Investigating the effect on post-prandial glycemic and venous serum insulin response of an apple drink following the conversion of its glucose to gluconate.
In a double-blind randomized placebo-controlled clinical trial with cross-over design, 30 male adults with impaired fasting glucose (IFG) received a drink of 500 ml: 1. Verum: Apple juice treated with invertase, glucose oxidase/catalase (glucose 0.05 g; gluconate 18.2 g); 2. Control: Untreated apple juice (free glucose 8.5 g; bound glucose 6.7 g; gluconate below detection limit). Postprandial fingerprick capillary blood glucose and venous serum insulin were measured twice at baseline and at times 0 (start of drink), 15, 30, 45, 60, 90 and 120 min. Gastrointestinal symptoms, stool consistency and satiety were also assessed.
The incremental area under the curve (iAUC120) of glucose levels (primary parameter) was significantly lower after verum (mean ± SD: 63.6 ± 46.7 min × mmol/l) compared to control (mean ± SD: 198 ± 80.9 min × mmol/l) (ANOVA F = 137.4, p < 0.001; α = 0.05). Also, iAUC120 of venous serum insulin levels (secondary parameter) was significantly lower after verum (mean ± SD: 2045 ± 991 min × mmol/l) compared to control (3864.3 ± 1941 min × mmol/l), (ANOVA F = 52.94, p < 0.001; α = 0.025). Further parameters of glucose metabolism and ISI = 2/[AUC venous serum insulin × AUC glucose +1] were also improved after verum compared to control. Verum increased stool frequency and decreased stool consistency, as assessed by Bristol stool form scale.
By enzymatic treatment of apple juice its sugar content could be reduced by 21% and postprandial glycemic and venous serum insulin response by 68 and 47%, respectively resulting in a reduction of glycemic load by 74.6% without any adverse gastrointestinal side-effects.
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We thank Andrea Liesegang, Maria Gatzmange, Tara Dezhahang and Hanne Zobel for their excellent support and for technical assistance. This research was financed by the “HealthBoost” project in the FORNY2020 verification program of the Research Council of Norway (Grant no: 243871). Additional financial support to SB and SHK was provided by a grant from the Norwegian Fund for Research Fees for Agricultural Products (Norwegian Research Council Grant no. 262300).
The study was conducted in line with the principles of the Declaration of Helsinki (32), the guidelines for Good Clinical Practice (ICH E6) (33), and in accordance with European and National regulatory requirements. All clinical data were collected at the study site of the Clinical Research Center Kiel GmbH. Supplementary information is available at EJCN’s website.
Conflict of interest
SB, SHK, JS: Are inventors of a patent on this matter  and hold shares (as does CL) in Glucozero GmBH. This company is currently licensing the patent from Nofima AS (full-time employer of SB and SHK). The remaining authors declare that they have no conflict of interest.
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Laue, C., Ballance, S., Knutsen, S.H. et al. Glycemic response to low sugar apple juice treated with invertase, glucose oxidase and catalase. Eur J Clin Nutr 73, 1382–1391 (2019). https://doi.org/10.1038/s41430-019-0421-1