(Cavendish Banana-Musa paradisiaca L.)
Mai Vu Hoang Giang, Truong Thi Chien, Dao Ngoc Anh, Do Thi Kim Trang, Tran Binh Minh, Vu Xuan Tao*
Center for Experimental Biology, National Center for Technological Progress, Ministry of Science and Technology
ABSTRACT
Banana is commonly grown in Vietnam for its nutritious fruit. Bananas have a high starch content, especially containing a lot of naturally resistant starch. Currently, the demand for resistant starch is increasing and the positive effects of this flour source on health have been proven. Research on creating resistant starch from bananas is very necessary, contributing to improving the value of bananas. This study has determined that the appropriate harvesting age for bananas to create resistant starch is 90 days from flowering. The appropriate catalyst for the denaturation process to create resistant starch is citric acid and the appropriate temperature is 70°C. The resistant starch content obtained after the modification process is 56.4%, 38.5% higher than the amount of resistant starch in banana starch before modification (40.7%). Furthermore, the banana resistant starch material obtained in this study had stable quality during 6 months of storage at 20°C. This is a potential source of resistant starch raw materials for the development of dietary products.
INTRODUCTION
According to FAO, bananas are the second most produced fruit globally, following citrus, accounting for approximately 16% of total world fruit production . India is the largest producer, contributing 27% of global output (FAO, 2009). The leading exporting countries include Ecuador, Colombia, Philippines, and Costa Rica. Bananas are exceptionally rich in phenolic and flavonoid compounds, which possess potent antioxidant properties. Green bananas are high in carbohydrates, with content ranging from 60% to 80%, including cellulose, hemicellulose, lignin, starch, dietary fiber, and resistant starch (RS). Due to their high starch content, which gradually converts into sugar during ripening, green bananas are considered a primary raw material source for resistant starch. Currently, interest in green banana starch production is surging because of its high nutritional value, specifically its significant levels of resistant starch, fiber, and bioactive compounds such as phenolic acids (Zhang et al., 2005).
Resistant starch is a type of starch that escapes digestion as it passes through the small intestine. It is not hydrolyzed into D-glucose within 120 minutes of ingestion but instead ferments in the colon. Numerous studies indicate that resistant starch is a linear molecule containing α-1,4-D-glucan, converted from retrograded amylose, with a relatively low molecular weight (1,2 x 105 Da). Currently, resistant starch is classified into five groups: RS1, RS2, RS3, RS4, and RS5 (Sajilata et al., 2006; Gutierrez & Tovar, 2021).
- RS1: Starch in this group is synthesized within the endosperm of cereal grains and is physically encased by protein matrices and cell walls. These physical structures limit the digestibility of RS1 starch.
- RS2: This group consists of starches with B-type or C-type crystalline structures, which are highly resistant to enzymatic hydrolysis. However, after processing, most of these starches undergo gelatinization, losing their B and C-type crystals and becoming easily digestible.
- RS3: This resistant starch group is formed through the retrogradation of starch after it has been cooked and then cooled. RS3 is considered highly stable against high temperatures and other processing agents.
- RS4: This is a group of resistant starches obtained through chemical modification. This type of RS is structurally diverse and does not occur naturally. RS4 includes chemically modified starches that have undergone etherification or esterification to reduce digestibility. The soluble polysaccharide form, known as resistant maltodextrin, is also classified as resistant starch.
- RS5: Formed when starch interacts with lipids; amylose and amylopectin create single-helical complexes with fatty acids, resulting in RS5 starch.
Among the various types of resistant starch, the RS3 group is considered the most significant due to its thermal stability and its wide application in the food industry. RS3 is not naturally available and is only obtained through processing (Haralampu, 2000). The consumption of resistant starch has positive impacts on gut health, blood sugar balance, lipid metabolism, and body weight management. Physically, resistant starch possesses properties equivalent to regular starch, leading to its widespread application in the food processing industry. Globally, several studies have focused on reducing the hydrolysis of starch into glucose using substances containing carboxyl groups (-C=O). The hydroxyl groups (-OH) of the starch molecules bind with molecules containing carboxyl groups (-C=O), such as citric acid, through esterification. This process transforms easily hydrolyzable starch into slowly digestible starch or resistant starch (Reddy et al., 2010; Dupuis et al., 2014).
