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Electronic Journal of Biotechnology ISSN: 0717-3458

https://www.wendangku.net/doc/a13951168.html,

DOI: 10.2225/vol14-issue2-fulltext-5 RESEARCH ARTICLE Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density

Ademola O. Olaniran1 · Yushir R. Maharaj1 · Balakrishna Pillay1

1 Discipline of Microbiology, School of Biochemistry, Genetics and Microbiology, Faculty of Science and Agriculture, University of KwaZulu-Natal, Republic of South Africa

Corresponding author: olanirana@ukzn.ac.za

Received May 3, 2010 / Accepted January 3, 2011

Published online: March 15, 2011

? 2011 by Pontificia Universidad Católica de Valparaíso, Chile

Abstract Production of good quality beer is dependent largely on the fermentation temperature and yeast strains employed during the brewing process, among others. In this study, effects of fermentation temperatures and yeast strain type on beer quality and spent yeast density produced after wort fermentation by two commercial yeast strains were investigated. Beer samples were assessed for colour, clarity and foam head stability using standard methods, whilst the compositions and concentration of Beer Volatile Compounds (BVCs) produced were assessed using GC-MS. The spent yeast density, measured as dry cell weight, ranged between 1.84 - 3.157 mg/ml for both yeast strains with the highest yield obtained at room temperature fermentation. A peak viable population of 2.56 x 107 cfu/ml was obtained for strain A, also during fermentation at room temperature. The foam head of the beers produced at 22.5oC was most stable, with foam head ratings of 2.66 and 2.50 for yeast strain A and B, respectively. However, there was no significant (p= 0.242) difference in colour intensity between the beers produced at the different fermentation temperatures. Eight different BVCs were detected in all beer samples and were found to affect the organoleptic properties of the beer produced. Further optimizations are required to determine the effects of other parameters on beer quality. Keywords: beer volatile compounds, fermentation temperature, organoleptic quality, spent yeast density

INTRODUCTION

Beer brewing is an established ancient art from as far back as 6000 B.C., during the building of the ancient cities of Mesopotamia (Cortacero-Ramirez et al. 2003) and has been practised for thousands of years. The practice of producing beer in small micro-breweries has been replaced by magnificent industrial production plants that push out volumes of beer that early brew-masters could only dream about (Rojas and Peterson, 2008). To facilitate effective fermentation process, the yeast is often pitched at a specific population size and allowed to grow via an aerobic step in the fermentation process (Tanguler and Erten, 2008). Fermentation temperature is known to influence beer aroma composition (Bekatorou et al. 2002). Low temperature brewing; in particular, has been reported to result in the production of beer with improved taste and aroma as well as high ethanol and beer productivities (Bardi et al. 1996a; Bardi et al. 1997). Immobilized cell technology processes have been shown to shorten the production time of beer from 12-15 days to 1-3 days, however, the major difficulty is to achieve the correct balance of sensory compounds to create an acceptable flavour profile within the time frame (Willaert and Nedovic, 2006). Beer produced by fermentation of wort by cells immobilized on glutten pellets have been reported to have reduced higher alcohols and higher ethyl acetate (Bardi et al. 1996b).

After the fermentation process, there is often a much greater amount of spent yeast present in the fermenter than that present at pitching (Shotipruk et al. 2005). The spent yeast generated during the fermentative process is often used as an inoculum for subsequent fermentations (Blieck et al. 2007). In

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addition, yeast cell wall fractions contain a large percentage of β-glucans, which is highly advantageous in improving the physical and functional properties of foods, as a thickening and water-holding agent (Thammakiti et al. 2004) and for the gelatinization and retrogradation of starch (Satrapai and Suphantharika, 2007). β-glucans isolated from the cell wall fractions of spent brewer’s yeast are good emulsifying stabilizer and are finding application as a form of fat replacement in the production of low-fat mayonnaise (Burkus and Temelli, 2000). The partial replacement of vegetable oil in mayonnaise using β-glucans derived from spent yeast extract has two distinct advantages; firstly, it decreases the calorie content of the emulsification and secondly, it results in the utilisation of industrial by-products (Worrasinchai et al. 2006). In addition, β-glucans have been reported to have been used as a form of immunomodulator in livestock (Eicher et al. 2006).

The fermentation step in beer production is facilitated through the metabolic activities of yeast, resulting in the conversion of fermentable sugars to carbondioxide (CO2) and ethanol (Pi?kur et al. 2006). Whilst these metabolic activities produce the required ethanol from the fermentation, they also result in the production of large amounts of metabolic by-products, beer volatile compounds (BVCs), such as esters, ketones and higher alcohols which if present in high concentrations can influence the final aroma and flavour profile of the beer (Hansen, 1999; ?mogrovi?oví and D?mény, 1999; Brown and Hammond, 2003; Vanbeneden et al. 2008). These compounds are derived from precursors of yeast metabolic pathways and some of them are essential for growth of the yeast (Brown and Hammond, 2003). Whilst the presence of these compounds may be considered as detrimental to many (especially those in industry), there are a select few that regard these compounds as important flavour enhancers, especially those with an acquired taste for speciality beers. It is therefore important to determine the effects of these BVCs on beer quality as well as the mechanisms involved in their generation in order to develop methods to facilitate their control.

Over the past three decades, research in brewing has focussed on the application of immobilized cells, mainly to facilitate continuous processing, shorten maturation time and consequently reduce production costs (Kopsahelis et al. 2007). However, there appears to be limited studies on the effects of fermentation parameters on the production of BVCs and the consequences on the organoleptic quality of the final product as well as on the spent yeast density produced. This study is therefore aimed at investigating the effects of fermentation temperatures and yeast strain type on the production of spent yeast and BVCs as well as on the overall quality of beer produced. This would have significant repercussions on the South African economy, especially because the beer industry is a considerable player in the country’s economy, and the continuous increase in demand by the consumer.

MATERIALS AND METHODS

Wort preparation and fermentation

The wort used for the fermentation was made using canned-hopped malt extract purchased from National Food Products (Johannesburg, South Africa) and was prepared according to the manufacturer’s instructions. Fermentations were set-up to determine the effects of different fermentation temperatures and commercial yeast strains on beer quality using mini-fermenters (3.5 L) designed to facilitate the fermentation process on a small scale. Two litres of wort was dispensed into each sterile fermenter vessels after being allowed to cool and sterile standard rubber tubing (5 mm inner diameter) was attached to the outlets for sampling. The free end of the tubing was placed into a 2 l flask containing sterile distilled water to form the air-lock. Two commercial yeast strains, National Food Product yeast and Anchor yeast (designated as “strain A” and “strain B”, respectively) were used to pitch the fermentation. The yeast strains were grown in malt extract broth for 24 hrs at 30oC with shaking at 120 rpm and then pitched at an optical density of 0.4 at an absorbance of 600 nm, which corresponds to a cell density of 5 x 106Colony forming units per millilitre (cfu/ml) according to the McFarland standard. The fermenters containing each type of yeast were then incubated at one of three fermentation temperatures viz., room temperature (RT) (± 18oC), 22.5oC and 30oC for a period of one week. These temperatures were chosen to check the effects of the varying temperature ranges on the composition and concentrations of volatile compounds in the final beer. Gas evolution was monitored from the air-lock mechanism to ensure that fermentations were not stuck.

Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density Bottling and bottle conditioning

After a period of one week, the beer from each fermenter was aseptically transferred into sterile 500 ml sample bottles. To each bottle, a teaspoon of sugar was added prior to the addition of beer for bottle conditioning and the bottles were sealed and allowed to condition for a period of one week. After bottle conditioning, all bottles were stored at 4oC to facilitate yeast settlement and the maturation process.

Measurement of spent yeast density and viability

Spent yeast density was measured by the method of Soley et al. (2005). Ten millilitre samples were removed from each fermenter after fermentation and centrifuged (6000 rpm for 10 min at 4oC). The pellet was washed and resuspended in a normal saline solution (0.9% w/v NaCl), filtered through a previously dried and pre-weighed Whatman grade GF/A (? 47 mm) glass microfiber filter, and dried to a constant weight at 105oC. Thereafter, weight of the filter was subtracted from the weight of the filter containing the dried cellular material to acquire the mass of spent yeast produced. Viable yeast cell population was determined by the method of Nagodawithana et al. (1974). Yeast cells present in fermentation reactor were first thoroughly dispersed to ensure equal distribution of cells. Thereafter, a 1-ml sample was serially diluted before spread plating 0.1 ml of appropriate dilutions onto malt extract agar. The plates were incubated at 30oC for 48 hrs, and the number of colonies on plates for the dilution containing 30 to 300 colonies were counted and expressed as colony forming units per millilitre (cfu/ml).

