Changes in the structural and physicochemical characterization of pea starch modified by Bacillus-produced α-amylase

Peas (Pisum sativum L.) are widely grown in temperate regions of the world and are the world's leading export crop, accounting for around 35–40% of the total trade in pulses (Ratnayake, Hoover, Shahidi, Perera, & Jane, 2001). Peas are now gaining more and more recognition due to their richness in starch, protein, resistant starch, dietary fiber and minerals (Zhou, Ma, Yin, Hu, & Boye, 2019). Traditionally, pea is consumed as dried seeds or as a fresh vegetable, the dried seeds are mainly applied in soups and are increasingly being processed into value-added food ingredients (Ren, Setia, Warkentin, & Ai, 2020). Pea flour has unique aromatic profiles and desirable functional properties and is often processed through milling, making it suitable for use in a variety of foods, including baked goods, noodles and meat products (Gu et al., 2021). Pea starch, accounting for about 40–50% of the seed, is the most abundant carbohydrate in pea seeds. The amylose content of pea starch is in the range of 30–60% with varying varieties and is considered to be an important factor determining the pea quality (Hoover, Hughes, Chung, & Liu, 2010). Compared to potato, wheat and maize starch, pea starch is considered as an inexpensive source of starch (Zhou et al., 2019). Industrially, starches obtained from maize, potato, cassava and wheat are almost exclusively natural and modified. Nowadays, starches isolated from peas are widely used in industry due to their unique properties such as extent of digestion, high resistant starch content as well as high elasticity of gels (Sun, Sun, & Xiong, 2014), making them suitable substitutes to modified starches in a range of products (Raphaelides & Georgiadis, 2008).

Native starches are not entirely applied in the food industry due to their poor water solubility and heat stability, which cannot meet the requirements of specific applications (Cui et al., 2023). Therefore, native starches are often modified by chemical, physical or enzymatic methods to improve their industrial applications. Compared to chemical and physical methods, the enzymatic approach has the advantages of simple operation, high reaction efficiency and high yield, which is conductive to meeting the requirements and suitability of food products. It has also been reported that enzymatic modification can effectively improve the utilization of the native starch (Chen et al., 2021). Alpha-amylase is a commonly used enzyme that usually cleaves the α-1, 4-glycosidic bond of amylose or amylopectin in the internal position to obtain a product with an α-configuration (Lin et al., 2016). Previous studies have shown that the modification of starch with α-amylase is effective in improving the structural and physicochemical properties of starch. Shariffa, Karim, Fazilah, and Zaidul (2009) have reported that sweet potato starch was higher in amylose content, water solubility and swelling power after fungal-produced α-amylase hydrolysis. Similarly, corn starch hydrolyzed by α-amylase had higher amylose content, longer amylopectin chains along with smaller granules (Song et al., 2020). When treated with maltogenic α-amylase, the molecular weight of rice starch was significantly reduced, while significant increase was observed in the short-chain levels (DP < 13) (Wang et al., 2022). Compared to fungal sources of α-amylase, the Bacillus-produced α-amylase has greater thermal stability and pH tolerance (Martínez, Ramírez, & Valle, 1997), making it more suitable for certain industrial applications, such as starch liquefaction or baking. Additionally, Bacillus strains are less susceptible to contamination and are highly capable of producing thermostable α-amylase (Schwab et al., 2009). The modified cereal starches have unique physicochemical properties and specially applications. However, previous studies have mainly focused on the modification of potato and maize starch by α-amylase, while few reports have been studied on the modification of pea starch by Bacillus-produced α-amylase, especially regarding the changes in structural, physicochemical and rheological properties, which limits the application of modified pea starch in the food industry. Therefore, there is a need to explore potential applications of pea starch modification based on α-amylase produced by Bacillus.

In this study, three pea varieties with different amylose content were used to investigate the effects of Bacillus-produced α-amylase on the particle size distribution, amylopectin chain length distribution, branching degree, crystalline structure, short-ranged ordered structure, light transmittance, water and oil absorption capacity, pasting and thermal properties of the native pea starch. The changes in structural, physicochemical and rheological properties of the modified pea starch and its applications were then further explored by comparing with the native pea starch. The purpose of this research was to provide a theoretical basis for the development of the modified starch and widen the applications of pea starch modified by Bacillus-produced α-amylase in the food industry.

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