Production and Gelatin Entrapment of Laccase from Trametes versicolor and its Application to Quantitative Determination of Phenolic Contents of Commercial Fruit Juices

Laccase (benzenediol: oxygen oxidoreductase; EC 1.10.3.2) is a particularly promising enzyme for several industrial fields, including food industries, since this enzyme catalyzes the oxidation of ortho and para-diphenols, amino-phenols, polyphenols, polyamines, lignins, and aryl diamines as well as some inorganic ions coupled to the reduction of molecular dioxygen to water. In this study, laccase was produced from one of the best laccase-producing organisms, Trametes versicolor. For this purpose, several phenolic acids were tested as laccase inducers. Caffeic acid and ferulic acid were determined to be the best inducers among the tested phenolic acids. Also, it was shown that laccase activity could be determined by using caffeic acid and ferulic acid as phenolic substrates by measuring the rates of oxygen consumption. Laccase was immobilized in gelatin under optimized conditions. Kinetic constants K _m and V _max for immobilized enzyme were estimated to be 74.758 μM and 0.744 μmol.ΔO₂/ml.min for caffeic acid and 0.999 μM and 57.80μ mol.ΔO₂/ml.min for ferulic acid, respectively. The immobilized enzyme exhibited the maximal activity at pH 4.5, and at 35°C. Immobilized enzymes were used for the determination phenolic contents of commercially prepared fruit juices. Caffeic acid contents of black cherry, apricot, and peach juice were determined to be 1640±33, 679±24 and 408±29 mg/L, and their ferulic acid contents were determined to be 1786±28, 800±30, and 444±28 mg/L, respectively.     

Degradation of aflatoxin B1 by fungal laccase enzymes

The enzymatic degradation of aflatoxin B₁ (AFB₁) by white rot fungi through laccase production was investigated in different liquid media. A significant (P < 0.0001) correlation was observed between laccase activity and AFB₁ degradation exhibited by representatives of Peniophora and Pleurotus ostreatus cultivated in minimal salts (MSM) (r = 0.93) and mineral salts — malt extract (MSB–MEB) (r = 0.77) liquid media. Peniophora sp. SCC0152 cultured in MSB–MEB liquid medium supplemented with veratryl alcohol and sugarcane bagasse showed high laccase activity (496 U/L), as well as 40.45% AFB₁ degradation as monitored using high performance liquid chromatography. P. ostreatus St2-3 cultivated in MSM liquid medium supplemented with veratryl alcohol resulted in laccase activity of 416.39 U/L and 35.90% degradation of AFB₁. Aflatoxin B₁ was significantly (P < 0.0001) degraded when treated with pure laccase enzyme from Trametes versicolor (1 U/ml, 87.34%) and recombinant laccase produced by Aspergillus niger D15-Lcc2#3 (118 U/L, 55%). Aflatoxin B₁ degradation by laccase enzyme from T. versicolor and recombinant laccase enzyme produced by A. niger D15-Lcc2#3 coincided with significant (P < 0.001) loss of mutagenicity of AFB₁, as evaluated in the Salmonella typhimurium mutagenicity assay. The degradation of AFB₁ by white rot fungi could be an important bio-control measure to reduce the level of this mycotoxin in food commodities.     

Fed‐batch l‐(+)‐lactic acid fermentation of brewer's spent grain hydrolysate

Brewer's spent grain (BSG) hydrolysates were used for l ‐(+)‐lactic acid (LA) fermentation by Lactobacillus rhamnosus ATCC 7469. The aim of this study was to evaluate fed‐batch LA fermentation of BSG hydrolysate with the addition of glucose, glucose and yeast extract, and wort during LA fermentation and its effect on fermentation parameters such as LA concentration, its volumetric productivity and yield, and L. rhamnosus cell viability. The highest LA yield, volumetric productivity and concentration of 93.3%, 2.0 g/L/h, and 116.1 g/L, respectively, were achieved with glucose and yeast extract addition during fermentation. In fed‐batch fermentation with glucose and yeast extract addition significantly higher LA concentration, yield and volumetric productivity (by 194.8; 2.2, and 20.7%, respectively) were achieved compared with batch fermentation. The results indicated that fed‐batch fermentation could be used to increase LA fermentation efficiency. Copyright © 2017 The Institute of Brewing & Distilling     

