• anthocyanins;
  • bacteria;
  • fungi;
  • kinetics

Abstract:  The unavoidable damage of açai (Euterpe oleracea) fruits (AF) during picking leads to microbial contamination and anthocyanin degradation, which prejudice the consumed fruit drink. Thirteen lots of AF (24 kg) from different municipal districts of the Pará State (Brazil) were monitored during a 75-h-long storage in the dark at 30 °C for microbial growth, and 7 lots for anthocyanin degradation. On arrival at the laboratory, anthocyanins presented a mean concentration of 828 mg kg−1 fruits with a standard deviation of 323 mg kg−1 fruits whereas mean microbial contamination was 2.64 106 CFU g−1 of dry matter for total mesophilic bacteria, 1.98 103 MPN g−1 DM for fecal coliforms, and 1.11 105 CFU g−1 DM for moulds and yeasts. Kinetic growth of the microbes could be fitted to a quadratic equation with an unusual rapid growth during the 1st 24 h. The kinetics of anthocyanin degradation fitted a 1st-order equation. The mean velocity constant of the reaction (k1) was of 0.0137 h−1 and the mean half-life (t½) of the anthocyanins was 50 h. These results indicate that the AF simultaneously suffer extensive anthocyanin degradation and explosive microbial growth during the postharvest period needing a special care.

Practical Application:  The data presented in this article help the industrial sector of açai (Euterpe oleracea) juice to understand: (1) the rapid kinetics of anthocyanin oxidation and (2) the uncommon kinetics of microorganism growth during a postharvest storage of açai fruits for up to 75 h. Our results allow to predict the global deterioration of açai fruits and pointed out the necessity of blanching the fruits or pasteurizing the juice.