Article Information
- Title: 전분함량이 높은 콩 유전자원 선발
- Authors: Sung Cheol Koo, Myeong Gi Jeon, Young Hoon Lee, Hyun-Young Kim, Beom Kyu Kang, Jong Min Go, In Youl Baek, Hong Tai Yun, In Youl Baek, and Man Soo Choi
- Published: March 2014
- Journal: Korean Journal of Breeding Science
- Volume: 46
- Issue: 1
- Pages: 52-57
- DOI: http://dx.doi.org/10.9787/KJBS.2014.46.1.052
Research Background
A. Research Context
- Soybean (Glycine max) is a vital crop rich in protein (43–48%) and lipids (18–21%) but has low starch content (<1% in mature seeds), limiting its industrial applications (e.g., processed foods like bread, noodles).
- Starch is a key carbohydrate for human/animal diets and industrial uses, but soybean’s starch content is significantly lower than other legumes (e.g., mung beans: 34–55%).
B. Knowledge Gap
- The molecular mechanisms behind starch synthesis/degradation during soybean maturation remain unclear.
- Limited studies explore how starch breakdown products influence protein/fat synthesis or genetic factors regulating starch content.
- No comprehensive screening of Korean soybean germplasms for high-starch traits has been conducted.
C. Research Objectives
- Screen 2,354 soybean germplasms to identify high-starch varieties using iodine-starch tests.
- Quantify starch, protein, fatty acid, and free sugar content in selected germplasms.
- Investigate correlations between starch content and other seed components (e.g., protein levels).
D. Significance
- High-starch soybeans could enhance food processing quality (e.g., texture, elasticity) and industrial utility.
- Findings may inform breeding strategies to develop dual-purpose soybeans (high protein + starch).
E. Additional Context
- Immature soybeans contain 10–20% starch, but levels drop to <1% upon maturity due to phosphorylase-driven degradation.
- Prior studies suggest starch structure (e.g., amylose content) varies with fatty acid composition, but data on mature seeds are lacking.
Materials and Methods
1. Experimental Materials
Plant Material: 2,354 soybean (Glycine max) germplasms from the National Institute of Crop Science (Korea), cultivated in Miryang and harvested in 2012.
2. Screening for High-Starch Germplasms
Iodine-Starch Test:
- Seeds were cross-sectioned and stained with iodine solution (2% I₂ + 0.5% KI).
- Reaction intensity graded on a scale of 1 (no reaction) to 4 (dark blue-black).
- 126 germplasms showed strong staining (Grade 4).
3. Quantification of Starch and Other Components
Starch Content:
- Method: Total starch kit (Megazyme) via glucose-oxidase assay (AOAC standard).
- Procedure:
- Samples (0.1 g) digested with thermostable α-amylase (6 min, boiling) and amyloglucosidase (30 min, 50°C).
- Glucose measured spectrophotometrically (510 nm); starch calculated as:
Starch (%) = ΔA × F / W × FV × 0.9
(ΔA: absorbance; F: glucose factor; FV: final volume; W: sample weight)
Protein Content:
- Method: Nitrogen analysis (Rapid N cube) using a conversion factor of 6.25.
Fatty Acid Content:
- Method: Soxhlet extraction with *n*-hexane (2 hrs), dried at 105°C.
Water Content:
- Method: Measured via moisture analyzer (MX-50).
Free Sugars:
- Method: HPLC (Agilent 1100) with Sugar-Pak I column and RI detection.
- Extraction: 80% ethanol (24 hrs shaking), filtered (0.45 μm), and diluted.
Key Notes on Methodology
- High-Throughput Screening: Iodine staining enabled rapid selection of high-starch candidates from 2,354 germplasms.
- Precision: Enzymatic starch quantification (Megazyme kit) ensured accuracy vs. traditional methods.
- Comprehensive Profiling: Parallel analysis of protein, lipids, and sugars revealed compositional trade-offs (e.g., starch vs. protein).
Results & Discussions
1. High-Starch Germplasm Identification:
- Iodine Screening: Among 2,354 germplasms, 126 (5.4%) showed strong iodine staining (Grade 4), indicating high starch content (Fig. 1).
- Quantitative Analysis:
- Grade 4 germplasms had 2.81–4.55% starch, versus <1% in low-starch controls (Grade 1–2) (Table 1).
- Top performers: Dacha (4.55%), Gwangjusetae (4.26%), and Mansu (4.03%).
2. Compositional Trade-Offs:
- Protein: High-starch germplasms had lower protein (33.33–35.63%) vs. low-starch (36.32–36.98%) (Fig. 2).
- Fatty Acids & Moisture: No significant correlation with starch content (15.40–19.66% fat; 7.85–9.48% water).
3. Free Sugars:
- Varied widely (e.g., Sobaegnamul: 94.4 mg/g; Soheonje: 39.4 mg/g) but showed no clear link to starch levels (Table 2).
4. Discussion Points
- Starch-Protein Inverse Relationship: Supports the hypothesis that starch degradation products (e.g., glucose) may fuel protein synthesis during maturation (Smith et al., 2005).
- Industrial Potential: Germplasms like Dacha (4.55% starch) could improve soybean-based food textures (e.g., bread elasticity; Urszula et al., 2010).
- Limitations:
- Environmental factors (temperature, light) during maturation were not controlled; may influence starch dynamics (Golombek et al., 1995).
- Genetic mechanisms behind starch retention remain uncharacterized.
Conclusion
1. Successful Screening
The iodine-starch test efficiently identified 126 high-starch soybean germplasms (Grade 4) from 2,354 candidates, with 7 accessions confirmed to contain 2.81–4.55% starch—significantly higher than controls (<1%).
2. Starch-Protein Trade-Off
High-starch germplasms exhibited reduced protein content (33–36%), suggesting starch degradation may redirect carbon toward protein synthesis during seed maturation.
3. Industrial Relevance
Germplasms like Dacha (4.55% starch) offer potential for enhancing food processing (e.g., texture, elasticity) and breeding programs targeting dual high-starch/high-protein traits.
4. Research Gaps
The study highlights the need to explore genetic and environmental (e.g., temperature, light) factors controlling starch retention in mature soybeans.
5. Final Statement
This study provides foundational data for utilizing high-starch soybean germplasms in food science and breeding, while underscoring the need for mechanistic research to optimize starch content without compromising nutritional quality.