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able to remove oil, grease and fat. Detergency test using AlEW shows that it is able to eliminate 100% of the animal and vegetable oil formed on the steel’s surface effectively (Shirota and Isaka, 2001). Since the properties of the AlEW are not affected by the heat effect, cleaning using AlEW at a higher temperature will contribute to higher cleaning efficiency (Dev et al., 2014). AlEW is also able to remove protein-based soil. For milking system that used cleaning-in-place (CIP) program for cleaning, AlEW has proven its potential to replace the sodium hydroxide (NaOH) (Dev et al., 2014; Wang et al., 2016). Whereas, acidic electrolysed water (AcEW) can be used to replace acidic-based detergent (Dev et al., 2014; Wang et al., 2016). Dev et al. (2014) and Wang et al. (2016) applied AcEW during cleaning- in-place (CIP) process to clean the milking system as fouling deposit consists of some minerals. Their experimental works show that AcEW can replace the acid-based detergent and the sanitiser for CIP process of the milking system. 3.4 Electrolyzed water as environmentally friendly cleaning medium Utilizing EW during cleaning is better for the environment, worker’s safety and food safety as EW is less toxic than petroleum-based cleaning chemical (Colangelo et al., 2015; Gil et al., 2015; Rood et al., 2018). Food manufacturer acceptance of EW as cleaning medium, however, will likely depend on how well they can overcome the stigma that EW can cause equipment surface corrosion. Cleaning food equipment directly with salt solution can damage and reduce the shelf life of the equipment. This is one of the worries raised from SMEs when EW was suggested as an alternative green cleaner (Khalid, Ab Aziz, Thani et al., 2020). However, Ayebah and Hung (2005) reported that EW is less corrosive to stainless steel. Carbon steel, copper, aluminium and stainless steel had a fair, good and outstanding corrosion resistance in EW, respectively. Ayebah and Hung (2005) also indicated that AcEW water did not have any adverse effect on stainless steel. Stainless steel is the safest and suitable material for food contact surface manufacturing. Stainless steel shows an outstanding corrosion resistance in EW (Khalid, Sulaiman, Ab Aziz et al., 2020). Rinsing is a very important step in protecting the shelf life of the equipment material to avoid corrosion and to remove the chemical residue. After disinfection, washing the food equipment with sterile water can completely avoid metal corrosion (Ayebah and Hung, 2005). The effectiveness of rinsing can be measured by monitoring the conductivity (Stanga 2010). Conductivity is a measure of the concentration of the dissolved mineral in water (Etienne, 2006; Stanga, 2010). Moreover, EW reverts back to the original state when in contact with organic matter or if it is diluted by tap water, osmosis water or distilled water (Hati et al., 2012), thus reducing cost for wastewater treatment. 3.5 Storage of acidic electrolyzed water Figure 2 shows properties (pH, ORP, free chlorine, total chlorine and hydrogen peroxide) of AcEW during the 7 days of storage. There were two main factors which can reduce the chemical properties of EW which are exposed to the atmosphere and long duration of storage (Hsu and Kao, 2004; Khalid et al., 2018). In this work, seven days of storage was set as storage time assuming the food industries generate EW (using an EW generator) once a week for weekly consumption. From the SMEs perspective, daily usage of EW generator might be costly as it requires electrical energy to operate. Moreover, the weekly operation of the EW generator will be more convenient for the workers. Moreover, the common design of EW generator has a storage tank for EW. During the sanitation process, the tank is used to maintain a high flow rate of EW supply. Therefore, it is important to determine the EW stability (AcEW and AlEW) during storage. As shown in Figure 2 (a), the pH of AcEW remained stable during the seven days of storage. Maintaining the acidic pH is very important to ensure that the AcEW can be used as acidic cycle chemicals. Acidic chemicals such as acetic acid and phosphoric acid are commonly used for dairy cleaning (Watkinson, 2008). Acids are generally used to remove mineral scales such as hard water and millstones scales. While the ORP as shown in Figure 2 (b) maintains at a plateau for the first 5 days of storage. After 5 days, the AcEW shows a decreasing profile. Both pH and ORP are important properties to maintain as these properties contribute to AcEW antimicrobial properties. The high ORP (Kim et al., 2000; Liao et al., 2007; Huang et al., 2008), low pH (McPherson, 1993; Huang et al., 2008), chlorine content (Park et al., 2004; Liu, Duan and Su, 2006; Huang et al., 2008) and hydrogen peroxide content (Rico et al., 2007) are important chemical characteristics that contribute to antimicrobial properties of AcEW. Since aerobic and anaerobic bacteria can grow optimally at an ORP range of +200 to 800 mV and -700 to +200 mV, respectively. Thus, our target is to maintain our AcEW more than 800 mV. At higher ORP, the metabolic fluxes and ATP production of bacteria are modified (Huang et al., 2008). The pH ranging from 4 to 9 is optimal growth for bacteria. Our target is to maintain our AcEW to be lower than the pH of 4. During the 4 days of storage, the free and total chlorine content maintained at 10 mg/L (Figure 2 (c) and Figure (d) respectively). After 4 days, the total and free chlorine were found to be reduced gradually. However, eISSN: 2550-2166 © 2020 The Authors. Published by Rynnye Lyan Resources Khalid et al. / Food Research 5 (Suppl. 1) (2021) 47 - 56 51 FULL PAPERPDF Image | Stability of electrolyzed water
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