2024 年 12 巻 p. 249-261
In this review paper, we provide a detailed overview of the influence of starch granule-associated proteins on the physicochemical properties of starch granules from diverse botanical sources. By examining the outcomes of protease treatments and other protein removal methods applied to starches from wheat, rice, corn, and buckwheat, we draw attention to the notable alterations in pasting characteristics, swelling power, crystallinity, and retrogradation tendency. We highlight that protein removal leads to varied functional behaviors and evaluate the possible molecular mechanisms through which these proteins exert their impacts. The review underscores the role of starch granule-associated proteins in determining starch functionality, which has profound implications for food technology and broader industrial applications. This synthesis of current research provides insights into the intricate relationship between starch structure and its functionality.
Starch is among the most abundant biopolymers, primarily synthesized by plants as an energy storage molecule. It is a carbohydrate composed of glucose units connected by glycosidic bonds, organized into two types of molecules: amylose, a linear chain of α-(1,4)-linked D-glucose units, and amylopectin, a highly branched molecule with α-(1,6)-linked branches [1, 2]. These two components vary in proportion depending on the plant species, and strongly affect the physical and chemical properties of starch. In addition to amylose and amylopectin, starch contains several non-starch constituents, such as proteins, lipids, and other compounds. Among these constituents, proteins are the most abundant and notably influence the physicochemical properties of starch.
Starch granule-associated proteins (SGAPs) differ from storage proteins. Storage proteins, which include gluten, gliadin, albumin, and prolamin, for example, are typically involved in nutrient storage and are essential for seed development and germination. Conversely, SGAPs are firmly attached, either on the starch granule surface or within the inner channels of starch granules after starch extraction. SGAPs are categorized based on their location within the granule: surface-associated proteins (SAPs) are present on the outer layers, and internal proteins are located within the granular structure, often being referred to as starch granule-channel proteins [3, 4]. Starch-channel proteins are more straightforward to identify as SGAPs due to their specific location and functional roles. However, the differentiation between storage proteins and SGAPs present on the surface (or SAPs) involves more complexity.
Some author suggested that SAPs are characterized by their lower molecular mass (5–30 kDa) and include proteins like friabilin, which are biologically distinct from storage proteins [5]. In recent studies, many authors have included residue of storage protein as part of SGAPs, referring to them as “starch surface proteins” [6, 7, 8]. This is because the extraction process typically does not completely remove storage proteins, and these residue proteins often adhere to the starch surface after extraction [9]. In this review, the term “starch surface proteins” will refer to both the residues originating from storage proteins and the SAPs. SGAPs have a profound impact on the physicochemical properties of starch [6, 7, 10, 11, 12]. They influence the granule interaction with water, its thermal properties, and its enzymatic digestibility [13]. During starch gelatinization, SGAPs can affect the temperature and enthalpy required to undergo the transition process; these are crucial parameters in food processing [6, 8, 10, 14]. SGAPs influence the pasting behavior of starch, which is important for the texture of cooked starch-based foods [15]. Moreover, SGAPs are associated with the rate and extent of starch retrogradation, which affects the texture and potentially leads to staling of foods [10, 16, 17, 18, 19]. Therefore, understanding the nature of SGAPs and their interaction with starch molecules is important to control starch functionality for specific applications in the food and other industrial sectors.
Removal of surface proteins from starch granules is an important step in studying starch properties because it directly impacts the purity and functionality of starch. Proteins on the starch surface can mask the true characteristics of the starch, complicating the analysis and prediction of its behavior. By eliminating these surficial proteins, researchers can examine the starch in its unadulterated form, leading to a more comprehensive understanding of its properties, such as gelatinization, retrogradation, and digestibility. This knowledge is essential in industries that rely on unique qualities of starch, such as food processing, where starch acts as a thickener and stabilizer, or in the pharmaceutical industry, where it serves as an excipient and drug delivery agent. In essence, the removal of surface proteins allows for a more accurate investigation of starch and its potential uses, fostering innovation and efficiency in starch-based applications.
