Zinash A. Belay

Anthracnose in guava fruit ( Psidium guajava L.) is one of the major problems in the fruit industry. This study investigated the antifungal effects of air and ozone (O ₃ ) micro-nano bubble (MNB) water against the identified fungal pathogen in- vitro and in- vivo (on ‘Fan Retief’ guava fruit). The internally transcribed spacer (ITS) universal primers (ITS1 and ITS4 pair) were used to conduct a polymerase chain reaction (PCR) on extracted fungal DNA. C olletotrichum gloeosporioides (C. gloeosporioides)  sensu lato was accurately identified as the isolate from diseased guava tissues. For the in- vitro study, 1 mL of spore suspension (1 × 10 ⁶ spores/mL) of C. gloeosporioides sensu lato was exposed to 9 mL of 200 mg/L sodium hypochlorite (NaOCl) for 5 min, and air-MNB or O ₃ -MNB for 30 min each, while the untreated suspension was used as the control. The microstructural and ultrastructural changes of the spores were analysed using confocal laser scanning microscope (CLSM) and scanning-transmission electron microscope (STEM). Fresh guava fruits were inoculated with 1×10 ⁶ spores/mL of C. gloeosporioides sensu lato and washed with distilled water (control), 200 mg/L of NaOCl for 5 min, air- or O ₃ -MNB for 30 min, and assessed for disease severity. A separate batch of non-inoculated fruits were pre-treated and packaged in non-hermetic polyethylene clamshells and stored for 21 days at 13 °C, 90 ± 2% relative humidity. Peel colour, weight loss, respiration rates (RR), total soluble solids (TSS), titratable acidity (TA) and TSS/TA ratio were monitored. Spore viability tests via CLSM revealed that NaOCl led to ≈76.45% dead spores, followed by O ₃ -MNB (≈54.44%), air- (≈39.27%), and control (≈8%). STEM micrographs showed vacuolization under both MNB and NaOCl treatments. While NaOCl showed significant ( P  < 0.005) inhibitory effects against anthracnose, O ₃ -MNB water was comparable to NaOCl at day 6 of storage. Treatment with O ₃ -MNB better maintained fruit quality and slowed down rapid ripening as observed by the low weight loss, RR and TSS/TA. This study provides alternatives to chlorine-based washing for fruits.

Chlorine‐based water treatment for fresh produce has diverse limitations including the production of disinfectant‐by‐product residue. Thus, this study characterized and investigated the impact of micro‐nano bubble (MNB) water (air and ozone (O ₃ )) on the quality attributes of guava fruit during storage. Air‐ or O ₃ ‐MNB were loaded on Malvern Panalytical NnanoSight NS300 and Zetasizer Nano ZS for characterization. Thereafter, batches of guavas were immersed for 30 min in air‐ or O ₃ ‐MNB and others in sodium hypochlorite (NaOCl) or sterile tap water (control) and stored for 21 days at 13°C with 90 ± 2%, relative humidity. The results indicated that zeta‐potential, electrical conductivity, and oxidation reduction potential of O ₃ ‐MNB were significantly higher than that of air‐MNB ( p ≤ 0.05). Both air‐ and O ₃ ‐MNB delayed the decrease in lightness ( L *), and significantly maintained low titratable acidity, total soluble solids, and microbial load compared to control ( p < 0.001). Higher changes in fruit TSS/TA and total color difference were associated with control samples, followed by NaOCl treated samples. O ₃ ‐MNB significantly slowed down physiological response compared to control ( p < 0.05). Practical Applications: This study successfully characterized micro‐nano bubble waters and offered a paradigm shift from chlorine‐based sanitizers to micro‐nano bubble waters as a promising technology to maintain quality, enhance bioactive compounds, and delay fruit decay.

