LF, which contains approximately 690 amino acid residues and has a molecular weight of approximately 80 kDa, is a functional glycoprotein first isolated from cow’s milk by Sorensen in 1939 and first separated from human breast milk by Sorensen and Sorensen (1939), Johanson et al. (1960), Zhang Y. Q. et al. (2021). Typically, LF is odorless, readily soluble in water, and exhibits a certain level of structural stability. It can withstand temperatures of 56°C for several hours but is rapidly inactivated at temperatures above 80°C (Kowalczyk et al., 2022). LF consists of two homologous globular lobes, where a carboxyl (C) and an amino (N) end are linked by an α-helix. Each lobe contains two structural domains, designated as C1, C2, N1, and N2, and they form a β-sheet (Gruden and Ulrih, 2021). The structure of LF makes it highly flexible and can form different variants after transcription, translation, and modification (phosphorylation, acetylation, lipidation, ubiquitination, or glycosylation, etc.). This enables it not only to be serve as a polymeric material, but also to exhibit multiple biological activities in vivo, such as tumor growth inhibition, and antibacterial, free radical scavenging, antiviral, and anti-inflammatory properties (Gruden and Ulrih, 2021). In addition, LF has a high affinity for trivalent iron (K_D ∼ 10^–20M), allowing it to regulate free iron in body fluids and perform multiple functions as an iron-binding glycoproteins (Zhang Y. Q. et al., 2021). LF with different iron saturation levels exhibits different biological functions. For instance, LF with higher iron content is thought to have antiviral capacity and bacteriostatic activity against both Gram-positive and Gram-negative bacteria, whereas LF with lower iron saturation could bind more iron, thereby reducing free radical damage caused by iron overload and exhibiting antioxidant capacity (Gruden and Ulrih, 2021; Zhang Y. Q. et al., 2021). Lactoferrin has a long history of dietary use and is classified as a Generally Recognized as Safe (GRAS) nutritional supplement by the U.S. Food and Drug Administration (Wakabayashi et al., 2006). Extensive studies in both animals and humans have shown that even in vulnerable populations with compromised immune systems or disease states, daily doses of lactoferrin ranging from 1.5 to 15 g for periods of 1 day–42 weeks have not demonstrated any significant toxicity-related outcomes in safety or tolerability assessments (Wakabayashi et al., 2006; Vishwanath-Deutsch et al., 2024). In recent years, as the relationship between dairy consumption and breast cancer risk reduction has become clearer, several scholars have also expressed interest in investigating the anti-breast cancer effects of LF-activated peptides.