Given the potential applications of resistant starch, researching conversion technologies to increase RS content in food raw materials is a necessary and scientifically significant task. Various technologies have been applied to increase RS content, such as the hydrothermal treatment of jackfruit seed starch (Ho Thi Hao et al., 2024). In this study, we utilize acid and thermal modification methods to enhance the resistant starch content in Red-tipped Cavendish banana starch. This RS-rich banana starch serves as a high-quality raw material for developing dietary products.
MATERIALS AND METHODS
Materials
Red-tipped Cavendish bananas were harvested from Khoai Chau district, Hung Yen province. The experimental subjects consisted of green bananas aged 80-100 days from the date of flowering. All chemicals used in this study were purchased from Sigma-Aldrich, Merck, and Biobasic, and were utilized according to the manufacturers' instructions.
Methods
Starch Content Determination Method
The starch content was determined following the TCVN 12382:2018 standard. A 1g test sample was placed in a 100 mL volumetric flask with 70 mL of warm water. After dissolution, 50 µL of heat-stable alpha-amylase was added, and the mixture was heated in a water bath at 90°C for 30 minutes. The sample was quickly cooled to 60°C in a water bath, and 5 mL of amyloglucosidase solution was added. Subsequently, the sample was cooled to room temperature, diluted to volume (100 mL), homogenized, and filtered through a 0.45 µm membrane. The extract was analyzed using an HPLC system (Shimadzu, Japan) comprising an LC-20AD pump, an SPD-20A UV detector, and an SIL-20A HT autosampler. The system utilized an Agilent C18 column (250 x 4.6 mm, 5 µm particle size). The mobile phase consisted of water and acetonitrile. The UV detector was set at 200 nm, with an injection volume of 10 µL.
Banana Starch Modification Process
The banana starch modification was performed according to Waliszewski (2003) with laboratory-specific modifications. Green bananas were washed, drained, and peeled. The pulp was sliced into thin pieces, washed, and soaked in a 0.5% NaHSO3 solution at a 1:2 (w/v) ratio at 40°C for 30 minutes. The mixture was then pureed using a specialized blender at 10,000 rpm and washed three times with an acid catalyst at a 1:2 (w/v) ratio. The filtrate was cooled at 8°C for 24 hours, and the starch was collected via decantation. The starch was dried at the appropriate temperature for 6 hours, finely ground, and filtered through a 200-mesh sieve (Waliszewski et al., 2003).
Determination of Optimal Conditions for Resistant Starch Formation
To identify the optimal conditions for forming resistant starch during the modification process, the study evaluated the impact of catalysts and modification temperatures on the final resistant starch (RS) content. Factors investigated included: catalysts (citric acid, lactic acid, and acetic acid) at a 2.5% concentration and modification temperatures (60, 70, and 80°C).
Resistant Starch Content Determination Method
The RS content was determined following the procedure by Hung et al. (2013): 1g of banana starch was mixed with 25 mL of acetate buffer (pH 6.0) and boiled in a water bath for 30 minutes. The suspension was treated with amylase enzyme (7,000 U/g starch) at 37°C for 2 hours, followed by treatment with amyloglucosidase enzyme (50 U/g starch) at 60°C for 30 minutes. The mixture was centrifuged at 1,500 rpm for 15 minutes. The residue was washed three times with distilled water and dried at 50°C for 48 hours. The resistant starch content (%) was calculated based on the weight of the recovered residue (on a dry weight basis) relative to the initial sample weight (Hung et al., 2013).
Data Processing Method
Research results were processed using biostatistical methods on Microsoft Excel 2016 software.
RESULTS AND DISCUSSION
Evaluation of Starch Content in Red-tipped Cavendish Bananas at Different Maturity Stages
Maturity (harvest age) is a crucial factor affecting the starch content in bananas. According to research by Le Van Trong and Nguyen Nhu Khanh (2021), the starch content in "Chuối Tây" (Musa paradisiaca L.) reaches its peak at 14 weeks of age. In subsequent stages, intensive metabolism occurs within the fruit, particularly respiration; consequently, starch is consumed more rapidly, leading to a gradual decrease in content as the fruit ripens. The variation in starch content aligns with fluctuations in $alpha$-amylase activity, which catalyzes the conversion of starch into sugar (Le Van Trong and Nguyen Nhu Khanh, 2021). Therefore, to select banana samples with the highest starch content, this study evaluated the starch levels in Red-tipped Cavendish bananas at different harvest intervals (80, 90, and 100 days).
