Korean Journal of Food Preservation

The Korean Society of Food Preservation

Korean J. Food Preserv. 2023; 30(2):321-333

pISSN: 1738-7248, eISSN: 2287-7428

DOI: https://doi.org/10.11002/kjfp.2023.30.2.321

Research Article

과일 껍질을 첨가한 콤부차의 발효 중 이화학적 특성

이태연¹

, 이영현¹^,^*

Physicochemical properties of kombucha with fruit peels during fermentation

Tae Yeon Lee¹

, Young Hyoun Yi¹^,^*

¹서울과학기술대학교 식품공학과

¹Department of Food Science and Technology, Seoul National University of Science & Technology, Seoul 01811, Korea

^*Corresponding author Young Hyoun Yi, Tel: +82-2-970-6454, E-mail: youngyi@seoultech.ac.kr

Citation: Lee TY, Yi YH. Physicochemical properties of kombucha with fruit peels during fermentation. Korean J Food Preserv, 30(2), 321-333 (2023)

Copyright © The Korean Society of Food Preservation. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Dec 31, 2022; Revised: Mar 31, 2023; Accepted: Apr 04, 2023

Published Online: Apr 30, 2023

4. 요약

배, 포도, 자두, 오렌지, 사과와 골든키위 껍질을 첨가한 콤부차의 pH, 산도, 가용성 고형분, 총당, 환원당, 폴리페놀 함량, 플라보노이드 함량, 안토시아닌 함량, DPPH 라디칼 소거능과 색도를 조사하였다. 모든 실험구와 대조구는 발효 진행에 따라 pH는 감소하고 산도는 증가하였다. 가용성 고형분도 증가하였고, 대부분의 실험구가 대조구보다 높았다. 총당은 시간이 지날수록 감소했지만 환원당은 증가하였다. Day 0에서 총당과 환원당은 껍질 첨가군이 대조군보다 높았다. 폴리페놀, 플라보노이드, 안토시아닌 및 DPPH 라디칼 소거능은 발효 진행에 따라 증가하였고, 배를 제외한 모든 첨가군은 비첨가군보다 높게 나타났다. 시간이 지남에 따라 Anthocyanins이 높은 자두와 포도를 제외하고 L값은 증가하였고, 자두와 포도의 a값은 증가하였다(p<0.05).

Abstract

The study investigated the pH, acidity, soluble solids, total sugar, polyphenol, flavonoid, anthocyanin content, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, and color of kombucha with a variety of added fruit peels during the fermentation process. Pear, grape, plum, orange, apple, and golden kiwi peels were added during fermentation. The pH showed a decrease, while an increase in acidity was observed. An increase in soluble solids, which was higher in most experimental groups than the control group, was also observed. A decrease in total sugar was observed over time. However, an increase was observed in reducing sugar. On Day 0, higher total sugar and reducing sugar were detected in the peel addition group compared with the control group. The antioxidant capacity of polyphenol, flavonoid, anthocyanins, and DPPH radicals scavenging increased with fermentation and was higher in all addition groups, except for pear, compared with the control group. Except for grapes and plums containing high levels of anthocyanins, an increase in the L-value was observed over time, and an increase in the a-value of grapes and plums was also observed (p<0.05). The possible utilization of inedible fruit peel in kombucha was shown. Applying inedible fruit peels to kombucha is proposed to increase antioxidant content and modulate color and pH.

Keywords: kombucha; fruit peels; fermentation; antioxidant

1. 서론

콤부차(kombucha)는 홍차 또는 녹차에 SCOBY(symbiotic culture of bacteria and yeast)와 설탕을 첨가하고 상온에서 6-10일 발효시켜 얻는다(Reiss, 1994; Villarreal-Soto 등, 2018; Watawana 등, 2015). 약 2,000년 전 동북아시아 대륙으로부터 중앙아시아, 중동 및 유럽으로 퍼져 음용되고 있다(Hartmann 등, 2000; Sreeramulu 등, 2000; Watawana 등, 2015).

SCOBY는 주로 초산균과 내삼투성 효모로 이루어진 symbiotic culture이다(Jayabalan 등, 2014; Kaashyap 등, 2021; Marsh 등, 2014). 발효 중 Acetobacter xylinum 등에 의해서 생성된 cellulose film (Blanc, 1996; Chawla 등, 2009; Laavanya 등, 2021)에 bacteria와 yeast가 붙어서 gel 모양의 피막(pellicle)이 형성된다(Sreeramulu 등, 2000).

효모 세포벽에 있는 invertase가 설탕을 포도당과 과당으로 가수분해한다(Koschwanez 등, 2011; Reiss, 1994). 분해된 당이 발효를 거쳐 알코올로 된 후 초산으로 된다. 초산균은 포도당을 이용하여 gluconic, glucuronic, acetic 및 lactic acids 같은 유기산을 생성하여 고유한 풍미와 기능성을 부여한다(Jayabalan 등, 2014; Leal 등, 2018). 콤부차의 항미생물(Battikh 등, 2012; Sreeramulu 등, 2000), 항산화(Chu와 Chen, 2006)와 항암성(Jayabalan 등, 2011; Srihari 등, 2013)도 보고되었다.