Several possible anti-breast cancer peptides have been identified in LF such as FKCRRWQWRMKKLGAPSITCVRRAF, RRWQWRMKKLG, RRWQWR, RRWQWRMKKLG, FKARRWQWRMKKLGA, GEQELRKCNQWSGLSEGSVT, WSGLSEGSVTCSSASTTEDC, and RWQWRWQWR (Table 1). These LF-peptides inhibit the growth, adherence, and migration of breast cancer cells, promote cell death, induce cell cycle arrest, and lead to the overexpression of apoptosis-associated proteins, including caspase-3, -7, -8, and -9, thus hindering breast cancer progression. For instance, Fatemi et al. separated three peptides from human LF, namely GEQELRKCNQWSGLSEGSVT, WSGLSEGSVTCSSASTTEDC, and CSSASTTEDCIALVLKGEAD. The latter two peptides exhibited very strong cytotoxicity in MCF-7 and MDA-MB-231 cells, with 50% cytotoxic concentration values of 100 μg/mL and 100 μg/mL, respectively, in MCF-7 and 950 μg/mL and 1,000 μg/mL, respectively, in MDA-MB-231 cells (Fatemi et al., 2018). However, this study primarily employed computerized techniques to identify the active peptide fractions in human LF and preliminarily measured their anti-breast cancer activity, without investigating their anti-metastatic and invasive capabilities or the action mechanisms of these active peptides. Rahman et al. discovered that FKCRRWQWRMKKLGAPSITCVRRAF (derived from bovine LF (BLF)) exhibited a pro-apoptotic effect on breast cancer cells, leading to decreased viability in four breast cancer cells, MDA-MB-231, MDA-MB-468, SKBR3 and MCF7, as demonstrated in the MTT assay (Rahman et al., 2021). In addition, this study also found that FKCRRWQWRMKKLGAPSITCVRRAF reduced the invasion of breast cancer tumors and limited tumor growth in mice. Similar findings were obtained by Furlong et al. and Zhang et al., who stated that FKCRRWQWRMKKLGAPSITCVRRAF can promote apoptosis, increase DNA fragmentation, cause morphological changes and cause cell cycle arrest at the G2 phase in breast cancer cells. These effects were attributed to the downregulation of the mTOR signaling pathway and the upregulation of the AMPK signaling pathway (Furlong et al., 2006; Zhang et al., 2014). However, although the obtained peptides have excellent antitumor activity, their sequences are too long, and whether they can tolerate gastrointestinal digestion and be absorbed by the human body needs to be examined by in vitro gastrointestinal simulation or in vivo digestion experiments. Some short-chain anti-breast cancer peptides have also been obtained by researchers. Insuasty-Cepeda et al., Casanova et al. and Guerra et al. isolated RRWQWRMKKLG and RRWQWR from BLF, both of which led to decreased viability, increased apoptosis, and morphological changes in breast cancer cells (Casanova et al., 2017; Guerra et al., 2019; Insuasty-Cepeda et al., 2020). Additionally, the two peptides also caused mitochondrial membrane depolarization and cellular calcium overload in breast cancer cells, suggesting the activation of the mitochondria-mediated apoptosis pathway. These active peptides are relatively short in length and derived from the longer peptide FKCRRWQWRMKKLGAPSITCVRRAF, which implies that this sequence is critical for the biological activity of LF. Overall, current research on the anti-breast cancer mechanisms of LF-activated peptides is not deep enough, and more effort needs to be invested in this area in the future.

Whey is a by-product of cheese manufacturing or other coagulated dairy product processing, containing 0.6% protein and 93% water, with a yellowish-green color (Zhang, 2022). Previously, whey separated from cheese production was considered a worthless by-product of the dairy industry and was difficult to process into other foods or sell as a food additive (Mehra et al., 2021). In recent years, liquid whey has gained attention for its mineral-rich, safe, easily digestible, and highly nutritious whey protein, resulting in increased effective utilization and conversion into various valuable human food supplements (Mehra et al., 2021). Whey can be converted into whey protein hydrolysate (WPH), whey protein concentrate (WPC), whey protein powder (WPP), whey protein isolate (WPI), and other metabolites using complex processing techniques including fermentation, membrane separation, chromatographic separation, and ultrafiltration (Zeng et al., 2024). These dry whey protein components consist of numerous subfractions such as β-lactoglobulin, α-lactalbumin, immunoglobulins, bovine serum albumin, proteose peptone, etc. (Zhang, 2022). In detail, WPP contains 63%–75% protein and 11.0%–14.5% lactose and its processing involves demineralization, acid, sweetening, and other reduced forms (Mehra et al., 2021). WPC has a protein content ranging from 25% to 80% and is a good source of lysine and sulfur-containing amino acids (Mehra et al., 2021; Zhang, 2022). WPI has the highest protein content (more than 90%), and generally undergoes an additional purification step to remove lactose and fat, making it popular among fitness enthusiasts (Chen et al., 2023). Interestingly, when WPP, WPC, and WPI are treated with acids, enzymes, or heat, the intact protein breaks down into polypeptides, smaller peptides, and amino acids, resulting in WPH (Mehra et al., 2021). Various whey proteins and WPH provide high-quality protein that can enhance athletic performance without toxic effects (Mangano et al., 2019; Zhao and Ashaolu, 2020). Specifically, whey protein, whey protein-derived peptides, and WPH are considered to have no adverse effects on body weight, food intake, behavior, organ weight, activity levels, or blood and urine parameters. They do not lead to abnormal changes in overall health, biochemical indicators, histopathological findings, or other observational metrics, nor do they exhibit acute or subacute toxicity (Zhao and Ashaolu, 2020). However, some studies suggest that excessive intake of certain bioactive peptides from whey protein may cause adverse reactions or allergies, though these anomalies can be mitigated through extensive hydrolysis (Cui et al., 2023). At present, scholars have isolated a large number of peptides from WPH, such as antioxidant peptides, anti-cancer peptides, ACE inhibitory peptides, anti-diabetic peptides, and immune-enhancing peptides (Zhao et al., 2022). These peptides typically exhibit stability to pH, ions, and heat, but their integrity may be compromised when exposed to the gastrointestinal environment (Adjonu et al., 2023; Wu et al., 2024). Importantly, research indicates that bioactive peptides maintain their biological activity, even when fully hydrolyzed into smaller peptide fragments (Tavares et al., 2011; Jiang et al., 2018).

