Effect of Addition of Citric Acid and Sodium Benzoate on pH and Microbial Profile of Soymilk

Abstract

Aim: To study the synergistic effect of chemical preservatives on the keeping quality of soymilk. Study Design: Ten soymilk samples were prepared and treated with different concentrations of citric acid and sodium benzoate and stored at ambient conditions. Place and duration of Study: The present study was conducted at the Department of Food Science and Technology, Nnamdi Azikiwe University, Awka between March 2015 and June 2016 Methodology: Ten (10) soymilk samples were prepared. Soybean seeds (2 kg) that are free of dirt and stones were weighed and steeped in 4 L of tap water, a 12 h steeping regime was adopted. Each soymilk sample was formulated by adding different concentrations of sodium benzoate and citric acid, while the control sample had no treatment. All soymilk samples were then boiled at 75oC for 15 minutes and stored in storage bottles. Standard microbiological techniques were employed in the isolation and enumeration of potential spoilage organisms in soymilk samples. pH analysis was conducted throughout the storage period. Results: There was a decrease in pH of all soymilk samples with increasing storage time. pH at day 0 ranged between 6.2 to 7.2. Isolated bacteria in 10 soymilk samples included Streptococcus sp., Pseudomonas sp., Proteus sp., Bacillus spp., Staphylococcus aureus, Klebsiella sp., Escherichia coli, and Enterobacter species. However, results obtained showed that soymilk could keep up to 7 days at ambient temperature, encouraging the use of citric acid and sodium benzoate as chemical preservatives. Conclusion: In the present study, preservation of soymilk samples from a combination of citric acid and sodium benzoate which are chemical preservatives was found to be more effective than several organic preservatives. Hence, they represent an alternative source of chemical antimicrobial substances for use in food systems to prevent the growth of food borne microorganisms and extend the shelf-life of processed food.