Flux control analysis of a lactate and sucrose metabolic network at different storage temperatures for Hami melon (Cucumis melo var. saccharinus)

Cold storage of fruits and vegetables is essentially a respiring and metabolic network flow and control process for which the further study of metabolic control rules are needed in order to improve the shelf-life of these living food products. This study used Hami melon as a test subject to study the respiratory metabolic network and flux control of fruits and vegetables during their storage. Hami melon was stored at different temperatures (0, 5, 10, 15, 20, 25, 30, 35, 40, 45 °C), in order to obtain the metabolic flux of the following pathways: Embden-Meyerh of pathway (EMP), pentose phosphate pathway (PPP), sucrose synthesis pathway (SSP) and TCA cycle (TCA). The quantity and activities of primary enzymes (enzymatic expression variate) were measured during storage. In addition, we got the control coefficients of synthesis flux to sucrose and metabolic flux to lactate. The results showed that sucrose had a higher synthesis flux at the temperatures of 5 °C and 45 °C, and lactate had a higher metabolic flux at the temperature of 5 °C. The study on flux control coefficients indicated that sucrose phosphate synthase (SPS, FCC = 0.424) produced a larger impact on sucrose flux control in the sucrose synthesis pathway. Lactic dehydrogenase (LDH, FCC = 0.143), triosephosphate isomerase (TPI, FCC = 0.136) and pyruvate kinase (PK, FCC = 0.136) had a large control effect on lactate flux, while glucose-6-phosphate dehydrogenase (G6PDH, FCC = −0.246) had a negative control function. These findings will enable future detailed investigation of metabolic mechanism of fruits and research of new preservatives.