Currently, the anti-breast cancer effects of whey protein-derived active peptides have received widespread attention. Various bioactive peptides, such as DYRWIAL, ARPKY, LIPRVKL, ALPMHIR, and LVMFQRR, have been isolated from fermented or enzymatically hydrolyzed whey proteins, demonstrating antitumor activity in breast cancer cells and/or animal models (Sahna et al., 2022; Taghipour et al., 2023). Except for individual active peptides, researchers have also investigated the anti-breast cancer effects of peptide mixtures from whey proteins of camel, goat, and cow (Dave et al., 2006; Sahna et al., 2022; Taghipour et al., 2023). Anti-breast carcinogenesis peptides and hybrid peptides identified from the aforementioned animal-derived whey proteins have shown effectiveness in reducing cancer cell proliferation, adhesion, and migration, promoting free radical accumulation, inducing apoptosis in cancer cells, and leading to the excessive expression of apoptosis-related proteins (Eason et al., 2004). Furthermore, investigations have reported that these peptides act mainly by activating several signaling pathways such as p38 MAPK and p53 signaling (Figure 2) (Dave et al., 2006).

Sahna et al. used pepsin and trypsin enzymes to hydrolysate goat casein and goat whey protein and obtained eight anti-cancer peptides consisting of 7–14 amino acids (Sahna et al., 2022). The research showed that the IC₅₀ values (the concentration of the peptide required to achieve 50% viability in MCF-7 cells) of pepsin-treated whey protein hydrolysate, trypsin-treated whey protein hydrolysate, pepsin-treated casein hydrolysate, and trypsin-treated casein hydrolysate were 33.38, 23.49, 34.83 and 34.23 μg/mL, respectively. Besides, these peptide fragments also downregulated the expression of GSK 3-β, PKM2, LDH B, and MUC 1, while regulating RIPK1 levels, which may reveal the anticancer mechanism of these active peptides. Whey protein hydrolyzed peptides are the most studied active peptides, and anticancer peptides have also been isolated from them for research purposes. According to Dave et al. and Eason et al., the whey protein hydrolysate exhibited anti-tumor effects in MCF-7 cell and rat models, as evidenced by a decrease in tumor diversity, tumor incidence, and cell proliferation, as well as reduction in the expression of cyclin D1 and IGF-2 (Eason et al., 2004; Dave et al., 2006). There was also an upregulation of apoptotic cell proportions and terminal end bud number per mm², along with the activation of some important anticancer factors (MCP-1, PTEN, PR) and inhibitory activation of oncogenic factors (p21, wip1, Sesn1, Mgmt, BRCA1, Bax), which may be attributed to the activation of multiple oncogenic signaling pathways such as p38 MAPK, Tp53, and PR signaling. However, neither study identified the specific anticancer peptide sequences contained in whey protein hydrolysates. Therefore, future studies could attempt to categorize the active whey protein-derived peptides into different fractions according to molecular weight and identify the most potent biopeptides with anti-breast cancer activity from these mixtures. In addition, probiotic fermentation presents a promising way to obtain active peptides from whey proteins, an area that has yet to be extensively explored.

