Phytic acid promotes the oxidative stress tolerance of Meyerozyma (Pichia) caribbica enhancing its efficacy against natural decay and retaining the quality of table grapes.

The sporogenous yeast Pichia caribbica, a part of the Meyerozyma guilliermondii species complex is found in various environmental niches due to its diverse physiological and metabolic capacities that enhance adaptation and survival. This study examined the application of phytic acid (PA) to improve the biological control efficiency of P. caribbica against natural decay and to preserve the quality of table grape berries. The mechanisms by which PA enhances P. caribbica's biocontrol efficiency were investigated. The yeast cultured in nutrient yeast dextrose broth (NYDB) with (YE) or without (Y) PA was assessed for its ability to produce biofilms and to withstand induced oxidative stress. It was observed that supplementation with 10 μmol/mL PA markedly increased the proliferation and the capacity of P. caribbica to form biofilms (OD₅₉₀ = 0.8) in vitro compared to the non-supplemented yeast (OD₅₉₀ = 0.69). Additionally, P. caribbica cultured with PA (10 μmol/mL) effectively improved tolerance to induced oxidative stress. Phytic acid pretreatment also boosted the activities of defense antioxidant enzymes including β-1,3-glucanase (GLU), catalase (CAT), and superoxide dismutase (SOD) in P. caribbica. The impact of 10 μmol/mL PA on the biocontrol efficacy of P. caribbica led to favourable changes in the physicochemical parameters of table grapes with significantly improved control of the natural decay for fruits stored at ambient and cold conditions. These findings suggest that PA enhances the biocontrol effectiveness of P. caribbica, paving the way for the development of sustainable alternative solutions to combat postharvest fungal phytopathogens. Moreover, consumers preferred table grape bunches treated with YE appreciating the overall cluster appearance, the berry's textural crunchiness, a pronounced berry fragrance, and limited decay. They prioritized fruits stored at 4 °C.