Inulin is widely distributed in nature and is a reserve polysaccharide in many species of plants, mainly originating from the roots and stems of natural plants such as onion, garlic, chicory and chrysanthemum. With the improvement of modern people’s living standard, the food industry is currently facing a considerable challenge to meet the consumers’ requirements for a healthy diet while also satisfying their corresponding nutritional needs.

Inulin has good water solubility, good color, suitable molecular weight, and similar powder properties with flour. Adding inulin to flour increases the content of dietary fiber in the product and also improves the product quality.

Rheological properties and processing performance of dough
Directly influenced by the morphology and distribution of moisture

Rodenlin added short-chain, natural and long-chain inulin to medium gluten flour, and investigated the effect of different polymerization degrees of inulin on the migration behavior of water with different mobility in the dough by differential calorimetric scanner (DSC) and nuclear magnetic resonance (NMR).

The DSC results showed that the water content of tightly bound water showed a positive correlation with the addition of inulin of different polymerization degrees, and the opposite was true for the water content of free and weakly bound water in the dough. And the NMR results showed that water interacted with macromolecules in the dough, in which the water migrated from weakly bound water to free water and tightly bound water.

The free water in the dough is more obviously affected by short-chain inulin and natural inulin, the tightly bound water is mainly affected by long-chain inulin, and all the three polymerization degrees of inulin affect the weakly bound water. Yang Duan found a similar water transfer pattern after adding inulin with different degrees of polymerization to the dough.

In general, with the addition of inulin, the water absorption of the dough decreased, which would significantly prolong the formation time of the dough, improve the stability of the dough, increase the resistance to elongation and viscoelasticity of the dough, and the increase of the gluten and strength of the dough, and the consequent decrease of the kneading resistance index.

Luo Denglin’s group also took the medium gluten flour commonly used in the preparation of steamed bread as the research object, and added the short-chain inulin to the medium gluten flour to study the dough powder characteristics and tensile properties of the dough, and examined the trends of the rheological parameters of the dough. The study showed that the elongation resistance, tensile ratio and tensile energy of the dough increased with the addition of short-chain inulin, and reached the maximum value when the addition amount of short-chain inulin was 7.5%, and the strength of the gluten was enhanced.

The effects of short-chain inulin on the appearance properties
and structural properties and aging process

JuanLiu’s group added short-chain inulin to steamed buns, which is a traditional Chinese staple food, to investigate its effects on the appearance and structural properties of steamed buns and the aging process. It was found that with the addition of inulin, the specific volume, size dimension and sensory tasting scores of steamed buns increased, and when the amount of inulin added was further increased, the above indexes began to decrease again, and the highest scores were obtained when the amount of inulin added was 5%. The authors evaluated the color index of steamed buns by the L*a*b value of colorimeter, and pointed out that the moderate addition of short-chain inulin improved the structural properties of fresh steamed buns, but also accelerated the aging rate of steamed buns.

It was revealed that moisture migration was an important factor affecting the aging rate of steamed buns. This study provides a theoretical basis for the application of inulin in steamed buns, and the steamed buns with the addition of inulin have better functionality and nutritional value.

Luo Denglin used a fermentation rheometer to simulate the fermentation process of dough to study the effect of different added amounts of natural inulin on the fermentation rheology of dough. Based on the results of a one-way test, the authors conducted a response surface center combination design to analyze the effects of different inulin additions and other factors on bread baking quality through weighted composite scores.

It was shown that increasing the addition amount of inulin was beneficial to increase the total air production of dough, reduce the maximum expansion height, and significantly shorten the time for the dough to develop cavities. It was also shown that this may be due to two factors: inulin contains a certain amount of monosaccharides and oligosaccharides, and the addition of inulin diluted the gluten protein content, which hindered the process of forming the gluten network structure and increased the dough resistance to extension.

The results showed that the addition of inulin reduced the hardness of the bread, had no significant effect on the elasticity of the bread, and the specific volume of the bread increased slightly with the increase of the amount of inulin added. The highest sensory evaluation and weighted composite score (94.17) was obtained at 5.0% of inulin addition, and the bread with this amount of addition was soft in texture, good in taste, and the internal stomata were uniform and small.

