2.6.2 Collection and detection of Volatile organic compounds (VOCs) from fresh ripe crown pears
A push-pull system was used to collect headspace VOCs as described in previous study (Lu et al. 2012). Briefly, fresh ripe crown pears (ca. 1,500 g) were placed into a glass jar (2000 mL) for extraction. Air aspirated with a vacuum pump (Qianxi Air Company, Beijing, China) was filtered through an activated-charcoal filter and a sorbent cartridge (Porapak Q, 50 mg, 80/100 mesh, Supelco, Bellefonte, PA, USA) with a 400 mL/min flow rate. The sorbents were held between plugs of glass wool in a glass tube (10 cm long, 0.5 cm inner diam). Samples were collected at 24±1 °C and 65–70 % RH for 8 h. Odor volatiles were eluted with 500 µL hexane (HPLC grade, Sigma-Aldrich) at room temperature. Sample volumes were condensed to 50 μL by using a slow stream of nitrogen. 0.5 μg benzaldehyde (99 %, Fluka, Switzerland) was added to each sample as an internal standard. Samples were analyzed by GC-MS. Identification of VOCs was verified by comparison with authentic samples. Three biological replicates were set in the experiments.