Use of spent brewer's yeast in L‐(+) lactic acid fermentation

The application of by‐products from the brewing industry in lactic acid (LA) production was investigated in order to replace expensive nitrogen sources (such as yeast extract) with cheaper and renewable nitrogenous materials such as brewer's yeast (BY). In this study, brewer's spent grain (BSG) hydrolysate was used for L‐(+)‐LA fermentation by Lactobacillus rhamnosus ATCC 7469. The effect of pH control during the fermentation and the addition of various BY contents (5–50 g/L) in BSG hydrolysate on fermentation parameters was evaluated. BY addition significantly increased free amino nitrogen (FAN) concentration (by 25.2% at 5 g/L to 616% at 50 g/L). A strong positive correlation between FAN concentration in the hydrolysate and concentration of L‐(+)‐LA produced was observed (correlation coefficient of 0.913). A high cell viability of L. rhamnosus ATCC 7469 (1.95–3.32 × 10⁹ CFU/mL at the end of fermentation) was achieved in all fermentations with the addition of brewer's yeast. The addition of BY increased L‐(+)‐lactic acid yield and volumetric productivity up to 8.4% (5 g/L) and 48.3% (50 g/L). The highest L‐(+)‐LA yield (89%) and volumetric productivity (0.89 g/L h^?1) were achieved in fermentation of BSG hydrolysate with 50 g/L of BY. © 2019 The Institute of Brewing & Distilling     

Lactic acid fermentation of brewer's spent grain hydrolysate by Lactobacillus rhamnosus with yeast extract addition and pH control

Lactic acid (LA) is a versatile chemical with a wide range of applications in food, pharmaceutical, cosmetic, textile and polymer industries. Brewer's spent grain (BSG) is the most abundant brewing by‐product. In this study BSG hydrolysates were used for LA fermentation by Lactobacillus rhamnosus ATCC 7469. The aim of this study was to evaluate the effects of pH control during fermentation, reducing sugar content and yeast extract content in BSG hydrolysate on LA fermentation parameters. The pH control greatly increased reducing sugar utilization, l ‐(+)‐LA content, yield and volumetric productivity. The highest l ‐(+)‐LA yield and volumetric productivity were achieved with the reducing sugar content of 54 g/L. Yeast extract addition significantly increased reducing sugar utilization, l ‐(+)‐LA content, L. rhamnosus cell viability, l ‐(+)‐LA yield and volumetric productivity. The highest l ‐(+)‐LA content (39.38 g/L), L. rhamnosus cell viability (9.67 log CFU/mL), l ‐(+)‐LA yield (91.29%) and volumetric productivity (1.69 g/L/h) were achieved with the reducing sugar content of 54 g/L and yeast extract content of 50 g/L. Copyright © 2017 The Institute of Brewing & Distilling     

Application of ultrafiltration in the study of phenolic isolates and melanoidins from pale and black brewers' spent grain

Two types of brewers' spent grain (BSG), pale and black, were studied employing ultrafiltration (UF cut‐off, 10 kDa) to obtain high‐molecular‐weight (HMW) and low‐molecular‐weight (LMW) phenolic fractions from one pale (P2) and one black (B2) BSG extracts. Of the four UF fractions obtained, the HMW B2 fraction had highest level of polyphenols (5.73 ± 0.25 mg GAE g^?1 BSG dw) and protein (18.82 ± 0.41 mg protein g^?1 BSG dw). Metal‐chelating ability and antioxidative properties were also identified. Antioxidant activity evaluated using the DPPH and FRAP assays, indicated that activity in B2 extracts was associated mainly with the HMW fraction (3.10 ± 0.10 and 2.49 ± 0.09 TE g^?1 BSG dw, respectively), whereas in P2 samples, antioxidant activity was highest in LMW fractions (0.58 ± 0.01 and 0.92 ± 0.03 TE g^?1 BSG dw, respectively). The high antioxidant activity and metal‐chelating ability observed for black BSG extracts may be attributed to the presence of coloured melanoidinic structures.     

