, encompassing product yield, quality enhancement, and the incorporation of beneficial plant-derived metabolites, are thoroughly discussed.

2. Vegetables as Natural Coagulants in Tofu Preparation

In tofu manufacturing, the use of plant-derived materials has become an increasingly widespread practice to replace traditional coagulants, enhance shelf life, and improve the overall nutritional profile. These plant materials are primarily utilized in the form of crude extracts, juices, or essential oils.

Conventionally, tofu is prepared by dissolving nigari (10-15 g) in water (100-150 ml) and adding it to 3-4 liters of soymilk. Prior to the addition of coagulant, the soymilk is heated to 80 °C. Following coagulant introduction under gentle stirring, the mixture is maintained at 80 °C for an additional 10 min, after which proteins aggregation occurs under static conditions. Once coagulation is complete, white curds separate from the whey. The curd is subsequently transferred into a perforated mold and then pressed. Varying the pressing duration yields tofu with distinct textural characteristics: 10–15 minutes produces soft (silken-style) tofu; 20–30 minutes yields medium-firm tofu; and 30–60 minutes results in firm tofu.

In terms of product yield, starting from 1 kg of dry soybeans processed with 10 liters of water typically yields, approximately 7 to 9 liters of soymilk [16]. From this volume, an average of 1.5–2.0 kg of tofu can be produced [16,17]. As a general order-of-magnitude estimate reported in literature and observed in industrial practice, depending on pressing conditions and final moisture content, 1 liter of soymilk yields approximately 150–250 g of firm tofu, 250–400 g of soft tofu, and up to 400–500 g of silken tofu [17].

2.1. Hibiscus sabdariffa L./Roselle

Hibiscus sabdariffa L. is a resilient tropical shrub belonging to the Malvaceae family, widely cultivated across Africa due to its exceptional hardiness and low water requirements (Figure 1A). Its characteristic red calyces (Figure 1B) serve as the primary raw material for traditional, refreshing beverages such as karkadè (Figure 1C) and zobo, which are renowned for their distinct, tart, and acidic profiles [10,18].

From a nutritional perspective, roselle calyces are exceptionally low in calories yet rich in vitamin C, flavonoids, anthocyanins, organic acids, tannins, minerals, and diverse antioxidants [19,20]. Consequently, regular consumption of hibiscus tea has been linked to multiple health-promoting benefits, including antioxidant, diuretic, digestive, antihypertensive, and hypolipidemic activities [21,22]. In vitro investigations further indicate that extracts, obtained from dried roselle calyces, possess antiproliferative and pro-apoptotic properties against specific cancer cell lines, as well as potential synergistic efficacy when combined with conventional chemotherapeutic agents [23]. Beyond functional health attributes, the natural high acidity of aqueous roselle extracts, which drives their characteristic tart flavor, presents promising industrial food, such as functioning as an alternative natural coagulant in tofu production [10,18].

Recent investigations have explored Hibiscus sabdariffa L. extract as a sustainable alternative to conventional coagulants in tofu production, assessing both coagulation efficiency and the enrichment of the final product with bioactive compounds.

Tofu yield varies slightly depending on experimental parameters such as extract concentration and soymilk preparation, but overall performance remains comparable to traditional coagulants.

Fasoyro et al. [18] reported a concentration-dependent increase in tofu yield from 500 mL of soymilk, recovering 87.3 g of tofu with a 2.5% hibiscus extract, which increased to 90.2 g at 5% and 95.5 g at 10%. Similarly, Pacifico et al. [10] established an optimal yield of 82.5 ± 5.8 g using 50 mL of hibiscus extract (5 to 7 mg/mL) per 500 mL of soymilk, demonstrating efficacy comparable to the 88.2 g achieved with nigari.

Beyond driving protein coagulation via acidification, hibiscus extract acts as a reservoir of bioactive phytochemicals that integrate into the protein network during gel formation, thereby enhancing the nutritional and functional profile of tofu. The primary metabolites retained within the tofu include phenolic acids, particularly chlorogenic acids (CQAs) and caffeoylshikimic acid; alongside flavonols such as rutin and quercetin; and anthocyanins, mainly cyanidin, delphinidin, and their derivatives. The total concentration of these metabolites has been estimated at approximately 2 mg per 100 g of tofu [10]. Their successful incorporation within the tofu matrix significantly contributes to a marked antioxidant capacity, as demonstrated by the ABTS radical scavenging assays, yielding a product with superior antioxidant properties compared to conventionally manufactured tofu [10].

From a sensory perspective, hibiscus extract imparts a mildly acidic, refreshing flavour reminiscent of karkadé infusions, alongside a distinctive reddish hue that distinguishes the product from conventional tofu. In addition, hibiscus-coagulated tofu typically exhibits a softer, more porous texture compared to the firmer, more granular structure characteristic of nigari-coagulated tofu [18].

Overall, current evidence demonstrates that H. sabdariffa extract is a viable natural coagulant capable of delivering yields comparable to traditional coagulants while simultaneously elevating both functional and sensory qualities. The optimal balance between coagulation yield and sensory acceptance appears to be achieved at an extract concentration of approximately 2.5% [10,18].

2.2. Hibiscus cannabinus Seeds Tofu

Alternatively, the production of tofu-like products has been proposed using protein extracts derived from Hibiscus cannabinus seeds [15]. Commonly known as kenaf, this notable horticultural plant offers significant nutritional and economic benefit [15]. Kenaf seeds are recognized as an abundant source of proteins, unsaturated fatty acids and antioxidants. Due to widespread agricultural cultivation, substantial quantity of seed by-products is generated, creating an opportunity to extract these proteins and use kenaf seed milk for tofu production [15].

Figure 2. A) Hibiscus cannabinus flowers; B) Hibiscus cannabinus seeds; C) seeds extract.

Figure 2. A) Hibiscus cannabinus flowers; B) Hibiscus cannabinus seeds; C) seeds extract.

