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Review

Strategies for Reducing Purine Accumulation in Beer: From Metabolic Mechanisms to Brewing Technology Innovations

by
Jun Liu
1,2,3,4,5 and
Jian Lu
1,2,3,*
1
Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China
2
National Engineering Research Center of Cereal Fermentation and Food Biomanufacturing, Jiangnan University, Wuxi 214122, China
3
Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi 214122, China
4
Key Laboratory of Functional Foods, Ministry of Agriculture and Rural Affairs, Guangdong Key Laboratory of Agricultural Products Processing, Sericultural and Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510610, China
5
Key Laboratory for Prevention and Control of Avian Influenza and Other Major Poultry Diseases, Ministry of Agriculture and Rural Affairs, Key Laboratory of Livestock Disease Prevention of Guangdong Province, Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
Fermentation 2025, 11(4), 193; https://doi.org/10.3390/fermentation11040193
Submission received: 7 March 2025 / Revised: 29 March 2025 / Accepted: 1 April 2025 / Published: 5 April 2025
(This article belongs to the Section Microbial Metabolism, Physiology & Genetics)
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Abstract

:
The rising prevalence of hyperuricemia and gout, driven by dietary purine intake, has intensified demand for healthier alcoholic beverages. Beer, a major contributor to exogenous purines, poses significant health risks despite its cultural and economic importance. This review systematically analyzes purine sources in beer, metabolic pathways leading to uric acid production, and cutting-edge strategies for purine reduction. We evaluate physical adsorption, enzymatic degradation, microbial fermentation, and yeast metabolic engineering, highlighting their efficacy and limitations in industrial applications. Challenges such as flavor preservation, regulatory compliance, and scalability are critically discussed. By integrating multidisciplinary approaches ranging from synthetic biology to process optimization, this work provides a roadmap for developing commercially viable low-purine beers, bridging the gap between public health priorities and brewing industry innovation.

1. Introduction

Hyperuricemia and gout have become the second most common metabolic diseases endangering human health [1]. Hyperuricemia and gout, affecting over 177 million individuals in China alone, have emerged as critical public health challenges linked to modern dietary habits. Alcoholic beverages, particularly beer, contribute substantially to purine intake due to their high purine contents and widespread consumption. Purine substances present in beer are mainly composed of bound purine nucleosides and free purine bases, which eventually generate uric acid under the action of the human purine metabolism enzyme system. Since humans lack the uric acid oxidase (UOX) enzyme, they are unable to metabolize uric acid to produce soluble allantoin, resulting in elevated blood uric acid; persistent hyperuricemia can lead to gout. Currently, the treatment of gout and hyperuricemia can be divided into two main categories: medication and dietary treatment. The former is effective in relieving gout pain, but medication is accompanied by many side effects such as impaired liver and kidney function. The latter is managed by restricting a high-excretion diet, which can reduce uric acid production in the body by 15–20 per cent by restricting dietary purine, which is enough to be a natural treatment for gout. However, research studies have shown that about 80% of patients claim to be unwilling to change their dietary and drinking habits. Therefore, the creation of low purine beer based on patients’ dietary habits has become an important direction in the control of gout and hyperuricemia.
The global beer industry, valued at $768 billion in 2023, faces dual pressures: escalating health-conscious consumer demands and regulatory incentives to mitigate metabolic disease burdens. However, conventional purine-reduction methods—such as barley substitution or chemical treatments—often impair flavor or lack scalability. Recent advances in enzyme engineering, microbial consortia design, and yeast genome editing offer transformative solutions, yet systematic evaluations of their industrial feasibility remain scarce. This review explores the sources of purines in beer, the metabolic processes involved in their production, and methods for reducing the purine content of beer.

2. Overview of Purines

2.1. Characterisation of Purines

Purines (C5H5N4) are amphoteric compounds that are highly soluble in water and alcohol but insoluble in non-polar solvents. They are formed by the condensation of a pyrimidine ring and an imidazole ring. First named by Emil Fischer, purines are essential components of nucleic acids and play crucial roles in genetic regulation, energy metabolism, coenzyme formation, and metabolic regulation in living organisms [2]. Purine analogs present in nature are shown in Figure 1, starting with simple units in the form of free nucleobases (adenine, guanine, xanthine, hypoxanthine), which consist only of purine or pyrimidine rings. When these nucleobases are bound to the ribose or deoxyribose through glycosidic bonding, nucleosides are formed (adenosine, guanine, inosine); these molecules can mediate cellular signaling, but still need to be linked to 1–3 phosphate groups on the 5’ carbon of the sugar via a phosphate bond to be upgraded to a nucleotide that functions as both a carrier of genetic information and an energy currency [3]. As purines contain conjugated double bonds, there is a strong absorption at the UV wavelength of 260 nm, which can be used for quantitative or qualitative detection of purines [4].

