Flavones isolated from celery varied in their stability and susceptibility to deglycosylation during thermal processing at pH 3, 5, or 7. Apigenin 7-O-apiosylglucoside was converted to apigenin 7-O-glucoside when heated at pH 3 and 100 C. Apigenin 7-O-glucoside showed little conversion or degradation at any pH after 5 h at 100 C. Apigenin, luteolin, and chrysoeriol were most stable at pH 3 but progressively degraded at pH 5 or 7. Chamomile and celery were used to test the effects of glycosidase-rich foods and thermal processing on the stability of flavone glycosides. Apigenin 7-O-glucoside in chamomile extract was readily converted to apigenin aglycone after combination with almond, flax seed, or chickpea flour. Apigenin 7-O-apiosylglucoside in celery leaves was resistant to conversion by b-glucosidase-rich ingredients, but was converted to apigenin 7-O-glucoside at pH 2.7 when processed at 100 C for 90 min and could then be further deglycosylated when mixed with almond or flax seed. Thus, combinations of acid hydrolysis and glycosidase enzymes in almond and flax seed were most effective for developing a flavone-rich, high aglycone food ingredient from celery.
Flavones are a class of flavonoids found in a variety of fruits and vegetables and are most abundant in artichoke heads, kumquats, parsley, and celery (Azzini et al., 2007; Justesen, Knuthsen, & Leth, 1998; Sakakibara, Honda, Nakagawa, Ashida, & Kanazawa, 2003). The flavone apigenin exhibits toxicity to cancer cells in vitro (Engelmann et al., 2002; Gupta, Afaq, & Mukhtar, 2002; Mak, Leung, Tang, Harwood, & Ho, 2006; Manthey & Guthrie, 2002; Piantelli et al., 2006) and animal studies with flavones demonstrate the ability to attenuate the inflammatory response (Nicholas et al., 2007; Ueda, Yamazaki, & Yamazaki, 2004). However, human trials with flavone rich foods such as parsley and celery show limited bioavailability of these compounds, with maximum plasma concentrations of <1 lM (Cao, Zhang, Chen, & Zhao, 2010; Meyer, Bolarinwa, Wolfram, & Linseisen, 2006). The time of maximum plasma concentration after eating these foods was over 7 h (Cao et al., 2010; Meyer et al., 2006), indicating that the flavones are likely absorbed in the colon rather than the small intestine. Future use of flavone-rich foods for health benefits requires a better understanding of the forms that are most readily absorbed and their stability during food processing.