Casein is a type of insoluble phosphoprotein and constitutes 80% of the milk proteins (Wusigale et al., 2020; Auestad and Layman, 2021). It is one of the predominant proteins in milk and can be isolated by precipitating milk at pH 4.6, as well as through techniques such as chromatography, electrophoresis, enzymatic treatment, and membrane filtration (Wusigale et al., 2020). Structurally, casein consists of four subfractions, αS1-, αS2-, β-, and κ-caseins, which account for approximately 38%, 10%, 36%, and 13% of the casein fraction, respectively (Auestad and Layman, 2021). These four casein subfractions are amphiphilic, with molecular weights ranging from 19 to 25 kDa and average isoelectric points between 4.1 and 5.3. This unique structure allows them to readily self-assemble into stable micellar structures in aqueous solutions, which can be destroyed in the presence of rennet (Wusigale et al., 2020). Casein is considered safe and non-toxic, with no mutagenic or clastogenic effects, and does not cause developmental, reproductive, or target organ toxicity (Dent et al., 2007; Phelan et al., 2009). Research by Dent et al., Doorten et al. and Phelan et al. robustly demonstrated that casein hydrolysates or their derived peptides, at doses not exceeding 2 g/kg body weight per day, did not induce any adverse reactions, nor did they cause abnormal changes in the eyes, nervous system, urine, blood, or kidneys (Dent et al., 2007; Doorten et al., 2009; Phelan et al., 2009). More importantly, casein provides the body with a well-balanced profile of essential amino acids, characterized by extremely high levels of proline (accounting for 16% of the total amino acids) and nearly complete absence of cysteine. This results in a structure that lacks the disulfide bridges and alpha-helices typically found in most proteins (Auestad and Layman, 2021). The biological activity of casein has also been widely reported by scholars. Some bioactive peptides have already been identified from casein by enzymatic hydrolysis methods, including alcalase, fermentation, and chemical and physical hydrolysis, and these peptides exhibit stability against heat, acidic conditions, and gastrointestinal enzymes (Quirós et al., 2009; Contreras et al., 2013; Wu et al., 2014; Kumar et al., 2016; Xue et al., 2021). Some of these bioactive peptides exhibit immunomodulatory, antioxidant, gut regulatory, and nutrient-absorption promoting effects locally in the intestinal cavity, while others need to be absorbed into the bloodstream to exhibit bioactivities. Therefore, studying both intact peptide absorption and peptide bioactivity is equally significant.

Anticancer peptides in casein proteins have been widely investigated, such as anti-ovarian cancer peptide PGPIPN, anti-melanoma peptide INKKI, and anti-leukemia peptide FFSDK (Sah et al., 2015). However, research on casein-derived peptides specifically targeting breast cancer has been limited, with only a few studies focusing on yak milk casein and human αS”-casein reporting the activities of anti-breast cancer peptides. For example, Gu et al. isolated three anti-breast cancer peptides, TPVVVPPFL, VAPFPEVFGK and NQFLPYPY, from yak milk casein and reported that these peptides exhibited excellent anticancer effects in both MCF-7 and MDA-MB-231 breast cancer cell models (Gu et al., 2022). These effects were characterized by an apparent increase in cancer cell death, a significant reduction in cell viability and cell cycle arrest at G2/M phase. Another study by KAMPA et al. also stated that YVPFP, an anti-breast cancer peptide derived from human αS”-casein, significantly (p < 0.05) decreased the proliferation of T47D cells (Kampa et al., 1996). Unfortunately, there is insufficient research on casein-derived anti-breast cancer peptides to draw definitive conclusions. Future efforts could focus on identifying active peptides from the four casein subfractions and comparing their anticancer activities in experimental models. In addition, while most of the identified active peptides or peptide mixtures have validated their anticancer activity in cancer cell models, animal transplantation tumor models are also very important for confirming experimental results or exploring anti-breast cancer mechanisms.