2.2. Purines and Gout

Gout is a chronic disease caused by disruptions in purine metabolism and impaired uric acid excretion. It is primarily characterized by elevated serum uric acid (SUA) levels, which lead to the deposition of urate crystals in and around the joints in the body [5]. In biological systems, purine analogues can be classified into two groups: endogenous and exogenous purines [6]. Endogenous purines are mainly produced through two metabolic pathways: the de novo synthesis pathway and the salvage pathway. These two pathways account for approximately 80% of the total purines in biological systems. The de novo synthesis pathway is energy-intensive and involves a series of enzymatic reactions. In the first stage, 5-phosphoribosyl-1-pyrophosphate (PRPP) is synthesized from the substrate ribose-5-phosphate, a product of the pentose phosphate pathway. PRPP then undergoes further chemical reactions to form inosine monophosphate (IMP). In the second stage, IMP serves as a purine nucleotide precursor to produce adenosine monophosphate (AMP) and guanosine monophosphate (GMP). The salvage pathway, on the other hand, recycles purine bases to synthesize purine nucleotides. The key enzymes involved in this pathway include adenine phosphoribosyltransferase (APT1, EC 2.3.2.7) and hypoxanthine-guanine phosphoribosyltransferase (HPT1, EC 2.3.2.8). These enzymes transfer a phosphoribosyl group from PRPP to adenine, xanthine, and guanine, respectively, to generate AMP, IMP, and GMP, which play important roles in the salvage pathway. However, abnormalities in the metabolism of these molecules can lead to elevated purine levels in the body.
Exogenous purines are primarily derived from the diet and account for about 20% of the total purines in biological systems. These purines are mainly metabolized by the liver, intestines, and kidneys. The basic degradation process involves enzymes like nucleotidase (NT) and purine nucleoside phosphorylase (PNP), which break down purines into free bases. Adenine and guanine are degraded to produce hypoxanthine and xanthine, respectively, through the action of adenine deaminase (ADA) and guanine deaminase (GDA). These intermediates are ultimately oxidized by xanthine oxidase (XOD) to form uric acid, which is excreted through the urine and sweat [2]. Inhibiting the activity of xanthine oxidase can reduce uric acid production in the body. Notably, uric acid also possesses antioxidant properties, allowing it to neutralize harmful substances such as hydroxyl radicals, superoxide anions, and methemoglobin [7]. Excessively low SUA levels increase the risk of neurological disorders, such as Parkinson’s disease and Alzheimer’s disease. Under normal circumstances, uric acid metabolism in the body remains in a state of homeostasis. However, the long-term intake of high-purine foods, fructose, and alcoholic beverages can lead to abnormal purine metabolism. When SUA levels exceed 7.0 mg·dL−1 (420 µmol·L−1) [8], urate precipitates due to saturation, forming sodium urate crystals that are deposited in the joints, cartilage, and kidneys, resulting in gout [9]. A gout attack is typically characterized by redness, swelling, and severe pain in the affected joints and may also be accompanied by a range of metabolic disorders, such as diabetes mellitus, renal damage, and cardiovascular and cerebrovascular conditions [10].
Both the alcohol and purines present in alcoholic beverages act as key contributors to hyperuricemia and gout in humans [11]. When blood alcohol levels exceed 200 mg·dL−1, lactic acid accumulates. This inhibits the renal excretion of uric acid and disrupts the balance of uric acid metabolism, thus triggering gout. In fact, consuming more than 15 g of alcohol per day increases the risk of gout by 93% [12]. Among the various alcoholic beverages available on the market, beer shows the strongest association with gout [13,14], followed by distilled spirits (Figure 2). In contrast, moderate wine consumption does not seem to affect gout patients, likely because wine contains a high content of polyphenols, which may counteract the inhibitory effect of alcohol on uric acid excretion [15]. Although beer has a relatively low alcohol content, it contains a significant amount of purine analogues. Clifford et al. [16] argued that adenine and hypoxanthine are the primary purine bases responsible for inducing gout. Yamamoto et al. [17] found that beer is rich in guanosine, which is more readily absorbed than other purine analogues and can be rapidly converted to guanine in the body via enzymes such as GDA and XOD, eventually producing xanthine and uric acid. To mitigate the risk of gout, China’s dietary guidelines for individuals with hyperuricemia and gout (WS/T 560-2017) recommend that men and women limit their alcohol intake to no more than two alcohol units and one alcohol unit per day, respectively. Here, one alcohol unit is roughly equivalent to 14 g of pure alcohol, corresponding to about 145 mL of wine (12% alcohol by volume), 497 mL of beer (3.5% alcohol by volume), or 43 mL of distilled spirits (40% alcohol by volume). People with elevated SUA levels are advised to avoid the regular consumption of beer and distilled spirits and instead choose moderate amounts of non-purine or low-purine beer (LPB).

2.3. Purine Content in Alcoholic Beverages and Corresponding Limits

Purines are widely present in foods [18,19,20,21], and foods can be classified into five categories based on their purine content [5] (Table 1). Beer contains significantly higher levels of purines than wine and distilled spirits. However, low-malt and low-purine beers have lower purine contents than regular beers, with their guanine content being higher than the content of other purine analogues (Table 2).
Currently, there is no clear definition of “low-purine beer”, and the upper limit for purine levels in this type of beverage remains variable. Analytical techniques have not been standardized, and the use of different testing methods can lead to considerable heterogeneity in data. According to current clinical definitions, low-purine foods must contain purine levels less than 50 mg·(100 g)−1, or approximately 500 mg·L−1. Commercially available regular beer typically has purine levels ranging from 40 mg·L−1 to 150 mg·L−1. The average purine content of beer is 74.89 mg·L−1 [22], which is below the standard threshold. However, the consumption of such beers can still contribute to hyperuricemia and gout. In Japan, beer-like beverages with purine levels under 40 mg·L−1 are classified as “low purine”, while those containing less than 5 mg·L−1 are considered “no purine” [23].
Owing to changes in dietary patterns, the consumption of high-purine foods is increasing, and the prevalence of hyperuricemia and gout is rising [4]. Normal healthy adults can consume 600–1000 mg of purines per day. For individuals with gout in remission, the recommended purine intake is typically 300–600 mg per day, while during acute attacks, the intake should ideally be restricted to below 150 mg per day. Reducing exogenous purine intake through a low-purine diet can decrease uric acid production in the body by 15–20% [24], significantly lowering SUA levels and mitigating the side effects associated with drug therapy. Therefore, optimizing the diet to ensure low purine intake can serve as an effective medical nutritional therapy (MNT) for managing and treating gout.