Improving Bioethanol Yield: The Use of Solid‐State Fermentation Products Grown on DDGS

In a climate of uncertain prices for grain and fuel, conservation and efficiency are more important than ever. Many agro‐industrial residues are excellent substrates for solid‐state fermentation (SSF). Dried distillers grains with solubles (DDGS) are an important co‐product of the ethanol industry and have potential as a substrate for solid‐state fermentation. SSF products were produced using DDGS from a distillery and DDGS from a fuel ethanol plant as the fungal growth substrate. The spent grains were inoculated with GRAS (Generally Regarded As Safe) organisms Aspergillus orzyae and Rhizopus oligosporus. After growth, the resultant SSF product was dried and used as an enzyme complex supplement that was added to laboratory scale standard fuel ethanol corn mash fermentations. Improved ethanol yields were consistently observed. The use of solid‐state fermentation to produce unique enzyme complexes on DDGS offers a novel way to increase the value of the DDGS and to enhance bioethanol fermentation.     

Simulated gastrointestinal digestion and in vitro colonic fermentation of date (Phoenix dactylifera L.) seed polyphenols

Date seeds are a by‐product of date fruit industry and a rich source of polyphenols. In this study, in vitro bioaccessibility and colonic fermentation of major polyphenols from date seed powder (DSP) and DSP‐fortified yoghurt (DSPY) were investigated using HPLC. Catechin, epicatechin and procyanidin A2, B1 and B2 were stable during simulated gastric and sequential intestinal digestion. Bioaccessibility was significantly (P < 0.05) higher for all compounds from DSPY compared with DSP. After in vitro colonic fermentation of insoluble digestion materials, most of the target compounds were metabolised by faecal bacteria to ferulic acid, 3‐hydroxyphenylacetic acid, 3‐phenylpropionic acid and 3‐(4‐hydroxyphenyl) propionic acid. DSPY contained significantly (P < 0.05) higher level of free polyphenols as indicated by higher bioaccessibility; however, the stability of the polyphenols and their fermentation products from DSPY were similar to that of DSP alone. These data would be useful in product developments incorporating DSP as a source of polyphenols in food products.     

Improvement of flavour compound synthesis in a mixed culture system at high temperature by solid‐state fermentation

In order to enhance the synthesis of flavour compounds in solid‐state fermentation (SSF) at a high temperature, Bacillus subtilis XJ‐013 and Saccharomyces cerevisiae Z‐06 were used as a mixed culture with Monascus HQ‐3. The culture temperature was enhanced from 37°C to 56°C by the synergetic effect, and the synthesis of esterase was enhanced from 85.43 U/g to 129.65 U/g in the mixed culture system (over 50% higher than that of the culture using a single strain). This resulted in the synthesis of favourable flavour compounds in the solid‐state fermentation. These results signified that a mixed culture of Monascus and S. cerevisiae was favourable for enzyme production. The mixed culture of Monascus and B. subtilis resulted in a high culture temperature that promoted flavour compound synthesis in the solid‐state fermentation system dramatically. These results present a model to explain the synergetic effects between the fungus and the Bacillus in the solid‐state fermentation. Copyright © 2015 The Institute of Brewing & Distilling     

A comparison of three amperometric phenoloxidase–Sonogel–Carbon based biosensors for determination of polyphenols in beers

