Abstract
α-Arbutin is an effective skin-whitening cosmetic ingredient and hyperpigmentation therapy agent. It can be synthesized by one-step enzymatic glycosylation of hydroquinone (HQ), but limited by the low yield. Amylosucrase (Amy-1) from Xanthomonas campestris pv. campestris 8004 was recently identified with high HQ glycosylation activity. In this study, whole-cell transformation by Amy-1 was optimized and process scale-up was evaluated in 5000-L reactor. In comparison with purified Amy-1, whole-cell catalyst of recombinant E. coli displays better tolerance against inhibitors (oxidized products of HQ) and requires lower molar ratio of sucrose and HQ to reach high conversion rate (> 99%). Excess accumulation of glucose (0.6–1.0 M) derived from sucrose hydrolysis inhibits HQ glycosylation rate by 46–60%, which suggests the importance of balancing HQ glycosylation rate and sucrose hydrolysis rate by adjusting the activity of whole-cell catalyst and HQ-fed rate. Using optimal conditions, 540 mM of final concentration and 95% of molar conversion rate were obtained within 13–18 h in laboratory scale. For industrial scale-up production, 398 mM and 375 mM of final concentration with high conversion rates (~ 95%) were obtained in 3500-L and 4000-L of reaction volume, respectively. These yields and productivities (4.5–4.9 kg kL−1 h−1) were the highest by comparing to the best we known. Hence, high-yield production of α-arbutin by batch-feeding whole-cell biotransformation was successfully achieved in the 5000-L reaction scale.
Highlights
Arbutin, as a natural hydroquinone (HQ) glucopyranoside derivative, is an effective and safe hyperpigmentation therapy agent and skin-whitening cosmetic ingredient (Desmedt et al 2016)
The drawbacks of chemical synthesis are obvious such as labor-intensive activation, protection procedures, low overall yields and a large amount of waste (Desmet et al 2012). α-Arbutin has been reported to be synthesized by environment-friendly one-step enzymatic transformation since 1990s (Seo et al 2012; Zhu et al 2018), but industrial production was limited by the low yield. α-Amylase was firstly reported with HQ glycosylation activity for α-arbutin production but with a low conversion rate of 32%, besides, the products were the mixture of α-arbutin and hydroquinone oligoglucosides (Nishimura et al 1994)
Better catalytic performance by recombinant E. coli cells than purified amylosucrase Amylosucrase Amy-1 from X. campestris pv. campestris 8004 could glycosylate HQ with high yield and high conversion rate as we previously reported (Zhu et al 2019) (Fig. 1), but its activity was seriously inhibited by oxidized HQ products
Summary
As a natural hydroquinone (HQ) glucopyranoside derivative, is an effective and safe hyperpigmentation therapy agent and skin-whitening cosmetic ingredient (Desmedt et al 2016). It strongly inhibits tyrosinase activity and reduces the formation of melanin without adverse side effects like irritation, allergic contact dermatitis, and other cytotoxicity. Sucrose phosphorylase from Leuconostoc mesenteroides and α-glucosidase from Xanthomonas campestris were reported with a higher molar conversion rate of 60% and 93%, respectively, but only a low concentration of α-arbutin (~ 10 g/L) was obtained (Kitao and Sekine 1994; Kurosu et al 2002; Sato et al 2012). We recently identified the amylosucrase (Amy-1) from Xanthomonas campestris with > 95% molar conversion rate and > 80 g/L of α-arbutin concentration (Fig. 1) (Zhu et al 2019). Remarkable progress in biosynthesis of α-arbutin has been made in recent years
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