The research results indicated that the starch content increased from 60.5% (at 80 days) to 66.7% (at 90 days), but then declined to 63.4% (at 100 days) (Figure 1). This suggests that Red-tipped Cavendish bananas harvested at 90 days yield the highest starch content. These findings are consistent with previous research by Nguyen Thi Quynh Mai et al. (2020) regarding the harvest maturity of Laba bananas (at 3 months of age). Consequently, 90-day-old green Red-tipped Cavendish bananas were selected for subsequent experiments.
Figure 1. Starch content in Red-tipped Cavendish bananas at different maturity stages
(A) Red-tipped Cavendish banana samples at different ages, (B) Starch content in Red-tipped Cavendish banana samples. Different letters above the bars indicate statistically significant differences (p < 0.05).
Determination of Optimal Conditions for Banana Starch Modification to Produce Resistant Starch
To obtain banana starch with high resistant starch content, the study evaluated the effects of catalysts and drying temperatures on the yield of resistant starch. The results concerning the influence of different catalysts (citric acid, lactic acid, and acetic acid) showed that the choice of catalyst is a critical factor affecting the final resistant starch content. Specifically, the resistant starch levels achieved using citric acid, lactic acid, and acetic acid catalysts were 56.4%, 49.7%, and 44.1%, respectively—all significantly higher than the control sample (40.7%) (Figure 2). Previous studies have also demonstrated that citric acid is the optimal catalyst in the process of modifying banana starch to create resistant starch (Olvera-Hernández et al., 2017). Therefore, citric acid was selected as the catalyst for subsequent experiments in this study.
Figure 2. Effect of different catalysts on the resistant starch content of modified banana starch
Different letters above the bars indicate statistically significant differences (p < 0.05).
Simultaneously, the study determined the effect of drying temperatures (60, 70, and 80°C) on the resulting resistant starch content. The results indicated that the drying temperature is a critical factor influencing the resistant starch level. When dried at 80°C, the resistant starch content was lower compared to drying at 60 and 70°C. Green bananas are rich in carbohydrates, starch, and resistant starch (RS2); when heated under high moisture and temperature conditions, steam penetrates and affects the RS2 structure, leading to partial structural disruption and a subsequent decrease in resistant starch content (Zhang et al., 2005; Bavaneethan, 2015). At drying temperatures of 60 and 70°C, there was no significant difference in resistant starch content (Figure 3) (p > 0.05). This is also the appropriate temperature range for drying resistant starch from rice (Nguyen Thi Quynh et al., 2020). However, the time required for the material to reach a moisture content of 7-8% was 12 hours at 60°C, while it took only 6 hours at 70°C. Shortening the drying time while maintaining the product's resistant starch content is a crucial condition in practical production. Therefore, this study selected a drying temperature of 70°C.
Figure 3. Effect of drying temperature on resistant starch content
(Different letters above the bars indicate statistically significant differences (p < 0.05).
Evaluation of Resistant Starch Content During Storage
Ensuring quality during raw material storage is crucial in the production process. In practical production, dry materials are typically stored in cold warehouses at temperatures of 15-20ºC. This study initially evaluated the resistant starch content in the obtained starch samples stored for different periods at 20ºC. After collection, the starch samples were packed in sealed PE bags, and samples were taken to analyze the resistant starch content after 2, 4, and 6 months of storage. The results showed that the resistant starch content did not change significantly after 6 months of storage at 20ºC (Figure 4) (p > 0.05). Thus, the resistant-starch-rich banana starch material obtained in this study maintains stable quality for 6 months of storage at 20ºC. However, the banana starch samples need further evaluation for resistant starch stability at other storage temperature ranges to select the most suitable storage temperature.
Figure 4. Evaluation of resistant starch quality during storage
The same letters above the bars indicate no statistically significant difference (p > 0.05).
CONCLUSION
This study identified that Red-tipped Cavendish bananas harvested at 90 days yielded the highest starch content at 66.7%. The optimal catalyst and drying temperature for the modification process to create resistant starch were citric acid (at a 2.5% concentration) and 70°C. Under these conditions, the resistant starch content obtained after modification was 56.4%, which is 38.5% higher than the resistant starch content in the banana starch before modification. Furthermore, the resistant-starch-rich banana starch material produced in this study maintained stable quality throughout 6 months of storage at 20°C.
Acknowledgements: This research was conducted with financial support from the grassroots-level science and technology project of the National Center for Technological Progress: "Research on modifying green banana starch to create resistant starch for food application orientation." The authors would like to express their sincere gratitude.
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