Noodles are a traditional Chinese staple food with a long history, many varieties, different flavors and local characteristics (such as Lanzhou Ramen, Shanxi knife-shaved noodles, Grandpa Zhang hollow noodles, etc.), and new varieties of noodles such as instant noodles, omnivorous noodles, LL noodles, and so on, have been produced in modern times. The starch added in noodle production includes raw starch, chemically modified starch (modified starch and its derivatives) and physically modified starch (pre-gelatinized starch), which not only improves the edible quality of noodles, such as sinewy, smooth, Q-bouncy, etc., but also gives the product functions, such as slow digestion, low GI, etc., and is the most widely used ingredient or quality modifier in noodle production.

Commonly used raw starch

In the raw state, the physical properties of noodle flakes or noodles are mainly determined by the gluten component, while in the cooked state, the most important factor affecting the eating quality of noodles is starch. The starch suitable for the production of noodle products is generally required to have the characteristics of easy expansion, low pasting temperature, high viscosity, etc. At present, the commonly used raw starch includes corn starch, tapioca starch, potato starch, etc., which can improve the quality of noodle processing, cooking, consumption and storage to a certain extent.
Table 1 Physical properties of starches from different plant sources

I. The source of original starch and its chemical composition
Starch is mainly composed of straight-chain starch (AM) and branched-chain starch (AP), but also contains a small amount of lipids, proteins and minerals. Root and tuber starches usually contain less lipid (0.1% for potato and 0.2% for cassava starch) than cereal starches (0.6%~1.2%), and the lipid content is positively correlated with the AM content.

Heating starch under excess water predisposes endogenous lipids to form lipid-starch complexes with AM, thereby inhibiting starch swelling and AM solubilization. Potato starch contains relatively high levels of phosphorus, which exists in the form of phosphate monoesters, mainly covalently bound to AP.

The presence of phosphate monoesters in potato starch has a significant effect on its swelling behavior. The negatively charged phosphate group causes repulsion between adjacent AP chains and results in rapid hydration of the starch granules and significant swelling of the granules. (The AM content of common starch is 14% to 29%). Starch without AM is called waxy starch, such as corn, cassava, wheat, potato; there are also some high straight-chain starch products (AM content > 30%).

Second, the application of raw starch in noodle processing
Potato starch is the only starch that can be covalently combined with phosphate in nature, so it is not easy to be aged. Adding potato starch can increase the viscoelasticity of noodles, promote the puffiness of noodles when cooking, and increase the transparency of noodles after cooking; potato starch particles are large, easy to paste, good expansion, easy to form micropores when frying, and can improve the rehydration of instant noodles. Ordinary corn starch is similar to wheat starch, with more straight-chain starch content, which makes the noodles hard and easy to age after adding; while waxy corn starch can make the texture of noodles soft and elastic after adding because it doesn’t contain straight-chain starch, and the noodles are not easy to age after being put in for a long time. In addition, tapioca starch contains less straight-chain starch, which can make the noodles more viscous and chewy, with a bright surface and smooth texture after addition.

The content of straight-chain starch, swelling, crystal structure, and starch granule size are all closely related to the edible quality of noodles, but the fine structural characteristics of straight-chain starch and branched-chain starch molecules, which play a decisive role, are not clear. The physicochemical properties of starch are closely related to the edible quality of noodles, which are also affected by the fine structure of starch. Therefore, a comprehensive understanding of the effect of starch structure on noodle quality is important for guiding the breeding of wheat for noodle use and the selection of starch auxiliaries for noodle use.

Commonly used chemically modified starches

Raw starch is an excellent texture stabilizer and improver for food systems, but its weak shear resistance, poor heat resistance, and ease of thermal degradation and regrowth limit its wide application in some industrialized foods. Modified starch, by changing the physicochemical properties of natural starch to improve its functional properties, can meet the specific needs of some food products, such as anti regrowth for cooked noodles and high water holding capacity for fresh noodles.

Starch modification methods include derivatization (e.g., etherification, esterification, cross-linking and grafting of starch), degradation (acid or enzymatic hydrolysis, oxidation of starch), or physical modification of starch by hygrothermal treatment (Table 2). Among them, starch derivatization is the introduction of functional groups into the starch molecule, which leads to significant changes in its physicochemical properties. This chemical modification of natural starch greatly alters its pasting, viscosity, and anti regrowth properties.

Table 2 Different modifications, preparation methods and uses of starch

I. Types of modified starch and their preparation methods
Food grade starch is chemically modified mainly to increase the consistency, smoothness and transparency of the starch paste and to confer freeze-thaw and refrigeration stability.

