Oxalic acid

Total VCC was determined reducing dehydroascorbic acid to ascorbic acid [16] , by highperformance liquid chromatography (HPLC) (Jasco, Cremella, Italy). In brief, 0.5 g of powder were mixed with 2 ml of a 20 g/l DL-dithiothreitol solution (Scharlab S.L., Barcelona, Spain) for 2 h at room temperature and in a dark condition. Afterwards, VCC was extracted [17] . For that, 1 g of this mixture was extracted with 9 ml 0.1% oxalic acid (Scharlab S.L, Barcelona, Spain) under stirring for 3 min and filtered through a 0.45 m membrane filter. Finally, the VCC was determined by HPLC with the following conditions: Kromaphase 100-C18 column (4.6 x 250 mm, 5 mm) (Scharlab S.L, Barcelona, Spain); mobile phase 0.1% oxalic acid, 20 ml volume injection, 1ml/min flow rate. Detection was made at 25ºC and at 243 nm using a detector UV-visible MD-1510. A standard solution of L (+) ascorbic acid (Scharlab S.L., Barcelona, Spain) in the range of 10-530 ppm was prepared.
The VCC was calculated as g of ascorbic acid (AA) per kg of OS (g AA/ kg OS).

Vitamin C (VC) was determined by high-performance liquid chromatography (HPLC) (Jasco, Italy). For the analysis, 0.075 g of powder was used. The procedure employed was the reduction of dehydroascorbic acid to ascorbic acid, using DLdithiothreitol (Scharlab S.L, Spain) as the reductant reagent, and extraction with oxalic acid (Scharlab S.L, Spain) (Igual et al., 2014; (link)Xu et al., 2008) (link). The HPLC conditions were: KROMAPHASE100-C18, 5mm (4.6x250mm) column (Scharlab S.L, Spain); mobile phase 0.1 % oxalic acid, volume injection 20 L, flow rate 1mL/min, detection at 243 nm (detector UV-visible MD-1510) and at 25 ºC. A standard solution of L(+) ascorbic acid (Scharlab S.L, Spain) solution was prepared. The vitamin C content was calculated as mg of ascorbic acid per 100 g of the grapefruit's own solutes (mg AA/100gGS, Agudelo et al., 2017) (link).