Polyphenol Oxidase and Peroxidase Enzyme Assays in Sweet Potato Cultivars Harvested at Different Times

Abstract

Enzyme assays are based on methodologies described in the literature. However, the enzyme kinetics must be adjusted to obtain more reliable results. This study aimed to adjust assays by testing different polyphenol oxidase (PPO) and peroxidase (POD) extract amounts and reaction times in sweet potato cultivars harvested at different times. Sweet potato cultivars Paraná, Mãe de Família, and ESAM1 were harvested at 120, 150, and 180 days after planting and minimally processed. A 0.25 g sample was used to determine PPO and POD activities immediately after minimal processing at each harvest. Extraction was performed in 1500 μL phosphate buffer (0.2 M, pH 6.0). The PPO assay was performed by adding 10-50 μL extract, 1490-1450 μL phosphate buffer (0.2 M, pH 6.0), and 1500 μL catechol (0.2 M). The POD assay was carried out by adding 10-50 μL extract to a reaction medium containing 1790-1750 μL phosphate buffer (0.2 M, pH 6), 100 μl guaiacol (5 g L-1), and 100 μL hydrogen peroxide (0.8 g L-1). In both cases, the evaluated reaction times were 1, 2, and 3 min. In the three cultivars, PPO and POD activities increased with the volume of extract and reaction time at all harvest times. The enzyme extract volume of 10 μL for 2 min promoted a continuous increase in PPO and POD enzyme activities in all studied cultivars and at all reaction times.

Root Rot Management in Common Bean (Phaseolus vulgaris L.) Through Integrated Biocontrol Strategies using Metabolites from Trichoderma harzianum, Serratia marcescens, and Vermicompost Tea

“…The enzyme assay results revealed general increases in peroxidase activity in bean leaves in response to the treatments, considered an important marker of systemic acquired resistance against pathogens [ 29 , 40 ]. The highest peroxidase induction by EM1 and EM1 + VCT aligns with findings describing EM formulations as strong elicitors of defense enzyme activity in various crops [ 41 ].…”

“…Results were expressed as units per gram fresh weight of leaf tissue. The key reagents, proportions, and readings have been retained while simplifying the terminology and phrasing [ 29 ].…”

“…One unit of PPO activity was defined as the amount causing an increase of 0.001 absorbance units per minute at 420 nm under the assay conditions. The final enzyme activity was expressed as units per gram of fresh weight of leaf tissue [ 29 ].…”

Harvest Time as a Modulator of Phytochemicals in Sweet Potato Cultivars for the Industry

“…The extractions and assays were carried out as proposed by Almeida et al (2019), with adaptations. Briefly, 0.25g samples were macerated in 6 mL of cold 0.2 M sodium phosphate buffer (pH 6.0), and the extract was then centrifuged at 7.960 g for 23 min at 4 ºC.…”