This review is focused on SGAPs, including surface proteins and channel proteins. Differentiation of these two types of proteins is often challenging because the distinction is not always clear in the literature. Many studies do not explicitly differentiate between proteins associated with the surface of starch granules and those located within the channels of the granules. Therefore, in this review we examine the collective impact of these proteins on starch properties rather than focusing narrowly on their specific locations. The objective of this review is to provide a comprehensive overview of current knowledge on the influence of SGAPs on starch properties and to discuss the effects of different methods of SGAP removal on the thermal behavior and retrogradation tendencies of starch. Through this assessment, we seek to highlight potential strategies to control starch properties in food science and technology, thereby enhancing the quality and functionality of starch-based products.
The protein content in starch extracted from various sources typically ranges from 0.1% to 0.7% by weight depending on the plant source and extraction method [20, 21]. Approximately 0.3% protein content in a well-washed cereal starch sample has been reported [22]. The protein concentration tends to increase with proximity to the surface of the starch granule. Surface proteins are predominantly within the molecular mass range of 5–60 kDa. In contrast, proteins associated with the interior of the starch granules are generally larger, mostly within the range of 60–150 kDa, as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses [3, 4]. The distinct molecular size distributions of surface and internal starch proteins suggest they serve differing roles in starch structure and functionality. Proteomic analysis has revealed that a significant proportion of SGAPs is involved in starch biosynthesis, with predominant functions in polyglucan elongation and granule structure trimming. These proteins are essential for understanding the mechanisms of starch biosynthesis and its coordination with other metabolic pathways, such as amino acid metabolism and glycolysis. For instance, in rice endosperm, proteomic dissection has identified 115 developmentally changed SGAPs, representing 37 unique proteins. Approximately 65% of these proteins exist as isoforms and 39% are directly involved in starch biosynthesis [5, 8]. This finding is indicative of a complex network in which SGAPs not only contribute to starch granule formation but also interact with various metabolic pathways to ensure efficient starch and protein storage. Typically, these enzymes are considered to be granule-channel proteins; however, some are also located on the surface of starch granules [4]. The presence of these enzymes on the starch granule surface can influence the interaction of granules with other molecules, such as water, proteins, and enzymes in the surrounding environment.
Beyond protein size and distribution, certain SGAPs, such as puroindoline and friabilin, are of interest for their role in determining grain hardness. Friabilin, a 15 kDa protein located on the surface of wheat starch granules, can influence the functional properties of starch within food. A soft texture results from a higher abundance of friabilin, whereas a hard texture results from a low abundance of friabilin on the starch grain surface. Therefore, they have considered friabilin as a marker of kernel texture [24]. The influence of friabilin on the hardness of wheat starch has been reconfirmed by multiple studies, including those by Darlington et al. (2000) and Iftikhar & Ali (2017) [25, 26]. This protein is believed to play a critical role in preventing starch granules from adhering to proteins within the wheat endosperm, thereby contributing to a softer endosperm texture. The presence of friabilin can significantly affect the interaction between starch and gluten during food processing, with potential implications for the textural properties of the final product. The tryptophan-rich domain of puroindoline is directly associated with SGAPs of wheat starch, playing important roles in determining hardness and providing antimicrobial activity [27]. Li et al. [28] observed that high-amylose wheat starch contains a higher granular protein content compared with that of the wild type. This observation suggests that variation in amylose content can strongly influence the SGAP composition. Further analysis using mass spectrometry-based proteomics revealed that granule-bound starch synthase (GBSS) is the predominant granular protein in isolated starch materials. Moreover, the GBSS content was reported to increase in tandem with the amylose content.
Most of the SGAPs identified are rich in basic and hydrophobic amino acids, contributing to their strong affinity for the hydrophobic regions of starch molecules [4, 29]. This characteristic underlies the rationale that alterations to SGAPs can significantly impact the functional attributes of starch, such as its solubility, gelatinization temperature, and interaction with other food components. Understanding the composition and distribution of proteins in starch granules is essential for manipulation of starch functional properties in food science and technology applications.
