Introduction
Global distillers’ grains co-products and production animal nutrition
The rapid growth of fuel ethanol and brewing industries has generated large quantities of distillers’ grains (DGS). Among these, corn distillers dried grains with solubles (DDGS) are the most representative. DDGS are the main co-product of corn dry-grind ethanol production; after starch is converted to ethanol, crude protein, crude fat, neutral detergent fiber (NDF), acid detergent fiber (ADF), phosphorus and vitamins become markedly concentrated. Crude protein in corn DDGS is around 30% of dry matter (DM), while crude fat varies with processing (e.g., about 12-13% in conventional DDGS), and DDGS have been widely used in both ruminant and monogastric diets
[1-3].
From a resource perspective, DDGS production has increased and become a global commodity. In the United States, distillers’ coproducts are used in beef and dairy cattle, swine and poultry feeds
[2,4]. With expanding production in Brazil, India and other countries, DDGS partially substitute soybean meal in some regions
[5]. Numerous trials have shown that, at appropriate substitution levels and with balanced formulations, DGS/DDGS can partly replace corn and soybean meal without impairing animal performance, and may help improve nitrogen use efficiency and fatty acid profiles
[3,6 -9].
As the scale of use has grown, DGS/DDGS have also shown notable issues, such as large batch-to-batch variation and the enrichment of sulfur and mycotoxins
[2,10]. Research focus has therefore shifted from “conventional substitute protein” toward “functional enhancement through fermentation and processing”. Within this context, distillers’ grains from solid-state brewing systems—particularly SBDG—provide a novel substrate for exploring potential postbiotic-rich functional feed resources.
Process characteristics and resource attributes of sauce-flavor Baijiu distillers’ grains (SBDG)
Unlike fuel ethanol DDGS, sauce-flavor Baijiu is produced primarily from sorghum using high-temperature
Daqu, a wheat-based solid starter manufactured by spontaneous fermentation and containing complex consortia of bacteria, yeasts and filamentous fungi together with their enzymes. The process includes starter preparation, stacking fermentation, cellar fermentation, distillation and blending/aging
[11]. Sauce-flavor Baijiu relies on high-temperature
Daqu, long cycles and multiple rounds of solid-state fermentation; temperature gradients and microbial succession create a distinctive metabolic network
[11,12]. The solid residue remaining after fermentation and distillation is SBDG, which is typically characterized by high moisture and organic load
[13,14].
In terms of nutrient composition, SBDG are characterized by “medium-to-high crude protein + functional fiber + mineral enrichment”, and are rich in polyphenols, organic acids, Maillard reaction products and other bioactive small molecules
[10,15]. Compared with corn DDGS, which are more “high-energy + protein-concentrated”, SBDG and DDGS are nutritionally complementary (see Section 3).
From a resource distribution standpoint, SBDG are mainly produced by large Baijiu enterprises located in highly concentrated production regions, with considerable and spatially clustered output. This facilitates long-term, stable cooperation with local livestock farms, reduces storage and transportation costs, and underpins “brewing-feed-livestock” circular utilization chains
[13,16]. At present, SBDG are used in feed production, functional ingredient extraction, anaerobic digestion for biogas and organic fertilizer production, among other pathways
[13,14]. These utilization modes are systematically reviewed in Section 2.
Postbiotic concept and core questions of this review
To achieve functional utilization of SBDG, it is necessary to define their status carefully within the postbiotic framework. According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a postbiotic is “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host”
[17,18]. The definition therefore requires both a characterized preparation containing inanimate microorganisms or their components and evidence of a host benefit; the presence of microbial residues or metabolites alone is insufficient. In this review, “postbiotic-rich matrix” and “postbiotic-rich feed resource” denote potential carriers of postbiotic-related components, whereas “confirmed postbiotic product” is reserved for preparations that satisfy the ISAPP criteria.
The processing and compositional features of SBDG provide a plausible material basis for a postbiotic-rich matrix, but composition alone does not establish postbiotic status. During multi-round high-temperature solid-state fermentation and distillation, lactic acid bacteria, yeasts and
Bacillus spp. may be inactivated or sublethally injured, while cell wall structures, exopolysaccharides, organic acids, polyphenol-related metabolites and bioactive peptides may be retained
[10,15]. Because conventional brewing does not necessarily provide standardized inactivation, compositional characterization or SBDG-specific demonstration of host benefit, unprocessed SBDG, fermented SBDG and SBDG-derived extracts should not automatically be labelled as postbiotics. Secondary fermentation followed by controlled inactivation, quality characterization and efficacy testing could support development of validated SBDG-derived postbiotic products.
Accordingly, this review addresses three core questions: (1) Which components of SBDG constitute candidate postbiotic-related materials or functional co-components? (2) How do fermentation and processing technologies reshape the composition of SBDG to form controllable process-composition-function relationships? (3) By separating direct SBDG evidence from indirect evidence based on CLDG, rice wine distillers’ grains, DDGS and defined postbiotic preparations, what preliminary application routes and dose ranges can be proposed for future SBDG-specific validation in ruminants, poultry and pigs?
The review is organized around two themes: the compositional and process basis for considering SBDG a potential postbiotic-rich matrix (Sections 2-6), and evidence for its use in sustainable livestock production (Sections 7-9). Section 10 summarizes the conclusions. This focused structure keeps DDGS and other distillers’ grains only as explicitly labelled indirect comparators.
Literature search strategy and evidence classification
This narrative review was supported by a structured literature search of Web of Science Core Collection, PubMed, Scopus and the China National Knowledge Infrastructure (CNKI). Searches covered January 2000 to 30 June 2026 and were supplemented by backward and forward citation checking. The core English search string was: ("sauce-flavor Baijiu" OR Moutai OR Maotai OR "Chinese liquor") AND ("distillers' grain*" OR spent grain* OR vinasse) AND (ferment* OR feed OR livestock OR postbiotic* OR polyphenol* OR polysaccharide* OR peptide* OR microbiota OR "life cycle assessment"). Species-specific terms (cattle, dairy cow, broiler, layer, pig or piglet) and Chinese equivalents were added as required. DDGS, rice-wine lees and defined postbiotic searches used the same outcome terms but were retained only as indirect comparator evidence.
