啤酒生产过程中氧化还原酶系的研究

啤酒生产过程中的氧化还原酶与啤酒风味陈化紧密相关。低水分下，其耐温活性远高于其它几种酶，在麦芽中酶活升高比例最大（与大麦中的酶活相比），其在糖化过程中氧化多酚的能力远大于多酚氧化酶。糖化过程中迅速失活，而脂肪酸氧化酶在糖化起始的低温阶段仍有部分酶活，影响不饱和脂肪酸的氧化。焙燥过程中适当延长50～70℃温度段时间，可有效降低麦芽中氧化还原酶的酶活。结合这些酶的性质，从部分抑制它们的活性角度出发，在糖化过程中，于50～60℃进行隔氧处理，可经济、有效的减少影响风味氧化的前驱物质的含量。同一质量等级不同品种的麦芽的氧化还原酶系差别相当大，相应制得的麦汁中与风味氧化有关的物质含量也有较大差别，这可能是造成不同批次原料酿造的成品啤酒风味保鲜期不稳定的原因之一。     

Changes in the Concentrations of the Polyphenolic Constituents of Sorghum during Malting and Mashing

Sorghum varieties differed widely in their content of polyphenolic compounds. The concentrations of all phenolic compounds increased several-fold during malting and the degree of increase differed with variety. The concentration of polyphenols extracted in wort was dependent, to a great extent, on the temperature of mashing.     

Online Monitoring of Gravity,FAN and β‐Glucan during Mashing

The paper presents a measurement system that is based on an array of non‐specific sensors and the installation of both in a pilot and in an industrial mash tun. Three calibration strategies were pursued to predict gravity, FAN and β‐glucan during mashing in combination with three different multivariate calibrations (PCR, CPCR, PLS). The over all best calibration had RMSPEs of 0.78%, 1.56 mg/100 mL and 181.73 mg/L for gravity, FAN and β‐glucan, respectively. The measurement system makes it possible to monitor online the three major sub‐processes of mashing (amylolysis, proteolysis, and cytolysis), which is the precondition for a situational control of the mashing process.     

The Formation and Hydrolysis of Barley Malt Gel‐Protein Under Different Mashing Conditions

The effect of oxidation and proteolysis on the amount of gel‐protein aggregate was investigated both in vivo during mashing and in vitro. The oxidation of the free thiol groups of proteins to disulphide bridges during mashing appeared to be a good indicator of the formation of gel‐protein aggregate. The pH optimum of the oxidation varied according to the isothermal mashing temperature. The results suggested that the oxidation of the thiol groups maybe a result of some kind of enzymatic activity. In vitro experiments showed that the proteolysis of the gel‐protein aggregate was strongest at pH 5.0 and temperature denaturation occurred only at temperatures over 80°C. Mashing experiments on the other hand suggested that the proteolysis of the monomer subunits of gel‐protein (i.e. B‐ and D‐hordein) had a stronger effect on the final amount of the gel‐protein aggregate than the hydrolysis of the aggregate.     

The Evolution of Dextrins During the Mashing and Fermentation of All‐malt Whisky Production

The production of malt whisky involves the mashing of barley malt, followed by the fermentation of the resulting wort without further treatment. While this process has many parallels to the production of an all‐malt beer, one of the main differentiating steps during substrate preparation is the inclusion of a boiling step for the wort in the production of beer. Other than the destructive action of the boiling process on microorganisms, the boiling also destroys all malt enzyme activity. Since a typical whisky wash is not boiled it carries through a certain proportion of microbial activity associated with the malt, but more importantly it retains some enzyme activity that has been activated during the malting and mashing processes. The changes in sugars and dextrins during both mashing and fermentation of the resulting wash were investigated. Evidence of the continuous amylolytic activity during an unboiled, all‐malt wash fermentation is shown; while no ongoing amylolytic activity could be deduced during the fermentation of a boiled all‐malt wort. Furthermore, the data suggests that the amylolytic activity during mashing and fermentation are different with regards to α‐amylase action linked to its multiple‐attack action pattern as a function of substrate conformation, temperature, and effectiveness of potential hydrolytic events.     

