The physicochemical and functional properties of red grape and peanut skin powders

Processing of fruits, vegetables, and oilseeds results in high amounts of by-products. The purpose of this study is to investigate the physicochemical and techno-functional properties of grape (GS) and peanut skin (PS) by-products. Moisture, protein, fat, fiber, ash and carbohydrate of GS and PS powders were (7.37 and 2.34%), (6.76 and 5.59%), (2.55 and 20.68%), (12.91 and 14.19%), (6.62 and 1.87%) and (63.79 and 55.33%), respectively. Total phenolic compounds (TPC), flavonoids and antioxidant activity (DPPH radical scavenging) of GS and PS powders were (41.60 and 212.21 mg GE/gm d.w.), (3.99 and 16.83 mg quercetin equivalent /gm d.w.) and (10.88 and 63.30%), respectively. Both GS and PS powders had remarkable color attributes with promising role as a food natural colorant. GS powder has reddish–purple color with L* (lightness) value by (46.93), a* (redness) value (7.64), and b*(yellowness) value(6.87). While PS powder color ranging from light brown to deep red, with values of L*, a* and b*were (60.83, 9.23 and 16.77), respectively. Functional properties of the GS and PS powders (mesh 60 = 0.25 mm), both powders exhibited bulk density (0.999 and 0.457 g/ml), water absorption index (2.87 and 4.02 g/g), water solubility index (0.51 and 0.08 %), oil absorption index (1.50 and 1.70 ml/g) and swelling index (1.06 and 1.20 ml/g) for GS and PS powder respectively. Considering these results, it's clear that the GS and PS powders can provide an inexpensive source of dietary fibers and polyphenols for use as functional ingredients in foods or dietary supplements. Moreover, they had distinguished techno-functional properties. Such findings could introduce/valorize the GS and PS powders to play technological and health promoting desirable roles in many food products.