Eligible records were peer-reviewed primary studies or authoritative consensus/review papers that reported material identity, processing conditions, composition, analytical methods, animal inclusion level, biological outcomes, safety or environmental assessment. Conference abstracts without sufficient methods, non-feed uses lacking relevance to SBDG, studies with unclear distillers’ grain identity and duplicate reports were excluded. English and Chinese records were considered. Evidence was classified a priori as direct SBDG/Moutai-distillers’ grain evidence, indirect evidence from other Chinese liquor or rice-wine distillers’ grains/DDGS, or analogue evidence from defined postbiotic preparations. Because material definitions, methods and outcomes were heterogeneous, findings were synthesized narratively rather than pooled statistically.
SBDG resource base and current utilization
This section summarizes the supply pattern, current utilization and material characteristics of SBDG. Other distillers’ grains are introduced only when they provide a necessary comparator (
Figure 1;
Tables 1 and
2).
Building on the basic features of global DGS and SBDG described in Section 1, this section focuses on “how much, where and how it is currently used” by examining production volume and spatial distribution, resource utilization pathways and positioning of Chinese liquor distillers’ grains, particularly SBDG. To visually anchor the “how much-where-how used” landscape and the major utilization spectrum of Chinese liquor distillers’ grains with a focus on SBDG,
Figure 1 summarizes the resource supply pattern, spatial clustering, and key utilization routes.
Production, supply and utilization
China’s Baijiu industry is highly concentrated in major production regions such as Sichuan-Guizhou-Chongqing and Jiangsu-Shandong-Henan-Anhui. Sauce-flavor Baijiu is mainly produced in Guizhou and the surrounding areas. Large Baijiu enterprises generate SBDG continuously through multiple rounds of fermentation and distillation, so supplies are temporally and spatially characterized by large volumes and strong clustering
[13,16]. Compared with small, dispersed distilleries, such centralized supply facilitates long-term, stable collaboration with nearby farms, reduces transportation and storage costs, and provides a material basis for closed loops of “brewing-feed-livestock-manure-to-land”.
Currently, SBDG are used in feed, functional ingredient extraction, anaerobic digestion for biogas and organic fertilizer production
[13,14]. To better capture the technical characteristics and application scenarios of each pathway, this section summarizes the main resource utilization modes of Chinese liquor distillers’ grains and their advantages and limitations (
Table 1), thus providing a reference background for subsequent discussion on upgrading from a “resource” to a “functional feed” platform.
Overall, compared with DDGS, SBDG display a more prominent combination of medium-to-high crude protein, structural/functional fiber and mineral enrichment, providing a basis to develop them both as feed ingredients and potential postbiotic-rich matrices
[10,13]. Because SBDG are produced via high-temperature, multi-round solid-state fermentation using polyphenol-rich raw materials, they are better viewed as a composite resource of crude protein, functional fiber, polyphenols and microbial derivatives, whereas corn DDGS more closely represent high-energy, protein-concentrated feeds.
From a feeding perspective, SBDG can be positioned between conventional fiber-rich co-products and high-protein concentrates with potential postbiotic-related carriers. Their protein and energy values may permit partial replacement of soybean meal and grains, whereas their non-starch polysaccharides, polyphenols and microbially derived structures provide candidate functional components whose host effects require SBDG-specific confirmation.
Physicochemical composition of SBDG and their candidate postbiotic-related precursor pool
Building on the resource background and utilization patterns described in Section 2, this section focuses on the material composition of SBDG. Conventional nutrients, bioactive small molecules and microbially derived components are considered as the basis for SBDG to function as a nutrient carrier and potential postbiotic-rich matrix, without assuming that the unvalidated material is itself a postbiotic product.
SBDG nutrient profile and protein quality
SBDG composition is shaped by sorghum, wheat-based Daqu, high-temperature fermentation, repeated fermentation-distillation rounds and subsequent drying or secondary fermentation. Data from other aroma types are not used to define SBDG composition because their raw materials and processing differ substantially.
Preliminary analysis of Moutai distillers’ grains reported 30.46% dry matter (DM) in the fresh material and, on a DM basis, 21.84% crude protein (CP), 36.85% neutral detergent fiber (NDF) and 24.72% acid detergent fiber (ADF)
[23]. They should not be treated as universal specifications because batch, fermentation round and drying conditions vary.
Regarding minerals, distillers’ grains generally have relatively high ash contents because most non-starch constituents are retained and concentrated after fermentable starch is converted to ethanol
[13,14,24]. Overall, compared with DDGS, sauce-flavor distillers’ grains exhibit more prominent medium-to-high crude protein, structural/functional fiber and mineral enrichment, supporting their development as feed ingredients and potential postbiotic-rich matrices.
Table 2 compares nutrient structure and potential functionality among distillers’ grains from different aroma types and corn DDGS. Values derived specifically from SBDG should be distinguished from those reported for other CLDG or DDGS; the comparison supports hypothesis generation but does not establish equivalent biological effects among these materials.
Protein and nitrogen fractions
Crude protein in corn DDGS is typically concentrated about 3-fold relative to the grain, but biologically available lysine and other heat-sensitive amino acids decline due to Maillard reactions
[24]. In sauce-flavor Baijiu production, prolonged heat exposure may alter protein crosslinking and glycation, affecting rumen-undegraded protein (RUP) and acid detergent-insoluble nitrogen (ADIN)
[10]. SBDG-specific protein degradability and intestinal digestibility must be measured before inferring its suitability for replacing soybean meal in high-yield dairy cow rations
[10,24].
Enzymatic hydrolysis and secondary fermentation can release multiple bioactive peptides. Studies have isolated peptides with angiotensin-converting enzyme (ACE) inhibitory, antioxidant or glucose-lipid metabolism-modulating activities from distillers’ grains protein hydrolysates
[25-28]. These peptides contribute to the candidate functional matrix, but purified peptides alone are not postbiotics under the ISAPP definition.
Structural carbohydrates and soluble dietary fiber
During sauce-flavor fermentation, starch is extensively utilized whereas cellulose, hemicellulose, lignin and protein-bound polysaccharides are relatively concentrated. The direct Moutai values of 36.85% NDF and 24.72% ADF (DM basis) indicate a materially more fibrous profile than the generic DDGS comparator
[23]. High fiber can dilute energy in monogastric diets but can contribute fermentable and physically effective fiber in ruminant diets; interpretation must therefore be species- and diet-specific.