3. Sources of Purines in Beer and Features of the Brewing Process

3.1. Purine Sources

Beer is one of the oldest and most widely consumed alcoholic beverages in the world [25,26]. Beer is a complex beverage brewed from malt, hops, water, and yeast.
In addition to barley malt and hops, other grains, such as wheat malt, corn, rice, and sorghum, as well as auxiliary ingredients like molasses, are used in beer production. Lin et al. [27] found that among the various raw materials used for peer production, barley malt has the highest purine content, while corn starch and molasses contain the lowest purine levels. The purine content of wheat malt is about half that of barley malt. Li et al. [28] demonstrated that reducing the proportion of barley malt to 40% can lower the total purine content in wort from 125.24 mg·L−1 to 67.48 mg·L−1. Similarly, Shang et al. [29] found that increasing the proportion of wheat malt to 40% can lead to a 15% reduction in the total purine base content of the beer. In the late 1990s, Happo-shu beer was developed in Japan by reducing the malt content to 25%, resulting in a final purine content of 249.4 μmol·L−1 (38.3 mg·L−1).
These studies collectively indicate that the purines in beer are primarily derived from barley malt, and reducing its proportion can effectively control the overall purine content of beer. However, beer fermentation is a complex process that involves various microbial physiological processes and biochemical reactions. Excessively limiting the use of barley malt can lead to a deficiency of nutrients such as α-amino nitrogen, which are required for the proliferation of yeast in the wort and affect their fermentation performance. This may prolong the fermentation time and induce premature yeast senescence or autolysis, releasing intracellular nucleic acids that add to the content of purine-like substances in beer.
In recent years, the development of new types of beer has broadened the range of brewing ingredients [30,31,32,33,34]. For example, fruits, vegetables, and herbs with specific nutritional properties are increasingly being added as adjuncts in the brewing process [35,36]. Additionally, efforts are being made to remove potentially hazardous substances, such as alcohols, purines, gluten, and carbohydrates [32], to produce tailor-made beers with optimal characteristics. However, auxiliary ingredients such as fruits and vegetables are highly susceptible to contamination by spoilage fungi during production, processing, transport, and distribution. The toxic metabolites of these fungi, known as mycotoxins, can be transferred to the beer [37]. These mycotoxins can interfere with the yeast cell cycle, disrupt purine metabolism, lead to cell apoptosis, and increase the purine content of the final product. The consumption of such beer may contribute to hyperuricemia and gout [36,38]. Under current production conditions, it is not feasible to completely eliminate mycotoxins from the human food chain. Therefore, effective measures for identifying and mitigating mycotoxin contamination are essential to reduce the risk of such contamination in the brewing process.
During the production of low-purine beers, accurately identifying and controlling fungal contamination is crucial when exploring alternatives to barley malt. This will help reduce the use of barley malt and the purine content of beer while ensuring the safety and quality of the final product.

3.2. Changes in Purine Analogues During the Brewing Process

During mashing, the RNA and DNA in barley malt are largely degraded through the action of ribonuclease enzymes and thermodynamic processes. This degradation produces soluble nitrogenous substances, including purine nucleotides, purine nucleosides, and purine bases. Free purine bases, such as adenine and guanine, account for about 6% of these substances and serve as important energy sources for yeast proliferation.
During beer fermentation, purines are primarily assimilated and absorbed by brewer’s yeast. In the initial phase of fermentation, yeast cells assimilate free purine bases through the purine salvage pathway to synthesize intracellular nucleic acids, which promote rapid yeast proliferation. This helps to shorten the growth retardation period and fermentation time. However, if the wort lacks free purine bases, yeast cells cannot activate the purine salvage pathway and must instead rely on the de novo synthesis pathway. This pathway requires sugars and amino acids to synthesize the necessary purine substances and thus consumes substantial energy; this impairs the proliferation and fermentation performance of yeast. Additionally, due to the absence of concentrative nucleoside transporter (CNT1) on the cell membrane of brewer’s yeast, nucleosides cannot be transported into the cell body or utilized [39]. As a result, the purine nucleosides from raw materials, such as barley malt, remain in solution, contributing to elevated levels of purine analogues in the final product.
In the yeast purine salvage pathway (Figure 3), the two most critical enzymes are HPT [40] and APT [41]. These enzymes catalyze the reaction between free purine bases and PRPP to produce corresponding purine nucleotides, thereby shortening the growth retardation period. The APT gene family consists of APT1 and APT2, with APT2 being a product of the whole-genome duplication of APT1. Yeast cells exhibit normal growth when only APT1 is null mutated, but when both APT1 and APT2 are null mutated, growth defects are observed [41]. PRPP is primarily synthesized by the enzyme PRPP synthetase (PRS), which is involved in both the de novo and salvage purine synthesis pathways, although the latter is dominant. The five subunits of PRS are encoded by the PRS1–PRS5 genes [42,43]. In PRS2 or PRS4 null mutants, cell growth and metabolism are largely unaffected. However, null mutations in PRS1 or PRS3 have a significant effect on cellular metabolism. This suggests that PRS1 and PRS3 serve as key functional genes, with PRS1 playing a significant role in the cell wall integrity (CWI) pathway [42]. Phosphoribomutase (PRM15) catalyzes the interconversion of ribulose-1-phosphate and ribulose-5-phosphate. Although this enzyme has some phosphoglucose translocase activity, it mainly acts as a phosphoribomutase in vivo, contributing to ribose recycling via the pentose phosphate pathway. PRM15 also alleviates the feedback inhibition of IMP on PRS, aiding purine synthesis.
Purine-cytosine permease (FCY) is a proton transporter that is responsible for transporting adenine, guanine, hypoxanthine, and cytosine into yeast cells from the extracellular environment. This process supports the salvage synthesis pathway [44]. Although FCY2 shares functional similarities with FCY21 and FCY22, neither of these proteins can compensate for the loss of FCY2 function [45]. Therefore, HPT1, APT1, PRM15, and FCY2 could all serve as potential metabolic engineering targets to enhance the ability of brewer’s yeast to assimilate and absorb free purines, thereby reducing the purine content of beer while improving yeast proliferation and fermentation performance.

