啤酒废酵母泥综合利用的研究

研究了利用啤酒废酵母泥制备酵母抽提物和β-葡聚糖的相关工艺条件。结果表明,自溶-酶联法是制备啤酒酵母抽提物的理想方法,用该法制备啤酒酵母抽提物的抽提率达68.6%、蛋白质利用率达87.3%,抽提物中蛋白质、游离氨基酸态氮和复合核苷酸的含量分别达10.6%、4.2%和3.9%,远高于普通自溶工艺的技术指标;将自溶后的酵母残渣进一步制备成β-1,3-葡聚糖,通过正交试验获得了其优化的工艺条件:酵母浓度10%、碱浓度2%、反应温度80℃、反应时间4 h、碱处理次数4次。在优化的工艺条件下,β-1,3-葡聚糖得率达26.8%、成品中杂蛋白含量仅0.4%、β-葡聚糖分子质量为158ku。实现了啤酒废酵母泥的综合利用和高值化。     

酵母自溶过程中的氨基酸溢出动力学

对不同自溶程度的干酵母细胞蛋白降解溢出的氨基酸摩尔组份(MF)进行了测定。结果表明,丙氨酸、赖氨酸和谷氨酸在自溶液中占有优势的MF值,高达41％。各种氨基酸的溢出速度变化与其分子结构特点,特别是R基的极性关系密切。氨基酸的溢出动力学方程基本可归纳为直线型、对数型和偏态钟型3组。在β—转角出现频率高和氨基酸种类的溢出初速度相对较大,含有非极性R基的氨基酸的溢出延滞期则相对较长。添加蛋白酶可促进在β—转角肽段中出现频率高的氨基酸的水解,增加鲜味和甜味氨基酸的MF值,减少苦味氨基酸的MF值,但有5种必需氨基酸的MF值也显著下降。浓缩处理使自溶液中的氨基酸含量减少,半胱氨酸和苏氨酸的MF值分别减少33％和25％。     

Effect of high pressure on the proteolytic activity and autolysis of yeast Saccharomyces cerevisiae

This work explores the effect of High Pressure (HP) treatment on the proteolytic activity and autolytic capacity of Saccharomyces cerevisiae suspensions, based on yeast extract production. Cellular suspensions were treated at 200–600 MPa for 0–120 min and the activity of vacuolar proteases was measured during autolysis. Moreover, the autolytic capacity of yeast was determined based on the physicochemical characteristics of the produced yeast extract. At pressures of 200 and 400 MPa, proteolytic activity was enhanced up to 160%, after 40 and 10 min of HP treatment, respectively, leading to significantly accelerated autolysis, in combination with cellular permeabilization achieved with HP treatment. However, at 600 MPa, despite the greater cell permeabilization, proteolytic enzymes were gradually inactivated (total inactivation after 15 min of HP treatment), leading to inhibition of autolysis. These results highlight HP as an effective process to enhance endogenous proteolytic activity and thus accelerate yeast extract production.     

THE RELATIONSHIP BETWEEN β-GLUCAN SOLUBILASE,BARLEY AUTOLYSIS AND MALTING POTENTIAL

There is a correlation between the autolysis of barleys and their β-glucan solubilase activities. There is no correlation between autolysis and nitrogen content, β-glucan level, Milling Energy or Zeleny sedimentation value of the barley. Activities of endo-β-glucanase are inversely related to coarse-grind Hot Water Extract obtained from malts grown for 4 days. Whilst β-glucanase is not involved in the early stages of autolysis, β-glucan solubilase, present in large amounts in untreated barley, has a role both in extracting and degrading β-glucan. Barleys with low β-glucan content or high β-glucan solubilase modify more rapidly.     

