Isolation and Identification of Bacteria Leading to Microbial Spoilage of Sweet Potato and Screening for Antistaling Agents Running Head

Abstract

To develop natural preservatives tailored for sweet potatoes, the control effect of essential oils on the spoilage microorganisms of sweet potatoes is uncertain. Therefore, we first isolated and identified the dominant spoilage bacteria from spoiled sweet potatoes. Micrococcus aloeverae, Priestia aryabhattai, and Glutamicibacter arilaitensis were identified through screening, morphological observation, gram staining, and 16S rDNA assays. Subsequently, five plant essential oils (citral, Litseacubeba, parsley, eugenol, and chinaberry tree oils) that significantly inhibited the spoilage bacterial species were identified after screening 20 plant essential oils using the zone of inhibition test. Minimum Inhibitory Concentrations (MICs) of Litsea cubeba, eugenol, and parsley oils against the above three spoilage bacteria were 320-1280, 640-1280, and 320-640 μL/L, respectively. The three essential oils exhibiting the most favorable inhibitory effects were selected for combinatorial studies. Finally, the response surface methodology was used to optimize the combination concentration of Litsea cubeba, eugenol, and parsley oils. The optimum concentration was identified as follows: 320 μL/L for Litsea cubeba oil, 716 μL/L for parsley oil, and 1280 μL/L for eugenol oil. At this concentration, the growth of three spoilage bacteria was almost completely inhibited (OD values of 0.067, 0.202, and 0.013). The optimized compound essential oil exhibited potent inhibitory activity against the spoilage bacteria of sweet potatoes. The aforementioned studies may provide important guidance for the development of efficient and broad-spectrum sweet potato preservatives.