Effects of Mashing Parameters on Mash β‐Glucan,FAN and Soluble Extract Levels

To gain further technological knowledge of mashing, pilot scale mashing trials were carried out varying mashing programme (upward/isothermal mashing), milling procedure, grist:liquor ratio, time of mash stands, and grist modification level (well and poorly modified malt). During mashing β‐glucan, free amino nitrogen (FAN) and extract contents were analysed as key indicators for cytolysis, proteolysis, and amylolysis, respectively. The malt modification was of major impact for the β‐glucan release in contrast to a variation of milling procedure and of grist:liquor ratio. Extended stands lead to increased final values only for poorly modified malt. Similarly, FAN release was predetermined by malt modification while variation of milling and of grist:liquor ratio was not relevant in contrast to stand extension. None of the variations applied influenced extract yield as long as gelatinization temperature was reached. Greatest gains occurred around 57°C. In conclusion, wort quality is critically determined by malt modification. Mashing with well modified malt in combination with short stands should result in a mash of low β‐glucan and sufficient FAN level without losing extract yield. However, for poorly modified malt the variation of mashing parameters has an impact on the key indicators in which cytolysis plays the dominating role.     

Optimisation of the Mashing Procedure for 100% Malted Proso Millet (Panicum miliaceum L.) as a Raw Material for Gluten‐free Beverages and Beers

Proso millet is a gluten‐free cereal and is therefore considered a suitable raw material for the manufacturing of foods and beverages for people suffering from celiac disease. The objective of this study was to develop an optimal mashing procedure for 100% proso millet malt with a specific emphasis on high amylolytic activity. Therefore, the influence of temperature and pH on the amylolytic enzyme activity during mashing was investigated. Size exclusion chromatography was used to extract different amylolytic enzyme fractions from proso millet malt. These enzymes were added into a pH‐adjusted, cold water extract of proso millet malt and an isothermal mashing procedure was applied. The temperatures and pH optima for amylolytic enzyme activities were determined. The α‐amylase enzyme showed highest activity at a temperature of 60°C and at pH 5.0, whereas the β‐amylase activity was optimum at 40°C and pH 5.3. The limit dextrinase enzyme reached maximum activity at 50°C and pH 5.3. In the subsequent mashing regimen, the mash was separated and 40% was held for 10 min at 68°C to achieve gelatinisation. The next step in the mashing procedure was the mixture of the part mashes. The combined mash was then subjected to an infusion mashing regimen, taking the temperature optima of the various amylolytic enzymes into account. It was possible to obtain full saccharification of the wort with this mashing regimen. The analytical data obtained with the optimised proso millet mash were comparable to barley wort, which served as a control.     

氧气对茶多酚化学氧化合成茶黄素的影响

研究了O2对茶多酚化学氧化(碱性氧化和酸性氧化)形成茶黄素类物质的影响。结果表明:在接近真空、露置空气和通氧等3种不同O2含量的条件下,茶多酚碱性氧化和酸性氧化均可得到茶黄素类物质,其含量随着2种反应体系中O2含量的增加而增加,且化学氧化中儿茶素消耗的主体是EGCG、EGC、C、EC,说明O2是茶多酚化学氧化形成茶黄素的一个重要影响因素,而相关研究报道却极少涉及到关于O2在茶多酚化学氧化合成茶黄素过程所发挥的作用;另外,比较茶多酚碱性氧化法和酸性氧化法形成茶黄素的情况,前者比后者得到更多茶黄素类物质。文中还考察了O2对茶黄素化学氧化形成的影响。     

Studies on the mashing conditions of teff (Eragrostis tef) malt as a raw material for lactic acid‐fermented gluten‐free beverage