Three phenoloxidases based biosensors were successfully developed using as electrochemical transducer a new type of electrode recently developed by our group: the “Sonogel–Carbon electrode”. The employed enzymes were Trametes versicolor laccase (Lac), Mushroom tyrosinase (Tyr), and Horseradish peroxidase (HRP). Immobilization step was accomplished by doping the electrode surface with a mixture of the individual enzyme and Nafion ion exchanger as additive-protective. The biosensor responses, optimized in beer real samples, were evaluated for five individual polyphenols. It was found that the developed biosensors were sensitive to nanomolar concentrations of the tested polyphenols. As example, the limit of detection, sensitivity, and response linear range for caffeic acid for Nafion-Lac/Sonogel–Carbon biosensor were 0.06 μmol L⁻¹, 99.6 nA μmol⁻¹ L, and 0.04–2 μmol L⁻¹, respectively. The stability and reproducibility of the biosensors were evaluated by applying them directly to beer real samples. It has been demonstrated that the Nafion-Lac/Sonogel–Carbon system is the more stable with a relative standard deviation of 3.3% (n = 10), maintaining 84% of its stable response for at least three weeks. Estimation of polyphenol index in eight lager beers and a comparison of the results with those obtained by a classical method was carried out.     

Isolation of peptides from a novel brewers spent grain protein isolate with potential to modulate glycaemic response

The in vitro dipeptidyl peptidase‐IV (DPP‐IV) inhibitory activity of a Brewers’ spent grain protein‐enriched isolate (BSG‐PI) Alcalase? hydrolysate (AlcH), which had previously been identified as a relatively potent angiotensin‐converting enzyme (ACE) inhibitor, was determined. The half maximal DPP‐IV inhibitory concentration (IC₅₀) value of AlcH following 240‐min digestion was 3.57 ± 0.19 mg mL^?1. Ultrafiltration fractionation did not significantly increase the DPP‐IV inhibitory activity of the AlcH fractions. Subjection of AlcH to simulated gastrointestinal digestion (SGID), which yielded SAlcH, resulted in a significant increase in DPP‐IV inhibitory activity (P < 0.05), particularly after the intestinal phase of digestion. Following semi‐preparative reverse phase high performance liquid chromatography (RP‐HPLC) fractionation of SAlcH, fraction 28 was identified as having highest mean DPP‐IV inhibitory activity. Two novel DPP‐IV inhibitory peptides, ILDL and ILLPGAQDGL, with IC₅₀ values of 1121.1 and 145.5 μm , respectively, were identified within fraction 28 of SAlcH following ultra‐performance liquid chromatography (UPLC)‐tandem mass spectrometry (MS/MS). BSG protein‐derived peptides were confirmed as having dual ACE and DPP‐IV inhibitory activities.     

Fungal Isolates from a Pu‐Erh Type Tea Fermentation and Their Ability to Convert Tea Polyphenols to Theabrownins

The natural microbiota involved in the fermentation influence the quality and taste of fully postfermented teas such as China's Pu‐erh tea. Ten microbial isolates representing 6 species were recovered from a solid‐state fermentation of a Pu‐erh type tea. The isolates were Aspergillus tubingensis, Aspergillus marvanovae, Rhizomucor pusillus, Rhizomucor tauricus, Aspergillus fumigatus, and Candida mogii. With the exception of A. marvanovae and C. mogii, all these microorganisms have been previously reported in solid‐state fermentations of native Pu‐erh tea. The ability of the isolates for converting the tea polyphenols to bioactive theabrownins in infusions of sun‐dried green tea leaves in a submerged fermentation process was subsequently investigated. All isolates except C. mogii TISTR 5938 effectively produced theabrownins in a 4‐d fermentation in shake flasks at 40 °C, 250 rpm. A. tubingensis TISTR 3646, A. tubingensis TISTR 3647, A. marvanovae TISTR 3648, and A. fumigatus TISTR 3654 produced theabrownins at particularly high levels of 6.5, 12.4, 11.1, and 8.4 g/L, respectively.     