4. Measures for Regulating Purine Levels in Beer

Current research on low-purine beer mainly focuses on the following aspects (Figure 4): (1) Physical and chemical methods, which involve the treatment of brewing raw materials and the development of specific adsorbents to reduce purine content; (2) Enzymatic methods, which regulate the release of free purine bases to enhance assimilation and absorption of free purines in yeast; (3) Biological methods, which involve the screening of suitable food-grade purine-reducing strains for co-fermentation with brewer’s yeast, thus reducing purine levels in beer; (4) Brewing process optimization methods, which adjust saccharification and fermentation processes to lower the purine content of beer; and (5) Modern bio-breeding methods, which focus on selecting and breeding low-purine brewer’s yeast strains that are capable of rapidly metabolizing and utilizing purines in the wort.

4.1. Physical and Chemical Methods

In beer production, physical adsorption is commonly used to remove impurities such as proteins and polyphenols, which enhances the abiotic stability of beer [3]. Purines, like polyphenols and proteins, possess functional groups that can be leveraged for their removal by specific adsorbents. These adsorbents can be employed to reduce the purine content of beer. The most common adsorbent materials used at present include activated carbon, artificial zeolite, and chitosan. Lin et al. [27] compared the effectiveness of different adsorbents for purine removal from beer and found that artificial zeolite and activated carbon exhibited the best adsorption properties, reducing the purine analogue content of beer by 65% and 85%, respectively. However, this adsorption process had a negative impact on the foam, taste, and flavor of the beer. Japanese beer companies have explored strategies to reduce the barley malt content of beer to 25% and combined these methods with the use of adsorbents to develop purine-free beer. Table 3 shows the purine-free foaming beer products available in the Japanese market. In 2004, the Kirin Brewery Company(Okayama-ken, Japan), led by Shunichi [46], applied for a patent on the use of zeolite for purine adsorption, while Asahi Brewery Company (Fukuoka ken, Japan) (led by Takeshi [47]) patented the use of activated charcoal for purine removal. Although both approaches achieved successful purine adsorption, supplementation with dark malt and bittering agents was required in both cases to compensate for the loss of color and bitterness. Despite these advancements, an adsorbent that offers both a high adsorption capacity for purines and minimal impact on beer flavor and mouthfeel is yet to be developed.
The chemical methods for purine reduction typically involve the degradation of purine nucleosides in the wort into free purine bases through sulfuric acid addition during the wort boiling process. This enhances the uptake of purines by yeast, thus reducing the purine content of beer. Li et al. [48] demonstrated that adding 0.8% sulfuric acid during the wort boiling process and adjusting the pH back to initial levels with solid sodium hydroxide could yield a final product with a purine content of approximately 10 mg·L−1. Nevertheless, the use of chemical methods to reduce purines in beer can introduce residual reagents, which may impact the taste, quality, and safety of the beer.