Formation of extracts and fermentable sugars during mashing can be limited by incomplete starch gelatinisation. The aim of this research was to develop mashing programme for 100% teff malt as a potential raw material for gluten‐free lactic acid‐fermented beverage. Isothermal mashing at temperatures ranging between 60 and 84 °C was conducted, and the highest extract (85%) was observed for the wort samples produced at temperatures higher than 76 °C. Sixty‐minute rest at 71 °C resulted in higher fermentable sugars than other tested conversion rest temperatures. Inclusion of lower mashing‐in temperature in the mashing programme also substantially improved the concentrations of free amino nitrogen (128 mg L^?1) and fermentable sugar (58 g L^?1) in the final wort. Therefore, 30‐min rest at 40 °C followed by 60‐min rest at 71 °C and 10‐min rest at 78 °C was found to be a suitable mashing programme for teff malt.     

中性亚硫酸盐苇浆氧脱木素的研究

对中性亚硫酸盐(NS)苇浆的氧脱木素(O)工艺及用H2O2强化的氧脱木素(OP)工艺进行了研究。NS苇浆适宜的氧脱木素条件为：NaOH用量4％。氧压0.6MPa。MgSO4用量0．05％，温度100℃。时间60min。浆浓12％。以此条件对NS苇浆进行氧脱木素，可以使浆白度从50.2％ISO提高到62．3％ISO。卡伯值从17.1降低到10.5。粘度从1144mL／g降低到1123mL／g。另外，H2O2对NS苇浆的氧脱木素具有促进作用，经H202强化的氧脱木素工艺(H20：用量1．0％)可使纸浆卡伯值降低率在常规氧脱木素基础上又降低5．8个百分点，浆的白度达69．7％ISO，卡伯值9.5，粘度1111mL／g。     

Functional Properties as Affected by Laboratory‐Scale Parboiling of Rough Rice and Brown Rice

ABSTRACT: Rough rice (RR) is the conventional feedstock for parboiling. The use of brown rice (BR) instead of RR is gaining interest because it results in shorter processing time and lower energy requirement. This study compared the functional properties of milled parboiled rice under different parboiling conditions from RR and BR. Presoaked RR and BR from cultivars Bolivar, Cheniere, Dixiebelle, and Wells were parboiled under mild (20 min, 100 °C, 0 kPa) and severe (20 min, 120 °C, 98 kPa) laboratory‐scale conditions. Head rice yield improved on the RR and BR samples subjected to severe parboiling and was comparable to that of a commercially parboiled sample. Mild parboiling of BR resulted in lower head rice yields. Parboiling generally resulted in decreased head rice whiteness, decreased apparent amylose, increased total lipid, and sparingly changed protein content. Under the same parboiling conditions, the extent of starch gelatinization was higher for BR compared to RR as manifested by some distinct differences in pasting and thermal properties. The cooking characteristics (water uptake ratio, leached materials, and volumetric expansion) and cooked rice texture (hardness and stickiness) of RR and BR subjected to severe parboiling were fairly comparable. Differences in parboiled rice functional properties due to cultivar effect were evident.     

Modeling of the Temperature Effect on Oxygen Absorption by Iron‐Based Oxygen Scavengers

A new engineering‐oriented model for prediction of the effect of temperature on the kinetics of oxygen absorption by iron‐based oxygen scavengers (IOSs) was developed. The model is based on the physicochemical mechanism of the O₂ scavenging process by the active component of the IOS (iron powder). The conclusions of this study are: (1) the iron deposits formed on the iron particles are composed of 2 different layers: an inner layer of Fe₃O₄ and an outer layer of FeOOH that vanishes with the depletion of oxygen. (2) The model considers the chemical processes in the heterogeneous closed system “Fe–H₂O–NaCl–O₂” and describes the kinetics of oxygen absorption by the powder, depending on the characteristics of the system. (3) The nonlinear ordinary differential equation (ODE) of the O₂ absorption kinetics was derived and a simple approximate solution to this ODE was obtained theoretically that is similar to the empirical exponential formula published in the relevant literature. (4) The temperature dependence of the oxygen absorption rate is more complicated than that described by the Arrhenius equation.     

