Influence of Different Types of Drying Methods on Color Properties, Phenolic Metabolites and Bioactivities of Pumpkin Leaves of var. Butternut squash (Cucurbita moschata Duchesne ex Poir)

Florence M Mashitoa; Tinotenda Shoko; Jerry L Shai; Retha M Slabbert; Yasmina Sultanbawa; Dharini Sivakumar

doi:10.3389/fnut.2021.694649

Influence of Different Types of Drying Methods on Color Properties, Phenolic Metabolites and Bioactivities of Pumpkin Leaves of var. Butternut squash (Cucurbita moschata Duchesne ex Poir)

Front Nutr. 2021 Jun 29:8:694649. doi: 10.3389/fnut.2021.694649. eCollection 2021.

Authors

Florence M Mashitoa^{1

2}, Tinotenda Shoko¹, Jerry L Shai³, Retha M Slabbert², Yasmina Sultanbawa⁴, Dharini Sivakumar^{1

4}

Affiliations

¹ Phytochemical Food Network Research Group, Department of Crop Sciences, Tshwane University of Technology, Pretoria West Campus, Pretoria, South Africa.
² Department of Horticulture, Tshwane University of Technology, Pretoria West Campus, Pretoria, South Africa.
³ Department of Biomedical Sciences, Tshwane University of Technology, Acadia Campus, Pretoria, South Africa.
⁴ ARC Training Centre for Uniquely Australian Foods, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Coopers Plains, QLD, Australia.

Abstract

Leaves of pumpkin species var. Butternut squash (Cucurbita moschata Duchesne ex Poir) is a popularly consumed leafy vegetable in the Southern African region. Traditional vegetables are commonly sun-dried as a method of postharvest preservation during the off-season. However, different drying methods affect the superior quality, functional properties, and bioactivities of the final product. Therefore, in this study, var. Butternut squash (C. moschata) underwent different drying methods, such as freeze-, oven, sun-, solar, and microwave drying to evaluate the color properties, pigments, phenolic metabolites, in vitro antioxidants, and antidiabetic activities. Results indicate that freeze-drying retained the total chlorophyll content with green color by reducing the color difference (ΔE), improved the concentration of different phenolic metabolites and the content of ascorbic acid, and enhanced the FRAP, ABTS activities and the inhibitory effects of α-glucosidase, and α-amylase. Freeze-dried leaves contained the highest concentrations of quercetin 3-glucoside 7-rhamnoside (rutin), quercetin 3-galactoside, isorhamnetin-3-galactoside-6″-rhamnoside, isorhamnetin-3-O-rutinoside compared with the leaves that underwent four other drying treatments and raw leaves. The OPLS-DA and the UPLC-QTOF/MS and chemometric approach showed that the peak at m/z 609, 1441 (quercetin 3-galactoside 7-rhamnoside) separated the freeze-dried leaves of var. Butternut squash (C. moschata) from the other four drying treatments. Therefore, freeze-drying is highly recommended to obtain good quality leaf powders that are rich in functional compounds and bioactive properties for use as functional ingredients.

Keywords: Cucurbitaceae; FRAP activity; chlorophyll; polyphenols; α-glucosidase.