提高酵母抽提物得率的工艺条件

以啤酒废酵母为原料 ,研究了影响酵母抽提物得率的因素和提高酵母抽提物得率的方法。结果表明 ,机械破碎可缩短自溶时间 ,提高酵母抽提物氨基酸态氮含量和得率 ,且以高压均质法破碎效果为好 ;均质条件是 1 0 %酵母悬浮液于 3 5MPa二次均质。均质后在 5 5℃、pH5 5下自溶4h ,添加 0 8%木瓜蛋白酶 (以酵母干重计 )自溶 2 8h ,酵母抽提液中氨基酸态氮含量达 7 1 4g/L ,得率 69 47% ,风味醇厚 ,与以NaCl为自溶促进剂的酵母抽提液相比 ,氨基酸态氮含量增加42 97% ,得率净增 2 1 97%。     

Simultaneous treatment of heat and high pressure homogenization of zein in ethanol–water solution: Physical,structural, thermal and morphological characteristics

The effects of high pressure homogenization (HPH) and/or heat treatment on the physical, structural, thermal and morphological characteristics of zein in ethanol–water solution were investigated. The results showed that HPH significantly reduced the size of zein nanoparticles. Both of HPH and heat treatment resulted in the increase of ultraviolet absorption and fluorescence intensity, as well as the enhanced thermal stability of zein. Compared with the individual HPH and thermal treatment, the coupled treatment of heat and HPH induced more obvious changes on the secondary structure of zein with the α-helix content increasing from 49.2% to 67.1%. The morphology of zein was greatly modified from sphericity to oval, dumbbell-like and random geometrical shape after HPH at 125 MPa. The synergistic effect was found between thermal treatment and HPH at 75 MPa, which resulted in size reduction of zein nanoparticles with the spherical shape and uniform distribution.Industrial relevanceThermal treatment has been extensively applied to modify the physiochemical properties of water soluble proteins like β-lactoglobulin, lactoferrin and livetins. However, the available reports on the heat-induced structural and physicochemical changes of alcohol-soluble proteins are limited.Nowadays, the new insight into protein modification is to apply physical treatments such as high pressure homogenization (HPH). HPH has been applied to modify the physiochemical, functional and structural properties of water soluble proteins, including faba bean protein, whey proteins, peanut proteins and soy protein isolate. However, little information is available about the effect of HPH treatment on structural modifications of alcohol-soluble proteins. Besides, according to the previous literatures, the combined treatment of thermal with HPH is commonly employed to improve the stability of dairy products. Nevertheless, to our best knowledge, there is no report about the coupled treatment of thermal and HPH on the modification of ethanol-soluble protein.Results from present work can be used to confirm the hypothesis that the simultaneous treatment of thermal and HPH would be an attractive modification method for zein with better thermal behaviors and structural properties to develop new food grade materials, which could be useful in the development of the potential delivery systems for bioactive compounds.     

VARIATION IN THE BIOCHEMICAL COMPOSITION OF ACID EXTRACTS FROM BARLEYS OF CONTRASTING MALTING QUALITY

Acid extracts from barleys of poor malting quality were characterized by high viscosity caused by enhanced concentrations of high molecular weight carbohydrates of which more than 80 per cent was β-glucan. Up to 67 per cent of the β-glucan in these barleys was soluble in the acid extracting solution. In contrast, only about 25 per cent of the β-glucan in good malting barleys was soluble, resulting in extracts having low viscosity. No evidence was found for autolysis in any of the extracts, and extracts from good malting varieties were characterized by high concentrations of fructose and sucrose. Protein concentration in the extracts varied little, although the protein content of the barleys ranged from 9·1 per cent to 15·4 per cent. Soluble protein has no effect on extract viscosity or the gel filtration properties of the carbohydrates. Some quantitative variation in acid-soluble and salt-soluble proteins was seen after electrophoresis on polyacrylamide.     

自溶-酶联技术制备啤酒废酵母抽提物工艺及产物理化参数研究

为了提高啤酒酵母的利用率,利用啤酒废酵母资源,采用自溶与添加外源酶相结合的方法制备酵母抽提物.以氨基氮得率、总氮得率和固形物得率为主要指标考察了对酵母自溶影响关键的几个因素,包括自溶促进剂、自溶时间、酶解时间,并在此基础上对酵母酶联自溶进行正交试验,结果表明:自溶-酶联技术是制备啤酒酵母抽提物的理想方法,制成品中氨基氮得率、总氮得率和固形物得率分别达到4.30%、8.98%和59.0%.并对其物理性状、溶解性、pH、干湿比、总氨基酸含量等理化参数指标进行评定.     