4.2. Enzymatic Methods

Enzymes have long played an important role in the brewing of alcoholic beverages. The enzymatic reduction of purine analogues in beer presents a safe and promising strategy for managing hyperuricemia [49].
Before selecting an appropriate purine-degrading enzyme, it is essential to understand the forms of purine analogues present in beer. Shibano et al. [50] tracked the changes in purine nucleoside and free purine content during the fermentation of 12.5 °P wort. They observed that free purine levels rapidly decreased from 70 mg·L−1 to 10 mg·L−1 in the early stages of fermentation, while the total purine nucleoside content remained stable at 90 mg·L−1. This suggests that the purines in beer are primarily present in the form of purine nucleosides, rather than free purine bases. The enzyme system responsible for degrading purine nucleosides is primarily purine PNP, which has been extensively characterized across various organisms. PNP can be broadly classified into two types: PNP-I and PNP-II [51]. PNP-I, found mainly in archaea, bacteria, and mycoplasmas, is a homohexameric enzyme with a subunit size of about 26 kDa. It can catalyze the conversion of 6-oxopurine nucleosides (such as guanosine and inosine) and 6-aminopurine nucleosides (such as adenosine). Meanwhile, PNP-II is primarily found in mammals, fungi, and some bacteria and is a homotrimer with a subunit molecular weight of about 30 kDa [52]. Guanosine and inosine are the substrates of PNP-II. The PNP-II family includes PNP and 5′-deoxy-5′-methylthioadenosine phosphorylase (MTAP) [53], which has broad substrate specificity, particularly for methylthioadenosine and adenosine, and acts as a rate-limiting enzyme in the purine salvage pathway.
In a study by Shibano [50], calf spleen-derived PNP was used to treat 12.5 °P wort, resulting in the degradation of 60% of purine nucleosides in the wort. Recombinant PNP from various sources has been successfully expressed in E. coli and shown to demonstrate high enzyme activity. For instance, Breer et al. [54] expressed bovine PNP with a specific activity of 30 U·mg−1 in E. coli, while Silva et al. [55] expressed human PNP in E. coli, achieving a 707-fold increase in enzyme activity compared to the control. Nevertheless, there has been limited research on PNP from food-grade microorganisms.
Kluyveromyces lactis is a microorganism deemed Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA) [56,57]. Thus, its enzyme system has potential applications in the food industry. In 2017, Durga et al. [57] successfully expressed K. lactis KlacPNP in E. coli and mutated it to KlacPNP (N256D). This enzyme variant demonstrated broad substrate specificity and remained stable for several months during storage at 8 °C. In 2018, Durga et al. [58] further enhanced the degradation efficiency of purine analogues by expressing K. lactis ADA and GDA proteins in E. coli. When these enzymes were added to the finished beer along with KlacPNP, the purine content of the beer was significantly reduced. However, the optimal temperature for this enzyme system was 25–30 °C, which did not align with the high temperatures required during the saccharification stage of beer production, limiting the practical applications of this approach. Blastobtrys adeninivorans is a yeast strain dominant during the Puerh tea curing process, comprising 64% of the total fungal population. This yeast can utilize adenine, guanine, xanthine, hypoxanthine, nucleosides, uric acid, and other substances as nutritional sources. Its well-developed purine-degrading enzyme system has also garnered significant attention. Jankowska et al. [59,60] explored the use of B. adeninivorans in food production, focusing on its endogenous and recombinant purine-degrading enzymes. The enzyme system, which consisted of ADA, GDA, xanthine oxidoreductase (XOR), and urate oxidase (UOX), was shown to reduce the purine content in ham slices. The same enzyme combination was applied during beer production and achieved a substantial reduction in adenine, hypoxanthine, xanthine, guanine, and uric acid levels. However, this four-enzyme system mainly targeted free purine bases. Since the main form of purine analogues in beer is purine nucleosides, the addition of PNP was necessary to further reduce the purine content in beer. Shi et al. [61] adopted a computer-assisted reconstruction of purine metabolic pathways in vitro to construct a three-layer backpropagation artificial neural network (BP-ANN) model. The model, combined with a genetic algorithm (GA), predicted the optimal proportions of the four enzymes—PNP, ADA, XOD, and UOX—needed to effectively reduce the purine content of food. Although the purine-degrading enzyme system represented by PNP was successfully expressed in E. coli through genetic engineering, safety concerns regarding the gene source, expression host, and enzyme characteristics remained. Additionally, the enzymes’ compatibility with the unique characteristics of beer, such as its high saccharification temperatures and low pH, still needs to be explored further and tested on a larger scale.
Currently, there are no reports on the heterologous expression of PNP in eukaryotic systems. Pichia pastoris, a widely used protein expressing strain second only to E. coli, is commonly employed for laboratory-based protein production, characterization, and structural analysis. It has also been recognized as a GRAS microorganism by the U.S. FDA, paving the way for its application in the food and pharmaceutical sectors. Edible fungi are known to be rich in purine analogues. Among them, Agaricus bisporus can utilize urate, allantoin, allantoic acid, and urea as nitrogen sources for its growth [62]. This implies that A. bisporus not only meets food safety requirements but also contains a well-developed system of purine-degrading enzymes. The purine-metabolizing enzyme system of A. bisporus demonstrates potential applications in the beer industry.

4.3. Biological Methods

Chen et al. [63] proposed a method for reducing the purine content of food by using specific microorganisms to degrade and absorb purine analogues, followed by timely filtration to remove the organisms and prevent autolysis. In their study, they added Aspergillus oryzae ATCC 26831 (1.3 × 106 cfu·mL−1) to three different aqueous mushroom extracts for 48 h, achieving total purine content reductions of 84%, 61%, and 97%, respectively. Deng et al. [64] applied B. adeninivorans CICC33223 and prion-producing pseudomimetic yeast (Candida utilis) CICC 32604 for co-fermentation during the preparation of low-purine soymilk powder. After filtration, concentration, and drying, the total purine content of the final soymilk powder was only 4.5–6.6% of the content found in regular soymilk powder. Recent studies have also found that certain strains of Lactobacillus, including Lactobacillus plantarum DM9218-A [65], Lactobacillus fermentum 9–4 [66], and Lactobacillus gasseri PA-3 [67], are involved in the metabolism and degradation of purines. This indicates that lactobacilli could be employed in the development of low-purine foods and beers. However, the use of these bacteria would significantly change the taste and aroma of the beer.
In summary, microorganisms such as filamentous fungi, yeasts, and lactic acid bacteria show great potential for use in the development of low-purine foods. However, when biological methods are applied to brew low-purine beers, factors such as the alcohol and hop tolerance of the strains, as well as the impact of their senescence and apoptosis on the body of the beer, need to be considered.