Analysis of BVCs

Analysis of BVCs present in the beer samples was measured using dynamic headspace extraction methods and analyzed by gas chromatography and mass spectrometry (GC-MS). The volatiles from 100 ml of each sample was assessed by enclosing the sample bottle in a polyacetate bag and pumping air from the bag through a small cartridge filled with 1 mg of tenax? and 1 mg of carbotrap? activated charcoal at a flow rate of 50 ml/min for 30 min. A control was taken from an empty polyacetate bag sampled for the same duration. GC-MS analysis of the samples was carried out using a Varian CP-3800 GC (Varian, Palo Alto, California) with a 30 m x 0.25 mm internal diameter (film thickness 0.25 μm) Alltech EC-WAX column coupled to a Varian 1200 quadruple mass spectrometer in electron-impact ionization mode. Cartridges were placed in a Varian 1079 injector equipped with a “Chromatoprobe” thermal desorbtion device. Helium was used as a carrier gas at a flow rate of 1 ml min-1. The injector was held at 40oC for 2 min with a 20:1 split and then increased to 200oC at 200oC min-1 in splitless mode for thermal desorbtion. After a 3 min hold at 40oC, the GC oven was ramped up to 240oC at 10oC min-1and held there for 12 min. Compounds were identified using the Varian workstation software with the NIST05 mass spectral library and verified, where possible, using retention times of authentic standards and published Kovats indices. Compounds present at similar abundance in the control were considered to be contaminants and excluded from analysis. To ensure accuracy with quantification of emission rates, standards were injected into cartridges and thermally desorbed under identical conditions to the samples.

Measurement of foam head stability

The foam head stability was assessed according to the modified mini foam shake test developed by Van Nierop et al. (2004). A 20 ml sample of each beer (in triplicate) was dispensed into 50 ml glass measuring cylinders and all of the cylinders were sealed with parafilm. Each set of cylinders were shaken at the same time, vigorously up and down 10 times, after which the cylinders were set down on the counter, the parafilm pierced, and a timer set for 15 min. The foam was evaluated visually and the cylinders were arranged from best to worst. Ratings of 1 through 3 were given, where 3 was the greatest stability and 1 the worst.

Analysis of beer clarity and colour

The clarity of the beer was determined using a Hach P2100 Turbidimeter, while beer colour was measured spectrophotometrically at a wavelength of 430 nm as described elsewhere (Seaton and Cantrell, 1993). In both cases, distilled water served as a blank and a commercial beer was included in the analysis as positive control.

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Organoleptic quality assessment

The taste profile of beer produced was assessed by a survey conducted with 10 independent samplers, with no previous beer quality assessment skills. The survey consisted of questionnaires asking the samplers to rate beer from 1 to 10 (1 being very bad and 10 being excellent), for the presence of 10 different characteristics such as; banana aromas, sour apple taste, sweet “butterscotch” aroma, etc. Samplers were asked to give a rating of 0 if they felt a certain trait was absent. These values were assigned categories such that a rating from 0 - 3 was regarded as “low”, 4 - 6 as “medium” and 7 - 10 “high”. The data obtained was then used to determine the percentage of samplers which felt that the presence of the compounds was “low”, ”medium” or “high”. A commercial beer was also sampled to serve as the control.

RESULTS AND DISCUSSION

Spent yeast density and viable yeast population recovery after fermentation

Effect of the different fermentation temperatures on the spent yeast density and viable yeast population was investigated. Spent yeast density decreases with increasing fermentation temperature (Figure 1a). Fermentation at room temperature produced the most spent yeast density with a yield of 2.47 mg/ml and 3.15 mg/ml obtained for strain A and strain B, respectively. Spent density of strain A produced at a fermentation temperature of 22.5oC was almost equal to that produced at room temperature, with only 1.215% reduction in the spent yeast density whilst only 8.25% less of strain B spent density was produced at 22.5oC compared to that produced at the room temperature. It is possible that the available fermentable sugars present at these temperatures were converted into biomass at a similar rate as these temperatures are relatively close to 18oC, which is the upper temperature limit that is commonly used for lager beer fermentations (Brown and Hammond, 2003). The 30oC fermentation resulted in the lowest spent yeast density production of both strains with a 25.50% and 32.06% reduction in spent density produced compared to the room temperature fermentations for strain A and strain B, respectively. The reduction of spent yeast density and viable yeast population after fermentation at 30oC could be attributed to increased metabolic rate at this higher temperature which could have led to faster utilization of sugars, and resulting in cell starvation, cell death and autolysis (Blieck et al. 2007).

Similarly, an increase in fermentation temperature led to a steady decrease in the viability of yeast cells (Figure 1b). A peak density of 2.56 x 107 cfu/ml was obtained for strain A at room temperature, which is about 2-fold higher than those obtained for strain B at 22.5oC fermentation. The least viable population of both strains was observed at 30oC fermentation, with about 11-fold and 3-fold reduction in population of yeast strain A and B, respectively, obtained compared to the peak population. In this study, fermentations was conducted for a period of 7 days disregarding the specific gravity of the wort, which is generally used to determine the remaining fermentable sugar concentrations in the wort solution in order to know when to terminate the fermentation process. Thus, it is possible that all fermentable sugars have been utilised before termination of the fermentation. Previous studies have shown a decrease in cell density as a result of decrease in fermentable sugars present in the wort. The decrease in cell viability with time has also been attributed to nutrient depletion and early entry of the organisms into the death phase (Blieck et al. 2007).

Beer colour, clarity and foam head stability

There was no significant (p = 0.242) difference in colour developed between the experimental beers produced by the yeast strains under the different fermentation temperatures; however, the colour intensity of all experimental beers was significantly (p < 0.05) lower than that of the control beer. The control beer had the deepest colour intensity with an absorbance of 0.198, while the maximum absorbance for beer produced with strain A and B at room-temperature was 0.149 and 0.143, respectively, with a maximum absorbance of 0.144 obtained for beer produced with the two strains at 22.5oC (Figure 2a). Also, the absorbance of beer produced with strain A and B at 30oC was 0.143 and 0.135, respectively (Figure 2a). Colour development in beer has been mostly attributed to the malt extract used in the respective beers instead of the fermentation parameters (Kopsahelis et al. 2007). Generally, the malt extract used has been reported to have the greatest effect on beer colour as the degree of colour intensity of the malt extract depends on the degree of kilning or roasting of the malted

Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density

barley (Seaton and Cantrell, 1993; Kopsahelis et al. 2007). Thus, it is possible that the control beer may have been produced from a malt extract which was differentially roasted compared to the malt extract used in this study.

There was no direct correlation between fermentation temperature and the clarity of beer produced with the two yeast strains. However, beers produced with strain B were generally clearer compared to those produced using strain A, with 56.13%, 21.46% and 57.58% reduction in turbidity at room temperature, 22.5oC and 30oC fermentation temperatures, respectively (Figure 2b). All the experimental beers produced were relatively turbid compared to the control. The extremely good clarity found in the control beer may be attributed to additional processing steps, such as centrifugation and microfiltration, that are used in the production of commercial beers (such as the control) to increase clarity (Seaton and Cantrell, 1993; Kuiper et al. 2002; Shotipruk et al. 2005). The beers produced in

this experiment were bottle conditioned and were not subjected to further processing as the control beer. Also, it has been generally observed that bottle conditioned beers are more turbid than their commercial counterparts due to the presence of the residual yeast used for conditioning (Kuiper et al. 2002). It was also noted that yeast strain A produced beer with higher turbidity than strain B and this could be that yeast strain A produced and released higher concentrations of haze active proteins since the presence of these proteins has been shown to increase turbidity in beer (Seaton and Cantrell, 1993).

The control beer used had the best foam head stability compared to the experimental beers. The foam head of the experimental beers produced at 22.5oC was most stable, retaining as high as 88.67% foam head stability compared to the control beer, while those prepared at room temperature had the least foam head stability rating (Figure 3). This could be due to variations in climatic temperature and light

Fig. 1 Spent yeast density (a) and Total yeast viable population (b) produced by different yeast strains at the different fermentation temperatures. Values are average from six values ± standard deviation

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intensity at room temperature which could have stressed the yeast cells and hence led to alterations in the yeast cell membranes, resulting in the release of free fatty acids into the beer samples (Rodriguez-Vargas et al. 2007). Also, at 30oC fermentations, yeast cell density may have been lost due to autolysis and could have resulted in an increase in free fatty acid concentrations in the beer because of solubilisation of membrane lipids, thus resulting in lower foam head stability. It has been previously reported that the presence of lipids or free fatty acids in beer could lead to a decrease in beer foam head stability (Dickie et al. 2001; Van Nierop et al. 2004).

Fig. 2 Colour profiles (a) and clarities (b) of beer produced by different yeast strains under varying fermentation conditions. Values are average from six values ± standard deviation.

Fig. 3 Foam head stability of beer produced by the different strains at varying fermentation temperatures. Values are average from six values ± standard deviation.

Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density Beer volatile compounds and organoleptic quality assessment

The relative percentages of the important volatile compounds detected in the beer samples are indicated in Table 1. Higher alcohol, isoamyl alcohol, constituted a large percentage of the BVCs in most samples, constituting up to 49% of the total BVCs in beer samples produced with strain B at room temperature fermentation. Most of the other compounds constituted below 15% of the total BVCs, however, isoamyl acetate constituted approximately 30% of the BVCs in the control sample and between 8.345-17.712% and 8.382-10.247% of the total BVCs in beer produced with strain A and B, respectively, at the different temperatures. Furthermore, ethyl caproate constituted roughly 10% or more of the volatiles found in all samples, while 2-phenylethyl acetate constituted between 4% and 7% in most samples except for the control, and beer samples produced at 22.5oC where it constituted greater than 10% of the total BVCs (Table 1). GC-MS chromatogram of beer samples showing the different peaks representing the BVCs detected is shown in Figure 4. The seven volatile compounds detected in the beer samples produced in this study have also been found in beer produced from a previous study (Kopsahelis et al. 2007).

quality of the different beer samples. As represented in Figure 5, about 35% of the samplers felt that the beers produced had a moderate sour apple taste. This taste profile is usually characteristic of the flavour, volatile esters; ethyl caprylate and ethyl caproate (Verstrepen et al. 2003). Also, roughly 65% of the samplers felt that all beers produced had a moderate warm mouth-feel and this characteristic is generally attributed to the presence of ethanol produced from fermentation as well as the presence of fusel alcohols (Ter Schure et al. 1998). Roughly 40% of samplers felt that a moderate medicinal aroma was present in beers produced at the 22.5oC and 30oC fermentations using strain A as well as the room-temperature fermentation for strain B. Generally, these characteristics are attributed to the presence of volatile phenolic compounds in beers (Vanbeneden et al. 2008), while the moderate solvent aroma felt by the samplers in some of the beers is usually attributed to the presence of ethyl acetate (Verstrepen et al. 2003). The non-detection of phenolic compounds could explain the general moderate medicinal smell feelings by most of the samplers. Perhaps, some of these compounds were not present in these beer samples since their generation depends on the activities of the yeast (Peddie, 1990; Brown and Hammond, 2003) as well as the composition of the wort (Kobayashi et al. 2008). Alternatively, the lack of detection could be attributed to limitation of the methods used for the analysis. Previous studies by Saison et al. (2008) and Pinho et al. (2006) have shown that fibres used for headspace analysis are efficient for detection of different classes of volatiles in beer. Thus, it is possible that the Tenax and Carbotrap fibres used in this analysis lacked the affinity required to detect some of the volatiles in the beer. This is a subject of further investigation in our laboratory.

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The percentage of samplers that agreed that specfic flavour or aroma characteristics were present in moderate levels in beers produced by different yeast strains at different fermentation temperatures.

Effects of fermentation temperature on the composition of beer volatile compounds, organoleptic quality and spent yeast density CONCLUDING REMARKS

Results from this study have shown that different yeast strains and fermentation temperatures affects beer quality, especially turbidity, foam head stability, spent yeast density and yeast viability. However, these parameters had not much effect on the colour profiles of the beers produced and no effect on the qualitative properties of volatiles produced but rather on the relative quantities of the BVCs as evident in the headspace GC-MS analysis. However, in order to increase accuracy of volatile detection, it would be prudent to investigate the effect of the different headspace trapping fibres on detectable BVCs profile. The presence of varying concentrations of BVCs appeared to affect the organoleptic properties of the beer; however, the employment of qualified beer samplers is required to provide a more accurate view. Further optimization is required to determine the effects of other fermentation parameters on overall beer quality as well as investigate gene expression profiles by the different yeast strains under the different fermentation conditions.

Financial support:This study was supported by the South African Breweries and Competitive Research Grant of the University of KwaZulu-Natal, Durban, South Africa.

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VERSTREPEN, K.J.; DERDELINCKX, G.; DUFOUR, J.-P.; WINDERICKX, J.; THEVELEIN, J.M.; PRETORIUS, I.S.

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酵母发酵问题

酵母发酵问题 面粉加水和酵母,在30~38度之间,就可以发酵。 不加酵母也可以发酵,面粉和水1:1,调成糊,放一天,加少量粉,每天重复,大概5~10天后,就可以做种,然后加面粉和水和面,也能做馒头或者面包。 这个很有意思,就像养小宠物一样。最好放点麦麸,可以快点。 酵母的新鲜是一方面。 水温是最重要的,水温以不烫手为准,否则酵母就会被烫死。 酵母的多少,只是发的快慢而已,但还是不要太多的好。 你先看看保质期,时间搁置太长的酵母会失效的。 水温30℃前后,你可以先把酵母调在水里,把白糖放进去,糖可以增加酵母菌的营养,加快发酵速度,静置两三分钟,然后再揉进面里,1000g面粉放15-20g酵母,不过也不是固定的,要根据面粉的筋度,水温,气温,酵母的质量来灵活调节。 高活性干酵母过了保质期还能用吗? 可以用,使用时的量要加大些,过了保质期只是其活性降低了,不会产生毒害。 如果是开封后时间太长,就有可能不会发面了。 如果是没有开封的,过期时间在半年之内的,都可使用,而且会发。建议使用量不超过面粉量的1%。正常时为0.3~0.5% 建议开封后放入冰箱的冷冻箱中。酵母是不怕冻的。在常温下保存会加快其失效。 酵母吃多了会腹泻是没有科学依据的,因为酵母是一种帮助消化的有益菌。是对人体有好处的。在药品中还有一味药叫酵母片,是帮助消化的药。 1、不管什么酵母,25-26度是酵母的繁殖问题哦,这个温度酵母是生长温度,不怎么产气的,酵母的最佳产气温度是36-37度,你的温度控制有一定的问题。 2、如觉得可能酵母问题,可将酵母先用温水(以不烫手为宜)化开放极少量的糖后等半小时再和面可解决问题。现在酵母一般都没问题,即便活力下降也可通过此种方式提供酵母营养复活酵母,要知道我家长期使用安琪酵母从没出过问题,毕竟是大公司产品哦。 3、如果面没发好,面团没发酸的情况下再参入一定的面粉并参入一定的酵母和面仍可以再发酵做馒头,这种馒头的风味更好哦,因为面团中的其他微生物生长会产生一些风味物质,缺点是时间长了的面团会发酸,杂菌多了怕不卫生,其中产酸的是乳酸菌,大量产酸就还要用食用碱中和了,一般人不好掌握。 4、和好的没发酵的面还可以吃啊,比如做煎饼、下面疙瘩。只要面不发酸就行,否则难吃了,呵呵。 不知道上面的回答能否帮助到您

酵母菌酒精发酵实验报告

实验方案 酵母菌酒精发酵的条件研究 学院(部):生物与化学工程学院 专业:生物工程 学生姓名:鑫 学号:11018150 班级:生物工程二班 指导教师:肖

一、实验目的 1、学会实验的设计和操作过程 2、找到酵母菌发酵时的最优条件 二、培养基和实验方法及材料的确定 1、玉米粉的糖化方法 玉米粉的糖化采用双酶法,其工艺流程如下 玉米粉→加水→液化→糖化→发酵→蒸馏→成品酒精 试验中,发酵培养按照三角瓶100ml培养。本次工做20组是要,共需发酵液20*100=2000ml。培养液按照100g玉米粉、300ml水。所以共需玉米粉700g。 液化:取100g玉米粉,加入300mL的水,液化温度为90℃,pH值为5.5,液化时间为3.5h,液化酶的添加量为0.035g/100 g玉米粉 糖化:糖化时的工艺条件为:糖化温度为58℃,pH值为4.5,糖化时间为3.5h,糖化酶的添加量为0.3g/100g玉米粉。 2、活化培养基 本实验在进行实验时采用察氏(czapck)培养基的配制,配方如下表一: 表一 3、扩大培养基 扩大培养仍然用察氏(czapck)培养基,由于要用液体的,所 以将其中的琼脂配料去掉。 4、发酵培养基

糖化液稀释至l0%浓度,添加辅料(硫酸铵0.4%),pH5.5 灭菌 三、培养基的制备及酵母的活化 1、准备酵母母菌一支常温下存放一天,增加菌种的活力。在母菌存放期间制作各时期培养基 2、准备固体培养基(察氏培养基)50ml,做成8支试管斜面,扩大培养基800ml(做扩大培养时使用)。做成8个三角瓶,每瓶200ml。120℃灭菌30min。 3、发酵液的制备 (1)玉米粉的筛选 实验前准备粉碎后的玉米粉700g。 (2)玉米粉的液化 按照100g玉米粉、300ml水的配比对玉米粉进行液化,液化方案上文已经交代。在1000ml烧杯里,或者500ml烧杯分两次,水浴液化。 器材:烧杯500ml两个,玻璃棒一个,水浴锅一个,糖化酶0.225g 步骤:1、将糖化酶,玉米粉,水按照比例配置好在烧杯里。2、将配好的玉米液放于水浴锅中90℃液化3.5h。边液化边搅拌。 (3)玉米粉的糖化 将液化后的玉米液中按照0.3g/100ml加入液化液中。再在水浴锅中,58℃糖化3.5h。 (4)过滤 糖化后的糖化液有可能有没有彻底液化的玉米颗粒,会造成浑浊,这时需要对糖化液进行过滤操作。 操作步骤: 最后与以上培养基一起进行灭菌处理。灭菌时,清洗16支移液管,与培养基一起灭菌。 (5)活化步骤 器材:酒精灯,接种针,母菌,斜面培养基,消毒酒精。 步骤:1、将器材放于实验台上。对双手合桌面进行灭菌。对接种针进行灼烧灭菌。2、在酒精灯旁按照无菌操作步骤在酒精灯火焰旁取

