Abstract
Immature Citrus unshiu pomace (ICUP) was hydrolyzed under organic acid-catalyzed, subcritical water (SW) conditions to produce flavonoid monoglucosides (hesperetin-7-O-glycoside and prunin) and aglycons (hesperetin and naringenin) with high biological activities. The results of single-factor experiments showed that with 8 h of hydrolysis and an increasing citric acid concentration, the yield of flavonoid monoglucosides (hesperetin-7-O-glycoside and prunin) increased from 0 to 7% citric acid. Afterward, the hesperetin-7-O-glycoside yield remained constant (from 7 to 19% citric acid) while the pruning yield decreased with 19% of citric acid, whereas the aglycon yield increased continuously. In response surface methodology analysis, a citric acid concentration and hydrolysis duration of 13.34% and 7.94 h were predicted to produce the highest monoglucoside yield of 15.41 mg/g, while 18.48% citric acid and a 9.65 h hydrolysis duration produced the highest aglycon yield of 10.00 mg/g. The inhibitory activities of the SW hydrolysates against pancreatic lipase (PL) and xanthine oxidase (XO) were greatly affected by citric acid concentration and hydrolysis duration, respectively. PL and α-glucosidase inhibition rates of 88.2% and 62.7%, respectively, were achieved with 18.48% citric acid and an 8 h hydrolysis duration, compared to 72.8% for XO with 16% citric acid and 12 h of hydrolysis. This study confirms the potential of citric acid-catalyzed SW hydrolysis of ICUP for producing flavonoid monoglucosides and aglycons with enhanced enzyme inhibitory activities.
Highlights
IntroductionCitrus fruits are widely consumed worldwide as juices
Academic Editor: Vitaly BuckinCitrus fruits are widely consumed worldwide as juices
The hesperetin-7-O-glycoside yield remained constant while the pruning yield decreased with 19% of citric acid
Summary
Citrus fruits are widely consumed worldwide as juices. After juice extraction, a large amount of pomace can be produced that includes peels, pulp, and seeds. Citrus pomace is a major potential source of flavonoid glucosides [1]. Many of these compounds have beneficial biological effects, including antioxidant, antimicrobial, anti-obesity, antihyperglycemic, anti-inflammatory, and anticancer effects [2,3,4]. Immature citrus fruits yield pomace with higher amounts of flavanones than mature fruits, and are potentially rich sources of flavonoids [5]. Most flavonoids are bound to sugars by glycosidic bonds in plants, and their biological activities depend on their glycosylation patterns and structural features [6]. Several studies have reported that the biological activities and bioavailability of flavonoid glucosides increase after deglycosylation; flavonoid monoglucosides and aglycons may have greater biological activities than their di-glycosylated flavonoids, and high potential for application in the food and pharmaceutical industries [7,8,9]
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