4.4. Brewing Process Optimisation Methods

4.4.1. Selection and Handling of Raw Materials

The selection and processing of raw and auxiliary materials are crucial factors affecting the purine content of beer, and there is a significant variation in purine content among different brewing ingredients. Barley malt, the main raw material for beer brewing, contains much higher levels of purines than auxiliary materials [21]. Li et al. [28] found that the purine content of wort tends to decrease as the proportion of auxiliary ingredients increases, confirming that barley malt is the main source of purines in beer. In 2004, Jiangsu Dafuhao Brewery Co., Ltd (Nantong, China). launched a low-purine beer called “Golden Peopeo Bell” that was suitable for patients with hyperuricemia and gout. This beer was prepared by reducing the use of barley malt to 25% and increasing the proportion of auxiliary materials; the final purine content of the beer was 7.0–25.0 mg·L−1. However, the use of a low proportion of barley malt did not meet the industry’s requirements for beer production, which dictate that malt should be the primary raw material (more than 50% of the total ingredients) used in beer production. Therefore, the use of ingredients and excipients with a lower purine content can radically and significantly reduce the purine content of wort and beer.

4.4.2. Optimization of the Mashing Process

Mashing is an important step in the wort preparation process. During this stage, the insoluble macromolecules in malt and adjuncts are broken down into smaller molecules through the hydrolytic action of various enzymes present in the malt and heat treatment, increasing the solubility of these compounds. During malt saccharification, several enzymes—including phosphodiesterase, phosphomonoesterase, nucleosidase, nucleoside phosphorylase, and nucleoside deaminase—are activated. These enzymes degrade most nucleic acids, producing nucleotides, nucleosides, purines, pyrimidine bases, phosphoric acid, and other substances. Adenine and guanine bases account for approximately 6% of the total soluble nitrogen compounds in the wort. The breakdown of nucleic acids during saccharification is influenced by factors such as mash pH, temperature, and substrate concentration. Therefore, changes in the saccharification process can lead to variations in the degree of nucleic acid breakdown. Lin et al. [27] added malt root and Ca2+₊ during mashing and optimized the mashing process by orthogonal tests. The content of purine bases was increased from 30.7 to 57.9 mg·L−1, i.e., by 90%, under the following conditions: malt root was added at 1.5%, the Ca2+ concentration was 50 mg·L−1, the protein rested at 45 °C for 30 min, the saccharification temperature was 68 °C, the pH of mash was adjusted to 5.6–5.8 with phosphoric acid, and the ratio of material to water was 1:3.5. This suggests that optimizing the mashing process helps to reduce the purine nucleoside content in beer.

4.4.3. Optimization of the Fermentation Process

Beer is wort that is fermented by yeast, and the types and concentrations of nutrients in the wort significantly influence the proliferation and fermentation performance of the yeast. In the early stages of fermentation, yeast cells utilize the free purine bases in the wort to synthesize intracellular nucleic acids, thereby shortening the latency of yeast growth. Shang et al. [29] examined purine levels across 12 batches of beer during fermentation and found that purine bases were mostly depleted within the first 3 days of fermentation. When the wort is low in purine and pyrimidine bases, yeast cells activate the de novo synthesis pathway, which consumes sugars, amino acids, and a substantial amount of energy, thus impairing yeast proliferation. In general, the purine and pyrimidine bases in wort are sufficient for yeast growth and metabolism. During beer fermentation, when the yeast inoculum is smaller, the value-added multiples and the purine base requirements are greater. Hence, lower inoculum quantities and higher temperatures are conducive to the uptake of purine bases by yeast during fermentation.
The dilution process, which is commonly used after high gravity brewing, is another effective method for reducing purine levels in beer. This process involves increasing the wort concentration to over 16 °P and then diluting the beer with deoxygenated water after fermentation. Lin et al. [27] reduced the purine content of beer to 30 mg·L−1 (10 °P) by increasing the wort concentration to 20 °P using 25% barley malt. However, the alcohol content and osmotic pressure created by high gravity brewing adversely affected yeast activity, leading to autolysis and fermentation failure [68]. The supplementation of small-molecule peptides during fermentation and beer production has been shown to address these challenges and improve yeast metabolism and fermentation efficiency in high-strength environments, thus reducing the purine content of beer. For instance, Kitagawa et al. [69] found that the addition of soy protein peptides during fermentation promoted yeast growth, fermentation performance, and β-phenylethanol production. Similarly, Mo et al. [70] found that wheat gluten protein hydrolysates can improve yeast proliferation, enhance the fermentation capacity, and increase ethanol production under high-strength beer brewing, effectively solving the challenges associated with high-strength brewing environments. Magdalena et al. [71] also found that L-actinomycin could stimulate yeast reproduction by increasing daughter cell production, while Jin et al. [72] isolated the small-molecule peptides LL, LML, and LLL from wheat gluten and found that they improved the yeast proliferation rate and fermentation performance under high gravity brewing conditions.
Additionally, the incorporation of fruits, vegetables, and herbs in the brewing process offers a potential approach for the development of low-purine beers [35]. Several fruits, vegetables, and herbs rich in anti-gout actives (including mango, cherry, bitter melon, celery, chrysanthemum, cinnamon, and rosemary) are used as alternative medicines and supplements for the management of gout. These extracts not only have a lower purine content but may also inhibit the inflammatory effects of XOR, thereby lowering the levels of uric acid in the blood.
In summary, by optimizing fermentation conditions, e.g., increasing the fermentation temperature, reducing the yeast inoculum, and combining the advantages of high-strength brewing with the supplementation of small-molecule peptides, the purine content of beer can be reduced. Meanwhile, the addition of adjuncts rich in anti-gout active compounds could provide additional nutritional elements to these beer products.

