Enhancement of functional and sensory properties of eastern prickly pear (Opuntia humifusa) by fermentation with yuza peel and guava leaf

Eastern prickly pear (Opuntia humifusa) is a medicinal plant containing multiple biological functions such as antioxidant, antidiabetic and immunological activities. However, it has been rarely used in food industry due to high viscosity as well as its own distinct flavor and bitter taste. This study was performed to enhance functional and sensory properties of O. humifusa by fermentation with yuza (Citrus junos) peel and guava (Psidium guajava L.) leaf. Changes in characteristics of three O. humifusa extracts fermented from different ingredients (O: O. humifusa; O–Y: O. humifusa + yuza peel; O-YG: O. humifusa + yuza peel + guava leaf) were investigated during traditional lactic acid fermentation at 25 °C. During the initial 3 d of fermentation, pH of O. humifusa extracts dropped to 3.6 and its viable cell number reached to 107 CFU/mL. The contents of isorhamnetin, quercetin, total polyphenols and total flavonoids increased in all O. humifusa extracts with fermentation time while the hesperidin and naringin contents decreased during 15 d of fermentation. O-YG fermented for 15 d was highest in the contents of total polyphenol, total flavonoid, quercetin, naringin and hesperidin while the isorhamnetin content was highest in O. Antioxidant activity and α-glucosidase inhibition activity were elevated in all extracts along with fermentation time. O-YG was highest in overall sensory acceptability and its DPPH radical scavenging activity was about 3 times higher than O and O–Y. The glycemic index value of O-YG from a glucose tolerance test was significantly lower than that of a commercial O. humifusa extract.