Four distinct coagulants were evaluated to produce tofu from kenaf (Hibiscus cannabinus) seed milk: glucono-delta-lactone, citric acid, aluminum potassium salt and calcium sulphate [15], alongside a conventional soymilk control coagulated with calcium sulphate. Processing 100 g of kenaf seeds were obtained 400 ml of milk extract using traditional tofu preparation methods. Coagulation yields varied by agent, reaching 220 g/L with glucono-delta-lactone, 200 g/L with aluminum potassium salt, 150 g/L with citric acid, and 106 g/L with calcium sulphate, compared to approximately 350 g/L for the soybean control, reflecting a lower overall coagulation efficiency [15]. Furthermore, texture profile analysis indicates that kenaf-based tofu exhibited lower springiness, cohesiveness, hardness and chewiness than the control [15].

These findings highlight the versatile utilization of the Hibiscus genus within plant-based food innovation, demonstrating a dual function capacity where Hibiscus sabdariffa calyces act as a natural coagulant, while Hibiscus cannabinus seeds serve as a protein source for milk extraction and subsequent curd formation.

2.3. Cynara cardunculus

Cardoon (Cynara cardunculus L.), a member of the Asteraceae family, is an annual herbaceous species, characterized by thorny leaves and flower heads morphologically similar to those of the globe artichoke, from which its common name “wild artichoke” is derived (Figure 3).

Widely distributed across the Mediterranean basin, cardoon has a long history of utilization in both culinary and pharmaceutical fields. Notably, extracts from its flowers have traditionally been used as natural milk coagulants in artisanal cheesemaking due to their robust proteolytic activity [24].

Furthermore, these flower extracts are rich in bioactive phytochemicals, predominantly phenylpropanoids and flavonoids, such as chlorogenic acid, dicaffeoylquinic acids, caffeic acid, and luteolin, which drive a broad spectrum of biological activities, including antioxidant, anti-inflammatory, hepatoprotective, choleretic, antimicrobial, hypolipidemic, and neuroprotective properties [25].

Building upon this coagulating heritage, cardoon flower extract has recently been evaluated as a novel natural coagulant for tofu production [8]. In this study, 3.5 g of dried cardoon flowers and 25 g of NaCl were finely ground using a mortar and pestle and subsequently blended with 1 L of water-soluble soybean extract prepared following established protocols [26]. Subsequently, 2 mL of the resulting cardoon extract was used to coagulate 2 L of soymilk, with nigari serving as the conventional reference coagulant [8].

The coagulating activity of the cardoon extract is mainly attributed to the presence of the aspartic proteases cardosin A and cardosin B, which hydrolyse peptide bonds within soybean proteins to induce protein aggregation and gel network formation.

Tofu produced using cardoon extract showed a significantly higher yield (195 g per 100 g of soybeans) compared to nigari-coagulated tofu (162 g per 100 g of soybeans). Moreover, the cardoon-derived product exhibited elevated protein and lipid contents alongside a slightly increased level of acidity [8].

Texture profile analysis revealed that tofu produced with cardoon extract exhibited lower hardness, adhesiveness, springiness, and cohesiveness than its nigari-coagulated counterpart, yielding a softer and less granular matrix. The product also displayed a marginally darker appearance while preserving a high antioxidant capacity, likely due to the incorporation of phenolic compounds natively present in cardoon flowers [8].

Taken together, these findings demonstrate that cardoon flower extract represents a promising plant-based coagulant for tofu manufacturing, effectively combining higher processing yields with enhanced nutritional quality and favorable textural properties. In addition, the inclusion of naturally occurring antioxidant phytochemicals elevates the overall functional value of the final product, making cardoon extract an attractive alternative to traditional mineral coagulants [8].

2.4. Kiwi fruit

Kiwi fruit is an edible fruit produced by several vine species belonging to the genus Actinidia (family Actinidiaceae), with Actinidia chinensis being the principal commercial species (Figure 4).

Kiwi fruit is characterized by a pleasantly acidic and refreshing taste alongside its high nutritional value. It is an excellent source of vitamin C (85 mg/100 g), potassium, magnesium, vitamin E, copper, iron, and dietary fiber. It is relatively low in calories (approximately 44 kcal/100 g), consisting of roughly 84% water, 9% carbohydrates, small amounts of lipids—including omega-3 fatty acids—and proteins. A distinctive biochemical feature of kiwi fruit is the presence of actinidin, a cysteine protease exhibiting proteolytic activity comparable to that of bromelain from pineapple. Furthermore, kiwi fruit contains a wide range of antioxidant compounds, including polyphenols, flavonoids, lutein, zeaxanthin, and β-carotene [27].

The application of kiwi fruit extract as a natural coagulant for soy proteins has attracted increasing attention due to its combined acidifying capacity and proteolytic activity [12]. Tofu manufacture using kiwi fruit extract has been successfully achieved by acidifying soymilk to pH 2.0 and maintaining the coagulation temperature at 80 °C [12].

Compared with conventional salt coagulants, such as calcium sulphate (CaSO₄), magnesium chloride (MgCl₂), and alum, kiwi fruit extract exhibits distinct effects on tofu yield, gel microstructure, textural properties, and storage stability.

Comparative studies have demonstrated that kiwi fruit extract produces higher tofu yields than other plant-derived coagulants, including lemon juice [12]. However, tofu coagulated with kiwi fruit extract also exhibits a higher syneresis index, indicating a greater tendency to release whey during storage, which may result in increased moisture, nutrient, and weight losses. Conversely, alum promotes the formation of finer protein networks with enhanced water-holding capacity, thereby reducing syneresis and maintaining higher moisture levels in the final product [3].

Coagulant selection markedly influences tofu texture. Magnesium chloride (nigari), forms a relatively homogeneous gel network yet acts rapidly, producing a firmer and more granular texture than acid-induced coagulation [2]. Calcium sulphate (CaSO₄) typically generates a coarse, granular structure characterized by high hardness and low elasticity [7]. Among salt coagulants, alum yields the highest hardness values (up to 84.55% in some studies), resulting in a dense and relatively dry tofu [11]. In contrast, tofu produced using kiwi fruit extract exhibits a firm, compact, and cohesive gel structure [12].

