Determination of aspartame in soft drinks should be carried out immediately after filling of beverages.
Calibration graph constructed as follows. In separate tubes are transferred to 6 cm 3 of each working solution and added to them by 3 cm3 ninhydrin solution. The tubes are kept exactly 16 minutes in a boiling bath, then cooled to 20 ° C for 20 min and from each tube was transferred to other tubes in 3 c cm3 of the solution was added thereto in 5 cm3 of 60% aqueous solution of ethanol and stirred.
The optical density of these solutions were determined by spectral photometer at a wavelength of 570 nm or at FEK with an average wavelength of 582 nm (filter number 6) in a cell thickness of 10 mm. Control solution is the solution of the tube number 9 (zero solution) and 60% ethyl alcohol, mixed in the same quantities as the other samples.
According to the analysis graph constructs by plotting on the abscissa the concentration of aspartame Cp, and the vertical axis - optical density.
The analysis. In these samples drinks removed carbon dioxide and filtered samples through a filter with a pore size of less than 0.5 microns. Then 20 cm3 of the filtrate is transferred into a volumetric flask and bring 100 cm3 of distilled water to the mark.
In test tubes with a capacity of 10 cm3 transferred to 6 cm3 of each diluted sample was added to them in 3 cm3 ninhydrin solution stand 16 minutes in a boiling bath, and cooled to 20 °C for 20 min. From each tube was transferred to a separate tube, 3 cm3 of the solution, which is then added 5 cm3 of 60% aqueous solution of ethanol.
The optical density of solutions of the samples is determined against a zero sample on a spectrophotometer at an average wavelength of 570 nm or at FEK at a wavelength of 582 nm (filter number 6) in a cell thickness of 10 mm.
By optical density on the plotted graph are the concentration of aspartame in a dilute solution (Cp), and the true concentration of aspartame (C) is calculated by the equation
C= Cp • K,
where K - the degree of a dilute solution. In our example, K = 5.
By this method it can determine the concentration of aspartame in the range of 20-50 mg per 100 cm3 of the drink.
Control questions
In what temperature do determine the taste and aroma of the drink?
How does determine the average filling of the bottle?
In which conditions determine the mass fraction of solids (density) of the drink?
By what formula does calculate the alcohol content in kvass?
On what reaction is based method for determining the concentration of aspartame in soft drinks?
Laboratory work # 12
Assessment of the quality of beer
Objective: To develop skills in the principles of the classification and the range of beers in the establishment of defects in the preparation of samples for the determination of quality in examination quality.
Materials and equipment: Analytical balance with a maximum weighing limit of 200 g; bath water; pycnometer flask at 75, 100 and 1000 ml separatory funnel of 100 ml and 1000, the centrifuge, pipettes, filter paper, desiccator oven, potassium dichromate; sulfuric acid; rectified ethyl alcohol; chromic mixture, 1.2 g of potassium dichromate was dissolved in 100 cm3 of sulfuric acid, chloroform, anhydrous sodium sulphate.
Theoretical part
The final stage of the technological control of the production of beer is the assessment of the quality of the finished product, which is carried out by organoleptic and physico-chemical parameters.
The main indicators of quality of beer as a beverage are transparency, color, taste, aroma, hop bitterness, foaming. All these properties are determined in the process of beer tasting.
By the physico-chemical parameters of beer include mass fraction of solids in the Wort, the mass fraction of the actual alcohol and extract, acidity, color, mass fraction of carbon dioxide (for bottled beer), stability of beer, while secondary fermentation. The taste of beer referred to as organoleptic characteristics. The bitter taste of beer caused mainly by bitter substances of hops, as well as tannins as hops and malt and unmalted shell grains. Bitter substances of hops presented soft and hard resins. Soft resins - is α-acid (humulone), β-acid (lupulon), soft α- and β-resin, γ-acid (gumulion), σ-acid (gulupon) and β-fraction (the amount of β-acids and soft resins). Solid resin is separated into γ- and σ-resin.
Among the bitter substances is dominated by α-acid. Upon drying and storage of hops it oxidizes and polymerizes to form α-soft resin and a deeper oxidation - solid resin. When boiling wortα-acid is converted into iso-α-acids having more bitterness and solubility in water.
As a part of β-acids prevails lupulon which when boiled wort remains in the hop pellet. When oxidation is converted into β-resin soluble in the wort and beer.
α-acid iso-α-acid
R: isobutyl (humulone); isopropyl (kogumulon); sec-butyl (adgumulon)
The solubility of the soft resin in the wort is higher than the acids from which they are formed.
