Effects of Semi-Solid Fermentation with Lactobacillus on the Bitterness and Active Components of Shatianyu (Citrus grandis L. Osbeck) Fruit Powder

The effects of semi-solid fermentation with different lactobacillus on the bitterness and active components in Shatianyu (Citrus grandis L. Osbeck) fruit powder (SFP) were explored. The aim of the present study was to establish the debitterizing technology and prepare low-bitterness SFP enriched in flavonoids and dietary fiber (DF), for providing the theoretical basis and technical support for the application of SFP in healthy food.

Shatianyu septum and pulp were dried and crushed to generate SFP, then, the bitterness of SFP and the equivalent main flavonoid glycosides (naringin and melitidin) in SPF were evaluated by sensory evaluation to clarify the bitter substance base. Lactobacillus plantarum GIM 1.1516 (LP1.1516), Lactobacillus casei GIM 1.411 (LC1.411), Lactobacillus acidophilus GIM 1.731 (LA1.731) and Lactobacillus rhamnosus GIM 1.325 (LR1.325) were used to ferment Shatianyu homogenate. During fermentation, the reducing sugar content, pH and acidity were dynamically monitored, the naringin and melitidin degradation rate were analyzed by HPLC, and the bitterness of Shatianyu homogenate after fermentation was also evaluated to determine the optimal fermentation conditions. Then, the fermented SFP was prepared, and its bitterness, together with total phenolic, total flavonoids, total DF (TDF), soluble DF (SDF), and insoluble DF (IDF) content were determined, respectively. Furthermore, the oxygen radical absorbance capacity (ORAC), ferric reducing antioxidant power (FRAP), ABTS free radical scavenging ability, together with water retention (WRC), water swelling (WSC), and oil adsorption capacity (OAC) of fermented SFP were determined, respectively.

SFP exhibited a more bitter taste, which was mainly caused by the co-flavor of naringin and melitidin, the main flavonoid components in SFP. During the first 12 h-fermentation, LP1.1516, LC1.411, LA1.731 and LR1.325 could use the reducing sugar in the homogenate and produce acids, while during 12-24 h-fermentation, only LR1.325 could still use the reducing sugar and produce acids. Shatianyu homogenate fermented by LR1.325 for 12 h showed the highest total degradation rates of naringin and melitidin (41.1%), also showed the highest sensory bitter removal rates (66.0%). Compared with unfermented SFP, the taste of SFP prepared by 12 h-LR1.325 fermentation changed from bitterer to between little bitter and slightly bitter, with a sensory bitter removal rate of 60.8%. Furthermore, the later showed higher total flavonoid content (increasing 19.8%), lower IDF (decreasing 9.6%), and higher SDF content (increasing 19.6%). Also, SFP prepared by 12 h-LR1.325 fermentation showed higher ORAC antioxidant activity (increasing 24.1%), higher water retention (increasing 20.8%) and water swelling capacity (increasing 32.0%).

12 h-LR1.325 fermentation of Shatianyu homogenate consisting of septum and pulp generates low-bitterness SFP enriched in flavonoids and DF, which could be used in the development of related functional foods.