Widely targeted metabolomics analysis reveals new biomarkers and mechanistic insights on chestnut (Castanea mollissima Bl.) calcification process.

Chestnut calcification is a quality deterioration due to fast water loss, which has been of deep concern for chestnut quality control because its mechanism is unclear. In order to find out the different key metabolites and metabolic pathways related to the occurrence of chestnut calcification, in this study, liquid chromatography-tandem mass spectrometry (LC-MS/MS) based widely targeted metabolomics analysis was performed on chestnuts that were stored at 50%-55% (low relative humidity, LRH) at 25 °C and 85%-90% (high relative humidity, HRH) at 25 °C. A total of 611 metabolites were detected, and 55 differentially accumulated metabolites were identified as key metabolites involved in chestnut calcification process. The decrease in some monosaccharides accompanied with the increase in some unsaturated fatty acids indicated the degradation of chestnut cell wall and cell membrane during calcification process. As a stress response, amino acid metabolism related to membrane stability was significantly activated. In addition, the enhancement of phenylpropanoid biosynthesis pathway and flavonoid biosynthesis pathway characterized by the accumulation of lignin precursors and antioxidants suggested that lignification process was triggered in calcified chestnut. Therefore, the degradation and hardening of the cell wall and membrane damage were proposed to be associated with the calcification occurrence of chestnut. The metabolic profile of chestnut characterized in this study provided new insights into chestnut calcification process and laid a foundation for further chestnut quality control.

Development and characterization of an edible chitosan-whey protein nano composite film for chestnut (Castanea mollissima Bl.) preservation.

Chitosan (CHI) and whey protein are usually used to prepare edible films for food preservation. However, the composite film composed of the two components does not yield satisfactory properties for chestnut preservation. In this study, nano-cellulose and cinnamaldehyde (CMA) were added to CHI and whey protein, creating a new composite film with strong water retention, bacteriostatic, and mechanical properties. The water vapor permeability (WVP) of the film decreased by 21.61% with the addition of 0.5% (w/v) nano-cellulose, and 23.02% with the addition of 0.3% (w/v) CMA. Furthermore, water solubility (WS) decreased 22.05%, and the density of the film was significantly improved with the addition of 0.3% (w/v) CMA. The optimized formula of the film was CHI 2.5% (w/v), whey protein 3.0% (w/v), nano-cellulose 0.5% (w/v), CMA 0.3% (w/v), and pH 3.8, as determined by orthogonal testing L9(34 ), with fuzzy comprehensive assessment, of WVP, WS, tensile strength, and elongation at break. The film clearly inhibited the growth of E. coli, S. aureus, and Chinese chestnut fungus, destroying the mycelial structure of the fungus. In addition, coating effectively reduced the weight loss, mildew rate, and calcification index during 16 days of storage of chestnuts at 25 °C.