Effect of accelerated aging on total phenolic content, antioxidant and anti-diabetic activities of Lebanese homemade pomegranate molasses with and without addition of glutathione

Abstract

The pomegranate fruit is considered a functional food because of its bioactive compounds mainly phenolic compounds. Pomegranate molasses (PM) is a key ingredient in the Lebanese and Middle Eastern cuisine. The effects of accelerated shelf life testing (ASLT) on the total phenolic content (TPC), total flavonoid content (TFC), the antioxidant and antidiabetic activities (% DPPH scavenging activity, DPPH IC50, % Fe2+ chelating activity, and α‐glucosidase and α‐amylase IC50 antidiabetic inhibitory activity) of the Lebanese homemade PM have never been evaluated. Moreover, the effect of glutathione (GSH), an antioxidant, on the preservation of PM has never been tested. During ASLT, as time in the incubator increased, the TPC increased in samples without added GSH (TPCs at T0, T6, and T10 were 46.83, 55.63, and 63.61 mg GAE/g PM, respectively), where T6 and T10 represent half and one year on shelves at ambient temperature of 23⁰C respectively. After the addition of 200 µg/L GSH, TPC0 was 38.85 mg GAE/g PM which was lower than the TPC0 of samples without added GSH at day 0. GSH addition did not contribute to the TPC. The TPC was decreased after the addition of GSH not only at T0 but at T1 to T10 as well At T0, the % DPPH scavenging activity increased in a concentration‐dependent manner from 21.5% to 47.71% as concentration of the PM extract without added GSH increased from 20 to 100 µg/ml and the Fe2+ chelating activity of 38% at 1000 µl/mg. The mean DPPH IC50 at T4 to T10 (151.34 ± 9.75 to 208.98 ± 12.40 mg GAE/g PM, respectively) was found to be statistically significantly greater than the mean DPPH IC50 at T0 (114.25 ± 9.04 mg/g PM) in PM samples without GSH; this means that there will be a gradual significant decrease in antioxidant activity (AA) of PM, reaching approximately 1.83 folds lower than initial AA, after approximately 100 days on the shelf. Unexpectedly, however, the mean DPPH IC50 of PM samples with added GSH was higher than those without added GSH at ecah of the different times in the incubator (T0 to T10), (for e.g., at T0, the mean IC50 of samples with added GSH vs. that of samples without added GSH: 141 mg GAE/g vs. 114.25 mg GAE/g, respectively), meaning that PM without added GSH has higher AA than PM with added GSH over one year on the shelf. In addition, at T0, PM without added GSH exerted an inhibitory activity of IC50 of 0.443 ± 0.05 mg/ml for α‐glucosidase and IC50 of 1.21 ± 0.4 for α‐amylase which is comparable to those exerted by acarbose, a pharmaceutical drug used for treatment of diabetes which was used as the reference standard with IC50 values of 0.277 mg/ml and 0.42 mg/ml for α‐glucosidase and α‐amylase, respectively. Meaning that PM can be considered as a potent antidiabetic natural food. Finally, a significant strong positive correlation was found between TPC and IC50 DPPH before and after addition of GSH (ρ = 0.879, p < 0.01) (ρ = 0.547, p >0.05), respectively), meaning that TPC alone does not contribute to the total AA of PM and the addition of GSH improves the AA. The latter correlation, however, did not reach statistical significance. This could be due to the small number of samples in our study and therefore warrants investigation in larger studies in the future.