Catherine Billaud

Apple polyphenoloxidase inactivation during heating in the presence of ascorbic acid and chlorogenic acid.

It was recently reported that during osmotic dehydration of ascorbic acid (AA)-treated apple cubes, losses in AA and phenolics could partly arise from enzymatic oxidation, provided polyphenoloxidase (PPO) was still active under the processing conditions. To determine the impact of dehydration temperatures on PPO action, as well as chemical and enzymatic oxidation reactions, apple PPO inactivation alone or with AA (1mM) and/or chlorogenic acid (CG, 3mM), as well as AA and CG levels evolution, during heating of the model solutions at 45 and 60°C were investigated. At pH 3.8, PPO was still functional, keeping 61 and 4% residual activity after 2h of heating at 45 and 60°C, respectively. The combined treatment of heating and AA was more effective in reducing PPO activity, while incubation at 60°C with AA and CG minimised the losses of PPO activity. CG remained stable during heating, even in the presence of AA which, in turn, was more affected by heating. Thus, during heating, provided PPO remained active with enough available O2 in the model systems, CG oxidation and coupled oxidoreduction with AA could readily develop.

Modelling the interactions between free phenols, L-ascorbic acid, apple polyphenoloxidase and oxygen during a thermal treatment

The kinetics of degradation of chlorogenic acid (CG), (-) epicatechin (EPI), L-ascorbic acid (AA) and polyphenoloxidase (PPO) activity from Marie-Ménard apple in pH 3.8 solutions at 20 and 50°C were investigated to provide information on the impact of the presence of CG, EPI and/or AA on PPO thermostability. The effect of the heat treatment on their degradation by enzymatic and/or nonenzymatic ways was also studied. Stoechiokinetic reactions on the basis of experimental data and literature and determination of the kinetic constants (k) at 20 and 50°C were elaborated before modelling the interaction among reactants, by fitting the reaction curves to predictive model. Apple PPO was thermolabile, denaturing after 10min at 70°C. Losses of PPO activity were favoured by the presence of EPI in model solutions, compared with CG, due to the formation of o-quinones of EPI (QEPI) lowering PPO stability. Temperature quickened both enzymatic phenol oxidations before PPO deteriorated and the whole set of the chemical reactions, including the production of secondary oxidation products and CG or EPI regeneration. Results also confirmed that AA in excess induced a fast regeneration of CG and EPI from the corresponding o-quinones formed enzymatically via redox chemical reactions.

Maillard reaction products derived from thiol compounds as inhibitors of enzymatic browning of fruits and vegetables: the structure-activity relationship.

Abstract: Some thiol‐derived Maillard reaction products (MRPs) may exert antioxidant activity, depending on the reaction conditions as well as on the sugar and the sulphydryl compound. Recently, we reported that MRPs derived from glucose or fructose with cysteine (CSH) or glutathione (GSH) mixtures greatly inhibited polyphenoloxidases (PPOs), oxidoreductases responsible for discoloration of fresh or minimally processed fruits and vegetables. Glucose and GSH were shown to be the most active in producing inhibitory MRPs. Therefore, we examined the way in which the nature of the reactants affected their synthesis, in order to establish a structure‐activity relationship for the inhibitory products. Various aqueous (0.083 M, 0.125 M, or 0.25 M) mixtures of a sugar (hexose, pentose, or diholoside) with either a CSH‐related compound (CSH, GSH, N‐acetyl‐cysteine, cysteamine, cysteic acid, methyl‐cysteine, cysteine methyl ester), an amino acid (γ‐glutamic acid, glycine, methionine), or other sulfur compound (thiourea, 1,4‐dithiothreitol, 2‐mercaptoethanol) were heated at 103°C for 14 h. Soluble MRPs were compared for their ability to inhibit apple PPO activity. In the presence of CSH, the rated sugars (same molar concentration) ranked as to inhibitory effect were pentoses > sucrose > hexoses ≥ maltose. In the presence of glucose, the simultaneous presence of an amino group, a carboxyl group, and a free thiol group on the same molecule seemed essential for the production of highly inhibitory compounds.

Louis‐Camille Maillard, 1878–1936

Abstract This review summarizes the life and work of Louis‐Camille Maillard, the most worldwide renowned French biochemist of the 20th century. It focuses on the main events in Maillards life and the reaction sugar–amino acids in his work, and offers an overview of the Maillard reaction in vitro and in vivo.

Heat Inactivation of Polyphenol Oxidase and Peroxidase as a Function of Water Activity: A Case Study of Mango Drying

An innovative method was developed to study the specific uncoupled effect of temperature and water activity (Aw) during mango drying. Thermal treatment of reconstituted lyophilized mango powder at targeted Aw enabled evaluation of the inactivation of polyphenol oxidase and peroxidase activity in a range 0.98–0.6 Aw and a time-temperature range of 1–4 h and 50–60°C. We established that thermal treatment of the enzymatic extract was not the same as the inactivation phenomena that occurred in the mango matrix, mainly due to differences in the pH of the buffer extract (6.4) and reconstituted food matrix (3.8). Even if the inactivation of these two enzymes was directly correlated with the temperature of the treatment, this behavior was also strongly linked to the Aw. A two-step change in the fruit was observed at high Aw (i.e., at 0.98 in fresh fruit), polyphenol oxidase (PPO) was shown to be more thermostable than peroxidase (POD), whereas when evaporation reduced the Aw to around 0.6, the opposite behavior was observed. As a consequence, enzymatic inactivation during drying should be considered as the result of the coupled effects of time-temperature and water activity.

Effects of harmane on growth and in vivo metabolism of aflatoxin B1 in male and female rats

The role of harmane, a beta-carboline formed during pyrolysis of tryptophan, on the metabolism of AFB1, growth and some parameters of the nutritional status was investigated in the rat. Male and female Wistar rats were fed a semi-synthetic diet containing AFB1 (2 ppm), harmane (250 ppm) or both compounds, for 33 days after weaning. Qualitative and quantitative differences in the urinary and faecal excretion of parental compound and metabolites were assessed by HPLC analysis. Harmane did not modify appreciably the growth and the other nutritional parameters studied. Similar excretion patterns of AFB1 metabolites were observed in males and females. Harmane caused a limited increase in the excretion of AFM1 in faeces but not in urine, without altering the growth process in rats of either sex.