Abstract
The waste of Sterculia nobilis fruit was massively produced during food processing, which contains lots of natural antioxidants. In this study, antioxidants in the Sterculia nobilis fruit waste were extracted using the green microwave-assisted extraction (MAE) technique. The effects of five independent variables (ethanol concentration, solvent/material ratio, extraction time, temperature, and microwave power) on extraction efficiency were explored, and three major factors (ethanol concentration, extraction time, and temperature) showing great influences were chosen to study their interactions by response surface methodology. The optimal conditions were as follows: 40.96% ethanol concentration, 30 mL/g solvent/material ratio, 37.37 min extraction time at 66.76 °C, and 700 W microwave power. The Trolox equivalent antioxidant capacity value obtained in optimal conditions was in agreement with the predicted value. Besides, MAE improved the extraction efficiency compared with maceration and Soxhlet extraction methods. Additionally, the phenolic profile in the extract was analyzed by UPLC-MS/MS, and eight kinds of phenolic compounds were identified and quantified, including epicatechin, protocatechuic acid, ferulic acid, gallic acid, p-coumaric acid, caffeic acid, quercetin, and p-hydroxycinnamic acid. This study could contribute to the value-added utilization of the waste from Sterculia nobilis fruit, and the extract could be developed as food additive or functional food.
Highlights
The imbalance between the production of reactive oxygen species and the antioxidant defense system could induce oxidative stress [1,2]
This study could contribute to the value-added utilization of the waste from Sterculia nobilis fruit, and the extract could be developed as food additive or functional food
The effect of ethanol concentration on extraction efficiency was studied with solvent/material ratio, 30 mL/g; extraction time, 30 min; temperature, 30 ◦ C; and microwave power, 500 W
Summary
The imbalance between the production of reactive oxygen species and the antioxidant defense system could induce oxidative stress [1,2]. There is growing scientific evidence that antioxidants could reduce or prevent the negative effects of oxidative stress on living tissues and inhibit aging processes and the development of many diseases [4,5,6]. Antioxidants play a vital role in the food industry, since they are required for the preservation of biological materials. Synthetic antioxidants such as BHA and BHT have been found very effective in the preservation of foods and in prolonging the shelf life of foods, but are considered to be controversial by consumers. Natural antioxidants have gained increasing attention due to their low toxicity, and they are widely produced by plants including medicinal plants, Molecules 2018, 23, 1059; doi:10.3390/molecules23051059 www.mdpi.com/journal/molecules
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