To study the effects of SGAPs on starch properties, the most common approach is to remove SGAPs and compare the treated starch with the untreated sample. The process of SGAP extraction is challenging owing to the strong binding of these proteins to the granule, particularly those embedded deep within the granule structure. The many methods for SGAP removal can be grouped into two basic methods: (1) removal by solvents and (2) removal by protease hydrolysis. The extraction method used can influence the properties of starch under study. This section focuses on the common methods for removing SGAPs and evaluates their effectiveness and impact on the structural integrity and functionality of starch granules.
3.1.1 SGAPs removal by solventsWith regard to SGAPs located on the surface of the granules, which are often of low molecular weight, initial extraction typically utilizes mild chemical solutions, such as NaCl, NaOH, or dilute SDS solutions [10, 13, 14, 30, 31]. These methods are designed to disrupt weak interactions between the proteins and the starch granules without causing excessive damage to the starch structure. However, these approaches often do not achieve complete removal of SGAPs. A higher concentration of SDS (10%) [32, 33] might prove more effective, although this concentration has not been validated for all types of SGAPs because of the potential risks of starch degradation or excessive denaturation of proteins. For internal SGAPs, which have a higher molecular weight, extraction requires more rigorous conditions that facilitate granule swelling. This approach often involves the use of SDS (at concentrations of 1%–2%) and strong reducing agents (e.g., dithiothreitol and 2-mercaptoethanol) in combination with high temperature [13, 34, 35].
3.1.2 SGAPs removal by protease hydrolysisWith regard to SGAPs located on the surface of the granules, which are often of low molecular weight, initial Recent advancements in SGAPs removal procedures include the use of proteinase-K treatments [10, 14, 17], which can degrade a broad range of proteins under various conditions, thereby representing a versatile tool to improve the efficiency of protein extraction from starch granules.
The removal of SGAPs by protease can significantly eliminate the SGAPs with minimizing the damage to starch structure [14, 36, 37]. Proteases specifically target protein structures for degradation, allowing for the selective removal of SGAPs without directly affecting the starch polysaccharide chains. Especially, Ma et al. [10] noticed that this process particularly affects small-granule starches such as oat, quinoa, amaranth, and rice starches as compared with large-granule such as waxy and normal maize starches. Although proteases appear to induce less damage to the starch granules as compared to SDS or alkaline treatment [14, 36, 37], there are still concerns regarding slight contamination of the amylases in protease preparation, which are responsible for degrading starch into sugars. Therefore, performing this treatment at low temperature can inhibit the amylolytic activity of amylase [16, 37] and ensure that the native structure of the starch granules is maintained as much as possible.
3.1.3 Effects of SGAPs removal method on starch propertiesThe types of extraction solutions and proteases strongly influence the starch properties. Table 1 summarizes the varied impacts of different treatment methods on starch properties. Li et al. [31] and Zhang et al. [36] explored the effects of SGAPs on wheat starch; however, their approaches and subsequent findings were notably divergent reflecting the difference in treatment methods. Li et al. employed a 0.2% NaOH treatment to remove SGAPs. Their results revealed an increase in crystallinity and pasting properties of the treated starch. This outcome suggests that the SGAPs were removed or modified, thereby facilitating a more ordered arrangement of starch molecules, which is reflected in the increase in crystallinity. The enhancement in pasting properties could be attributed to the greater water absorption capacity and swelling power of the starch granules. In contrast, Zhang et al. used protease hydrolysis which leads to a significant decrease in the pasting properties and crystalline regions of the starch [14]. This finding implies that SGAP removal through protease hydrolysis compromises the integrity and rigidity of the starch granules, which are less capable of retaining their structure and viscosity upon gelatinization. Tao et al. [18] utilized SDS to remove SGAPs from starch. SDS is a detergent that can solubilize proteins and disrupt non-covalent bonds in molecules. The results revealed an increase in crystallinity and thermal properties following SGAP removal. This finding suggests that the SDS treatment, similar to the NaOH