The order of performance of job
To determine porosity apply an apparatus of Juravlev, which consists of metal body, cylinder and wooden plug(втулки). For sampling preparation from the middle of product grave a piece (slice of bread) by width at least 7-8 cm. From piece of crumb in the distance at least 1 cm to crust groove (делают выемки) by cylinder of apparatus.
The sharp end of cylinder prelube by plant oil. Cylinder entry into the crumb by round moving. Cylinder with the crumb put on the metal body so that ring fits snugly (плотно входил) into hole. Then crumb put out from cylinder by wooden plug at 1sm and cut by knife at the end of cylinder. Left in the cylinder crumb push by plug to the wall of body and cut at the end of cylinder. Volume of crumb’ cylinders ought to be 7 sm3, because internal diameter of cylinder equal to 3sm and distance from the wall of tray (лоток) to the hole -3,8sm.
Prepared 3 samples weight with accuracy 0,01g and then calculate the porosity by formula:
X=(V-(m/p)100/V, where
V- common volume of the bread grooves, sm3;
m- mass of grooves, g ;
p- density of nonporous mass of bread, g/ sm3;
(1,25- for black and wheaten bread)
Definition of acidity. During processing of the dough beside of alcohol fermentation formation of acids flows in chief lactic acid and a few acetic acid. The great amount of acids forms in rye bread, which is made at sourdough. A few acids accumulate in wheaten bread, which is made at yeast.
The order of performance of job.Fordefinition of acidity cut a slice of bread (mass about 70g), cut off crust and subcrustal layer from it. Prepared crumb carefully grind up by knife on the glass leaf and take 25g of the sample, which put in the 500sm3 bottle with well gauged tube plug.
Previously measure 250 sm3 of distil water. 1/4 part of it add into the bottle, where the bread is ground up prior receipt of indiscrete mass without nubbles.
To gotten mixture add residual water. The bottle close by tube plug, shake mixture strenuously 2min and leave for 10min. Then again shake mixture strenuously 2min and leave for 8min.
As time passes settled liquid layer carefully pour through sieve into dry bowl. Carry out two 50 sm3’ samples of solution by pipette into cone flasks (of 100-150 sm3) and titrate by alkali of 0,1n concentration at the presence of the indicator - phenolphtalein before occurrence of weak - pink colouring which is not disappearing during 1 min.
Acidity count by formula:
X=(25·50·4VK)/250·10=2VK, where
V- amount of a solution of alkali of concentration 0,1 n, used by titration, sm3;
K- amendment to a titer of a solution of alkali of concentration 0,1 n;
10-coefficient of alkali concentration’ change;
25- mass of sample,g;
4- re-count of sample to 100g;
250-volume of water taken for extraction of acids, sm3;
50- volume of titrated solution, sm3.
The form of record:
The name of a grade of bread _______________________________________ _
Weight of a product ___________ g, deviation(отклонение) __________ g, ___________ of %
Results of an estimation:
1. Appearance of bread _______________________________________ _____
Condition of a surface _______________________________________ ___
Colouring and thickness of crust_______________________________________ __
2. Condition of crumb _______________________________________ ______
Transition from crust to crumb _______________________________________
Distribution of pores (porosity)__________________________ ______________
Elasticity _______________________________________ ____________
Degree of baked _______________________________________ ___
Freshness of crumb _______________________________________ ______
3. Taste _______________________________________ __________________
4. Smell _______________________________________ _________________
5. Crunch at mouth feeling _______________________________________
6. Humidity of crumb_________________________________________
7. Porosity of crumb_________________________________________
8. Acidity of crumb___________________________________________
Questions:
1. What diseases of bread do you know and why do they appear?
2. By what indexes is organoleptical estimation of quality carried?
3. What apparatus is used by definition of humidity of bread crumb?
4. Why is the bread with thin-walled pores the best?
5. What acids form during processing of the dough?
Laboratory work # 3
Definition of physicochemical parameters of sugar-beet.
Purpose of the work: experimental determination of physicochemical parameters of fruits and vegetables.
1.1. The task
1. Define physicochemical parameters of fruits and vegetables.
2. Calculate content of ascorbic acid by formula.
3. Draw up report about the effort.
Definition of titrable acidity.
Theoretic part
Titrable acidity of fruits and vegetables characterize taste and food value of product. Fruits and vegetables content several acids, but only one of them predominates. So, apple acid predominates in seed-bearing fruit, beet, and carrot. Citric acid predominates in citrus plants, grape, potatoes, raspberry, cranberry and others. Definition of titrable acidity is based at ability of alkali to neutralize quantitatively as free acids as their salts in researched solution. According to quantity of alkali it is necessary to re-count it according predominated acid.
Technique definition.
Necessary materials and facility:
1.Fruits and vegetables. 2.Porcelain cup. 3. Measuring flask. 4. Counter balance. 5.Litmus- paper.
6. Glass rod. 7.Boiling-water bath. 8. Chemical reagents for titrating.
At Counter balance weigh 25gr of pulp in porcelain cup and put it into 250 ml’ measuring flask through feeder with the help of glass rod, adding some water in order the volume of it was 2/3 of flask volume. Then content of the flask heat on boiling-water bath to 800C and hold it 10-15 min. After quenching of flask’ content add water till mark and filter. 50ml of gotten filtrate carry over by pipette into cone flask, add 3 drops of phenolphthalein and titrate by 0,1n alkali until pink color. If filtrate is colored, litmus- paper as indicator can used. Titrating ends, if the drop of liquid doesn’t color litmus- paper to red.
Calculation of titrable acidity of fruits and vegetables (Xt) is carried by formula:
Xt=V·K·K1·V1·100/m·V2 , where
V-consumed at titration quantity of 0,1n alkali, ml;
K-correction coefficient of alkali concentration;
K1 - correction coefficient of corresponding acid; for apple acid - 0,0067; for lemon acid-0,0064; for tartaric acid-0,0075;
V1- volume of extract, prepared from weighed amount of being investigated product, ml;
100-correction coefficient of 100g of product;
V2- volume of filtrate of being investigated product, taken for titration, ml;
m-weighed amount of product, g.