전 세계 콤부차 시장 규모는 2021년 기준으로 약 3조 4천억 원이며 2030년까지 연평균 성장률은 15.6%로 예상된다(Grand View Research, 2022). 국내 콤부차는 중소기업에서 2018년에 시작하였고, 2021년에는 대기업에서도 제품을 출시하였다. 한 기업의 2020년 매출은 205억 원에서 2021년 407억 원으로 거의 100%에 가까운 성장을 했다(Ha, 2022).

과일은 가식 부위 과육과 비가식 부위 껍질이나 씨로 나뉜다. 과육의 항산화(Hassimotto 등, 2005; Saravanan과 Parimelazhagen, 2014), 항미생물(Saravanan과 Parimelazhagan, 2014)과 항당뇨(Saravanan과 Parimelazhagan, 2014; Sharma 등, 2006)가 보고되었다. 과육을 아이스크림(EL-Samahy 등, 2009), 맥주(Alves 등, 2020), 요구르트(Sengul 등, 2012), 치즈(Ramteke 등, 2020) 등에 첨가하여 식감, 기능성 및 풍미를 향상시켰다.

한국의 과일 생산액은 2005년 2조 5,290억 원에서 2019년 4조 1,879억 원으로 매년 꾸준히 증가했다(Yoon 등, 2021). Ruiz-Torralba(2018)에 따르면 52종 과일의 평균 비가식 부위는 약 16%이다. 과일 생산 증가에 따라 비가식 부위인 껍질과 씨의 증가가 추정된다. 석류(Fawole 등, 2012)와 바나나(Ehiowemwenguan 등, 2014) 껍질의 항미생물 그리고 오렌지(Hegazy와 Ibrahium, 2012)와 사과(Wolfe 등, 2003) 껍질의 항산화 효과도 보고되었다.

콤부차의 경우, snake furit(Zubaidah 등, 2019), red raspberry와 blackthorn(Ulusoy와 Tamer, 2019), 그리고 blackberry와 red goji berry(Akarca, 2022) 과육 활용 시 항산화 효과가 증가되었지만 미활용 껍질 활용 연구는 미미한 실정이다. 만약 미활용 껍질을 활용한다면 색, 맛, 향과 기능성 성분의 증진뿐만 아니라, 음식물 쓰레기 처리비용 및 관련 시설 설치와 유지비 절감이 기대된다. 본 연구에서는 껍질을 넣은 콤부차의 특성과 제품 가능성을 검토하기 위해서 발효 중 pH, 산도, 가용성 고형분, 총당, 환원당, 폴리페놀, 플라보노이드, 안토시아닌 함량, DPPH(2,2-diphenyl-1-picrylhydrazyl) 라디칼 소거능 및 색도를 조사하였다.

2. 재료 및 방법

2.1. 실험 재료

SCOBY와 콤부차는 Y-Biotic(Y-biotic Co., Ltd., Seoul, Korea)에서 구매하였다. 홍차잎(Ceylon Tea, Ahmad Tea Ltd., Ras Al Khaimah, UAE), 설탕(Samyang Co., Ltd., Ulsan, Korea), 배(Pyrus pyrifolia), 포도(Vitis vinifera), 자두(Prunus salicina), 오렌지(Citurs sinensis), 사과(Malus domestica)와 골드키위(Actinidia chinensis)는 시중에서 구매하여 사용했다.

2.2. 과일 건조

분리한 과피를 60°C에서 4시간 건조(JSOF-150, JS Research Inc., Gongju, Korea) 후 믹서기(WSG-9100, Joong San Co., Ltd., Seoul, Korea)로 분쇄했다. 과피 가루를 ziploc(Thai griptech Co., Ltd., Bangkok, Thailand)에 넣어 밀봉한 후 −20°C 냉장고(R-B63AM, LG Electronics Inc., Seoul, Korea)에 사용 시까지 보관하였다(Sogi 등, 2013).

2.3. 콤부차 제조

물 1.0 L를 전기 포트(P-5580TP, Zhongshan Xinhao Electric Co., Ltd., Zhongshan, China)에서 80°C까지 끓였다. 홍차잎 6 g이 담긴 티백(DP-5580TP, Zhongshan Xinhao Electric Co., Ltd., Zhongshan, China)을 넣고 15분간 우려 홍차를 만들었다. 홍차 395 mL와 설탕 50 g을 Clear Laboratory Bottle(BWK Life Sciences, Mainz, Germany)에서 섞고 식힌 후 SCOBY 25 g과 콤부차 30 mL를 첨가하였다. 면포를 씌워 25°C에서 12일간 배양하여 대조구를 제조했다(Neffe-Skocinska 등, 2017). 실험구는 면포를 씌우기 전 건조된 과피 10 g을 첨가하였다(Table 1).