The demand for fermented milk has been rapidly increasing due to the growing vegetarian population and the rising popularity of high-protein diets (Sakandar and Zhang, 2021). The global fermented milk market was valued at USD 320.60 billion in 2022 and is expected to grow at a CAGR of 4.9% from 2022 to 2031, potentially reaching nearly $500 billion by 2031 according to Straits Research. Fermented milk is produced through the fermentation and acidification of milk by live microorganisms, typically Lactobacillus bulgaricus and Streptococcus thermophilus, resulting in the breakdown and utilization of macromolecules in the milk, and further the production of peptides, bacteriocins, free fatty acids, and conjugated linoleic acid, finally enhancing bioavailability and thickness of the products, increasing the number of viable bacteria, and prolonging their shelf life (Alhaj and Kanekanian, 2014; Hadjimbei et al., 2022). Traditionally, milk from various mammalian species, including cows, sheep, goats, camels, mares, buffaloes, and yaks, can be used to prepare fermented milk products. However, the flavor, composition, and nutritional value of the final product are affected by factors such as geographic and climatic conditions, animal health, species, feeds, seasons and stages of lactation, strains of fermenting bacteria, and fermentation conditions (Bintsis and Papademas, 2022). Commonly used milk starters are Lactococcus lactis subsp. cremoris, Str. Thermophilus, Lc. lactis subsp. lactis, Lb. delbrueckii subsp. delbrueckii, Lb. delbrueckii subsp. lactis, Lb. helveticus, Leuconostoc spp., etc. (Bintsis and Papademas, 2022). They are safe and beneficial for enriching the natural flora of the human gut. Additionally, fermented milk is a good source of calcium, phosphorus, potassium, vitamin A, vitamin B2, vitamin B12, high biological value proteins and essential fatty acids (Ilesanmi-Oyelere and Kruger, 2020). They also offers unique flavors, smooth textures, appealing appearances, enhanced digestibility and specific benefits such as anti-fatigue, antioxidant, anti-inflammatory, anti-cancer, intestinal modulation, cardiovascular disease improvement, serum cholesterol-lowering effects, etc., as compared to regular milk, which makes them popular among consumers and researchers (HoSoNo et al., 2002; Szajnar et al., 2020; Abdelrazik and Elshaghabee, 2021; Zhang D. J. et al., 2023; Zhang Z. Q. et al., 2023).

Due to the existence of various anticancer components, such as active peptides, probiotics, short-chain fatty acids, and probiotic metabolites, the effect of fermented milk on cancers has been widely studied. Some scholars have focused on identifying anticancer peptides from fermented milk. Abdel-Hamid et al. used Lactobacillus casei ATCC 393 to prepare fermented milk and characterized the composition of the obtained products (Abdel-Hamid et al., 2019). They found that the fermented milk contained a bacterial population exceeding 9 log cfu/g, with a pH value of 4.52, titratable acid content of 0.73%, and proteolytic activity of 0.36. Additionally, both the water extract of fermented milk (WSE) and the fermented milk extract with a molecular weight of less than 2 kDa (F1) exhibited ACE-inhibitory, antioxidant, and anti-breast cancer activities. Notably, the antiproliferative activity of the F1 fraction was 64.25% on day 0 and this value increased to 78.90% on days 21 of storage. Finally, they also identified the sequences of active peptides in F1 and successfully obtained several peptides such as DKIHPF, VVPPFLQPE, ELQDKIHPF, LHLPLPLLQSW, NLHLPLPLLQSW, LYQEPVLGPVRGPFP. However, a limitation of this study is that no specific anti-breast cancer studies were conducted on the identified active peptides. Biffi et al., de LeBlanc et al., de LeBlanc et al. and Rachid et al. fermented cow’s milk with different starter bacteria and found that the extracts inhibited breast cancer progression in mouse and cellular models (Biffi et al., 1997; de LeBlanc et al., 2005a; de LeBlanc et al., 2005b; Rachid et al., 2006). Specifically, fermented milk inhibited breast cancer cell proliferation, reduced tumor size, and modulated cytokines (downregulated IL-6 levels and upregulated TNF-α, IL-4, and IL-10 levels). In addition, fermented milk enhanced the immune function of BALB/c mice, as evidenced by an increase in the number of CD4⁺ and CD8⁺ T cells. In recent years, the addition of other natural anticancer-active ingredients into fermented milk has become a hot topic. Hassan et al. discovered that incorporating fresh royal jelly into Lactobacillus helveticus Lh-B02 fermented milk significantly increased its anti-breast cancer activity, with the IC₅₀ value of the fermented milk extract decreasing from 32.15 μg/mL to 9.89 μg/mL as the royal jelly addition concentration increased from 0.5% to 1.5% (Hassan et al., 2022). The addition of natural components, especially polyphenols, significantly improves the anticancer activities of fermented milk, although it may also alter other properties, such as color, viscosity, texture and sensory scores. Thus, these indicators should be taken into account when preparing fermented milk with added anticancer components. Some scholars have also explored the anti-breast cancer effects of fermented camel milk. On the first day of fermentation, fermented camel milk showed lower antiproliferative activity (41.5%) against MCF-7 cells compared to fermented cow’s milk (44.9%), however, after 21 days of post-ripening, the antiproliferative activity of fermented camel milk (47.9% (fermented camel milk) vs. 44.8% (fermented cow’s milk)) was significantly enhanced. Therefore, camel milk might be a better anticancer food ingredient than cow’s milk, and future research on fermented camel milk could focus on identifying anti-breast cancer peptides, and exploring the in vivo anticancer effects and anticancer mechanisms. In addition, the anti-breast cancer activity of dairy products such as fermented sheep, goats, mare, buffalo, and yak milk is also worth exploring.

