우리밀 사워도우의 이화학적 및 미생물학적 특성 비교

다국어 초록 (Multilingual Abstract)

Comparison of Physicochemical and Microbiological Characteristics of Korean Wheat Sourdoughs
Baek Seeun
Advisor : Prof. Baek Jihwan, Ph.D. Department of Food and Nutrition, Graduate School of Gwangju University
This study aimed to investigate the effects of lactic acid bacteria (LAB) inoculation and fermentation temperature (21°C, 24°C, and 28°C) on the physicochemical properties and microbial dynamics of sourdough prepared using Korean wheat (whole wheat and refined wheat). Sourdoughs prepared with Korean wheat, with and without LAB inoculation, were subjected to different fermentation conditions, and their physicochemical characteristics (pH, Brix, total titratable acidity), antioxidant activity, and microbial populations were analyzed. During fermentation, pH showed a decreasing trend in all samples. Initial pH values from 5.73 to 6.41 across treatments, and on day 1, pH values were 5.04 (CG), 4.48 (KF), 5.37 (WF), while the LAB-inoculated samples (KL, WL) showed significantly lower pH values of 4.09 and 3.92, respectively. By day 5, pH converged to 3.74–3.99 across all treatments. Total titratable acidity (TTA) increased from 0.10–0.29% on day 0 to 0.80– 1.65% in non-LAB samples (CG, KF, WF) and 0.96–2.03% in LAB-inoculated samples by day 5. Lactic acid content differed markedly from the early stage. On day 1, lactic acid levels were 420.16 mg/L (CG), 1070.33 mg/L (KF), 1186.74 mg/L (WF), 3477.88 mg/L (KL), and 3933.92 mg/L (WL), with significantly higher values in LAB-inoculated samples. A pronounced increase occurred between days 2 and 3, reaching the highest levels on day 5. The initial Brix values were 0.97 (CG), 0.76 (KF), 1.12 (WF), 1.68 (KL), and 1.71 (WL), indicating significantly higher initial values in LAB-inoculated samples. From day 2 onward, Brix values gradually decreased or stabilized. The reducing sugar content on day 0 was 0.20% (CG), 0.16% (KF), 0.26% (WF), 0.45% (KL), and 0.54% (WL), again showing higher initial levels in LAB-inoculated samples. On day 1, all treatments exhibited a sharp increase, followed by partial decreases on day 2, and then a gradual decline or stabilization depending on temperature conditions. Antioxidant characteristics also improved during fermentation. Total phenolic content (TPC) increased from 0.017–0.034 mg GAE/g on day 0 to higher levels by day 5, with greater increases in LAB-inoculated samples. Total flavonoid content (TFC) showed a similar trend, rising from 0.052–0.056 mg QE/g on day 0 in all samples, with LAB-inoculated samples exhibiting a larger increase by day 5. DPPH radical scavenging activity increased steadily during fermentation and was higher in LAB-inoculated samples than in non-inoculated samples on day 5. Microbiological analysis revealed the largest difference in total plate counts depending on LAB addition. Total plate counts were at the level of <2-3 log CFU/g on day 0, but increased during the fermentation and reached 10.58-11.46 log CFU/g on day 5. The number of yeast cells started at <1-2 log CFU/g initially and reached 8.65-9.29 log CFU/g on day 5 during fermentation. In non-LAB samples, the number of lactic acid bacteria started at <1.0 log CFU/g on day 0 and reached 9.94-10.43 log CFU/g by day 5. In contrast, LAB-inoculated smaples started at <3.0 log CFU/g on day 0 and increased to 10.11-11.47 log CFU/g by day 2. Based on the preceding experimental results, the WF and WL samples under the DAY5–28°C condition, which exhibited the most distinct fermentation characteristics, were selected for 16S rRNA amplicon sequencing. The sequencing results showed that Pediococcus pentosaceus was dominant in WF at 69.96%, followed by Levilactobacillus brevis (5.69%) and Latilactobacillus curvatus (2.95%). In contrast, Lacticaseibacillus paracasei was the most abundant species in WL at 48.86%, followed by P. pentosaceus (17.59%), L. brevis (0.64%), and L. curvatus (0.09%). Overall, characteristic lactic fermentation patterns were observed during sourdough fermentation, including pH reduction, increased acidity, lactic acid accumulation, and sugar depletion. The antioxidant content was also improved throughout the fermentation. Additionally, LAB-inoculated samples consistently showed superior characteristics in terms of physicochemical change rate, improved antioxidant activity, and increased LAB counts. These results confirmed that LAB addition contributes to quality improvement by enhancing fermentation safety and reorganizing the microbial community into LAB-dominant structure.
Keywords: sourdough, korean wheat, korean whole wheat, fermentation, lactic acid bacteria (LAB)

목차 (Table of Contents)

• 제1장 서론 01
• 제2장 실험 재료 및 방법 03
• 제1절 실험 재료 및 시료 제조법 03
• 1. 실험 재료 03
• 2. Sourdough starter용 유산균 배양 03
• 3. Sourdough 제조 방법· 04
• 제2절 실험 방법 07
• 1. 이화학적 특성 07
• 1.1. pH 측정 07
• 1.2. 총산 측정 07
• 1.3. 가용성고형분(Brix) 측정 08
• 1.4. 환원당 분석 08
• 1.5. Lactic acid 분석 09
• 2. 항산화 함량 측정 11
• 2.1. 총 폴리페놀 함량 11
• 2.2. 총 플라보노이드 함량 11
• 2.3. DPPH radical 소거능 12
• 3. 미생물학적 특성 13
• 3.1. 총균수 측정 13
• 3.2. 효모균 수 측정 13
• 3.3. 유산균 수 측정 14
• 3.4. 16S rRNA amplicon sequencing 14
• 4. 통계분석 15
• 제3장 결과 및 고찰 16
• 제1절 결과 및 고찰 16
• 1. 발효과정 중 Sourdough의 이화학적 특성 16
• 1.1. pH 16
• 1.2. 총산 함량 18
• 1.3. 가용성고형분(Brix) 함량 20
• 1.4. 환원당 함량 22
• 1.5. Lactic acid 함량 24
• 2. Sourdough의 항산화 함량 26
• 2.1. 총 폴리페놀 함량 26
• 2.2. 총 플라보노이드 함량 28
• 2.3. DPPH radical 소거능 30
• 3. 발효과정 중 Sourdough의 미생물학적 특성 32
• 3.1. 총균수 측정 32
• 3.2. 효모균 수 측정 36
• 3.3. 유산균 수 측정 40
• 3.4. 16S rRNA amplicon sequencing 44
• 제4장 요약 48
• 1. 이화학적 특성 48
• 1.1. pH, 총산(TTA), Lactic acid 48
• 1.2. 가용성고형분(Brix), 환원당 49
• 2. 항산화 함량 50
• 3. 미생물학적 특성 51
• 3.1. 총균수, 효모균 수, 유산균 수 51
• 3.2. 16S rRNA amplicon sequencing 52
• 참고문헌 53