Table 1. Composition of kombucha

Ingredient	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
SCOBY (g)	25	25	25	25	25	25	25
Kombucha (mL)	30	30	30	30	30	30	30
Sugar (g)	50	50	50	50	50	50	50
Black tea (mL)	395	395	395	395	395	395	395
Fruit peel (g)	0	10	10	10	10	10	10

Download Excel Table

2.4. pH 측정

시료 20 mL를 100 mL 비커에 담아 pH meter(Strarter 3100, Ohaus Instrument Co., Ltd., NJ, USA)로 발효 0일부터 12일까지 매 3일 간격으로 측정하였다(Ko 등, 2017).

2.5. 산도 측정

시료 10배 희석액 10 mL를 Petri dish(SPL Co., Ltd., Pocheon, Korea)에 넣고 1%(v/v) phenolphthalein (Daejung Chemicals & Metals Co., Ltd., Daegu, Korea) 지시약을 2-3방울 넣었다. Burette을 이용하여 0.1N NaOH(Samchun Pure Chemical Co., Ltd., Pyeongtaek, Korea)를 첨가하여 pH 8.3까지 적정하였다. NaOH 소비량을 아래 식에 대입하여 산도(%)를 구했다(Ko 등, 2017).

산도 % = 0.1 N NaOH 소비량 × NaOH 역가 × 0.006 × 희석배수 시료량(mL) × 100

2.6. 가용성 고형분 측정

당도계(Master Refractometer, Atago Co., Ltd., Tokyo, Japan)로 20°C 시료를 측정하여 °Brix로 나타내었다(Kwon 등, 2012).

2.7. 총당 측정

Glucose(Sigma Aldrich Co., Saint Louis, MO, USA) 용액 0-100 μg/mL를 spectrophotometer(Genesys 10 UV, Thermo Scientific, Inc., Waltham, MA, USA) 480 nm에서 측정하여 standard curve를 만들었다. 적정하게 희석한 시료 1 mL를 15 mL conical tube(SPL Life Science Co., Ltd., Pocheon, Korea)에 넣고 95%(v/v) sulfuric acid(Daejung Chemicals & Metals Co., Ltd., Daegu, Korea) 3 mL를 첨가한 후 1분간 실내에 놔두었다. 실온의 water bath(BW-20G, Jeio Tech Co., Ltd., Daejon, Korea)에 넣어 식힌 후 90%(v/v) phenol (Daejung Chemicals & Metals Co., Ltd., Daegu, Korea) 50 μL를 넣고 섞었다. 상온에 30분간 놔둔 후 480 nm에서 측정한 흡광도를 회귀곡선식에 대입하여 총당 함량(%)을 나타냈다(Salari 등, 2019).

2.8. 환원당 측정

시료 1 mL를 15 mL conical tube에 넣고 DNS(3,5-dinitro salicylic acid) reagent 1 mL를 첨가했다. Water bath 100°C에서 5분간 놔둔 후 상온에서 식혔다. 증류수를 넣어 8 mL로 보정하고 spectrophotometer 540 nm에서 흡광도를 측정했다. Glucose standard curve를 이용하여 환원당 함량(%)으로 나타냈다(Aung과 Eun, 2021).

2.9. 폴리페놀 함량 측정

Pipet으로 10배 희석된 시료 0.1 mL를 15 mL conical tube에 넣고 10%(v/v) Folin-Ciocalteau reagent(Sigma Aldrich Co., Saint Louis, MO, USA) 0.75 mL를 첨가했다. 상온에서 10분간 놔둔 후 2%(w/v) sodium carbonate (Daejung Chemical & Metals Co., Ltd., Siheung, Korea) 0.75 mL를 넣었다. 암실에서 45분 놔둔 후 spectrophotometer 765 nm에서 흡광도를 측정했다. Gallic acid(Sigma Aldrich Co., Saint Louis, MO, USA) standard curve를 이용하여 폴리페놀 함량(%)으로 표시했다(Lu 등, 2011).

2.10. 플라보노이드 함량 측정

시료 4배 희석액 0.5 mL, 10%(w/v) aluminum choride (Junsei Chemical Co., Ltd., Tokyo, Japan) 0.1 mL, 1M potassium acetate(Lugen Sci. Co., Ltd., Seoul, Korea) 0.1 mL와 증류수 2.8 mL를 15 mL conical tube에 넣고 섞어주었다. 상온에서 30분간 방치한 후 spectrophotometer 415 nm에서 흡광도를 측정했다. Quercetin(Sigma Aldrich Co., Saint Louis, MO, USA) standard curve를 이용하여 flavonoid 함량(%)으로 표현했다(Shahbazi 등, 2018).