发酵工业中常用常见的酵母菌

发酵工业中常用常见的酵母菌 (一)酿酒酵母(Saccharomyces cerevisiae) 这是发酵工业上最常用的菌种之一(图2-84)。按细胞长与宽的比例可将其分为三组。 1)细胞多为圆形或卵形,长与宽之比为1~2。这类酵母除了用于酿造饮料酒和制作面包外,还用于乙醇发酵。其中德国2号和12号(RasseII和RasseXII)最有名,但因其不能耐高浓度盐类,故只适用于以糖化的淀粉质为原料生产乙醇和白酒。 2)细胞形状以卵形和长卵形为主,也有些圆形或短卵形细胞,长与宽之比通常为2。常形成假菌丝,但不发达也不典型。这类酵母主要用于酿造葡萄酒和果酒,也可用于酿造啤酒、蒸馏酒和酵母生产。葡萄酒酿造业称此为葡萄酒酵母(Sac.ellisoideus)。 3)大部分细胞长宽之比大于2,它以俗名为台湾396号酵母为代表。我国南方常将其用于糖蜜原料生产乙醇。其特点为耐高渗压,可忍受高浓度盐类。该酵母原称魏氏酵母(Sac.willanus)。 在啤酒酿造中最早采用的酵母是卡尔斯伯啤酒厂的E.C.Hansen(1842~1909年)在1883年分离的卡尔斯伯酵母(Saccharomyces carlsbergensis),这是一种底面发酵酵母。酿酒酵母也可用于啤酒酿造,但属上面发酵酵母,这两种酵母发酵的过程和啤酒风味都有所不同。 目前在分类上皆采用酿酒酵母的学名。 底面发酵酵母其细胞为圆形或卵圆形,直径为5~10μm。它与酿酒酵母在外形上的区别是,卡氏酵母部分细胞的细胞壁有一平端。另外,温度对这两类酵母的影响也不同。在高温时,酿酒酵母比卡氏酵母生长得更快,但在低温时卡氏酵母生长较快。酿酒酵母繁殖速度最高时的温度为33℃,而卡氏酵母需在36℃。但在8℃时卡氏酵母较酿酒酵母繁殖速度几乎快一倍。

浅谈酵母以及发酵原理

浅谈酵母 邬大江 4000年前,古埃及人已经开始利用酵母酿酒与制作面团了;中国的殷商时期(约3500年前),会利用酵母酿造白酒,而酵母馒头、饼等开始于汉朝。

酵母(Yeast) ,是一种单细胞真菌,在有氧和无氧环境下都能生存,属于兼性厌氧菌。有细胞核、细胞膜、细胞壁、线粒体、相同的酶和代谢途径。酵母无害,容易生长,空气中、土壤中、水中、动物体内都存在酵母。酵母有着天然丰富的营养体系。酵母细胞中含有大量的有机物、矿物质和水分。有机物占细胞干重的90%-94%,其中蛋白质的含量占细胞干重的35%-60%,碳水化合物的含量在35%-60%,脂类物质的含量在1%-5%。酵母细胞中还富含多种维生素、矿物质和多种酶类,能促进其被消化吸收。此外它还含有多种鲜为人知的活性物质,如麦角固醇、谷胱甘肽、超氧化物歧化酶、辅酶A等。

酵母菌细胞宽度(直径)约2~6μm,长度5~30μm,有的则更长,个体形态有球状、卵圆、椭圆、柱状和香肠状等。酵母菌的生殖方式分无性繁殖和有性繁殖两大类。 酵母菌能在PH值为3.0~7.5的范围内生长,最适PH值为4.5~5.0。像细菌一样,酵母菌必须有水才能存活,但酵母需要的水分比细菌少,某些酵母能在水分极少的环境中生长,如蜂蜜和果酱,这表明它们对渗透压有相当高的耐受性。在低于水的冰点或者高于47℃的温度下,酵母细胞一般不能生长,最适生长温度一般在20~30℃。酵母菌在有氧和无氧的环境中都能生长,即酵母菌是兼性厌氧菌,在有氧的情况下,它把糖分解成二氧化碳和水且酵母菌生长较快。在缺氧的情况下,酵母菌把糖分解成酒精和二氧化碳。

酵母在面团发酵中起着关键作用,面团发酵是一个复杂的过程。简单的说,酵母分解面粉中的淀粉和糖分,产生二氧化碳气体和乙醇。二氧化碳气体被面筋所包裹,形成均匀细小的气孔,使面团膨胀起来。在面团发酵初期,面团中的氧气和其他养分供应充足,酵母的生命活动非常旺盛。酵母在进行着有氧呼吸作用,能够迅速将面团中的糖类物质分解成二氧化碳和水,并释放出一定的能量(热能)。在面团发酵的过程中,面团有升温的现象,就是由酵母在面团中有氧发酵产生的热能导致的。 酵母在面团发酵中的作用: ①生物膨松作用——酵母在面团发酵中产生大量的CO2,并由于面团网状组织结构的形成,而被留在网状组织内,使面团疏松多孔,体积变大膨松。

酵母 发酵实验

实验一、二甜酒酿的制作品尝 1.实验目的 (1)通过甜酒酿的制作了解酿酒的基本原理 (2)掌握甜酒酿的制作技术。 2.实验原理 以糯米(或大米)经甜酒药发酵制成的甜酒酿,是我国的传统发酵食品。我国酿酒工业中的小曲酒和黄酒生产中的淋饭酒在某种程度上就是由甜酒酿发展而来的。 甜酒酿是将糯米经过蒸煮糊化,利用酒药中的根霉和米曲霉等微生物将原料中糊化后的淀粉糖化,将蛋白质水解成氨基酸,然后酒药中的酵母菌利用糖化产物生长繁殖,并通过酵解途径将糖转化成酒精,从而赋予甜酒酿特有的香气、风味和丰富的营养。随着发酵时间延长,甜酒酿中的糖分逐渐转化成酒精,因而糖度下降.酒度提高,故适时结束发酵是保持甜酒酿口味的关键。 3.实验材料 3.1 材料糯米、酒药。 3.2器具及其他用品手提高压灭菌锅、滤布、塑料盒、不锈钢锅。 4.实验流程 酒药 洗米蒸饭淋水降温落缸搭窝发酵甜酒酿5.实验步骤 5.1 洗米蒸饭将糯米淘洗干净,用水浸泡过夜,捞起放于置有滤布的蒸屉上,于锅内蒸熟(约15-20min),使饭“熟而不糊”。 5.2 淋水降温用清洁冷水淋洗蒸熟的糯米饭,使其降温至35℃左右,同时使饭粒松散。 5.3 落缸搭窝将酒药均匀拌入饭内,并在洗干净的塑料盒内洒少许酒药,然后将饭松散放入塑料盒内,搭成凹形圆窝,面上洒少许酒药粉。盖上塑料盒盖。 5.4保温发酵于30℃进行发酵,待发酵2 d后,当窝内甜液达饭堆2/3高度时,进行搅拌,再发酵1 d左右即可。 6.实验结果 (1)发酵期间每天观察、记录发酵现象。 (2)对产品进行感官评定,写出品尝体会。 7.思考题 (1)制作甜酒酿的关键操作是什么? (2)发酵期间为什么要进行搅拌?

初级中学八年级生物《酵母菌发酵》教案

山东省肥城市湖屯镇初级中学八年级生物 《酵母菌发酵》教案 一、教学目标: 知识目标:1、通过观察酵母菌发酵现象,掌握其发酵原理。 2、通过探究“影响酵母菌发酵的因素一温度”实验,巩固探究实验的过程。能力目标:通过探究活动,提髙实验设计及动手能力,培养分析问题及解决问题的能力。情感态度及价值观目标:1、体验知识和技术在生活和生产中的应用价值。 2、体验小组合作学习与交流的乐趣。 二、教学重点:1、生物发酵现象及原理。 2、巩固探究实验的过程。 三、教学过程: (一)情境导入: 师:同.学们,你们有谁蒸过馒头吗?(没有) 那你们见过家长蒸过馒头吗?(有的见过) 有谁知道蒸馒头时需要加入一种什么物质吗?(酵母菌) 师:很好,请大家观察桌子上的两个馒头,看有什么不同? (提示:可以用手捏一捏或掰开看一看) 生:一个松软多孔、一个硬而无孔。 师:同学们观察得很仔细,请猜测一下哪一个馒头在制作过程中加入了酵母菌? 生:松软多孔的。 师”:对,为什么加入了酵母菌馒头会变得松软多孔?酵母菌有什么作用呢?请大家欣赏一段视频后来回答。 播放视频:酵母菌发酵 (二)(学习任务一)酵母菌发酵现象 生:加入了酵母菌馒头内会产生一种气体 师:很好,这位学生看得很认真。 (讲述)酵母菌是一种真菌,适于在温暖且富含糖分的环境中生存,它能把糖分分解产生气体等物质,这个过程就是我们常「说的发酵,蒸馒头就是利用了酵母菌发酵的这一原理。 (展示)课前做的发酵装置。 (强调:为了保持酵母菌的生长,把装垃放在约30度温水中水浴保持恒温) 请大家仔细观察现象? 生:液体中有气泡岀现,气球胀大。 师:气球内的气体是什么? 生:猜测(二氧化碳) 师:如何证明? 生:通入澄淸的石灰水。 师:好,我们验证一下。 (取两只试管,各倒入少许澄淸的石灰水,导气管的一端通入其中一只试管) 引导学生思考:另一试管有必要吗?起什么作用?(强调对照) 生:石灰水变浑浊,证明产生了二氧化碳。

