Sodium Alginate Composite Coating Inhibited Postharvest Greening and Improved Nutritional Quality of Potato Tubers by Regulating Chlorophyll Biosynthesis

Potato tuber (Solanum tuberosum L.) was prone to greening and quality deterioration during postharvest storage due to various factors, affecting the regulation of chlorophyll biosynthesis. In the present study, potato tubers were placed at 600 lux and 25 °C after sodium alginate—xanthan gum—glycerin composite coating. During storage, the apparent color changes and a* value of the surface were observed and determined, meanwhile the contents of nutrients, chlorophyll, and its intermediates in photosynthetic metabolism were analyzed. The results showed that after 9 d, compared to the control group, the sodium alginate coating treatment significantly inhibited greening, delayed the decline of appearance quality and nutrients including dry matter, starch, reducing sugar, soluble protein, and ascorbic acid. Furthermore, the sodium alginate coating promoted the contents of 5-aminolevulinic acid (ALA) (1.33 fold), porphobilinogen (PBG) (1.06 fold), and uroporphyrinogen III (Uro III) (1.07 fold), meanwhile, inhibited the production of protoporphyrin IX (Proto IX) (13.86%), Mg-protoporphyrin IX (Mg-Proto IX) (14.15%) and protochlorophyllide (Pchlide) (25.97%), which were key intermediates in the chlorophyll synthesis, indicating that the sodium alginate coating delay the greening by blocking the conversion of Uro III to Proto IX. These results provided valuable insights for the postharvest preservation of potato tuber.