2.11. 안토시아닌 함량 측정

비커에 0.2M potassium chloride(Junsei Chemical Co., Ltd., Tokyo, Japan) 125 mL와 0.2M hydrochloric acid(Daejung Chemicals & Metals Co., Ltd., Daegu, Korea) 375 mL를 혼합하여 pH 1.0 buffer solution으로 그리고 1M sodium actate(Daejung Chemicals & Metals Co., Ltd., Daegu, Korea) 400 mL, 1M hydrochloric acid 240 mL와 증류수 360 mL로 pH 4.5 buffer solution을 만들었다. 시료 0.5 mL가 담긴 conical tube에 각각의 buffer solution을 따로 넣고 512와 700 nm에서 흡광도를 측정하였으며, 아래 식에 대입하여 안토시아닌 함량을 구했다(Ulusoy와 Tamer, 2019).

총안토시아닌 함량 = A × M W × D f × 1, 000 ε × I

A = (A_λ512 − A_λ700) of pH 1.0 buffer solution − (A_λ512 − A_λ700) of pH 4.5 buffer solution

MW = Molecular weight (449.2 for cyanidin-3-glucoside)

Df = Dilution factor

ε = Absorbance coefficient (26,900)

I = Path length of cuvette (1 cm)

2.12. DPPH 라디칼 소거능 측정

Methanol(Samchun Pure Chemical Co., Ltd., Pyeongtaek, Korea) 99.5%(v/v)로 40배 희석한 시료 0.5 mL를 15 mL conical tube에 넣고 0.1 mM DPPH 용액 1.5 mL(Alfa Aesar, Inc., Tewksbury, MA, USA)를 첨가하였다. 실온의 암실에 20분간 둔 후 spectrophotometer 517 nm에서 실험구 흡광도를 얻었다. 공시료는 시료 희석액 대신 메탄올을 사용하였다. 각각의 흡광도를 아래 식에 대입하여 소거능(%)을 구했다(Kaewkod 등, 2019).

DPPH 라디칼 소거능 (%) = 공시료의 흡광도 - 실험구의 흡광도 공시료의 흡광도 × 100

2.13. 색도 측정

직경 5.5 cm와 높이 1.2 cm Petri dish(Doowon Meidite. Co., Ltd., Yongin, Korea)에 콤부차 4 mL를 넣고 색채색차계(CR-20, Konica Minolta, Inc., Tokyo, Japan)를 이용하여 측정했다. 색도는 명도를 나타내는 L값, 적색도를 나타내는 a값과 황색도를 나타내는 b값으로 나타냈다(Cho 등, 2006).

2.14. 통계처리

측정 결과는 SPSS program(ver. 26.0, SPSS Inc., Chicago, IL, USA)을 이용하여 분산 분석(ANOVA)을 하였다. 유의적 차이가 있는 경우 Duncan법을 이용하여 p<0.05 수준에서 유의성 검증을 하였다.

3. 결과 및 고찰

3.1. pH

콤부차 pH는 미생물의 성장과 물리화학적 변화 및 발효 진행의 지표가 된다(Hur 등, 2014; Malbasa 등, 2008). 발효 중 pH는 Table 2와 같이 Day 0, pH 3.08-3.44에서 Day 12, pH 2.40-2.81로 감소하였다(p<0.05). 미생물에 의해 생성된 acetic acid나 gluconic acid와 같은 유기산에 의해 pH가 감소한 것으로 여겨지며, Sreeramulu 등(2000), Tanticharakunsiri 등(2020) 그리고 Aung과 Eun(2021)의 결과와 유사하였다.

Table 2. pH of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	3.08±0.04^Ea1)2)3)	3.15±0.02^Da	3.15±0.01^Da	3.08±0.04^Ea	3.44±0.02^Aa	3.33±0.32^Ba	3.29±0.03^Ca
3	2.99±0.04^Eb	3.09±0.01^Cb	3.08±0.02^Cb	2.86±0.01^Fb	3.28±0.04^Ab	3.13±0.01^Bb	3.05±0.01^Db
6	2.64±0.03^Fc	2.84±0.02^Bc	2.82±0.02^Cc	2.72±0.01^Ec	2.91±0.02^Ac	2.76±0.02^Dc	2.92±0.01^Ac
9	2.52±0.02^Fd	2.70±0.02^Cd	2.70±0.01^Cd	2.63±0.01^Ed	2.81±0.01^Bd	2.66±0.02^Dd	2.89±0.01^Ad
12	2.40±0.01^Ee	2.49±0.01^Ce	2.49±0.01^Ce	2.44±0.02^De	2.63±0.02^Be	2.44±0.01^De	2.81±0.02^Ae

