Effect of substrate levels and polyphenol oxidase activity on darkening in sweet potato cultivars

Abstract

Homogenization of sweet potato in the presence of oxygen causes differing degrees of brown discoloration to occur, depending upon the cultivar. When browning occurs in processed sweet potato, it is a serious quality defect. In order to better understand browning, five sweet potato cultivars produced in two crop years were evaluated by relating browning to phenolic content, polyphenolase activity, and ascorbic acid levels. Browning was found to be significantly correlated only to phenolic content. Considerable within-year and year-to-year cultivar variation was observed in browning potential.

Characterisation of ‘Starking’ apple polyphenoloxidase

“…Several methods have been described to prevent the reaction of phenols with PPO, including the use of phenol-binding agents such as polyethyleneglycol (PEG) (Benjamin and Montgomery 1973 ;Park and Luh 1985), or soluble and insoluble polyvinyl pyrrolidone and polyvinilpolypyrrolidone (PVP and PVPP) Benjamin and Montgomery 1973). Several investigators successfully used PVP in plant enzyme extraction due to its ability to bind to the phenols and, therefore in preventing phenolÈprotein interaction (Walter and Purcell 1980 ;Smith and Montgomery 1985 ;Wesche-Ebeling and Montgomery 1990).…”

Physicochemical, Thermal, Rheological and Morphological Characteristics of Starch from Three Indian Lotus Root (Nelumbo Nucifera Gaertn) Cultivars

“…Starch slurry readily turned brown during the preprocesses, which included peeling, shredding, and grinding. This may be due to the high level of polyphenol oxidase enzymes [18]. The shredded roots were treated with KMS and citric acid to improve the color of starch.…”

Monophenolase Activity of Polyphenol Oxidase from Artichoke Heads (Cynara scolymusL.)

“…It is known that severe extraction methods cause loss of the monophenolase activity because V max / K m (catalytic power) for the diphenolase activity is much higher than that for the monophenolase activity of PPO (16,17), and therefore slight changes in the enzyme mainly alter the monophenolase activity. This may explain why many PPOs from fruits and vegetables lack monophenolase activity (1,20,21). In order to confirm the validity of the proposed reaction mechanism for artichoke PPO, the dependency of the steady state rate and the lag period were studied vs. several assay conditions (pH, monophenol, o-diphenol and enzyme concentrations) (17)(18)(19).…”

“…This is mainly due to the lability of the enzyme during the purification process (1). This phenomenon is well known in other plant PPOs (20) and results from changes in the structure of the protein during purification (21).…”