Enhancing bread storage stability with chitosan oligosaccharides of different molecular weights: inhibiting spoilage microorganisms and retarding starch retrogradation.

Microbial spoilage and starch retrogradation remain major challenges in the baking industry. This study evaluated the antimicrobial and anti-staling effects of three chitosan oligosaccharides (COS) with different molecular weights (MWs), namely, low molecular weight (LMW, 1000 Da), medium molecular weight (MMW, 1509 Da), and high molecular weight (HMW, 2225 Da) in bread. In vitro assays showed that antifungal activity against Aspergillus niger and Penicillium chrysogenum increased with MW, whereas both LMW- and HMW-COS exhibited stronger antibacterial activity against Bacillus subtilis. Incorporation of COS notably prolonged the microbial shelf life of bread stored at 25 °C, extending it to 21, 15, and 24 d for LMW-, MMW-, and HMW-COS, respectively. The anti-staling effect of COS was also MW-dependent. Specifically, compared with the control, LMW-, MMW-, and HMW-COS reduced crumb firmness by 48.5%, 43.1%, and 29.8%, respectively, and decreased retrogradation enthalpy by 43.8%, 36.3%, and 20.7%, respectively, after 7 d of storage at 4 °C. Mechanistically, this effect is attributed to the reduction in starch relative crystallinity and the restriction of water migration from bound to free state. Overall, LMW-COS exhibited the greatest potential as a dual-functional improver, delivering superior anti-staling performance without compromising antimicrobial efficacy.