Notably, SBDG also contain soluble dietary fiber and arabinoxylans. These are functional fibers rather than postbiotics, although they may complement inanimate microbial components within a composite feed matrix. Extrusion and fermentation can yield polysaccharide fractions with higher solubility and antioxidant capacity; in vitro studies and a colitis mouse model reported enhanced short-chain fatty acid (SCFA) production and improved barrier- and inflammation-related outcomes
[29-31]. These findings are indirect evidence and should not be interpreted as proof of equivalent effects from whole SBDG in production animals.
Polyphenols and other bioactive small molecules
SBDG polyphenols originate principally from sorghum and wheat, while
Daqu enzymes and microbial metabolism can release bound phenolics or transform their profiles during repeated high-temperature fermentation. In 61 Maotai-flavor fermented-grain samples, 12 phenolic compounds were identified and total phenolic content tended to increase during single-round fermentation, although patterns depended on production stage and workshop
[32]. Thus, the brewing process does not produce a uniform concentration effect.
A universal SBDG polyphenol-content range cannot presently be stated because studies use different sampling stages, extraction solvents, reporting bases and colorimetric standards. For example, optimized ultrasonic extraction from Moutai distillers’ grains yielded 25.39 ± 5.05% crude flavonoid extract, but this extraction yield is not equivalent to whole-material flavonoid content
[33]. Future reports should provide total phenolics as mg gallic-acid equivalents per g DM and quantify individual phenolics by HPLC or LC-MS. Plant sterols and unsaturated fatty acids are additional non-postbiotic co-components; their SBDG-specific concentrations and animal dose-response relationships remain insufficiently characterized.
Indigenous microbiota and the natural precursor pool of postbiotic-related components
Beyond the brief overview in Section 1, this section emphasizes the microbial-derived components of SBDG. Multi-round stacking and cellar fermentation in sauce-flavor Baijiu production give rise to complex and dynamic microbial communities, including lactic acid bacteria, Bacillus spp., yeasts and filamentous fungi
[11,12]. High-throughput sequencing shows that Lactobacillus, Pediococcus, Bacillus, Saccharomyces, Kazachstania and others dominate fermented grains and distillers’ grains, accompanied by Aspergillus and Rhizopus residues from the starter
[34,35].
Although distillation and drying may reduce viable counts, non-viable microbial structures and fermentation metabolites may be retained, forming integrated systems of cell walls, exopolysaccharides, enzymes and organic acids
[10]. This composition constitutes a candidate precursor pool for a potential postbiotic-rich matrix, but does not by itself meet the ISAPP definition. Section 4 discusses how controlled fermentation, inactivation and characterization could be used to develop more reproducible SBDG-derived preparations.
Microbial fermentation-driven routes for upgrading SBDG toward a potential postbiotic-rich matrix
Building on Section 3, this section examines how single-strain fermentation, mixed or synthetic consortia and process parameters modify the nutritional and postbiotic-related component profiles of SBDG. The objective is to move from nutrient-recovery co-products toward standardized functional feed matrices that can subsequently be tested against postbiotic criteria.
Current evidence and relevant fermentation approaches
Early distillers’ grains fermentation largely targeted “increasing crude protein, reducing crude fiber and mycotoxins”
[24,36]. With growing interest in gut health and antibiotic reduction, research has gradually shifted towards organic acids, SCFAs, cell wall fragments, peptides, polyphenols and enzymes/antimicrobial compounds, aiming to achieve both nutritional modification and functional enhancement through solid-state fermentation
[10,37].
Existing studies can broadly be classified into three routes: (1) single-strain solid-state fermentation, dominated by lactic acid bacteria,
Bacillus spp. or filamentous fungi, targeting protein enrichment, fiber reduction, detoxification or acid production
[36,38]; (2) mixed consortia plus enzyme-assisted fermentation, which can increase organic acid, peptide and polyphenol release while modifying nutrients
[39,40]; and (3) multi-stage solid-state fermentation with staged inoculation aligned to oxygen requirements, including synthetic microbial community solid-state fermentation (SMC-SSF), to increase protein while reducing fiber and mycotoxins
[41,42].
Figure 2 distinguishes documented process effects in DDGS or CLDG from proposed translation to SBDG.
Fermentation of corn DDGS with
Aspergillus ibericus can increase crude protein, reduce non-starch polysaccharides (NSP) and improve both polyphenol content and fiber-degrading enzyme activities; feeding the fermented product to European seabass improves protein, lipid, starch and energy digestibility
[38]. Fermentation of DDGS with
lactic acid bacteria and
Bacillus spp. can significantly increase crude protein and small peptides, reduce NDF/ADF and mycotoxins, and enhance organic acid and multiple enzyme activities, thereby improving average daily gain in broilers without histopathological lesions
[36,39].
Bacillus subtilis-fermented wet distillers’ grains used in pig diets improve feed conversion and meat quality while reducing backfat thickness
[43].
Collectively, these studies show that single-strain fermentation can selectively modulate protein, fiber, organic acids and toxins. Because most supporting studies used DDGS or other distillers’ grains, they provide process analogues rather than direct confirmation of postbiotic enrichment or host benefit in SBDG.
Current SBDG animal studies used a biological starter and silo fermentation for 15 d, but did not establish a standardized fungi-yeast-lactic acid bacteria sequence
[23,44]. A preliminary screening condition for Chinese distillers’ grain fermentation used
Aspergillus niger,
Trichoderma viride,
Lacticaseibacillus casei,
Bacillus subtilis and
Saccharomyces cerevisiae simultaneously at a 1:1:1:1:1 ratio, 10% total inoculum, 2% added urea and 50% water content, 30°C and 5 d
[42]. This is direct CDG process evidence but not proof of an SBDG-specific sequential process.
Similar studies indicate that rational combinations of functional microbes, including
Lactobacillus,
Bacillus, yeasts and
Aspergillus spp., together with optimized temperature, moisture and inoculum levels, can increase crude and soluble protein fractions and reduce fiber; under specific conditions, solid-state fermentation can also reduce selected mycotoxins in corn DDGS
[39,40]. For SBDG, applying exogenous functional consortia to the indigenous matrix is a plausible but still unvalidated strategy for developing products with higher nutrient density and reproducible postbiotic-related component profiles.
