Energy vs. Nutritional Potential of Virginia Mallow (Sida hermaphrodita L.) and Cup Plant (Silphium perfoliatum L.)

Abstract

The world today faces several pressing challenges: energy from non-renewable sources is becoming increasingly expensive, while at the same time the use of agricultural land for food production is decreasing at the expense of biofuel production. Energy crops offer a potential solution to maximizing the use of land. In order to provide new value to the by-product, it is necessary to investigate its possible nutritional and functional potential. Therefore, the main objective of this study was to determine the energetic, nutritional, and functional potential of the species Sida hermaphrodita L. and Silphium perfoliatum L. in different phenophases. The analyzed energy potential of the mentioned species is not negligible due to the high determined calorific value (17.36 MJ/kg for Virginia mallow and 15.46 MJ/kg for the cup plant), high coke content (15.49% for the cup plant and 10.45% for Virginia mallow), and desirably high carbon content, almost 45%, in both species. The phenophase of the plant had a significant influence on the content of the analyzed specialized metabolites (SM) in the leaves, with a high content of ascorbic acid at the full-flowering stage in Virginia mallow (229.79 mg/100 g fw) and in cup plants at the end of flowering (122.57 mg/100 g fw). In addition, both species have high content of polyphenols: as much as 1079.59 mg GAE/100 g were determined in the leaves of Virginia mallow at the pre-flowering stage and 1115.21 mg GAE/100 g fw in the cup plants at the full-flowering stage. An HPLC analysis showed high levels of ellagic acid and naringin in both species. In addition, both species have high total chlorophyll and carotenoid concentrations. Due to their high content of SM, both species are characterized by a high antioxidant capacity. It can be concluded that, in addition to their energetic importance, these two plants are also an important source of bioactive compounds; thus, their nutritional and functional potential for further use as value-added by-products should not be neglected.

Keywords: agriculture biomass; antioxidant capacity; individual polyphenolics; renewable energy sources; specialized metabolites.

Figure 1

Dry matter content (%) of leaves of Virginia mallow and cup plant at different phenophase. Ph1—pre-flowering, Ph2—full flowering, and Ph3—end of flowering. Different letters indicate significant differences between means at p ≤ 0.0001.

Figure 2

Climate diagram with data from the meteorological station ‘Maksimir’ for the period of June (6) to September (9) (Croatian Meteorological and Hydrological Service, 2022).

Figure 3

Antioxidant capacity (µmol TE/L) of fresh leaf of Virginia mallow. Results are expressed as mean ± standard deviation. Different letters indicate significant differences between mean values.

Figure 4

Antioxidant capacity (µmol TE/L) of fresh leaves of cup plant. Results are expressed as mean ± standard deviation. Different letters indicate significant differences between mean values.

Figure 5

HPLC chromatogram of phenolic compounds profile of Sida hermaphrodita L. recorded at 360 nm, at (A) pre-flowering, (B) flowering, and (C) end of flowering stage; 1—caffeic acid, 2—coumaric acid, 3—ellagic acid, 4—ferulic acid, and 5—naringin.

Figure 6

HPLC chromatogram of phenolic compounds profile of Sylphium perfoliatum L. at (A) pre-flowering, (B) flowering, and (C) end of flowering stage; 1—caffeic acid, 2—coumaric acid, 3—ellagic acid, 4—ferulic acid, and 5—naringin.