Structures and functional properties of apple (Malus domestica Borkh) fruit starch

Structures and functional properties of fruit starch of six apple cultivars (Gala, Golden Delicious, Granny Smith, Jerseymac, Jonagold and Royal Gala) were investigated. Apple starches exhibit CA-type X-ray diffraction patterns, and granule diameters ranged from 2 to 12 μm. Immature apple fruit had 44–53% starch (dry basis). The apparent amylose content was high (40–48%), but the average branch chain-length of amylopectin was long (DP 27.9–29.6), resulting in the absolute amylose content of 26–29%. The weight-average molecular weight of amylopectin ranged from 4.6 to 11.1×108. The proportion of long-branch chains of amylopectin (DP≥37), determined by anion-exchange chromatography with a post-column amyloglucosidase reactor and a pulsed amperometric detector, ranged from 29.7 to 32.4%. The onset gelatinization temperature of the starch ranged 64–66 °C, and the ΔH of starch gelatinization was 16–18 J/g. The percentage retrogradation of the gelatinized starch, after being stored for 7 d at 4 °C, ranged 42–47%. Most distinctive characteristic of apple starch was that three cultivars had extremely low breakdown (<4 RVU) and high setback (>100 RVU) at 8% (w/w) starch concentration. Peak and final viscosities ranged 99–148 RVU and 144–224 RVU, respectively. Pasting temperature was around 70 °C.