Effect of Mashing Temperatures and Endo-β-Glucanase on β-Glucan Content of Malt Worts

Similar basal levels of β-D-glucans were released into worts produced at 45°C from enzymically active or inactivated flours of milled malts. In contrast, significantly higher levels of β-D-glucans were found in worts derived from either enzymically active or inactivated malt flours mashed at 65°C. In general, mashing temperature may play a more important role in releasing β-D-glucans during mashing than enzymes described as β-glucan-releasing. In this context, the physical release of β-D-glucan during mashing should be separated from the enzymic release and degradation of β-D-glucan which occur during malting.     

An investigation of two xylan‐degrading enzymes and a novel xylanase inhibitor in malted barley

Two enzymes with activity on xylan and xylan‐based substrates were isolated from malted barley. One appears to be relatively anionic and the other more cationic. Both are endo‐acting enzymes. The first of these was studied in more detail and shown to be of molecular weight ca. 59,000 and capable of acting through the pH range 5–7.5. It is relatively heat tolerant, with 30% of its activity surviving for 30 min at 70 °C. A low‐molecular‐weight (ca. 1300) inhibitor of xylanase that developed during germination was investigated. Its potency was not lowered by treatment with proteolytic enzymes, but treatment with polyvinylpolypyrrolidone did reduce its impact. Ultraviolet spectrophotometry and Fourier transform infrared spectroscopy, as well as staining with Folin–Ciocalteu reagent, indicated the presence of phenolic species, while mass spectroscopy studies suggested the presence of arabinose and possibly poly‐hexose. The presence of material that stained with aniline phthalate would be consistent with the presence of reducing sugar in the inhibitor. Copyright © 2013 The Institute of Brewing & Distilling     

氧脱木素过程中非过程元素影响的研究

研究了用EDTA和CaSO4 作为螯合剂预处理马尾松硫酸盐浆前后非过程元素含量的变化 ,探讨了非过程元素在氧漂中对木素脱除率和纸浆粘度的影响 ,结果表明非过程元素对脱木素的选择性有很大影响 ,Ca元素的富集降低脱木素率的同时使纸浆粘度损失加大     

A Comparative Study on the Various In Vitro Assays of Active Oxygen Scavenging Activity in Foods

ABSTRACT: Various in vitro assays of active oxygen-scavenging activity in foods were compared by evaluating the activity of 13 food phenolic compounds and Trolox. 1,1-Diphenyl-2-picrylhydrazyl (DPPH)-HPLC and liposome oxidation methods were sensitive for these compounds, while deoxyribose oxidation and Randox kit methods were less sensitive. The deoxyguanosine oxidation method could not determine the activity since food polyphenols were pro-oxidative in this assay. Among these assays, the DPPH-HPLC method was shown to be the best since the liposome oxidation method is affected more by the structure of phenolic compounds than the DPPH-HPLC method.     

蔗渣氧碱浆的臭氧漂白研究

本研究对清洁的臭氧以及过氧化氢氧系漂白工艺的蔗渣氧碱浆漂白效果进行了探索与优化.结果表明,在浆浓40％、臭氧浓度为0.9 kg/(min·t)(以绝干浆计)、常温漂白10 min、复合酸用量1.5％、pH值2.5的条件下,可获得理想的臭氧漂白蔗渣氧碱浆.该浆在氧碱浆基础上,白度从58.6％提高到74.5％,增加15.9...     

抑制多酚氧化酶提高甘薯淀粉白度的研究

甘薯加工过程中容易产生褐变。不同的抑制剂能降低多酚氧化酶的活力,在甘薯破碎的同时加入抑制剂能提高淀粉的白度。