Abstract: This study examined the effects of combined treatment with chitosan (CTS), nisin and melatonin (MT) on the quality, softening and antioxidant properties of “Hongbeibei” small-fruited tomatoes. Water treatment served as the control. Three experimental groups were established: 1.5% CTS, 1.5% CTS + 0.4 g/L nisin, and 1.5% CTS + 0.4 g/L nisin + 150 μmol/L MT. Following treatment, the tomatoes were stored at (25.0 ± 0.5) ℃ for up to 10 days. During this period, fruit quality, color, decay incidence, mass loss rate, sensory score, texture, softening, and antioxidant properties were evaluated every two days. The findings revealed that compared with CTS alone, its combination with nisin and nisin + MT significantly reduced the mass loss and decay incidence of tomatoes, while maintaining higher sensory scores. All three treatments effectively delayed the reduction in fruit hardness. Notably, both CTS and its combination with nisin + MT significantly enhanced fruit elasticity (on day 1) and adhesiveness (on day 4) during the early storage period and delayed the decline in the brightness L* value. The CTS + nisin treatment maintained fruit color by inhibiting the rise of a* and b* values. In addition, the combined treatment delayed cell wall degradation through a dual regulatory mechanism, not only reducing the rate of protopectin‌ decomposition (94.01% lower on the 8th day compared with the control), but also inhibiting the accumulation of soluble pectin. The CTS + nisin + MT treatment resulted in a higher accumulation of protopectin during the late period (on day 6) compared with the control. Both CTS alone and its combination with nisin postponed the peak time of total phenol content, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate and ferric ion reducing antioxidant power (FRAP) to the 6th day. The CTS + nisin + MT treatment provided better maintenance of antioxidant activity during the late storage period (on day 10), resulted in 11.8% and 11.5% increase in total phenol content and DPPH radical scavenging rate respectively, compared with the CTS + nisin treatment. Meanwhile, the CTS treatment maintained a higher FRAP in the late period. The CTS + nisin treatment delayed the peak time of titratable acid to the 6th day, CTS + nisin + MT treatment enhanced its content at the 10th day, resulting in 9- and 2.36-fold increase in the value of titratable acid relative to CTS alone at the 6th and 10th day, respectively. Moreover, both combined treatments deferred the peak time of VC to the 10th day, with the CTS + nisin + MT treatment exhibiting a 70.9% increase in the VC peak over CTS alone. To summarize, combined treatment with CTS, nisin and MT provided better maintenance of the quality of “Hongbeibei” small-fruited tomatoes, which provides a theoretical basis for the development of preservative coatings with good controlled-release effects for fresh fruits.

Key words: “Hongbeibei” small-fruited tomato; softening; texture characteristics; antioxidant; quality preservation