Quantified process conditions and conversion efficiency
For the CDG consortium, the subsequent 7-d fermentation increased true protein from 14.83% to 19.77% (a 33.32% relative increase); crude fiber, ethanol, lactic acid and acetic acid decreased by 20.46%, 64.28%, 93.73% and 90.96%, respectively; ZEN and AFB
1 decreased by 9.32% and 63.75%; and in vitro crude protein digestibility increased from 17.90% to 29.08% (a 62.46% relative increase)
[42]. These values are reported as a comparator, not transferred as expected SBDG conversion efficiencies. SBDG-specific studies must report initial and final values on the same analytical basis and calculate recovery as well as concentration, because apparent CP enrichment can arise from dry-matter loss.
No validated high-then-low temperature schedule for secondary SBDG fermentation was identified. A staged fungi-yeast-lactic acid bacteria route remains a development hypothesis: aerobic saccharification, facultative bioconversion and anaerobic acidification should be compared factorially against simultaneous inoculation while measuring temperature, oxygen, pH, microbial succession, viable counts, organic acids, true-protein recovery, fiber loss and marker compounds. Numerical temperature-time targets should be derived from SBDG pilot trials rather than copied from DDGS.
Reported DDGS and non-SBDG efficiencies are retained only where they define testable benchmarks. For SBDG, the development sequence should be: define the intended product; optimize fermentation against mass-balanced nutrient and marker recovery; apply a controlled inactivation step if a postbiotic product is intended; confirm absence of relevant pathogens and contaminants; and demonstrate a host benefit for the finished preparation. Without the inactivation and host-benefit steps, the product remains a fermented feed rather than a confirmed postbiotic.
These fermentation-driven upgrading routes and their staged logic are schematized in
Figure 2, highlighting how process design can reshape protein quality, fiber structure, detoxification outcomes, and candidate component profiles in an integrated manner.
These results indicate that solid-state fermentation can enrich protein, reduce fiber and lower selected mycotoxins in DDGS or CLDG models, making fermented SBDG a candidate high-protein concentrate and potential postbiotic-rich carrier
[36,41,42]. However, process improvement and in vitro antibacterial activity do not establish a postbiotic health benefit. Economic assessment should therefore consider both nutritional recovery and the additional costs of standardized inactivation, safety testing and efficacy validation.
Dividing fermented SBDG into coarse, high-fiber and fine, high-protein fractions may support species-specific use in ruminant total mixed rations (TMRs) and monogastric concentrates (a proposed strategy requiring validation). Online monitoring of temperature, humidity, carbon dioxide (CO
2) and ammonia (NH
3) may improve process reproducibility, but candidate postbiotic-related component profiles must be verified analytically rather than inferred from process signals alone
[10,13,45].
In summary, fermentation technology shapes the nutritional composition and candidate postbiotic-related component profile of SBDG. Section 5 therefore defines the evidentiary threshold required before mechanistic or postbiotic claims are made.
Postbiotic framework, candidate components and quantitative assessment
After describing the compositional and processing basis of SBDG in Sections 3-4, this section summarizes the ISAPP definition and the major response domains reported for validated postbiotic preparations. These concepts provide a cautious framework for evaluating, rather than presuming, SBDG-specific mechanisms.
Definition and evidentiary criteria
Earlier literature often used “postbiotics” loosely for probiotic fermentation products, cell lysates or fermentation supernatants
[19,46,47]. The ISAPP consensus defines a postbiotic as “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host”
[17,18]. Accordingly, the preparation should contain inanimate microorganisms or their components, the method of inactivation and composition should be characterized, and a host benefit should be demonstrated for the preparation under evaluation
[18,48].
Postbiotics should therefore be distinguished from purified microbial metabolites, plant-derived bioactives and fermented feeds whose benefits are solely nutritional or have not been validated. This distinction is particularly important for SBDG: the terms “postbiotic-rich matrix” and “candidate postbiotic-related components” are used descriptively, not as regulatory or efficacy claims
[49,50].
Postbiotic preparations are produced from previously viable microorganisms that are subsequently rendered inanimate; they may contain intact cells, cell fragments and matrix-associated metabolites retained with those microbial components
[17,18,51]. For mechanistic discussion, their constituents can be grouped into structural components, such as cell walls and exopolysaccharides (EPS), and co-retained metabolites, such as organic acids or bacteriocins. Purified metabolites alone, and fermented DDGS or CLDG/SBDG without demonstrated host benefit, should not be classified as postbiotics.
Validated postbiotic preparations have been associated with antimicrobial, immunomodulatory, antioxidant/anti-inflammatory and metabolic responses, although effects overlap and depend on strain, inactivation method, matrix, dose and host species
[52-56]. Section 6 uses these response domains to organize candidate components in SBDG while explicitly treating SBDG-specific mechanisms as proposed until directly tested.
Candidate components, analytical methods and proposed response domains
Evidence from defined postbiotic preparations indicates four interrelated response domains: (1) modulation of gut microbiota and microbial metabolites; (2) epithelial barrier support through interactions between microbial structures and pattern-recognition receptors (PRRs); (3) mucosal and systemic immune modulation; and (4) downstream effects on nutrient utilization and energy or lipid metabolism
[49,50,54,57 -59]. Effects are preparation-, dose-, species- and context-dependent. For example, heat-killed
Lactobacillus plantarum L-137 altered immune-gene expression in pigs but did not significantly change the villus-height-to-crypt-depth ratio
[60].
Figure 3 presents these domains as proposed pathways relevant to SBDG, not mechanisms already confirmed for SBDG.
Building on the four interrelated action axes summarized above,
Figure 3 integrates candidate SBDG postbiotic-related component classes with proposed mechanistic targets/pathways and potential outcomes.
To provide a concise visual summary of the resource context, upgrading strategies, postbiotic fingerprints, mechanistic axes, and cross-species applications discussed in this review, a graphical abstract is presented in
Figure 4.
The ISAPP framework provides a useful hypothesis-generating lens for SBDG because solid-state brewing and secondary fermentation may leave mixtures of inanimate cells, cell walls, EPS, organic acids, peptides, polyphenols and enzymes
[46,49,50]. Nevertheless, SBDG should presently be described as a potential postbiotic-rich matrix or carrier, not a confirmed composite postbiotic.
