Effect of Bacillus amyloliquefaciens GSBa-1 on Polyphenol Synthesis and Phenylpropanoid Metabolism in Citrus medica L. var. sarcodactylis Swingle

In order to investigate the effect of Bacillus amyloliquefaciens GSBa-1 on polyphenol synthesis and phenylpropanoid metabolism in Citrus medica L. var. sarcodactylis Swingle stored at normal temperature, C. medica L. var. sarcodactylis Swingle was soaked in a 1 × 10⁸ CFU/mL suspension of B. amyloliquefaciens GSBa-1, taken out and air-dried before being stored at room temperature. The contents of total soluble solids (TSS) and titratable acids (TA), ethylene release, respiration intensity, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, H₂O₂ concentration, polyphenol content and enzyme activities related to the phenylpropane metabolic pathway were measured. The results showed that treatment with GSBa-1 reduced ethylene release and respiratory intensity, inhibited peel color change and fruit softening, induced an increase in phenylalanine ammonia lyase (PAL) and cinnamate-4-hydroxylase (C4H) activities, rapidly promoted the synthesis of gallic acid and caffeic acid as representatives of phenolic acids, induced the accumulation of flavonoids and flavanols such as hesperidin, seroxin and diosmin, increased the contents of total phenols and total flavonoids, and improved DPPH radical scavenging capacity and H₂O₂ content and consequently fruit resistance. It can be concluded that B. amylolytic GSBa-1 can activate the phenylpropane metabolic pathway, and stimulate the synthesis and accumulation of polyphenols, thereby delaying post-ripening and senescence and improving storage quality of C. medica L. var. sarcodactylis Swingle.