Efficacy of chlorine, peroxyacetic acid and mild-heat treatment on the reduction of natural microflora and maintenance of quality of fresh-cut calçots (Allium cepa L.)

Combined Ascorbic Acid and Mild Heat Treatment to Improve the Quality of Fresh-Cut Carrots

Mild heat (MH) treatment and ascorbic acid (AsA) addition can improve the quality of fresh-cut produce when used individually; however, their combined effect remains unclear. Herein, fresh-cut carrots were used as models to explore the effects of MH (50 °C)-AsA (0.5%) on quality properties including reactive oxygen species (ROS) metabolism, antioxidants, lignin metabolism, naturally present microbes, and inoculated pathogens (Escherichia coli O157: H7 and Salmonella Typhimurium) during storage (0-5 d, 4 °C). The results indicate that the antioxidant properties in the MH-AsA group were consistent with those of single treatments, resulting in a consistent ROS-scavenging effect. From day 3-5, lignin synthesis was significantly inhibited by MH-AsA as compared with single treatments, probably because the two enzymes (phenylalanine ammonia-lyase and peroxidase) responsible for lignin synthesis exhibited lower expressions. Microbial analysis revealed that MH-AsA treatment led to the lowest counts of both pathogens and aerobic mesophilic bacteria at 0-5 d. Conversely, the inhibitory effect of MH-AsA treatment on mold and yeast was consistent with the single treatments. These results suggest that MH-AsA is a low-cost and safe approach to improve the physiological characteristics of fresh-cut produce while reducing microbial risk.

Study on the characteristics of gluten/alginate-cellulose/onion waste extracts composite film and its food packaging application

The study aimed to improve the properties of SA-CMC film by gluten (G) blends and bioactive compounds from onion waste extracts (OWEs) peel (OPE) and stalk (OSE). The applicability of film on the quality of peeled shallot onion during storage was also examined. Water barrier (0.62 g/msPa × 10^-14) and tensile strength (11.50 MPa) of G/SA-CMC film improved more than SA-CMC film (1.55 g/msPa × 10^-13 and 7.05 MPa). OPE and OSE increase the total phenolic content (43.86 and 38.35 mgGAE/g) and radical scavenging activity (88.74 and 68.30 %) of G/SA-CMC film than control (20.33 mgGAE/g and 39.20 %). Microbial load (logCFU/g) in terms of total bacterial count, yeast and mold count of shallot onion packed in OPE (5.34 and 5.21) and OSE (4.26 and 4.21) film was reduced than control (6.03 and 4.68). Thus, the G/SA-CMC/OWEs film had improved properties than SA-CMC film and can be used to store peeled onion at 4℃ for 21 days.

Single and Combined Effect of Mild-Heat Treatment and Alginate Coatings on Quality Preservation of Minimally Processed Bunching Green Onions

Bunching green onion is an Allium species that has been widely used in food flavorings and seasonings. This vegetable experiences a rapid loss of quality during storage due to physiological changes and microbial spoilage. In the current work, the single and combined effect of mild-heat treatment (55 °C for 60 s) and alginate edible coatings on the quality preservation of minimally processed bunching green onions was studied. Control and treated samples were stored at 4 °C for 15 days and examined periodically in terms of their respiration rate, weight loss, pH, soluble solids content, firmness, total polyphenol content, antioxidant activity, microbial count, decay ratio, and overall visual quality. The results showed that the combination of mild heat and alginate edible coatings was the most effective approach to slow down the respiration rate and the incidence of decay in the minimally processed bunching green onions. In addition, the treatments with alginate coating alone or combined with mild-heat treatment showed the best performance for maintaining the overall visual quality of the products during the storage.

Effects of long-term controlled atmosphere storage, minimal processing, and packaging on quality attributes of calçots (Allium cepa L.)

Calçots are the immature floral stems of the second-year onion (Allium cepa L.) resprouts. Modified atmosphere packaging or vacuum packaging are suitable alternatives to preserve fresh-cut vegetables. The objective of this study was to evaluate the effect of postharvest storage time of raw vegetable stored under controlled atmosphere and used packaging system after minimal processing on the quality of fresh-cut calçots. Calçots used for minimal processing were stored under 1.0 kPa O₂ + 2.0 kPa CO₂ at 1 ℃ for 30 and 60 days. Fresh-cut calçots were packaged using passive modified atmosphere packaging or vacuum packaging and were stored at 4 ℃ for 15 days. Calçots stored under controlled atmosphere for 30 days presented better retention of quality and in turn, being more suitable for minimally processing. Vacuum packaging preserved the physicochemical quality of fresh-cut calçots better after 15 days. Mesophilic aerobic counts were also higher in fresh-cut calçots stored under modified atmosphere packaging, but all counts were below the recommended limits during and at the end of their shelf-life (15 days). The most suitable conservation strategy might be to store whole calçots under controlled atmosphere for 30 days and after minimally processing, packaged under vacuum in order to extend the shelf-life of fresh-cut calçots.