Solid resin formed by the oxidation of acids have little bitterness, only σ-solid resin has a coarse and bitter soluble in wort and beer.
In the process of producing beer portion of bitter substances is lost due to adsorption on the yeast and the ascent to the CO2 bubbles. Only 20-40% of the original bitter substances present in the beer.
Thinner bitter compounds in beer as well as in the wort, is a chloroform, and it should be noted that out of the whole complex of bitter substances α-bitter acid (humulone) at a pH of beer has the highest solubility and many times superior in this regard β-bitter acid (lupulon).
Experimental part
Determination of the bitter substances in beer. Beer previously freed of the main mass of the carbon dioxide agitation and filtration. What beer in an amount of 250-400 ml was poured into a flask of about 1 dm3 and stirred at room temperature its closed throat and opening the receptacle palm vessel from time to time until the stop feeling of pressure from within. Opaque beer should be filtered.
400 ml (V) of beer is placed in a glass flask stoppered with a capacity of 750 - 1000 ml, acidified with 5 ml of dilute sulfuric acid and 50 ml of chloroform. The flask was placed in "vibrating conveyor" and the contents are vigorously shaken for 30 minutes, after which it was poured into a separatory funnel and allowed to 500-750 ml within a few hours peel aqueous portion of chloroform. The chloroform resultant emulsion to break centrifuged for 10 - 15 minutes at 2000 - 3000 rev / min. The aqueous portion in centrifuge tubes carefully decanted and the clear chloroform extract sedimented at the bottom of the tubes, suction filtered pipette tip thrusting it through a layer of light-gray mass accumulated over chloroform and collect it in a separatory funnel for 80 - 100 ml.
After 5-10 minutes of settling the chloroform layer was collected in a flask with a capacity of 100 - 150 ml with ground glass stopper. In the flask was placed beforehand about 15 g of anhydrous sodium sulfate for drying the chloroform extract. Content flasks for 5 - 10 minutes of stirring, after which the chloroform extract was filtered through a small filter paper.
30 ml (V1) of the filtrate pipetted into preweighed round flask with a capacity of about 75 ml. Chloroform was removed under vacuum on a boiling water bath until its complete removal. Flask with the residue is kept 1 hour in a desiccator (preferably in a vacuum desiccator with a dehydrating agent) and weighed. Allowed without vacuum distillation of chloroform on a water bath at 65-70 ° C and the residue in a round bottom flask can be dried in an oven at 70 ° C for 1 hour. The content of bitter substances (X) in grams per 1 dm3 of beer is given by:
where: m - weight of residue in the flask after the distillation of chloroform g;
V - volume of beer taken for analysis, in ml;
V1- filtrate volume for analysis in ml.
Normally in beer contains about 0,03-0,09 g of bitter substances in 1 dm3.
Determination of relative density: pycnometer carefully washed chromate solution and distilled water and dried to constant weight and weighed up to the fourth decimal place. Double-distilled water it is filled with a temperature 19-21 ° C higher bit tags stoppered and immersed waterbath with temperature (20,0 ± 0,2) ° C so that the water level in the bath was a little above the water level in the pycnometer. After 20-30 minutes, without removing the pycnometer from the bath at a temperature of 20 ° C, determine the level of water in it so that the bottom edge of the meniscus was level with the mark. Excess water is collected in the pycnometer strip of filter paper. The inner surface of the neck above the pycnometer label carefully wiped with filter paper.
Stoppered pycnometer, is removed from the bath, wipe dry with a dry towel, and weighed up to the fourth decimal place.
Filling the pycnometer with water, the installation of the water level in it and weighing spend 3-4 times as long as the difference in weight is not more 0,0030g. Calculate the arithmetic mean value of the mass of the pycnometer with water.
Then pycnometer freed from water, rinsed 2-3 times with the test solution (solution distillate) and filled pycnometer just above the label.
Tempering, the installation level of the solution and weighing the pycnometer method described above is carried out at a temperature of 20 ° C. Spend at least two parallel determinations.
The relative density of the solution of the distillate (d) is calculated by the formula:
where m - mass of the pycnometer with the solution of the distillate, g;
m1- mass of the pycnometer, g;
m2- mass of the pycnometer with distilled water, the
The weight proportion of alcohol in a percentage depending on the relative density of the distillate is determined by solution Table. 1 of Schedule 2.
If the weight of distillate sample differs from the mass of beer, the value obtained by Table 1 is multiplied by the correction coefficient (K) computed by formula:
where m4 - weight distillate g; m5 - lotsofbeer, g
Control questions