treatment, might lead to changes in the starch granule surface that promote a more ordered molecular alignment, resulting in enhanced crystallinity. The increased crystallinity observed in starch samples treated with SDS could be attributed to the ability of SDS to form inclusion complexes with glucan chains (amylose or amylopectin) [38]. These examples underscore the important influence of treatment methods on the structural and functional properties of starch. Zhang et al. [14] studied the impact of removing surface proteins from starch using two methods separately: SDS treatment and protease treatment. These methods had opposite effects on the viscosity of the treated starches. Although both methods were effective in removing surface proteins, the mechanisms by which they influenced starch properties differed significantly. SDS has been observed to form complexes with amylose that affect starch physicochemical properties [11, 17]. The presence of SDS-amylose complexes suggests that SDS treatment introduces changes other than protein removal, thereby complicating the interpretation of its impact on starch properties. Conversely, protease treatment directly targets and degrades the proteins without forming complexes or introducing additional compounds that might interact with the starch. This approach leads to a decrease in the stability of starch granules, providing a clearer understanding of how the removal of surface proteins alone affects starch behavior. Given this specificity, the results from protease treatment were selected for further analysis and discussion in Zhang’s research [14]. This distinction highlights the importance of selecting appropriate treatment methods based on the specific research objectives and the desired clarity of the results. It is crucial to minimize damage to the starch granules while effectively removing SGAPs. Among various techniques, protease treatment at low temperature is a superior approach owing to its efficiency in removing SGAPs and its ability to preserve the integrity of starch granules [16, 39].
3.2 Effects of SGAPs on starch properties 3.2.1 Effects of SGAPs on starch structureSGAPs contribute to maintenance of the integrity and rigidity of swollen starch granules [21, 40]. This function is crucial during gelatinization, in which starch granules absorb water and swell upon heating. SGAPs act by reinforcing the structure of the granules, preventing them from disintegrating under thermal stress. The surface of starch granules also acts as the primary barrier to various processes, such as granule hydration, enzyme digestion, and chemical interactions with other components. The presence, orientation, and nature of SGAPs and lipids, especially at the granule surface, influence critical properties, such as gelatinization, pasting characteristics, and enzyme resistance. For example, the removal of surface proteins impacts on the swelling properties of starch. Partial removal of these proteins can enhance the rate and extent of granule swelling compared with those of native granules [13, 21, 31, 41, 42, 43]. Israkarn et al. [12] proposed that SGAPs help to preserve the structure of the starch granule, particularly the ghost remnant structure that is redistributed to the granule envelope upon heating in excess water. This protein fraction is considered to maintain the integrity of the envelope, thereby retaining the starch content after heat treatment [12].
3.2.2 Effects of SGAPs on starch structureSGAPs play crucial roles in the starch–water interaction, which is one important factor contributing to starch functionality. It is a critical factor in determining the gelatinization, retrogradation, and pasting properties of starch. These properties are fundamental to understanding how starch behaves under different conditions, such as during cooking or processing. Although the mechanisms by which SGAPs influence these interactions are incompletely understood, researchers have proposed several hypotheses. These include the possibility that SGAPs may affect hydrogen bonding within starch or between starch and water molecules or may influence the microstructure of the starch granules [11, 41, 44, 45]. The modification in water interaction suggests that SGAPs may form a barrier to prevent water penetration or interact with the starch molecules themselves, thereby hindering their organization and crystallization. The impact of SGAPs on the crystalline structure of starch is particularly evident, with an increase in crystallinity being a common outcome after SGAP removal, suggesting that surface proteins may restrict the orderly arrangement of starch molecules. Understanding these mechanisms is important because it assists in predicting and controlling the behavior of starch in food products and other applications.