4.5. Modern Bio-Breeding Methods

Although the purine content of beer can be reduced to below 40 mg·L−1 through process adjustments, this often results in poor flavor or high production costs, hindering large-scale industrial adoption. A more economical solution to the high purine content of beer involves the selection and breeding of brewer’s yeast strains that efficiently utilize purines. The most commonly used breeding methods for this purpose are mutagenesis breeding and genetic engineering.
Mutagenesis breeding is a technique that involves the induction of mutations in microbial genes using mutagens to improve the yield and performance of microbial strains. This technique is characterized by its speed and non-directionality and is commonly performed via chemical mutagenesis, physical mutagenesis, and biological mutagenesis. Among these methods, physical mutagenesis technology based on Atmospheric Room Temperature Plasma (ARTP) is frequently used. ARTP mutagenesis relies on active particles in the plasma that affect cellular structure and permeability, causing significant changes in microbial gene sequences and metabolic networks to induce mutations. The main advantage of mutagenesis breeding is that it avoids the need for genetic manipulation, thus mitigating potential food safety hazards. However, this process is associated with drawbacks such as a long breeding cycle, low efficiency, and poor stability when using random mutagenesis to develop industrial strains. Kang et al. [73] utilized ARTP technology to mutate brewer’s yeast. While maintaining yeast fermentation performance and beer quality, they obtained strains that could reduce the purine content of beer by up to 23.6% compared to the original strains.
Genetic engineering involves the introduction of specific genes into vectors and then into engineered strains to achieve targeted gene rearrangements. This method can overcome the limitations of distant gene integration and allow for precise modifications to meet specific needs. However, its application in food products remains limited due to safety concerns. Genetically engineered microbial strains and crops have yet to gain widespread consumer acceptance in the food and beverage industry. Nevertheless, genetic improvements can be achieved through selfclonal and non-selfclonal techniques based on the origin of the genes being introduced [74]. One promising technique is yeast “genetic self-cloning”, which modifies the yeast genome without introducing foreign heterologous DNA, thereby avoiding the consumer concerns associated with genetically modified organisms [75]. According to the Cartagena Protocol on Biosafety, such modifications do not require regulation as they do not involve heterologous DNA introduction [26].
Wu et al. [76] used self-cloning technology to modify the arginine metabolic pathway in the yellow wine industrial yeast strain N85, successfully reducing the levels of harmful substances such as ethyl carbamate (EC) in yellow wine by 55.3%. In industrial yeasts that are widely used for beer production (Table 4), researchers used self-cloning to increase the glutathione content, reduce proteinase A levels and achieve foam stability, enhance yeast flocculation, boost acetaldehyde reduction, and decrease lianedione levels [77,78,79,80,81,82]. Therefore, gene self-cloning appears to have valuable applications in constructing industrial yeast strains with excellent characteristics. However, so far, there have been no studies on the use of self-cloning technology to modify brewer’s yeast specifically for lowering purine levels.
The primary problem is to select suitable yeasts from a population of germplasm resources before directed domestication or genetic modification. Industrial brewer’s yeast has a complex genetic background, with diploids, polyploids, and aneuploids being relatively common and polyploids and aneuploids accounting for the majority of the population. The yeast strains used in domestic and international beer brewing vary widely, making the germplasm resources very rich [83]. If we only start from the phenotypic aspect, screening specific yeast strains will yield multiple yeast strains with similar values of phenotypic traits, and most of the phenotypic traits are quantitative traits, which are greatly affected by environmental factors, which leads to the difficulty of screening the target departure strains; therefore, this is not conducive to the management and utilization of brewer’s yeast.
Table 4. Summary of the genetic self-cloning technique for the modification of brewer’s yeast.
Table 4. Summary of the genetic self-cloning technique for the modification of brewer’s yeast.
StrainsCharacterizationReference
S. pastorianusFY-2Decrease in diacetyl precursors[84]
S. cerevisiae QY5, QY31 Decrease in diacetyl and increase in glutathione[85]
S. cerevisiae Y1 Decreased acetaldehyde and increased glutathione[86]
S. cerevisiae YSF-5 Increased glutathione, more stable foam[87]
S. cerevisiae 396-9-6V Increased flocculation[88]
In order to improve the screening efficiency of germplasm resources, Frankel [84] first proposed the concept of Core Collection in 1984 and further developed it with Brown et al. [85] in 1989. The concept refers to the maximum representation of the genetic diversity of a whole population with the minimum number of germplasm resources. The Core Collection contains a lot of important genetic information, which is the basis for mining and discovering superior alleles in whole resource populations, and provides an easy screening pathway for the utilization of germplasm resources. So far, researchers in many countries have constructed core germplasm libraries for more than 100 crops, laying the foundation for in-depth research and the efficient use of genetic resources [86,87,88].
At present, in the field of yeast, Liu et al. [83] have established a Core Collection of Saccharomyces cerevisiae, which can effectively screen out genotypically rich and phenotypically excellent starting strains, laying the foundation for directed evolution and metabolic engineering modifications of yeast.

