Investigation of antimicrobial activity of orange and pomegranate peels extracts and their use as a natural preservative in a functional beverage

The aim of this study was to investigate the effect of orange peel extract (OPE) and pomegranate peel extract (PPE) as natural preservatives on the characteristics of a functional drink (FB). These FBs were produced using fruit concentrates and agricultural waste (melon seed and tea stalk caffeine) as well as malt extract and powder. First, OPE’s and PPE’s antimicrobial activity (AMA) was tested in vitro on two pathogenic bacteria (Staphylococcus aureus and Escherichia coli). Then their effects were investigated on the FBs’ quality. Although both extracts showed significant AMA against bacteria, it was higher in OPE than PPE sample (p < 0.05). The results show that the minimum inhibitory concentration (MIC) for PPE samples was 1.5 and 2.5 times that of OPA against Gram-positive and Gram-negative bacteria, respectively. Increasing the levels of extracts in beverages, especially OPE, can reduce the pH during 27-day in refrigeration storage and also significantly reduce the growth of total bacterial, molds, and yeasts. Adding the PPE reduced sensory scores, while OPE had no adverse effect on sensory characteristics. Samples containing PPE showed approximately 25% higher antioxidant activity and 45% higher total phenolic content (mg Gallic acid/g extract) than OPE samples. The sample containing 15% OPE was introduced as the best natural preservative to improve the functional beverage’s quality and shelf life.