From a microbiological perspective, tofu prepared with kiwi fruit extract remains stable after seven days of storage, without detectable signs of spoilage. These findings suggest that endogenous compound within the kiwi fruit extract inhibit bacterial and fungal growth, potentially extending product shelf life [12]. Nevertheless, the retention of bioactive antioxidant compounds derived from kiwi fruit extract within the final tofu matrix remains an area requiring empirical investigation [12].

Overall, current evidence indicates that kiwi fruit extract is a promising plant-based coagulant for tofu production, providing high manufacturing yield while producing a compact and cohesive gel matrix. Nevertheless, its higher tendency toward syneresis compared with conventional salt coagulants highlights the need for further optimization of processing conditions to improve water retention and storage stability [12].

2.5. Tamarindus indica

Tamarindus indica is a tropical evergreen tree belonging to the family Fabaceae (subfamily Detarioideae) and represents the only species of the genus Tamarindus [28]. It is a slow-growing and exceptionally long-lived tree that may exceed 30 m in height under favourable environmental conditions. The fruit is an indehiscent legume (lomentum), approximately 10–15 cm long, containing an edible brown pulp and several hard, flattened seeds (Figure 5).

Tamarind has a long-standing history of use as a culinary ingredient, ornamental plant, and medicinal resource. Beyond its use in beverages and traditional dishes, the fruit contains several bioactive compounds, notably the polyphenol tamarindin, which exhibits documented antimicrobial, antibacterial, and antiviral activities [29]. Different parts of the plant, including the pulp, leaves, and bark, are extensively employed in traditional healing systems; for instance, Ayurvedic medicine employs tamarind to manage gastrointestinal disorders and toothache, whereas leaf infusions are frequently consumed to alleviate malarial fever. Moreover, tamarind exerts dose-dependent effects on gastrointestinal function, acting as a mild digestive aid at lower doses and functioning as a laxative at higher concentrations [30].

Recently, T. indica has attracted interest as a sustainable natural coagulant for tofu manufacturing, with the fruit pulp, seeds, and flowers all evaluated as sources of coagulating extracts [4,11,13]. In these studies, aqueous extracts were prepared from these different plant materials, filtered, standardized to a titratable acidity equivalent to 2% anhydrous lactic acid, and incorporated into heated soymilk at a ratio of 20 mL per 200 mL of soymilk [4]. Soy protein coagulation is mainly driven by the naturally occurring tartaric acid within tamarind. Following standard tofu manufacturing procedure, the extract is added to soymilk heated to approximately 80 °C, though coagulation requires approximately 15 min, which is notably longer than the duration typical of conventional coagulants [4,13].

Tamarind extracts demonstrate promising coagulation performance. Fruit pulp extract yielded 21.0 ± 0.72 g of tofu per 100 mL of soymilk, outperforming the 17.3 g achieved using nigari, while seed extract produces the highest yield overall, reaching approximately 27 g per 100 mL of soymilk. Flower extracts yield comparatively lower amounts, averaging around 16.5 g per 100 mL [4]. The resulting tofu typically contains approximately 12% protein, 1.8% fat, and 86% moisture [4,13], alongside a relatively high vitamin C content (2.69 mg/100 g), and appreciable concentrations of iron and potassium [11], maintaining a final product pH of approximately 5.5 [13].

From a technological perspective, tamarind-coagulated tofu exhibits a compact structure, but lower firmness compared to tofu produced using conventional salt-based coagulants or alum. Texture profile analysis reported was hardness and chewiness when pulp extract was used as the coagulant [11,13]. Furthermore, tamarind extracts impart characteristic fruity and green aroma notes associated with volatile compounds such as trans-2-hexen-1-ol and cis-3-hexen-1-ol, resulting in exceptional consumer acceptance and high sensory ratings for flavour. [4,11].

Microbiologically, freshly prepared tamarind-coagulated tofu is free from detectable coliform bacteria [11]. However, compared to tofu coagulated using Epsom salt, it exhibits reduced ambient storage stability showing higher fungal and total viable microbial counts after six days of storage. This accelerated deterioration was primarily attributed to the higher nutrient availability provided by the tamarind extract matrix [13].

2.6. Rhododendron arboreum

Despite the well-established toxicity of Rhododendron species and other members of the Ericaceae family, the traditional consumption of both honey and plant-derived products, particularly flowers (Figure 6), has long been documented in several countries.

Nevertheless, the primary use of Rhododendron species remains medicinal. These plants have been extensively employed in traditional medicine across Asia, Europe, and the Americas, as well as in Ayurvedic medicine, homeopathy, and aromatherapy. Across different cultural and geographical contexts, the most common therapeutic applications include the management of hypertension, pain, inflammatory disorders, and infectious diseases [31].

Beyond their ethnopharmacological relevance, Rhododendron flowers have recently attracted interest as functional food ingredients, with R. arboreum floral juice evaluated specifically as a natural coagulant for tofu production [7]. Tofu manufacture is conducted at 85 °C using floral juice supplemented with 0.25% citric acid and incorporated into soymilk at a concentration of 1% (v/v). This floral extract successfully induces soy protein coagulation, cleanly separating the protein-rich curd from the whey. Following filtration through a muslin cloth and pressing for 30 min, the final tofu yield reaches approximately 13.5 g per 100 mL of soymilk [7].

Chemical characterization of the tofu demonstrates high concentrations of isoflavones, including glycitin, glycitein, daidzin, and daidzein, suggesting that the incorporation of R. arboreum floral juice enriches the profile of health-promoting phytochemicals [7]. Consequently, R. arboreum floral juice emerges as a promising plant-based coagulant capable of enhancing both the nutritional and functional properties of tofu [7].