5. Conclusions and Future Perspectives

With the continuous improvement in living standards and public awareness regarding health and nutrition, beer producers are facing increasing demands to enhance the features of their beer products. To fulfil these demands, further in-depth research on the development of low-purine beer is warranted. The potential areas of investigation include examinations of the structure of purines and their metabolic mechanisms in the context of barley breeding, the exploration of various enzymatic, physical, and chemical methods for lowing purine levels, and the development of safe and reliable purine adsorbents for direct application in beer fermentation to achieve rapid and efficient purine removal. Additionally, mutation breeding or self-cloning technology can be used to cultivate yeast strains with enhanced purine utilization abilities. Combining these techniques with the application of high-performance purine nucleic acid-targeting enzyme preparations could potentially allow beer to reach a low purine or even purine-free state. In summary, with increased research and technological advancements, the scope of purine removal from food products will broaden, and the effectiveness of purine elimination methods will improve. This will be beneficial for individuals with gout, providing new food options while also helping the general public make healthier dietary choices.

Author Contributions

Conceptualization, investigation, writing—original draft preparation, J.L. (Jun Liu); writing—review and editing, supervision, J.L. (Jian Lu). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the GuangDong Basic and Applied Basic Research Foundation (2023A1515111173); Key Laboratory for prevention and control of Avian Influenza and Other Major Poultry Diseases, Ministry of Agriculture and Rural Affairs, P.R. China/Guangdong Province Key Laboratory of Livestock Disease Prevention (YDWS202405); the Program of Introducing Talents of Discipline to Universities (111-2-06).

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Structure of purine bases and nucleosides.
Figure 1. Structure of purine bases and nucleosides.
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Figure 2. The correlation between beverages and serum urate concentrations [14]. Purple: Serum urate-raising effect; Yellow: Serum urate-lowering effect; Red line: Bonferroni corrected multiple-testing significance threshold (p < 7.94 × 10−4); Blue line: Nominal significance level (p < 0.05).
Figure 2. The correlation between beverages and serum urate concentrations [14]. Purple: Serum urate-raising effect; Yellow: Serum urate-lowering effect; Red line: Bonferroni corrected multiple-testing significance threshold (p < 7.94 × 10−4); Blue line: Nominal significance level (p < 0.05).
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Figure 3. Purine salvage pathway in yeast.
Figure 3. Purine salvage pathway in yeast.
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Figure 4. Regulation methods for purines in beer.
Figure 4. Regulation methods for purines in beer.
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Table 1. Classification of purine content of food.
Table 1. Classification of purine content of food.
CategoriesPurine Content/mg·(100 g)−1
very-low-purine foodsless than 50
low-purine foods50–100
medium-purine foods100–200
high-purine foods200–300
very-high-purine foodsgreater than 300
Table 2. Purine content in alcoholic beverages. (mg·L−1) [18].
Table 2. Purine content in alcoholic beverages. (mg·L−1) [18].
Alcoholic Beverages AdenineGuanineHypoxanthine XanthineTotal Purines
whiskey00.90.10.21.2
0.61.00.80.73.1
brandy01.51.80.53.8
Sake00.20.00.00.2
00.10.00.00.1
sake0.20.03.18.812.1
grape wine0.303.10.53.9
0.31.01.713.216.2
Beer (regular)15.736.715.316.684.2
Beer (low malt)5.316.42.14.628.4
7.016.85.49.939.1
Beer (low alcohol)14.99.42.50.627.4
36.066.615.012.3129.9
Beer (low malt and low purine)1.80001.8
Table 3. Japanese purine free Happōshu.
Table 3. Japanese purine free Happōshu.
BrandMerchandiseSourcePurine Content mg·L−1Alcohol % Vol
KirinNodogoshi StrongJapan≤5.04.0
SapporoGoku ZeroJapan≤5.05.0
KirinTanrei Platinum DoubleJapan≤5.05.5
AsahiOffJapan≤5.03.0–4.0
SuntoryAll freeJapan≤5.00.0
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Liu, J.; Lu, J. Strategies for Reducing Purine Accumulation in Beer: From Metabolic Mechanisms to Brewing Technology Innovations. Fermentation 2025, 11, 193. https://doi.org/10.3390/fermentation11040193

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Liu J, Lu J. Strategies for Reducing Purine Accumulation in Beer: From Metabolic Mechanisms to Brewing Technology Innovations. Fermentation. 2025; 11(4):193. https://doi.org/10.3390/fermentation11040193

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Liu, Jun, and Jian Lu. 2025. "Strategies for Reducing Purine Accumulation in Beer: From Metabolic Mechanisms to Brewing Technology Innovations" Fermentation 11, no. 4: 193. https://doi.org/10.3390/fermentation11040193

APA Style

Liu, J., & Lu, J. (2025). Strategies for Reducing Purine Accumulation in Beer: From Metabolic Mechanisms to Brewing Technology Innovations. Fermentation, 11(4), 193. https://doi.org/10.3390/fermentation11040193

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