提高酵母抽提物得率及氨基氮含量的研究

本文以新鲜面包酵母为原料,通过研究高压均质,外加蛋白酶及酵母抽提物,搅拌条件,离心次数等对酵母自溶的影响,得出了提高酵母抽提物得率臁氨基氨含量的优化工艺条件,产品最终得率为75．9％,氨基氮含量为4．75％。     

Using high-pressure homogenization as a potential method to pretreat soybean protein isolate: Effect on conformation changes and rheological properties of its acid-induced gel

This study evaluated the conformational changes and rheological properties of acid-induced gels of insoluble soybean protein isolate (SPI) pretreated with high-pressure homogenization (HPH) under different pressure and cycles. Results showed that HPH pretreatment destroyed the spatial structure of the insoluble SPI, significantly decreased the particle size of the SPI dispersion, and increased the SH content. Through the characterization of its acid-induced gelation product, the best ability to withstand small strains (< 3%) of gel was found in a single HPH cycle under 100 MPa. The SPI gels with a relatively compact structure transformed from strain stiffening to strain softening with the strain increased, and it provided satisfactory stability to withstand large-amplitude oscillatory shear in three-time HPH cycles under 100 MPa. Meanwhile, SPI gels exhibited a more chaos spatial topology network after HPH pretreatment through fractal analysis, and the gels eventually exhibited “soft gel” and shear-thinning behavior with HPH pretreatment. This provides an evidence for the beneficial effect of HPH on the structural homogenization and subsequent gel formation stability of protein gels, and explores its potential applications in the food industry.     

Effect of fermentation on content,molecule weight distribution and viscosity of β-glucans in oat sourdough

This study investigated the effect of fermentation on the physicochemical properties of β-glucans in oat sourdough. Sourdoughs were produced from oat using homo-fermentative lactic acid bacteria, Lactobacillus plantarum 22134. The contents of total β-glucan and soluble β-glucan, the molecular weight (MW) of β-glucan and the viscosity of the extracted β-glucans were determined at 0, 4, 8, 10 and 12 h of fermentation. The total β-glucan content decreased from 4.89% to 4.23% after 12 h of fermentation. The soluble β-glucan concentration increased from 1.89% to 2.18% and then decreased to 1.97% after 8 h of fermentation. The content of β-glucans with MW > 10⁵ decreased from 0 to 4 h of fermentation, followed by an increase and then a decrease after 8 h. The oat sourdough fermented for 8 h had high viscosity, which could be more beneficial for health and bread texture quality, especially for gluten-free breads.     

啤酒酵母自溶动力学的研究

研究了啤酒酵母自溶过程中溶出产物随自溶时间的变化 ,建立了啤酒酵母自溶过程中产物溶出的非结构性动力学模型 .应用非线性最小方差回归方法得到自溶反应的速度常数Ka及产物生成系数αKP、βLP等 .酵母自溶过程中产物溶出遵循一级反应速度方程 .     

Effects of wheat sourdough process on the quality of mixed oat-wheat bread

The aim of this work was to study the effects of sourdough fermentation of wheat flour with Lactobacillus plantarum, on the quality attributes of mixed oat-wheat bread (51 g whole grain oat flour and 49 g/100 g white wheat flour). Emphasis was laid both on β-glucan stability as well as bread structure and sensory quality. The variables of the sourdough process were: dough yield (DY), fermentation time, fermentation temperature, and amount of sourdough added to the bread dough. The sourdough process was shown to be a feasible method for mixed oat-wheat bread, and, when optimized, provided bread quality equal to straight dough baking. A small amount (10g/100 g dough) of slack sourdough fermented at high temperature for a long time resulted in the most optimal sourdough bread with the highest specific volume (3.5 cm³/g), the lowest firmness after 3 days storage (0.31 kg), and low sensory sourness with high intensity of the crumb flavour. Wheat sourdough parameters did not affect the content of oat β-glucan in the bread. Additionally, both straight dough and sourdough bread contained 1.4-1.6 g β-glucan/100 g fresh bread. The average molecular weight of β-glucan was 5.5 × 10⁵ in both types of bread, while that of oat flour was 10 × 10⁵. This indicates that a slight degradation of β-glucan occurred during proofing and baking, and it was not affected by variation in the acidity of the bread between pH 4.9-5.8.     

