Coconut (Cocos nucifera L.) is a horticultural crop that grows extensively in a tropical climate and coastal areas. Thailand is one of the best-known coconut-producing countries. According to the Food and Agriculture Organization of the United Nations (FAO, 2022), Thailand ranks as a top 10 country for the production of coconuts, mostly producing coconut oil and whole coconut.

Tender coconut water (TCW) is one of the products that are manufactured for both domestic consumption and export. TCW, or coconut liquid endosperm, is acquired from young coconut that is rich in beneficial nutrients, e.g. vitamins, minerals and growth hormones (Zulaikhah, 2019), and is also a natural refreshing beverage. It is a popular isotonic drink that has a unique sensory characteristic, especially in terms of aroma and flavour. It is also a low-energy drink that has a rehydration potential containing a high concentration of total soluble solids and minerals, especially potassium, manganese and iron (Donsingha & Assatarakul, 2018). Moreover, TCW is considered a natural alternative sports drink (Kanjanapongkul & Baibua, 2021). Although TCW is stable and sterile when it is inside the coconut endosperm, the inconvenience of transporting and drinking from a whole coconut in the modern lifestyle is the main reason that the coconut water must be extracted, processed and packaged in appropriate containers (Kanjanapongkul & Baibua, 2021). In order to extend the shelf-life of TCW, thermal processes, including pasteurization and sterilization, have been introduced. However, these thermal processes can affect quality in terms of colour, odour, flavour and sensory characteristics. Likewise, the thermal process also impacts on some heat-sensitive compounds and unique nutrients of fresh TCW (Rajashri, Roopa, Negi, & Rastogi, 2020; Sucupira et al., 2017). Consumers' preference in terms of purchasing decisions is fresh-like characteristics, especially for TCW. Thus, thermally processed TCW does not quite meet the needs of this consumer group. Therefore, manufacturers are currently seeking alternative treatments to avoid using heat. Non-thermal processing is now used in the beverages industry and in many juices – for example, pulsed electric fields (PEF), ultraviolet irradiation (UV) and high-pressure processing (HPP) (Prithviraj et al., 2021). However, applying PEF with low-acid juice like TCW has not yet been investigated.

PEF is a novel and promising non-thermal technique for preserving foods. It is a suitable substitute for thermal processing methods for inactivating spoilage and pathogenic microorganisms and enzymes, while minimizing nutritional losses and changes to the sensorial characteristics of fruit juices (Arshad et al., 2021; Urugo et al., 2023). PEF is a safe process and the United States Food and Drug Administration (USFDA) has issued a letter of no objection to PEF as an alternative method for preserving food (Rahman, 2020). The USFDA regulation for PEF is >5 log reductions of pathogenic microorganisms in fruit juices (USFDA, 2004). The parameters affecting the efficacy of PEF are the process parameters (e.g. processing time, inlet temperature, electric field strength, pulse width and specific energy), product parameters (e.g. electrical conductivity, composition and pH value) and microbial characteristics (e.g. size and type) (Kaavya et al., 2021; Li, Yang, & Zhao, 2021). The pulses normally start from nanoseconds to milliseconds, with electric field strength in the range of 100 V/cm to 80 kV/cm (Kaavya et al., 2021). The electric field strength used in typical process settings reported in the literature normally ranges from 15 to 40 kV/cm. Microorganisms are inactivated by the effect of a combination of electroporation and electropermeabilization of cell membranes caused by high-intensity PEF. The shape and size of the microbial cell also has an effect on inducing electroporation (Timmermans et al., 2019).

The main spoilage and pathogenic microorganisms associated with coconut water have been reported and include Escherichia coli and Staphylococcus aureus under conditions of low-temperature storage (Donsingha & Assatarakul, 2018). A previous study described using UV to inactivate Lactobacillus plantarum, Salmonella enteritidis, Staphylococcus aureus and Escherichia coli O157:H7 in coconut water. The results found that the process effectively inactivates E. coli at the highest log reduction (Donsingha & Assatarakul, 2018). Published research has revealed that applying PEF decreases microorganisms in liquid food by up to 2.0–8.2 log CFU/ml in ambient temperature (Arshad et al., 2021). Moreover, Salehi (2020) reported that PEF can be applied in the juice industry for improving physicochemical, antioxidant and organoleptic properties, resulting in better properties than thermal pasteurized juice. Although several previous studies have revealed the effectiveness of PEF on microbial inactivation in beverages, there have been a limited number of reports on the use of an industrial-scale machine, especially for low-acid beverages, e.g. TCW.

As mentioned above, PEF have demonstrated potential for improving the quality and microbiological safety of liquid food. The aims of this study are to investigate optimum conditions for Escherichia coli K12 (ATCC 10798) and Listeria innocua (JCM 32814) inactivation in TCW using pulsed electric fields and to evaluate the physicochemical properties of TCW treated by PEF compared with untreated and pasteurized samples.