(完整版)馒头发酵方法与过程实验报告

馒头发酵方法与过程实验报告 馒头的发酵方法很多,有老面发酵法、酒曲发酵法、化学膨松剂发酵法、酵母发酵法等等。实验证明无论从食品营养的角度,还是从操作的角度,酵母发面都有很强的优势。用酵母发面不仅适合家庭和工业化生产线,也适合小型作坊式馒头房,特别是对于要求不增加成本的用户也是非常合适的。酵母发酵是馒头生产中最关键的环节,它对于馒头质量的好坏有着直接的关系。 一.常见的酵母发酵工艺 酵母的发酵原理是利用面粉中的糖份与其他营养物质,在适宜的生长条件下繁殖产生大量的二氧化碳气体,使面团膨胀成海绵状结构。 在酵母馒头的生产中,常见的发酵工艺简单的归纳起来主要有以下两种: 1.一次发酵法 原辅料: 和面、压面、成型、发酵、汽蒸 (1)操作方法: 和面: 将所有的原辅料一次加入和成面团,干酵母用量0.3%,鲜酵母用量为1%左右,加水量38-40%,和好的面团温度一般应控制在28℃。 成型: 馒头成型由馒头成型机来完成,家庭制作由手工完成,根据需要制成各种形状和大小的馒头坯。 发酵: 在温度30-32℃,湿度为75-80%的条件下让面团发酵35分钟。没有恒温恒湿条件的,也可以采取其它相应的保温措施。 蒸煮: 面团发酵完成以后,沸水上笼蒸20分钟。 (2)发酵特点: 用一次发酵法生产馒头,具有工艺线路短,生产周期短,生产效率高劳动强度低等许多优点,并且生产出来的馒头有很好的咀嚼感。因此该方法被许多馒头厂家广泛使用。 2.二次发酵法 部分原辅料:第一次和面、第一次发酵、第二次和面 压面、成型、第二次发酵、汽蒸 (1)操作方法: 第一次和面取30%左右的面粉加入所需的干酵母(添加量以第一次所加面粉量的0.16%计)再加上50%左右的水(加水量以第一次所加面粉量计),和成面团。 第一次发酵和好的面团在温度26-28℃,湿度70-80%的条件或温暖的自然条件下发酵8-12小时。发酵时间也可以根据自己生产的实际情况通过调整酵母的用量、两次和面时面粉的配比以及发酵温度、湿度来灵活调节。

温度对酿酒酵母的影响

温度对酿酒酵母的影响 酿酒是一个复杂的生化反应过程。影响微生物生长发育的环境因素很多,常见的有温度、pH、氧气、搅拌等环境因素。其中温度具有极其重要的作用。本实验探讨温度对酵母酿酒产酒量的影响,检验不同温度下酿酒酵母的出酒率。结果表明:酵母菌在28℃出酒率最高。低温下发酵品质好。 酿酒过程实质上是一个微生物摄取原料中的养分,通过体内的特定酶系,经过复杂的生化反应,把原料转化为酒精的过程。工业上主要是由薯类和谷类以及野生植物原料经过蒸煮,淀粉糊化成为溶解状态,再加入一定量的糖化剂,使溶解状态的淀粉,变为酵母能够发酵的糖类(糖化醪)。这一个由淀粉转变为糖的过程,称为糖化过程。糖化过程是由淀粉酶或酸水解的作用,使淀粉糖化转变为可发酵性糖。最后由酿酒酵母发酵产生酒精。生产上常用的糖化剂有麦芽和酒曲两种。我国普遍使用酒曲作为糖化剂。酒精是由微生物通过糖酵解(EMP)途径将葡萄糖分解而产生,是酵母菌的代谢产物。影响微生物生长的因素很多,其中环境因素对微生物的生长影响比较大。在生产上最常遇到的是温度、水分、氧气、pH、某些重金属离子、乙醇及发酵副产物等的影响。温度是影响微生物生长和存活的主要环境因素之一。对发酵的影响很大。温度对微生物生长发酵的影响具体表现在:①影响酶的活性。每种酶都有最适宜的酶促反应温度,温度的变化影响着酶促反应率,最终影响细胞物质合成。②影响细胞质膜的流动性。温度高细胞质流动性大,有利于物质的运输;温度低细胞质的流动性降低,不利于物质的运输。因此温度影响微生物对营养物质的吸收和代谢产物的分泌和运输。③影响物质的溶解度。物质只有溶于水才能被微生物吸收或分泌,除了气体外,物质随着温度的升高而溶解度增加,温度的降低,物质的溶解度也降低,最终影响微生物的生长。酿酒酵母是一种嗜温性微生物,它的最低温度是1—3℃,最高温度是54℃(几乎致死)。本实验目的在于探讨温度对酵母酿酒产酒量的影响,检验不同温度下酿酒酵母的出酒率。 可以看出,温度不仅影响着酒的颜色,还影响着酵母菌的酶促反应,最终影响代谢产物的类型及产量。温度高,颜色深;温度低,颜色浅。温度过高或过低,糖发酵不完全,糖度高,酒精相对含量少;温度在26℃~30℃之间,特别是在28℃,糖度低,酒精相对含量高。原因是温度对酶的结构和组成有较大的影响,它关系到代谢途径和代谢产物的生物合成。因此,根据不同的需要及发酵微生物的不同,可以通过调节温度来得出所需要代谢产物或提高产量。 有研究表明低温发酵最好。因为发酵过程比较缓慢,代谢产物反应完全、彻底。营养成分也发酵完全、彻底,脂化时间充分,营养价值高,有利于口感和品质的改善。这与本实验结果相一致,低温酿出来的酒, 清澈透明,香味浓溢,口感好。若要求酒质和口感更佳,发酵时间要延长到20~30天,因此低温发酵周期长。工业上常要求在高温下发酵,在高温下发酵具有反应迅速、发酵快、经济利益高等优点。但也影响了酒的口感和品质。寻求发酵周期短、经济利益高且酒的口感和品质好的最适条件,还有待进一步研究。

酵母菌在发酵工业中的应用

酵母菌在发酵工业中的应用 摘要:我国劳动人民在几千年前就利用酵母制酱酿酒等,酵母菌在人类的食品化工能源等方面有重大作用。酵母菌发酵食品可改善其风味及提高营养价值。随着生物技术的发展,基因工程在改造酵母方面获得了很多成功,使酵母获得了很多对人类有益的性状。在能源匮乏的今天,利用酵母发酵生物质产酒精作为能源代替品已越来越引起重视。但还需解决纤维素难利用等问题,因此亟需改造酵母,使其适应于纤维素等发酵。 关键词:酵母菌食品风味可再生能源基因工程 The role of yeast in fermention industry Abstract:The people of our country make sauce and alcohol .Yeast play a important role in food chemeical-industry and energy and so on .Food ferment by yeast has a special taste and nutrient .Along the development of biotechnology ,gene engineer succeeds to change the characters of yeast and get many new properties of yeast to fit the fermentation .Because the short of energy , it is importanceto use yeast to ferment alcohol as a substitution . But yeast can't use fiber to ferment effecient . Gene engineer may solve this problem . Key words:yeast ,flavor of food ,renewable energy sources ,gene engineer . 1 酵母在发酵中的历史回顾 中国是世界上在食品生产中利用微生物发酵技术最早的文明古国,具有许多民族特色的发酵食品,如豆腐乳、豆豉、酱油、酱、醋和白酒等,这些食品的制造工艺属传统的发酵工业[1]。利用 酵母对肉制品进行发酵,如腊肉,可以提高肉制品的消化吸收率及营养价值[2]。酵母菌与人类 生活密切相关,除了发面做馒头、面包和酿造各种饮料酒外,还能生产酒精、甘油、甘露醇、有机酸、维生素等等。酵母以通气方式培养可产生大量菌体,其蛋白质含最可达千酵母之50%。食用酵母多以糖蜜为原料,生产饲料酵母则以酒精工业、淀粉工业、制糖工业、啤酒工业、千酪工业、造纸工业(亚硫酸盐纸浆废液)等废液以及石腊油、木材水解液为原料生产。生产设备 向着大型化和自动化方向发展[3]。使用化学超声波等方法使酵母细胞破碎入醪液发酵,可以缩 短发酵周期,提高酱油质量[4]。 2 酵母抽提物的呈味作用原理 一般用酵母菌分为啤酒酵母和卡尔酵母,啤酒酵母属于上面酵母,而卡尔酵母属于下面酵母。酵母的发酵产物可以改善食品风味,能使人增强食欲。例如天然调味料——酵母抽提物(也称“酵母精”) 是以酵母发酵液为原料经自溶等工序而制得[5], 它不同于味精只含单一谷氨酸钠, 除了谷氨酸钠外, 还含丰富的其它10 多种氨基酸、肽以及多肽类、呈味核苷酸、维生素及微量元素等, 多种成分形成一种复杂的复合效应, 不仅具有味精的鲜味, 而且还具有浓郁的肉香味,

