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a-Galactosidase activity from Thermomyces lanuginosus strain of CBS 395.62/b was investigated in cultivation media with various compositions. Among the seven nitrogen sources only three L-asparagine, yeast extract and ammonium acetate supported the a-galactosidase synthesis. Ammonium acetate proved to be the best candidate as nitrogen source. When glucose or galactose was used as main carbon source, very low level, constitutive a-galactosidase activity was observed. In presence of raffinose, considerable a-galactosidase activity was detected. Raffinose can be replaced by sucrose in the cultivation medium, because the productivity reached by it was superior to that of raffinose. a-Galactosidase activity was improved by the optimisation of the concentrations of sucrose and ammonium acetate in the medium. Applying medium composition with 3% (w/v) sucrose and 0.6% (w/v) ammonium acetate led to at least 5 times higher activity which was observed in the reference medium containing 1.5% (w/v) raffinose and 0.45% (w/v) L-asparagine.
The role of zinc in beer production I.
Wort production
The most sensitive and time-consuming technological step of beer production is the fermentation of wort. Problems during fermentation will not only prolong production time but it will lead to the deterioration of beer quality. Most often it is due to low zinc concentration of the wort or the yeast. Due to lack of zinc the fermentation lasts longer, composition of fermentation by-products changes, maltose intake slows down, sedimentation ability and heat sensitivity of the yeast increase. In Part I of our work, the factors affecting the degree of zinc supply of wort were examined. During the examination of zinc supply of wort two kinds of beer were produced: all-malt beer and beer with adjunct. Change of zinc concentration was followed throughout the brewing process at every technological step. It was found that concentration of zinc gradually decreases during production of wort, and only a small fraction of the calculated amount appears in it. Wort made with adjunct has even lower zinc concentration than all-malt wort. In all malt wort 3.4%, while in wort containing adjunt only 0.4% of the zinc appeared in the wort. Yeast can absorb only the ionic form of zinc during fermentation, thus we had elaborated a method for the separation of the organic and inorganic form of zinc, which was followed by the determination of the concentration of ionic zinc in wort prior to fermentation.
The role of zinc in beer production
II. Fermentation
Fermentation of wort is the most critical step of beer production. Fermentation difficulties may be caused by inadequate wort composition, i.e. insufficient supply of trace elements. Wort provides trace elements for yeast. Among them zinc, which is essential for beer fermentation, is not available in the required amount in wort. Zinc utilization in fermentation was studied in beers made with adjunct (maize, barley). Inductively coupled plasma-atomic emission spectrometry was used as analytical method for the determination of zinc concentration. Addition of zinc made the fermentation faster. The best result was achieved at 0.4 mg l-1. Synthesis of aroma compounds was also promoted at this concentration. Concentrations higher than 0.4 mg l-1 did not affect significantly either the fermentation rate or the maximal ethanol concentration. Addition of zinc at the end of wort boiling did not prove to be practical, it is better to supply yeast with zinc.
Glycosyltransferase activity of Pectinex ultra SP-L (from Aspergillus aculeatus) commercially available enzyme preparation was studied in mono- and bisubstrate systems using different donors (maltose, lactose, and sucrose) and acceptors (fructose, galactose, glucose, maltose, mannose, xylose, lactose, and sucrose). Oligosaccharides consisting of three monomers were detected in the cases of maltose, sucrose, and lactose as monosubstrates, thus this preparation should contain glucosyl-, fructosyl-, and galactosyl-transferase activity. Generally, yields of oligosaccharides synthesized were higher in bisubstrate systems maltose:sucrose, maltose:lactose, and sucrose:lactose than on monosubstrates. Use of maltose:sucrose bisubstrate resulted new oligosaccharide(s) (fructosyl-maltose or glucosyl-sucrose). The optimal ratio of substrates in the case of maltose:sucrose was determined to be 1:9. Increase of the dry content of the reaction mixture induced the transfer reaction. The highest oligosaccharide content was obtained at 60% (w/v) substrate concentration. In the case of the optimal ratio and dry content, 4.02% (w/v) oligosaccharide (DP3) concentration was achieved. These oligosaccharides may alter prebiotic and biochemical properties in food applications.
Twenty-six Bifidobacterium strains were isolated from human faeces. Seven strains were identified as B. bifidum, 4 strains as B. breve, 10 strains as B. longum, 2 strains as B. pseudocatenulatum and 3 strains as B. dentium by 16S rDNA analysis. The isolates from human origin showed strong adherence to the human tissue cultures. Three out of the 12 tested isolates repressed the growth of enteropathogenic bacteria. Utilisation of 9 commercially available oligosaccharides was tested by both Bifidobacteria and enteropathogens. Pro-, pre- and synbiotic food was made. Their effect was evaluated in in vivo feeding experiments, where healthy and antibiotic treated mice were used as test animals. During the four-week feeding period the composition of the colonic microbiota of the healthy mice did not change characteristically in any feeding group. However, the microbiota of mice in which it had been killed by antibiotic treatment was recovered by feeding with synbiotic food.