However, given the natural presence of toxic diterpenoids within Rhododendron species, rigorous safety assessment, precise processing optimizations, and comprehensive evaluations are essential before commercial food applications can be pursued [7].

2.7. Grape pomace

Grape pomace, the solid residue remaining after grape pressing, comprising skins rich in polyphenols, anthocyanins, and aroma compounds alongside tannin- and oil-dense seeds (Figure 7), serves as a promising natural coagulant for tofu manufacturing [6].

Due to its high content of organic acids, grape pomace has been investigated as a natural coagulant for tofu production. Investigating this by-product of the wine industry provides an innovative valorisation strategy by converting winery waste into a functional ingredient [6]. Research has evaluated various cultivars, including red varieties (Barbera and Pinot Noir) and aromatic white varieties (Chardonnay and Moscato), testing both fresh and distilled pomace sources [6]. Following drying, milling below , and aqueous extraction via gentle heating for 15 to 20 minutes, the filtered extract is incorporated into soymilk at 75 °C using optimized concentrations of 2.5% to 5% [6]. Grape pomace acts as both an acid and salt coagulant driven by native organic acids, principally tartaric, malic, and citric acids, as well as mineral salts, especially potassium.

Although tofu yield was comparable to that obtained using conventional coagulants, the use of grape pomace as a natural coagulant significantly altered the characteristics of tofu compared with conventional coagulation methods. The most evident difference was colour, with samples ranging from amber-yellow when produced with Chardonnay or Moscato pomace to blue-violet when Barbera or Pinot Noir pomace was used [6].

Chemically, pomace-coagulated tofu shows slightly lower protein content and pH than conventional tofu but a higher carbohydrate content, reaching up to 15% in tofu produced with Moscato pomace, due to the presence of residual grape sugars, alongside a 2- to 10-fold increase in total polyphenols and a remarkable 9- to 80-fold radical-scavenging antioxidant activity [6].

Textural properties differ heavily by cultivar: Barbera pomace yields an extremely soft, almost spreadable texture, whereas Pinot Noir produces a firmer, drier tofu and Moscato and Chardonnay pomace tofu with a semi-solid structure. Overall, pomace-coagulated tofu exhibits greater hardness and adhesiveness coupled with lower cohesiveness and springiness relative to magnesium chloride or citric acid controls [6].

Sensory evaluation shows strong consumer acceptance, appreciating the characteristic wine-derived aromas and mild sweetness, particularly at 5% pomace extract concentration [6].

In conclusion, the use of grape pomace as a tofu coagulant is not only technologically feasible but also represents a sustainable strategy for valorising a wine industry by-product, while delivering an antioxidant-enriched functional food [6].

2.8. Moringa olifera

Moringa oleifera, commonly referred to as the horseradish tree, is a rapid-growing, drought-resistant tree belonging to the Moringaceae family, widely distributed across tropical and subtropical regions worldwide, and capable of reaching heights of approximately 7 m (Figure 8 A).

The root system emits a characteristic pungent aroma and flavour reminiscent of horseradish, which accounts for its common vernacular name. Virtually all anatomical parts of the plant are edible and possess significant nutritional value. Specifically, the bipinnately compound leaves, composed of numerous distinct leaflets (Figure 8 B), serve as an excellent source of high-quality plant proteins, essential vitamins, and bioavailable minerals. Exhibiting a mildly pungent and palatable organoleptic profile, the foliage is suitable for consumption either fresh or thermally processed.

The flowers are small, numerous (Figure 8 C), and edible, and are commonly incorporated into salads or other culinary preparations. M. oleifera is also recognized as an important nectar-producing species, supporting honey production from its abundant blossoms.

The fruits are elongated pods (Figure 8 D) that are typically consumed after boiling and have an organoleptic profile resembling that of asparagus. In traditional Siddha medicine, the pods have historically been regarded as potent aphrodisiacs for both males and females.

Moringa oleifera seeds (Figure 8 E) can be milled into flour or consumed after boiling or roasting, yielding a flavour profile comparable to that of chickpeas.

Preclinical studies have extensively documented the therapeutic potential of Moringa oleifera, revealing a broad spectrum of pharmacological activities. Ethanolic leaf extracts exhibit significant anti-inflammatory activity comparable to that of ibuprofen [32], alongside potent antioxidant effects driven by free radical scavenging mechanisms [33]. Furthermore, M. oleifera extracts demonstrate anticancer and pro-apoptotic efficacy in murine models without detectable toxicity, as well as hepatoprotective effects by promoting recovery from antitubercular drug-induced liver injury [34,35]. Collectively, these findings underscore the potential of Moringa oleifera as a valuable source of bioactive phytochemicals possessing antioxidant, anti-inflammatory, hepatoprotective, and chemo preventive properties [35], though rigorous and well-designed clinical studies remain necessary to validate these effects in humans. Beyond its ethnopharmacological relevance,

M. oleifera seed extract functions as an effective natural coagulant for tofu production, successfully inducing curd formation, while substantially upgrading the nutritional and sensory profiles of the final product [11].

The coagulant extract is prepared by decorticating the seeds to isolate the kernels; subsequently, 300 g of kernels are wet ground with an equal volume (300 mL) of water and the resulting slurry is filtered, to yield the active coagulant solution [11].

Tofu is produced according to the conventional manufacturing process through the incorporation of the plant extract, specifically by introducing 200 mL of M. oleifera seed extract per 10 L of soymilk. The mixture is allowed to coagulate for approximately 4 h prior to thermal treatment at elevated temperature for 30 minutes. The resulting curd is subsequently drained and pressed to separate the whey, followed by cutting into uniformly sized blocks [11].

The tofu yield reaches 12.84 g per 100 mL of soymilk, a performance comparable to traditional coagulating agents. Notably, Moringa-coagulated tofu exhibits a higher total protein content, likely due to the incorporation of residual seed proteins into the soy protein matrix during coagulation, alongside an enhanced concentration of B-complex vitamins [11].