Bioconversion of agro‐industrial by‐products to lactic acid using Lactobacillus sakei and two Pediococcus spp. strains

The aim of this study was to evaluate the bioconversion efficiency of rich in cellulose agro‐industrial by‐products such as wheat bran (WB), spent distiller's grain with solids (DGS), brewer's spent grain (BSG) and lupin (Lupinus angustifolius L.) wholemeal fraction (LF) to lactic acid (LA) using acid tolerant lactic acid bacteria (LAB) strains Lactobacillus sakei KTU05‐06, Pediococcus acidilactici KTU05‐7 and P. pentosaceus KTU05‐9. Carbohydrase preparation Depol^? 692L was used for the hydrolysis of non‐starch polysaccharides. Analysed raw materials were suitable substrates for LAB propagation and L‐lactic acid production. The lowest pH (3.6) was found in LF medium after 48 h fermentation with P. acidilactici and P. pentosaceus strains. The lowest pH (3.86) was measured in WB fermented with L. sakei, and in DGS and BSG (pH 3.8 and 3.9 respectively) fermented with P. acidilactici. The highest endoxylanase activity was excreted by the P. acidilactici and P. pentosaceus (84 and 69 XU g^?1 respectively), and the highest α‐amylase activity was of L. sakei (255.6 AU g^?1) after 24 h incubation in WB medium. The L‐lactic acid concentration of 86.11 g kg^?1 was reached after the bioconversion of hydrolysed WB in combination with 48 h fermentation by P. pentosaceus KTU05‐9 strain. LA contents between 222 and 282 mg kg^?1 was produced from lupin processing residues via fermentation using P. acidilactici and P. pentosaceus KTU05‐9 strains. The major challenge within the presented study is the viability of tested LAB in cereal waste media and effective LA production at a low pH (3.6–3.8).     

Statistical optimization,partial purification,and characterization of coffee pulp β-glucosidase and its application in ethanol production

Extracellular β-glucosidase was produced using coffee pulp as a sole carbon source by Penicillium verrucosum by solid state fermentation and 897.36±59 U/g enzyme activity was obtained. Increase in 2.21-fold of enzyme activity on optimizing the bioprocess parameters by response surface methodology based on central composite rotatable design is illustrated. Maximum production level of 1,991.17 U/g was obtained with optimum values of pH 4.2, moisture 66.8%, and fermentation duration of 56 h. The enzyme was partially purified and the enzyme activity was optimum at 50°C temperature and at pH 6. The metal ions such as Mg²⁺, Zn²⁺, Ca²⁺, K⁺, detergents, and chelator such as EDTA were effective and further increased the β-glucosidase activity. On application of β-glucosidase for simultaneous saccharifiation and fermentation, 3.3% ethanol was obtained. Thus, this study provides insight on exploitation of P. verrucosum for synthesis of of β-glucosidase using coffee pulp which is available abundantly in coffee processing industries.

     

Influence of aeration and agitation modes on solid‐state fermentation of apple pomace waste by Phanerochaete chrysosporium to produce ligninolytic enzymes and co‐extract polyphenols

The effect of different types of agitation (i) continuous agitation (C); (ii) continuous, discontinuous, continuous agitation (C/D/C); (iii) discontinuous, continuous, discontinuous agitation (D/C/D) and aeration (0.87, 1.25, 1.66 vvm) on ligninolytic enzyme production and polyphenolic compounds extraction by solid‐state cultures of Phanerochaete chrysosporium BKM‐F‐1767 was investigated. Higher production of manganese peroxidase (MnP) (1690.3 ± 87.6), lignin peroxidase (LiP) (387.9 ± 14.3) and laccase (898.9 ± 53.3 U gds^?1) and liberation of total polyphenolics (ranging from 12.22 ± 1.1 to 30.12 ± 0.88 mg gallic acid equivalents per gram DW) was obtained after 195, 147, 219 and 204 h of fermentation, respectively, using 1.66 vvm as airflow and (C/D/C) agitation mode. Maximal enzyme production and total polyphenolic content were influenced by aeration, and higher values were obtained using 1.66 vvm as airflow rate, followed by 1.25 and 0.83 vvm, respectively. They were also influenced by agitation, and maximal values were obtained using C/D/C, followed by D/C/D and continuous agitation, respectively. The agitation modes influenced the production of ligninolytic enzymes and simultaneous extraction of polyphenols.     

