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Impact of activated water treatments and packaging systems on physiological responses, phytonutrients and overall quality of minimally processed Swiss chard (Beta vulgaris L.)
Author(s)
Masilela, Ayanda Gift
Date Issued
2026
Type
master thesis
Publisher
Cape Peninsula University of Technology
Abstract
Swiss chard is highly susceptible to postharvest handling practices that compromise its physicochemical quality and significantly reduce its shelf life, despite its richness in essential nutrients and health promoting compounds. Similar to other fresh-cut leafy vegetables (FCLVs), Swiss chard is prone to oxidative stress, microbial contamination, and physiological degradation during storage. To mitigate these challenges, postharvest sanitisation treatments, particularly those that contain oxidising and chlorine-based agents have been widely applied to preserve the nutritional value and overall quality of both whole and FCLVs. However, growing scientific evidence regarding the environmental persistence and health risks associated with synthetic chemical sanitisers have driven a global transition toward safer, eco-friendly alternatives. Among these, non-thermal activated water treatments, such as micro-nano bubble (MNB) technologies, have gained attention for their antimicrobial efficacy and broad applications across agricultural and food sectors. The aim of this study was to investigate the impact of MNB water technology and packaging systems on the overall quality, physiological responses, phytonutrients and microbial quality of minimally processed Swiss chard. MNB systems, namely air-generated MNB water and ozone micro-nanobubble (O3-MNBs), were evaluated for their effectiveness in improving post-harvest quality and storage stability of Swiss chard (cv. Fordhook Giant). Two experiments were conducted under identical storage conditions (5 °C) with samples packaged in BOPP films. In the first experiment, whole Swiss chard was treated for 10-min with air-MNB and compared against conventional sodium hypochlorite (NaOCl) and tap water (TW) over an 8-day storage period. In the second experiment, fresh-cut Swiss chard was treated with O3-MNBs and tap water for 5, 10, and 15 min, followed by storage for 15 days. The potential of air-MNBs as an alternative for conventional chlorine-based washing methods in leafy vegetables was investigated. The study examined the physiological responses, as well as the physicochemical and microbiological qualities, of packaged whole Swiss chard leaves. Results showed that air-MNB treatment significantly preserved chlorophyll contents, minimised moisture loss, and maintained leaf colouration better than both NaOCl and TW (p ≤ 0.05). Additionally, air-MNBs achieved a comparable ≤ 1-log reduction in aerobic mesophilic bacteria counts to that of NaOCl. At the end of storage duration, treatment with air-MNBs resulted in better visual quality compared to the control samples. To further elucidate the influence of activated water systems on the postharvest quality of minimally processed leafy vegetables, O3-MNB water was applied to fresh-cut Swiss chard (cv. Fordhook Giant). Fresh-cut Swiss chard pre-treated with O₃-MNBs exhibited significantly lower weight loss compared to those pre-treated with tap water treatments (p ≤ 0.05). In addition, O3-MNBs preserved leaf colour, and suppressed ethylene production relative to tap water. All the O₃-MNB treatments resulted in a decrease of total soluble solids and titratable acidity, however they were better retained in control tap water pre-treated samples (p ≤ 0.05). Notably, O₃-MNB-treated samples stimulated an early storage increase in phenolic content and induced the formation of new volatile compounds such as 1- Pentanol, associated with improved sensory attributes. Microbial analyses revealed that O₃-MNB treatments significantly reduced the populations of aerobic mesophilic bacteria, yeasts and moulds, with the 10-min exposure achieving the greatest microbial inhibition throughout storage and resulted in ≈ 1.6 Log reduction in total aerobic mesophilic bacteria and ≤ 1 Log reduction for yeast and moulds. Collectively, these findings underscore the potential of micro-nanobubble technology as an innovative, environmentally friendly postharvest intervention. By providing strong antimicrobial activity without the environmental and toxicological drawbacks of synthetic chemicals, MNB treatments effectively mitigate physiological deterioration while maintaining the sensory and nutritional integrity of leafy vegetables.
Additional information
Thesis (MAgric)--Cape Peninsula University of Technology, 2026
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Ayanda Gift_Masilela_222348453.pdf
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