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.2. 산도

총산 함량은 콤부차의 독특한 맛과 향에 영향을 미친다(Leal 등, 2018). 발효 중 생성된 유기산(Sreeramulu 등, 2000)에 의해서 Day 0, 1.2-1.4에서 Day 12, 8.9-20.3% (Table 3)로 증가하여 Sreeramulu 등(2000), Tanticharakunsiri 등(2020) 그리고 Aung과 Eun(2021)과 유사한 경향을 보였으며, pH(Table 2) 감소와도 부합하였다. 자두의 산도가 가장 높은(p<0.05) 것은 배, 사과(Omer과 Matjafri, 2013)와 골든키위(Jeong 등, 2007)보다 높은 자두 과육(Jung 등, 2006)의 산도에 기인하는 것으로 보인다.

Table 3. Total acid (%) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	1.3±0.25^ABCe1)2)3)	1.3±0.18^ABCe	1.4±0.28^ABe	1.4±0.29^Ae	1.3±0.22^ABCe	1.2±0.13^BCe	1.2±0.01^Ce
3	2.5±0.31^CDd	2.7±0.31^Cd	2.9±0.22^Bd	5.2±0.29^Ad	2.4±0.24^DEd	2.30±0.31^Ed	3.0±0.64^Bd
6	5.0±0.27^Cc	4.5±0.36^Dc	5.6±0.30^Bc	6.7±0.31^Ac	3.2±0.30^Fc	3.5±0.25^Ec	5.6±0.29^Bc
9	8.0±0.30^Eb	8.8±0.29^Db	9.3±0.31^Cb	13.4±0.39^Ab	4.4±0.27^Fb	9.2±0.30^Cb	12.2±0.58^Bb
12	12.5±0.38^Ea	15.9±0.60^Da	17.5±0.38^Ca	20.3±0.47^Aa	8.9±0.40^Fa	18.4±0.30^Ba	18.6±0.53^Ba

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.3. 가용성 고형분

가용성 고형분은 식품 속에 녹아있는 모든 유기물과 무기물의 함량이다(Zubaidah 등, 2019). Day 0, 8.8-9.8에서 Day 12, 10.2-13.2 °Brix(Table 4)로 증가(p<0.05)하였다. 실험구가 대조구보다 높은 경향을 보였으며, 껍질의 비타민과 같은 수용성 성분 용출에 기인하는 것으로 보인다(Zhou 등, 2019).

Table 4. Total soluble solid (°Brix) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	8.8±0.17^Ee1)2)3)	9.2±0.00^Ce	9.2±0.09^Ce	9.2±0.09^Ce	9.8±0.09^Ae	9.4±0.09^Be	9.0±0.15^De
3	9.4±0.09^Fd	9.7±0.09^Dd	10.1±0.09^Cd	9.6±0.00^DEd	10.5±0.18^Ad	10.3±0.17^Bd	9.6±0.09^Ed
6	9.8±0.17^Fc	10.2±0.17^Dc	10.4±0.00^Cc	9.9±0.09^Ec	10.8±0.17^Bc	11.9±0.09^Ac	9.8±0.15^EFc
9	10.2±0.15^Db	11.1±0.09^Cb	11.1±0.09^Cb	10.2±0.15^Db	11.9±0.30^Bb	12.7±0.17^Ab	10.0±0.15^Eb
12	10.7±0.17^Ea	12.0±0.09^Da	12.2±0.09^Ca	10.4±0.15^Fa	12.7±0.30^Ba	13.2±0.15^Aa	10.2±0.15^Ga

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.4. 총당

Day 0, 9.78-10.86에서 Day 12, 5.97-7.48%(Table 5)로 감소하였는데, 미생물이 당을 이용하여 SCOBY의 cellulose 및 유기산을 생산(Zubaidah 등, 2019)한 것으로 여겨진다. Zahid 등(2022)의 연구처럼 요거트에 과일껍질 첨가가 총당을 증가시키듯 동일한 발효일에는 실험구가 대조구보다 높았다. 당 함량이 높은 포도 껍질(Maurer 등, 2019)은 동일 발효일에 다른 실험구보다 같거나 높게 나타났다(p<0.05).

