An emulsional rollercoaster: Saponin profile and concentration are moderately associated with carotenoid bioaccessibility from spinach (Spinacia oleracea)

Authors: MEHRANI, HAANIYA - Rice University; Dzakovich, Michael

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/16/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carotenoid content and bioaccessibility are key factors determining the nutritional value of spinach and other crops, but these traits are often poorly correlated. While carotenoid content refers to the amount of carotenoids in the plant, bioaccessibility describes how easily the body can absorb these nutrients. The gap between these two traits is thought to be influenced by the food matrix, which includes various chemical factors that can affect nutrient absorption. Spinach produces a unique set of emulsifying compounds called "yossosides" (triterpenoid saponins), which may play a role in improving carotenoid bioaccessibility. However, whether and how yossosides contribute to carotenoid absorption remains unclear. In this study, we investigated the relationship between carotenoid content, bioaccessibility, and saponin levels in 30 genetically diverse spinach accessions, including both commercial varieties and wild types. The plants were grown under controlled conditions, and we measured carotenoid bioaccessibility using a three-stage in vitro digestion model, alongside quantifying carotenoids and saponins using advanced chemical analysis techniques. We found that carotenoid bioaccessibility was only weakly correlated with carotenoid content, indicating that other factors influence nutrient absorption. While saponin content varied significantly across the spinach varieties, the concentration of yossosides showed a complex relationship with carotenoid bioaccessibility. Interestingly, higher yossoside levels were negatively associated with carotenoid content, suggesting a competition for metabolic precursors, but they were moderately positively associated with carotenoid bioaccessibility. This research provides new insights into how spinach’s unique saponins, despite their emulsifying properties, contribute to carotenoid bioaccessibility. The study suggests that other components in the spinach matrix play a more significant role in determining carotenoid absorption. These findings pave the way for future research aimed at identifying the key molecules involved in carotenoid bioaccessibility. Ultimately, this knowledge could help plant breeders develop spinach and other crops with improved nutritional profiles, enhancing the bioavailability of important nutrients like carotenoids.

Technical Abstract: Carotenoid content and bioaccessibility are definitively separate traits in spinach as well as many other crops. The disconnect between these traits is hypothesized to be due to chemical factors that comprise the food matrix. Spinach produces a unique array of triterpenoid saponins, termed “yossosides,” which are naturally occurring emulsifiers. Given that carotenoid transport from the intestinal lumen into the body largely relies on emulsifier-containing mixed micelles, we hypothesized that saponins contribute to differential carotenoid bioaccessibility observed in spinach. We assembled a genetically diverse population of 30 spinach accessions containing both commercial varieties and wild germplasm and cultivated this population under controlled conditions. Carotenoid bioaccessibility was determined using a three-stage in vitro digestion while carotenoids and saponins were quantified using UHPLC-PDA and UHPLC-MS/MS, respectively. Carotenoid bioaccessibility was poorly associated with initial content (R=0.13 and 0.25 for lutein and ß-carotene, respectively). Saponin content varied (3.65 – 14.68 mg/100g DW) and the absence of specific yossosides in some varieties indicates natural variation in structural or regulatory genes. Interestingly, yossoside concentration was negatively associated with lutein (R=-0.53) and ß-carotene (R=-0.46) suggesting competition for metabolic precursors. Despite the emulsifying properties of saponins, total yossosides were moderately positively associated with lutein (R=0.41) and ß-carotene (R=0.34) bioaccessibility. These data indicate that other molecules in the spinach matrix are playing a more prominent role in determining carotenoid bioaccessibility. Future research will focus on elucidating these factors to create molecular targets for plant breeders developing nutritionally enhanced cultivars of spinach and potentially other fruits and vegetables.