X-ray Fluorescence Analysis and Consumer Preference Assessment Unveils that Sweet Potato Shoot-Tops are a Safer Alternative to Water Spinach, a Leafy Vegetable Prone to Bioaccumulation of Heavy Metals

Abstract

Purpose: Water spinach (WS) (Ipomoea aquatica) is a popular leafy vegetable. However, WS is highly prone to bioaccumulation of toxic heavy metals. Sweet potato (SP) (Ipomoea batatas) is primarily a root tuber crop with fast growing shoots that can be used to replace WS to safe guard the human and livestock health. However, SP is an under-utilized leafy vegetable and no studies have been conducted to assess the consumer preference and food safety except photochemical assessments to profile its high nutritious value. Therefore, in the present study, we assessed the heavy metal content, consumer preference and phytochemical contents to test the applicability of using shoot-tops of SP to replace bioaccumulation prone WS if grown in polluted sites. We also conducted a DNA barcoding analysis to discriminate SP from WS.Research Method: We obtained three greenhouse grwon shoot-top samples from WS (WS1, WS2 and WS3) and two greenhouse grown SP samples (SP1 and SP2) for all the analyses and two additional WS collected from the market (WSC) and a polluted site (WSP) a for XRF analysis. To assess the consumer preference we carried out a taste panel with 30 human subjects. For qualitative detection of the phytochemical contents, we performed routine laboratory tests. Finally, we carried out molecular based analyses using agarose gel electrophoresis and DNA barcoding using the markers rbcL and ITS.Findings: The sensory analysis revealed that human subjects equally preferred both WS and SP dishes. According to phytochemical assessment, SP contained higher amounts of anthocyanin, flavonoids, phlobatannins, reducing sugars, tannins and terpenoids. The XRF analysis revealed that SP shoot-tops did not accumulate toxic heavy metals while WS shoot-tops grown in the same garden soil accumulated toxic heavy metals in trace amounts. Commercially available WS in Sri Lanka contained Hg (4500 mg/Kg), Cd (1056 mg/Kg), As (598 mg/Kg) and Cr (74 mg/Kg). WSP contained Hg (1820 mg/Kg), Cd (228 mg/Kg), As (126 mg/Kg), Cr (138 mg/Kg), Sb (114 mg/Kg), Sn (464 mg/Kg) and Pb (2100 mg/Kg) and the highest amount of Fe (6894 mg/Kg).Research Limitation: It is imperative to study the heavy metal profiles of WS samples grown in diverse locations of Sri Lanka in collaboration with state consumer protection agencies to profile the food safety levels.Originality/ Value: It is apparent from the present study that the consumption of WS is unsafe to human and animal health. DNA barcoding assays can be successfully employed by the consumer protection agencies to confirm the identity of SP. Out of the two tested markers, ITS is more straight forward in exhibiting the length polymorphism. The sequence data confirms band sizes detected using agarose gels and ITS is more informative in studying the genus Ipomoea than rbcL.