Table 5. Total sugar (%) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	9.78±0.17^Eb1)2)3)	10.10±0.22^Db	10.82±0.25^Ab	10.26±0.26^Cb	10.86±0.26^Ab	10.75±0.12^Aa	10.51±0.25^Ba
3	9.94±0.17^Ea	10.39±0.29^Da	11.27±0.24^Aa	10.45±0.33^CDa	11.13±0.23^Aa	10.96±0.22^Ba	10.58±0.25^Ca
6	8.29±0.34^Ec	8.46±0.23^DEc	9.51±0.40^Ac	8.60±0.189^CDc	9.04±0.32^Bc	8.76±0.33^Cb	8.68±0.29^Cb
9	6.42±0.20^Dd	6.74±0.34^Cd	7.90±0.35^Ad	6.87±0.30^Cd	7.71±0.51^ABd	7.50±0.56^Bc	6.86±0.31^Cc
12	5.97±0.27^Ee	6.55±0.21^De	7.48±0.27^Ae	6.77±0.26^Cd	7.25±0.43^Be	7.12±0.33^Bd	6.66±0.37^CDd

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.5. 환원당

환원당은 유리 알데하이드기 또는 케톤기를 가지고 있어 환원제 역할을 할 수 있는 당이다. 일부 다당류, 이당류 그리고 모든 단당류가 이에 속하며, 과당, 포도당과 galactose가 대표적이다(Dimowo 등, 2021). Day 0에 총당과 같이 껍질 첨가군이 대조군보다 높았고, Day 0, 0.95-2.25에서 Day 12, 7.83-13.69%(Table 6)로 증가(p<0.05)하였다. 비환원당인 sucrose가 환원당인 포도당과 과당으로 분해되었기 때문이라 여겨지며(Loncar 등, 2014; Siever 등, 1995), Aung과 Eun(2021)의 결과와 유사하였다.

Table 6. Reducing sugar (%) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	0.95±0.03^Ge1)2)3)	1.06±0.02^Fe	1.14±0.03^Ee	1.26±0.03^De	1.35±0.04^Ce	2.25±0.07^Ae	1.67±0.07^Be
3	2.34±0.07^Ed	2.66±0.06^Dd	3.17±0.04^Cd	3.37±0.08^Ad	2.21±0.06^Fd	2.67±0.06^Dd	3.21±0.06^Bd
6	8.75±0.19^Dc	8.15±0.11^Ec	10.05±0.11^Bc	10.56±0.11^Ac	5.20±0.12^Gc	7.86±0.09^Fc	9.05±0.11^Cc
9	11.28±0.20^Db	11.23±0.22^Db	12.56±0.15^Bb	12.81±0.19^Ab	6.70±0.19^Fb	10.31±0.21^Eb	12.03±0.12^Cb
12	12.58±0.27^Ca	12.23±0.30^Da	13.69±0.12^Aa	13.16±0.10^Ba	7.83±0.41^Fa	11.68±0.23^Ea	12.20±0.14^Da

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.6. 폴리페놀 함량

콤부차의 폴리페놀은 찻잎에서 추출되며(Coelho 등, 2020), 항산화능에 기여하는 주요 물질이다. 발효가 진행될수록 증가하여 Tanticharakunsiri 등(2020) 및 Zubaidah 등(2019)의 보고와 같았다. 발효 중 thearubigins가 탈중합되어 항산화 활성이 더 높은 작은 분자로 되거나, 미생물에서 나온 효소가 복잡한 폴리페놀을 작은 분자로 분해하기 때문이라 여겨진다(Ulusoy와 Tamer, 2019). 동일 발효일에는 배를 제외하고 모든 실험구가 대조구보다 높았다(Table 7). 자두는 Day 3에서 급격히 증가한 후 항상 다른 시료보다 높았는데(p<0.05), 높은 자두 껍질의 폴리페놀(Lee 등, 2012)의 영향을 받은 것으로 보인다.

Table 7. Total phenolic contents (μg/mL) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	616.04±10.25^Fe1)2)3)	477.07±13.31^Ge	638.50±11.02^Ed	672.37±6.26^De	688.58±4.83^Ce	716.09±18.31^Be	726.66±10.55^Ae
3	638.50±10.97^Fd	489.20±8.73^Gd	687.86±18.09^Ec	767.97±12.06^Ad	699.39±9.84^Dd	736.51±7.50^Cd	743.95±5.85^Bd
6	653.63±8.25^Dc	500.37±7.42^Ec	756.92±5.23^Bb	782.27±13.80^Ac	705.04±7.57^Cc	756.92±5.51^Bc	760.65±6.35^Bc
9	668.28±8.50^Eb	513.94±5.19^Fb	768.57±5.53^Ca	795.00±8.26^Ab	711.76±10.15^Db	769.30±6.00^Cb	775.66±5.38^Bb
12	684.50±9.39^Ea	529.08±9.59^Fa	774.22±7.70^Ca	818.66±7.44^Aa	730.62±10.32^Da	777.34±4.90^Ca	785.27±6.87^Ba

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.7. 플라보노이드 함량

플라보노이드는 관속식물에 광범위하게 존재하는 페놀화합물(Dwiputri와 Feroniasanti, 2019)로 콤부차의 주요 항미생물 성분이다(Bhattacharya 등, 2016). SCOBY의 미생물이 폴리페놀을 분해하여 플라보노이드를 생성(Dwiputri와 Feroniasanti, 2019)하듯이 시간이 지날수록 증가(Table 8)하였다. 폴리페놀과 같이 자두도 Day 3에서 급격히 증가하였고 다른 시료보다 높았다(p<0.05).