The antioxidant, anti-inflammatory and gut-related findings reported for CLDG fractions, rice wine distillers’ grains or defined postbiotic products provide indirect support for testable SBDG hypotheses
[31,42,61]. Section 6 therefore distinguishes candidate components detected or expected in SBDG from mechanisms inferred from related materials.
Candidate components are organized by chemical identity and evidentiary status rather than being labelled collectively as postbiotics.
Table 3 links microbial structures, matrix-associated metabolites and non-postbiotic co-components to proposed animal response domains. No validated SBDG compound-specific animal thresholds currently exist.
A minimum analytical panel for an SBDG-derived candidate postbiotic should include: culture-based viable counts combined with viability-sensitive molecular or flow-cytometric methods; β-glucan, mannan or peptidoglycan markers for microbial structures; HPLC or GC measurement of lactic, acetic, propionic and butyric acids and residual ethanol; chromatographic peptide and phenolic profiling; and species-relevant contaminants. Animal studies should report both dietary inclusion and marker exposure (e.g., g component/kg diet and intake per kg body weight). At present, the literature supports no defensible universal threshold for SBDG polyphenols, acids, peptides or microbial cell-wall components; such thresholds require SBDG-specific dose-response studies.
During sauce-flavor fermentation and secondary fermentation, lactic acid bacteria, yeasts and anaerobes may produce lactic, acetic, propionic and succinic acids and smaller amounts of butyrate. These acids are matrix-associated microbial metabolites; when present without inanimate microorganisms or their components, they should not be called postbiotics under the ISAPP definition. Once ingested, however, they may contribute to luminal acidification or signal through G protein-coupled receptors (GPRs), including GPR41, GPR43 and GPR109A, as reported in broader metabolite and postbiotic literature
[62-64,77].
Propionate contributes to gluconeogenesis and cholesterol metabolism, whereas butyrate can affect oxidative and inflammatory pathways through histone deacetylase (HDAC) inhibition
[65,66]. These mechanisms provide hypotheses for fermented SBDG, but require confirmation by measuring actual acid intake, gastrointestinal exposure and host responses in SBDG-specific trials.
Candidate structural microbial components in SBDG include yeast
β-1, 3/1, 6-glucans and mannans, together with lactic acid bacterial peptidoglycan, teichoic acids and EPS
[67,78]. Their abundance and structural integrity in finished SBDG products have not yet been standardized.
The immunological activity of yeast
β-1, 3/1, 6-glucans depends on branching, molecular weight, conformation and solubility. These features influence recognition by PRRs, including Dectin-1 and complement receptor 3 (CR3), with context-dependent cooperation from Toll-like receptors 2 and 4 (TLR2 and TLR4), and may affect macrophage, dendritic-cell and immunoglobulin A (IgA) responses
[78-81].
Feeding studies with isolated yeast cell wall ingredients in poultry support the biological plausibility of these structural components, but they are analogue evidence rather than direct SBDG evidence
[68,69,81]. Therefore,
β-glucan branching, aggregation and solubility should be measured in SBDG before inferring immunomodulatory potency.
EPS produced by lactic acid bacteria are structurally diverse, and their immune or antioxidant effects are strain- and structure-dependent
[82-85]. In SBDG, yeast-derived glucans and mannans and lactic acid bacterium-derived EPS constitute candidate structural modules; proposed synergy with fungal polysaccharides remains to be tested directly.
Future studies should characterize the amounts, branching and solubility of these microbial structures across SBDG batches and relate them to barrier and immune outcomes. Until such structure-function relationships and host benefits are demonstrated, SBDG should be described as a carrier of candidate structural components rather than a structural composite postbiotic.
Repeated hydrolysis and glycation during high-temperature, multi-round fermentation can generate diverse peptides. ACE-inhibitory, antioxidant and insulin-sensitizing activities have been reported for peptides isolated from distillers’ grain protein hydrolysates
[26-28,37]. These peptides may contribute functional activity within SBDG, but purified peptides are not postbiotics and their bioavailability and efficacy in production animals require direct testing.
SBDG originate from polyphenol-rich cereals, but evidence for specific profiles frequently derives from broader Baijiu distillers’ grains or DDGS. More than 30 phenolic acids and flavonoids have been reported in related materials, with antioxidant capacity correlated with polyphenol content
[15,21,22]. Microbial conversion of polyphenols may influence nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) and nuclear factor kappa B (NF-κB)/mitogen-activated protein kinase (MAPK) pathways, but these mechanisms have not been confirmed for whole SBDG in livestock
[65,66,71,86].
Accordingly, grain tannins and fermentation-derived phenolic acids are non-postbiotic functional co-components that may contribute to antioxidant or metabolic responses. Their concentration, bioavailability and transfer to meat, milk or eggs should be quantified in SBDG-specific dose-response studies before product-quality claims are made.
SBDG and their fermented derivatives may contain extracellular hydrolases produced by moulds, lactic acid bacteria and
Bacillus spp., as well as bacteriocins or bacteriocin-like inhibitory substances (BLIS)
[36,38,72,73,87]. Enzymes can improve nutrient accessibility by degrading plant cell walls, whereas antimicrobial proteins or peptides may suppress selected pathogens. Evidence for these functions largely comes from non-SBDG systems
[74,75,88].
Introducing bacteriocin-producing lactic acid bacteria into secondary SBDG fermentation may therefore create a matrix enriched in antimicrobial factors. Classification as a postbiotic product would additionally require controlled inactivation, compositional specifications and demonstration of a host benefit for the finished SBDG preparation.
Fermented SBDG contain multiple interacting nutritional and functional components rather than a single active principle. The four response domains summarized in Section 5 provide a framework for testing these interactions, but evidence that the complete SBDG matrix produces additive or synergistic host effects is currently insufficient
[49,50,54,76].
Evidence for antimicrobial activity of postbiotic-related preparations comes largely from non-SBDG systems
[72,89]. Beneficial or antagonistic interactions among SBDG matrix components remain to be tested directly.
Accordingly, fermented SBDG can be evaluated as a proposed network-type matrix in which microbial structures, matrix-associated metabolites and plant-derived co-components may interact. This backbone-module model is a testable research framework, not evidence that all fermented SBDG preparations are postbiotics
[10,17,18].