The effect of moderate pulsed electric fields on autolysis of Saccharomyces cerevisiae and the amino acid content in autolysates

The effect of moderate pulsed electric fields (MPEF) strength on autolysis of Saccharomyces cerevisiae was evaluated in this study. After exposure to MPEF with intensity of 7 kV cm⁻¹ for 4 ms, the integrity of the cell wall was obviously destroyed and the inactivation of S. cerevisiae reached 99.43%. During the subsequent 42-h autolysis process, the release of free α-amino nitrogen of MPEF-treated cells, as well as extracellular protease activity, was significantly (P < 0.05) higher than that of untreated cells. Moreover, exposure to 7 kV cm⁻¹ led to an increase of the total amino acid of 149.36%. In particular, the content of aspartic acid and glutamic acid which are important umami flavour precursors increased by 232.55% and 209.40%, respectively. These results indicate that MPEF will be an effective method to accelerate autolysis of S. cerevisiae for obtaining high-quality yeast extract as flavour enhancers and nutrition supplements.     

Pressurized aqueous ethanol extraction of β-glucans and phenolic compounds from waxy barley

Beta-glucans and phenolics were extracted from waxy barley using pressurized aqueous ethanol in a stirred batch reactor at 25 bar and 500 rpm. The effect of temperature (135–175 °C), extraction time (15–55 min) and ethanol content (5–20%) was evaluated. Temperature had an opposite effect on the extraction of both compounds. The higher the temperature, the lower the β-glucan extraction yield due to fragmentation, but a significant increase on the phenolic recovery was observed. Long extraction times favored the extraction of β-glucans at low temperatures and phenolics at any temperature. The ethanol content was not statistically significant on the β-glucan extraction, but helped to maintain the molecular weight of the extracted β-glucan. To obtain liquid extracts rich in high molecular weight β-glucans and phenolics, mild conditions of 151 °C, 21 min and 16% ethanol are needed, leading to 51% β-glucan extraction yield with a molecular weight of 500–600 kDa and 5 mg GAE/g barley.     

Non-thermal plasma as an innovative pretreatment technology in delignification of brewery by-product

Non-thermal plasma was applied as an innovative pretreatment for the delignification of brewery by-products. The influence of different plasma gases (pure air or air/argon), time and solids concentration (7.5, 10 and 12.5%) was evaluated during the delignification tests. The levels of cellulose, hemicellulose and lignin were monitored before and after treatment. The reduction in lignin content was approximately 50% after 5 min using pure air in all tested solids concentrations. Longer pretreatment times (60 min) influenced the removal of hemicellulose (50%) and cellulose (12%), also indicated by morphological changes. After 5 and 60 min of plasma application, the physical-chemical characteristics showed minor changes in its chemical composition, mainly affected by the losses of lignocellulosic compounds. Non-thermal plasma is considered an attractive alternative for the pretreatment of brewery by-products, resulting mainly in removing lignin, assisting in subsequent processes such as the enzymatic hydrolysis of the spent solid.     

Utilizing high-pressure homogenization for the production of fermented plant-protein yogurt alternatives with low and high oil content using potato protein isolate as a model

