Abstract
Whole crop rice (WCR) is used as an important feed for livestock ruminants. In this study, “Yeongwoo” variety WCR (cultivated on the Korean peninsula) was harvested at three different maturity stages (booting, heading, and milk) and their phenolic acid and flavonoid profiles in the lactic acid bacteria (LAB)-inoculated and noninoculated silage, hay, and fresh freeze-dried WCR extract were quantified. The alterations in the phenolic and flavonoid contents of the selected WCR during maturation in different samples were analyzed by the High-Performance Liquid Chromatography- Diode Array Detector (HPLC–DAD) technique. The six phenolics (caffeic acid, ferulic acid, p-coumaric acid, chlorogenic acid, dihydroxy benzoic acid, and prophyl gallate) and six flavonoids (rutin hydroxide, luteolin, kaempferol, vitexin, myricetin, and quercetin) were noted to have slight differences between the LAB-inoculated and noninoculated silage samples; however, the phenolics and flavonoids were higher in hay WCR at the milk stage compared to the silage and fresh freeze-dried samples. The results indicate that WCR harvest times have different phenolic compounds in the WCR silage, hay, and fresh samples. The phenolic and flavonoid compounds were higher (p < 0.05) with the increase in maturity (Stage 1–3). The stage of WCR maturity was positively related (p < 0.05) to the amount of phenolic acid and flavonoid contents (µg/g) in hay, silage, and fresh freeze-dried extract. We observed the WCR had high amounts of phenolic acid and flavonoid concentrations at milk stage (Stage 3) hay (quercetin, kaemferol, luteolin, ferulic acid, caffeic acid, and coumaric acid were 1.28, 1.29, 0.54, 1.54, 1.92, and 1.81 µg/g, respectively) compared with the booting and heading stages (Stages 1 and 2), with acceptable accuracy on a pilot scale. Based on these results, it could be concluded that LAB (Lactobacillus plantarum)-inoculated whole crop rice silage (WCRS) did not affect the phenolics and flavonoids of secondary plant metabolites in fermented silage. However, phenolics and flavonoids were of higher rations in WCR at the milk stage. Furthermore, this phenolic acid and flavonoid effect needs to be confirmed using large-scale in vivo analysis.
Highlights
Phenolics consist of a broad range of secondary metabolites that are subdivided into different classes, including phenolic acids, flavonoids, coumarins, lignans, and tanninsAppl
The flavonoid compounds, luteolin and myricetin, were identified at the milk stage of lactic acid bacteria (LAB)-noninoculated Whole crop rice (WCR) silage, which was not detected at the booting and heading stages of the LAB-inoculated WCR sample
We report the phenolic acid and flavonoid contents of Yeongwoo–WCR silage, hay, and fresh freeze-dried extract may be influenced by the stage of maturity; no significant changes were observed in phenolic compounds in LAB-inoculated WCR silage compared with the LAB-noninoculated silage
Summary
Phenolics consist of a broad range of secondary metabolites that are subdivided into different classes, including phenolic acids (hydroxybenzoic and hydroxycinnamic acid derivatives), flavonoids (flavonol, flavanol, isoflavonoids, and anthocyanin), coumarins, lignans, and tanninsAppl. The phenolic compound contents and their pharmacological functions are vitally dependent on pre- and postharvest factors such as environmental and agronomic conditions, cultivar selection, stage of maturity, and extraction procedure [4]. It is important to determine the optimal harvesting time for the highest amount of active ingredients ( phenolic acids and flavonoids) and maximum pharmacological activity [5,6]. Plant maturation analysis may be used as a low-cost tool to analyze the nutritive composition of forages that provide relationships between nutritive value and suitable harvest time [7]. Kim et al [8] studied the forage growth stage as one of the most important factors influencing nutritional composition. The concentrations of phenolic acids and flavonoids in WCR may differ based on the different cultivar, environment, and stages of maturity [9]
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