The new functional properties of chemically modified starch mainly depend on the starch source, the ratio of straight-chain starch to branched-chain starch, the granule morphology, and the type and concentration of the reactants, which can be used by selecting the appropriate modifier (type of substituent), the natural starch source (distribution of substituents in the starch molecule), and the reaction conditions (concentration of the reactants, time, pH, and presence of catalysts) to prepare the starch with the desired properties and degree of substitution of the modified starch with desired characteristics and degree of substitution.

Nutrition and safety of modified starch
Starch derivatives are increasingly used as fat replacers or fat substitutes that are partially or wholly undigested and therefore have zero caloric contribution when consumed.

The physiological effects of chemically modified starch are influenced by the type of modification. Chemical modification of starch by acetylation improves satiety, postprandial glucose and insulin response in humans. Phosphorylated/crosslinked starches are easily digestible and are thought to provide nutrition for humans; slow-digesting modified starches are used in the treatment of certain diabetes mellitus.

Resistant starch (RS), obtained by chemical modification, has attracted attention for its potential health benefits and functional properties. Compared with ordinary dietary fibers, RS has a low impact on the product structure, white color, and better texture, and its food products have better consumer acceptance and taste than those made from traditional dietary fibers.

Resistant starch has low water-holding properties, making it particularly suitable for the production of medium- and low-moisture foods, such as pasta, baked goods and fried foods, and can be easily labeled with simple starch labels. Several RS products have been launched in the international market, such as Hylong VII, Fibesol2, Crystalean, Hi-Maize, Nutriose and Novelose.

III. Application of modified starch in noodle processing
GB 2760-2014 specifies that in raw and wet noodle products, fermented noodle products, instant noodle products and frozen noodle products, there are 13 types of modified starch that can be used, such as acetate starch, phosphate ester double starch and hydroxypropyl starch, etc. The following describes the two types of modified starch that are most commonly used in noodle products.

(I) Acetate starch
Acetate starch is a low-substituted starch with 0.5% to 2.5% acetyl group by treating the original starch with acetic anhydride under alkaline condition.

A small amount of acetic acid group introduced into the starch molecule, hindering or reducing the straight chain starch molecules between the hydrogen bonding, and thus its pasting temperature and the degree of regeneration is reduced, it is not easy to form a gel, the starch paste has a high degree of transparency.

Adding starch acetate in instant noodle formula can effectively improve the texture of noodles, reduce the oil consumption during production and significantly improve the rehydration of noodles.

(II) Hydroxypropyl Starch
Hydroxypropyl starch is produced by etherification reaction between starch and propylene oxide under alkaline condition. Due to the introduction of hydrophilic hydroxypropyl, the internal hydrogen bond strength of starch granule structure is weakened, so that it is easy to swell and pasting; at the same time, hydroxypropyl will produce spatial resistance effect, preventing starch chain aggregation and crystallization, thus improving the transparency of starch paste and freeze-thawing stability, and preventing starch paste from aging, so it is suitable for frozen noodle products.

The study showed that adding 1% of hydroxypropyl corn starch or esterified glutinous corn starch to the flour amount of noodles, the cooking loss rate is reduced; the degree of regrowth is slowed down, and the wet noodles that have been refrigerated for a long time still have a softer texture.
In conclusion, adding an appropriate amount of modified starch to wheat flour can significantly improve the hydrophilicity of the mixed flour, which is easy to absorb water and swell, and can make the gluten and starch particles, the broken gluten and the starch particles well bonded together during the process of mixing to form a fine-organized dough with good viscoelasticity; it can improve the elasticity and cohesion of noodles and reduce the loss in cooking; it can also improve the sense of tenderness and smoothness of cooked noodles and is not easy to age, but adding too much can cause adverse effects on the dough, and it will have a soft taste. However, adding too much of it will adversely affect the dough.

Commonly used physically modified starch

Pregelatinized starch is a kind of physically modified starch, which is often produced by both drum drying and extrusion cooking. Pregelatinized starch can swell rapidly in cold water and has large viscosity, which can give ideal texture characteristics to food products. It has the advantages of room temperature water solubility, gelatinization, water retention and swelling.

Pre-pasteurized modified starch is similar to a “gluten” agent, when the gluten protein content is low or the quality is not ideal, adding pasteurized modified starch can make the gluten and starch particles well bonded, so as to enhance the tensile strength of the noodles. The addition of pregelatinized starch in the production of mixed grain pasta can significantly improve the texture and sensory quality of mixed grain pasta. It was found that the use of too much pregelatinized starch in noodles would increase the breaking rate, and the amount of pregelatinized starch added is usually controlled at 1%~5%.