Sensory evaluation confirms high overall consumers acceptability, driven by favourable textural characteristics and structural consistency. Consequently, Moringa oleifera seed extract represents an effective natural coagulant capable of producing a functional tofu variant with superior nutritional profiles and desirable organoleptic properties relative to conventional mineral coagulants.

2.9. Maize

Maize (Zea mays L.), an annual cereal crop belonging to the Poaceae family is one of the most vital staple crops worldwide. Originally domesticated by indigenous populations in Mesoamerica (present-day Mexico) approximately 10,000 years ago, it has evolved into a cornerstone of human nutrition, agricultural economies, and industrial processing. The edible caryopses, borne on the ear (cob), represent the primary harvested product.

Beyond direct consumption, maize is extensively refined for starch and vegetable oil production and serves as a major substrate for industrial fermentation, encompassing both alcoholic beverages [36] and bioethanol for renewable energy applications [37]. In addition to its nutritional and energetic value, maize is a rich source of bioactive phytochemicals, particularly antioxidant compounds, whose composition and concentration vary considerably among genotypes and kernel phenotypes [38].

Yellow maize is particularly rich in carotenoids, the lipophilic pigments responsible for its distinct coloration. The predominant fractions comprise lutein and zeaxanthin, xantophylls with well-established roles in ocular health, notably in mitigating the risk of age-related macular degeneration, alongside β-carotene, the main provitamin A compound [38].

Conversely, red, blue, and purple maize varieties, particularly those cultivated in the Andean region, accumulate high concentrations of anthocyanins, which dictate their distinctive chromatic profiles and exhibit potent antioxidant activity [38].

Furthermore, maize is among the richest cereal sources of ferulic acid, a cell wall-bound phenolic acid with strong antioxidant properties that mitigates oxidative stress and cellular aging [38]. Beyond nutritional and phytochemical applications, fermented maize liquor—commonly known as ogi steep water—has garnered attention as a natural, cost-effective coagulant in tofu manufacture, particularly for household and small-scale production [3,39].

Beyond nutritional and phytochemical applications, fermented maize liquor, commonly known as ogi steep water or simply ogi water in several West African countries, has garnered attention as a natural, cost-effective coagulant in tofu manufacture, particularly for household and small-scale production [3,39].

This coagulant is traditionally produced by steeping maize kernels in water at a maize-to-water ratio of 1:3 (w/v) for 3 to 4 days to allow spontaneous fermentation. Following steeping, the kernels are washed, wet-milled, and filtered; the resulting slurry is allowed to settle, and the fermented supernatant, referred to as steeped ogi water, is decanted for use [3,18]. The coagulating efficacy is primarily driven by lactic acid bacteria, which lower the pH of the liquor to approximately 3.45–3.80 [3,18]. When added to soymilk heated to roughly 80 °C, this acidic medium shifts the suspension toward the isoelectric point of soybean proteins (approximately pH 4.5), inducing targeted protein aggregation and curd formation at an optimized ratio of 1.5 L of ogi water per 3 L of soymilk [3].

This sustainable coagulation method provides high tofu yield (approximately 94.2 g per 500 mL of soymilk) with a robust protein content of approximately 25.9% and enhanced retention of nutritionally important minerals, such as calcium, magnesium, and potassium [3,18,39].

Furthermore, sensory evaluations demonstrate high consumer acceptability; volatile compounds generated during lactic acid fermentation effectively mask the characteristic beany off-flavour of soymilk, resulting in a milder taste profile alongside a firm, elastic, smooth texture and a uniform creamy-white appearance [3,18].

Consequently, fermented maize steep water emerges as a promising, eco-friendly coagulants that bridges high industrial efficiency, favourable nutritional retention, and excellent sensory characteristics.

2.10. Different Vegetables

Sanjai and colleagues [4] evaluated various plant or fruit extracts for their efficacy as natural soymilk coagulants, specifically using Garcinia indica, Averrhoa carambola, Averrhoa bilimbi, Passiflora edulis and Phyllanthus distichus (Figure 9).

In this protocol, 25 g of each plant material was soaked in 50 ml of distilled water for 30 min and ground using a pestle and mortar. The resulting slurries were filtered through cheesecloth, and the filtrate volumes were adjusted to 100 mL with distilled water. The extract acidity was calculated as a percentage of anhydrous lactic acid and standardized to 2% of anhydrous lactic acid using distilled water. For coagulation, 20 mL of each extract was added to 200 mL of soymilk, pre- heated to 95 °C for 5 min and cooled to 80 °C, and stirred for 5 min. A 15 min incubation period was used to allow complete curd formation prior to textural and sensory evaluations [4].

2.10.1. Garcinia indica

Garcinia indica, a member of the Clusiaceae family, is a tropical evergreen tree native to specific regions of India. Its fruit, known as kokum, resembles a small apple measuring 2.5–5.0 cm in diameter, ranging in colour from red to deep purple, and contains 5–8 large kidney-shaped seeds embedded in a juicy, slightly acidic pulp (Figure 9 A).

G. indica has a long-standing history in traditional medicine for the treatment of inflammation, dermatitis, and diarrhea, as well as for promoting digestion. Several studies demonstrate that G. indica exhibits diverse biological activities, including antioxidant, anti-obesity, anti-arthritic, anti-inflammatory, antibacterial, hepatoprotective, cardioprotective, antidepressant, and anxiolytic properties, in both in vitro and in vivo models [40]. These therapeutic effects are primarily attributed to its rich phytochemical profile, notably compounds such as garcinol, hydroxycitric acid (HCA), cyanidin-3-sambubioside, and cyanidin-3-glucosideisolated from the fruit [40].

Beyond its medicinal use, kokum is widely utilized in culinary and industrial applications, as a natural acidulant in curries, pickles, health beverages, wine, and butter. More recently, it has been investigated as an alternative natural coagulant for soymilk in tofu manufacture, with its performance assessed through yield, texture, and sensory attributes [4]. Tofu produced using kokum yields approximately 24.5 g per 100 mL of soymilk, and exhibits a firmer texture compared to tofu produced using conventional coagulants. Furthermore, the presence of specific volatile compounds, namely cis-3-hexen-1-ol and cis-3-octen-1-ol, shapes the final flavour and aroma profile by imparting characteristic green and herbaceous notes [4].