Researchers have also explored the beneficial effects of fermented milk as an immunoadjuvant in breast cancer chemotherapy. In one study, milk fermented by Lactobacillus casei CRL431 not only enhanced the therapeutic efficacy of capecitabine but also effectively prevented cancer cell metastasis and alleviated the toxicity associated with capecitabine treatment (Utz et al., 2021). This was evidenced by reduced weight loss in mice, restored leukocyte counts and hematocrit levels, decreased diarrhea scores, improved inflammatory markers (IL-6, TNF-α, IL-10, IFN-γ, and MCP-1), and a higher villi length to crypt depth ratio. Overall, fermented dairy products are most likely to be initially applied as adjunctive agents in the clinical treatment of breast cancer.

Yogurt is one of the most widely consumed and oldest fermented dairy products. It is prepared by fermenting and acidifying milk with bacterial culture (primarily Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, but some products also use Bifidobacterium species, Lactobacillus helveticus, etc.), resulting in a thickened, more easily digestible product with an attractive flavor and a longer shelf life (Olson and Aryana, 2022; Hasegawa and Bolling, 2023). Yogurt is typically made from the milk of cows, buffalo, sheep, goats, and other livestock, and it can be categorized into various types, including plain yogurt, whipped yogurt, fruit-flavored yogurt, Greek yogurt, and frozen yogurt (Aryana and Olson, 2017; Oz et al., 2023). According to Statista, yogurt sales in the U.S. reached $7.24 billion in 2021, compared to $5.58 billion in 2011, implying a robust growth rate in the yogurt market over the past decade (Olson and Aryana, 2022). Nutritionally, yogurt provides highly digestible and bioavailable proteins, calcium, potassium, vitamin A and vitamin B₁₂, and its rich components of live microorganisms and their metabolites also serves to nourish the intestinal tract (Webb et al., 2014). From a flavor perspective, more than 90 different volatile compounds have been detected in yogurt, including acids, alcohols, aldehydes, ketones, esters, etc. Key contributors to the desirable flavor of yogurt include lactic acid, acetoin, acetaldehyde, diacetyl, and 2-butanone (Chen et al., 2017).