Table 8. Total flavonoid contents (μg/mL) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	38.70±1.26^De1)2)3)	36.23±1.08^Ee	34.07±1.29^Fe	41.83±1.53^Ce	45.78±1.84^Be	51.05±1.93^Ae	36.92±1.18^Ee
3	41.92±1.04^Ed	38.55±1.68^Fd	44.74±1.69^Dd	67.18±1.75^Ad	52.02±1.72^Cd	53.40±1.58^Bd	38.99±1.67^Fd
6	43.84±0.81^Ec	40.22±1.36^Fc	46.48±1.01^Dc	70.18±0.97^Ac	54.02±1.58^Cc	55.72±1.47^Bc	40.53±2.01^Fc
9	45.73±0.82^Eb	41.44±1.20^Gb	49.59±1.02^Db	72.51±0.98^Ab	55.50±1.52^Cb	57.13±1.54^Bb	43.18±1.12^Fb
12	46.99±1.15^Ea	43.44±1.44^Ga	51.11±1.17^Da	74.87±1.54^Aa	56.95±1.98^Ca	58.87±1.56^Ba	45.29±1.02^Fa

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.8. 안토시아닌 함량

안토시아닌은 밝은 색을 띠는 포도, red onion, red cabbage 등에 있으며, 색과 맛에 기여한다(Ayed 등, 2016). 색을 띤 과일을 첨가한 콤부차의 안토시아닌이 많은 것(Ulusoy와 Tamer, 2019)처럼 대부분의 실험구가 대조구보다 높은 경향을 보였다. 과피의 안토시아닌(Shehata 등, 2020; Shim 등, 1994) 햠량 순서와 동일하게 사과, 자두와 포도로 나타났다(p<0.05). Day 3에서 자두와 포도의 급격한 증가는 플라보노이드(Table 8) 변화와 유사하였고, Day 6부터 자두의 감소(Table 9)는 미생물이 안토시아닌을 활용(Ayed 등, 2016)한 것으로 보인다.

Table 9. Total anthocyanins contents (mg/100L) of the kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	ND^1)2)3)4)	ND	317±7.02^Ab	153±2.68^Bd	2±1.31^Ca	18±2.30^Ca	ND
3	ND	ND	2,124±5.35^Aa	375±6.67^Ba	ND	15±1.67^Ca	ND
6	ND	ND	2,123±6.77^Aa	343±6.66^Bb	ND	14±3.05^Ca	ND
9	1±0.27^Ca	ND	2,103±.98^Aa	324±8.89^Bc	1±0.63^Ca	17±3.18^Ca	ND
12	1±0.07^Ca	ND	2,099±9.36^Aa	316±8.76^Bc	1±0.17^Ca	17±4.78^Ca	ND

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

ND, not detected.

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3.9. DPPH 라디칼 소거능

유리기는 산화적 손상을 일으켜 노화를 촉진시키지만 페놀화합물과 결합하여 안정화된다. 유리기 DPPH의 전자 공여 기능을 측정하여 소거능으로 표현한다. 폴리페놀과 플라보노이드의 증가에 따라 소거능도 증가하였다(Table 10). 음용이 권장되는 Day 9부터(Reiss, 1994) 배와 자두를 제외한 모든 시료가 대조구보다 높았다(p<0.05). 배는 낮은 폴리페놀(Table 7) 및 플라보노이드(Table 8), 그리고 자두 폴리페놀의 제한적 DPPH 소거능(Lee 등, 2012)에 기인하는 것으로 보인다.

Table 10. DPPH radical scavenging activity (%) of kombucha with fruit peels during fermentation at 25°C

Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
0	85.61±0.94^Bd1)2)3)	76.80±1.26^Ed	80.08±0.84^Dd	76.87±1.19^Ee	83.76±0.90^Ce	87.64±1.17^Ad	85.49±1.31^Bd
3	86.74±1.41^Bc	77.65±1.02^Fc	80.42±0.65^Dd	79.64±1.03^Ed	84.21±0.0^Cd	88.27±1.10^Ac	86.12±1.27^Bc
6	87.44±0.90^Cb	78.08±0.65^Fc	87.96±0.73^Bc	83.20±1.53^Ec	86.72±0.58^Dc	89.19±0.28A0^b	88.92±0.53^Ab
9	88.04±0.37^Ea	80.29±0.38^Gb	89.02±0.33^Cb	85.42±0.33^Fb	88.67±0.23^Db	89.67±0.31^Aa	89.46±0.34^Bab
12	88.50±0.40^Ca	81.53±0.62^Ea	90.04±0.28^Aa	86.88±0.52^Da	89.15±0.26^Ba	89.82±0.37^Aa	89.90±0.26^Aa

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

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3.10. 색도

콤부차 색은 폴리페놀 함량에 영향을 받는다(Abuduaibifu와 Tamer, 2019). 발효 중 색을 띠는 thearubigins 변화(Chu와 Chen 등, 2006)에 따라 자두와 포도를 제외하고 L값은 증가하였다. 자두와 포도의 높은 anthocyanins (Table 9)로 L값은 감소하였고 a값은 증가(p<0.05)한 것으로 보인다(Table 11).

