Study of Strawberry Guava (Psidium Cattleianum) on Properties and Volatiles at Two Ripening Stages

Abstract

The physical and chemical properties of strawberry guava (Psidium Cattleianum) at two ripening stages were studied. The fruit studied was picked in New Zealand locally. The extraction method was optimized with the orthogonal design for the strawberry guava properties analysis. The total phenolic content was valued by Folin-Ciocalteu assay with gallic acid as standard, total flavonoid content was valued with catechin as standard, total anthocyanin content was valued with pH difference method, and total procyanidin content was valued by determination of total procyanidins method (DMAC) with procyanidin A2 (PCA2) as standard. The strawberry guava at both the ripening stage showed rich TPC, TFC, total anthocyanin and total procyanidin content. The TPC and TFC are more abundant in the unripe strawberry guava, while total anthocyanin and total procyanidin content were less compared to the ripen strawberry guava. Detailed phenolic compounds were profiled with LC-ESI-MS/MS (liquid chromatography system with diode array detector). A total of 44 compounds were qualified and quantified in the unripe strawberry guava. And 45 compounds were qualified and quantified in the ripen strawberry guava. The antioxidant activity was analysed with three methods, including 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 2,2- diphenyl-1-picrylhydrazyl (DPPH) and fluorescence recovery after photobleaching (FRAP). All three methods showed excellent correlations (r²>0.99, correlations were all 1.0). The antioxidant activity determined was around 247.83 mM TE per gram freeze-dried powder in unripe fruit and was around 225.54 mM TE per gram freeze-dried powder in ripening fruit. This value was high in both ripening stages compared to the data acquired from previous studies. Besides, the higher value (247.83 mM TE per gram freeze-dried powder) on average determined in unripe ones suggested a slightly higher antioxidant activity. GC/MS equipped with DB-WAX and RT-5MS column was applied for the analysis of the volatile compounds of the strawberry guava volatiles. A total of 122 volatile compounds were identified. AR2000 enzyme was also applied to hydrolyse the glycoside-bound volatile compounds, and a total of 68 compounds was identified. The OAV of the free and bound volatiles were also evaluated for their aroma contribution. The evaluation explained the fatty green aroma presents in the free volatile of strawberry guava at two ripening stages contributed by hexanal. For the bound volatiles, the rose-orange odour was contributed by the nonanal and octanal in both the ripening stages of strawberry guava. However, the contribution of those two compounds are in different orders for unripe and ripen strawberry guavas.