Improvement of viscous substance production during Cheonggukjang fermentation added with glycine
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Improvement of viscous substance production during Cheonggukjang fermentation added with glycine Ha Gyoon Na1 • Min-Ah Kim1 • Ji Woo Shin1 • Yun Ju Cha1 • Beom Soon Park1 Mi-Ja Kim1 • Jae-Cheol Lee1 • SangGuan You2 • Ki-Hyo Jang1
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Received: 10 December 2019 / Revised: 13 February 2020 / Accepted: 21 February 2020 Ó The Korean Society of Food Science and Technology 2020
Abstract When Bacillus subtilis NB-NUC1 associated with Cheonggukjang fermentation was aerobically grown in a synthetic medium containing 1 to 2% glycine (w/v), cell growth was inhibited in a dose-dependent manner. Subsequently, different concentrations of glycine (0, 1, and 2%) were used in Cheonggukjang fermentation for 96 h at 40 °C. Supplementation of 1% glycine increased extracellular c-glutamyl transpeptidase (c-GTPase), responsible for the production of viscous substance. Based on correlation studies, we conclude that the production of viscous substance is correlated with viscous extension (r = 0.867), extracellular proteins contents (r = 0.821), and c-GTPase activity (r = 0.807). The molecular weight of the viscous substance obtained during Cheonggukjang fermentation by B. subtilis NB-NUC1 was also affected by glycine supplementation. Our results demonstrate that glycine supplementation before solid-state fermentation may increase the mass production of mucilage in food industry. Keywords Bacillus spp. Cheonggukjang Glycine Secretion Viscous substance
& Ki-Hyo Jang [email protected] 1
Department of Food and Nutrition, Kangwon National University, Samcheok 25949, Republic of Korea
2
Department of Marine Food Science and Technology, Gangneung-Wonju National University, Gangneung 26403, Republic of Korea
Introduction A number of health products containing Bacillus species are available worldwide (Jang et al., 2007). Cheonggukjang is a non-salty fermented soybean food produced using Bacillus subtilis as a starter, and is similar to Natto, which is a popular fermented soybean product grown in Japan. Cheonggukjang is rich in protein and easy to manufacture. Various metabolites including soy protein hydrolysates, glucoside isoflavones, enzymes, and viscous substances are produced during Cheonggukjang fermentation. These metabolites are under great scrutiny as food supplements to prevent hypertension (Shin et al., 1995), cancer (Hara et al., 1992), atherosclerosis (Kwon et al., 2004), and obesity (Na et al., 2019). Among the different metabolites of Cheonggukjang, the viscous substance is composed of levan and poly gamma glutamate (c-PGA), and its composition varies according to the type of starter used in fermentation and aging processes (Lee and Hahm, 2005; Son and Lee, 2011). In Cheonggukjang fermentation, B. subtilis is responsible for the production of levan and c-PGA. Levan is a homopolymer composed of D-fructofuranosyl residue connected by b(2,6) and b-(2,1) linkages (Han and Clarke, 1990). c-PGA is a polypeptide composed of glutamic acid residues joined by linkages between the a-amino and c-carboxylic acid groups (Jang
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