Heat-treatment as a measure for microbiological quality improvement of walnuts and peanuts

  • Bernadeta Žudytė
  • Sigita Ramonaitė
Keywords: moulds, walnuts, peanuts, heat-treatment


The aim of this research was to evaluate the influence of heat-treatment on the  microbiological indexes of walnuts and peanuts. Two separate experiments were performed; each of them was replicated 3 times. Walnuts were blanched with 40, 60, 80 and 100 °C water for 1, 2 and 5  min. Peanuts were roasted at 100, 110 and 120 °C for 20, 40 and 60 min. The prepared samples were inoculated in disposable Petri dishes with the DG18 medium and held for 5 days at 25 °C temperature. After the  incubation the  amount of moulds was quantified. The experiment showed that the heat-treatment of ≥80 °C completely destroyed moulds in walnuts, the heat-treatment of 60 °C was effective for reducing of microorganisms, and the heat-treatment of 40 °C only slightly reduced their number (p < 0.05). The effect of blanching time on walnuts at selected temperatures was insignificant (p > 0.05). Both analysed factors were significant for roasted peanuts (p  >  0.05). The  number of moulds was reduced by 51.47% after roasting peanuts for 20 min at 100 °C. Despite the fact that roasting is an effective method to reduce the number of microorganisms, moulds were completely destroyed only in one sample, which was roasted at 120 °C for 60 min.