3.2.3 Effects of SGAPs on thermal propertiesThe changes in thermal properties, such as gelatinization temperature and enthalpy, are also important. Gelatinization enthalpy measures the energy required to disrupt the crystalline structure of starch granules, leading to gelatinization [46]. The changes reported in thermal properties of starch after the removal of surface proteins vary among studies. Some studies indicate that removal of surface proteins promotes starch gelatinization, contributing to a higher degree of crystalline stability and homogeneity after protein removal, which provides structural stability and resistance to gelatinization [14, 16, 18, 31]. Conversely, other studies have noted a decrease in gelatinization temperature and enthalpy following protein removal, particularly via protease hydrolysis, likely due to the resulting instability of starch granules after SGAP removal. Moreover, the presence of proteins may affect the interaction between starch and water. Proteins typically have higher denaturation temperatures than starch gelatinization temperatures, and an increase in the protein proportion in starch-protein blends results in a higher gelatinization temperature. Protein presence may hinder the access of water to starch molecules, weakening starch–water interactions and thus reducing gelatinization enthalpy [17]. The variability among studies in the impact of SGAPs on the thermal properties of starch may be attributed to differences in experimental conditions, treatment methods, and the specific type of starch investigated. Despite these differences, the findings collectively underscore the pronounced influence of SGAPs on the thermal behavior of starch, whether by diminishing or enhancing these properties upon their removal.
3.2.4 Effects of SGAPs on starch digestibilityThe removal of SGAPs not only influences the physical and chemical characteristics of starch, but also significantly impacts its digestibility by altering the accessibility of enzymes to the starch. Yet et al. [47] observed that the absence of either granule-channel proteins alone or total SGAPs leads to significant changes in the contents of rapidly digestible starch, slowly digestible starch, and resistant starch. This effect is considered to be due to changes in the accessibility of amylase to the starch granules and the structural properties of the SGAPs. Ma et al. [13] examined the effects of SGAPs on the rate of starch hydrolysis by amyloglucosidase (AMG) and observed that, following SGAP removal, the rate of AMG hydrolysis increased. This finding suggests that SGAPs may act as inhibitors of AMG by providing binding sites; without SGAPs, the starch is more readily hydrolyzed by AMG, leading to a notable increase in hydrolysis rate. Wang et al. [43] demonstrated that alkali treatment, which removes surface proteins and lipids from starch granules, significantly modifies the functionality and in vitro digestibility of wheat starch granules. These findings underscore the crucial role of SGAPs in serving as a barrier to enzyme access, thereby affecting starch digestibility. In addition, the results highlight that SGAPs interact not only with starch itself but with other components, including starch hydrolytic enzymes. In summary, the semi-crystalline structure of starch granules, which is stabilized by SGAPs, contributes to their resistance to enzymatic attack. Removal of SGAPs can increase the susceptibility of starch to enzymatic hydrolysis, leading to a higher rate of starch digestibility and higher glycemic index of the food. This insight into the role of SGAPs in starch digestibility suggests avenues for modification of starch properties through targeted manipulation of its protein content, with potential applications in nutrition and the development of functional food products.
3.2.5 Effects of SGAPs from different sources on starch propertiesTable 1 summarizes research findings on how SGAP removal from starch of different sources affects the physicochemical properties. The SGAP removal results in a decrease in pasting properties and stability, particularly during shearing, as observed for rice starch [14]. Conversely, wheat starch exhibits an increase in pasting properties following SGAP removal, indicating a distinct differential response possibly due to the varying protein compositions between A- and B-type starch granules (>10 µm and <5 µm in diameter, respectively) [47]. In addition, the swelling power and water solubility of starch granules are altered upon the removal of these proteins, generally leading to an increase in capacity for water uptake, although a decrease in swelling power in rice starch has also been reported. Specific types of starch, such as corn, rice, and buckwheat starches, demonstrate unique changes upon SGAP removal. For instance, protease treatment of corn and rice starches retards short-term retrogradation and decreases retrogradation enthalpy, suggesting surface proteins play an important role in maintaining the granular structure during thermal processing. The mechanisms behind these effects, although not fully elucidated, point to SGAPs forming a structural barrier, interfering with molecular interactions, and providing resistance to enzymatic hydrolysis, ultimately contributing to the integrity and stability of starch granules. The differential effects observed among various starch sources underscore the complexity of SGAP–starch interactions and warrant further investigation to fully understand the underlying molecular dynamics and their implications for starch utilization in food and industrial applications.