Fermentation trials were conducted in all-malt wort with mixed cultures of SaccharomycescerevisiaeWS 34/70 and one of two non-Saccharomycesyeast strains: Saccharomycodesludwigiiand Torulaspora delbrueckiiDSM 70607. Interactions were observed between the two yeasts during the alcoholic fermentation process started with eight different initial cell ratios ranging from 1:1 to 1:20 (Saccharomyces yeast : non-Saccharomyces yeast). Composition of the medium greatly affected the cell yield, degree of attenuation and ethanol concentration due to the maltose-negative characteristic of the non-Saccharomycesyeast strains. Starting cell ratios had less effect on the outcome of the fermentation experiments. S. cerevisiaelimited the growth of T. delbrueckiito a great extent, overgrowing it in the course of fermentation. On the other hand, S. cerevisiaedid not grow as dynamically in mixed culture with S. ludwigiias the composition of the medium would have suggested.
Effects of mixed cultures of Saccharomyces cerevisiae Levuline FB — higher ethanol tolerance — and different Kluyveromyces strains — higher inulinase activity — on the production of ethanol from Jerusalem artichoke extract were investigated. Among the investigated strains, combination of S. cerevisiae and K. marxianus strain Y00959 with simultaneous saccharification and fermentation gave the best efficiency (76%) of bioconversion. The optimal ratio of mixed cultures was determined to be 1:1 of K. marxianus and S. cerevisiae. Central composite design (CCD) was adapted to find the optimum initial substrate concentration and inoculum size for the maximal production of ethanol from Jerusalem artichoke juice. The optimum fermentation conditions were found to be 24% (m/w) substrate concentration and 45 OD600nm ml/100 ml inoculum size of mixed culture. Use of these conditions, about 10.67% (v/v) was produced at 148 h of alcoholic fermentation given. Results of this work provide benefits of mixed culture on production of bioethanol from Jerusalem artichoke.
In the course of our work we aimed to develop a product from gluten-free raw materials (millet, sorghum and buckwheat) that is similar to beer made of barley malt but is consumable by coeliacs. Our measurements were started by qualification of cereal/pseudo-cereal grains. Next malts were made of them with different steeping, germination and kilning parameters, and their most important quality characteristics were determined. Qualification of grains were done by grading, determination of thousand-kernel and hectolitre weight, and protein content, while malts were examined with congress mashing, Hartong mashing and lauter test, as well. Gelatinization point of the starch found in grains and malts were determined by Brabender amyloviscograph which helped to set the temperature of β-amylase rest in future mashings. The gelatinization points were higher in our samples, than in the barley’s starch.Optimization of mashing was continued with malts that fulfilled requirements needed for brewing. Mashing programs were written for each raw material with the help of our laboratory mashing equipment, and resulting worts were analysed (for extract content), then carbohydrate content was measured by HPLC, α-amylase activity by Phadebas test, and free α-amino nitrogen (FAN) content by the ninhydrin method. Those worts were selected for further fermentation tests that had the highest extract and FAN content, best filtration time and appropriate sensory characteristics. Optimal malting temperatures and time periods, aeration and water uptake were determined, and then the duration and temperature of protein and enzyme rests of mashing were set.The malting process that proved to be the most suitable for brewing requirements (high extract content, good lautering characteristics, high FAN content) has the following parameters: steeping with 25 °C water for 18 h with aeration in every 5 h; germination at 15 °C for 84 h; kilning at 50 °C for 48 h.
Currently gluten-free beer is not produced in Hungary for coeliacs. The goal of our research was to develop brewery products made of domestically grown millet (Alföldi 1) and buckwheat (Oberon) that are similar to traditional beer of barley malt regarding taste, aroma, consistency, colour, foam stability and alcohol content.On a micromalting equipment malts were made of buckwheat and millet. Beer was produced on pilot plant scale (50 l) with decoction process (mashing program with rests at 50 °C, 65 °C and 72 °C) and was supplemented with a highly heat-stable bacterial α-amylase, a fungal α-amylase and β-glucanase. Malts were evaluated by congress mashing (extract content, extract difference, pH, and colour); wort and final beer analyses were performed as well (pH, extract, iodine test, FAN, colour, bitterness, alcohol and extract content). Finally, sensory characterization was carried out. Difficulties with lautering were encountered during the brewing process with buckwheat. The analytical results indicated that the buckwheat and millet beer had different values compared with a typical barley beer with regard to pH, FAN, fermentability, and total alcohol. The extracts of the buckwheat and millet wort were lower, resulting in a final attenuation of 61.5% and 73.2%.In laboratory experiments optimal temperature of β-amylase found in domestically grown buckwheat (64 °C) and millet (62 °C) was determined by detecting maltose production with HPLC. Data was used to set the rest temperature of the enzyme during mashing. Inhibiting effect of certain substances on proteolytic enzymes was investigated by measuring the extract, FAN, and soluble nitrogen contents. Inhibition was detected in case of both raw materials, although to a different extent. Inhibition is influenced by tannins and polyphenols found in the grain (Chethan et al., 2008).
