Influence of preservation methods on ph and microbiological quality of tiger nut (<i>Cyperus esculentus</i>) milk

Abstract

The deteriorating effect of microorganisms on tiger nut (Cyperus esculentus) milk has hampered its large-scale production and profitability. To study the effect of preservation on the pH and microbiological quality of the milk, big yellow tiger nuts were soaked in 3 L of tap water at 60^oC for 6 hours, additives such as coconut, date, cinnamon and ginger were added and blended. The extracted milk was divided into twenty five portions and subjected to the following treatments: pasteurization, sterilization, ultraviolet light, freezing and sodium benzoate. The pH and microbiological quality of both the fresh and preserved samples were investigated over 9-day storage period. The pH of the milk samples significantly decreased (p<0.05) over the period due to microbial activity. There were significant (p<0.05) decrease and increase in the pH values of the preserved samples with negative control (FTM) and positive control samples (TMA) respectively. The less acidic the products are the higher the bacterial load. The values of the total bacterial count for the preserved milk ranged from 5.19±0.06 to 6.84±0.03 log10cfu/ml. The values within this range were significantly lower (p<0.05) than FTM  (6.58±0.05log10cfu/ml) but higher than TMA (4.44±0.02 to 5.85±0.06  log10cfu/ml). The organisms isolated from the samples were Staphylococcus species (16%), Clostridium species (11%), Bacillus species (10%), Acinetobacter species (3%), Enterobacter species (6%), Corynebacterium species (4%), Neisseria species (1%), Vibrio species (1%), Micrococcus species (4%), Aeromonas species (5%), Saccharomyces species (35%) and Rhizopus oryzae (4%). The results suggest that ultraviolet light and sterilization methods were more effective at eliminating most of the bacteria implicated in milk spoilage.

Keywords: Fresh, large-scale production, microbiological quality, preserved, tiger nut milk.