酵母发酵的影响因素

酵母发酵的影响因素 在面包的实际生产中,酵母的发酵受到以下因素的影响: 1 温度 在一定的温度范围内,随着温度的增加,酵母的发酵速度也增加,产气量也增加,但最高不要超过38℃~39℃。一般正常的温度应控制在26℃~28℃之内,如果使用快速生产法则不要超过30℃,因为超过该温度,将发酵过速,面团未充分成熟,保气能力则不佳,影响最终产品品质。 2 pH值 PH值:面团的PH值最适于4~6之间。 3 糖 糖的影响:可以被酵母直接采用的糖是葡萄糖,果糖。蔗糖则需要经过酵母中的转化酶的作用,分解为葡萄糖和果糖后,再为发酵提供能源。还有麦芽糖,是由面粉中的淀粉酶分解面粉内的破碎淀粉而得到的,经酵母中的麦芽糖酶转化变成2分子葡萄糖后也可以被利用。 4 渗透压 渗透压:渗透压是指为阻止渗透作用所需要加给溶液的额外压力,外界介质渗透压的高低,对酵母的活力有较大的影响。是因为酵母细胞的外层的细胞膜是个半透膜,即具有渗透作用,故外界介质的浓度会直接影响酵母的活力,高浓度的糖,盐,无机盐及其他可溶性的固体物质都会造成较高的渗透压力,抑制酵母的发酵。其原因是当外界介质浓度高时,酵母体内的原生物渗出细胞膜,原质浆分离,酵母因此被破坏,而无法生存。在这方面,干酵母比鲜酵母更有较强的适应能力。当然也有一些酵母在高浓度下仍可生存,并发酵。 在面包生产中,影响渗透压大小的主要是糖,盐这两种原料。当配方中的糖量为0%~5%时,对酵母的发酵不起抑制作用,反而可促进酵母发酵作用。当超过6%时,便会抑制发酵作用,如果超过10%时,发酵速度会明显减慢,在葡萄糖,果糖,蔗糖和麦芽糖中,麦芽糖的抑制作用比前三种糖小,这是因为麦芽糖的渗透压比其他糖要低。 盐的渗透压更高,对酵母发酵的抑制作用更大,当盐的用量达到2%时,发酵即受影响。

酵母的发酵原理

酵母的发酵原理: 酵母菌作为发酵素,吸收面团中的养分并生长繁殖,将面粉中的葡萄糖转化为水和二氧化碳气体,使面团膨胀、松软,产生蜂窝状的组织结构。当然还有一个前提,是面团在揉面时产生了足够的面筋,这些面筋能够包裹这些二氧化碳气体,并且能使这些气体不外溢,保持住面团膨胀和松软的状态。酵母菌必须有水才能存活,最适合生长的温度是在20℃~35℃,0℃以下或者高于47℃的温度下,酵母细胞一般不能生长,最适合作用的湿度是75%左右。酵母的种类: 1.鲜酵母,鲜酵母是酵母乳液经过压榨,色泽为淡黄色或乳白色的方块状。鲜酵母活细胞数量大,所以发酵速度快,产品香气足,而且价格便宜。但是鲜酵母的发酵作用不稳定,而且使用前需要活化(用35℃温水将酵母浸泡,搅拌均匀),再者它对保存温度要求严格(在0~4℃的低温下保存)不适合运输,保质期也比较短,大概1个月吧。所以鲜酵母都是生产厂家专用,家庭用户一般也不容易购买到。鲜酵母的用量一般是面粉的2%-4%。 2.活性干酵母:是将鲜酵母压榨后低温干燥制成的细小淡黄色的小颗粒。这种酵母保质期很长,大约2年。干酵母活力大也很稳定,但是这种酵母发酵时间很长,并且事先也需要20多分钟的活化,才能放入面粉使用。所以并不广泛被使用。 3.即发干酵母:是目前家庭最常用的一种,它是最新工艺将酵母乳液分离低温脱水干燥而成。色泽呈微淡黄色细小颗粒。一般用真空包装。密封时酵母聚集成块状。打开包装后,呈松散颗粒状。密封情况下,可在常温贮存,保质期未开封时大约1年,开封后要尽快使用,如果存放时间长要加大使用的剂量。一般使用量是面粉的0.6-1.5%。即发的干酵母使用比较简单,直接跟所有材料混合,或者先跟少量液体混合再混入面粉,经过搅拌后即可进行发酵。 影响发酵的因素: 1.温度,是影响酵母发酵的重要因素。酵母在面团发酵过程中要求有一定的温度范围,一般控制在25~30℃。如果温度过低就会影响发酵速度。温度过高,虽然可以缩短发酵时间,但会给杂菌生长创造有利条件使面团发酸。 2.酵母的用量:一般酵母的使用是根据面粉来计算0.6%-1.5%,根据面包的品种不同,加入的酵母份量也不一样,如果酵母作用力不佳时需要加大酵母的用量。 3.面粉:不同成熟度、筋度的面粉,或其淀粉酶的活性受到抑制的面粉都会影响酵母的作用。 4.水:在一定范围内,面团中含水量越高,酵母芽孢增长越快,反之,则越慢。所以,面团越软越能加快发酵速度。 5.其他配料的影响:首先是盐,盐能抑制酶的活性。因此,食盐添加量越多,酵母的产气能力越受到限制。但食盐可增强面筋筋力。使面团的稳定性增大。所以盐是面团发酵必不可缺的配料之一。其次是糖,糖的使用量为面粉的4%-6%时能促使酵母发酵,超过这个范围,糖量越多,发酵能力越受抑制。所以如果是高糖的配方尽量要选用耐高糖的专用酵母。还有其他乳制品、蛋等配料使用过多都会对发酵有影响,所以要注意按配方说明份量来制作最好。 面团发酵的次数、时间和温度: 一般的面包需要两次发酵,一次是基础发酵,就是面团揉好后整块进行的第一次发酵。基础发酵的理想温度为28度,相对湿度为75%,发酵时间根据面团的份量和配比不同需要50-90

酵母菌发酵

酵母菌发酵 酵母菌发酵是一个很神奇的过程,大家应该都知道很多奶制品或者豆制品都会进行发酵,而且发酵出来的产品对我们人体有很大的好处。比如我们常常喝的酸奶,就是酵母菌发酵后的成果,还有一些人在制作酒的时候,会把糯米放上发酵粉,在温度、湿度适合的条件下进行发酵,最后得到的成果很让人喜悦。 酵母发酵后会产生很多的菌类,酸奶中含有的菌类对我们的身体有益,能够帮助胃部消化,增强人们的免疫力。所以常喝酸奶可是一个不错的选择。不过酵母菌也是有很多分类的,有些酵母要求的温度不同,对环境的适应也不会,那么我们就来了解下吧。 酵母的种类: 1.鲜酵母,鲜酵母是酵母乳液经过压榨,色泽为淡黄色或乳白色的方块状。鲜酵母活细胞数量大,所以发酵速度快,产品香气足,而且价格便宜。但是鲜酵母的发酵作用不稳定,而且使用前需要活化(用35℃温水将酵母浸泡,搅拌均匀),再者它对保存温度要求严格(在0~4℃的低温下保存)不适合运输,保质期也比较短,大概1个月吧。所以鲜酵母都是生产厂家专用,家庭用户一般也不容易购买到。 2.活性干酵母:是将鲜酵母压榨后低温干燥制成的细小淡黄色的小颗粒。这种酵母保质期很长,大约2年。干酵母活力大也很稳定,但是这种酵母发酵时间很长,并且事先也需要20多分钟

的活化,才能放入面粉使用。所以并不广泛被使用。 3.即发干酵母:是目前家庭最常用的一种,它是最新工艺将酵母乳液分离低温脱水干燥而成。色泽呈微淡黄色细小颗粒。一般用真空包装。密封时酵母聚集成块状。打开包装后,呈松散颗粒状。密封情况下,可在常温贮存,保质期未开封时大约1年,开封后要尽快使用,如果存放时间长要加大使用的剂量。一般使用量是面粉的0.6-1.5%。即发的干酵母使用比较简单,直接跟所有材料混合,或者先跟少量液体混合再混入面粉,经过搅拌后即可进行发酵。 以上就是酵母的种类,对于不同种类的酵母,对我们的生活也有着不同的影响。要知道影响酵母发酵的因素也是有很多的。如果放的酵母多了或者是少了,又或者是使用的面粉量多了或者是少了对于酵母的发酵都会产生很大的影响。所以在制作食物的时候,我们要慢慢的放,不要一次性放的太多。

