Water absorption, water solubility and swelling power
The water absorption, swelling power, and solubility of the samples were tested at two temperatures: 30°C and 85°C, to preliminarily determine the impact of protein addition on the product manufacturing process. Adding protein increased the water absorption, solubility, and swelling power at 30°C. The results for water absorption, water solubility, and swelling power of rice flour and isolated protein are presented in Figs. 1 and 2 at 30°C and 85°C, respectively. As the reaction temperature increased, water absorption, water solubility, and swelling power also increased. Soy protein had higher water absorption, water solubility, and swelling power than pea and rice protein at 30°C, being 1.8 times higher than pea protein and 2.9 times higher than rice protein. When added to rice flour, soy protein resulted in the highest solubility and swelling power, while rice protein had the lowest at 30°C. Compared to isolated soy protein, the addition of soy protein to rice flour showed a higher increase, while pea protein and rice protein showed a decrease. Soy protein had a higher water absorption capacity than rice protein. Soybean protein had higher water absorption capacity than rice and pea protein, which was 1.5 times that of pea protein and three times that of rice.38
Adding rice protein to rice flour showed lower water absorption index and swelling power in comparison to pasta with soy and pea protein. The swelling power was corrected with amylose, amylopectin and lipid, the polysaccharide which leached out from the damaged starch has a more efficient effect on starch swelling.40, 41 The results showed that the addition of soy protein had a greater effect than rice and pea protein on the absorption, solubility, and swelling power at 85°C. On the other hand, rice protein increased all the parameters on rice flour in 85°C hot water. Rice protein had a lower water absorption index and swelling power than rice flour, pea protein, and soy protein. The water holding capacity of rice was 2.81 and 3.02; while these were lower than soy protein, they were higher than viscous food. Hence rice protein could be used to make required high water retention products.42 Solubility of protein was affected by pH value because of the different isoelectric points; for example from pH 6–7, the solubility of plant protein in descending order was soybean, pea and rice protein.38 WSI increased with temperature for starch; swelling power was related to the viscoelastic properties of starch solution as well as correlated with the eating quality of noodles.43 By testing the viscosity of different starches under the same concentration, heating conditions and stirring speed, the results showed that the viscosity of each starch after stirring and heating showed significant differences.44 These differences in viscosity indicated a relationship to the colloidal properties of starch. The change of the colloidal properties of the material requires a specific heating method to initiate change. Until the heating of the starch solution, water was absorbed into starch granules at room temperature and the starch started to swell. After increasing the temperature to the gelatinization temperature, the swelling becomes irreversible.45
The RVA profile
The texture and pasting characters of rice flour were affected by several parameters; using measure pasting analysis was an easier and less costly method for classifying rice. 46 The RVA test was conducted after adding 10% protein to rice flour. The results are presented in Fig. 3. It was observed that the addition of protein had an impact on the viscosity and gelatinization performance of rice flour, resulting in a decrease in peak, trough, final viscosity, and setback viscosity. Adding pea protein only led to a decrease in breakdown viscosity and pasting temperature, while soy protein had the opposite effect. The results also showed that adding rice protein to rice flour led to an increase in pasting temperature and a significant reduction in peak viscosity, trough, final viscosity, and setback during gelatinization.