Changes in volatile compound composition of Antrodia camphorata during solid state fermentation

BACKGROUND: Although the volatiles present in mushrooms and fungi have been investigated by many researchers, including Antrodia camphorata in submerged fermentation, there are few data available regarding changes in volatile compounds during fermentation. Our research has revealed that solid state fermentation of A. camphorata is highly odiferous compared with submerged cultures and the odor changed with increasing culture time. Therefore the aim of this study was to investigate the changes in volatile compound composition of A. camphorata during solid state fermentation. RESULTS: Altogether, 124 major volatile compounds were identified. The volatile compounds produced by A. camphorata during growth in solid state fermentation were quite different. Oct‐1‐en‐3‐ol, octan‐3‐one and methyl 2‐phenylacetate were predominant in exponential growth phase production, while the dominant volatiles produced in stationary phase were octan‐3‐one and methyl 2‐phenylacetate. In stationary phase, lactone compounds in A. camphorata, such as 5‐butyloxolan‐2‐one, 5‐heptyloxolan‐2‐one, 6‐heptyloxan‐2‐one, contributed greatly to peach and fruit‐like flavor. Terpene and terpene alcohol compounds, such as 1‐terpineol, L ‐linalool, T‐cadinol, (E, E)‐farnesol, β‐elemene, cis‐α‐bisabolene and α‐muurolene, made different contributions to herbal fresh aroma in A. camphorata. Nineteen volatile sesquiterpenes were detected from solid state fermentation of A. camphorata. The compounds 5‐n‐butyl‐5H‐furan‐2‐one, β‐ionone, (?)‐caryophyllene oxide, aromadendrene oxide, diepi‐α‐cedrene epoxide, β‐elemene, α‐selinene, α‐muurolene, azulene, germacrene D, γ‐cadinene and 2‐methylpyrazine have not hitherto been reported in A. camphorata. CONCLUSION: The preliminary results suggest that the aroma‐active compounds produced by A camphorata in solid state fermentation might serve as an important source of natural aroma compounds for the food and cosmetic industries or antibiotic activity compounds. The sesquiterpenes could be identified as possible taxonomic markers for A. camphorata. Copyright © 2011 Society of Chemical Industry     

Brewers' spent grain and thin stillage as raw materials in l‐(+)‐lactic acid fermentation

Brewer's spent grain (BSG) hydrolysates were used for l ‐(+)‐lactic acid (LA) fermentation by Lactobacillus rhamnosus ATCC 7469. In this study the effect of the addition of various amounts of thin stillage (TS) in BSG hydrolysate on LA fermentation parameters were evaluated. TS addition significantly increased utilization of glucose by up to 43.0%. In batch fermentation the highest LA concentration and volumetric productivity of 31.0 g/L, and 0.93 g/L/h, respectively, were obtained with the addition of 50% TS. L. rhamnosus cell viability also increased with the addition of 50% TS (by 2.4%). TS addition significantly increased free amino nitrogen concentration (by up to 209%) which is important for bacterial growth. A strong positive correlation between free amino nitrogen and LA concentration was noted. Compared with the results obtained in the batch fermentation (50% TS), significantly higher LA concentration, yield and volumetric productivity (54.8, 1.9 and 4.0%, respectively) were achieved in fed‐batch fermentation with glucose and TS addition. The results suggest that the combination of the by‐products of brewing and bioethanol industries could be suitable for LA production. Copyright © 2017 The Institute of Brewing & Distilling     