酵母发酵力测定试验步骤

酵母发酵力的测定 一、目的 通过测定酵母发酵力,筛选发酵力强的酵母。 二、实验原理 酵母在微酸性糖液中起发酵作用,其中的糖逐渐减少,乙醇及CO 2 则依比例 而增大,CO 2 是气体,除溶解于醪中者外,都跑向外面,所以测定酵母的发酵力,或测糖液比重的减小,或测糖的减少,或乙醇的增加,或称培器为减轻量,以 CO 2的失去多少,或用NaOH等固定CO 2 然后称其量,或将培养器密闭,由其中压 力的增大,而定发酵的强弱等。本实验采用乙醇浓度增大、CO 2 含量、糖的减少、培养器的减轻四个方面测定其发酵力强弱。 三、实验材料 1.菌种:本公司实验室分离所得。 2.试剂:葡萄糖、果糖、蔗糖、硫酸镁、磷酸二氢钾、蛋白胨、酵母浸膏、菲林试剂、碳酸氢钠。 3.器具:大三角瓶、小三角瓶、胶塞、玻璃管、1ml移液管、10ml移液管、天平、酒精计、温度计、蒸馏器、培养箱。 4.培养基 四、方法步骤 1.从斜面菌种接种到小三角瓶(100ml培养基)28℃培养24h; 2.摇匀小三角瓶菌种,吸取10ml接种到大三角(1000ml),装好CO 2 收集装置,称重,记录其重量,置28℃培养,每天称重一次,直到重量减少量小于0.5g; 3.发酵结束后,通过测量排水量测定CO 2 含量; 4.取一定量的发酵醪液,测定其残糖量,以测定其发酵力; 5.取100ml发酵醪液,加100ml水蒸馏出100ml溶液,用酒精计测定其乙醇含量。 (注:如果用酒精计不能测出,则改用重铬酸比色法或气相色谱法)

重铬酸比色法所需试剂如下: (1)0.1%(v/v)标准乙醇溶液;(2)2%重铬酸钾溶液;(3)浓硫酸;铬酸比色法 酒精糟中微量乙醇的测定 酒精糟中乙醇的含量是蒸馏时的一个重要指标。但酒精糟中乙醇含量甚微,不宜采用酒精计测量,需用比色法测定,比色法测定乙醇其浓度下限可达 0.02%。 1、原理 酒精糟中残余乙醇的测定采用蒸馏法,蒸出的乙醇用重铬酸钾氧化为乙酸,而六价铬被还原为三价铬,以比色法测定。 3CH 3CH 2 OH+2K 2 CrO 7 +8H 2 SO 4 =3CH 3 COOH+2Cr 2 (SO 4 ) 3 +2K 2 SO 4 +11H 2 O 2、试剂 (1)0.1%(v/v)标准乙醇溶液 (2)2%重铬酸钾溶液 (3)浓硫酸 3、测定步骤 (1)标准系列管的制备 在10毫升比色管中,按下列加入各溶液 各管中加1毫升重铬酸钾溶液,5毫升浓硫酸,摇匀。于沸水浴中加热10分钟,取出冷却。 (2)试样管的制备 称取100克酒精,放入500毫升圆底烧瓶中,加200毫升水,蒸馏,用100毫升容量瓶正确接收馏出液100毫升,摇匀。 取5毫升馏出液,放入10毫升比色管中,加1毫升2%重铬酸钾溶液,5毫升浓硫酸,摇匀,与标准系列管一起于沸水浴中加热10分钟,取出冷却。

酵母菌在人类生活中的应用

酵母菌在人类生活中的应用 摘要:涉及到人类食品中的酵母菌种类繁多,其中不同种类有不同的功能,这使得酵母菌在食品中有着广泛的用途,与人类的生活息息相关,随着科学技术的发展,酵母菌一定可以为人类的生活做出更大的贡献。 关键字:酵母菌应用前景 酵母菌是子囊菌、担子菌等几科单细胞真菌的通称。依照荷兰科学家Loddoy在1970年提出的分类系统,将有无形成有性孢子作为分类的起点,属上的分类主要依据形态,种的规划主要依据生理的特性,将酵母菌分为三个亚门:1.能形成子囊孢子的酵母属子囊亚门,共4个科22个属139种酵母。2.能产生冬孢子和担孢子的酵母菌,属于担子菌亚门、冬孢子纲、黑粉菌目、黑粉菌科共9个科。3.能产生掷孢子的酵母菌,属于担子菌亚门、东孢子纲、掷包酵母科、科内有三属。4.不能产生有性孢子,尚未发现有性过程的酵母属于半知菌亚门,共12个属170个种。但就我国目前所常用的分类是将酵母菌分为:鲜酵母、活性干酵母、即发酵母。酵母菌在生物界中的种类繁多,其在人类生活中也得到广泛的应用。据科学家推测,早在史前三千多年,人类就已经懂得酵母的发酵技术,虽不知原理,但却已有相当丰富的经验。据考古学家考证,在史前2500年的埃及Theban法王填墓内找到经发酵的面包实体和证明酒和啤酒酿造的壁画和宝物,以及在公元前2698年中国史记记载了自黄帝开始已有教民烹煮面食的记载,都证明人类在这之前就已懂得种植稻米、小麦以及储存、磨粉和利用酵

母调制不同的食物。由此看来,酵母菌的利用已深入人类的发展史。 1.酵母菌在发酵乳制品中的应用 随着科学技术的发展,酵母菌在酿造、奶制品、焙烤食品等有着飞速的发展。内蒙古农业大学的贺银风教授探究了国内外传统的发酵乳制品中乳酸菌和酵母菌的相互作用关系,指出了酵母菌在发酵品中的与乳酸菌有着同样的作用,菌种间相互促进和相互制约控制产品的风味特点、营养特征、医疗和保健作用。这为研究酵母菌在乳制品中的应用提供了理论的参考,不同的乳制品中的酵母菌存在着多样性,往往是多种酵母菌的共同作用形成不同的风味,不同的品质,而不同地区也有着自己特有的酵母菌,这是由于酵母菌的多样性所决定的。酵母菌在发酵乳制品中存在着许多的优点,主要是对于干酪的成熟有着诸多作用,例如:“(1)酵母菌能利用凝乳中由于乳酸菌的乳糖发酵所产生的乳酸,使凝乳的pH值有所提高,由起初的5到6左右。酸度的降低,刺激了对干酪成熟也有促进作用的细菌的生长繁殖;(2)某些酵母菌能产生胞外蛋白分解酶和脂肪分解酶,分解干酪中的蛋白质和脂肪,加速干酪的成熟,使干酪中可溶性含蛋物和辛酸、癸酸等其他高级脂肪酸增加L3J,对干酪的风味和结构起着至关重要的作用;(3)干酪内部的某些酵母菌能发酵牛奶中的乳糖,产生少量的CO,影响干酪的组织结构;(4)某些酵母菌能影响干酪某些风味物质如甲基酮的形成[IJ];(5)酵母菌能产生多种水溶性维生素,增加干酪的营养价值;(6)酵母菌在干酪中的生长繁殖和代谢作用,还能抑制腐败微生物和梭状芽孢杆菌的生长LIJ5。酵母菌在乳制食品中的主要

酵母菌发酵实验

酵母菌发酵实验 一、实验在教材中所处的地位与作用 本实验位于生物学八年级上册第五单元第五章第二节人类对细菌和真菌的利用。酵母菌在日常生活中很常用,可以用来发包子、馒头和酿酒,很具有代表性。该实验属演示实验,可直观地向学生展示酵母菌发酵现象,在实验过程中观察到液体中冒气泡,同时气球胀大,说明酵母菌发酵过程中产生了气体,与生活联系紧密,还可鼓励学生自己动手实践。 二、实验原型及不足之处 实验原型:生物学八年级上册教材P71 演示实验发酵现象在一杯温开水中加入一大勺糖和一小包酵母,进行搅拌。将这个杯子中的液体倒入透明的矿泉水瓶或玻璃瓶内,再往瓶内加一些温开水。将一个小气球挤瘪套在瓶口。将瓶子放在教室内的窗台上,每天观察瓶中的情况,看看瓶中的液体会不会冒出气泡,气球会不会胀大。 不足之处:该实验观察到液体中冒气泡,同时气球胀大,说明酵母菌发酵并产生了气体,但无法测知发酵过程中产生的是何种气体,也无法深入理解酵母菌在日常生活中的应用。 三、实验创新与改进之处 1、改用一个带橡胶塞的锥形瓶。 2、瓶口插一根“Y”形玻璃导管,排气端分别连挤瘪的小气球和橡胶管,橡胶管再连一根直的玻璃导管,橡胶管用夹子夹住。(见后图)

3、另用一个玻璃杯盛半杯澄清的石灰水,用来检测气体。 4、经过改进之后,就可以检测发酵过程中产生的是何种气体了。 四、实验器材 1、锥形瓶一个,“Y”形玻璃导管一根,直玻璃管一根,橡胶管一根,夹子一个,小气球一个,捆扎带一根,玻璃杯两个。 2、一杯温开水,一大勺糖,一小包酵母,半杯澄清的石灰水。 五、实验原理及装置说明 1、实验原理:酵母菌是兼性厌氧型真菌,喜欢含糖的环境,有氧时将葡萄糖分解成 co和水,无氧时将葡萄糖分解成酒精和二氧 2 化碳,同时都释放出能量。 2、装置如下图: 六、实验过程 1、在一杯温开水中加入一大勺的糖和一小包酵母,进行搅拌。将混合液倒入锥形瓶时,再将瓶内加一些温开水。