Effects of different amounts of inulin on the rheology of flour properties and tensile properties
Fan Wenjing also took bread as the research object, and investigated the effects of different added amounts of inulin on the rheological properties of flour flour and tensile properties by using a powder meter and a tensile meter, and evaluated the textural properties of the bread after adding inulin by using a texture meter, and carried out the sensory evaluation.

The results showed that the rheological properties of the flour doughs were improved by the addition of inulin, the consistency was increased, and the formation and stabilization times of the doughs were increased. The tensile curves of the dough, tensile resistance, maximum tensile resistance and tensile ratio increased and then decreased, and did not show a certain increasing trend with the dough elongation. The addition of inulin increased the water holding capacity and decreased the hardness of the bread, and the best overall sensory score of the bread was obtained at an addition level of 6%.

Rheological characterization
Bojnanska et al. investigated the rheological properties of products made with the addition of inulin and wheat flour as the main ingredient. The authors added 5%, 10%, 15%, 20% and 25% of inulin instead of wheat flour and found that the rheological parameters (dough water binding capacity, dough formation time, dough stability, degree of weakening, etc.) were changed.

In particular, low inulin additions (5% and 10%) led to a decrease in dough water-binding capacity, whereas high inulin additions (15% to 25%) led to an increase in dough water-binding capacity. The addition of inulin also prolonged the dough formation time and dough hardness, and it was analyzed that inulin might affect the formation of the gluten network, resulting in the viscoelasticity and strength of the whole dough, as well as the interactions between the gluten.

At the same time, the authors also examined the quality of breads made with different levels of inulin addition and conducted sensory evaluation tests. It was found that the quality of the bread decreased and sensory satisfaction decreased when the amount of inulin added was more than 10%. Breads made with 5% of inulin were highly acceptable in terms of organoleptic quality.

The study indicated that the addition of appropriate percentage of inulin could not change the desired product characteristics and could reasonably control the color and textural quality of the bread, which is an effective method to produce functional wheat flour bread. This is also in general agreement with the findings of Rubelab et al. who used inulin to prepare dietary fiber-rich bread.

Pourfarzad et al. used Fourier transform infrared light to analyze the role of inulin with the main biopolymers inside the matrix in terms of structural organization after the addition of inulin to bread, revealing that the reaction between inulin and gluten proteins had a more significant effect on the dough structure.

Effects of adding inulin on extending the shelf-life of sugar-free shortbread cookies
An accelerated test was conducted by Chongwan Liu to investigate whether the addition of inulin could extend the shelf-life of sugar-free shortbread cookies. The moisture content of sugar-free shortening cookies gradually increased with time, and the higher the temperature, the faster the moisture content increased.

The moisture content of shortbread cookies was significantly inhibited by inulin. The authors added 3% of inulin into the flour and tested the moisture content changes of sugar-free shortbread cookies at different temperatures of 30℃, 40℃ and 50℃, and investigated the shelf-life of the cookies at the respective temperatures, and derived the shelf-life of the cookies under the condition of ambient temperature (25℃, T=298K).

The results showed that the shelf-life of shortbread cookies could be extended from 90 d to 150 d with the addition of 3% inulin. He added different percentages of inulin to the flour to investigate the effects of inulin on the dough’s textural properties, tensile properties, sensory properties, water-holding properties and textural properties. The study showed that the water absorption of the dough decreased significantly with the increasing amount of inulin, the dough formation time and stabilization time were obviously prolonged, and the inulin increased the water-holding capacity of the cookies, which improved the sensory quality and textural properties of shortbread cookies.

Krystyjan et al. used inulin to replace 20% to 50% of the fat in cookies to investigate how this preparation process would change the rheological parameters and structural properties of dough and cookies. It was found that the replacement of 20% fat by inulin did not deteriorate the sensory rating of the cookies and had only a minimal effect on the texture, and that this formulation reduced the fat content of the product accompanied by an increase in the sugar content and a decrease in the calorie value.

In addition, the soluble dietary fiber content increased even though the polyphenol content and activity of the product decreased compared to the blank. In contrast, fat substitution above 20% resulted in excessively hard cookies and a significant reduction in polyphenol content and antioxidant activity.

María investigated the effect of four sources of dietary fiber, including inulin, on the nuclear structure of properties related to the rheology of high-fat, high-sugar cookie doughs. The main results showed that the addition of inulin during the baking process increased the ductility of the dough, thus improving the quality of the cookies and increasing the total dietary fiber content of the cookies.