Abstract

The green walnut husk (Juglans regia L.), is a waste from the walnut industry generated at harvest and has little use. However, it is a potential source of active compounds, antioxidants, and antimicrobials, which are essential for food preservation. Actually, in the food science area, the green walnut husk has been little studied as a food additive, as an economical source of natural additives. In this study, the effect of two ripeness stages of the green walnut husk (open and closed) on the antioxidant and antimicrobial activity of hydroethanolic extracts and their impact on the oxidative stability of a real food matrix (mayonnaise) was analyzed. The dried samples were characterized through proximal analysis, and then hydroethanolic extracts were obtained through ultrasound-assisted extraction. An optical and chemical characterization for polyphenol content and antioxidant activity in the extracts was performed. Furthermore, the oxidative stability in mayonnaise without additives and the antimicrobial activity against Escherichia coli was determined. The ripeness stage was significantly affected by the total polyphenol content and antioxidant activity of the extracts (closed husk TPC= 10.1 ± 0.3 mg GAE/g sample; DPPH=3.21 ± 0.02 g trolox/g sample; open husk TPC= 4.8 ± 0.3 mg GAE/g sample; DPPH= 2.18 ± 0.03 g trolox/g sample). The best results were obtained for closed husk, to the more considerable amount of extracted polyphenols. This result demonstrated the potential of the green walnut husk, principally closed husk extract as an economical source of antioxidant and antimicrobial agents with potential use in the food industry.