2.10.2. Averrhoa carambola and bilimbi

Averrhoa carambola, a member of the Oxalidaceae family, is a tropical tree widely distributed throughout Southeast Asia. It produces the characteristic yellow star fruit (carambola), which is commonly used as a candied fruit and as a culinary garnish due to its distinctive five-pointed star-shaped cross-section (Figure 9 B). The fruit is a rich source of vitamin C, potassium, and antioxidant compounds, including gallic acid, catechin, and quercetin. In addition to its culinary applications in fruit salads and desserts, A. carambola has long been employed in traditional Asian medicine for treating fever, haemorrhage, and inflammatory disorders [41].

Tofu produced using A. carambola extract as a coagulant demonstrates high production efficiency, yielding 21.3 ± 0.51 g per 100 mL of soymilk [4]. The resulting product contains 58.2% protein and 25.4% fat on a dry weight basis, alongside a moisture content of 68.7%. It is characterized by a soft and smooth texture, while the carambola extract imparts an exotic aroma profile driven by volatile compounds such as cis-3-hexen-1-ol and trans-3-hexen-1-ol [4]. consequently, A. carambola shows considerable potential as a natural coagulant for tofu manufacture.

A closely related species is Averrhoa bilimbi, whose fruit is well known for its intensely sour taste (Figure 9 C). The pulp is particularly rich in oxalic acid and contains high levels of ascorbic acid, together with citric, tartaric, and malic acids. It also harbours several bioactive phytochemicals, including flavonoids such as cyanidin-3-O-β-D-glucoside and various catechins, which exhibit strong antioxidant activity, as well as tannins, terpenoids, and saponins.

Tofu produced using A. bilimbi extract exhibits an excellent yield of 21.6 ± 0.42 g per 100 mL of soymilk, with a moisture content of 71.6%, 57.2% protein (dry weight basis), and 26.8% fat (dry weight basis). Notably, this represents the highest fat content among all natural and synthetic coagulants evaluated in the study [4].

The physical characteristics of A. bilimbi-coagulated tofu indicates a well-balanced structure that is firm without being excessively hard. Sensory evaluation also reveals favourable overall consumer acceptability; similar to A. carambola, A. bilimbi imparts distinctive exotic aromatic notes to the tofu, primarily driven by the volatile compounds cis-3-hexen-1-ol and trans-3-hexen-1-ol [4].

These findings underscore the potential of A. bilimbi as a promising natural coagulant for tofu production, offering both desirable technological performance and superior sensory attributes.

2.10.3. Passiflora edulis

Passiflora edulis, a tropical vine belonging to the Passifloraceae family and native to South America, is widely cultivated for its edible fruit, commonly known as passion fruit (Figure 9 D). The fruit is highly appreciated for its aromatic pulp containing numerous small seeds, making it a key ingredient in juices, ice cream, beverages, and other commercial food products.

Passion fruit pulp is a rich source of bioactive compounds, vitamins, and minerals, notably high concentrations of vitamin C (ascorbic acid), B-complex vitamins (niacin and riboflavin), essential minerals (potassium, iron, magnesium, zinc, and selenium), soluble dietary fibers (mainly pectin), essential fatty acids, simple sugars and various phenolic antioxidants [42].

Beyond its nutritional profile, passion fruit pulp has attracted interest as a natural acid coagulant for tofu production due to its endogenous oxalic acid content. When used as a coagulant, P. edulis extract yields approximately 21.3 ± 0.40 g of tofu per 100 mL of soymilk [4]. The resulting product features a moisture content of 72.1% and contains 58.2% protein and 26.0% fat on a dry matter basis [4].

Technologically, passion fruit extract produces tofu with a soft, smooth, and homogeneous texture. In addition, its incorporation enhances sensory properties by imparting pleasant exotic flavour notes derived from naturally occurring flavonoids and volatile compounds, such as trans-3-hexen-1-ol and cis-3-octen-1-ol [4]. The final product typically exhibits a pale-yellow coloration, a characteristic attribute of tofu coagulated using acidic plant extracts [4].

Consequently, P. edulis shows considerable potential as a plant-based coagulant, efficiently driving protein precipitation while elevating both the sensory appeal and functional nutritional value of the final product [4].

2.10.4. Phyllantus distichus

Phyllanthus distichus (syn. Phyllanthus acidus), a flowering plant belonging to the Phyllanthaceae family, commonly known as Otaheite gooseberry or Tahitian gooseberry, produces edible, fleshy drupes that are pale yellow and nearly spherical with a slightly ribbed (lobed) appearance (Figure 9 E). The fruits are characterized by a crisp, juicy, and highly acidic pulp enclosing a single hard seed and serve as an excellent source of vitamin C and antioxidant compounds. In traditional Asian medicine, these fruits have long been used for their astringent and digestive properties [43].

The fruit extract exhibits one of the highest natural acidities among plant-derived coagulants investigated for tofu production. In addition to its organic acid content, it contains endogenous volatile compounds such as cis-3-hexen-1-ol and 1-octen-3-ol, which contribute distinct aromatic notes to the final product [4].

Tofu produced using Phyllanthus fruit extract yields an average of 15.6 ± 0.42 g per 100 mL of soymilk, accompanied by a relatively high moisture content of 73.6%, resulting from reduced whey expulsion during pressing. On a dry matter basis, the tofu contains 58.6% protein and 25.4% fat [4].

Despite its relatively high moisture content, Phyllanthus-coagulated tofu develops a firm and cohesive gel structure. Sensory evaluations demonstrate high consumer acceptability, with the product receiving favourable scores for its overall sensory quality [4].