| Starch source | SGAP removal method | Change in properties | Reference |
|---|---|---|---|
| Wheat starch | SDS 1% NaOH 0.2% |
Increased crystallinity Increased retrogradation Increased gel firmness (SDS) |
[18] |
| Wheat starch | Protease | Decreased pasting viscosity No change in thermal properties Increased crystalline region |
[14] |
| SDS 2% and mercaptoethanol 2% | Increased pasting viscosity Increased thermal properties Increased crystalline region |
||
| Wheat starch (Normal and waxy wheat) | NaOH 0.2% | Increased crystallinity, swelling power and syneresis Changed in pasting properties (increased the peak, setback, final, breakdown viscosity; decreased the pasting temperature, peak time and trough viscosity) Changed in thermal properties (increased in temperatures; decreased in enthalpy) |
[31] |
| Buckwheat starch | Protease treatment | Decreased gel strength Reduced density of starch aggregate Decreased retrogradation |
[17] |
| Rice starch | SDS 2% | Decreased pasting properties No changes in thermal properties Increased swelling power |
[41] |
| Rice starch | SDS 1.5% and mercaptoethanol 2% | Decreased pasting properties Changed in thermal properties (decreased gelatinization temperature, no change in gelatinization enthalpy) Reduced stability of starch granules Increased amylose leaching, swelling power, solubility |
[6] |
| Corn and rice starch | Protease treatment | Decreased pasting viscosity Increased relative crystallinity No significant changes in thermal properties Retarded short-term retrogradation |
[7] |
| Maize starches (Normal and waxy maize) |
SDS 1.5% and mercaptoethanol 2% | Increased pasting viscosity No change in relative crystallinity Increased rapidly digestible starch Reduced resistant starch |
[35] |
Many studies have reported that the removal of SGAPs significantly impacts on retrogradation, with outcomes varying between reduced and increased retrogradation rates [10, 16, 17, 18, 19]. This variability suggests that SGAPs play a critical role in modulating starch interactions during gelatinization and cooling, which in turn influences the retrogradation behavior of starch. Retrogradation, a process whereby gelatinized starch molecules gradually reassociate or recrystallize upon cooling, affects the textural qualities of starch-based foods [48]. Bae et al. [16] reported that SGAP removal from rice and corn starches could slow down long-term retrogradation. Proteins (with a water affinity more than two-fold higher than starch in cereal crops) promote more frequent contact between starch molecules owing to their higher water-holding capacity, thereby facilitating starch retrogradation. Consequently, the observed reduction in retrogradation likely results from diminished starch interactions after SGAP removal. Conversely, Ma et al.[13]discovered that removal of SGAPs promoted recrystallization of starch molecules and facilitated retrogradation, resulting in starch gels with higher hardness than that of native starches. Tao et al. [18] reported similar findings, indicating that SGAP removal from wheat starch accelerates retrogradation, evidenced by increases in storage modulus and setback viscosity. These divergent results could be due to differences in protein content and composition among starch sources. Du et al. [17] reported that SGAP presence influences the water distribution within starch gels by low-field nuclear magnetic resonance, suggesting that these proteins may create a microenvironment that restricts water movement and thus alters the recrystallization of starch molecules. This is crucial in food systems in which moisture migration can lead to textural degradation over time. The structural implications of SGAPs on starch retrogradation are also important. SGAPs contribute to the formation of denser and more uniform gel networks; upon SGAP removal, the gel structure becomes looser and less uniform, which correlates with a decrease in gel strength and density. This morphological change supports the hypothesis that SGAPs enhance the physical interactions between starch molecules, promoting a more stable network that resists the syneresis (water expulsion) commonly observed in aged starch gels [17, 49].
The effects of SGAPs on starch retrogradation are multifaceted and involve a variety of interactions at the molecular level, which can be summarized as the following mechanisms:
These mechanisms highlight the complex roles that SGAPs play in starch retrogradation, which has pronounced implications for the texture and quality of starch-containing foods during storage.