Table 11. Hunter color value of the kombucha with fruit peels during fermentation at 25°C

	Day	Control	Korean pear	Grape	Plum	Orange	Apple	Golden kiwifruit
L	0	48.9±0.63^Ae1)2)3)	49.1±0.53^Ae	47.7±0.43^Ba	46.6±1.88^Ca	49.2±0.46^Ae	48.7±1.02^Ad	49.3±0.34^Ae
	3	49.7±0.28^BCd	49.7±0.56^BCd	42.8±0.75^Eb	45.9±2.09^Dab	50.4±0.35^Ad	49.2±0.34^Cc	49.9±0.43^ABd
	6	50.6±0.41^ABc	50.4±0.26^ABc	36.2±2.41^Dc	45.5±2.42^Cab	51.0±0.27^Ac	49.9±0.38^Bb	50.6±0.33^ABc
	9	50.9±0.29^Bb	50.8±0.31^Bb	35.3±0.81^Dd	45.2±2.64^Cab	51.7±0.312^Ab	50.5±0.34^Ba	51.0±0.31^Bb
	12	51.3±0.39^Ba	51.1±0.20^Ba	35.2±0.55^Dd	44.4±2.77^Cb	52.3±0.37^Aa	50.8±0.48^Ba	51.3±0.58^Ba
a	0	0.7±0.12^Da	0.7±0.13^Da	3.2±0.18^Be	10.6±0.31^Ae	0.0±0.14^Fa	0.9±0.25^Ce	0.5±0.14^Ea
	3	0.5±0.17^Db	0.6±0.14^Db	12.6±0.62^Ad	12.0±0.57^Bd	−0.4±0.17^Fb	1.2±0.24^Cd	0.2±0.12^Eb
	6	0.4±0.07^Dbc	0.5±0.09^Dc	28.6±0.95^Aa	12.4±0.30^Bc	−0.4±0.17^Fb	1.4±0.13^Cc	0.0±0.11^Ec
	9	0.3±0.35^Dcd	0.4±0.09^Dc	25.5±0.46^Ab	12.9±0.28^Bb	−0.6±0.16^Fc	1.5±0.13^Cb	−0.2±0.12^Ed
	12	0.3±0.33^Dd	0.4±0.08^Dc	24.5±0.95^Ac	13.3±0.31^Ba	−0.7±0.11^Fd	1.8±0.22^Ca	−0.3±0.10^Ed
b	0	6.4±0.43^Aa	5.7±0.73^Ba	4.8±0.49^Ca	4.1±0.73^Da	6.6±0.34^Aa	6.4±0.28^Aa	6.5±0.34^Aa
	3	5.9±0.45^Ab	5.1±0.72^Cb	1.6±0.35^Eb	3.4±0.37^Db	4.9±0.32^Cb	5.6±0.46^Bb	5.1±0.26^Cb
	6	5.2±0.70^Ac	4.3±0.65^Bc	0.2±0.27^Ec	2.6±0.21^Dc	4.6±0.58^Bc	5.2±0.33^Ac	3.6±0.57^Cc
	9	3.9±0.42^Bd	3.2±0.49^Cd	−0.3±0.19^Fd	2.2±0.21^Ed	4.1±0.48^Ad	4.3±0.60^Ad	2.8±0.24^Dd
	12	3.7±0.13^Ad	3.0±0.48^Bd	−0.6±0.29^Ee	1.9±0.25^De	3.6±0.50^Ae	3.9±0.75^Ae	2.5±0.45^Ce

All values are presented as mean±SD (n=5).

^A-GMeans within a row not followed by the same letter are significantly different (p<0.05).

^a-eMeans within a column not followed by the same letter are significantly different (p<0.05).

Download Excel Table

Conflict of interests

The authors declare no potential conflicts of interest.

Author contributions

Conceptualization: Lee TY, Yi YH. Investigation: Lee TY, Yi YH. Data curation: Lee TY, Yi YH. Formal analysis: Lee TY, Yi YH. Methodology: Lee TY, Yi YH. Validation: Lee TY, Yi YH. Writing - original draft: Lee TY. Writing - review & editing: Lee TY, Yi YH.

Ethics approval

This article does not require IRB/IACUC approval because there are no human and animal participants.

ORCID

Tae Yeon Lee (First author) https://orcid.org/0000-0003-2928-0731

Young Hyoun Yi (Corresponding author) https://orcid.org/0000-0003-2579-0259

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