Animal applications and preliminary dosing framework for SBDG
Evidence in this section is separated into three levels: (i) direct evidence from studies that clearly identified SBDG or Moutai distillers’ grains; (ii) indirect ingredient evidence from other CLDG, rice wine distillers’ grains or DDGS; and (iii) analogue evidence from defined commercial or experimental postbiotic preparations. These levels are not interchangeable. Indirect and analogue findings are used only to formulate hypotheses and starting doses for SBDG-specific studies.
Table 4 summarizes indirect distillers’ grain and defined-postbiotic analogue evidence alongside material type, processing, inclusion level and response. Direct SBDG studies are discussed in the text. Proposed SBDG inclusion ranges are labelled preliminary and should not be interpreted as regulatory limits, established safety ceilings or feeding recommendations for commercial use.
All ranges below are hypothesis-generating starting points for controlled trials. They require validation in SBDG-specific dose-response studies with nutritionally balanced diets, adequate replication, batch characterization and species- and physiological-stage-specific safety endpoints.
Ruminants
Direct SBDG evidence is limited. Cheng et al.
[23] evaluated fermented Moutai distillers’ grains in finishing cattle, providing SBDG-specific evidence for growth, meat-quality and blood-metabolite outcomes. Broader evidence that distillers’ grains can maintain milk yield or growth and sometimes improve feed efficiency comes mainly from DDGS or other distillers’ grain studies
[97-101]. High-sulfur DDGS studies are indirect safety evidence but show the need to account for total dietary sulfur from feed and water
[102].
SMC-SSF studies in CLDG report higher crude and true protein and lower fiber, organic acids and selected mycotoxins
[42,90]. These process and in vitro results support product-development feasibility but do not by themselves establish animal safety, postbiotic status or a safe SBDG inclusion level.
Rice wine distillers’ grains are indirect evidence because their rice-based substrate, starter, fermentation temperature and residual matrix differ from SBDG. The relevant similarity is limited to a fermented cereal matrix containing protein, fiber, organic acids and phenolic compounds; neither equivalent microbial structures nor equivalent postbiotic exposure has been demonstrated. In heat-stressed Holstein cows, a rice-wine-lees mixture at approximately 11% of dietary DM maintained intake and milk yield and was associated with antioxidant and milk-fatty-acid responses
[61]. This study justifies analogous endpoints in SBDG trials, but cannot support the conclusion that SBDG has the same postbiotic effect.
Mechanistic evidence should be separated by material and component. Rice-wine-lees studies report rumen-fermentation and antioxidant outcomes but do not isolate a postbiotic fraction. CLDG-derived arabinoxylan and polysaccharide studies implicate fermentation to SCFAs and barrier-related outcomes, whereas defined yeast
β-glucans or heat-killed bacteria provide separate pattern-recognition-receptor evidence
[29,31,61]. Accordingly, future SBDG studies should test a component-exposure → rumen/gut microbiota and SCFA → barrier/immune or Nrf2-related antioxidant pathway using nutritionally matched controls; the pathway is not established by changes in serum antioxidant indices alone.
Accordingly, a fiber-microbiota-SCFA-inflammation pathway should be presented as a proposed mechanism for SBDG rather than a confirmed mode of action.
In the rice-wine-lees trial, improved rectal temperature, respiratory rate and antioxidant indices were associations with the complete feed matrix, not evidence that microorganisms or postbiotics caused the response
[61]. The cited study did not provide an SBDG-like inanimate microbial composition or a causal microbiota-antioxidant axis. The interpretation therefore treats these endpoints as targets for SBDG trials and requires concurrent measurement of microbial structures, metabolites, rumen microbiota, systemic redox markers and animal performance.
Integrating this with evidence that diets combining former foodstuff and wheat distillers’ co-products can alter fiber utilization and rumen fermentation and reduce modeled environmental impacts
[103,104], SBDG can be viewed as a potential “hub ingredient” linking heat-stress mitigation, performance maintenance and environmental performance optimization. This provides a clear experimental framework for evaluating the combined effects of fermented SBDG in heat-stressed or periparturient cows.
Direct evidence is available for finishing cattle: 15% and 30% FMDG (DM basis) for 60 d did not significantly impair DMI, average daily gain or feed efficiency, although selected carcass and blood indices changed
[23]. These levels define tested conditions for that product and animal class, not a universal SBDG recommendation. For new products, a lower starting dose (e.g., 5-10% DM) with escalation to 15% and 30% may be used, provided diets are isoenergetic and isonitrogenous and each batch is characterized. Compound exposure should be reported, but no SBDG-specific acid, polyphenol or cell-wall threshold is currently validated.
Poultry
Direct broiler evidence is now available. Zheng et al.
[44] tested Moutai dried distillers’ grains (MDDG) and fermented Moutai distillers’ grains (FMDG) at 2.5%, 5% and 10% of complete diets for 42 d. MDDG at 10% reduced growth performance, whereas FMDG at up to 10% maintained growth and altered meat-quality and intestinal-barrier indices. Thus, 5% MDDG and up to 10% of the specifically characterized FMDG are evidence-based tested levels for broilers; they are not postbiotic-dose thresholds or automatic recommendations for other SBDG batches.
Defined-postbiotic meta-analysis remains analogue evidence
[76]. Future broiler trials should retain 0%, 2.5%, 5% and 10% product levels where appropriate, quantify digestible amino acids and metabolizable energy, and report marker exposure so that nutritional and candidate postbiotic-related effects can be separated.
No SBDG-specific layer dose-response trial was identified. Layer recommendations therefore cannot be inferred from the broiler study, DDGS or general fermented feeds. A staged 2.5%, 5% and 7.5% trial can be used as a research design, with laying performance, egg quality, yolk oxidative stability, palatability, digestible amino acids, energy and marker exposure measured; this is a proposed design rather than a recommended commercial range.
Polyphenols and peptides may be quantified as exploratory exposure markers, but neither their deposition in eggs nor a causal effect on egg flavor has been demonstrated for SBDG. Sensory claims require blinded sensory evaluation together with volatile-compound analysis and appropriate controls.
Poultry diets require tight control of metabolizable energy, digestible amino acids, fiber, fat quality and mycotoxins. The broiler evidence supports product-specific testing of FMDG up to 10%, whereas layers still require direct trials. Factorial controls are needed when a defined postbiotic is added to SBDG so that effects of the nutrient matrix, fermentation and added preparation can be distinguished.