Yogurt hydrolysates are rich in bioactive peptides and free amino acids, making them important resources for cancer prevention (Çakmakoglu et al., 2024). Kefir is one of the best-known branches of yogurt, with origins tracing back to the Balkans, Eastern Europe and the Caucasus, but nowadays its consumption has expanded to other parts of the world due to its excellent health-promoting effects (Azizi et al., 2021). Kefir is also an acidic and viscous fermented beverage prepared by fermentation carbonation of kefir grains with milk or water, typically composed of 89%–90% water, 6.0% sugar, 3.0% protein, 0.2% lipids, 0.7% ash, and 1.0% lactic acid and alcohol (Azizi et al., 2021). The main fermenting bacteria in kefir are lactic acid bacteria and yeasts, with the former mainly comprising Lactobacilli, Lactococci, Streptococci, etc., while the latter primarily containing Candida sp., Kluyveromyces sp., Saccharomyces sp., etc. (Arslan, 2015). The symbiotic metabolism of these complex mixtures contributes to protein hydrolysis and lipolytic degradation, thereby imparting a unique flavor to kefir (mainly derived from lactic-, acetic-, hippuric-, butyric-, pyruvic-, propionic-acid, diacetyl and acetaldehyde) (Arslan, 2015). However, due to the complexity of kefir colonies, the biological activity of the obtained kefir products varies largely, sparking interest among researchers in optimizing fermentation conditions and ingredients to enhance the functional properties of fermented dairy products.

The anti-breast cancer effects of kefir have been revealed in several studies. Scholars have stated that kefir reduces tumor cell viability and growth rates, regulates cytokine expression in tumor tissues (e.g., downregulates IL-6, IL-10 and IL-1β, upregulates TNF-α, IL-10, and IL-4), promotes apoptosis, and exerts immune-enhancing effects. As reported by Zamberi et al., kefir inhibited the growth and metastasis of breast cancer in both in vitro and in vivo experiments (Zamberi et al., 2016). In addition, kefir reduced lipid peroxidation and NO levels in vivo, attenuated the accumulation of inflammatory factors of IL-4, TNF-α, iNOS, IL-10, and IL-1β, enhanced the occurrence of blocked angiogenesis as well as induced a 5-fold increase in CD4⁺ T levels and a 7-fold increase in CD8⁺ T cells. These findings were corroborated by studies conducted by de LeBlanc et al. (de LeBlanc et al., 2006; de LeBlanc et al., 2007). The anticancer effects of kefir may stem from its ability to activate a series of apoptotic pathways (Bcl2↓, bax, caspase3↑) and tumor signaling inhibitory pathways (p53, p21, p27↑), as well as to induce immune enhancement, such as upregulation of CD4⁺ T and CD8⁺ T cells (El-Din et al., 2020). However, there are few studies that simultaneously focus on the quality, anticancer effects and anticancer components of kefir.

In addition to kefir, plain yogurt also exhibits anti-breast cancer activity in several studies. Parvarei and Mortazavian found that yogurt fermented with Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus acidophilus ATCCSD 5221 significantly reduced the activity of MDA-MD- 231 cells (Parvarei and Mortazavian, 2022). However, this study did not measure other anti-cancer indicators. A more popular research direction involves the addition of natural anticancer substances to yogurt. For example, Al-Quwaie et al. incorporated Portulaca oleracea extract into yogurt and evaluated its fat (1.45%), pH (4.50), titratable acid (81.33 mg/10 mL), viscosity (198.2 cP), and water holding capacity (7.7 mL/g) (Al-Quwaie et al., 2023). The addition of Portulaca oleracea not only improved the acceptability and Lactobacilli content of yogurt but also enhanced its anticancer potential and effectively inhibited the accumulation of malondialdehyde (MDA). Further investigations are needed to explore the effects of adding various probiotics or natural actives to yogurt to further enhance its anticancer efficacy.

