Production of phenolic compounds and biosugars from flower resources via several extraction processes

Highlights

• Enzymatic treatment was highly effective to release gallic acid from the flowers.

• Rose and camellia flowers are abundant sources of natural gallic acid.

• Protocatechuic acid achieved the highest levels using aqueous ethanol at 180 °C.

• Enzyme-assisted process resulted in the maximum sugar yields (380–596 mg/g).

• Co-production of phenolic compounds and sugars in flowers is a potential strategy.

Introduction

Edible flowers have been used to improve the appearance, taste, and nutrition of daily meals in European and Asian cuisines for 2000 years (Loizzo et al., 2016) and have recently been receiving increased attention from researchers, with more than 1880 food science technology and pharmacology studies being conducted in the last 15 years (2000–2015) (Lu et al., 2016). Edible flowers are rich sources of natural antioxidants, including phenolic acids, flavonols, flavones, anthocyanins, and other phenolic compounds. Bioactive compounds have been found in a variety of resources, such as fruits, vegetables, and herbs, have now been identified in edible flowers, which are abundantly available sources. These molecules have demonstrated diverse biological activities, including antioxidant, anti-inflammatory, anticancer, anti-obesity, and neuroprotective effects (Chena et al., 2018; Lu et al., 2016). The methanol extracts of several edible flowers exhibit even higher levels of phenolic compounds content and free radical-scavenge abilities than those from other plant organs (Ksouri et al., 2009; Mato et al., 2000). In a recent study, rose extracts, which were extracted with tetrahydrofuran and subsequent acidified methanol by a maceration process, were found to have the highest amount of phenolic compounds and greatest antioxidant activity among 51 edible flowers investigated (Li et al., 2014). In addition to antioxidant effects, methanol extracts from rose have been reported to exhibit anti-inflammatory, analgesic, and anticancer effects (Choi and Hwang, 2003; Hu et al., 2013). Roselle flower, another popular edible flower and also a source of natural colorants for food applications is consumed worldwide because it is a potential source of anthocyanins, one of the most important plant pigments (Grajeda-Iglesias et al., 2017). The aqueous and methanol extracts of roselle have demonstrated anti-inflammatory, anticancer, anti-obesity, hepatoprotective, and antidiabetic properties in in vivo and in clinical assays (Beltran-Debon et al., 2010; Chang et al., 2005; Kim et al., 2007; Lee et al., 2009). Camellia flowers (Camellia japonica) are frequently used in folk and traditional medicines in Japan, Korea, and China. In addition to showing anti-inflammatory effects, the ethanol extracts of camellia flower exhibit antioxidant properties in vitro by scavenging reactive oxygen species and enhancing the activity of antioxidant enzymes (Piao et al., 2011). Extracts of camellia flower are present in a variety of cosmetics and skin care products in Korea. Phenolic compounds in flowers, such as phenolic acids and their derivatives, flavonoids, and anthocyanins are assumed to contribute to the biological properties of flowers, including their antioxidant, anti-inflammatory, anticancer, and neuroprotective effects (Lu et al., 2016).

Phenolic compounds in plant tissues occur in free, esterified, and insoluble-bound forms. Soluble phenolic molecules can be extracted easily using solvent-based methods. Insoluble-bound phenolics are attached to the cell walls; therefore they need to be liberated from the cell wall matrix prior to identification and determination. Chemical hydrolysis using acids or bases is the most common method for extracting insoluble phenolics from a variety of sources, including cereals and legumes. Enzymatic hydrolysis has emerged as a promising and green method for isolating bound forms of phenolic compounds via degradation of cell wall structures, enabling better-yielding extraction processes (Shahidi and Yeo, 2016). The demand in the food and pharmaceutical industries for bioactive ingredients natural sources obtained by environmentally friendly techniques is increasing. Rose species contains high levels of hydrolysable tannins, which are expected to release their constituent phenolic acids, such as gallic acid using enzymatic or chemical hydrolysis (Cunja et al., 2014; Hashidoko, 1996). Gallic acid was reported a major phenolic acid in rose petal and its products (Vinokur et al., 2006). Protocatechuic acid was found as a main phenolic compound in roselle calyces and camellia flower in literature (Nakajima et al., 1984; Peng et al., 2011; Tseng et al., 1998). In the current study, we investigate the effect of extraction techniques on the total amounts of phenolic compounds, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging capacities, and the levels of gallic acid and protocatechuic acid in rose, camellia, and roselle flowers. The extraction of bioactive compounds was carried out using pressurized hot water, both with and without an organic acid catalyst, aqueous ethanol at different temperatures, and an enzyme-assisted process. These processes can also be used to extract soluble sugars and hydrolyze insoluble polysaccharides into simple sugars. This study suggests new resources for the manufacturing of beverages, syrups, and food ingredients in which the available sugars in flowers significantly reduce the additional sugars during the processing. Interestingly, bioactive compounds, which could provide more benefits and values, were found abundantly in flowers but less in common plant sources such as sugar cane and sugar beet.

Read more: https://www.sciencedirect.com/science/article/abs/pii/S0926669018308069