3. Vegetables in tofu shelf live

Several studies into food preservation highlights that incorporating specific plant extracts, herbs and essential oils into tofu or its storage medium can effectively suppress microbial proliferation and lipid peroxidation. These botanical additives contain bioactive constituents, such as phenolic compounds and volatile oils, that exhibit broad-spectrum antimicrobial and antioxidants properties helping to maintain product quality and extend the shelf life.

3.1. Ocimum sanctum/Holy Basil

Holy basil (Ocimum sanctum L., syn. Ocimum tenuiflorum), also known as Tulsi, an annual aromatic herb belonging to the Lamiaceae family is widely recognized in traditional Ayurvedic medicine for its adaptogenic, anti-inflammatory, antioxidant, digestive, antimicrobial, and immunomodulatory properties (Figure 10 A). Historically, it has been employed to manage conditions such as bronchial asthma, stress-induced hypertension, mood disorders, immune dysfunction, gastric ulcers, arthritis, and chronic fatigue syndrome [44].

The foliar essential oil and aqueous extracts are rich in bioactive phytochemicals, predominantly eugenol, ursolic acid, rosmarinic acid, β-caryophyllene, and oleanolic acid, which dictate its therapeutical and biological efficacy [44].

Beyond its medicinal applications, Tulsi aqueous extract has been specifically investigated as a natural preservative for extending the shelf life of tofu, particularly in rural areas lacking refrigeration [2]. Treatment with Tulsi extract extends ambient shelf life from 3–4 days up to 7–8 days [2]. This preservation is driven by eugenol and ursolic acid, which exert potent antimicrobial and antioxidant effects that suppress bacterial protease activity by roughly 50%, thereby mitigating off-odour formation, while simultaneously inhibiting lipid peroxidation [2].

Furthermore, Tulsi-treated tofu retains a softer textural profile compared to untreated controls while absorbing the characteristic aromatic notes of the herb, a sensory modification generally well-accepted by consumers [2].

3.2. Alpinia galanga/Galangal

Galangal (Alpinia galanga), an herbaceous plant belonging to the Zingiberaceae family and native to Southeast Asia produces a rhizome widely used as both a culinary spice and a medicinal agent in traditional Eastern healthcare (Figure 10 B). Characterized by a pungent aroma and a complex flavour profile featuring citrus, black pepper, and pine-like notes, it has traditionally been employed to treat catarrh and respiratory disorders. The rhizome contains a wealth of bioactive phytochemicals, including flavonoids (galangin and quercetin), phenolic acids, and essential oil constituents such as 1,8-cineole, α-bergamotene, β-bisabolene, and eugenyl-acetate [45].

The essential oil of A. galanga demonstrates significant potential as a natural preservative for tofu [14]. Treatment maintains textural integrity for up to 8 days and preserves overall physicochemical quality for approximately 4 days under ambient storage conditions [14]. This efficacy is mainly driven by its high concentration of oxygenated compounds, notably 1,8-cineole (eucalyptol), which exhibit robust antibacterial and antifungal activities [14]. In addition, galangal essential oil suppresses surface slime formation and off-odour development while imparting the characteristic aromatic profile of galangal to the product [14].

3.3. Zingiber officinale/Ginger

Ginger (Zingiber officinale), an herbaceous perennial species within the Zingiberaceae family, is widely cultivated throughout tropical and subtropical regions for its rhizome (Figure 10 C). Rich in flavonoids, diarylheptanoids, and terpenoids, ginger phytochemicals exhibit notable antiproliferative effects [46]. Moreover, specific phenolic compounds such as 6-gingerol and 6-shogaol possess well-documented antiemetic properties, serving widely as adjuvant agents to alleviate chemotherapy-induced nausea and vomiting in patients with breast cancer [47].

Ginger essential oil also acts as a natural preservative, although its efficacy appears to be slightly lower than that of galangal essential oil. Applied at a concentration of 6.26 mg/mL, ginger essential oil extends ambient tofu preservation by approximately 4 days [14]. Its antimicrobial activity stems largely from compounds like geranial and geranyl acetate, which inhibit microbial growth [14]. Nevertheless, compared to galangal oil, ginger exhibits comparatively weaker antimicrobial performance and results in less favourable textural maintenance during prolonged storage [14].

3.4. Hibiscus sabdariffa L./Roselle

Although Hibiscus sabdariffa extract is primarily used as a coagulant in tofu manufacture (see paragraph 2.1), it concurrently contributes to product stability [10]. Rich in anthocyanins and phenolic acids, extract becomes physically entrapped within the protein matrix during coagulation, providing sustained antioxidant protection that limits the oxidation of polyunsaturated fatty acids throughout processing and storage. Consequently, hibiscus-enriched tofu retains substantial antioxidant capacity well past initial production [10].

In additional to botanical extracts, preservation solutions combining lemon juice and sodium chloride (10% lemon juice and 4% NaCl) significantly reduce the microbial load of fresh tofu, maintaining stability for up to 10 days of storage at 24 °C [2].

4. Vegetables as Tofu Additives

The incorporation of plant-derived ingredients to modify the flavour and colour of tofu has been widely investigated [11]. These additives, encompassing spices, culinary herbs, plant extracts, and natural pigments, not only tailor sensory profiles but frequently confer additional functional properties.

4.1. Plant-Derived Ingredients for Flavour Enhancement

Plant-derived ingredients are commonly incorporated into tofu formulations to mitigate the characteristic beany flavour of soybeans and develop distinct sensory profiles [3,11,14,48].

In specific production protocols, soymilk is blended with onion, pepper, salt, and bouillon prior to coagulation, followed by incubation for approximately 4 h and a thermal treatment at 80 °C for 30 min, yielding a product with high sensory acceptability [11].

Among these components, onion plays a central role; because it is co-cooked with the soybean curd, it imparts a more complex, intense flavour than that observed in conventional tofu.

Alternatively, sliced pepper can be incorporated directly into the curd during the draining stage to retain its flavour within the protein matrix [3].