Pigs
Direct pig evidence is now available. Lu et al.
[105] tested
Saccharomyces cerevisiae-fermented Moutai distillers’ grains (FMDG) at 0%, 5% and 10% in three growing-finishing phases (30-50, 50-75 and 90-130 kg body weight). Inclusion up to 10% did not impair growth; 5% produced the clearest later-finishing economic and carcass responses, while barrier and inflammatory indices also changed. These are product- and stage-specific tested levels, not proof of a postbiotic mechanism.
For growing-finishing pigs, 5% can therefore be considered the best-supported practical starting level for the tested FMDG, with 10% as a tested upper level under the reported formulations
[105]. No direct evidence supports transferring these values to weaned piglets.
Weaned-piglet evidence derives primarily from fermented soybean meal, fermented liquid feeds, enzymatically hydrolysed diets and defined heat-killed bacterial preparations. These interventions can reduce dietary pH or antinutritional factors and may influence diarrhoea, villus morphology, microbiota and immune responses
[60,96,106]. Heat-killed
Lactobacillus plantarum L-137 is defined-postbiotic analogue evidence, not evidence for SBDG.
Organic acids, arabinoxylans, polyphenols and peptides detected in SBDG or related materials provide a rationale for piglet studies
[29-31,107,108]. However, reduced diarrhoea, improved microbiota or enhanced immunity should be framed as testable outcomes rather than expected SBDG benefits.
Weaned-piglet SBDG trials should begin conservatively (e.g., 2.5% and 5%) and measure diarrhoea, intake, digestibility, barrier function and contaminants before dose escalation. Growing-finishing trials may use 0%, 5% and 10% based on direct FMDG evidence
[105]. Both inclusion rate and marker exposure should be reported; extracted fractions or added defined postbiotics require independent dose finding and factorial controls.
Cross-species synthesis and implications for SBDG
Direct SBDG/Moutai-distillers’ grain evidence now includes finishing cattle (0%, 15% and 30% DM), broilers (2.5%, 5% and 10% MDDG or FMDG) and growing-finishing pigs (0%, 5% and 10% FMDG)
[23,44,105]. Evidence remains absent or insufficient for dairy cows, layers, weaned piglets and species-specific postbiotic-component thresholds. These direct findings should be distinguished from the indirect and analogue evidence in
Table 4.Laboratory-scale SBDG or CLDG processing studies support the feasibility of protein enrichment, fiber modification and reduction of selected acids or mycotoxins
[42,90]. The principal evidence gap is therefore an SBDG-specific chain linking batch characterization, dose, postbiotic-related component exposure, animal responses and production outcomes.
Safety and quality-control framework
Each SBDG batch should be released against a predefined specification rather than accepted solely on the basis of fermentation history. Incoming and finished materials should be tested for dry matter or moisture, water activity where relevant, pH, titratable acidity and the concentrations of major organic acids. Wet SBDG require a validated preservation strategy, storage duration and temperature because high moisture increases heating, yeast and mould growth and nutrient loss. Residual ethanol should be quantified by a validated analytical method, and acid or ethanol targets should be set according to species, total diet and intended storage form.
Sulfur should be measured in SBDG and evaluated together with sulfur from water and other dietary ingredients; DDGS-derived sulfur limits cannot be assumed to apply directly to SBDG
[102]. Risk-based mycotoxin panels should include aflatoxin B
1, deoxynivalenol, zearalenone, fumonisins, ochratoxin A and T-2/HT-2 toxins as relevant to the raw materials and jurisdiction. Fermentation-related detoxification must be verified in every batch and should not be inferred from a single process study
[10,24,42].
Batch-to-batch control should further cover crude protein, amino-acid availability or heat-damaged protein indicators, NDF and ADF, fat quality, ash, viable microbial counts, absence of relevant pathogens and marker levels for candidate postbiotic-related components. Representative sampling, lot traceability, retention samples and stability testing are required to relate product specifications to animal responses. Species-specific acceptance criteria should comply with applicable feed regulations and be validated in SBDG-specific safety and dose-response studies.
Environmental and techno-economic implications of postbiotic-based utilization of SBDG
Building on process and application-level discussions in previous sections, this section examines SBDG from environmental and techno-economic perspectives, emphasizing their roles in “soybean meal reduction and replacement”, “high-value utilization of brewing co-products” and “circular bioeconomy”.
Environmental footprint, resource efficiency and the circular bioeconomy
The structured search identified general LCA studies for DDGS and broader distillers’ grain pathways, but no comparative cradle-to-farm-gate LCA specific to SBDG-derived feed. Consequently, claims that fermented SBDG reduces greenhouse-gas or reactive N/P emissions are presently hypotheses rather than demonstrated outcomes. Broader distillers’ co-product LCA results are retained only to identify relevant system boundaries and allocation choices
[104,109].
An SBDG-specific LCA should compare fresh local feeding, preservation, drying, secondary fermentation, anaerobic digestion and fertilizer routes; include energy, water, transport, avoided waste treatment, feed substitution and manure effects; and report sensitivity to economic versus mass allocation. The functional unit should include both tonne of SBDG managed and unit of digestible nutrient or animal product. Until such analysis is available, environmental superiority should not be asserted.
Process costs, economic trade-offs and product portfolio design
From a techno-economic standpoint, adding synthetic consortia solid-state fermentation increases capital, energy and labor costs. Comparative SBDG-specific assessments of digestible nutrient recovery and processing costs across fermentation, silage and other utilization routes are still needed
[14]. At the same time, detoxification and reduced organic acid load could lower health risks and improve economic returns, but these potential savings require validation.
In terms of product portfolio design, grading fermented SBDG into a “coarse, high-fiber fraction” and a “fine, high-protein fraction” could support targeted marketing to ruminant TMRs and monogastric protein concentrates/functional additives, subject to validation of fraction yield, composition, efficacy and cost. Leveraging existing solid-state fermentation equipment and online monitoring systems in Baijiu plants, retrofitting may be possible to establish “fermented SBDG-postbiotic feed” production lines, although marginal costs require assessment
[13,45].
“Liquor-feed-livestock integration” and integrated biorefinery concepts
For sauce-flavor Baijiu producers and regional livestock sectors, demonstration projects spanning the entire chain of “brewing-fermented SBDG production-diet formulation-demonstration farm application-environmental and economic evaluation” could position SBDG as a key “hub resource” linking Baijiu manufacturing with green livestock production and provide real-world tests of the “composite postbiotic carrier” concept and its economic feasibility.
