Dextrins, molasses, glucose and other products widely used in the confectionery industry are produced from starch. Starch is a carbohydrate, its chemical formula (C6Н10О5) n
The starch content in various raw materials is given in table. 49. Starch is obtained from potatoes, corn, and significantly less from wheat and rice.
Starch is most easily extracted from potatoes and much harder from other raw materials where proteins are present. In this case, the grain is soaked using chemical means * coarse and fine crushing and other operations.
Table. 49. The average starch content of the raw
|name of raw materials||% Starch||Starch, based on dry substance|
|Potatoes||From 14 — 29||74|
|Wheat||67,8||58 – 76|
|rice||76,75||75 - 80|
Starch refers to polysaccharides and its calorific value is within 418 kcal.
Physico-chemical properties of starch
Starch consists of amylose and amylopectin in the ratio 1: (3,5 — 4,5). The content of amylopectin and amylose in starch (in%) are given in table. 50.
50 Table. The content of amylopectin and amylose in the starch
|Type of starch||Amiloza||Amilopektin|
|Potato||19 22||81 – 78|
|Corn (maize)||21-23||79 – 77|
Starch is insoluble in water, readily soluble in 30% salicylic sodium solution. Amylose is soluble in hot water and forms clear solutions. Amylopectin dissolves in water when heated under pressure. Viscous solutions are obtained. In hot water without overpressure, amylopectin swells. When starch is brewed with water, a starch paste is formed, which consists of a colloidal solution of amylose with swollen amylopectin particles distributed in it. Iodine stains amylose in blue, amylopectin in red * violet, and starch in intense blue.
Gelatinization of starch is an irreversible process. The data on the starch gelatinization (Table. 51).
Table 51. Temperature of gelatinization of starches
|The name of the starch||Gelatinization temperature in ° C|
|made of corn||68,0|
Starch when swelling is able to absorb the following amount of water: potato 37,1%, maize to 35%, wheat 31,63% and rice 26,79%. The heat that develops during swelling is for 31,71 potato starch feces, wheaten 28,79 feces and rice 28,62 feces.
The heat capacity of the absolutely dry starch is 0,2697. To calculate the heat capacity of starch, the following formula is used:
where: Cр1 - heat capacity of regular starch;
Ср - heat capacity of absolutely dry starch (0,2697);
and - the content of absolutely dry substances in starch.
The heat capacity of commodity starch at temperatures from 0 to 20 ° —0,2765, from 21 to 42 ° —0,2978 and from 43 to 62 ° - 0,3061.
The size and quantity of starch grains are shown in Table. 52.
Table 52. Starch grain size
|Starch||Grain size in mm|
|Potato||0,05 – 0,08|
|made of corn||0,02-0,03|
|wheaten||0,03 – 0,05|
Specific weight of commercial potato starch 1,648, maize 1,623, wheat 1,629 and rice 1,620.
Bulk weight of commercial starch: potato 650 kg / g3,
maize 550 kg / m3.
Starch solutions are able to rotate the plane of polarization of the light beam in the polarimeter. The specific rotation of potato starch + 184,4 ° with fluctuations from + 177,19 to + 204,3; specific rotation of corn starch + 201,5; wheat starch + 202 „4 — 204,3 and rice starch + 202,5.
The starch saccharification rate is expressed in milligrams of maltose per starch 1 g, it depends on the size of the starch grains. Large starch grains are broken down by enzymes approximately 2 times weaker than small ones. Saccharification of wheat starch is characterized by the following data (according to M. I. Knyaginichev): soft wheat (medium) 36,8, hard (medium) 42,3.
The average chemical composition of bone dry starch in% is given in Table. 53.
53 Table. The chemical composition of starch
Starch is very hygroscopic. Soluble potato starch at a relative humidity of 99% through 27 days increases the humidity to 40,6%, and soluble maize starch at the same relative humidity through 25 days increases the humidity to 31,7%.
The use of starch
Starch is widely used in the production of flour confectionery (biscuits, biscuit cakes and pastries, cupcakes) and in the development of hand-made sweets. The consumption of starch by weight of flour is provided by recipes in the following quantities: for long pastry varieties up to 7,5%, sugar to 10%, in biscuit cake mix for cakes and pastries 25 — 12%, and in almond cake even 100%.
In the production of flour confectionery usually used maize and potato starch. In addition, wheat starch in flour,
54 Table. to starch quality requirements
|The organoleptic and physico-chemical parameters||Type of starch||starch Grades|
|Appearance and color||made of corn||—||—||White||White||White with gray shade|
|Potato||Crystal white||White||—||White||White with a grayish tint|
|wheaten||White||White||White with a grayish tint|
|Humidity in% max||made of corn||—||__||13||13||13|
|Total ash content on dry matter in%, no more than||made of corn||0,2||0,3||0,5|
|Acidity in cm3 0,1N NaOH dry substance, max||made of corn||20||25||30|
|Number of Krapina; 1 sm2 starch surface, not more||made of corn||2||5||10|
|Content of free mineral acids and chlorine||made of corn|
|sulfurous acid content in mg per kg 1 air-dry starch, max||made of corn||100||100||100|
|Impurities other types of starch||made of corn|
Note. In all types of starch intended for food purposes, crunching during chewing, foreign smell, unusual for starch, and the presence of zinc, lead, copper, tin, arsenic and antimony should not occur.
Starch has the following influence in the preparation of dough and finished products:
reduces the content of gluten in the flour, it specifically) is added to the flour with a high gluten content too;
increases the plasticity of the dough during processing, so that the products are given greater brittleness;
dextrins formed during baking, give a smooth and shiny surface, especially of long grades of cookies;
welding starch is widely used in the manufacture of gingerbreads to improve their quality.
Maize and rice starch, as a molding material, has found wide application in the production of soft candy varieties. Preference should be given to rice starch, as it is fine-grained and has a high temperature of gelatinization.
It has been established (E. I. Zhuravleva) that with a decrease in the moisture content of starch, the shedding of forms significantly increases. So, at the moisture content of starch 5%, 27% cells fall off, while at the humidity level 12% only 3% cells fall off.
Starch in casting enclosure must meet the following requirements:
1) nonshattering cells;
2) minimum adhesion to the surface of the candy shells;
3) sanitary and hygienic cleanliness.
Requirements for starch
Corn starch is packed in bags weighing from 60 to 85 kg. Potato, wheat and rice starch are packed in bags of 50, 80, 100 kg each. Bags can be linen and jute, but must be clean, dry and whole, new and used. Deviation in bag gross weight + 50 g%
In manufacturing plants, starch is stored in heated premises at the optimum temperature 15 — 18 °, i.e. at the temperature closest to the temperature of the dough kneading.
If the moisture content of starch is within the normal range, then this slightly increased storage temperature (15 — 18 °) does not affect the quality of the starch.
Low room temperature does not affect the quality of starch. When starch is stored together with flour, it should be noted that the room temperature above 10 ° favors the development of insecticides and microorganisms.
It is possible to prevent their appearance and reproduction by keeping the room clean and ventilated. The relative humidity of the air during storage of starch in warehouses is recommended to keep no higher than 70%.
B and by a tio n NA, Boorman ME, Solntseva NV, Handbook of starch and syrup production Pishchepromizdat, 1952.
Kravchenko, SF, T p x and y h e c a AA, technical-chemical control of corn-starch production Pishchepromizdat, 1952.
The technology of starch and syrup production, ed. prof. A. C and n i n g and a, Pishchepromizdat, 1950.