Storage Stability and Anthocyanin Degradation Kinetics of Alginate/Carboxymethyl Cellulose–based Emulsion Fortified with Red Onion Peel Extracts and its Application in the Preservation of Fresh Strawberries

Currently, the valorization of agricultural waste, such as red onion peel, has gained more attention due to their rich source of antioxidants and antibacterials with potential applications in the post-harvest preservation of fruits. In this study, methanolic extracts from red onion peel were incorporated into the oil-in-water emulsion stabilized by alginate (1% and 2%) with and without 0.5% carboxymethyl cellulose (CMC). The results showed that the mixture of 2% alginate and 0.5% CMC retained the antioxidant activity, especially ABTS free radical scavenging activity (827.26–1112.56 mg/L) during the first 27-day refrigeration of emulsions. Additionally, the degradation of anthocyanins was divided into two phases following Weibull model. Phase 1 lasted for 23 days with high stability of anthocyanin (33.61–39.28 mg/L, 82.6–89.7% retention) while this value decreased to 49.1–65.2% (19.27–21.90 mg/L) over the remaining 10 days (phase 2) for 2% alginate samples. Meanwhile, the figures for 1% alginate samples were 76.5–78.8% (31.09–31.27 mg/L) and 70.2–76.3% (21.83–23.85 mg/L) for phases 1 and 2, respectively. The addition of 0.5% CMC retained anthocyanin for a longer time at 1% alginate but retained more anthocyanin at higher alginate concentration although for a shorter duration. As an edible coating for strawberry preservation, an emulsion composed of red onion peel extracts stabilized by 2% alginate and 0.5% CMC was utilized. The coating effectively inhibited total aerobic microbes, particularly total coliforms, as evidenced by their non-detection during the initial 4–6 days of refrigeration. Moreover, no signs of E. coli or Salmonella were found throughout storage. Nevertheless, it is noteworthy that coating lacked the capacity to retard the growth of yeasts and molds (about 2.7 log CFU/g for all samples).