Acid hydrolysis and fermentation of brewer's spent grain to produce xylitol

The hemicellulosic fraction of brewer's spent grain (BSG) was hydrolysed with diluted acid under different conditions of liquid/solid ratio (8–12 g g⁻¹), sulfuric acid concentration (100–140 mg g⁻¹ dry matter) and reaction time (17–37 min) in order to produce a liquor with a large amount of xylose and good fermentability to produce xylitol. Results showed that all the evaluated reaction conditions were able to hydrolyse xylan and arabinan with efficiencies higher than 85.8 and 95.7% respectively, and even under the mildest reaction condition a considerable amount (92.7%) of the hemicellulosic fraction could be extracted. The hydrolysates presented different fermentabilities when used as fermentation media for xylitol production by Candida guilliermondii yeast, owing to the differences in their composition. Based on statistical analysis, the best condition for BSG acid hydrolysis was the use of a liquid/solid ratio of 8 g g⁻¹, 100 mg H₂SO₄ g⁻¹ dry matter and a reaction time of 17 min. Under this condition a high extraction efficiency of hemicellulosic sugars (92.7%) and good fermentation results (Y_P/S = 0.70 g g⁻¹ and Q_P = 0.45 g dm⁻³ h⁻¹) were attained. Copyright © 2005 Society of Chemical Industry     

Purification and characterisation of an acid protease from the Aspergillus hennebergii HX08 and its potential in traditional fermentation

A protease AP3 from Aspergillus hennebergii HX08 was purified by ammonium‐sulphate precipitation, followed by anion‐exchange chromatography and gel filtration. The molecular weight of acid protease AP3 was 33 kDa (SDS‐PAGE and MALDI‐TOF‐MS). The protease AP3 was identified as an acid protease with MALDI‐TOF/TOF tandem MS. Its optimal temperature and pH were 60°C and 4.0, respectively. Its K _max and V _max were 57.92 mg/mL and 32.57 U/mL, respectively. The enzyme was active over a broad pH and temperature range (pH 3.0–5.0 and 30–60°C), and exhibited high activity and stability in 2–12% (v /v) ethanol solvent. Subsequent studies suggest that the enzyme presents a relatively high substrate affinity to wheat protein (98% of total activity). Its application to solid‐state fermentation of wheat flour with Saccharomyces cerevisiae could increase the hydrolysis degree of wheat protein (28.26%) and amino acid nitrogen concentration of fermented grains (34.21%). Additionally, enhanced S. cerevisiae biomass (37.09%) and alcohol concentration (38.29%) were also observed during the process. Volatile compounds analysis of fermented grains by headspace solid‐phase micro‐extraction and GC‐MS revealed more flavour compounds. These results suggest its potential in food and alcohol industries. Copyright © 2017 The Institute of Brewing & Distilling     

The Effect of Proanthocyanidins on Growth and Alcoholic Fermentation of Wine Yeast under Copper Stress

Proanthocyanidins (PAs) derived from the grape skin, as well as from grape seeds, grape stems, are an important group of polyphenols in wine. The aim of this study was to understand the effect of PAs (0.1, 1.0 g/L) on growth and alcoholic fermentation of 2 strains of Saccharomyces cerevisiae (commercial strain FREDDO and newly selected strain BH8) during copper‐stress fermentation, using a simple model fermentation system. Our results showed that both PAs and Cu²⁺ could pose significant inhibition effects on the growth of yeast cells, CO₂ release, sugar consumption, and ethanol production during the initial phase of the fermentation. Compared to PAs, Cu²⁺ performed more obvious inhibition on the yeast growth and fermentation. However, adding 1.0 g/L PAs increased in the vitality and metabolism activity of yeast cells at the mid‐exponential phase of fermentation in the mediums with no copper and 0.1 mM Cu²⁺ added, shortened the period of wine fermentation, and decreased the copper residues. It indicated that PAs could improve the ability of wine yeast to resist detrimental effects under copper‐stress fermentation condition, maintaining cells metabolic activity, and fermentation could be controlled by manipulating PAs supplementation.