Cheese is one of the most ancient dairy-based fermented products that was first produced in various Western Asia countries around 8,000 years ago. It is consumed by a huge amount of the world’s population, regardless of age or origin (Zheng et al., 2021; Zhang et al., 2024a). Recently, cheese consumption has been growing at an average annual rate of 3%, with global sales reaching $122.1 billion due to increased demand for healthier, more nutritious, and more convenient foods (Hutchins and Hurley, 2024; Zhang et al., 2024a). About 2,000 types of cheese are reported, with well-known varieties including Cheddar, Mozzarella, and Parmesan (Feeney et al., 2021). These cheeses are generally made from natural ingredients, such as fresh milk (cows, buffaloes, camels, goats, sheep and donkeys), starter culture, salt and enzymes, through a series of fermentation processes (Ozcan and Kurdal, 2012; Feeney et al., 2021; Bittante et al., 2022). Most cheeses are prepared by coagulating milk with rennet and then ripening for about 2 weeks to 2 years. Other cheeses are manufactured via acid coagulation or a combination of heat and acid and are typically consumed fresh (Feeney et al., 2021). From a nutritional standpoint, cheese can be recognized as a promising macronutrient-rich food, with a high fat and protein content, as well as a micronutrient-rich food, with considerable concentrations of vitamins A, B₂ and B₁₂ and calcium (Zhang et al., 2024a). The ultimate consumer acceptance of cheese largely depends on its sensory characteristics, such as flavor, texture and aroma, which are determined by the various compounds and molecules that constitute it, including fatty acids, ketones, amines, free amino acids, active peptides, alcohols and aldehydes (Zheng et al., 2021).

The frenzy of cheese consumption has also prompted researchers to investigate its potential health benefits. It is well established that cheese has anti-hypertensive, antifungal, antibacterial, antioxidant, and gut-regulating properties. Thus, isolating highly active substances from cheese, including anticancer peptides, is of high value and can promote the development of functional foods (Sprong et al., 2010; Bernabucci et al., 2014; Théolier et al., 2014; Chen et al., 2019). According to Akilli et al., the active peptide content in digested and undigested enzyme-modified cheese was found to be 678.5–764.5 mg tryptone/g DM (dry matter) and 14.4–231.5 mg tryptone/g DM, respectively (Akilli et al., 2023). These active peptides exhibited anti-breast proliferative effects against MCF-7 cells. In addition, the anticancer activity of cheese became higher with the extension of storage time, likely due to an increase in the proportion of small peptides resulting from protein hydrolysis during ripening, thus enhancing cancer cytotoxicity. The study of Ayyash et al. found that the anti-proliferation activity of cheese against MCF-7 cells (about 55%) reached the highest at camel milk to bovine milk ratio of 30:70 (Ayyash et al., 2021). After 30 days of storage, the anti-proliferation activity of cheese further increased to ∼90%. However, this study did not explore the effects of ripening time on the active components of cheeses, leaving the specific reasons for the enhanced anticancer activity unclear. The effect of different starter cultures on the anticancer activity of cheese was also investigated. Cheeses fermented with Lactobacillus plantarum NCDC 012, Lactobacillus casei NCDC 297, or Lactobacillus brevis NCDC 021 presented a significant increase in anticancer activity compared to cheeses without starter bacteria. However, no significant differences in proliferation inhibition were observed between different cheese extracts. The enhanced anticancer activity could be due to the massive release of bioactive peptides triggered by the starter culture, thus initiating a cascade of caspase cleavage, or it might be attributed to the competitive binding of peptides and cancer growth factors to cancer cell membrane receptors, leading to apoptosis of cancer cells.

Several active or functional ingredients can be added to cheese for a variety of reasons, such as enhancing flavor, increasing bioactivity and therapeutic effects, and improving texture and sensory scores. There are few studies focused on incorporating anticancer ingredients into cheese. In one notable study, saffron, a traditional Chinese medicine known for its antidiabetic, antithrombotic, anti-depression, anti-anxiety, and insomnia-relieving effects, was added to cheese curd. The obtained cheeses exhibited higher anti-breast cancer activity than cheeses made by adding saffron directly to cheese milk. In addition, stronger anticancer effect was observed after 19 months of cheese ripening, with the cheese extract reducing the activity of MDA-MB-231 cells to less than 60%. This study lays the foundation for supplementing other anticancer ingredients into cheese. Polysaccharides and protein hydrolysates have been reported to improve cheese quality as well as inhibit the growth of breast cancer cells making them potential candidates for blending into cheese milk in the future (Taniya et al., 2020; Wan et al., 2020; Zhang D. J. et al., 2021; Zhang et al., 2024b).