Fresh ginger juice has also been used during soymilk coagulation to produce douhua (soy pudding) rather than firm tofu; ginger induces mild coagulation, resulting in a delicate, soft-gel well-suited for dessert applications [14].

Furthermore, the incorporation of cocoa powder has been evaluated by Ajewole et al. [48] who added 5–7% cocoa powder to beske (a traditional soymilk-based curd) to produce a novel chocolate variant. Cocoa supplementation increased production yield from 6.50% to 8.00% and shifted the product coloration from dark yellow to light brown without adversely affecting its overall quality [48].

4.2. Plant-Derived Pigments and Colorants

Natural pigments derived from plants and microorganisms have been explored to generate coloured tofu variants, thereby enhancing both visual appeal and antioxidant capacity [6,10,49].

Curcumin has been successfully incorporated to produce yellow tofu characterized by a stable chromatic profile and enhanced antioxidant activity, overcoming the colour instability often associated with fruit or vegetable juices [49].While curcumin supplementation does not significantly affect tofu yield or pH relative to conventional white tofu, it increases hardness and chewiness, suggesting the formation of a denser protein network, while preserving desirable technological and sensory properties [49].

Similarly, Monascus red, a natural pigment produced by fermenting rice with fungi of the genus Monascus (e.g., Monascus purpureus), has been used to manufacture red-coloured tofu, which exhibits significantly higher antioxidant activity alongside increased hardness and chewiness and overall consumer acceptance [49].

Comparable effects are observed with Gardenia blue, another natural pigment, which yields a bluish-coloured tofu while concurrently boosting antioxidant capacity, texture, and sensory quality [49].

In addition to their primary role as coagulants, botanical extracts such as grape pomace and hibiscus impart distinct pink to reddish-purple hues through their endogenous pigments [6,10].

5. Discussion

The growing interest in plant-based diets, sustainable food systems, and clean-label products has stimulated the search for innovative alternatives to conventional tofu manufacturing. The studies reviewed herein clearly demonstrate that plant-derived coagulants represent a promising strategy not only to replace traditional mineral salts but also to improve the nutritional, functional, and sensory characteristics of tofu [4,6,10]. Plant materials contribute to tofu production through different mechanisms. Organic acid-rich extracts, obtained from Hibiscus sabdariffa, tamarind, grape pomace, passion fruit, or Averrhoa species, promote protein aggregation by shifting the pH of soymilk toward the isoelectric point of soybean proteins [4,6,10].

Conversely, extracts containing proteolytic enzymes, such as cardoon flowers and kiwi fruit, facilitate protein network formation through enzymatic hydrolysis, yielding tofu with distinct structural properties [8,12]. Furthermore, fermented plant-derived products, such as maize steep water (ogi), combine acidification with fermentation metabolites that enhance both coagulation efficiency and sensory quality [3,18].

Beyond coagulation, a primary advantage of plant-derived coagulants is their ability to enrich tofu with endogenous phytochemicals. Polyphenols, flavonoids, anthocyanins, carotenoids, and vitamins become partially incorporated into the protein matrix during gel formation, increasing the antioxidant potential and functional value of the final product. Extracts from grape pomace, hibiscus, cardoon, and Moringa are particularly effective, transforming tofu into a multifunctional food while fostering the valorisation of agricultural by-products within a circular economy perspective [6,8,10,11].

The choice of coagulant also strongly influences technological characteristics. Mineral coagulants generally produce firmer and more compact gels, whereas plant-derived acid coagulants frequently generate softer and more porous structures (Table 2). Depending on the intended application, these differences represent distinct advantages or limitations: softer textures are often desirable for fresh or dessert-style tofu, whereas firmer products remain preferable for culinary and industrial processing.

Yield similarly vary; while extracts from Moringa and Rhododendron result in lower yields than nigari, tamarind, Garcinia indica, carambola, bilimbi and passion fruit achieve higher yields than conventional methods (Table 2).

Further studies are needed to investigate the stability and bioavailability of plant-derived bioactive compounds during processing, storage, and human digestion to better understand their real nutritional contribution.

Future research should therefore focus on optimizing extraction methods, identifying the active compounds responsible for coagulation, standardizing processing conditions, and evaluating consumer acceptance in different markets. Comprehensive life cycle assessments and techno-economic analyses will also be essential to determine whether these novel coagulants can provide genuine environmental and economic advantages over conventional mineral salts.

6. Conclusions

Despite these promising findings, several challenges remain before plant-derived coagulants can be widely adopted at an industrial scale. Many published studies have been conducted under laboratory conditions using different soybean varieties, extraction procedures, coagulation temperatures, and extract concentrations, making direct comparisons difficult. Furthermore, the chemical composition of plant extracts is inherently variable and depends on cultivar, geographical origin, environmental conditions, harvest stage, and extraction method. Such variability may affect coagulation efficiency, product quality, and batch-to-batch reproducibility, emphasizing the need for standardized extraction protocols and rigorous quality control procedures.

Another critical consideration concerns food safety and regulatory approval. While most plant-derived coagulants originate from edible species, others require careful toxicological evaluation prior to commercial application, particularly species containing potentially toxic secondary metabolites, such as Rhododendron arboreum. An emblematic case is the use of sodom apple (Calotropis procera) extract, an evergreen plant widely used in traditional medicine, textiles, paper industry and fuel purposes [18,50]. as soymilk coagulant. Although rich in proteases capable of inducing coagulation [18], tofu produced via this extract exhibits poor consumer acceptance in comparative sensory evaluations due to adverse appearance, colour, and flavour profiles [18].

Ultimately, the available evidence indicates that plant-derived coagulants offer a versatile platform for producing innovative tofu products characterized by enhanced nutritional value, improved functional properties, distinctive sensory attributes, and greater sustainability.

Although additional research is still required to support industrial implementation, leveraging vegetables, fruits, flowers, and agro-industrial by-products as natural coagulants aligns strongly with current industry trends toward functional foods, waste valorisation, and environmentally responsible food production.