The potential of high-pressure homogenization (HPH) to allow the production of a fermented potato protein isolate-based yogurt alternative with low and high oil concentration was investigated. The yogurt alternatives containing different oil concentrations (1.5%, 3%, and 10%) were obtained by inoculating the homogenized (0.1 MPa, 30 MPa, and 200 MPa) emulsions. HPH reduced emulsion particle size (all oil levels) compared to the non-homogenized samples (0.1 MPa). The overall emulsion whiteness index increased after HPH treatment while the highest value was obtained for 200 MPa 10% oil, 76.01 ± 0.50, compared to 65.33 ± 2.05 obtained for 0.1 MPa 10% oil. The creaming velocity was decreased by HPH, e.g., for 3% oil from 10.70 ± 0.11 (0.1 MPa) to 0.59 ± 0.04 after 200 MPa. Microscopic images of gels from HPH treated emulsions revealed smaller oil droplets and narrower component distribution. This study further highlights the possibility of HPH technology to produce plant-protein-based yogurt alternatives with different oil concentrations.Industrial relevanceIn recent years, the food industry has changed rapidly and has faced new consumer demands and global food trends. Consumers pay attention to food and its effect on their health, and the popularity of dairy alternatives with reduced-oil and, on the other hand, Greek-style yogurt analogs has grown. (Ultra) high-pressure homogenization ((U)HPH) is a continuously emerging technology that can potentially provide simultaneous homogenization and microbial inactivation and induce changes in solution physicochemical properties such as emulsion stabilization mainly by significantly reducing oil droplet size and improving interactions between emulsifiers and oil phase. By utilizing HPH, plant-based yogurt alternatives can be formed with a wide range of oil concentrations and similar texture profiles and water holding capacity, free of additional stabilizers and artificial emulsifiers. The results of this bottom-up approach study could be of great importance for considering the potential for scaling-up and future implementation of (U)HPH in the food industry to produce plant-based milk and yogurt alternatives with low and high oil content, having a clean label.     

Impact of high-pressure homogenization pretreatment on recovery of curcumin from turmeric by different combinations of extraction and drying methods

This study reports the effect of different extraction and drying techniques in the recovery of curcumin, where the impact of the pre-treatment step on turmeric rhizome using high-pressure homogenization (HPH) was evaluated. Soxhlet extraction (SE) and ultrasound-assisted extraction (UAE) followed by drying (oven drying, vacuum drying, and freeze drying) were applied to HPH-treated and control (non-HPH) samples. The HPH treatment condition of 100 MPa for 10 cycles demonstrated the lowest particle sizes in the turmeric suspensions and the highest curcumin content in the aqueous supernatant. It was also found that HPH treatment increased the release of curcumin from the freeze-dried turmeric extracts obtained from SE (+76.2%) and UAE (+57.5%). Besides, freeze drying was the best drying method demonstrating higher antioxidant activity of extracts than other thermal drying methods. The total phenolic content was increased by about 65.5% upon HPH treatment on turmeric extract obtained from UAE followed by vacuum drying.     

THE RELATIONSHIP BETWEEN TOTAL β-GLUCAN OF MALT AND MALT QUALITY

The total β-glucan content of barley and malts has been determined using a direct enzyme degradation method incorporating measures to ensure inactivation of any contaminating amyloglucosidase. Results for barleys range between 2·7 and 4·4% w/w and indicate genetic variation in the β-glucan content. Malts produced by both a laboratory micromalting procedure and commercially have been analysed for total β-glucan, extract and 70°C mash viscosity at different stages of germination and in the end product. A very good correlation has been found between total β-glucan and fine-concentrated extract difference values showing that in a fully modified malt having a negligible extract difference value, all the β-glucan material is degraded. The extract difference value had been demonstrated earlier to be closely linked with brewhouse extract yield. The total β-glucan of malt, therefore, is directly associated with achievable extract in the brewhouse and is the most important biochemical factor determining the extractability of a malt.     

Effect of antioxidants in combination of VCO nanoemulsion on gel properties and storage stability of refrigerated sardine surimi gel

Impacts of β-glucan–virgin coconut oil (VCO) nanoemulsion containing epigallocatechin gallate (EGCG) and α-tocopherol at levels of 0–3.0 g kg⁻¹ on properties and storage stability of surimi gel were investigated. Augmented breaking force, deformation and fracture constant were obtained in gels containing 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol (P < 0.05). Expressible moisture content increased as EGCG levels were more than 2.0 g kg⁻¹. Smoother microstructure was observed in gels containing 2.0 g kg⁻¹ EGCG. Whiter gels were obtained when β-glucan–VCO nanoemulsion was incorporated. No change in protein pattern of gels was observed regardless of antioxidant incorporation. Viscoelastic moduli decreased as β-glucan–VCO nanoemulsion was added; however, incorporation of 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol lowered the decrease in G'. β-glucan–VCO nanoemulsion containing gels had higher likeness scores than the control (P < 0.05). Gels containing EGCG and α-tocopherol at selected levels had the improved oxidative stability and lowered microbial loads.