Microbes on fresh produce are often controlled by chlorine-based sanitizers, due to there is growing demand for safe alternatives. This work investigated effects of micro-nano bubble (MNB) water generated using air, oxygen (O₂), or ozone (O₃) against bacteria contaminants encountered along the fresh produce value chain. Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) broth were treated with distilled water (DW), sodium hypochlorite (NaOCl, 200 mg/L, 5 min), air-MNB, O₂-MNB, and O₃-MNB for 30- and 60-min. Scanning-transmission electron microscopy confirmed that the bacterial survival population was reduced via various types of cell damage under O₃-MNB. S. aureus was more resistant than E. coli to the MNB treatments. This could be due to the thicker layer of peptidoglycan surrounding the cell membrane protecting against oxidative species. On guava fruits, O₃-MNB-60 min lowered E. coli counts immediately after treatment (p < 0.05). MNB water offers a new paradigm for fruit decontamination. Graphical

This work investigated the impact of low‐pressure cold plasma (CP) as a pretreatment with polyethylene terephthalate (PET) plastic trays or open corrugated cardboard (OCC) boxes on the overall quality of “Fan Retief” guava fruits stored for 28 days at 13°C. Untreated samples placed in PET and OCC served as control. Guava fruits followed typical climacteric responses, but CP‐treated samples significantly slowed down respiration (RRCO ₂ ) and ethylene production rate during storage ( p ≤ 0.05). On day 28, CP‐treated samples retained the highest titratable acidity and total phenolics compared to untreated samples ( p ≤ 0.05). Overall, CP pretreatment better maintained the relative abundance of characteristic volatile compounds for guava fruits during storage, effectively delayed decay incidence, and inhibited the growth of Colletotrichum gloeosporioides in vivo compared to control. Practical Application: This study demonstrated low‐pressure cold plasma as a potential alternative phytosanitary tool for the postharvest handling of guava fruit.

(A) PLS-DA score plot of the VOCs at different sampling points. (B) Heatmap of the volatiles distributed across the treatment conditions and storage durations. (C) Venn diagram depicting the total proteins identified in different treatments.

Fresh apples are among the most important fruits, consistently in demand for their high nutritional quality; however, they have shelf -life under commercial handling condition due to their active metabolic processes and associated quality loss. Hence, this study explored the impact of plasma - activated sodium alginate (SA) edible coating (CCP) on 'Granny Smith' apples, focusing on respiration rate (RRCO₂), physical and biochemical quality attributes, natural microbial load and fruit surface morphology. The effects of CCP treatment were compared with apples only coated (CO), plasma treated (CP) and un-treated (Control) during the duration of five weeks at 15°C storage. The results indicated that CCP treatment significantly reduced fruit weight loss and degradation of titratable acidity (TA), while preserving fruit firmness and colour (a*) more effectively than the other treatments. Notably, all treatments (CO, CP, and CCP) significantly slowed down the RRCO₂ of apples (p = 0.000) and reduced total aerobic mesophilic bacteria count (p < 0.001) compared to the control samples. The evaluation of the scanning electron microscopy (SEM) images of the 'Granny Smith' apple fruit surface demonstrated the presence of different patterns amorphous wax layer, and microcracks on control samples, whereas plasma treatment improved the homogeneity of sodium alginate coating on the fruit surface. This study demonstrated that plasma-activated coatings can enhance the quality of edible coatings, offering a promising alternative to conventional packaging material.

Ready-to-eat fresh-cut apples deteriorate rapidly in visual quality due to browning, leading to consumer rejection and food waste. In addition, minimal processing induces tissue damage and releases organic substrates, which could accelerate microbial growth. The present study evaluated the impacts of alkaline and acidic electrolyzed water (AIEW and AEW) on natural microbial load and bioactive compounds on fresh-cut ‘Granny Smith’ apples. Minimally processed apples were dipped for 10 min in AEW and AIEW solutions (200 mg L⁻¹), packed in PET containers with lids, and stored for 9 days at 2 °C. Overall, fresh-cut ‘Granny Smith’ apples treated with AEW significantly (p < 0.05) maintained higher total phenolics (99.4 ± 4.3 mg GAE L⁻¹) and antioxidant capacity (79.5 ± 6.5 mg VitCE L⁻¹) compared to the non-treated control samples (42.9 ± 5.1 mg GAE L⁻¹, 31.9 ± 8.1 mg GAE L⁻¹, respectively). Similarly, pretreatment with AIEW maintained the highest total flavonol content (55.71 ± 1.5 mg QE L⁻¹) compared to the AEW-treated samples and control (p < 0.05). AEW pretreatment led to a 2 Log and a 1 Log decline in total aerobic mesophilic bacteria and yeasts and moulds, respectively. The best visual quality and highest visual score was maintained by AEW and followed by AIEW. This study further demonstrated the effectiveness of electrolyzed water treatments in minimizing browning and enhancing bioactive compounds in fresh-cut ‘Granny Smith’ apples.