面包的发酵原理

面包的发酵原理 面包面团的发酵原理,主要是由构成面包的基本原料(面粉、水、酵母、盐)的特性决定的。 1.面粉作用 面粉是由蛋白质、碳水化合物、灰分等成分组成的,在面包发酵过程中,起主要作用的是蛋白质和碳水化合物。面粉中的蛋白质主要由麦胶蛋白、麦谷蛋白、麦清蛋白和麦球蛋白等组成,其中麦谷蛋白、麦胶蛋白能吸水膨胀形成面筋质。这种面筋质能随面团发酵过程中二氧化碳气体的膨胀而膨胀,并能阻止二氧化碳气体的溢出,提高面团的保气能力,它是面包制品形成膨胀、松软特点的重要条件。面粉中的碳水化合物大部分是以淀粉的形式存在的。淀粉中所含的淀粉酶在适宜的条件下,能将淀粉转化为麦芽糖,进而继续转化为葡萄糖供给酵母发酵所需要的能量。面团中淀粉的转化作用,对酵母的生长具有重要作用。 2.酵母作用 酵母是一种生物膨胀剂,当面团加入酵母后,酵母即可吸收面团中的养分生长繁殖,并产生二氧化碳气体,使面团形成膨大、松软、蜂窝状的组织结构。酵母对面包的发酵起着决定的作用,但要注意使用量。如果用量过多,面团中产气量增多,面团内的气孔壁迅速变薄,短时间内面团持气性很好,但时间延长后,面团很快成熟过度,持气性变劣。因此,酵母的用量要根据面筋品质和制品需要而定。一般情况,鲜酵母的用量为面粉用量的3%~4%,干酵母的用量为面粉用量的1.5%~2%。 3.水的作用 水是面包生产的重要原料,其主要作用有:水可以使面粉中的蛋白质充分吸水,形成面筋网络;水可以使面粉中的淀粉受热吸水而糊化;水可以促进淀粉酶对淀粉进行分解,帮助酵母生长繁殖。 4.盐的作用 盐可以增加面团中面筋质的密度,增强弹性,提高面筋的筋力,如果面团中缺少盐,饧发后面团会有下塌现象。盐可以调节发酵速度,没有盐的面团虽然发酵的速度快,但发酵极不稳定,容易发酵过度,发酵的时间难于掌握。盐量多则会影响酵母的活力,使发酵速度减慢。盐的用量一般是面粉用量的1%~2.2%。 综上所述,面包面团的四大要素是密切相关,缺一不可的,它们的相互作用才是面团发酵原理之所在。其他的辅料(如:糖、油、奶、蛋、改良剂等)也是相辅相成的,它们不仅仅是改善风味特点,丰富营养价值,对发酵也有着一定的辅助作用。糖是供给酵母能量的来源,糖的含量在5%以内时能促进发酵,超过6%会使发酵受到抑制,发酵的速度变得缓慢;油能对发酵的面团起到润滑作用,使面包制品的体积膨大而疏松;蛋、奶能改善发酵面团的组织结构,增加面筋强度,提高面筋的持气性和发酵的耐力,使面团更有胀力,同时供给酵母养分,提高酵母的活力。

酵母菌

酵母的营养价值及在水产养殖中的应用 一、营养价值 酵母含有水分、矿物质和有机物。矿物质占干酵母菌含量的6.0%-10.0%,包含钾、镁、钙、铁、硅、硫、磷等元素。有机物占干酵母的90%-94%,蛋的质是其中最主要的成分,一般占细胞干物质的30%-50%,蛋白质中含有鱼类、甲壳类等所需的10种必需氨基酸,脂类中含有较丰富的不饱和脂肪酸,此外,有机物中还包括生长刺激素、维生素、助消化的酶类等,因而酵母是一种营养丰富的活饵料。 二、酵母在水产名的应用 酵母中水产动物养殖中的应用价值主要体现在苗种培育上,酵母菌个体为4x5微米,粒径大小适合于各类育苗幼体作为早期开口饵料或整个幼体时期的饵料。此外,其营养丰富,运输、保藏和使用都比较方便,无毒副作用。目前已在河蟹、海参、对虾、海湾扇贝等育苗生产中得到了应用。从使用效果来看,酵母主要有如下四大功效: (一)强化营养 酵母菌体内各种营养成份非常丰富,其蛋白质除色氨酸和甲硫氨酸含量略低外,其它氨基酸都非常丰富,为鱼类和甲壳类所必需。它还含有一般饵料所缺少的必需脂肪酸,维生素和矿物质的含量也较为丰富。酵母所具有的这些营养成分弥补了其它常规

饵料的不足,对鱼、虾、蟹早期幼体和贝类、海参等浮游期幼体起到重要的营养强化作用。 (二)净化水质 酵母是活的菌体,投入水体中可继续进行新陈代谢活动,育苗水体中的有机物、氨态氮、硫化氢等对幼体有害的物质能够被酵母菌迅速降解利用,从而保证了育苗水体水质理化指标的稳定。 (三)抑制病害 酵母作为幼体饵料,它在育苗水体中是占有绝对优势的种群,致使其它微生物被排斥和抑制,防止了有害细菌的繁殖,起到生物抑制作用。除此以外,酵母体内含有丰富的免疫活性物质,幼体摄食酵母后,能够增强对外界恶劣条件和病害的抵抗力,有利于提高幼苗的成活率。 (四)培养饵料生物 轮虫、丰年虫、水等是水产动物苗种培育过程中不可缺少的活饵料。因酵母菌大小适宜,又含有丰富的氨基酸、脂肪酸、维生素等生理活性物质,在培养这些活的饵料生物过程中投喂酵母菌,对这些饵料生物的生长繁殖有明显的促进作用。 三、酵母在水产养殖中的使用方法 在河蟹育苗中,Z1-Z2变态阶段对营养十分苛求,如果在Z1期开始使用酵母,直到幼体变成Z2期,保持酵母在水中的密度为每毫升7-10万个菌体,并搭配投喂藻粉5-10ppm,蛋黄1-2ppm,

温度对发酵的影响

温度对发酵的影响 (1)影响产物生成速率和产率.温度越高,酶反应速度越快,微生物细胞生长代谢加快,产物提前生成。 (2)改变发酵液的物理性质而间接影响发酵. 改变培养液的物理性质会影响到微生物细胞的生长。例如,温度通过影响氧在培养液中的溶解、传递速度等,进而影响发酵过程。 (3)影响生物合成的方向:金色链霉菌的四环素发酵中,在低于30℃主要合成金霉素,温度达35℃则只产四环素。通过改变酶的调节机制实现。 (4)影响酶系组成及酶的特性:温度越高,酶反应速度越快,微生物细胞生长代谢加快,产物提前生成。但温度升高,酶的失活也越快,表现出微生物细胞容易衰老,使发酵周期缩短,从而影响发酵过程最终产物的产量。 (5)同一种生产菌,菌体生长和积累代谢产物的最适温度也往往不同。 最适温度:最适于菌的生长或发酵产物生成的温度。如谷氨酸菌的生长最适温度为30℃-32℃,产谷氨酸的最适温度为34℃-37℃。 pH值对发酵的影响 发酵液pH的改变将对发酵产生很大的影响。 ①改变细胞膜的电荷性质,影响新陈代谢的正常进行。原生质体膜具有胶体性质,在一定pH时原生质体膜可以带正电荷,而在另一pH值时,原生质体膜则带负电荷。这种电荷的改变同时会引起原生质体膜对个别离子渗透性的改变,从而影响微生物对培养基中营养物质的吸收及代谢产物的分泌,妨碍新陈代谢的正常进行。如产黄青霉的细胞壁厚度随pH的增加而减小,其菌丝的直径在pH 6.0时为2~3um,在pH 7.4时,则为2~1.8um,呈膨胀酵母状细胞,随pH下降菌丝形状可恢复正常。 ②影响菌体代谢方向。培养液的pH对微生物的代谢有更直接的影响。在产气杆菌中,与吡咯并喹呤醌(PQQ)结合的葡萄糖脱氢酶受培养液pH影响很大。在钾营养限制性培养基中,pH 8.O时不产生葡萄糖酸,而在pH 5.0~5.5时产生的葡糖酸和2-酮葡萄糖酸最多。此外,在硫或氨营养限制性的培养基中,此菌生长在pH 5.5下产生葡萄酸与2-酮葡萄酸,但在pH 6.8时不产生这些化合物。发酵过程中在不同pH范围内以恒定速率(O.055%/h)加糖,青霉素产量和糖耗并不一样,见表8—4。 表8—4 在不同pH范围内恒定速率加糖,青霉素产量和糖耗的关系 ③影响代谢产物合成。如采用基因工程菌毕赤酵母生产重组人血清白蛋白,生产过程中最不希望产生蛋白酶。在pH 5.0以下,蛋白酶的活性迅速上升,对白蛋白的生产很不利;而pH在5.6以上则蛋白酶活性很低,可避免白蛋白的损失。不仅如此,pH的变化还会影响菌体中的各种酶活以及菌体对基质的利用速率,从而影响菌体的生长和产物的合成。故在工

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