Increasing the amount of rice protein in rice flour increased the pasting temperature. Rice protein restricts the diffusion of water into the starch granules, causing a delay in the pasting temperature.47 In a report using rapid viscosity analysis, it was found that pasting temperature and setback were negatively correlated with RDS, and positively correlated with SDS and RS.48 Adding pea protein can change the pasting temperature of rice flour during the heating and cooling periods due to its higher thermal transition temperature.49 Adding soybean flour to replace rice flour would decrease all pasting properties because the amylose and amylopectin content cause a dilution effect.50 RDS was found to be negatively correlated with pasting temperature, setback, and final viscosity, but positively correlated with SDS and RS (Chung et al., 2011). The cell structure of ingredients with intact botanical or physical structures, including viscous dietary fiber or amylose-amylopectin, can cause a restriction of starch swelling and reduce the digestion rate (Bjorck et al., 1994). RDS were negatively correlated with pasting temperature, setback and final viscosity but positively correlated with SDS and RS 48. Cell structure causes restriction of starch swelling and reduce digestion rate. The cell structure of ingredients with an intact botanical or physical structure, including viscous dietary fiber or amylose-amylopectin, can cause a restriction of starch swelling and reduce the digestion rate.18 Protein can affect the characteristics of rice flour, especially its gel-forming properties, depending on whether it is high-molecular or low-molecular polypeptide. Additionally, protein in rice flour can change the water absorption of starch granules and the hardness of rice gel.51
Protein affects rice flour characteristics; especially gel-forming property was its high-molecular polypeptide instead of low-molecular one. In addition, protein in rice flour changed starch granule water absorption and hardness of rice gel.51 Adding denatured pea protein led to a lower degree of gelatinization and greater binding of protein to the starch matrix 39 & Forde, 2019. Pea protein has higher solubility than rice flour; in addition, blending pea and rice decreased the intensity to a greater extent of. Pea protein hindered rice protein structure or increased aggregation inducing enzyme activity to be reduced.52 Soybean protein had more larger protein subunits in the size range of 50–500 kDa, and free sulfhydryl groups decreased upon increasing temperature that affected water absorption and viscosity.53 Rice protein exhibited lower breakdown and final viscosity perhaps affected by higher solubility and lower swelling power. A greater degree of breakdown led to lower retrogradation because of its lower final viscosity.54
Table 3
Texture characters and cooking properties of cooked rice pasta
Pasta
|
Texture characters
|
Cooking properties
|
Hardness(g)
|
Tensile Strength(g)
|
Elasticity (mm)
|
loss (%)
|
yield (%)
|
RFN
|
334.5 ± 35.3 a
|
28.9 ± 3.0 a
|
18.4 ± 2.4 a
|
5.56 ± 0.25 d
|
100.53 ± 3.24 b
|
SPN
|
86.5 ± 9.1 c
|
-
|
-
|
7.46 ± 0.51 c
|
114.43 ± 0.68 a
|
PPN
|
181.4 ± 12.8 b
|
23.0 ± 2.0 b
|
12.3 ± 2.0 b
|
10.54 ± 0.07 b
|
89.77 ± 0.94 c
|
RPN
|
53.8 ± 5.8 d
|
13.2 ± 0 c
|
11.8 ± 0.1 b
|
16.36 ± 0.84 a
|
87.25 ± 2.13 d
|
The texture of cooked rice pasta was measured using a texture analyzer and the results are presented in Table 3. When comparing the texture of cooked rice flour pasta to those with added isolated protein, the pasta made with rice flour alone was found to be the hardest, while the addition of isolated protein led to reduced tensile strength and elasticity. The impact on texture was less pronounced when using pea protein compared to rice and soy protein. Additionally, soy protein pasta had a lower cooking loss and higher cooking yield compared to pea and rice protein pasta. The addition of rice protein to rice flour led to an increase in cooking loss. Despite having better cooking properties, soy protein pasta began to break after being cooked for more than 6 min.
Adding 10% plant protein to make rice pasta was similar to regular pasta making; the water adding and process wouldn’t be changed. Adding protein would change pasta color because of the original protein color, and soy protein pasta had dark color between all samples. After cooking, the color was still darker than that of the rice flour pasta. The substitution of rice flour with defatted soybean flour would increase cooking loss while the cooking yield was reduced. 50 Not only do the main methods of making noodles differ, including sheets and extrusion, but also the material is different. Besides the flour could affect noodle texture, color and cooking properties.55 Adding rice flour which was not treated to make pasta was related to changing the amylopectin fraction; the interior structural had changed affecting the final product quality. 56 Materials, ingredients, processing, and method were the critical points to making pasta, not only affecting quality but also starch hydrolysis. Adding fiber or resistant starch was one way, and changing method was the another. Gluten free pasta for consumers is more popular in the world using corn flour, rice flour or pseudo-cereals by replacing durum or wheat flour. For suitable eating quality and higher fiber content, ingredients and novel processing have been developed. 7, 57–59
Table 4
RDS, SDS. RS and estimated GI of cooked rice pasta
|
RFN
|
PPN
|
SPN
|
RPN
|
RDS
|
70.35 ± 2.3 b
|
81.06 ± 1.47 a
|
71.62 ± 1.73 b
|
72.08 ± 0.8 b
|
SDS
|
22.46 ± 3.37a
|
2.07 ± 1.25d
|
7.27 ± 1.29c
|
10.91 ± 0.26 b
|
TDS
|
91.58 ± 2.3a
|
83.31 ± 1.45 b
|
78.20 ± 0.93 c
|
82.02 ± 0.91 b
|
RS
|
0.56 ± 0.1a
|
0.38 ± 0.01b
|
0.53 ± 0.03 a
|
0.51 ± 0.07 a
|
eGI
|
85.43 a
|
75.48 b
|
82.03 a
|
83.80 a
|
(RFP: Rice flour pasta, SPN: soybean protein within rice flour pasta, PPN: pea protein within rice flour pasta. RDS: rapid digestible starch, SDS: slowly digestible starch, TDS: total digestible starch, RS: resistant starch, eGI: estimated glycemic index) |
Rice flour exhibited higher levels of total starch, slowly digestible starch, and total starch content. When blended with soy protein, the resulting rice pasta had a lower slowly digestible starch (SDS) content than 100% rice flour, indicating that adding soy protein did not increase SDS. However, the addition of pea protein resulted in a significantly higher resistant starch (RS) content compared to rice pasta made with 100% rice flour, while the addition of soy and rice protein resulted in lower RS content. Despite the fact that adding the same amount of plant protein to rice flour resulted in the same amylose dilution ratio, the starch hydrolysis was not the same. The addition of isolate protein to rice flour resulted in a decrease in SDS of rice pasta, but RDS and RS varied depending on the type of protein used. The addition of soy protein to rice pasta led to lower RS, while pea protein rice pasta had higher RS.