At a broader scale, SBDG utilization can be integrated into a biorefinery framework: Baijiu plants serve as the core, upstream-linked to grain production and quality control, and downstream to fermented SBDG production, functional feeds and pet foods, and organic fertilizer/soil amendment products, forming “liquor-feed-livestock-crop” integrated layouts. Regional “liquor-feed-livestock integration” pilots, supported by LCA and techno-economic analysis (TEA) assessments, could generate replicable technical and business models for low-carbon transitions in both the Baijiu and livestock industries.
Challenges and future research directions
Having systematically examined SBDG postbiotic material bases, process routes, animal applications and environmental-economic implications, this section highlights key scientific and engineering challenges and outlines future research and innovation priorities.
From “empirical co-products” to “quantifiable composite postbiotic platforms”
Within the ISAPP framework, SBDG should first be classified as a fermented feed material or potential postbiotic-rich matrix. Future products may be separated into: (1) nutritional fermented materials dominated by protein and fiber; (2) candidate composite preparations containing characterized inanimate microbial components plus associated metabolites; and (3) extracted functional ingredients such as arabinoxylans or peptides, which are not postbiotics when used alone. Only category 2 should be considered for a postbiotic claim, and only after a host benefit has been demonstrated
[17,18].
For each class, specifications should include protein fractions, microbial viability and inactivation, cell-wall markers, organic-acid profiles, polyphenols, peptides and relevant in vitro functions. This framework would allow SBDG-derived products to move from descriptive concepts toward reproducible and potentially registrable categories without prematurely labelling all products as postbiotics
[10,24].
Multi-omics evidence chains and “microbiota-barrier-hepatic lipid metabolism axis” mechanisms
Current animal studies are largely limited to endpoint production metrics and selected blood or tissue indices. Future SBDG-specific work should link characterized exposure to rumen or gut microbiota and metabolome, barrier and immune responses, liver metabolism and production outcomes. Designs may combine 16S ribosomal RNA gene sequencing or metagenomics with transcriptomics and untargeted metabolomics, followed by structural equation modelling or causal-inference approaches
[89,110,111].
A testable hypothesis is that nutritional supply interacts with microbial structures, functional fibers, organic acids, polyphenols and peptides to influence microbiota, barrier and metabolic responses. This proposed network must be evaluated against nutritionally matched controls and cannot be inferred from component presence alone.
Scale-up, process control and formulation-based design
From an engineering standpoint, scaling up solid-state fermentation and achieving robust process control remain major bottlenecks for postbiotic utilization of SBDG. Future work should prioritize: (1) Adapting Baijiu industry monitoring tools for temperature, humidity and volatile compounds to secondary fermentation of SBDG, and correlating “organic acid generation, gas composition and redox status” with postbiotic profiles and in vitro activity
[13,45]. (2) Systematic comparisons of loading height, aeration and turning strategies in pilot-scale trials to determine their effects on protein, fiber, polyphenols and cell wall structures, thereby informing parameter spaces for formulation-based “process-composition-function” design
[41,42]. (3) At the product level, exploring flexible combinations of “coarse, high-fiber fractions” and “fine, high-protein/postbiotic-enriched fractions” across species and production stages to balance nutrition, functionality and economics.
Priority research and innovation areas
Priority areas are: (1) SBDG-specific dose-response trials across species and physiological stages; (2) factorial studies that separate effects of the SBDG nutrient matrix from defined microbial structural components or added postbiotics; (3) compositional and inactivation standards linked to host-benefit endpoints; and (4) regional life cycle assessment (LCA) and techno-economic analysis (TEA) of liquor-feed-livestock-crop systems.
Conclusions
SBDG are a regionally concentrated co-product of high-temperature, multi-stage solid-state fermentation. Their mixture of nutrients, inanimate microbial biomass or structural components, organic acids, peptides, polyphenols and complex polysaccharides makes them a potential postbiotic-rich matrix with several valorization routes. This description does not mean that every raw or fermented SBDG product is a postbiotic. Controlled processing and safety characterization should determine whether a batch is routed to nutritional feed use, further development as a candidate composite preparation or extraction of separate functional fractions.
Direct SBDG animal evidence remains limited. Findings from fermented Moutai distillers’ grains and indirect evidence from other CLDG, rice wine distillers’ grains, DDGS and defined postbiotics support carefully designed SBDG-specific trials, but do not yet confirm the proposed microbiota-barrier-immunity-metabolism mechanisms or the preliminary inclusion ranges. Translation therefore requires: (i) marker-based standardization and batch-level safety control; (ii) SBDG-specific dose-response and mechanistic studies; and (iii) demonstration-scale deployment coupled with TEA and LCA.
Abbreviations
ACE Angiotensin-converting enzyme
ADIN Acid detergent-insoluble nitrogen
ARE Antioxidant response element
BLIS Bacteriocin-like inhibitory substance
CLDG Chinese liquor distillers’ grains
CR3 Complement receptor 3
DCP Digestible crude protein
DDGS Distillers dried grains with solubles
GPR G protein-coupled receptor
ISAPP International Scientific Association for Probiotics and Prebiotics
LCA Life cycle assessment
MAPK Mitogen-activated protein kinase
NF-κB Nuclear factor kappa B
NDF Neutral detergent fiber
Nrf2 Nuclear factor erythroid 2-related factor 2
NSP Non-starch polysaccharides
PRR Pattern-recognition receptor
RUP Rumen-undegraded protein
SBDG Sauce-flavor Baijiu distillers’ grains
SCFA Short-chain fatty acid
SMC-SSF Synthetic microbial community solid-state fermentation
SSF Solid-state fermentation
TEA Techno-economic analysis
This work was supported by the internal research program of Kweichow Moutai (Group) Circular Economy Industrial Investment and Development Co., Ltd.
Ethics approval and consent to participate
The authors declare that they have no competing interests.
Declaration of Generative AI and AI-assisted technologies in the writing process
During manuscript preparation, ChatGPT (OpenAI) was used for English linguistic proofreading and assistance with reference verification and correction of citation-related statements. The authors conducted comprehensive review and revision of the manuscript, and bear full responsibility for the content herein.
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