The role of SGAPs in starch functionality is of considerable interest because of the implications for food texture, stability, and nutrition. SGAPs influence the physicochemical properties of starch, which in turn affects the quality of starch-based food products. For example, the removal of surface proteins from starch markedly alters its physicochemical and structural properties, such as gelatinization and pasting properties, which are critical in the processing of foods such as bread and noodles. Surface proteins, which are often dominated by storage proteins in cereals, can differ in molecular weights and are located on the surface and within starch granules, affecting the interaction of starch with other ingredients in a food matrix [31]. The impact of starch and starch-associated proteins on wheat grain quality has been extensively reviewed, highlighting how these components influence the functional properties of food systems. The interactions between starch and its associated proteins can drive starch responses in complex dough systems, affecting the dough behavior during processing and differentially impacting the product qualities [31, 51, 52]. In addition, the surface localization of storage proteins in starch granules has been studied to understand their role in the integrity of starch granules and their subsequent behavior during food processing [53]. Knowledge of SGAPs provides insights into how manipulation of SGAPs can be used to develop new food products with desired qualities or to improve the processing and nutritional quality of existing products. SGAPs can affect the texture, stability, and shelf life of starch-based foods, which are critical parameters in food quality and consumer acceptance. For instance, understanding how SGAPs influence starch retrogradation can assist in improvement of the storage conditions for starchy foods, as retrogradation affects the palatability and texture of products such as bread and cooked rice over time. By manipulating SGAP concentrations, food scientists could potentially control the rate of retrogradation, leading to products with a prolonged desirable texture and taste. Moreover, the role of SGAPs in the interaction between starch and water can be leveraged to create foods with specific hydration properties. This is particularly relevant in the production of instant foods, where the rehydration rate is a crucial factor that determines product quality and acceptance. Appropriate adjustment and modification of SGAPs may enable optimization of the rehydration process, ensuring that instant foods have the right texture and consistency when prepared. In addition, the encapsulation capabilities of starch, as influenced by SGAPs, can be utilized to create functional foods with encapsulated health-promoting compounds. These could be designed to release their contents at specific points in the digestive system, enhancing the bioavailability and effectiveness of nutrients and pharmaceuticals. With regard to food packaging, starch-based films with modified SGAPs could lead to improved mechanical and barrier properties, improving their capability for protection of food products from environmental factors, thereby extending the shelf life of the product.
5.2 Future prospectsThe study of SGAPs has been advanced with the application of mass spectrometry and high-performance liquid chromatography. However, detailed information on the amino acid composition of SGAPs remains limited. The sequence and composition of amino acids are crucial because they may play an important role in determining the properties and interactions of SGAPs within starch-based systems. Understanding these interactions could enable greater precision in the control and modification of starch behavior. Moreover, the mechanism by which SGAPs affect starch properties has not been definitively elucidated. Most studies have focused on comparisons with natural starch following SGAP removal. Incorporation of protein on the starch surface is an intriguing method with potential to confirm and explore the function of SGAPs on starch granules. In addition, the interaction between starch and water is a crucial factor in starch functionality, but the mechanisms remain to be resolved. Further research on this topic could provide valuable insights into starch–water interaction at the molecular level, facilitating the design of starch-based materials with customized properties for specific applications. The field of starch research is vibrant and continues to grow, with potential implications extending beyond the food industry to include material sciences. The development of innovative starch-based materials could lead to new applications in biodegradable products and pharmaceuticals, for example. Future starch research holds considerable promise to contribute to technological advancements and an improved understanding of biopolymer interactions.
This review emphasizes the impact of SGAPs on the functional properties of starch from different cereal sources. The removal of these proteins by extraction with chemical solutions, such as NaOH or SDS, often leads to enhanced crystallinity and varied effects on pasting and swelling behaviors, indicating their role in restricting granular water uptake and molecular organization. The use of proteases for SGAPs removal has considerable advantages over chemical extraction methods, particularly in preserving the structural integrity of the starch granules. The alteration of retrogradation processes upon protein removal signifies the potential of protein in stabilizing the starch matrix. Although the specific mechanisms through which these proteins influence starch properties are intricate and incompletely understood, it is apparent that SGAPs play an essential role in the functional behavior of starches. The insights gained from this review will help to improve starch modification techniques and customize starch functionalities for specific industrial applications. Consequently, the manipulation of starch surface-associated proteins is a pivotal area of research into enhancing the quality of starch-based products.
We thank Robert McKenzie, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.