Protein played an important role in starch digestibility as well as its restrict enzyme hydrolysis. During cooking, furthermore, starch-protein interaction cause flour in a slowly digestible state 60. RS content and starch hydrolysis were not only affected by amylose, but also other characteristics; protein and starch resource showed a wider range between estimated glycemic index.61, 62 Protein isolation resistant to pepsin or the in vitro gastric stage differed from protein fraction; in pea protein, both albumin and globulin fractions underwent hydrolysis in proteolysis and subsequent intestinal digestion, while rice protein were resistant to pepsin hydrolysis because its prolamin was undigested.63 eGI of rice pasta was similar to rice pasta and rice flour with soybean. Starch hydrolysis was more than 85% after 30 min hydrolysis, leading to higher eGI (Fig. 4). The way food is processed, such as through heat treatment or blending time, can affect starch digestibility and the glycemic response by changing the starch-protein interaction and contact surface area. 64 Cooking legume seeds can change their starch structure, resulting in lower SDS and RS compared to raw seeds. 65, 66 In comparing starch hydrolysis content only using pepsin at KCl-HCl (pH 1.5) without adding amylase to the reaction, the starch hydrolysis was more than 55%.
Table 5
Correction of RDS, SDS, RS and protein
|
RDS
|
SDS
|
TDS
|
RS
|
Protein
|
RDS
|
1
|
|
|
|
|
SDS
|
-0.6308
|
1
|
|
|
|
TDS
|
-0.1997
|
0.8709
|
1
|
|
|
RS
|
-0.9708
|
0.6088
|
0.2365
|
1
|
|
Protein
|
0.2577
|
-0.9072
|
-0.9949
|
-0.2729
|
1
|
Although the research showed that total starch was not correlated to protein67, our results show that it was negatively correlated with total digestible starch and slowly digestible starch, while resistant starch was negative correctly with rapid digestible starch; however, total digestibility was positive with slowly digestible starch. In other words, protein and resistant starch significantly affected starch digestibility. Starch digestibility was restricted by peptides after protease hydrolyzing soy protein through retard starch swelling and gelatinization, further reducing starch digestibility.68
Resistant starch was negative correlated with GI and HI; research also showed soluble starch synthase21 increasing resistant starch, which would require granule bound starch synthase to regulate RS and amylose content in rice grain predominately altering starch composition. Starch was pre-treated with pepsin or without, following by treatment with human saliva -amylase, the ratios with or without pepsin were 1.5 ~ 1.8, similar to our result (1.7); the research indicated that this was due to their starch granule hardness.69 Amino acid inhibited amylase inhibition from porcine pancreatin through a physical barrier between the enzyme and starch. Amino acid retarded the digestible rate and enhanced the order of starch structure. 70 Starch digestibility was suppressed by two α-amylases: native and pepsin hydrolyzed protein by increasing the molecular orders of starch, while pepsin pancreatin hydrolyzed protein migrated starch digestibility via increasing V-type structures.71
Our result showed rice protein restricted α-amylase activity; however, pea and soybean increased α-amylase activity. Plant isolation protein apparently would not undergo α-glucosidase inhibition; inspecting pea protein showed higher inhibition of α-Glucosidase from Saccharomyces cerevisiae. Soybean and pea protein obtained small sequence peptide with α-glucosidase-inhibitory activity.72–74